High Amorphous Vinyl Alcohol-Silica Bionanocomposites: Tuning

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High Amorphous Vinyl Alcohol-Silica Bionanocomposites: Tuning Interface Interactions with Ionic Liquids Katarzyna Zawada Donato, Marino Lavorgna, Ricardo Keitel Donato, Maria Grazia Raucci, Giovanna G. Buonocore, Luigi Ambrosio, Henri Stephan Schrekker, and Raquel Santos Mauler ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02379 • Publication Date (Web): 17 Nov 2016 Downloaded from http://pubs.acs.org on November 22, 2016

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ACS Sustainable Chemistry & Engineering

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High Amorphous Vinyl Alcohol-Silica

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Bionanocomposites: Tuning Interface Interactions

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with Ionic Liquids

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Katarzyna Z. Donato,a,b Marino Lavorgna,b* Ricardo K. Donato,a,c Maria G. Raucci,b

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Giovanna G. Buonocore,b Luigi Ambrosio,b Henri S. Schrekkera*and Raquel S. Maulera

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a

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Gonçalves 9500, Bairro Agronomia, Porto Alegre, RS, CEP: 91501-970, Brazil, P.O. Box

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15003.

Institute of Chemistry, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento

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b

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1, Loc. Granatello, 80055 Portici, NA, Italy.

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c

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University, Rua da Consolação 896, São Paulo, SP, CEP: 01302-907, Brazil.

Institute of Polymers, Composites and Biomaterials (IPCB)-CNR c/o ENEA, P. le E. Fermi

MackGraphe (Graphene and Nano-Material Research Center), Mackenzie Presbyterian

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*Corresponding authors:

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Henri S. Schrekker, Phone: +55 51 33086302 ; E-mail: [email protected]

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Marino Lavorgna, Phone: + 39 0817758838; E-mail: [email protected] 1 ACS Paragon Plus Environment


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ABSTRACT

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Herein, we demonstrate the effect of imidazolium ionic liquids (IL) applied as additives in

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the in situ formation of high amorphous vinyl alcohol (HAVOH)-silica bionanocomposites,

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using a simple sol–gel process approach. A complementary set of alkyl-, ether- and carboxy-

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functionalized IL was used, allowing the silica structure control and the polymer-silica

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interphase tuning. Consequently, hybrids with diverse morphologies, as well as improved

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thermo-mechanical and barrier properties, were obtained. This diversity also highlighted the

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systems’ dependency on the IL’s molecular structure, where both cation and anion influenced

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the hybrids’ final properties. This could be evidenced as the polar group functionalized-IL

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(ether- and carboxy-functionalized IL) allowed forming multiple hydrogen bonds at the

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organic-inorganic interphase, inducing a fine hybrid morphology with well-dispersed silica

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nanodomains. This significantly increased the storage (~50%) and tensile moduli (~20%),

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extensibility (up to 300%), glass transition temperature (>20 °C) and decreased the water

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vapor permeability (~50%), which are desirable characteristics for potential food and medical

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packaging.

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KEYWORDS

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Imidazolium ionic liquid, Sol–gel silica, High amorphous vinyl alcohol, Bionanocomposite,

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Water vapor permeability, Packaging

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1 Introduction

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Biodegradable and biocompatible polymers such as poly(vinyl alcohol) (PVOH), are

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strong competitors for conventional non-degradable polyolefins in high performance

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packaging for food,1 electronics2 and pharmaceuticals.3,4 However, they suffer from three

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main drawbacks: (i) low water and oxygen barrier properties, (ii) poor thermo-mechanical

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properties and (iii) limited processability through melt extrusion.5 In this context, both

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physical and chemical modifications of PVOH have been investigated to overcome these

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issues and obtain innovative functional materials with broader range of applications.

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Chemical crosslinking,6-8 filling3,9,10 or grafting11 are some of the common techniques used

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for enhancing PVOH performance. In particular, its elevated hydrogen bonding (H-bond)

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capacity, high chain flexibility and excellent water solubility open the way for incorporating

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various nanofillers9,12-16 and obtain nanocomposites with tunable morphology and interfacial

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interactions. The in situ formation of sol–gel silica was also allowed the successful

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preparation of PVOH-based hybrid nanocomposites with improved thermo-mechanical and

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barrier properties.3,17-19 On the other hand, PVOH processability enhancement has been

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obtained by chemical modifications.20 Recently, a new biodegradable polymer based on

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modified PVOH has been patented and commercialized with the trade name of G-Polymer

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(Nippon-Goshei, Japan). It is a novel high amorphous vinyl alcohol (HAVOH) particularly

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interesting due to its excellent extrusion processability, ease for coating and outstanding

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oxygen barrier properties. For this reason, it is used in applications where high barrier

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materials are needed, such as food or medical packaging. However, due to its low water

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barrier resistance, it is often used together with polyolefins in multilayer structures14

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decreasing product’s biodegradability.



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Ionic liquids (IL) are biodegradable21 organic salts with ionic-covalent crystalline

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structures that keep the liquid state at 100 °C or below. These multifunctional IL present high

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thermal and chemical resistance, stability in air and moisture, insignificant flammability and

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volatility,22 as well as promising antimicrobial (in solution and into materials surfaces)23,24

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and antidermatophytic activity.25 Additionally, feasible structural alterations of hydrophobic

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and hydrophilic regions allow task-specific IL synthesis and optimization of the

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intermolecular forces for each modification. Specific structural changes, e.g., anion exchange,

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differences in alkyl imidazolium side-chain length or its functionalization, cause variations in

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viscosity, ionic conductivity and solubility, as well as shifts in degradation and glass

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transition temperatures.22,26 The IL are being explored as additives in polymers due to their

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potential as plasticizers, lubricants and reinforcing or interfacial agents; improving, e.g.,

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barrier, mechanical and thermal properties.27

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Our group has been studying the effects of imidazolium IL application as

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“morphology drivers” on the sol–gel silica formation process28,29 and their role as

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compatibilizers and properties enhancers in various polymeric systems.30-32 Neat imidazolium

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IL self-assemble into supramolecular structures due to the H-bond-co-π-π stacking

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mechanism.33 Moreover, the C-H units within the imidazolium ring and, depending on the

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alkyl imidazolium side-chain length, methylene and/or methyl groups of the alkyl chains are

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H-bond donors. Further cation functionalization with carboxylic or ether groups increases the

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possibility of multiple H-bonding among IL’s molecules.34 Thus, when applied into sol‒gel

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process, these drive silica evolution processes and allow structure control.28 It is known that

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size, geometry, polarity and interaction forces between ionic parts have definitive

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contributions to the final silica particle size, compactness and morphology. Furthermore, the

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presence of IL from the first moments of sol‒gel silica formation speeds up the gelation 4 ACS Paragon Plus Environment

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time,28 hence tailor-made silica/IL hybrid synthesis becomes more suitable for in situ

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applications in water soluble polymers. It has been found that in situ silica/IL hybrids

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formation in diverse polymeric matrices improves the nanofillers’ dispersion and provides an

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increase in the nanocomposites’ thermo-mechanical properties.30-32 To the best of our

