Fiber Alignment and Liquid Crystal Orientation of Cellulose

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Fiber Alignment and Liquid Crystal Orientation of Cellulose Nanocrystals in the Electrospun Nanofibrous Mats Weiguang Song, Dagang Liu, Nana Prempeh, and Renjie Song Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.7b00927 • Publication Date (Web): 19 Sep 2017 Downloaded from http://pubs.acs.org on September 20, 2017

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Biomacromolecules

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Fiber Alignment and Liquid Crystal Orientation of

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Cellulose Nanocrystals in the Electrospun Nanofibrous

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Mats

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Weiguang Song,a,b Dagang Liu,*a,b,c Nana Prempeh,b Renjie Song a

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a

Department of Chemistry, Nanjing University of Information Science and Technology, Nanjing 210044, China

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Collaborative Innovation Center of Atmospheric Environment and Equipment

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Technology, Nanjing University of Information Science and Technology, Nanjing

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210044, China

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Department of Physics, University of Colorado, Boulder, CO 80309, USA

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ACS Paragon Plus Environment

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ABSTRACT:

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Sulfate cellulose nanocrystal (CNC) dispersions always present specific self-assembled

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cholesteric mesophases which is easily affected by the inherent properties of particle size,

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surface charge and repulsion or affinity interaction, and external field force generated from ionic

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potential of added electrolytes, magnetic or electric field, and/or mechanical shearing or

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stretching. Aiming at understanding the liquid crystal orientation and fiber alignment under high-

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voltage electric field, randomly distributed, uniform-aligned, or core-sheath nanofibrous mats

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involving charged CNCs and PVA were electrospun; and amongst them, specific straight arrayed

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fine nanofibers with average diameter of 270 nm were manufactured by using a simple and

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versatile gap collector. Moreover, arrayed composite nanofibers regularly aligned along the

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vertical direction of gap plates and selectively reflected frequent and continuous birefringence

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which was regarded as nematic phases of CNCs induced by the uniaxial stretching under high-

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voltage electric field. As a synergic effect of rigidness of nanocrystals and stretching orientation

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of nematic phases, the aligned nanofibrous arrays exhibited a higher tensile strength and strain

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than the randomly-oriented or core-sheath nanofibrous mats at the same loading of CNCs. By

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contrast, mesophase transition of CNCs from cholesteric to nematic occurred in the coaxially

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spun core-sheath nanofibers at a loss of long-ranged chiral twist. Hence, the structure-effect

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relationship between liquid crystal orientation of charged nanorods in polymer-based fine

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nanofibers and the flexibility or mechanical integrity of the aligned fiber array will be favorable

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for strategic development of functional liquid crystal fabrics.

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Keywords: Cellulose nanocrystals, PVA, Electrospinning, Nanofibrous mats, Alignment


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Biomacromolecules

INTRODUCTION

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Up until now, electrospinning has been accepted as a simple and efficient method for

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developing polymer nanofibers with width range from 3 nm to 5 µm,1,2 depending on the

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spinning parameters. Under a high-voltage electric field the electrospinning process itself

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involves polymer droplets stretching and deformation into conical cylindrical threads with a

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rapid evaporation of the solvent.3 Electrospun nanofibers have several remarkable characteristics

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such as porosity,4 high aspect ratio,5 flexibility in surface functionalities, and special mechanical

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and biological properties which makes them excellent candidates for applications such as

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nanofibrous membranes or filters,6 mats in tissue engineering constructs and wound dressings,7,8

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military wears with chemical and biological toxin-resistance,9 electronic sensors,10 and so on.

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Generally, the flow rate, voltage, and tip-to-collector distance are thought as very important

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processing parameters that directly affects the morphology, size distribution, and mechanical

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performance of nanofiber,11,12 whereas, instability of polymer jet streams has often led to poorly

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aligned fibers with varying morphology and diameters during the electrospinning process.

