Polyaniline Hybrid through Diazonium Chemistry: Conductive

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Clay/polyaniline hybrid through diazonium chemistry: conductive nanofiller with unusual effects on interfacial properties of epoxy nanocomposites Khouloud Jlassi, Sarath Chandran Chandrasekhara Kurup, Mohammed Arif Poothanari, Memia Benna-Zayani, Sabu Thomas, and Mohamed M Chehimi Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b04457 • Publication Date (Web): 10 Mar 2016 Downloaded from http://pubs.acs.org on March 15, 2016

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Clay/polyaniline hybrid through diazonium chemistry: conductive nanofiller with unusual effects on interfacial properties of epoxy nanocomposites Khouloud Jlassi1,2,3,*, Sarath Chandran4, Mohammed A.Poothanari 5, Mémia Benna-Zayani1,2*, Sabu Thomas4,5*,Mohamed M. Chehimi3,6* 1

Laboratoire d'Application de la Chimie aux Ressources et Substances Naturelles et à l'Environnement (LACReSNE), Faculté des Sciences de Bizerte, University of Carthage, 7021 Jarzouna-Bizerte (Tunisia) 2 Institut Supérieur des Sciences et Technologies de l’Environnement (ISSTE), Borj Cédria, 2050 Hammam-Lif, Tunisia 3 Univ Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR CNRS 7086, 15 rue JA De Baïf, Paris, France 4 School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala, India 686 560 5 International and Interuniversity Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, India 686 560 6 Université Paris Est, UMR 7182 CNRS, UPEC, 94320 Thiais, France

Abstract The concept of conductive network structure in thermoset matrix without sacrificing the inherent mechanical properties of thermoset polymer (e.g. epoxy) is investigated here using “hairy” bentonite fillers. The latter were prepared through the in-situ polymerization of aniline in presence of the 4-diphenylamine diazonium (DPA)-modified bentonite (B-DPA) resulting in a highly exfoliated bentonite-DPA/polyaniline (B-DPA/PANI). The nanocomposite filler was mixed with diglycidylether of bisphenol A (DGEBA) and the curing agent (4,4’diaminodiphenyl sulphone) (DDS) at high temperature in order to obtain nanocomposites through the conventional melt mixing technique. The role of B-DPA in the modification of the interface between epoxy and B-DPA/polyaniline (B-DPA/PANI)is investigated and compared with the filler B/PANI prepared without any diazonium modification of the bentonite. Synergistic improvement in dielectric properties and mechanical properties points to the fact that the DPA aryl groups from the diazonium precursor significantly modify the interface by acting as an efficient stress transfer medium. In DPA-containing nanocomposites, unique fibril formation was observed on the fracture surface. Moreover, dramatic improvement (210-220%) in fracture toughness of epoxy composite was obtained with B-DPA/PANI filler as compared to the weak improvement of 20-30% noted in the case of the B/PANI filler. This work shows that the DPA diazonium salt has an important effect on the improvement of the interfacial properties and adhesion of DGEBA and clay/PANI nanofillers. Keywords: Clay, diazonium salts, polyaniline, DGEBA, nanocomposites *corresponding authors: Dr K. Jlassi, [email protected] Dr M. M. Chehimi, [email protected]. Prof. M. Benna, [email protected] Prof. S. Thomas, [email protected]

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Introduction Diglycidylether of bisphenol A (DGEBA) epoxy nanocomposites are one of the most important engineering materials used in the 21st century owing to a wide span of applications such as food packaging,1 adhesives,2 electronics,3 coatings4 and aerospace.5 This success story is due to their good chemical resistance and excellent thermal and electrical insulating properties. However, the highly brittle nature and low resistance to crack propagation arising from the high cross-link density significantly limits its applications. Therefore, the modification of epoxy matrices in order to improve their mechanical properties, flame retardancy and resistance to humidity is an important issue and needs to be addressed. In this regard, the use of clay-based fillers to control the properties of epoxy is an efficient strategy adopted by many researchers.6 In addition, electrical properties is another feature that needs to be considered for the fabrication of e.g. capacitors, computer memory devices and artificial muscles.7,8,9 .Towards this end, incorporation of conductive fillers permits to tune the dielectric properties of epoxy matrices. Recent years witnessed an important number of reports on the preparation of composites of epoxy resins and inherently conductive polymers such as polypyrrole10 and polyaniline (PANI).11,12 These inherently conductive polymers are easily synthesized in high yield, exhibit environmental stability and could, under certain synthesis conditions, have high electrical conductivity.13 At the percolation threshold, the conductive polymer creates a conductive network within the matrix; however, it must be kept as low as possible in order to achieve high conductivities without damaging the mechanical properties of the host matrix. The standard PANI synthesis method results in a more or less globular morphology which results in low aspect ratio14 whereas nanostructured PANI with high aspect ratio is known to yield conductivity at low percolation threshold.15 Long et al.16 have reported different methods to

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increase the aspect ratio of PANI: hard physical template-guided and soft chemical template synthesis procedures. In the present study, clay was selected as a hard nanostructured template for the in-situ synthesis of PANI resulting in clay/PANI nanocomposites. Clays are low cost and abundant natural materials, known to impart remarkable properties to polymer matrices such as high storage modulus and flame retardancy.17 However, there are some key issues sought for in this work: dispersion in polymer matrices and electrical conductivity. This can be achieved by making clay/PANI nanocomposite fillers for epoxy. These nanocomposites would best be exfoliated if swellable clays are selected for improving the mechanical and electric properties of the epoxy matrix under test. Bentonite is one of the swellable clays; it is composed of thin aluminosilicate layers (length ~ 500 nm, thickness ~ 1.3 nm) organized in parallel stacks with regular interlayer spacing. These galleries contain Na+ cations that can be easily exchanged with alkyl ammonium ions.18,19 The latter are employed to prepare organophillic clay that is compatible with several types of organic polymers such as epoxy, poly(methacrylates) and conductive polymers, e.g.polyaniline. Organophilic clays permit to prepare exfoliated claypolymer nanocomposites through melt mixing, reaction of clays with polymers, or by in-situ polymerization.17,20,21,22,23,24,25 As alternative to ammonium salts, we have recently described the use of diazonium salts to intercalate bentonite prior to in-situ polymerization of aniline.26 In this seminal work, we have efficiently intercalated bentonite with diphenylamine diazonium salt precursor (DPA). This diazonium is readily exchanged with sodium to give an intercalated layered nano-platform for the in-situ graft oxidative polymerization of aniline. In addition, DPA species attach to the clay nano-sheets upon curing at 60 °C and further act as coupling agents for PANI to clay through covalent bonding. This novel strategy resulted in highly exfoliated clay/PANI nanocomposites with remarkable conductivity. Without any diazonium pretreatment, the 3


