Adhesion Properties between Swollen Hydrogels in Air
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0897-J08-10.1
Adhesion Properties between Swollen Hydrogels in Air Daisuke Sakasegawa, Takaya Sato, Motoaki Goto1, and Atsushi Suzuki Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama, 240-8501 Japan. 1 Saitama Daiichi Pharmaceutical Co., Ltd, Kasukabe, Saitama, 344-0057 Japan. ABSTRACT Adhesion between swollen hydrogels was studied using a simple tack-evaluation technique by a point contact in air at room temperature. The hydrogel used here was poly(sodium acrylate) (PSA) gel physically cross-linked by aluminum ions. The adhesion force and the separation energy showed a power-law increase with separation velocity, normal force, and waiting period prior to separate. Effects of the degrees of protonation in PSA as well as of dehydration on the adhesive properties are also presented. The results are discussed in terms of the surface molecular interaction and the bulk elastic and viscous properties.
INTRODUCTION Hydrogel refers to a chemically- or physically- crosslinked network of linear polymers immersed in water. Such structures have been shown to exhibit unique properties related to the super water absorbents as well as the stimuli-responsive devices. Among the properties, controlling the adhesion between polymer gel surfaces is of great importance in many applications. However, systematic studies on the adhesion have not been extensively studied until now. Especially, the mechanism of the adhesion between gel/gel interfaces is still missing. Among several techniques to evaluate the adhesion properties of the soft materials, the peel test, the rolling ball test and the probe tack test have been widely accepted for evaluating the adhesion properties of the soft materials [1-5]. Recently, we developed a new technique for measuring the surface adhesion between soft materials [6], where the adhesion force, FA, of a point contact and the total energy, EA, required to separate the contact can be measured using the springs of phosphor-bronze thin plates with strain gauges. This specific experimental geometry was used to minimize the effects of the interface boundary conditions. The adhesion between swollen hydrogels was studied by this simple technique on seven anti-inflammatory analgesic cataplasms on the market. It was found that the ranking of FA and EA was consistent with the results of the easiness to separate obtained by organoleptic evaluations. The technique is relatively simple to implement and can be widely applicable for weakly adhering soft materials with relative high accuracy and reproducibility. In this paper, the adhesion properties were preliminarily studied on poly(sodium acrylate) (PSA) hydrogels that were physically crosslinked by aluminum ions. The surface adhesion between swollen hydrogels was studied by this simple technique under several different conditions in air at room temperature. In the present experiment, FA and EA were measured under the three experimental parameters; the waiting period prior to the separation, tw, the separation velocity, v,
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