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Moreover, the disorderliness in fiber formation is problematic as much more applications

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requiring the use of fibrous mats relies heavily on well-aligned and highly ordered

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architectures.13 Up to now, several approaches such as modification of the collection devices by

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the use of rectangular metal frame,14 central point electrode and peripheral ring electrode,15 a pair

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of parallel electrodes or addition of electrode,16 circular copper wire drum collector, 17 or an

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additive electric field,18 have been considered for the development of aligned and continuous

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nanofibers.

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Sulfuric acid hydrolysis of native cellulose microfibrils produces suspensions of cellulose

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nanocrystals (CNCs), which are highly stable in aqueous suspensions because of the repulsion


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among negatively charged sulfate ester bearings on the surface of CNCs.19,20 While the

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homogeneous suspension of sulfate CNCs is solidified after a slow evaporation induced self-

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assembly process, cholesteric liquid crystalline films with chiral reflective iridescence are

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formed.21,22 Namely, the solidified films generated from liquid crystalline suspensions inherits a

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short-range position arrangement and long-range chiral nematic orientation of 3-D photonic

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CNC colloids.23 This fascinating liquid crystal properties of CNCs have received an increasing

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attention for the fabrication of novel functional chiroptical materials.24,25 At hand, the scalization

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and industrialization of CNC based materials of film, coating, fiber, etc., are confined by the

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stiffness and fragile nature of CNCs. Several researches involving neutral polymers of PEG,26

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PEO,27 and PVA,28 with excellent compatibility and affinity with/to CNCs was performed to

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improve the flexibility of generated composites. More interestingly, both PEG,26 and PVA,28

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presented severe impact on the structure-color and chiral nematic mesophases of CNCs due to

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microphase separation, thereby leading to the loss of the long-range orientation and chiroptical

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reflectivity of bulk coatings, films or fibers exceeding a critical loading content of the compatible

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polymers.

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More recently, nanofibrous composite mats of PVA was electrospun by employing CNCs

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with loading dose of 0-15 wt% as effective reinforcement agents.29-31 As a matter of fact, it was

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thought that overall tension in the spinning dope of CNCs with a high charge density on the

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surface would self-repulse the excess charges on the jet, thus, as the charge density increase, the

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continuity, stability, and alignment of the fibers meet great challenges in electrospinning.

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Notwithstanding the foregoing, no research work on the alignment of nanofibrous CNC

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composite mats as well as the orientation of CNCs in a liquid jet under high voltage electric field

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during electrospinning is reported and discussed in detail. In this work, single-fluid of composite


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dispersions or dispersion mixture containing CNC and hydrophilic PVA was deployed as

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spinning dope and a tailored gap between a couple electrode plates or a rotating roller was

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applied as a collection device of electrospinning. Aiming at improving the alignment of

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nanofibers and orientation of highly surface-charged CNCs, we attempted to set up a new

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approach to fabricate nanofiber arrays by controlling the physicochemical properties of spinning

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dope and processing parameters, and tended to understand the mesophase orientation and

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alignment of fibers under electrical stretching or repulsive and attractive interaction, and

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anticipated to build up the relationship between the tailored composing structure of random

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distribution, uniformed alignment, or core-sheath and properties of as-spun fibrous mats.

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MATERIALS AND METHODS

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Materials. PVA (AH-26, Mw = 114,400) having a degree of polymerization (DP) of about

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2600 and saponification of 98% and microcrystalline cellulose (MCC, 9004-34-6) of analytical

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grade were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

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Concentrated sulfuric acid of analytical grade was purchased from Shanghai Lingfeng Chemical

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Reagent Co. Ltd.