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knowledge, IL have been applied to PVOH matrices mainly for improving their electrical,

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electrochemical or thermal properties.35-37

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Within this context, the present work has brought attention for the first time to the use

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of IL as multifunctional agents in nanocomposite systems based on HAVOH to improve its

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water barrier and mechanical properties. The proposed approach is based on the development

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of hybrid nanocomposites by combining HAVOH and silica that has been synthesized and

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modified in situ with IL. This allowed tuning the interphase interactions and enhance the

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polymer’s thermo-mechanical and water barrier properties. We show that the addition of

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small amounts of in situ-formed homogeneously dispersed silica/IL hybrid nanofillers

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effectively improves the pristine properties of HAVOH. The in situ formation of modified

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and non-modified silica allowed observation of both the silica effect in the presence of the

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matrix and the IL effect in the polymer-filler interphase. Samples were prepared by solvent

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casting and two post-drying times were applied to evaluate how the water content affects the

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nanocomposites properties. The systems were investigated as for their structural,

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morphological, thermo-mechanical and barrier properties, as well as biocompatibility.

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2 Experimental

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2.1 Materials

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High amorphous poly vinyl alcohol (G-Polymer, grade OKS-8049 with a viscosity of

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4.6 mPa.s (4%aq at 20 °C)) was purchased from the Nippon Synthetic Chemical Industry Co., 5 ACS Paragon Plus Environment


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Ltd. (Japan). The chemical structure of this polymer consists of large PVOH units that

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alternate to modifying monomers, bringing hydrophilic branching units along the main chain

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of the polymer (Figure 1a). Three classes of IL were used; alkyl-, ether- and carboxy-

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functionalized IL (Figure 1b).

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Figure 1. (a) the chemical structure of HAVOH, and (b) alkyl-IL: [C4MIm][NTf2] and

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[C4MIm][Cl]; carboxy-IL: [CH2CO2HMIm][NTf2] and [CH2CO2HMIm][Cl]; and ether-IL

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[C7O3MIm][MeS] and [C7O3MIm][NTf2]; applied in this work.

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Alkyl-IL:

1-n-butyl-3-methylimidazolium

bis(trifluoromethylsulfonyl)imide

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[C4MIm][NTf2], 1-n-butyl-3-methylimidazolium chloride [C4MIm][Cl] were purchased from

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Sigma-Aldrich. A procedure reported previously in the literature38 was used for the synthesis

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of

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methanesulfonate [C7O3MIm][MeS], which was used as precursor for the preparation of the

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ether-IL

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bis(trifluoromethylsulfonyl)imide [C7O3MIm][NTf2]. This anion exchange was performed by

the

ether-IL

1-triethylene

1-triethylene

glycol

glycol

monomethyl

monomethyl

ether-3-methylimidazolium

ether-3-methylimidazolium


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applying [C7O3MIm][MeS] and lithium bis(trifluoromethylsulfonyl)amide (LiNTf2) in 1:1

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molar ratio. The salts were stirred for 2 days in dichloromethane. Formed LiMeS was

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removed by filtration and [C7O3MIm][NTf2] was obtained after solvent removal under

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vacuum. The purity was evaluated by 1H NMR, where spectral data of [C7O3MIm][MeS]

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were in accordance with those reported in the literature (Figure S1, Supporting

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Information).38 Also a previously published method was applied for the synthesis of the

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carboxy-IL 1-methyl-3-methylcarboxylic acid imidazolium bis(trifluoromethylsulfonyl)imide

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[CH2CO2HMIm][NTf2] and 1-methyl-3-methylcarboxylic acid imidazolium chloride

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[CH2CO2HMIm][Cl].39 Before application, IL were dried for 3 h at 60 °C under vacuum. The

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silica precursor tetraethoxysilane (TEOS) was purchased from Sigma-Aldrich. Hydrochloric

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acid (HCl), and ethanol (EtOH) were purchased from VETEC Química Fina LTDA and used

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without further purification. Deionized water was purchased from Best-Chemical s.r.l.

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2.2 The in situ preparation of HAVOH-based films with 3.0 wt.-% of silica

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An adapted literature procedure28 was used for preparing the pre-hydrolyzed TEOS/IL

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solution: the molar ratios of nEtOH/nTEOS, nH2O/nTEOS and nIL/nTEOS were fixed at 5.0, 3.0 and

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0.03, respectively. An aqueous acid solution (0.01 M) was prepared by dilution of 0.82 mL of

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concentrated HCl in water (1000 mL) (HClaq, pH = 2). One of the IL (Figure 1b, Table 1)

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and EtOH (310 mg) were sonicated until homogenous (~5 min). Next, TEOS (250 mg) and

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subsequently HClaq (64 mg) were added. The reaction mixture was mechanically stirred for

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10 min and then left for 1 h to pre-hydrolyze. The 10 wt.-% solution of polymer was prepared

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by adding HAVOH (2.40 g) into deionized water (21.60 g) and stirring until homogenous (~3

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h at 60 °C). The HAVOH solution was cooled to room temperature and the pre-hydrolyzed

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sol was added drop-wise. After stirring for 5 min, the mixture was poured into a Petri dish.

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All samples were left to cast at room temperature for 48 h and then dried under vacuum (8 h 7 ACS Paragon Plus Environment


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at 60 °C). Before analysis, in order to evaluate how the water content affects the systems’

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properties, casted films were submitted to two additional procedures of drying under vacuum;

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15 min at 120 °C or 1 h at 120 °C. For the reader’s clearer understanding, shorthand notations

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were used for the HAVOH nanocomposites. The abbreviation HAVOH-IL (e.g. HAVOH-

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C4MImNTf2) was used for samples modified with the corresponding silica/IL hybrid and the

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abbreviation HAVOH-Silica was used for the IL-free one.

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2.3 Characterization methods

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Thermogravimetric Analyses (TGA): A TA Instruments QA-5000 instrument was used and

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the analyses were carried out at a heating rate of 10 °C/min from 40 to 800 °C. All

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experiments were conducted under air or nitrogen atmosphere with a gas flow rate of 25

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mL/min. The samples (~10.0 mg) were placed in platinum crucible and an empty platinum

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pan was used as reference for all measurements. The inorganic content (residual mass left at

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800 °C), temperature of highest degradation rate (Td) as well as temperatures at 5%, 10% and

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50% of weight loss (T5%, T10% and T50%) were determined. The Td relates to the temperature at

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maximum weight loss rate of the first TGA derivative curve (DTG) in either an inert (TN2) or

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oxidative atmosphere (TO2).

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Differential Scanning Calorimetry (DSC): A TA Instruments DSC Q1000 instrument

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calibrated with indium standards was used for analyses. The entire thermal scan was

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conducted under a nitrogen atmosphere with a gas flow rate of 50 mL/min. Each sample had

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an initial weight ~10 mg and was placed in a closed aluminum specimen holder before

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placing it in the oven. The thermal history of the samples was erased by a preliminary heating

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run, which was applied from 0 to 240 °C (isotherm at 240 °C for 5 min) at a rate of 20

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°C/min. The results were obtained from the first cooling and from the second heating scan at

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a rate of 10 °C/min between 0 and 240 °C. The melting (∆Hm) and crystallization (∆Hc) 8 ACS Paragon Plus Environment

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enthalpies were obtained by integrating the areas of the endothermic and exothermic peaks,

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respectively. A rough estimation of the HAVOH’s crystallinity degree (Xc) was calculated

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from Equation 1.

