Swelling Behavior of Chitosan Hydrogel in Ionic Liquid-Water Binary System
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0915-R03-08
Swelling Behavior of Chitosan Hydrogel in Ionic Liquid-Water Binary System Chang Kee Lee, Sang Jun Park, Seong Gil Yoon, Kwang Min Shin, Su Ryon Shin, Bon Kang Gu, Min Sup Kim, Min Kyoon Shin, Yu Jin Kim, and Seon Jeong Kim Hanyang University, Seoul, Korea, Republic of
ABSTRACT The swelling behavior of chitosan hydrogels in ionic liquid–water binary systems was studied using hydrophilic room-temperature ionic liquids (RTILs) to elucidate the swelling properties of chitosan hydrogels. It was confirmed that chitosan hydrogels are much stiffer after immersing in a pure RTIL because the water existing inside the chitosan polymer network is extracted into the RTIL. The pH of the binary system changes when the RTIL is in contact with water. The chitosan hydrogels were fully dissociated at a 90% water content in the BMI-BF4-water binary system. The equilibrium binary system content behavior of the chitosan hydrogels depended upon the amount of free water present. The water behavior in a pure RTIL was examined using differential scanning calorimetry. INTRODUCTION The swelling of hydrogels is an important characteristic that defines their applications. Hydrogels show a large degree of swelling in an aqueous environment, and a differential shrink– swell response occurs in different solvents, including organics and salt solutions. The determination of the swelling range and swelling behavior of a hydrogel is necessary to investigate its applicability to many biological applications, such as wound dressings, drug and protein delivery systems, and as tissue matrices. Recently, an attractive field of study for hydrogels is in artificial muscles and actuators, because they provide a mechanical response to electrical stimulation [1,2]. Hydrogels can control their degree of swelling in response to a specific electrical stimulus, and this is of interest because of its similarity in mimicking the functions of bio-muscles. Some hydrogels have been developed as polymer gel electrolytes for use in soft actuators [3], because the hydrogels can act as electrolytes themselves, and they can also house an electrolyte by dissolving the electrolyte in the hydrogel network. Chitosan is used as a component of hydrogels, and it is also a polymer electrolyte [4,5], because of its ease in forming a positive charge in a low pH environment. Chitosan is biocompatible and is an abundant material that has a long and well-established technological base. However, hydrogels have a serious lack of electrical stability in electrolytes under ambient conditions, because of the high volatility of water. This means that there is a limit to the application lifetime of hydrogels in polymeric conducting systems [6]. Room-temperature ionic liquids (RTILs) are interesting liquid electrolytes for electrochemical applications. Previous workers have shown the utility of RTILs as electrolytes in electrochemical systems by achieving unprecedented environmental and electrochemical stability [7, 8]. Spinks and coworkers [6, 9] have reported on the electrochemis
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