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Preparation of spinning dope. Referring to our previous work,23 MCC was hydrolyzed by

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sulfuric acid (64 wt%) at 50 oC in a water bath under vigorous mechanical stirring for 2.5 h. The

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resultant suspension was diluted 5-fold by deionized water and then poured into cellulose

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dialysis tube with MWCO of 8,000-14,000 to dialyze against deionized water for more than one

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week to remove residual sulfuric acid and many small molecules. Subsequently, impurities and

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unmodified coarse particles in the dialyzed suspension was removed by centrifugation at 12000

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rpm for 10 min. The as-prepared CNCs after a mild sonication have a length of 150 ± 30 nm and

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width of 35 ± 5 nm, and a negative surface charge density of 0.60 e/nm2.23 Alternatively, PVA


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was dissolved in deionized water at 90 oC under strong mechanical stirring for 1 h to produce a

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homogeneous solution with a concentration of 10 wt%. Subsequently, CNC suspension and PVA

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solution were mixed in specific proportions under continuous agitation for 4 days at 30 oC. The

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individual resultant PVA/CNC mixture as a single fluidic spinning dope was then stored in the

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refrigerator to allow a slow evaporation and absolute self-assembly at 10 oC until a desired

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concentration of the spinnable dope was obtained.

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Electrospinning of PVA/CNC nanofiber mats. As illustrated in Supplementary Figure

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S1a, the electrospinning set-up of roller-collection comprised of a high voltage power supply (0-

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50 DC kV), a micro-syringe pump (V = 20 mL) connected to a metal needle (di = 0.40 mm) or

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coaxial spinneret (do = 2.00 mm; di = 0.40 mm), and a collector of grounded rotating cylindrical

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roller (D = 4 cm; L = 15.5 cm) with a tip-to-collector distance of 0-20 cm. In this roller-

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collection device, the spinneret acting as a positive electrode was connected to the high voltage

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power supply to generate electric field. During the electrospinning process, the dope was

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pumped through a polytetrafluoroethylene (PTFE) tube, and then injected from the metal

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spinneret as a fluidic jet at a specific rate. After water evaporation, the solidified jet in the form

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of nanofibers were collected on the metallic cylindrical roller. According to mass ratio of

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CNC/PVA at 1:9, 1:3, and 1:1, the manufactured nanofibers mats with random orientation were

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denoted as PVA/CNC10R, PVA/CNC25R, and PVA/CNC50R, respectively. Alternatively, in a

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coaxial electrospinning process, CNC suspension and PVA solution were independently fed into

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a coaxial spinneret at a speed of 0.2 mL/h and 0.6 mL/h, respectively, and spun in a core-shell

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manner. The fine core-sheath nanofibers of PVA/CNC collected on the metallic cylindrical roller

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were denoted as PVA@CNC10 and CNC10@PVA corresponding to mass ratio (1:9) of CNCs to

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PVA in the fabricated core-sheath nanofibers.


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Specifically, we set up a tailored gap collector with a couple of parallel plates (Figure S1b)

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involving a negative metal plate of 30-mm thickness and a ground polyoxymethylene (POM)

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plate of 30-mm thickness. On the upper right side of the POM plate a small thin metal sheet with

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thickness of 5 mm was covered. The tailored gap-collector was built up to collect the well-

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aligned nanofibrous mats of PVA/CNC by adjusting the applied voltage, needle-to-collector

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distance, working temperature, and the gap distance between two plates. In this case, additional

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substrates could be placed within the gap to support or collect the nanofibers without any

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significant influence on the quality of the resultant nanofibers. The as-manufactured fine

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nanofibers with good alignment were denoted PVA/CNC10A, PVA/CNC25A, and

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PVA/CNC50A corresponding to the weight ratio of CNC/PVA at 1:9, 1:3, and 1:1, respectively.

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The as-manufactured nanofibrous mats were vacuum dried at 40 °C for 24 h to remove any

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residual water, and then vacuum-stored for further analysis.