=

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∆ × % ° × ∆

Equation 1.

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° where, ∆ is the reference melting enthalpy value of 138.60 J/g40 for 100% crystalline

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PVOH and f is the polymer fraction. Melting (Tm) and crystallization (Tc) temperatures were

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taken from the maxima of the endothermic and exothermic peaks, respectively. The glass

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transition temperatures (TgDSC) were obtained from the melting curves at transition’s

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midpoint.

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Transmission Electron Microscopy (TEM): The dispersion and size of nanofillers were

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examined by TEM using a FEI Tecnai G12 Spirit Twin equipment operating at an

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accelerating voltage of 120 kV. Ultra-thin sections of nanocomposites (70 nm) were prepared

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at room temperature and retrieved on 300 mesh Cu grids directly from the diamond knife

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without any liquid medium.

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Scanning Electron Microscopy (SEM): The surfaces of the residues obtained from TGA

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(oxidative atmosphere) were analyzed with a FEI Quanta 200F microscope operating at 30

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kV. The specimen was placed on a sample holder covered with a Carbon Tab and sputtered

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with platinum to increase the electric conductivity.

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Small and Wide Angle X-ray Scattering (SWAXS): The analyses were performed using an

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Anton Paar SAXSess camera equipped with a 2D imaging plate detector. Cu Kα 1.5418 Å

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wavelength X-Rays were generated by a Philips PW3830 sealed tube source (40 kV, 50 mA)

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and slit-collimated. Thin rectangular films were placed in the mold before obtaining the 9 ACS Paragon Plus Environment


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spectra. The time of exposition was 15 min. All scattering data were corrected for the

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background and normalized for the primary beam intensity. In order to remove the inelastic

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scattering from the data, the SAXS profiles were additionally corrected for both the Porod

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constant and desmearing effect.

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Water vapor barrier properties: The measurements of water vapor permeability were

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performed using the infrared sensor technique by means of a Permatran W3/31 (Mocon,

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Germany). Samples with a surface area of 5 cm2 were tested at 23 °C and relative humidity at

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upstream side of ~80 % until a stable permeability value was obtained (48 h). Only samples

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submitted to shorter post-drying (15 min at 120 °C) were analyzed.

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Dynamic Mechanical Analyses (DMA): A TA model QA 800 instrument was used at a fixed

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frequency of 1 Hz and strain amplitude of 0.05%. DMA analyses were performed in the

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tensile mode, and the rectangular specimens were heated from 30 to 140 °C at a rate of 3

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°C/min. Before analysis, the samples were conditioned at 25 °C for 24 h. The glass transition

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temperature (TgDMA) was obtained from the tan delta curve’s maximum. The DMA

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measurements were performed for the samples submitted to both post-drying procedures (15

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min and 1h at 120 °C).

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Tensile tests: The tensile strength and modulus were determined with an Instron 5565

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(Instron, Canton, MA) instrument at a crosshead speed of 20 mm/min. The tensile specimens

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were cut out (21 × 5 mm) with a CEAST cutting tool and submitted to the shorter post-drying

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protocol (15 min at 120 °C). An extensometer was used to directly monitor the strain

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variation and to determine the modulus. The values reported are averages of five

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measurements.


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In vitro Elution Materials and AlamarBlue® Assay: The HAVOH systems (0.1 g) were

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dissolved into 2.5 mL of Dulbecco's Modified Eagle's Medium (DMEM) according to the

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ISO 10993-5 guidelines. Next, 500 µL of each solution was pipetted into sterile 48-well cell

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culture plates (Falcon USA) previously seeded with 5,000 L929 cell line cells. The negative

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(nontoxic) control was a tissue culture plastic in DMEM without a HAVOH solution. The

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plates were further incubated (37 °C, 5% CO2, 95 % humidity) for 24 and 48 h of exposure.

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AlamarBlue® was used as assay to evaluate the biocompatibility. This assay quantified the

8

redox indicator, which changed to a fluorescent product in response to the chemical reduction

9

by mitochondrial enzymes such as flavin mononucleotide dehydrogenase, flavin adenine

10

dinucleotide dehydrogenase and nicotinamide adenine dinucleotide dehydrogenase. This

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redox phenomenon allowed the quantification of the cell viability (living and metabolic

12

active cells). At selected time points of 24 and 48 h, the medium was removed from the wells

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and an aliquot of 500 µL of AlamarBlue® diluted 1:10 in phenol red-free medium was added

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to each well and incubated for a further 4 h at 37 °C (5 % CO2). Afterwards, 100 µL each

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solution was transferred to a 96-well plate for colorimetric analysis (n = 6). Wells without

16

any cells were used to correct any background interference from the redox indicator. The

17

absorbance was measured at 570 nm and the subtracting background absorbance was

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determined at 600 nm.

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Surface wettability: The contact angle was evaluated with an OCA 20 Dataphysics instrument

20

in the sessile drop mode using 1 µL of water. Samples were measured seven times at room

21

temperature and the contact angles were expressed as average values.

22 23



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3 Results and discussion

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3.1 Thermal behavior

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DSC and TGA were used to study the effect of the in situ formation of silica/IL

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hybrids on the thermal transitions as well as the thermal degradation. Figure 2 shows

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polymer characteristic curves with both exothermic and endothermic events obtained by DSC

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for the samples submitted to two post-drying times. In comparison to the Tc of neat HAVOH,

7

the incorporation of siloxane phase caused a significant Tc shift to the lower temperatures,

8

which corresponds to the crystallization deceleration (Figure 2a and 2b; curves 1, 2 and 1’,

9

2’).41

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Figure 2. DSC crystallization (a, b) and melting (c) curves for (1) HAVOH; (2) HAVOH-

12

Silica;

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CH2CO2HMImCl; (6) HAVOH-CH2CO2HMImNTf2; (7) HAVOH-C7O3MImMeS and

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(8) HAVOH-C7O3MImNTf2. Samples numbered with ’ (e.g. 1’, 2’) correspond to the ones

15

submitted to longer post-drying (1 h at 120 °C).