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clay/PANI nanocomposites were about 5 orders of magnitude less conductive, hence the central role of diazonium salts. It is to note that diazonium salts raised a huge interest as they are able to efficiently modify the surface of quasi all materials, however through specific mechanisms.27,28,29,30,31 . Taking advantage of (i) the interfacial chemistry of diazonium salts in obtaining conductive clay/PANI nanocomposites, and (ii) the concept of clay/polymer hybrid fillers (e.g. for high performance epoxy resin composites6 or for dental adhesives32), we propose for the first time to make conductive clay/PANI fillers for epoxy matrices. In this way, we tackle an interesting aspect of diazonium coupling agents: their effect on mechanical and dielectric properties of epoxy, a resin of fundamental and technological importance.

In the present work, we have prepared ternary epoxy composites using clay/PANI hybrids as nanofillers. The latter were prepared by oxidative polymerization of aniline in the presence of pristine or DPA-modified bentonite (B and B-DPA, respectively). The B-DPA/PANI is used for the first time as filler for DGEBA epoxy matrix. The dielectric and mechanical properties of the host epoxy matrix were thoroughly investigated. The rheological behaviors of the uncured samples (liquid phase); namely viscosity at steady state, complex viscosity, and storage and loss moduli; were studied. For the cured samples (solid phase), mechanical (tensile strength and Young's modulus) and thermomechanical properties (including storage and loss moduli and glass transition temperature) were assessed. We shall demonstrate the synergetic effects of DPA and PANI to significantly improve the mechanical and dielectric properties of the epoxy matrix.

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2.Experimental 2.1. Reagents The

DGEBA

(bisphenol

A

diglycidyl

ether)

and

the

curing

agent,

4,4'-

diaminodiphenylsulfone (DDS) were provided by Sigma Aldrich and used as received. The raw clay was extracted from the Gafsa-Metloui basin (Tunisia; Lambert coordinates: the longitude is about 6 grads and 69 minutes (east) and the latitude is 38 degrees and 27 minutes North). The clay was purified according to standard procedure described in references33,34 in order to obtain the final ~80µm-sized soda clay (B-Na) particles. The cationic exchange capacity (CEC) of the clay was assessed using methylene blue35 and found to be equal to 101.9meq/100 g of clay. N-phenyl-p-phenylenediamine (Acros, 98% purity), isopentyl nitrite (Alfa Aesar, purity 97%), ammonium persulfate (APS, Acros, 98% purity) and nitric acid (Carlo Erba, 60% purity) were used as received. Aniline (Aldrich, 99.5% pure) was purified by passing it through a column of basic alumina powder (Merck, size ~ 63 µm) and then stored at low temperature prior to use. Deionized water was used throughout all the experiences for various cleaning and dilution. 2.2. Synthesis of clay/polyaniline nanocomposites The hybrid nanocomposites clay/polyaniline were previously prepared by in-situ oxidative polymerization of aniline in the presence of 4-diphenylamino diazonium-exchanged clay as a function of the cation exchange capacity (CEC).26,36 Hereafter, unmodified and diazonium-modified clay-polyaniline nanocomposites will be abbreviated as B/PANI and B-DPA/PANI, respectively. 2.3. Reinforcement of epoxy resin by nanocomposite Ternary composites were prepared by dispersing the bentonite, B/PANI and B-DPA/PANI nanofillers in 35 g of epoxy resin using a probe sonicator (Biometric company) for 5 min then 5


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DDS was added at180°C temperature under agitation. The target mass loading of the hybrid filler in the final composites was 0.1, 0.5and 2 mass loading (wt %) unless otherwise indicated. The solutions were homogeneously stirred and then poured in metallic mold (rectangular shape, 12x15 cm, 3 mm thick) for curing (4 h at 180°C) then post cured at 200°C for 1 h. For comparison, and in order to investigate the effect of the diazonium salts grafted to clay on the final properties of the DGEBA epoxy resins, B/PANI nanofiller was mixed with the epoxy resin under similar conditions.

2.5. Characterization Scanning electron micrographs (SEM) were taken with a Zeiss Supramke apparatus and Jeol 100 CX-II served for recording transmission electron microscopy (TEM) images. For TEM imaging, clay/PANI nanocomposites were mixed with a resin prior to microtome sample cutting. Tensile properties were tested by using a Shimadzu Universal Testing Machine (UTM), equipped with a 10 kN load cell at a displacement rate of 5 mm/min at room temperature as per ASTMD 638. The flexural properties were determined using rectangular bars having a dimension of 127 mm × 12.5 mm × 4 mm on the same machine, at a speed of 10 mm/min as per ASTM D 790. Rectangular specimens (45x8x3.5 mm) were subjected to DMA in three-point bending mode at a frequency of 1 Hz and oscillation amplitude of 0.05 mm using a PerkinElmer DMA8000. The blend specimens were characterized in the 30-250 °C temperature range. Modulated force thermos-mechanometry (mf-TM) studies were carried out using Perkin Elmer DMA 8000 in single cantilever mode in the 30-250 °C temperature range and

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frequency between 0.01 and 100Hz. 45x8x3.5 mm-sized rectangular test specimens were used for this purpose. The viscoelastic properties of DGEBA/B-DPA/PANI and DGEBA/B-DPA/PANI/DDS blends were measured using TA instruments ARES Rheometer using parallel plate geometry (25µm plates) in oscillatory shear. Measurements were carried out in the linear viscoelastic domain, and variation of moduli was recorded between 0.01 to 100 rad·s-1 with five data per decade. The dielectric measurements were carried out at room temperature using an Agilent E4980A impedance analyzer (100 Hz – 2 MHz).