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Characterization. Zeta potential of the spinning dope was measured using a dynamic light

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scattering (DLS, ZS90, Malvern Instruments, U.K.) with a combined laser Doppler velocimetry

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(LDV) and phase analysis light scattering (PALS). The viscosity of the spinning dope was tested

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using a RS6000 rheometer (Thermo Scientific, Karlsruhe, Germany) with a parallel plate

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geometry (25 mm diameter, 0.3 mm gap) at 25 °C. Nanofibrous mats were deposited onto a

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rectangular glass slide for liquid crystal phase observation on a polarized optical microscope

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(POM; LV100POL, Nikon, Japan). Morphology observations were carried out on a field

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emission scanning electron microscope (FE-SEM, Hitachi S-4700 microscope) with an

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accelerating voltage of 20 kV. The sample mats were fixed on conductive carbon tape and then

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sputtered with gold for SEM observations. Size distribution of nanofibers was statistically

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analyzed by using the ImageJ Tool. Fourier-transform infrared spectroscopy (FTIR) of


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nanofibrous mats was performed on a Bio-Rad FTS 6000 FTIR spectrometer equipped with an

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IR microscope (UMA-500); the polarized infrared beam, with rays in parallel, goes through the

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microtomed sample mats, while the transmittance was measured with the aid of a liquid nitrogen

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cooled Mercury Cadmium Telluride (MCT) detector. The spectra were recorded at a resolution

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of 8 cm-1 with a spectral range of 650-4000 cm-1. During the measurement, a home-built sample

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holder was employed to keep the mats in position at a constant inclination angle θ while a set of

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different polarizer positions φ was scanned. Tensile properties of the standard rectangular strips

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(40 × 100 mm2) of nanofibrous mats were performed on a Shimadzu SLBL-500N tensile tester

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(Shimadzu Inc., Japan) at a crosshead speed of 5 mm/min. The testing results were evaluated as

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an average of at least 10 measurements.

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RESULTS AND DISCUSSION

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Homogeneous composite dispersions of PVA/CNC as spinning dopes were sprayed in a

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single-fluid manner and collected on a rotating cylindrical roller as shown in Figure S1a.

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Judging from the fineness, continuity, defect-free, and uniformity of nanofibers, the

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optimized spinning parameters of nanofibers obtained by roller collector were 10-16 wt%, 12 kV,

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35 °C, 51%, 0.3 mL/h, 13 cm, and 94.7 mm/min corresponding to dope concentration, voltage,

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temperature, relative humidity, flow rate, needle-to-collector distance, and nozzle translational

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velocity, respectively as demonstrated in Table S1 and Figure S2-5. The as-spun winding

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nanofibers of PVA/CNC10R presents a randomly distributed diameter widely ranging from 300

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to 600 nm (Figure 1a), indicating the spiral path and whipping of flexible macromolecular

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chains of PVA.

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Interestingly, while a tailored gap between double electrode plates was substituted for roller

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collector (Figure S1b) under voltages of 12 kV, needle-to-collector distance of 11 cm, flow rate,


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0.3 mL/h; translational velocities of 28.8 mm/min (Figure S6-7), multiple jets were released and

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the individual jets simultaneously traveled from one end of collecting electrode plane, and then

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crossed the gap to the other end of electrode plane whilst undergoing a stretching and

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disintegration process as shown in Video S1. The generated uniaxially aligned nanofibrous

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arrays were finally deposited across the gap (7 cm) with the longitudinal fibrous axes

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perpendicular to the gap plate, and the arrayed fine nanofibers of PVA/CNC10A display mean

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diameters of 270 ± 25 nm (Figure 1b), much more uniform and smaller than PVA/CNC10R,

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indicating a pretty strong stretching underwent between the gap plates.

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Nonetheless, while concentrated CNC dispersion and hydrophilic PVA solution were ejected

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in a coaxial manner, no arrayed nanofiber mats could be collected on either gap or rollers

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because of the distinctly different fluidic properties and discordant fiber-formation behavior of

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individual dope. Specifically, limited by the low viscosity, poor spinnability and inadequate

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water evaporation of CNC dispersions, PVA@CNC10 with a diameter varied from 288 to 1007

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nm displays flat and occasionally collapsed surface (Figure 1c). In the case of CNC10@PVA

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with a wide diameter distribution (98 - 1359 nm), some droplets of CNCs caused by insufficient

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water evaporation had a strong tendency to pool together with PVA nanothreads after a

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continuous deposition, thereby continuously aggregating into crosslinked porous fibrous network

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(Figure 1d). Therefore, morphology and size of four kind of nanofibers could be controlled by

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the tailored spinning approaches and optimized processing parameters.

