Stress development in drying coatings

Abstract

As a solvent-cast polymeric coating dries, each part reaches a concentration at which it solidifies and develops elastic modulus. Thereafter, as further solvent departs, that part shrinks out-of-plane, but not in-plane, if the coating adheres to its substrate. Hence, it develops in-plane elastic stress. If the stress grows large enough, the stress-free state may yield, which reduces the final stress level. A theoretical model of diffusion and mass transfer, large shrinkage-induced deformation, and elastic stress, together with yielding and postyielding viscous deformation, was developed to predict stress evolution in one-dimensional drying of polymer coatings. Concentration varies only perpendicularly to the substrate, the coating shrinks only in that direction, and the stress varies only in that direction but is in-plane isotropic. The predictions are compared with measurements of evolving stress in various solvent-cast polymer coatings and aqueous gelatin coatings by a cantilever-deflection method.

A study of stress development in aqueous gelatin coatings

“…Comparing these results with theoretical modeling of stress development in elasto-viscoplastic coatings, 30 the change in structure may be explained in terms of yielding and a change in the stressfree state of the coating. 30,31 When the coating on a substrate yields as it develops stress, it does not undergo a permanent shape change, but rather, its equilibrium stress-free state changes. Reintroducing moisture into the coating after yielding will result in a different state of stress.…”

“…These ideas and the modeling results are the subject of another article. 30 Figure 13 demonstrates this phenomena for a coating cycled between 40 and 0% RH. Note the slight stress recovery at high humidities in Figure 13.…”

Nanocomposite coatings for healing surface defects of glass fibers and improving interfacial adhesion

“…Because of the compression closing surface flaw, the strengthening can be increased by increasing the magnitude of the compressive stress [25]. Stress development in drying coatings and explanations for the different stress levels measured for the various polymers can be found elsewhere [26]. Throughout most of a coating, the stress is solely inplane tensile stress, at edges and inclusions of nanoparticles, more complex concentrations of stress arise and its effect on the efficiency of flaw healing need further investigation.…”

Low-cost replication of self-organized sub-micron structures into polymer films

“…Both theoretical [6][7][8][9] and experimental [10,11] approaches have been used to explain the phenomenon. Utilization of the self-organized patterns in various applications is of high interest [12] and it has been applied for example in the case of curved photonic crystals by Kolaric et al [13].…”