3. Results and discussion

3.1. The effect of diazonium cation intercalation of bentonite on the properties of clay/polyaniline nanofillers. The conductive clay/PANI nanocomposites were prepared by sequential diazonium cation exchange reaction of the clay and in-situ oxidative polymerization of aniline as previously described.26 The clays were first intercalated by the diazonium of DPA, cured at 60 °C to covalently bind the DPA aryl groups to the bentonite sheets and served as a support for the insitu oxidative polymerization of aniline. The resulting nanocomposites are noted B-DPA/PANI. For comparison, untreated clay served for the in-situ oxidative polymerization of aniline to obtain the nanocomposite B/PANI (Figure 1, upper panel). In the particular case of B-DPA/PANI, the lower panel of Figure 1 shows the interface chemistry of the nanofiller with the epoxy resin and the hardener. The exfoliated clay has NH groups from either DPA or PANI which react with epoxy groups via ring opening therefore ensuring covalent attachment of the resin to the clay sheets (via PANI and DPA). Similarly, DDS has two amino groups 7


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which react with epoxy by ring opening leading to crosslinking of the resin. Supporting Information SI1 displays digital photographs of pristine and modified clays, and the final epoxy composite. The figures of merit of the two types of nanocomposites are summarized in Table 1.

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Clay nanosheet Diazonium PANI

NO3

NO3 N

N

OH

CH3 CH2 CH

R

N

OH

S

O

C

O

CH2

CH2

CH3 CH2

O

CH3

C n=0.14

OH

CH3 R

CH

N

O

CH2

CH

CH3

OH

CH3

CH2

O

CH2

O

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N

CH2

CH2

CH

O

C

O

CH3

CH2

CH

CH2

O

C CH3

n=0.14

O

CH2

CH OH

OH

Clay/DPA nanosheet DDS

DGEBA PANI

Figure 1. Upper panel: schematic illustration of the preparation of clay/polyaniline nanofillers with and without diazonium cation intercalation step. Lower panel: molecular view of the epoxy-DDS-B-DPA/PANI interface. 9


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Table 1: Summary of preparation methods and electrical and morphological features of clay/PANI nanocompositesa Surface modifier Experimental details

Structure and cristallinity

Morphology

B-DPA/PANI

B/PANI

4-Diphenylamine diazonium salt (DPA) Purified bentonite (B) was first cationically exchanged with DPA, followed by the in- situ oxidative polymerization of aniline Exfoliated B-DPA/PANI nanocomposite crystalline structure of PANI chains on clay surface (no diffraction peak from clay)

-

Straight and twisted rods of polyaniline of about 40 nm diameter and 200 nm length σ= 2.4 x10-3 S.cm-1

In situ oxidative polymerization of aniline in the presence of purified bentonite Same interlamellar distance as in pristine bentonite (1.38 nm).

mixed regions from uncoated bentonite and PANI deposits

Conductivity σ= 2.1 x10-8 S.cm-1 for full details about the synthesis and the physicochemical properties of the nanocomposite fillers, see ref. [26].

a

From Table 1, it is clear that diazonium salts are essential intercalants for making exfoliated, conductive clay/polyaniline nanofillers. We shall investigate hereafter the effect of these conductive nanofillers on the morphology, mechanical properties, rheological behaviour and dielectric properties of epoxy matrix.

3.2. TEM and XRD of epoxy filled with nanofiller TEM image and XRD pattern of a crosslinked epoxy sample filled with B-DPA/PANI at 0.5 wt % mass loading are depicted in SI2. For comparison, TEM images and XRD patterns are also displayed in SI2 for bentonite, B-DPA and B-DPA/PANI fillers. Clay sheets are well dispersed with individualized sheets. There is also evidence for intercalated region as we have demonstrated previously. Most probably, intercalated B-DPA/PANI regions are due to the kaolinite fraction of bentonite. Indeed, it is well-known that kaolinite cannot be swollen and therefore not be fully exfoliated.37 For this reason, intercalated regions are persistent but at a very low extent. In the XRD pattern of the epoxy matrix filled with B-DPA/PANI loaded at 10


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0.5 wt % there is no sign for a diffraction peak at low angle indicating a high degree of exfoliation of the filled epoxy, a result that parallels the TEM observation

3.2.2. Microstructure of fracture surface

Figure 2. SEM images of the fracture surfaces taken from tensile specimens of (a) cured pure epoxy, (b) 0.5 wt % B/PANI,(c) 2 wt % B/PANI,(d) 2 wt % B/PANI, (e) 2 wt % B-DPA/PANI. Upper and low rows display high and low magnification SEM images.

In order to understand differences in mechanical behavior of the composites, the tensile fracture surface of the cured pure epoxy and the epoxy nanocomposites (with 0.5 and 2 wt % nanofiller) were examined by SEM. Figure 2 shows fracture surfaces for neat epoxy, and epoxy filled with B-DPA/PANI and B/PANI at indicated mass loadings. In the case of the cured, pure epoxy, Figure 2(a) exhibits a very smooth fracture surface together with the riverlike markings (commonly observed in the cured epoxy tensile specimens)38 without any obvious plastic deformation.39 However, the fracture surface of the cured epoxy nanocomposites becomes very rough and dramatically changes after addition of the B-DPA/PANI nanofillers. The fractured surfaces (Figure 2(c),(e)) reveal extensive fibril, distinct and continuous formation, and indicate that the B-DPA/PANI nanoparticles induce 11


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the formation of a network structure within the epoxy matrix. This peculiar structure is most probably induced by a very strong filler-matrix adhesion40 between B-DPA/PANI and epoxy. The morphology of epoxy filled with B-DPA/PANI was compared with that of B-PANI so as to qualitatively evaluate the effect of DPA on fracture mechanics. Figures 2(b) and 2(d) display significantly distinct morphologies and thus highlight a very clear effect of DPA on the fracture surface. Indeed, in the absence of any DPA, dispersed droplets are formed, a situation that contrasts with the formation of fibrils in the case of fractured DPA-containing composites. This fibril formation has not been reported previously which highlights an unusual effect of B-DPA/PANI nanofillers on the fracture surface of the ternary epoxy nanocomposites. Additionally, extensive crack blunting, arresting and bifurcations could be seen in the B-DPA/PANI/Epoxy system. No such observations could be seen in B-PANI/Epoxy system. In addition, the investigation of the mechanical properties shows that addition of DPA results in a synergetic improvement in fracture toughness. Thus DPA aids in a total change in morphology of the dispersed phase (clay/PANI) followed by an improvement in fracture toughness by acting as an effective stress transfer agent between epoxy (matrix) and filler (dispersed phase).