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In general, due to the structure anisotropy of the CNCs,32 its aqueous dispersions at a high

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concentration always display self-assembled tactoids with fantastic fingerprint textures as shown

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in Figure 2a. As one component in the coaxial spinning dope, CNC fluid was discontinuously

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ejected and elongated, thus leading to intermittent shiny birefringent segments evenly distributed


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inside the long fiber of PVA@CNC10 (Figure 2b), 33 otherwise, reflective iridescent CNC beads

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(diameter of 0.7-3 µm) were dotted along the long PVA threads (average diameter of 279 nm) to

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form into regular pearl-chain structure in CNC10@PVA (Figure 2c). When a compensator of

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530 nm retardation plate was inserted between the polarizer and analyzer at a fixed angle of 45°,

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nematic rather than cholesteric mesophases of CNCs were randomly distributed in the core of

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PVA@CNC10 or at the outer surface of CNC10@PVA (Figure S8), indicating a mesophase

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transition from the chiral twisting lamella to nematic phases of CNCs.

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In the single-fluidic spinning dope, no mesophase of CNCs was recognized due to the

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homogeneous and isotropic dispersion of nanorods (Figure 2d). However, under polarized light,

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shining overlaid birefringence could be visualized in the randomly-distributed nanofibers of

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PVA/CNC10R (Figure 2e). Moreover, frequent and continuous birefringence with selective

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reflection was obviously visualized and regarded as nematic CNCs in the PVA/CNC10A (Figure

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2f). Micrographs of nanofibrous mats in the presence of a 530-nm retardation plate between

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crossed polarizers are shown in Figure 3. By changing the rotation angle of the sample,

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continuous transition of alternating blue and orange bands were visualized in the arrayed

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nanofiberous mats of PVA/CNC10A (Figure 3e,f) and PVA/CNC50A (Figure 3h,i).

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Accordingly, the fuchsia-colored image regions corresponded to uniaxially fibrous orientation (n)

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roughly parallel to the slow axis (γ) of the retardation plate whereas the orange-red hue

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corresponded to n⊥γ, indicating high refractive index of the axis (γ) or the uniaxial fiber axis due

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to positive birefringence anisotropy (ne > no) of CNCs.34 Specifically, PVA/CNC50A exhibited a

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relatively strong coloration difference between longitudinal and transverse fiber axis, suggesting

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more uniform and strong orientation along uniaxial fiber axis as a result of the intra-particle

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repulsion of surface-charged nanorods and stretching-induced alignment under electric field


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(Figure 3h,i).35 In contrast, as no accordance of the γ axis to the fibrous axis, randomly-

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distributed PVA/CNC10R did not present overall arrangement and mesophase orientation of

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CNCs but a tilt with respect to the longitudinal axis (Figure 3a,b).

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Polarized FTIR spectra was deployed to verify the particle orientation in the nanofibers

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(Figure S9). The characteristic band centered at 1160 cm-1 is associated with stretching and

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asymmetric pyranose ring breathing vibrations of cellulose; the peak at around 1100 cm-1 is

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assigned to C-O stretching vibrations of PVA;36 and the band at around 1060 cm-1 is attributed to

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stretching vibration of C-OH of cellulose. Polar plots of absorbance of ν

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(1100 cm-1), ν

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three bands of PVA/CNC10R have very few response to the rotational angle of incidence

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polarized light from 0° to 360° and present a circular shape, indicating a total isotropic character

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under polarized infrared light (Figure 4a). However, as evidenced by the ellipsoid or dumbbell

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shape, polar plots of IR bands in the aligned nanofibrous arrays exhibits a significant response to

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the polarization angle with the maximum difference occurring between absorbance of ν C-OH or ν

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C-O-C at

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indicator of the degree of uniaxial orientation of CNCs in the mats, dichroic ratio (R) was

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calculated according to the following equation.36

