Study on Volume-Phase Transition in Polyelectrolyte Gels at the Molecular Level

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The purpose of this study is to experimentally demonstrate that the volume-phase transition in polyelectrolyte gels can be explained by our hypothesizing balance model (F. Ilmain, T. Tanaka, E. Kokufuta, Nature, 349, 400-401 (1991)). In this model, the transition is accounted for by hypothesizing a balance between the repulsion and attraction among functional groups attached to the network which arise from a combination of four interrmolecular forces : ionic, hydrophobic, van der Waals and hydrogen bonding. When a repulsive force, usually electrostatic in nature, overcomes an attractive force such as hydrogen bonding or hydrophobic interaction, the gel volume should increase discontinuously in some cases and continuously in others. The variables that trigger the transition influence these intermolecular forces and thereby the balanced state of the attractive and repulsive forces. We thus focused on the effect of charge distributions on the swelling of polyelectrolyte gels. Our gel samp … More les ranged from the usual bulk gel to nano-sized particles in shape. The charge distribution within the gel phase was created by different ways : binding of ionic surfactants, physical entrapment of polyions ; and immobilized enzyme reaction. It has became apparent that an charge inhomogeneity plays an important role in the swelling of ionic gels which takes place when the repulsion among the polymer-bound negative or positive charges overcomes hydrogen bonding and/or hydrophobic interaction as the attractive force. This is not able to explain in terms of Flory's model based on net osmotic pressure arising from mobile ions. The conclusions obtained from the present study have been applied in the construction of 〓biochemo-mechanical systems〓 capable of converting biochemical energy created as a result of an immobilized enzyme reaction into mechanical work through the swelling and shrinking of the gel. In addition, polyelectrolyte nanogel particles with diameters in the range of tens to hundreds of nanometers have been designed and synthesized on the basis of the present conclusions. Less