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3.3. Viscoelastic properties of unfilled and filled epoxy by DMA 1E8

1E8

(a1)

(a2)

1E7

100000 10000

Neat DGEBA 0.1 % nanocomposite 0.5 % nanocomposite 2 % nanocomposite

1000 100

12 10 8 6 4 2 0 -2 -4 -6 -8 -10 120

140

160

180

220

240

100000 10000 1000 100

260

12 10 8 6 4 2 0 -2 -4 -6 -8 -10 150 160 170 180 190 200 210 220 230 240 250 260

Temperature (°C)

0,1 Frequency (Hz)

1E8

200

1000000

at

loss modulus (Pa)

1000000

at

Storage modulus (Pa)

1E7

Temperature (°C)

1E-3 Frequency (Hz)

1E9

1E7

1E8

(b1)

(b2) 1E7

10 8 6 4

100000

2 0 -2

0.1 % nanocomposite 0.5 % nanocomposite 2 % nanocomposite

10000 1000

1000000 100000 10000

-4 -6

1000

-8 160

180

200

220

240

at

1000000

loss modulus (Pa)

1E7

at

Storage modulus (Pa)

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10 8 6 4 2 0 -2 -4 -6 -8 160

Temperature (°C)

0,1

1E9

Frequency (Hz)

1E-3 Frequency (Hz)

180 200 220 Temperature (°C)

240

1E7

Figure 3.Storage and loss moduli master curves for neat epoxy resin, epoxy resin/B/PANI samples (shown as a1 and a2) followed by that of epoxy resin/B-DPA/PANI samples shown as (b1 and b2). Plots of aτ (shift factor) vs temperature are shown in insets of Figures a1, a2, b1 and b2.

The long term mechanical properties of DGEBA/B-PANI and DGEBA/B-DPA/PANI nanocomposites were investigated using the William-Landel and Ferry (WLF) equation, which is derived from the Doolittle equation : β(

η = Be

v* ) vf

(1)

where B is the pre-exponential factor, β is an empirical constant approximated to 1, v* is the void volume and vf is the free volume.

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The WLF equation is expressed by:

log aτ =

− C1 (T − Tg ) C 2 + (T − Tg )

(2)

where aτ is the shift factor and C1 and C2 are universal constants. C1 can give information on the free volume at the glass transition whilst C2can give information on the thermal expansion as well as the underlying glass transition.41 An exponential decay for the shift factor shows that WLF equation can be applied to the nanocomposites under consideration. Figure 3 shows the master curves obtained by the horizontal shift procedure of the experiments carried out between temperature ranges of 150250 °C. This needs to be considered on the basis of the fact that Time Temperature Superposition (TTS) cannot be applied when there is large scale segmental motion (like melting, or crystallization). A linear increase in the value of loss modulus C1 and C2values indicate the improvement in long term mechanical properties and thus the ability of the nanocomposite to be used in engineering applications. Actually, the loss modulus values of C1 was found to increase from 20.9 to 27.18 in the case of DGEBA/B-PANI and up to 34 in the presence of DGEBA/B-DPA/PANI while the C2 value increased from 51.7 to 144.8 and reached 204.6 respectively for the two previous nanofillers (See SI3). The grafting of PANI chains to clay and particularly to the diazoniummodified clay (B-DPA) induces exfoliation of the clay and thus improves the dispersion of clay in the DGEBA matrix. This results in an improvement in the long termproperties (increase in C1 and C2 values). Indeed, up to 0.5 wt% loading of the nanofillers both NH from PANI and from DPA participate with DDS to epoxy curing. The combined reactivity of DPA, PANI and DDS aid to the dispersion of clay and prevent its agglomeration. 14


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However, for the 2wt % added nanofillers, there is a decrease in long term mechanical properties compared to the pure DGEBA matrix. The C1 value decrease from 21.9 for the neat DGEBA matrix to 8.62 and 21.5for the matrix filled with B/PANI and B-DPA/PANI, respectively, most probably due to the agglomeration of the nanofiller particles. α relaxation in DGEBA epoxy resin, DGEBA-B/PANI, and DGEBA-B-DPA/PANI samples were modeled using the Vogel-Fulcher-Tamman equation.42

τ=τ0 exp(B/T-Tk)

(3)

where Tk is the Kouzmann temperature, B is a parameter that defines the energy barrier for molecular rearrangement. The value of τ0 was set to 1*10-14 which corresponds to the time required to move a molecule near the Debye frequency. Alternatively the activation energy for α relaxation (B) can also be calculated using the WLF equation as,

C1 =

B 2.303(Tref − T0 )

C 2 = T ref − T 0

(4)

(5)

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Figure 4: Activation energy for αrelaxation B(K) values calculated for epoxy resin and epoxy resin-DPA/PANIand epoxy resin-B/PANI nanocomposites versus the mass loading.

Figure 4 shows a plots of B(K) versus the filler mass loading. There is an initial increase in B(K) value probably due to a plasticizing action of B-DPA/PANI, however up to 0.5 wt % loading only. The plot for epoxy filled with B-DPA/PANI suggests an increase of interfacial regions at low mass loading of the filler. This also points to the fact that at low amounts of BDPA/PANI and B/PANI there is homogenous mixing. However as the amountof filler is increased the homogeneity is lost partly due to the decreased reactivity of the secondary amine (from PANI) and partly due to the agglomeration of the B-DPA/PANI. A similar decrease in B(K) value is observed for the B/PANI filler too but at a much lesser extent. It is important to note that in the case of the B-DPA/PANI filler a highest value of B value at 0.1 wt % compared to the B/PANI containing composite is very likely to be due to the effective role of the secondary amine of DPA coupling agent.

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Figure 5. Plots of (a) G′, (b) G″and (c) Tan (δ) vs temperature for the cured pure epoxy and filled epoxy with 0.1, 0.5 and 2 wt % B-DPA/PANI loadings.