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R=

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where A// and A⊥ are IR absorbance at parallel and perpendicular mode, respectively. R of the

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randomly-distributed nanofiber of PVA/CNC10R, as listed in Table 1, is nearly equal to 1 due to

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the isotropic character. In the case of a perfectly uniaxial orientation along the fiber axis, R

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should be theoretically equal to infinity.37 In the arrayed fibers, R of ν

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was high up to 1.35-1.58 or 1.52-2.09, respectively, suggesting that the orientation of CNCs

A //

C-O-C

C-OH

(1060 cm-1), ν

C-O

(1160 cm-1) of spun nanofibers are shown in Figure 4. The peak value of

parallel mode (A//) and perpendicular mode (A⊥) to the fiber axes, (Figure 4b,c,d). As an

(1)

A⊥


C-OH

and ν

C-O-C of

CNCs

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rather than PVA occurred along the fiber axis.38 Therefore, in the gap region, the stretching and

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the Coulombic force possibly synergistically induced the orientation of charged nanorods and

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initiated the nematic phase formation in the jet.39,40

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Typical stress-strain profiles of 4 nanofiber mats are shown in Figure 5, and the resultant

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averaged stress, stain, and elastic modulus are listed in Table 1. Reinforcement effects of a

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certain amount of CNCs (10 wt%) are distinguished, e.g., mean tensile strength of

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PVA/CNC10R and PVA/CNC10A were 8.27, and 10.25 MPa, respectively, much higher than

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that of PVA (7.50 MPa); meanwhile, the modulus of PVA/CNC10R, PVA/CNC10A,

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CNC10@PVA, and PVA@CNC10 were all much higher than that of PVA since the rigidity of

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CNCs played a crucial role in the enhancement of tensile strength. However, fibrous mats with

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high loading doses of CNCs (≥ 25 wt%) exhibit a sharply decreasing stress and strain in

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comparison to PVA/CNC10. Meanwhile, tensile strength and elongation at break of

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CNC10@PVA are higher than that of PVA@CNC10 due to the crosslinking network effects of

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CNCs as depicted in Figure 1d. That is to say, interface contact and evaporation rate of dope

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components are dependent factors that influence the structure, morphology and mechanical

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properties of coaxial nanofibrous mats. Interestingly, the aligned nanofibers of PVA/CNC at the

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same loading doses of CNCs exhibit a higher tensile stress than that of randomly distributed

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nanofibers along the fibrous axis because both good alignment of nanofibers and continuous

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nematic segments of CNCs in aligned nanofibers provided a substantially strong resistance to

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external stretching force. However, the increment in tensile strength of the aligned nanofibers of

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PVA/CNC didn’t occur at the expense of tensile strain but exhibit a higher elongation at break

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than that of randomly distributed nanofibers at the same loading doses of CNCs. This is ascribed

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to the fact that under uniaxial drawing along fiber axis the nematic mesophases of CNCs were re-


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orientated, thus leading to an extended deformation and improved flexibility.28 The aligned

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nanofibrous mats is somewhat analogy to liquid crystal elastomers with macroscopic elastic

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response arising from the phase separation under large deformations.

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CONCLUSIONS

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In this work, CNC dispersion and aqueous PVA solution as a mixed spinning dope or

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separated dopes were sprayed in a manner of single-fluid or coaxial electrospinning and

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collected on a rotating cylindrical roller or across a gap. Without any doubt, fine nanofibers

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generated from single fluidic dope was continuous, smooth, and uniform due to homogenous

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dispersion of CNC into PVA, whereas coaxial nanofiber had a larger average diameter, broader

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size distribution and rough surface. The single-fluidic jet deposited across gap plates were well

275

aligned along the direction vertical to plates because the gap was favorable for the electric-ﬁeld-

276

induced-alignment of CNCs by the uniaxial stretching as well as the movement of CNCs

277

unrestricted by the length of nanofibers as far as possible. The anisotropic and birefringent

278

character of fiber arrays oriented along the uniaxial fiber axis were certified by polarized IR and

