We studied the drying process of polymer solution drops placed on a substrate having a large contact angle with the drop. The drying process takes place in three stages. First, the droplet evaporates keeping the contact line fixed. Second, the droplet shrinks uniformly with receding contact line. Finally the contact line is pinned again, and the droplet starts to be deformed. The shape of the final polymer deposit changes from concave dot, to flat dot, and then to concave dot again with the increase of the initial polymer concentration. This shape change is caused by the gradual transition from the solute piling mechanism proposed by Deegan to the crust buckling mechanism proposed by de Gennes and Pauchard.
The swelling dynamics of long cylindrical gel is analyzed by the stress diffusion coupling model [T. Yamaue and M. Doi, Phys. Rev. E 69, 41402 (2004)]. Two situations are analyzed: (i) stress induced swelling, where the swelling is caused by an elongational force applied on the gel, and (ii) free swelling, where the swelling is caused by thermodynamic force. The relaxation times characterizing these processes are calculated. It is shown that earlier calculations for the relaxation time, which are based on some physical or mathematical approximations, give results surprisingly close to the rigorous calculation, but the difference can be still seen experimentally.
Recently, the swelling kinetics of thin-plate gels with rectangular surfaces under mechanical constraint was experimentally investigated [J. Chem. Phys. 114, 5012 (2001)]]. In this system, the top and bottom surfaces of gels were chemically clamped on the glass plates, and the gels could swell and shrink only along the thickness direction when the osmotic pressure of the solvent is changed. Here, we analyze this process using the linearized stress-diffusion coupling model of gels based on the two fluids model. The result is somewhat unusual in that the time evolution of the thickness is described by a single exponential even though the swelling is governed by the diffusion of solvent. This result and that the characteristic relaxation time depends on the lengths of the rectangular surfaces and not on the thickness of gels agree well with the experiment.
To describe the deformation dynamics of polyelectrolyte gel, we formulate the electrostress
diffusion coupling model. The model describes the interplay of the deformation of gel, permeation of water,
and the transport of ions. The model gives a microscopic expression for the Onsager coefficient and allows
us to discuss the effect of ionic radius. The model is then applied to the bending dynamics of a thin strip
of ionic gels under stepwise application of electric field. The model qualitatively explains the relaxation
behavior of an ionic gel (Nafion 117) for various kinds of ions including large counterions such as TEA+
(tetraethylammonium).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.