Estimation of the Intrinsic Birefringence of Cellulose Using Bacterial Cellulose Nanofiber Films

Abstract

The intrinsic birefringence of cellulose is one of the most fundamental optical parameters for analyzing and developing various cellulosic materials. However, the previously reported values greatly vary depending on the problems occurred due to the measured cellulose sample or method, and it is still a challenge to evaluate the intrinsic birefringence of cellulose using suitable cellulose samples and methodologies by taking account into the recent knowledge and techniques. Here, we estimated the intrinsic birefringence of cellulose to be 0.09 by a procedure with three valid factors: (1) bacterial cellulose nanofibers consisting of extended chain crystals of cellulose are used, (2) films with relatively small orientation degrees are fabricated, and (3) the in-plane retardation maps are measured. The resultant eigenvalue is greater than those reported for cellulose and many petroleum-based polymers. Therefore, cellulose could be used to develop high-performance light compensation films with large optical anisotropies for use in future optoelectronic devices.

Checkered Films of Multiaxis Oriented Nanocelluloses by Liquid-Phase Three-Dimensional Patterning

“…A hydrophilic poly (tetrafluoroethylene) membrane filter (H010A090C or H010A142C, Advantec Toyo Kaisha, Ltd., Tokyo, Japan) was used for patterning the base materials to easily remove the nanocellulose gels or dried films from the glass Petri dish. The 2D x-ray diffraction (2D-XRD) measurements were outsourced to EAG Inc. (San Diego, CA, USA) in the same manner as previous studies [10,11]. A Siemens/Bruker GADDS system with a Hi-Star detector and a Huber goniometer was used with Cu Kα radiation (λ = 1.54059 Å) at 50 kV and 40 mA to obtain 2D diffraction frames five times at 200 s per frame, which were summed and averaged for better statistics without detector saturation issues.…”

“…The average retardation and standard deviation were calculated from the retardation mapping data of 384 × 288 pixels in each image. The distribution of the slow axis corresponding to the higher refractive index direction (i.e., the cellulose chain direction) [11] was also extracted from each pixel data. Infrared thermography (CPA-E40, FLIR Systems Inc., Wilsonville, OR, USA) with preinstalled emissivity of 0.7 for paper was used to visualize the temperature distributions of the checkered films.…”

“…Nanocelluloses extracted from natural resources have large dimensional and functional anisotropy derived from their intrinsic extended chain crystal of cellulose I, so the various oriented structures of nanocelluloses have stunning properties in various materials including actuating plant cell walls [1], photonic structures with the chiral nematic phase [2,3], and fibers [4][5][6][7] or films [8,9] with high mechanical strength. In particular, recent studies have revealed that unidirectionally oriented nanocellulose films anisotropically conduct heat [10] or control optical retardation [11]. With regard to the thermal conductivity and optical controllability of nanocelluloses, for future paper electronics, the development of sophisticated materials such as phonon management film elements or polarizing arrays is expected by constructing fine multidirectional alignment structures within the film planes, rather than in the thickness direction like the self-assembling chiral nematic structure.…”

“…Various orientation techniques for nanocelluloses have been reported including shearing under evaporation [12,13], magnetic field orientation [14], biodirected epitaxial nanodeposition [15], wet spinning [4][5][6][7], cold drawing [8], doctor blade coating [9], gel stretching [10,11], evaporation-induced droplet casting [16,17], interfacial polyelectrolyte complex spinning [18], confinement-induced ordering [19], hydrodynamic alignment [20], and three-dimensional (3D) printing [21]. However, none of these methods can produce films with in-plane multiaxis oriented nanocelluloses because methods based on spinning, stretching, evaporation, and magnetic treatment only make the nanocellulose unidirectionally align.…”

Thermal diffusivity modulation driven by the interfacial elastic dynamics between cellulose nanofibers

“…Since the BC pellicles are formed by discharging CNF along with the movement of bacteria, there are large variations of ber density and orientation. 39 Even at applying $34 MPa, the relative standard deviations for the thermal diffusivity of the CNF lm were found as small as 1.67, 2.64 and 3.95% in x, y, and z directions, respectively.…”