Study of Thickness Dependent Density in Ultrathin Water Soluble Polymer Films

Abstract

Density of the polyacrylamide ultrathin films has been studied using X-ray reflectivity technique. Two sources (one powder and another aqueous solution) of polyacrylamide were used to prepare spin coated films on silicon substrate. Light scattering measurements show that the polymer chains were unentangled in a concentrated (4 mg/ml) as well as in a dilute (2 mg/ml) solution prepared from the powder, whereas the solution (4 mg/ml) prepared by diluting the solution source shows entangled chain morphology. Three sets of films of different thicknesses were prepared using the three solutions by spin coating on silicon substrates. Comparison of X-ray reflectivity data for as prepared and dry films reveals that the shrinkage of the films decreases with increasing thickness. Average electron densities of the films were found to follow a trend of higher density for thinner films with a maximum increase of about 12% compared to the bulk. The densities of all the films irrespective of the nature of entanglement and concentration of their source were found to increase with spin speed of coating and attain saturation at higher speed. Absence of correlation between shrinkage and density data and the fact that the densities of all the films follow a master curve irrespective of their origin suggest that the higher density of the films result from the higher orientation of chains as a consequence of an interplay between stretching and stronger attractive interactions of polar nature.

Study of structural evolution during controlled degradation of ultrathin polymer films

“…This initial "slow" reduction of thickness may be attributed to the compaction of the films due to larger mobility of the polymer chains above the glass transition temperature (165 o C for polyacrylamide) as observed earlier. 23,27 The increase of rate of thickness reduction above 210 o C indicates possibility of additional chemical changes in the film. In the cooling cycle there was a small reduction of the film thickness at the initial stage probably due to the inertial effects of the slow chain dynamics, thereafter the thickness of the film remains constant.…”

“…In figure 6 we have plotted the average electron density for all the films before and after annealing as a function of spinning speed of their preparation. 23 In table 1 percentage increase of density values with respect to dry films are tabulated for all the films. The reduction of film thickness for various films was between 8.4 to 16.7% and the increase of density ranges from 0-12.6% (compared to those of the dry films) without having any systematic dependence between the two.…”

“…Two solutions of concentrations 2 mg/ml and 4 mg/ml were prepared from the powder source (molecular weight 5-6 ×10 6 ). A third solution of concentration 4 mg/ml was prepared from the partially entangled 23 solution source (molecular weight 5 ×10 6 ). The solutions are denoted as solutions A, B and C respectively.…”

Surface engineering of polystyrene–cerium oxide nanocomposite thin films for refractive index enhancement

“…A schematic regarding this is shown in Figure 3.This renders lower entanglement of the polymer chains thereby leading to a higher order of orientation of the polymer chains because of the stronger polymer-solvent, polymer-polymer, and polymer-substrate interactions. Highly ordered polymer chains result in a higher density of the polymer chains leading to an enhancement in the refractive index [67][68][69] .…”

Temperature-Controlled Solvent Vapor Annealing of Thin Block Copolymer Films

“…Polymer films represent one of the most used classes of soft matter with applications ranging from functional coatings and sensors to separation membranes and organic electronics. Along with the chemical composition, the conformations of macromolecular chains determine the properties of polymer films such as glass transition temperature ( T g ) [1,2], electron densities [3], wetting [4,5], rheology [6], solvent absorption, and swelling dynamics [7,8]. Extensive research has revealed that characteristics of thin polymer films strongly deviate from the properties these polymers exhibit in bulk [9].…”