(3)

HAVOH-C4MImCl;

(4)

HAVOH-C4MImNTf2;

(5)

HAVOH-

16


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All six IL increase the Tc in up to 15 °C in comparison to HAVOH-Silica (Figure 2a

2

and 2b, Table 1), indicating the HAVOH crystallization induction caused by the IL confined

3

on the silica surface.30 The HAVOH-C4MImCl presented the maximum increase of the Tc

4

only for the longer post-drying procedure (Figure 2b; curve 3’), which, most likely, was

5

promoted by partial phase separation and/or formation of larger nucleation centers. This can

6

be evidenced when correlating the SAXS determined scattering invariant (INV) with the Tc,

7

where particle size and Tc seem to follow a defined pattern. The silica/IL influence on

8

crystallization is explained in more details in the structural investigation section. The Xc

9

decreased for all hybrid systems when compared to neat HAVOH and this decrease was more

10

pronounced (up to 5 %) for the systems submitted to shorter post-drying procedure. In

11

comparison with the neat HAVOH matrix, the TgDSC of all silica-filled samples increased

12

independent of post-drying time, confirming the direct interaction of in situ formed hybrids

13

with the polymer matrix. The TgDSC positive shifts cannot be attributed to the water

14

absorption from the ambient atmosphere, since the post-drying process was performed under

15

vacuum and samples were further stored in a desiccator. This TgDSC shift is a consequence of

16

HAVOH-silica interactions, which would work as “physical crosslinks”, decreasing the

17

molecular mobility of polymer chains and organizing the system. Samples HAVOH-

18

CH2CO2HMImCl and HAVOH-CH2CO2HMImNTf2 (Figure 2c; curves 5’ and 6’) showed

19

the most significant TgDSC increase (almost 10 °C, when compared to HAVOH) which is an

20

indication of more intense multiple H-bonding formation among HAVOH, silica and

21

carboxy-IL. The Tm slightly increased (max 2 °C) for most of the HAVOH-IL systems, while

22

it decreased for the HAVOH-Silica (~2 °C), which could also indicate multiple H-bonding

23

for HAVOH-IL. Altogether, the DSC results show that the IL applied in HAVOH-silica

24

hybrids work as compatibilizers rather than plasticizers.



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Page 14 of 42

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The measurements obtained by TGA revealed an important role of the in situ silica/IL

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hybrids formation in the nanocomposites’ thermal resistance. Figure S2 shows representative

3

TGA/DTG curves for samples degrading under both inert and oxidative atmospheres.

4

Table 1. Mass of IL applied in the for nanocomposites preparation and the DSC thermal

5

properties determined after two post-drying procedures; 15 min at 120 °C and 1 h at 120 °C

6

(shadowed). mIL*

TgDSC

Tm

Tc

Xc

[mg]

[°C]

[°C]

[°C]

[J/g]

[J/g]

[%]

66.1

184.3

156.4

29.5

36.2

21

73.4

186.3

163.1

28.6

29.4

21

74.0

181.8

143.5

23.6

24.0

18

76.2

184.1

147.7

21.5

23.2

16

73.8

186.2

160.2

27.4

28.4

20

73.8

186.5

154.3

21.2

28.5

16

74.3

184.8

154.3

24.9

25.4

19

74.1

185.8

150.3

18.9

28.0

14

75.3

183.4

150.7

23.4

25.2

17

75.6

184.4

152.3

21.2

24.5

16

75.2

184.5

153.3

23.5

25.9

17

76.0

184.9

153.5

21.5

24.3

16

74.6

184.9

153.9

25.1

26.9

19

73.8

186.2

151.8

27.5

26.2

20

74.2

185.2

155.2

25.5

25.8

19

73.8

185.2

149.2

19.0

26.4

14

Sample

-

HAVOH

-

HAVOH-Silica

12.6

HAVOH-C4MImCl

30.2

HAVOH-C4MImNTf2

HAVOH-CH2CO2HMImCl

HAVOH-CH2CO2HMImNTf2

HAVOH-C7O3MImMeS

HAVOH-C7O3MImNTf2 7

12.8

30.4

23.4

36.6

* mass of the corresponding IL applied for the nanocomposite formation.

8 14 ACS Paragon Plus Environment

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1

Table 2. TGA determined thermal properties after two post-drying procedures; 15 min at 120

2

ºC and 1 h at 120 ºC (shadowed). T5%a

T10%a

T50%a

TN2b

T50%c

TO2d

Res.e

[°C]

[°C]

[°C]

[°C]

[°C]

[°C]

[%]

285.7

306.4

360.6

363.9

364.9

352.8

0

283.7

305.2

363.0

366.3

376.7

368.0

0

278.9

292.8

362.9

358.1

379.6

354.7

3.2

183.5

283.8

364.2

355.3

400.0

359.6

3.2

276.9

291.7

363.0

363.6

394.2

373.6

2.9

270.1

303.6

378.0

374.2

394.4

369.1

2.5

288.0

310.4

381.6

374.6

382.2

357.4

3.1

280.4

296.9

369.1

369.7

404.3

365.7

3.2

298.6

320.7

381.5

371.5

391.6

355.1

3.4

273.9

289.9

363.6

362.1

403.3

364.9

3.0

290.4

305.6

370.8

367.2

382.6

355.0

3.1

276.3

301.1

368.4

365.3

399.3

366.6

3.2

285.9

308.3

377.9

372.5

383.8

353.6

3.0

262.5

296.7

373.0

371.7

403.3

368.2

3.0

282.5

306.5

379.1

375.2

378.9

353.0

3.0

276.8

300.9

371.6

369.0

403.7

366.9

3.0

Sample

HAVOH

HAVOH-Silica

HAVOH-C4MImCl

HAVOH-C4MImNTf2

HAVOH-CH2CO2HMImCl


HAVOH-C7O3MImMeS

HAVOH-C7O3MImNTf2 3

a

from TGA measurements under nitrogen;

4

b

maximum degradation temperature from DTG curve under nitrogen;

5

c

from TGA measurements under air;

6

d

maximum degradation temperature from DTG curve under air;

7

e

at 800 °C under air;

8



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Page 16 of 42

1

In general, all the samples presented two or three broad degradation peaks when

2

analyzed under nitrogen (Figure S2a and S2c) or air (Figure S2b and S2d), respectively. As

3

both HAVOH and LI28 do not completely degrade under a nitrogen atmosphere, an oxidative

4

atmosphere was used to determine the inorganic filler contents in the nanocomposites (Table

5

2; 3 ± 0.4 wt.%). The general small standard deviation suggests that the synthetic process

6

itself induces the formation of nanocomposites with very well dispersed silica. Longer post-

7

drying produced samples with higher thermal resistance and these were examined in more

8

detail. All HAVOH-IL nanocomposites presented a higher T50% (up to 20 °C under nitrogen

9

and 30 °C under air), however only the samples HAVOH-CH2CO2HMImCl, HAVOH-

10

CH2CO2HMImNTf2, HAVOH-C7O3MImMeS and HAVOH-C4MImNTf2 presented better

11

thermal resistances in all evaluated weight loss steps (T5%, T10% and T50% under nitrogen)

12

(Table 2). The addition of any of the six presented IL resulted in a Td increase in comparison

13

to the neat HAVOH. The most significant TN2 (maximum degradation temperature in

14

nitrogen) improvement (~10 °C) was observed for the systems containing the thermally more

15

stable [NTf2] anion-based IL with either alkyl or polar cation side chain. As for the oxidative

16

degradation curves, the maximum increment of degradation temperature (TO2) was observed

17

for HAVOH-C4MImCl (~30 °C) and this could be related to the formation of weaker

18

bounded silica particles, which would enable their migration to the surface and act as thermal

19

insulation layer.42

20

The TGA ashes obtained in oxidative atmosphere at 800 °C were investigated by

21

SEM to evaluate the influence of the IL’s on the in situ silica orientation. Despite the polymer

22

matrix used is biodegradable, the evaluation of nanocomposites’ calcination process could

23

also indicate their recyclability. It was noted that the addition of any of the six presented IL

24

induced formation of ordered microstructures with different morphologies. Figure 3 16 ACS Paragon Plus Environment

Page 17 of 42

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1

represents the three most contrasting structures observed. Calcinated HAVOH-Silica (Figure

2

3a) displayed a porous surface, which is typical for amorphous materials.

