Chemomechanical response

Brazel, C. S. and Peppas, N. A. Synthesis and characterization of thermo- and chemomechanically responsive poly(A-isopropylacrylamide-co-methacryhc acid) hydrogels. Macromolecules 1995, 28, 8016-8020. 

Without using ions, electric field or heat, electrochemically synthesized PPy films may exhibit fast and intensive bending in ambient air on the basis of a reversible van der Waals adsorption of polar, organic or water molecules in the vapor state [139-141]. As shown in Table 8.13, the chemomechanical response of the actuator strongly depended on the adsorbate [139]. It was reported that PPy film exhibited contraction when an electric field was applied in ambient air because of the contraction caused by desorption of water vapor and thermal expansion of polymer chains [142]. 

TABLE 8.13 Chemomechanical Response of the PPy/CI04 Film to Various Adsorbates... 

Figure 4.16. Chemomechanical response at temperature variation of the PVME gel crosslinked by y radiation [98].

Researchers are facing difficulties in improving the properties and response rates of chemomechanical andelectrochemomechanical systems based on polymer gels or proteins that are intended to be used as actuators in robotics. Lack of mechanical toughness and long-term durability are other problems to be solved. A basic improvement in the low efficiency... 

Reports of building up two-dimensional polymers have been published by several research groups [9-12]. Additional reports [13-15] and a review [16] have appeared on stimuli-responsive polymer gels and their application to chemomechanical systems. The preparation and application of new monosized polymer particles have been reviewed [17]. 

Figure 16 is a schematic representation of an electrically activated chemical valve membrane whose pore size expands and contracts reversibly in response to an electrical stimulus. When the chemomechanical contraction is developed iso-metrically, i.e., keeping the membrane dimensions constant, the contractile stress... 

Boissonade etal. consider the chemoelastodynamics of responsive gels in Chapter 9. This chapter is devoted to the spontaneous generation of mechanical oscillations by a responsive gel immersed in a reactive medium away from equilibrium. Two important cases are considered. In the first case, the chemomechanical instability is mainly driven by a kinetic instabiUty leading to an oscillatory reaction. The approach is applied to the BZ reaction. The second case is a mechanical oscillatory instability that emerges from the cross-coupUng of a reaction-diffusion process and the volume or size responsiveness of the supporting material. In this case, there is no need for an oscillatory reaction. Bistable reactions, namely, the chlorite-tetrathionate (CT) and the bromate-sulfite (BS) reactions, were chosen... 

Finally, the numerical simulations showed that the frequency of chemical oscillations within the heterogeneous BZ gels depends on whether the gel is responsive or not, and changes upon deformation of the sample. Figure 8.8 shows the oscillation frequency a>o as a function of the stretch X for the responsive (black symbols and Hnes) and nonresponsive (red symbols and Unes) gel having one patch of length Ip = 5Lo at/ = 0.7. The frequency of the chemomechanical oscillations in the responsive gel is seen to be lower than that of the purely chemical oscillations in the nonresponsive gel. In Figure 8.8, the open symbols mark the data obtained... 

Yoshida, R. (2009) in Chemomechanical Instabilities in Responsive Materials, Springer NATO series A (eds P. Borckmans, P. De.Kepper, A. Khokhlov, and S. Metens), p. 39. 

Osada Y, Gong J. Stimuli-responsive polymer gels and their application to chemomechanical systems. Progr Polym Sci 1993 18 187-226. 

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