Thermal Properties and Depth Profile Studies on Polymer-Polymer-Solvent Coatings

Abstract

The designing of the multi-polymer-solvent coatings is done by single thick layer and layer-by-layer techniques in order to minimize the residual solvent. The average concentrations of the polymers and solvent, change in coating thickness with time have been calculated from the gravimetric weight loss data. In the case of poly(styrene)-(poly(methyl methacrylate)-tetrahydrofuran (PS-PMMA-THF) and poly(styrene)-poly(methyl methacrylate)-toluene system, (PS-PMMA-TOL) the doubling the poly(styrene) mass fraction does not change the mass transfer mechanism within these coatings. However, doubling the poly(methyl methacrylate) mass fraction changes the mass transfer mechanism very significantly which leads to very slow diffusion process within these coatings.

In case of poly(styrene)- poly(methyl methacrylate)-ethylbenzene (PS-PMMA-EB), doubling of both the polymer mass fraction does not change the mass transfer mechanism within these coatings. However, the drying time is much higher as compared to the other two systems, that is poly(styrene)- poly(methyl methacrylate)-tetrahydrofuran, and poly(styrene)- poly(methyl methacrylate)-toluene coatings.

The effect of change of polymer and solvent has been studied. PMMA has been replaced by amorphous PEG to study the effect of its mass fraction on the residual solvent and morphology of the coatings. The results indicate that the single thick layer technique should be used to minimize the residual solvent in the coatings studied herein. However, these coatings are taking longer time to dry as compared to the layer-by-layer technique. Hence, higher energy demands for the drying operation.

The morphological studies of poly(styrene)-poly(ethylene glycol)-chlorobenzene films have been performed using scanning electron microscopy. The average diameter of the holes present in the coatings decreased from 7.68 mm to 3.74 mm with the increase in the polymer content from 5% to 10%. The solvent played a major role in forming ordered porous polymer films. Asymmetric membrane formed at different concentrations of the ternary system. The effects of various parameters like polymer mass fraction, initial film thickness, and technique of application on the pore size and uniformity have been studied. Membrane type coating is observed at different concentrations of the ternary system.

The effect of molecular weight on the residual solvent, change in coating thickness, and polymer and solvent concentration of the coatings have been investigated in the case PS-PMMA-EB coatings. The molecular weight of poly(styrene) has a significant effect on the residual solvent as compared to the molecular weight of poly(methyl methacrylate). The residual solvent and coating thickness are lowest in the case of higher molecular weight of PS.

The effect of molecular weight of polymers on the glass transition temperature and morphological behavior of the coatings have been investigated over a broad range of molecular weights of polystyrene (35000, 192000, 280000 and 350000), and poly(methyl methacrylate) (120000, 350000 and 996000) in ethylbenzene. The prepared coating are analyzed by their glass transition temperatures (Tg) using differential scanning calorimetry, and their morphological behavior using scanning electron microscopy. The molecular weight of PS has shown significant effect on the glass transition temperature, and coating morphology.

The concentrations of the solvent and polymer have been measured inside dried poly(styrene)-poly(methyl methacrylate)- tetrahydrofuran coatings using confocal laser Raman spectroscopy. The PS-THF and PMMA-THF binary calibration plots have been used to determine the concentrations of ternary coatings. This study also substantiates that the concentrations of PS, PMMA, and THF change in the same manner as has been computed from their gravimetric studies. The distribution of the polymers is not in equal proportion from the substrate to the top. The percentage of PS is higher on the top as compared to PMMA.