Dynamic mechanical analysis (DMA) provides information on the storage modulus (G′) and loss modulus (G”) in the test temperature range. Figure 5 shows storage modulus (G′), loss modulus (G”) and Tan (δ) versus temperature for the cured, pure epoxy and epoxy/B-DPA/PANI nanocomposites at indicated nanofiller mass loading. The storage modulus represents the elastic behavior of the materials and the energy storage during the elastic deformation, while the loss modulus reflects the viscous behavior of the materials and the energy dissipation during the test. It is clear that there are huge improvements of (G′) and 17


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(G″)in the nanocomposites upon incorporation of a small amount of nanofiller (0.1 and 0.5 wt %) to the epoxy matrix. Itis primarily due to the exfoliation of the nanoclay sheets that causes the formation of physical connectivity or percolated network of the filler at very small volume fractions owing to the large aspect ratio and the high surface area of the starting bentonite (736 m2/g). Therefore, the exfoliation of the nanoclays dispersed in polymer matrix may exhibit highest improvements in viscoelastic properties for a very low quantity of nanofiller since a perfect exfoliation imparts both high surface area and aspect ratio to the dispersed nanoclay. The exfoliation of nanocomposites was confirmed with XRD although persistent intercalated structures were observed in TEM images.26 However, for the modulus and storage modulus of the 2 wt % added nanofiller, there is a very small relative decrease from the pure epoxy matrix most probably due to the agglomeration of the clay nanofiller particles in the DGEBA matrix. The latter phenomenon could be ascribed to the high number of crosslinks present in the cured DGEBA. Indeed, PANI can act also as a crosslinker and its presence at high concentration with the DDS (principal hardener) can cause the agglomeration of the nanofiller, hence the decrease of mechanical properties. Figure 5c displays the Tan δ spectra of the nanocomposites at indicated filler mass loading. The main relaxation peak of the 0.1 and 0.5 wt % B-DPA/PANI filled epoxy matrix is shifted towards the higher temperatures as compared to the neat epoxy (peak centred at170 °C). The peak position is a measure of glass transition temperature of the epoxyand reflects the degree of cross-linking in the materials.43It is worth to note that the peak amplitude is significantly increased

from

0.61

(neat

epoxy)

to

1

(epoxy

filled

with

0.1

wt

%

B-DPA/PANI). The height of the Tan δ peak is a measure of the damping properties imparted by the hybrid filler at 0.1 and 0.5 wt %, (this also indicates the improved fracture toughness of the nanocomposites as an energy absorbing system on high impact loading), it correlates well 18


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with the increase of as high as 50 °C for the Tan δ peak peak position. These results are in line with a better high resistance to temperature and mechanical stress. The increased Tg is attributed to the fact that the added clay nanofiller restrict the segmental movement of the polymer chains.47 In contrast, in the case of 2 wt % B-DPA/PANI filled epoxy a small decrease in Tg was observed because of the agglomeration of the nanofiller (Tg = 150 °C compared to 170 °C for the neat epoxy). Here again, the exfoliation of the nanoplatelets into the host matrix and the chemical binding between the matrix and the organoclay through the amine functions of the PANI chains could explain these huge improvements in the thermomechanical properties of the epoxy upon addition of the hybrid filler, however at 0.1 and 0.5wt % but not more.

3.4. Tensile mechanical properties The tensile strength of epoxy filled with B-DPA/PANI is displayed in SI4a. The variations of tensile and flexural strengths are more or less similar as reported in SI4b. Epoxy filled with BDPA/PANI (0.1wt %) composites displayed the highest (53.16 MPa) tensile strength while pure epoxy and that filled with B-DPA/PANI (2wt %) showed the lowest (about 31.57 MPa). Indeed the tensile strength increases dramatically at low nanofiller loading (0.1 and 0.5 wt %) and its rate of improvement decreases with increasing concentration of nanofiller (2wt %). This is can be attributed to the effective dispersion of nanofiller particles at (0.1 and 0.5 wt %) loading as well as the good interfacial adhesion between the particles and the epoxy matrix which restricts elongation and hence deformation. However, the observed lower tensile with 2wt % of nanofiller content can be due to the presence of un-exfoliated aggregates as described previously. The effect of DPA on the mechanical properties was measured for comparison and Figure 6 shows the same. 19


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Figure 6. Fracture toughness measurement of neat epoxy resin, DGEBA/B/PANI and DGEBA/B-DPA/PANI samples.

One can note that the fracture toughness shows a synergetic improvement with the addition of the different kind of nanofillers. In the case of B/PANI samples an improvement of 20-30% was observed while the addition of B-DPA/PANI increases the fracture toughness by 210-220 %. This dramatic improvement in fracture toughness shows that the DPA acts as a very effective stress transfer medium.

3.5. DSC study DGEBA-B-DPA/PANI samples with curing agent (DDS) were subjected to dynamic DSC study at 5 different heating rates. The results obtained were used to calculate the cure activation energy using Kissinger model.44,45

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( (

∆ ln β / T p2 ∆ (1 / T p )

)) = − E R

a

(6)

Here β is the heating rate, Ea is the activation energy and R is the universal gas constant. Thus a plot of β/Tp2 against 1/Tp gives activation energy as the slope.

Figure 7. Activation energy of epoxy curing versus the amount of B-DPA/PANI for DGEBA nanocomposites. It has been proposed that the nature of amino group plays a major role in the curing process. Primary amines act strong curing agents whereas tertiary amines are cure accelerators.46,47 Secondary amines are known to act both as curing agents and accelerators;47,48 their reaction of with epoxy can take place and is usually catalyzed by OH groups resulting from the reaction of primary amines with epoxy.49 Thus the aim of this study was to confirm the role of PANI in curing of DGEBA.50,51 It can be seen from Figure 7 that the cure activation energy decreased as the amount of B-DPA/PANI increased indicating the secondary amino group of PANI acts as a cure accelerator. On increasing the amount of B-DPA/PANI (above 2 wt %)

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the activation energy increases which can be due to the steric crowding caused by the addition of clay.

3.6. Glass transition study: Glass transition temperature (Tg) studies for the DGEBA-B/PANI nanocomposites were carried out at a heating rate of 10 °C·min-1. An endothermic deviation during the second heating cycle was used for further studies and the results obtained are shown in SI5.

The samples showed an initial increase in Tg (from 194 to 199.5 °C) followed by a sharp decrease down to 154 °C at 5 wt %.∆Cp is a measure of the degree of freedom due to segmental motion. The segmental motion shows an initial decrease followed by an increase indicating that the degree of freedom for segmental motion increases. The decrease in Tg values observed can be due to the plasticization effect of clay.

3.7. In-situ monitoring of cure by rheology Rheology studies were carried out at a temperature of 200 °C, constant frequency of 1.592 Hz, in oscillatory shear mode to follow the curing process.

22


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Figure 8. Complex viscosity-vs-time plots for DGEBA/B-DPA/PANI samples at 200°C.

Figure 8 displays plots of complex viscosity η* versus time at 200 °C for neat and filled epoxy. The deviation from initial linearity is considered as the onset of gelation. The gelation time (Tgel) indicates the rate of cure reaction and is an important parameter in processing. The Tgel is found to decrease with increasing amount of B-DPA/PANI (particularly at 2 wt % loading, although a decrease has been noticed at 0.5 wt % loading on account of effective exfoliation) confirming the catalytic activity of the secondary amino group present in PANI. This is parallels the DSC resultsshown in Figure 7.