3

4 5

Figure 3. SEM images of microstructures obtained after calcination under oxidative

6

atmosphere at 800 °C: (a) HAVOH-Silica; (b) HAVOH-CH2CO2HMImCl and (c)

7

HAVOH-C4MImCl.

8 9

The residue from HAVOH-CH2CO2HMImCl presented needle-like morphology

10

(Figure 3b), also observed for HAVOH-C7O3MImMeS (Figure S3a) and HAVOH-

11

C7O3MImNTf2 (Figure S3b), while HAVOH-C4MImCl formed much thicker bead-like

12

structures (Figure 3c). The pristine silica glass first transformation from amorphous silica

13

into β-Cristobalite occurs only at temperature ~1000 °C. Thus, as herein samples were

14

thermally treated only up to 800 °C, the applied IL were most likely responsible for

15

catalyzing/inducing crystallite growth. This phenomenon was exclusive for samples

16

submitted to the post-drying procedure. When the same calcination process was applied to

17

non-post-dried

18

C4MImNTf2 (Figure S3d), no organized silica-carbon species could be observed (similar to

samples,

HAVOH-CH2CO2MImNTf2

(Figure

S3c)

or

HAVOH-



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Page 18 of 42

1

HAVOH-Silica, Figure 3a). The post-drying process seems to cause a reproducible

2

organization of the film due to the increase of internal pressures. Apparently, this initial

3

organization caused by the volume decrease (water loss), facilitated the further organization

4

at higher temperatures. Additionally, by changing the IL applied, it is also possible to control

5

the microstructure morphology. The calcinated products could be considered as recycled

6

fillers in new materials synthesis. Nevertheless, a more detailed investigation is necessary to

7

discover the exact compositions and structures of formed species.

8

3.2 Morphology and structural organization

9

All obtained films were homogenous and transparent, suggesting the absence of large

10

clusters and good silica dispersion. This was also observed in TEM images (Figure 4). In the

11

cases of HAVOH-Silica (Figure 4a) and HAVOH-C4MImCl (Figure 4b) it is rather

12

difficult to determine the particle size, since these form co-continues networks. Independent

13

of this, it is possible to notice that the alkyl-IL favors a more pronounced silica

14

agglomeration, which could be ascribed to the alkyl-IL’s tail-tail interaction (Scheme 1a). On

15

the other hand the HAVOH-CH2CO2HMImCl (Figure 4c) promoted excellent silica

16

dispersion, where particles (2-4 nm) were evenly spread across the sample. The high

17

compatibility of all components of this system, as after TEOS hydrolysis practically all the

18

components are able to form H-bonding, makes it more difficult to segregate into isolated

19

domains up to a later stage of condensation, not allowing considerable coalescence into big

20

silica domains. Additionally, the acid character of this IL could promote a lower pH of the

21

system retarding the condensation process (cluster-cluster mechanism).28,43 This effect of IL

22

as silica morphology and agglomeration controllers has also been observed in different in situ

23

silica based nanocomposites.32,43


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1 2

Figure 4. TEM images of (a) HAVOH-Silica, (b) HAVOH-C4MImCl and (c) HAVOH-

3

CH2CO2HMImCl.

4 5

The structural organization of the hybrid films was investigated by SWAXS analysis

6

and the obtained plots are gathered in Figure 5. Based on the SAXS profile, neat HAVOH

7

presents structural organization where the layer-like lamellar crystallites form spherical

8

domains embedded in an amorphous continuous phase (Figure 5a; curve 1’). With the

9

addition of a siloxane phase, the scattering profile of HAVOH completely changed (Figure

10

5a). The diffraction spectra for all hybrids show the characteristic knee diffraction feature,

11

which is ascribed to the presence of small particles (likely spherical) and is a common

12

hierarchical structure of the siloxane phase aggregate that results in these secondary

13

structures.44 The hybrids’ Porod corrected SAXS plots showed differences in profiles and

14

scattering intensities depending on the IL applied. It was possible to obtain slope values in the

15

linear fractal region, as well as scatter vectors at the transition from the Guinier region to the

16

fractal region (qG) and at the transition from Porod to fractal region (qP) (Table S1).45



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Page 20 of 42

1 2

Figure 5 SWAXS profiles: (a) Porod plot after subtraction of the Porod constant; (b) the q vs.

3

q2I(q) plots representing the transition of qmax values with and increased drying time and (c)

4

WAXS region for; (1) HAVOH; (2) HAVOH-Silica; (3) HAVOH-C4MImCl; (4) HAVOH-

5

C4MImNTf2; (5) HAVOH-CH2CO2HMImCl; (6) HAVOH-CH2CO2HMImNTf2; (7)

6

HAVOH-C7O3MImMeS; (8) HAVOH-C7O3MImNTf2. Curves with ’ (e.g. 1’, 2’)

7

correspond to the samples with longer post-drying (1 h at 120 °C).

8 9

The average characteristic dimensions of both long amorphous-crystalline period in

10

neat HAVOH and silica particles in hybrids (long period, δ) was roughly estimated based on

11

Equation 2:

12

δ=2π/qmax

Equation 2 20

ACS Paragon Plus Environment

Page 21 of 42

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1

where, qmax is the scattering vector modulus at the maximum of the q vs. q2I(q) plot (Figure

2

5b). The systems showed variations of qmax and invariant values (INV, Equation 3);

3

= .

Equation 3

4

which depend on the electron density difference between the siloxane domains and the

5

surrounding polymer. This is an estimation of the scattering phase densification extent

6

(mainly as primary particles), which depends on the hybrid formulation. The δ for neat

7

HAVOH, ascribed only to the presence of lamellar crystalline domains, slightly increased

8

when submitted to the longer post-drying (Figure 5b; curves 1 and 1’). In the case of the

9

hybrids, the silica primary particles were estimated to have the average size in the range of

10

~3-8 nm (Table S1). In agreement with the literature,45 for the samples with larger silica

11

primary particle sizes (HAVOH-C4MImCl and HAVOH-C4MImNTf2), the scattering

12

intensity at low wave vectors decreased, while this scattering intensity increased for the

13

samples with the smaller silica primary particle sizes (HAVOH-CH2CO2HMImCl and

14

HAVOH-CH2CO2HMImNTf2) (Figure 5a). However, the differences in silica porous

15

structures and the spatial arrangements of the nanoparticles can also contribute to the total

16

scattering intensity and have to be taken into account. The scattering properties values are

17

presented in Table S1. More detailed structural investigations were performed only for the

18

samples submitted to longer post-drying, and an interesting trend between INV and Tc has

19

been found (Figure 6). In the case of the case of HAVOH-Silica, denser and smaller

20

particles ~5 nm (high INV value) and very strong HAVOH-silica polar interactions shifted

21

significantly the Tc to lower temperatures. This behavior was “softened” by IL addition into

22

the system, shifting Tc to the higher temperatures, as previously mentioned in the DSC

23

description. Simultaneously, the type of IL applied induced the formation of particles with

24

different sizes. Samples modified with carboxy-IL showed the highest value of INV (denser 21 ACS Paragon Plus Environment


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Page 22 of 42

1

and smaller particles, ~3 nm) and presented the lowest Tc values, in opposition to the alkyl-IL

2

modified ones presenting the lowest INV (looser and bigger particles, ~7 nm) and highest Tc

3

(negligible interaction with the polymer).