279

POM with a retardation plate. The alignment of nanofibers was highly dependent on the

280

processing condition, and the orientation of CNCs with positive refractive index anisotropy and

281

surface charges was related to the high voltage electric field. Being different with single-fluidic

282

jet, coaxially-electrospun core-sheath nanofibers also showed birefringence under polarized light

283

because nematic mesophases of CNCs in the concentrated dispersions was switched. The

284

uniaxial, continuous orientation of CNCs played an important role in enhancement of mechanical

285

properties of the nanofibrous composite mats, e.g., average tensile strength (10.25 MPa) and

286

elongation at break (87.91%) of PVA/CNC10A were much higher than that of other spun

287

nanofibrous mats. In this work, we have provided a strategy for encapsulating homogeneously


Biomacromolecules

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

288

nematic nanorods into nanoscaled fibrous mats which is anticipated to be explored as novel

289

photonic and biological tissues, biosensors, and environmental-friendly filters.

290

Supporting Information Available. Diagram of electrospinning set-up, properties of

291

spinning dope, optimization for randomly-distributed and aligned electrospun nanofibers, POM

292

of CNCs in the core-sheath nanofibers, polarized FTIR spectra of nanofibers. This material is

293

available free of charge via the Internet at http://pubs.acs.org.

294

AUTHOR INFORMATION:

295

Corresponding author

296

∗

297

ORCID

298

Dagang Liu: 0000-0002-1320-7030

299

Notes

300

The authors declare no competing financial interest.

301

ACKNOWLEDGEMENTS

302

The authors are grateful to National Natural Science Foundation of China (Nos. 51473077 and

303

21277073), CSC scholarship (201608320064), and Six Talents Summit Program and 333 High-

304

Level Talent Cultivation Program of Jiangsu Province for financial support.

305

REFERENCES

E-mail: [email protected] (D. Liu)

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Page 18 of 25

Table 1. Dichroic ratio (R) and mechanical properties of as-spun nanofibrous mats. Nanofibrous

R

R

mats

(ν C-OH)

PVA

-

-

PVA/CNC10R

0.94

PVA/CNC10A

R

Tensile

Elongation at

Elastic

stress (Pa)

break (%)

modulus (MPa)

-

7.50±0.43

77.00±7.22

38.01±2.32

1.03

0.96

8.27±0.25

20.17±4.23

853.15±14.13

1.40

1.06

1.52

10.25±0.34

87.91±7.34

185.33±4.17

PVA/CNC25R

-

-

-

4.03±0.24

3.13±0.81

430.79±7.15

PVA/CNC25A

1.58

1.08

1.86

6.48±0.13

29.51±3.33

342.72±6.8

PVA/CNC50R

-

-

-

0.40±0.032

2.86±0.31

16.96±2.02

PVA/CNC50A

1.35

1.11

2.09

2.79±0.02

8.12±0.92

236.39±5.32

CNC10@PVA

-

-

-

8.82±0.26 109.19±10.73 115.29±1.71

PVA@CNC10

-

-

-

6.84±0.32

(ν C-O) (ν C-O-C)

37.53±6.28

367


837.12±13.76

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Biomacromolecules

368

Figure Captions:

369

Figure 1. SEM micrographs and histograms of width distributions for randomly orientated

370

nanofibers of PVA/CNC10R (a), well-aligned nanofibers of PVA/CNC10A (b), and core-sheath

371

nanofibers of PVA@CNC10 (c), CNC10@PVA (d), respectively.

372

Figure 2. Polarized optical micrographs of spinning dope of CNC (a) and PVA/CNC10 (d), and

373

electrospun nanofibers of PVA@CNC10 (b), CNC10@PVA (c), PVA/CNC10R (e),

374

PVA/CNC10A (f), respectively.

375

Figure 3. POM images of nanofibrous mats of PVA/CNC10R (a), PVA/CNC10A (d),

376

PVA/CNC50A (g), and POM images of nanofibrous mats of PVA/CNC10R (b,c),

377

PVA/CNC10A (e,f), PVA/CNC50A (h,i) with a full-wavelength (530 nm) retardation plate with

378

a slow axis (γ) marked by a yellow arrow.