The evolution of G’(t) and G”(t) is measured in small amplitude oscillatory shear as a function of cross-linking time (s) (see SI6) at constant frequency. For about 1000 s elapsed time, G” is higher than G’ whilst this order is reversed at the completion of the reaction where 23


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elastic component dominates over the viscous component. According to Tung and Dynes52 the gel point (GP) occurs at the time when G’ and G” moduli are equal.

The Tgel and gel point (see SI7) increase on going from the neat epoxy to the 0.5wt % nanocomposite and thereafter decrease. The initial increase in Tgel and gel point can be due to the effective dispersion of the B-DPA/PANI, which hinders the availability of DGEBA monomers for curing reaction. An increase in the amount of B-DPA/PANI results in a dramatic decrease in Tgel and gel point indicating the catalytic activity of PANI.50,53

3.8. Dielectric properties of composites

(a)

(b)

Figure 9. Dielectric permittivity vs frequency: (a) real part, and (b) imaginary part.

To study the dielectric properties, silver paste was applied on both sides of samples. The values were calculated using following equations. ɛ'= Cp*d/ɛoA

(7)

ɛ''= ɛ'TanD

(8) 24


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where ɛ0 is permittivity of free space, Cp is parallel capacitance, d is the thickness of sample, A is the area of sample, D is the dissipation factor, and ɛ' and ɛ'' are the real and imaginary parts of the complex dielectric constant (ɛ*), respectively. The real part measures the alignment of the dipoles, and the imaginary part represents the energy required to align the dipoles and move the ions. Figure 9 shows the variations of ɛ' and ɛ'' versus frequency. For all samples, ɛ' and ɛ'' increase upon filling the epoxy matrix with B-DPA/PANI filler. The plots indicate that that the systems exhibit strong interfacial polarization.54,55 At low frequencies, the dipoles have sufficient time to align with the field before it changes direction and the dielectric constant is high, but at high frequencies, the dipoles do not have enough time to align before the field changes direction and hence the dielectric constant is lower. The dielectric constant is increased from 7.3 to 14.3 by introduction of only 0.5 wt % BDPA/PANI due to the network formation of B-DPA/PANI in the epoxy matrix as revealed by SEM analysis.56 At nanoscale, interfacial polarization becomes prominent; it is due to the short range dipole interaction and Maxwell-Wagner-Sillers mechanism.55 It is shown that dielectric loss factor (imaginary part) is increasing at low frequency range and then gets constant with increasing at high frequency. As the amount of B-DPA/PANI increases, the dipole density increases along with the movement of the dipoles which in turn depends upon the mobility of the polymer chains. As a result, an increase in the value of real part of permittivity and dielectric loss factor (imaginary part) is observed with the increase of loading of B-DPA/PANI in the composite.

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4. Conclusion Clay/polyaniline nanocomposites were prepared by in-situ oxidative polymerization of aniline in the presence of 4-diphenylamino diazonium-exchanged clay. This exfoliated and conductive nanocomposites were used for the first time as nanofiller of DGEBA matrix. DPA/PANI grafted to the bentonite sheets served not only to disperse clay but also as a curing agent of the epoxy resins. Indeed, the curing activation energy was found to decrease as the amount of B-DPA/PANI increased. It has been demonstrated also that the introduction of a very small amount of B-DPA/PANI nanofiller (0.1 and 0.5 wt %) can improve dramatically the mechanical and dielectric conductivity with a percolation threshold as low as 0.5 wt %. A network structure within the matrix DGEBA has been noted from the SEM portion of the fractured surface of the epoxy resin reinforced by B-DPA/PANI, resulting in a very strong adhesion between the nanofiller and the matrix induced by the diazonium coupling agent. Improvement in tensile and flexural strength shows that the B-DPA/PANI can be considered as ideal filler for high performance applications. Similarly, the fracture toughness showed a synergetic improvement by 210-220% when compared to the samples without diazonium salt indicating that DPA acts as an effective stress transfer agent in the nanocomposites. It also confirms that DPA modifies the interface between epoxy and clay/PANI. Measurements of dielectric properties revealed that with filler loading, the dielectric constant increased from 7.3 to 14.3 by introduction of only 0.5 % B-DPA/PANI due to the network formation of BDPA/PANI in the epoxy matrix. In contrast, for the DGEBA filled with B/PANI, c.a. without any diazonium pre-modification, we did not get any network structure formation, thereby they were non-conductive and only a small increase of mechanical properties(20-30%) was achieved compared to the effect of B-DPA/PANI filler. It follows that DPA diazonium salt has an important effect on the improvement of the interfacial properties and adhesion of DGEBA and clay/PANI nanofillers. 26


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Beyond these results, this work highlights another side of the interface chemistry of aryl diazonium salts as it demonstrates the direct effect of these compounds on the mechanical properties of high performance composites.

Acknowledgements KJ would like to thank the IFCEPAR/CEFIPRA for providing 6 month Raman-Charpak fellowship to visit Mahatma Gandhi University, Kottayam, Kerala, India.

Supporting Information Digital photographs of pristine and modified clays, and the final epoxy composite; TEM and XRD of filled epoxy; C1 & C2 universal values; Tensile mechanical properties; Tg and ∆Cp values; storage and loss moduli versus time; temperature of gelification and gel point of nanocomposites. This material is available free of charge via the Internet at http://pubs.acs.org. References 1

Shi, Y.; Kashiwagi, T.; Walters, R. N.; Gilman, J. W.; Lyon, R. E.; Sogah, D. Y.

Ethylenevinyl acetate/layered silicate nanocomposites prepared by a surfactant-free method: Enhanced flame retardant and mechanical properties. Polymer 2009, 50, 3478–3487. 2

Yang, L.; Phua, S. L.; Teo, J. K. H.; Toh, C. L.; Lau, S. K.; Ma, J.; Lu, X. A biomimetic approach to enhancing interfacial interactions: polydopamine-coated clay as reinforcement for epoxy resin. ACS Appl. Mater. Interfaces 2011, 3, 3026–3032.

3

Ho, T. H.; Wang, C. S. Modification of epoxy resins with polysiloxane thermoplastic polyurethane for electronic encapsulation. Polymer 1996, 37, 2733–2742. 4

Bagherzadeh, M. R.; Mahdavi, F. Preparation of epoxy–clay nanocomposite and investigation on its anti-corrosive behavior in epoxy coating. Prog. Org. Coat. 2007, 60, 117– 120.