4

5

6

Figure 6. Correlation between invariant values ( = . ) obtained from SAXS

7

analysis and Tc obtained from DSC measurements.

8 9

In comparison to the alkyl- and ether-IL, a more effective HAVOH-silica-IL multiple

10

H-bonding for the samples with carboxy-IL caused the formation of smaller primary

11

particles. Those presented a broader filler-matrix interphase, due to higher surface area,

12

delaying the crystallization process. In the case of HAVOH-Silica, the crystallization occurs

13

with more significant delay (-10 °C) than in the systems with IL. This can be explained by

14

the existence of almost twice bigger primary particle, than for HAVOH-CH2CO2HMImCl,

15

which would reduce the active surface and HAVOH-silica interactions. Moreover the

16

presence of alkyl-IL on the silica surface decreased the HAVOH-silica affinity causing partial

17

phase separation and allowing the formation of larger nucleation centers. As a result, the

18

crystallization was favored and occurred at higher temperatures. The polarity of anion-cation 22 ACS Paragon Plus Environment

Page 23 of 42

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1

combinations played also an important role in the strength of the HAVOH-silica-IL

2

interactions. It was noted that IL of imidazolium cations substituted with polar functional

3

groups (carboxy-IL or ether-IL) with more coordinative [Cl] or [MeS] anions increased the

4

strength of HAVOH-silica-IL interactions, in opposition to the less coordinative [NTf2]

5

anion. On the other hand, when the alkyl-IL was paired with the [Cl] anion, the HAVOH-

6

silica-IL interactions decreased, while this interaction increased with the [NTf2] anion. This

7

suggests a completely different interphase interaction mechanism when using an IL with

8

either a polar or a non-polar cation side chain, where alkyl-IL interact through hydrophobic

9

tail-tail interaction (Scheme 1a). In contrast, carboxy- and ether-IL produce interphases

10

mainly based on H-bonds (Scheme 1b and 1c).43 Thus, by changing the IL structure it was

11

possible to control both primary particle size as well as the strength of the interphase

12

interactions.

13

14 15

Scheme 1. Representation of possible interactions in hybrid systems between HAVOH, silica

16

and (a) alkyl-IL, (b) ether-IL and (c) carboxy-IL.

17 18

Based on the WAXS patterns (Figure 5c), the crystalline structure of HAVOH

19

changes when the siloxane phase is present in the system. It seems that the intensity of the

20

crystalline peaks of all modified samples decreased, however, with the multiple overlapping 23 ACS Paragon Plus Environment


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Page 24 of 42

1

peaks in the scattering pattern it is difficult to quantify with accuracy the crystallinity

2

reduction.46 Nevertheless, this observation is consistent with the DSC results (Table 1) where

3

Xc decreased significantly for the hybrid systems, which indicates the formation of more

4

spread HAVOH crystals as a result of the added inorganic nanosized filler.

5 6

3.3 Mechanical properties

7

The DMA and tensile measurements were performed to study the reinforcement of the

8

HAVOH matrix with the addition of the silica/IL filler. Table 3 summarizes the storage (E’)

9

and tensile (Young modulus) moduli as well as TgDMA and tensile strength. Figure 7 presents

10

E’ and tan delta curves of the hybrids. All modified samples presented higher E’ than the neat

11

HAVOH independent of post-drying time (Figure 7a and 7b). The HAVOH-

12

CH2CO2HMImCl showed the largest E’ increase of 2.2 and 1.5 GPa for shorter and longer

13

post-drying time, respectively (Figure 7a and 7b; curves 5 and 5’). Also HAVOH-

14

C7O3MImNTf2 and HAVOH-CH2CO2HMImNTf2 presented significant improvements of

15

1.9 and 1.6 GPa for shorter post-drying. It was noted that longer post-drying caused a

16

decrease in the E’ values for most of the IL-modified samples, while TgDMA strongly

17

increased in all cases (up to 30 °C), when compared to shorter post-drying. In comparison

18

with neat HAVOH (curve 1 or 1’), shorter post-drying of modified samples caused a TgDMA

19

increase (up to 22 °C) (Figure 7c), while it slightly decreased for the longer one (Figure 7d).

20

Comparing the Tg results from DMA and DSC it is possible to notice significant differences

21

especially for samples with longer-post drying. Since the thermal memory was erased in the

22

first DSC heating scan, the TgDSC values were much lower than TgDMA. Additionally, the

23

longer-post drying resulted in free volume reduction, due to improved packing, which caused

24

internal stresses resulting in samples with higher TgDMA.


Page 25 of 42

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1 2

Figure 7. E’ (a,b) and tan delta (c,d) DMA curves of (1) HAVOH; (2) HAVOH-Silica; (3)

3

HAVOH-C4MImCl; (4) HAVOH-C4MImNTf2; (5) HAVOH-CH2CO2HMImCl; (6)

4

HAVOH-CH2CO2HMImNTf2;

5

C7O3MImNTf2. Curves with ’ (e.g. 1’, 2’) correspond to the samples submitted to longer

6

post-drying (1 h at 120 °C). In Figure 7b, only curves 1’ and 5’ were numbered due to

7

overlapping.

(7)

HAVOH-C7O3MImMeS;

(8)

HAVOH-

8 9

Since E’ values for nanocomposites submitted to shorter post-drying were mostly

10

higher than for those submitted to the longer post-drying, the tensile tests were carried out

11

only for this setup. Moreover, longer post-drying led to too brittle samples for the use in the

12

toughness dependent measurements. The results from tensile testes are gathered in Table 3

13

and representative stress-strain curves are presented in Figure 8. Rigid fillers, like silica, with 25 ACS Paragon Plus Environment


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Page 26 of 42

1

a density higher than the polymer matrix, can enhance not only polymer’s rigidity, hardness

2

and modulus, but also toughness. The increase in toughness is directly proportional to the

3

filler content, its dispersion and the area and quality of polymer-filler interfacial interactions.