379

Figure 4. Polar plots of the normalized absorbance as a function of rotational angle (α) for ν C-OH

380

(1060 cm-1), ν

381

PVA/CNC25A, (d) PVA/CNC50A.

382

Figure 5. Typical stress-strain profiles of PVA/CNC10R, PVA/CNC25R, PVA/CNC50R (a);

383

PVA/CNC10A,

384

PVA@CNC10 and CNC10@PVA fiber mats (c). The tensile test was performed along the fiber

385

axis.

C-O (1100

cm-1), ν

C-O-C (1160

PVA/CNC25A,

cm-1) of (a) PVA/CNC10R, (b) PVA/CNC10A, (c)

PVA/CNC50A (b);

and


coaxial

nanofiber mats

of

Biomacromolecules

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Page 20 of 25

386

387 388

Figure 1. SEM micrographs and histograms of width distributions for randomly orientated

389

nanofibers of PVA/CNC10R (a), well-aligned nanofibers of PVA/CNC10A (b), and core-sheath

390

nanofibers of PVA@CNC10 (c), CNC10@PVA (d), respectively.


Page 21 of 25

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

Biomacromolecules

391 392

Figure 2. Polarized optical micrographs of spinning dope of CNC (a) and PVA/CNC10 (d), and

393

electrospun nanofibers of PVA@CNC10 (b), CNC10@PVA (c), PVA/CNC10R (e),

394

PVA/CNC10A (f), respectively.


Biomacromolecules

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Page 22 of 25

395 396

Figure 3. POM images of nanofibrous mats of PVA/CNC10R (a), PVA/CNC10A (d),

397

PVA/CNC50A (g), and POM images of nanofibrous mats of PVA/CNC10R (b,c),

398

PVA/CNC10A (e,f), PVA/CNC50A (h,i) with a full-wavelength (530 nm) retardation plate with

399

a slow axis (γ) marked by a yellow arrow.


Page 23 of 25

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

Biomacromolecules

400 401

Figure 4. Polar plots of the normalized absorbance as a function of rotational angle (α) for ν C-OH

402

(1060 cm-1), ν

403

PVA/CNC25A, (d) PVA/CNC50A.

C-O (1100

cm-1), ν

C-O-C (1160

cm-1) of (a) PVA/CNC10R, (b) PVA/CNC10A, (c)


Biomacromolecules

a 12

b12

PVA/CNC10R PVA/CNC25R PVA/CNC50R

10

8

8

8

6

6

6

4

4

4

2

2

2

0.06 0.04 0.02 0.00

0.06 0.04 0.02 0.00

0.06 0.04 0.02 0.00

0

5

10

15

20

25

Strain (%)

404

c 12

PVA/CNC10A PVA/CNC25A PVA/CNC50A

10

Stress (MPa)

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 24 of 25

0

20

40

60

80

PVA@CNC10 CNC10@PVA

10

100

0

Strain (%)

20

40

60

80 100 120

Strain (%)

405

Figure 5. Typical stress-strain profiles of PVA/CNC10R, PVA/CNC25R, PVA/CNC50R (a);

406

PVA/CNC10A,

407

PVA@CNC10 and CNC10@PVA fiber mats (c). The tensile test was performed along the fiber

408

axis.

PVA/CNC25A,

PVA/CNC50A (b);

and

409


coaxial

nanofiber mats

of

Page 25 of 25

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Biomacromolecules

410

For Table of Contents Use Only

411

Graphical Abstract:

412 413

414

415

Fiber Alignment and Liquid Crystal Orientation of Cellulose Nanocrystals in the

416

Electrospun Nanofibrous Mats

417

Weiguang Song,a,b Dagang Liu,*a,b,c Nana Prempeh,b Renjie Song a


Fiber Alignment and Liquid Crystal Orientation of Cellulose

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