Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada.
Transformation and Interfaces Group, Bioproducts Innovation Centre of Excellence, FPInnovations, 2665 East Mall, Vancouver, British Columbia V6T 1Z4, Canada.
Biomacromolecules. 2023 Feb 13;24(2):896-908. doi: 10.1021/acs.biomac.2c01325. Epub 2023 Jan 31.
Photonic materials based on composite films of cellulose nanocrystals (CNCs) and polymers are promising as they can be renewable and show tunable optical and mechanical properties. However, the influence of polymers on CNC self-assembly is not always well understood, and conflicting results are present in the literature. In this study, we incorporate three neutral, water-soluble polymers-poly(ethylene glycol) (PEG), poly(vinyl pyrrolidone) (PVP), and poly(acrylic acid) (PAA)-with different molecular weights into CNC suspensions at various concentrations prior to obtaining iridescent composite thin films by solvent evaporation. Through spectroscopic, potentiometric, and rheological analyses, we find that PVP physically adsorbs to the surface of CNCs resulting in a bathochromic shift in film color with both increasing concentration and polymer molecular weight. In contrast, PEG induces depletion interactions that result in a decrease in the size of chiral nematic CNC domains, with a negligible change in film color. Finally, PAA hydrogen bonds to the hydroxyl groups of CNCs, resulting in a bathochromic color shift along with interesting rheological and liquid-state properties. This work demonstrates a deeper understanding of CNC-polymer interactions during coassembly and formation of iridescent chiral nematic films, allowing for greater control over optical properties of future CNC-based materials.
基于纤维素纳米晶体（CNC）和聚合物的复合薄膜的光子材料很有前途，因为它们可以是可再生的，并具有可调节的光学和机械性能。然而，聚合物对 CNC 自组装的影响并不总是被很好地理解，文献中存在相互矛盾的结果。在这项研究中，我们在获得各向异性复合薄膜之前，将三种中性、水溶性聚合物-聚乙二醇（PEG）、聚乙烯吡咯烷酮（PVP）和聚丙烯酸（PAA）-以不同的分子量分别掺入 CNC 悬浮液中，浓度不同。通过光谱、电位和流变分析，我们发现 PVP 物理吸附在 CNC 表面上，导致薄膜颜色发生红移，随着浓度和聚合物分子量的增加而增加。相比之下，PEG 诱导的空间位阻相互作用导致手性向列 CNC 畴的尺寸减小，而薄膜颜色几乎没有变化。最后，PAA 与 CNC 的羟基形成氢键，导致颜色发生红移，同时表现出有趣的流变学和液态特性。这项工作更深入地了解了在各向异性手性向列薄膜形成过程中 CNC 与聚合物的共组装相互作用，从而可以更好地控制未来基于 CNC 的材料的光学性能。
