Phase Separation and Interfaces of Confined Aqueous Colloidal Systems

CTS-9700147 Robert Marc/莱斯U提出了研究受限水胶体体系相分离、张力和界面结构的方法。受限胶体系统在几个技术应用中发挥着重要作用，如造纸、农药、化妆品、制药、陶瓷粉末材料的加工以及木材和砖石(砖、混凝土、水泥、石材、灰泥)涂料(涂料)的配方。目前严格的环境和安全法规，特别是减少或消除VOC(挥发性有机化合物)的法规，推动了对水性胶体体系的研究。在该项目中，重点放在技术上重要的水性配方上，例如那些含有非离子水溶性聚合物HEC(纤维素醚羟乙基纤维素)的配方，以及由专门为水分散体设计的HMHEC进行疏水性改性的配方。HEC和HMHEC是乳胶漆中使用最广泛的增稠剂/稳定剂，也是油墨、化妆品、药品、食品和陶瓷等多种材料中的基本添加剂。要研究的体系是由非吸附、水溶性聚合物稳定的胶体悬浮液。研究了受限体系的相分离(可逆絮凝)随组成和颗粒/聚合物尺寸比的变化，并将实验结果与统计力学的预测进行了比较。对于受限体系，通过数字视频显微镜确定界面结构，即界面区域内胶体浓度和配对分布(相关)函数的变化。这些实验确定的界面结构将与统计力学预测的结构进行比较。对于受限和非受限胶体系统，流体界面的张力将通过毛细上升和固定下降法以及数字视频显微镜来确定，在后一种情况下，根据远离样品细胞壁的半月板的形状来确定。这项研究及其对能源和环境问题的潜在有益影响，如果成功，将通过首次确定受限几何结构中胶体体系的流体相分离，确定受限和非受限胶体体系的界面张力，以及实验确定受限二维流体的界面结构和临界界面张力，从而促进知识的进步。***

ABSTRACT CTS-9700147 Robert Marc/Rice U. It is proposed to study the phase separation, tension and structure of interfaces of confines aqueous colloidal systems. Confined colloid systems play important roles in several technological applications, such as paper, pesticides, cosmetics, pharmaceuticals, the processing of materials from ceramic powders, and the formulation of coatings (paints) for wood and masonry (brick, concrete, cement, stone, stucco). The study of aqueous colloidal systems is motivated by current stringent environmental and safety laws enforcing, in particular, the reduction or elimination of VOC (volatile organic compounds). In the project, emphasis is given to technologically important aqueous formulations such as those containing the nonionic water-soluble polymer HEC (cellulose ether hydroxyethylcellulose) and its hydrophobically modified from HMHEC specifically designed for aqueous dispersions. HEC and HMHEC are the most widely used thickeners/stabilizers in latex paints and essential additives in numerous materials such as inks, cosmetics, pharmaceuticals, foods, and ceramics. The systems to be studied are aqueous colloidal suspensions stabilized by non-adsorbing, water-soluble polymers. Phase separation (reversible flocculation) is investigated for confined systems as a function of composition and particle/polymer size ratio, and experimental results are compared with predictions of statistical mechanics. For confined systems, the interfacial structure, i.e., the variation of the colloidal concentration and the pair distribution (correlation) function in the interfacial region, are determined by digital videomicroscopy. These experimentally determined interfacial structures will be compared to those predicted by statistical mechanics. The tensions of the fluid interfaces will be determined for confined and unconfined colloidal systems, by the capillary rise and sessile drop methods and by digital videomicroscopy, in the latter case from the shape of the meniscus away from the sample cells walls. Together with its potential beneficial impact on energy and environmental issues, this research, if successful, will contribute to the advancement of knowledge by providing for the first time the determination of fluid phase separation of colloidal systems in confined geometries, the determination of interfacial tension of confined and unconfined colloidal systems, as well as the experimental determinations of interfacial structure and of critical interfacial tension of a confined, two-dimensional fluid. ***