Switching of Water Flow Through Stimuli-responsive Hydrogels
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0947-A09-02
Switching of Water Flow Through Stimuli-Responsive Hydrogels Atsushi Suzuki and Go Kondo Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501, Japan ABSTRACT The friction between the polymer network and the solvent water was measured by a newly designed simple apparatus where the hydrogel was mechanically constrained in a glass microcapillary. The water-flow through the hydrogel could be continuously controlled by more than ten times only by adjusting the temperature in the vicinity of the transition temperature (around the human body temperature). The concentration of polymer network and cross-linker as well as the inhomogeneity of polymer networks introduced at gelation was found to determine the overall flow velocity and the amount of change during the phase transition could be controlled by the temperature change. The principle to control the solvent flow will be discussed on the basis of the material parameters and the experimental conditions.
INTRODUCTION Hydrogels are three-dimensional polymer network, containing a large amount of water, and exhibit many unique properties, which are attracting much interest, and many researchers from various fields have studied extensively the fundamental science and technology. Hydrogels are used for many practical purposes as retainers of water and solutes in many industries. On the other hand, the gels are known to exist in two distinct phases, swollen and collapsed; the volume phase transition [1,2] can occur between the phases in response to physical and chemical stimuli. It has been expected that hydrogels could be used as fundamental components in many potential applications, such as actuators, sensors and separators. After the pioneering works [3-6], the water flow in the hydrogels has not been extensively studied until now. Recently, the friction between the polymer network and the solvent water was measured by a newly designed simple apparatus [8], where the hydrogel was mechanically constrained in a glass microcapillary at gelation and hydrostatic pressure was directly applied to the cross-section of the cylinder. Using this technique the friction between a polymer network of poly(N-isopropylacrylamide) gels and solvent water was investigated temperature for gels with different lengths, l0, at gelation [9]; the temperature dependence of the flow velocity was extensively measured in the vicinity of the transition. As the temperature increased, the friction slightly decreased at the transition point and increased rapidly in the collapsed phase. Although the average flow velocity, u depended on l0, the friction in the vicinity of the transition point was well scaled by l0 based on the Hagen-Poiseuille equation for the flux of water flow in a capillary. The results suggested that the gel is assumed as a bundle of microcapillaries with inner diameter ξ (N microcapillaries per unit area), which can be applicable to the water flow through the hydrogel. The applied pressure, ∆p
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