5

Tian, N.; Gong, J.; Wen, X.; Yao, K.; Tang, T. Synthesis and characterization of a novel organophosphorus oligomer and its application in improving flame retardancy of epoxy resin. RSC Adv. 2014, 4, 17607-17614. 6

Kiliaris, P.; Papaspyrides, C. D. Polymer/layered silicate (clay) nanocomposites: an overview of flame retardancy. Prog. Polym. Sci. 2010, 35, 902–958. 7

We, H.; Zhang, Y.; Zhang, H.; Jiang, Z. Research on performance and preparation of graphene/epoxy high dielectric permittivity polymer composites. High Perform. Polym. 2015, 27, 911-917. 8

Qiang, Z.; Liang, G; Aijuan, Gu.; Yuan, L. The dielectric behavior and origin of high-k composites with very low percolation threshold based on unique multi-branched polyaniline/carbon nanotube hybrids and epoxy resin, Composites Part A 2014, 64, 1-10.

27


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 31

9

Rao. Y.; Takahashi, A.; Wong, C.P. Di-block copolymer surfactant study to optimize filler dispersion in high dielectric constant polymer-ceramic composite. Composites Part A 2003, 34, 1113–6.

10

Yan, X.; Guo, J.; Li, Z.; Jiang, D.; He, Q.; Wei, H.; Gu, H.; Colorado, H. A.; Zhang, X.; Wei, S.; Guo, Z. Polypyrrole doped epoxy resin nanocomposites with enhanced mechanical properties and reduced flammability. J. Mater. Chem. C 2015, 3,162-176. 11

Teh, C. H.; Rasid, R.; Daik, R.; Ahmad, S. DGEBA-grafted polyaniline: synthesis, characterization and thermal properties. J. Appl. Polym. Sci. 2011, 121, 49-58. 12

Bagherzadeh, M. R.; Mahdavi, F.; Ghasemi, M.; Shariatpanahi, H.; Faridib, H. R. Using nanoemeraldine salt-polyaniline for preparation of a new anticorrosive water-based epoxy coating. Prog. Org. Coat. 2010, 86, 319–322.

13

Bhadra, S.; Khastgir, D. ; Singha, N. K. ; Lee, J. H. Progress in preparation, processing and applications of polyaniline. Prog. Polym. Sci. 2009, 34, 783–810.

14

Wu, X.; Qi, S.; He, J.; Duan, G. High conductivity and low percolation threshold in polyaniline/graphite nanosheets composites. J. Mater. Sci. 2010, 45, 483-489. 15

Oyharcabal, M.; Olinga, T.; Foulc, M.; Lacomme, S.; Gontier, E.; Vigneras, V. Influence of the morphology of polyaniline on the microwave absorption properties of epoxy polyaniline composites. Compos. Sci. Technol.2013, 74, 107-112. 16

Long, Y.-Z. Li, M.-M.; Gu, C.; Wan, M.; Duvail, J.-L.; Liu, Z.; Fan, Z. Recent advances in synthesis, physical properties and applications of conducting polymer nanotubes and nanofibers. Prog. Polym. Sci. 2011, 36, 1415–1442. 17

Ray, S. S.; Okamoto, M. Polymer/layered silicate nanocomposites: a review frompreparation to processing. Prog. Polym. Sci. 2003, 28, 1539–1641. 18

Kornmann, X.; Lindberg, H.; Berglund, L. A. Synthesis of epoxy–clay nanocomposites. Influence of the nature of the curing agent on structure. Polymer 2001, 42, 4493–4499.

19

Utracki, L. A. Clay-containing polymeric nanocomposites. Arab.J. Sci.Eng. 2002, 27, 4367.

20

Yagci, Y.; Jockusch, S.; Turro, N. J. Photoinitiated polymerization: advances, challenges,

and opportunities. Macromolecules 2010, 43, 6245–6260. 21

Chiu, C.-W. ; Huang, T.-K. ; Wang, Y.-C. ; Alamani,B. G. ; Lin, J.-J. Intercalation strategies in clay/polymer hybrids. Prog. Polym. Sci. 2014, 39, 443–485. 22

Djouani, F.; Herbst, F. ; Chehimi, M. M. ; Benzarti, K. Synthesis, characterization and reinforcing properties of novel, reactive clay/poly(glycidyl methacrylate) nanocomposites. Construct. Build. Mater. 2011, 25, 424–431. 23

. Bayram, I.; Oral, A.; Şirin, K. Synthesis of poly(cyclohexene oxide)-montmorillonite

nanocomposite via in situ photoinitiated cationic polymerization with bifunctional clay. J. Chem., 2013, Article ID 617498, 6 pages, http://dx.doi.org/10.1155/2013/617498 24

Jlassi, K.; Benna-Zayani, M.; Yagci, Y.; Chehimi, M. M. Efficient photoinduced in- situ preparation of clay/poly(glycidyl methacrylate) nanocomposites using hydrogen-donor silane. J. Polym. Sci. Polym. Chem. Ed. 2015, 53, 800–808. 28


Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

25

Chang, K. C.; Jang, G.-W.; Peng, C.-W.; Lin, C.-Y.; Shieh, J.-C.; Yeh, J.-M.; Yang, J.-C.; Li, W.-T. Comparatively electrochemical studies at different operational temperatures for the effect of nanoclay platelets on the anticorrosion efficiency of DBSA-doped polyaniline/Na+– MMT clay nanocomposite coatings. Electrochim. Acta.2007, 52, 5191-5200.

26

Jlassi, K.; Mekki, A.; Benna-Zayani, M.; Singh, A.; Aswal, D. K.; Chehimi, M. M. Exfoliated clay/polyaniline nanocomposites through tandem diazonium cation exchange reactions and in situ oxidative polymerization of aniline. RSC Adv. 2014, 4, 65213–65222. 27

Pinson, J.; Podvorica, F. Attachment of organic layers to conductive or semiconductive surfaces by reduction of diazonium salts. Chem. Soc. Rev. 2005, 34, 429-439.

28

Bélanger, D. ; Pinson, J. Electrografting: a powerful method for surface modification. Chem. Soc. Rev. 2011, 40, 3995-4048. 29

Gooding, J. J.; Ciampi, S. The molecular level modification of surfaces: from selfassembled monolayers to complex molecular assemblies. Chem. Soc. Rev. 2011, 40, 2704– 2718.

