Swelling-deswelling oscillation

Figure 2, (a) Periodical redox changes of the miniature cubic poly(NlPAAm-co-Ru(bpy)j) gel and (b) the swelling-deswelling oscillation at 20 C. Transmitted light intensity is expressed as an 8-bit grayscale value. Outer solution [MA] = 62.5mM [NaBrOs] = 84mM [HNOsJ = 0,6M. 

The following assumptions were used to develop a mathematical model of swelling/deswelling oscillations ... 

In these experiments, the volume of the confined gel is constant its main role is to damp hydrodynamical motions that would otherwise perturb the chemical intrinsic patterns. More recently it has been shown experimentally that the coupling of a volume phase transition with a chemical oscillator can generate a self-oscillating gel (i, 4). More precisely, if one of the chemical species taking part in the chemical reaction modifies the threshold for the phase transition, then the time periodic variation of this concentration can generate autonomous swelling-deswelling cycles of the gel even in absence of any external stimuli (5, 6). This device thus provides a novel biomimetic material with potential biomedical and technical applications. 

Fig. 9.9 (a) Plots indicating occurrence of swelling-deswelling for a stimuli responsive vs. a self-oscillating gel. (b) Chemical structure of poly(NIPAAM-co-Ru(bpy)3) BZ gel. Reprinted with permission from [67]. (Copyright 1999 American Chemical Society)... 

Typically, the oscillation period increases with a decrease in the initial concentration of the substrates. Further, in general, the oscillation frequency (the reciprocal of the period) of the BZ reaction tends to increase as the temperature increases, in accordance with the Arrhenius equation. The swelling-deswelling amplitude of the gel increases with an increase in the oscillation period and amplitude of the redox changes. Therefore, the swelling-deswelling amplitude of the gel is controllable by changing the initial concentration of the substrates as well as the temperature. 

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