Department of Chemical Engineering, McMaster University, Hamilton L8S 4L7, Canada.
Biomacromolecules. 2013 Sep 9;14(9):3130-9. doi: 10.1021/bm400752k. Epub 2013 Aug 2.
Cellulose nanocrystals (CNCs) are a sustainable nanomaterial with applications spanning composites, coatings, gels, and foams. Surface modification routes to optimize CNC interfacial compatibility and functionality are required to exploit the full potential of this material in the design of new products. In this work, CNCs have been rendered pH-responsive by surface-initiated graft polymerization of 4-vinylpyridine with the initiator ceric(IV) ammonium nitrate. The polymerization is a one-pot, water-based synthesis carried out under sonication, which ensures even dispersion of the cellulose nanocrystals during the reaction. The resultant suspensions of poly(4-vinylpyridine)-grafted cellulose nanocrystals (P4VP-g-CNCs) show reversible flocculation and sedimentation with changes in pH; the loss of colloidal stability is visible by eye even at concentrations as low as 0.004 wt %. The presence of grafted polymer and the ability to tune the hydrophilic/hydrophobic properties of P4VP-g-CNCs were characterized by Fourier transform infrared spectroscopy, elemental analysis, electrophoretic mobility, mass spectrometry, transmittance spectroscopy, contact-angle measurements, thermal analysis, and various microscopies. Atomic force microscopy showed no observable changes in the CNC dimensions or degree of aggregation after polymer grafting, and a liquid crystalline nematic phase of the modified CNCs was detected by polarized light microscopy. Controlled stability and wettability of P4VP-g-CNCs is advantageous both in composite design, where cellulose nanocrystals generally have limited dispersibility in nonpolar matrices, and as biodegradable flocculants. The responsive nature of these novel nanoparticles may offer new applications for CNCs in biomedical devices, as clarifying agents, and in industrial separation processes.
纤维素纳米晶（CNC）是一种可持续的纳米材料，其应用涵盖复合材料、涂料、凝胶和泡沫。为了充分发挥这种材料在新产品设计中的潜力，需要通过表面引发接枝聚合 4-乙烯基吡啶来优化 CNC 界面相容性和功能的表面改性途径。在这项工作中，通过表面引发接枝聚合 4-乙烯基吡啶和引发剂硝酸铈（IV）铵，使 CNC 具有 pH 响应性。聚合反应是一种一锅法、水基合成反应，在超声处理下进行，可确保纤维素纳米晶在反应过程中均匀分散。所得的接枝聚（4-乙烯基吡啶）-纤维素纳米晶（P4VP-g-CNCs）悬浮液在 pH 值变化时表现出可逆的絮凝和沉淀；即使在低至 0.004wt%的浓度下，通过肉眼也可以看到胶体稳定性的丧失。接枝聚合物的存在以及调整 P4VP-g-CNCs 的亲水性/疏水性的能力通过傅里叶变换红外光谱、元素分析、电泳迁移率、质谱、透光率光谱、接触角测量、热分析和各种显微镜来表征。原子力显微镜显示，接枝聚合物后，CNC 的尺寸或聚集程度没有观察到明显变化，并且通过偏光显微镜检测到改性 CNC 的液晶向列相。P4VP-g-CNCs 的可控稳定性和润湿性在复合材料设计中是有利的，因为纤维素纳米晶在非极性基质中的分散性通常有限，并且作为可生物降解的絮凝剂。这些新型纳米粒子的响应特性可能为 CNC 在生物医学设备、澄清剂和工业分离过程中的应用提供新的机会。