30

Aryl Diazonium Salts: New Coupling Agents in Polymer and Surface Science, Chehimi, M. M. (Ed.), 2012 Wiley-VCH, Weinheim, Germany (ISBN: 978-3-527-32998-4). 31

Mohamed, A. A.; Salmi, S. ; Dahoumane, S. A. ; Mekki, A.; Carbonnier, B. ; Chehimi, M. M. Functionalization of nanomaterials with aryldiazonium salts. Adv. Colloid Interface Sci. 2015, 225, 16-36. 32

Atai, M.; Solhi, L.; Nodehi, A.; Shahin, K.; Khatereh, A.; Babanzadeh, S. PMMA-grafted nanoclay as novel filler for dental adhesives. Synth. Met. 2009, 25, 339-347.

33

Benna, M.; Kbir-Ariguib, N.; Clinard,C.; Bergaya, F. Static filtration of purified sodium bentonite clay suspensions. Effect of clay content. Prog.Colloid Polym. Sci. 2001,117, 204– 210. 34

Othmani-Assmann, H.; Benna, M.; Geiger, S.; Fraisse, B.; Kbir-Ariguib, N.; TrabelsiAyadi, M.; Ghermani, N. E.; Grossiord, J. L. Physico-chemical characterizations of Tunisian organophilic bentonites. J. Phys. Chem. C. 2007, 111, 10869-10877. 35

Brindley, G. W.; Thompson, T. D. Methylene blue absorption by montmorillonites. Determinations of surface areas and exchange capacities with different initial cation saturations (Clay-Organic Studies XIX). Isr. J. Chem. 1970, 8, 409–415. 36

Kaur,T.; Kumar, S.; Sharma, J .; Srivastava, A. K. Radiation losses in the microwave Ku band in magneto-electric nanocomposites. J. Nanotechnol. 2015, 6, 1700–1707.

37

Frost, R. L. ; Van Der Gaast,S. J. ; Zbik, M. ; Kloprogge, J. T. ; Paroz, G. N. Birdwood kaolinite: a highly ordered kaolinite that is difficult to intercalate—an XRD, SEM and Raman spectroscopic study. Appl. Clay Sci. 2002, 20, 177–187

38

Liu, W.; Hoa, S. V.; Pugh, M. Fracture toughness and water uptake of high-performance epoxy/nanoclay nanocomposites. Compos. Sci. Technol.2005, 65, 2364–2373. 39

Guo, Z.; Liang, X.; Pereira, T.; Scaffaro,R.; Thomas Hahn, H. CuO nanoparticle filled vinyl ester resin nanocomposites: Fabrication, characterization and property analysis. Compos. Sci. Technol. 2007, 67, 2036–2044.

29


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 31

40

Kitey, R. ; Tippur, H. V. Role of particle size and filler–matrix adhesion on dynamic fracture of glass-filled epoxy. II. Linkage between macro- and micro-measurements. Acta Materialia 2005, 53, 1167–1178. 41

Zhu, Y. ; Liu, Q. ; Liu, B. ; Jiang, J. Theory of time-temperature-stress equivalent principle based on Schapery equation and its application on granite. Mater. Sci.(Medžiagotyra) 2014, 20, 522-528. 42

Lu, H.; Huang, W. M. On the origin of theVogel-Fulcher-Tammann law in the thermoresponsive shape memory effect of amorphous polymers. Smart Mater. Struct., 2013, 22. Article No 10. 43

Binitha, N. N.; Sugunan, S. J. Polyaniline/pillared montmorillonite clay composite nanofibers. J. Appl. Polym. Sci.2008, 107, 3367–3372. 44

Budrugeac, P.; Segal, E. Applicability of the Kissinger equation in thermal analysis.J. Therm. Anal. Calorim.2007, 88, 703–707.

45

Boey, F. Y. C.; Qiang,W. Determining the gel point of an epoxy hexaanhydro-4methylphthalic anhydride (MHHPA) system. J. Appl. Polym. Sci.2000, 76, 1248–1256. 46

Montserrat, S. ; Flaqué, C. ; Calafell, M. ; Andreu, G. ; Málek, J. Influence of the accelerator concentration on the curing reaction of an epoxy-anhydride system. Thermochim. Acta 1995, 269/270, 213-229 47

Lee, H. ; Neville, K. (Eds.).Handbook of epoxy resins. McGraw-Hill, New York 1967.

48

Marsella, J. A.; Starner, W. E. Acceleration of amine/epoxy reactions with N-methyl secondary amines. J. Polym. Sci. A Polym. Chem. 2000, 38, 921-930. 49

Karkanas, P. I. PhD Thesis, Cranfield University, Cranfield UK (1998).

50

Ayad, M. M.; Salahuddin, N.; Ali, M. Polyaniline–organoclay nanocomposites as curing agent for epoxy: Preparation and characterization. Polym. Compos.2009, 30 ,467-473. 51

Jang, J.; Bae, J.; Lee, K. Synthesis and characterization of polyaniline nanorods as curing agent and nanofiller for epoxy matrix composite. Polymer 2005, 46, 3677-3684. 52

Tung, C. Y.; Dynes, P. J. Relationship between viscoelastic properties and gelation in thermosetting systems. J. Appl. Polym. Sci. 1982, 27, 569–574. 53

Fu, T.; Liu, J. ; Wang, J. ; Na, H. Cure kinetics and conductivity of rigid rod epoxy with polyaniline as a curing agent. Polym. Compos. 2009, 30, 1394-1400. 54

Belaabed, B. ; Wojkiewicz, J. L.; Lamouri, S.; Kamchi, N. E.; Redon, N. Thermomechanical behaviors and dielectric properties of polyaniline-doped para-toluene sulfonic acid/epoxy resin composites. Polym. Adv. Technol. 2012, 23, 1194–1201.

55

Belaabed, B.; Lamouri, S.; Naar, N.; Bourson, P.; Hamady, S. Polyaniline-doped benzene sulfonic acid/epoxy resin composites: structural, morphological, thermal and dielectric behaviors. Polym. J. 2010, 42, 546–554. 56

Poonam,Y .; Srivastava, K.; Manoj, K.; Kripal, R.; Singh, V.; Lee, D. B.; Lee, J. H. Synthesis and dielectric characterization of polycarbonate/multi-wall carbon nanotubes nanocomposite. Arab. J. Chem.2015.doi:10.1016/j.arabjc.2015.10.015 .

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Polyaniline Hybrid through Diazonium Chemistry: Conductive

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