Study of Structural Evolution During Controlled Degradation of Ultrathin Polymer Films

TL;DR

This study investigates the structural changes in ultrathin polyacrylamide films during controlled thermal degradation, revealing two distinct degradation pathways with different time scales and their effects on film thickness and density.

Contribution

It introduces a detailed in situ analysis of polymer film degradation, modeling the process with two exponential decay functions and identifying two separate chemical modification pathways.

Findings

Thickness decreases significantly with annealing time.

Density increases as the films degrade.

Two distinct degradation modes with different time scales were identified.

Abstract

The structural aspects of polyacrylamide thin films annealed at degradation threshold temperature have been studied as a function of annealing time using in situ X-ray reflectivity technique in vacuum. We observe significant decrease of thickness and increase of density with annealing time for all the films. The dynamical behavior of the changes was modeled in terms of two distinct exponential decay functions, following our earlier observation of two different time scales for the chemical modification pathways, and was found to be in excellent agreement with the data. The diffusion coefficients of the polymer chains corresponding to the two modes are found to be different by an order of magnitude. It was found that the two dynamical modes correspond to the formation of two degradation products at two different rates. The larger time constants for both the modes in case of thickness reduction compare to the chemical changes was explained in terms of inter-chain entanglement and attachment of the polymer with the substrate.