4

Samples modified with polar-IL showed increased Young moduli and such behavior is

5

generally a result of reduced chain mobility and increased rigidity, which normally leads to

6

decrease in toughness due to low extensibility.47 However, all the IL-modified

7

nanocomposites presented toughness increase, where some polar-IL-modified samples had

8

more than three times increase in comparison to HAVOH-Silica. Since the filler content and

9

dispersion for all IL-based samples were very similar, the significant toughness differences

10

indicate that the interfacial interaction plays a very relevant role in the final nanocomposites’

11

properties. At the same time, this increase in filler-matrix interphase interaction resulted in a

12

reduced mobility of the matrix and, as a consequence a decrease in the tensile strength when

13

compared to neat HAVOH. Systems containing IL with the more hydrophobic [NTf2] anion

14

tend to present higher elongation, indicating lubrication of the interphase (Figure 8; curves 4,

15

6 and 8). Toughness, calculated from the area under the curve, increased for all modified

16

samples, especially for the ones with the [NTf2] anion.

17

Corroborating with previous results,31,43 systems with the IL of imidazolium cations

18

substituted with polar functional groups, especially carboxy-IL, showed the best balance of

19

mechanical properties. The mechanical performance suggests higher organization of HAVOH

20

chains, good dispersion of the silica/IL domains and strong interfacial interaction due to

21

multiple H-bonding.

22 23 24 26 ACS Paragon Plus Environment

Page 27 of 42

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1

Table 3 DMA and tensile tests results for HAVOH samples after two post-drying procedures;

2

15 min at 120 °C and 1 h at 120 °C (shadowed). E’a

TgDMAb

Modulusc

Tensile Strength

Toughness

[GPa]

[°C]

[GPa]

[MPa]

[J/m-3]

5.0

94.1 4.0±0.2

87 ±12

405

4.6

62.4

5.9

90.9 3.5±0.2

73 ±12

504

5.4

79.9

5.3

88.7 3.3±0.5

74 ±8

590

5.2

72.5

5.7

90.4 3.7±0.2

79 ±4

1212

5.8

76.1

6.4

92.4 4.1±0.1

82 ±4

777

6.8

67.6

5.7

91.6 4.6±0.1

82 ±2

1614

6.2

83.9

5.3

89.1 4.7±0.3

83 ±7

716

5.9

77.8

5.5

92.5 4.1±0.3

88 ±6

1176

6.5

73.9

Sample

HAVOH

HAVOH-Silica

HAVOH-C4MImCl

HAVOH-C4MImNTf2

HAVOH-CH2CO2HMImCl


HAVOH-C7O3MImMeS

HAVOH-C7O3MImNTf2

3

a

storage modulus at 30 °C obtained from DMA;

4

b

tan delta peak maximum;

5

c

Young modulus at 25 °C.

6



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Page 28 of 42

1 2

Figure 8. Stress-strain curves of samples submitted to the shorter post-drying procedure: (1)

3

HAVOH; (2) HAVOH-Silica; (3) HAVOH-C4MImCl; (4) HAVOH-C4MImNTf2; (5)

4

HAVOH-CH2CO2HMImCl;

5

C7O3MImMeS; (8) HAVOH-C7O3MImNTf2.

(6)

HAVOH-CH2CO2HMImNTf2;

(7)

HAVOH-

6 7

3.4 Barrier properties

8

The water vapor barrier property was measured via a water vapor permeation test.

9

HAVOH polymer presents very good oxygen barrier properties but is particularly sensitive to

10

water, thus a reduction of water permeability is highly desirable. Based on possible

11

applications, the barrier properties were tested only for the samples submitted to shorter post-

12

drying, since this procedure produced samples with better mechanical properties. All the

13

hybrids presented lower water vapor permeation values at different extent than neat HAVOH

14

(Figure 9). Since both SWAXS and DSC confirmed that the crystallinity of the hybrid

15

systems decreased, the observed reduction in permeation can be attributed to the presence of

16

silica and/or IL.

17


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1 2

Figure 9. The water vapor permeability for: (1) HAVOH; (2) HAVOH-Silica; (3) HAVOH-

3

C4MImCl; (4) HAVOH-C4MImNTf2; (5) HAVOH-CH2CO2HMImCl; (6) HAVOH-

4

CH2CO2HMImNTf2; (7) HAVOH-C7O3MImMeS and (8) HAVOH-C7O3MImNTf2.

5 6

In

particular,

the

hybrids

HAVOH-CH2CO2HMImCl

and

HAVOH-

7

CH2CO2HMImNTf2 presented the most significant decrease in permeation (~50 %),

8

indicating that the carboxy-IL allow more efficient silica dispersions and the formation of

9

more stable HAVOH-silica-IL physical crosslinks, which decreased the chain mobility and

10

created a more tortuous path for water diffusion. This improvement of water barrier

11

properties has been achieved despite the possible sorption of water molecules by IL, which

12

was already reported even for more hydrophobic IL.48,49 The obtained result, in term of

13

permeability reduction, is especially interesting since it is higher than that obtained for PVOH

14

films loaded with cellulose nanocrystals isolated from banana pseudostems fibers (28 %)49 or

15

with micro and nanocellulose crosslinked with tertbutyl acrylate-co-2-hydroxyethyl

16

methacrylate (23 %).51 Similar value reductions, to those obtained in our study (~45 %), have

17

been reported by Aloui et al.52 and by Spoljaric et al.53 However, the presented decrease in

18

permeability is related to PVOH samples loaded with much higher amounts of filler than that

19

used in this work (3 wt.-%), i.e. 10 wt.-% as total amount of halloysite and nanocellulose and

20

50 wt.-% of commercial nanofibrillated cellulose, respectively. Higher permeability reduction 29 ACS Paragon Plus Environment


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Page 30 of 42

1

(~65 %) has been obtained only by loading 5 wt.-% of quaternized cellulose.47 In this case,

2

despite the enhancement of water barrier properties, the produced film was not transparent

3

and a significant reduction (84 %) of elongation at break has been observed whereas our

4

results show, mainly for the HAVOH-CH2CO2HMImCl sample, a 50 % permeability

5

reduction and a simultaneous increase (~60 %) of elongation at break. Based on this, the

6

developed material can be certainly considered a good candidate as a single-layer material

7

exhibiting simultaneously enhanced water barrier, as well as good mechanical properties,

8

overcoming the previously described drawbacks related to the use of vinyl alcohol-based

9

materials.

10 11

3.5 Surface wettability

12

The intermolecular interactions between material surfaces and water were studied by

13

the contact angle method. Figure 10 shows differences in the water droplet shape when

14

deposited over neat HAVOH (Figure 10a) or HAVOH-CH2CO2HMImCl (Figure 10b)

15

surfaces. The contact angle measurements were also performed for the HAVOH-Silica

16

(Figure S4), however no significant difference in wettability was noticed when compared to

17

neat HAVOH. Contact angles of 91° ± 2.9 for HAVOH and 55.2° ± 2.4 for HAVOH-

18

CH2CO2HMImCl were obtained. The difference of ~36° clearly indicates higher surface

19

wettability for this nanocomposite. Increased water adhesion can be directly connected with

20

the number of available interactions (H-bond) in the silica/CH2CO2HMImCl hybrid. The

21

relatively small standard deviation, comparable to the one obtained for neat polymer, also

22

indicates good filler dispersion and film homogeneity. The same system also presented a

23

strong interaction with the polymer matrix, confirmed by combined SAXS, thermo-

24

mechanical and barrier results, once more emphasizing the high capacity of multiple H-

25

bonding. Furthermore, surface wettability is an important feature for evaluating the fungal 30 ACS Paragon Plus Environment

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1

biofilm adhesion at the polymer surface. Higher wettability is directly related to better

2

antifouling ability where a tightly bound water layer hinders the surface adsorption of fungi

3

and bacteria.54 The decreased contact angle indicates this system as potential material for

4

medical and food packaging.

