Effect of Electrical Double Layer on Interfacial Electrical Potential and Interfacial Energy of P(AN-co-AAm-co-AA) and PVA-g-SSS Hydrogels in Electrolyte Solutions

• Main Author: 李耿裕
• Other Authors: 胡孝光
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/10556049072819626219

碩士 === 國立臺灣科技大學 === 纖維及高分子工程技術研究所 === 85 === Part Ⅰ Ionizable groups in polyelectrolyte gel interact electrostatically with ions in surrounding electrical potential. This work studies the swelling kinetics via water uptake by dry samples and zeta potentials by streaming potential measurement of Poly (vinyl alcohol-g-sodium styrenesulfonate) (PVA-g-SSS) and Poly (acrylonitrile- acrylamide-acrylic acid) (P(AN-AAm-AA)) gels in aqueous KCl solutions. The water absorption increase and then decreases with the concentration of KCl, and the diffusion coefficient of water into dry gels is maximal at the minimum water uptake. The maximum ion shielding on the gel surface occurs to the situation with lowest water uptake at intermediate electrolyte concentrations, and then excess K+ ions enters the swollen network, subsquently being hydrated at the higher electrolyte concentrations. Moreover, the water swelling deviates more significantly from the Fickian mode with the higher electrolyte concentrations, due to hysteresis on the swelling-driven mechanical relaxation caused by the K+. Both gels, have negative zeta potentials, whose absolute value increase with KCl concentration and becomes zero at intermediate KCl concentrations. Such a point-of-zero-charge phenomenon is also a manifestation of ion shielding on the gel at interface. Part Ⅱ The contact angle of air and n-octane on P(AN-AAm-AA) and P(VA-g-SSS) hydrogels in aqueous KCl solutions at 25℃ were measured. The interfacial energy between gels and water decreases with the decreasing water content of gels. The water content of gels decreases and then increases with the concentration of surrounding KCl solutions, and the minimum point implies the maximum shielding on the gel surface, maximum water-gel interaction energy at interface, and minimum interfacial energy. The relations between zeta potential of gel interface and interfacial energy of gels leads to the conclusions that the surface charge density of gels decreases with the ion content of gel bulk, and the capacity of electrical double layer is non-zero. The valence data of mobile ions in diffuse layer indicate that the permeability of gel interface make the electrical behavior of gel-ion interface different from the rigid interface.