5

6 7

Figure 10. Contact angle measurements for (a) neat HAVOH and (b) HAVOH-

8

CH2CO2HMImCl.

9 10

3.6 Biocompatibility

11

Toxicity of crosslinkers51 and fillers55 is an important issue when new developed

12

material has its application in food or medical field. Thus, the evaluation of nanocomposites’

13

cytotoxicity was performed using the L929 cell line. The cell metabolic function and

14

proliferation assessment was used as a quantitative method to determine the biocompatibility

15

of the nanocomposites. The results after 24 and 48 h of cells exposure to the nanocomposites

16

are shown in the Figure 11. A general trend of increasing cell response with increased

17

exposure time to materials was observed for the negative control (CTR) and tested

18

nanocomposites. This indicates that L929 cells were able to express increased metabolic

19

activity either through increased population density or cellular function. Neat HAVOH (1)

20

was found to be a biocompatible material independent of exposure time when compared to

21

CTR. The same behavior was observed for HAVOH-CH2CO2HMImCl (5) and HAVOH-

22

C7O3MImMeS (7), which presented an increased growth at both exposure times. This

23

indicates more favorable conditions for the cell growth, which was most likely due to the 31 ACS Paragon Plus Environment


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Page 32 of 42

1

materials higher hydrophilicity (Figure 10). The samples HAVOH-Silica (2), HAVOH-

2

C4MImNTf2 (4) and HAVOH-C7O3MImNTf2 (8) demonstrated better results after 48 h of

3

incubation time, suggesting slower cell growth rates. The strong HAVOH-silica interaction

4

and/or more hydrophobic character of the [NTf2] anion containing IL could retard this

5

process. Results for HAVOH-C4MImCl (hydrophobic cation, 3) and HAVOH-

6

CH2CO2HMImNTf2 (hydrophobic anion, 6) indicate the formation of a more hostile

7

environment for the cells. Despite that, no severe inflammatory response was observed in any

8

of the demonstrated cases and all tested samples can be considered as biocompatible.

9

10 11

Figure 11. AlamarBlue assay to determine the proliferation of L929 cells after 24 and 48 h

12

of cell culture on: control (CTR); (1) HAVOH; (2) HAVOH-Silica; (3) HAVOH-C4MImCl;

13

(4)

14

CH2CO2HMImNTf2; (7) HAVOH-C7O3MImMeS and (8) HAVOH-C7O3MImNTf2.

HAVOH-C4MImNTf2;

(5)

HAVOH-CH2CO2HMImCl;

(6)

HAVOH-

15 16

Conclusions

17

The in situ sol–gel technique in the presence of six different IL was used to prepare

18

biocompatible HAVOH hybrid films. Very efficient filler hybrid dispersions were achieved,

19

causing a positive reflex on the thermal, mechanical and water vapor barrier properties. By

20

changing the IL structure and, as a consequence, its characteristics it was possible to control 32 ACS Paragon Plus Environment

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1

the primary silica particle size and strength of interfacial interactions, which reduced polymer

2

mobility and crystallinity near the organic-inorganic interphase. The carboxy - and ether-IL

3

exerted a stronger influence on both silica dispersion and nanocomposite properties,

4

indicating the importance of the polar functionalized IL in the formation of a multiple H-

5

bonding network throughout HAVOH-silica-IL. The system HAVOH-CH2CO2HMImCl

6

presented the best balance of thermo-mechanical and barrier properties than the other

7

materials. Altogether, the presented sol–gel strategy provided a promising approach to

8

prepare reinforced silica/IL-based single-layer polymeric nanocomposites in aqueous

9

solutions for biomedical and food packaging applications.

10 11

ASSOCIATED CONTENT

12

Supporting Information. 1H-NMR spectra of the IL’s anion exchange process from

13

[C7O3MIm][MeS] to [C7O3MIm][NTf2],TGA/DTG curves, SEM images of ashes obtained

14

from TGA, comparison of contact angle images of neat HAVOH and HAVOH-Silica and

15

table with SAXS scattering properties of nanocomposites are available free of charge via the

16

Internet at http://pubs.acs.org.

17 18

AUTHOR INFORMATION

19

*Corresponding authors:

20

Henri S. Schrekker, Phone : +55 51 3308.6302 ; E-mail: [email protected]

21

Marino Lavorgna, Phone: + 39 0817758838; E-mail: [email protected]

22 23 33 ACS Paragon Plus Environment


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Page 34 of 42

1

ACKNOWLEDGMENTS

2

The authors thank the Brazilian funding agencies CNPq (Science without Borders Special

3

Visiting Scientist project 400531/2013-5), CAPES and FAPERGS for financial support, as

4

well as CNR-Italy and AVCR-Czech Republic for funding the cooperation project “New

5

sustainable approaches in the synthesis of epoxy-silica hybrids with tunable properties (2013-

6

2015)”. R. K. Donato is thankful to FAPERGS-CAPES for the DOCFIX post-doctoral

7

fellowship and to the Short Term Mobility Program 2015 funded by CNR (Prot. N. 26996).

8

The authors are thankful to Ewa Pavlova (IMC Prague) for the TEM images.

9 10

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(54) Jäger, E.; Donato, R. K.; Jäger, A.; Donato, K. Z.; Höcherl, A.; Perchacz, M.; Konefał,

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R.; Surman, F.; Kredatusová, J.; Bergamo, V. Z.; Schrekker, H. S.; Fuentefria, A. M.; Raucci,

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M. G.; Ambrosio, L.; Štěpanek, P. Biocompatible succinic acid-based polyesters for potential

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biomedical applications: fungal biofilm inhibition and mesenchymal stem cell growth. RSC

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Adv. 2015, 5, 85756-85766.

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(55) Jorda-Beneyto, M.; Ortuño, N.; Devis, A.; Aucejo, S.; Puerto, M.; Gutiérrez-Praena, D.;

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Houtman, J.; Pichardo, S.; Maisanaba, S.; Jos, A. Use of nanoclay platelets in food packaging

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materials: technical and cytotoxicity approach. Food Addit. Contam. A 2014, 31, 354-363.

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1

Graphical Abstract for: High Amorphous Vinyl

2

Alcohol-Silica Bionanocomposites: Tuning

3

Interface Interactions with Ionic Liquids

4

Katarzyna Z. Donato, Marino Lavorgna, Ricardo K. Donato, Maria G. Raucci, Giovanna G.

5

Buonocore, Luigi Ambrosio, Henri S. Schrekker and Raquel S. Mauler

6

7 8

Synthesis of HAVOH-silica-ionic liquid bionanocomposites with improved thermo-

9

mechanical and barrier properties for sustainable packaging applications.

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High Amorphous Vinyl Alcohol-Silica Bionanocomposites: Tuning

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