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Competition between dewetting and cross-linking in poly(N-vinylpyrrolidone)/polystyrene bilayer films

Citation

Telford, AM and Thickett, SC and James, M and Neto, C, Competition between dewetting and cross-linking in poly(N-vinylpyrrolidone)/polystyrene bilayer films, Langmuir, 27, (23) pp. 14207-14217. ISSN 0743-7463 (2011) [Refereed Article]

Copyright Statement

Copyright 2011 American Chemical Society

DOI: doi:10.1021/la2029577

Abstract

We investigated the dewetting of metastable poly(N-vinylpyrrolidone) (PNVP) thin films (45 nm) on top of polystyrene (PS) thin films (58 nm) as a function of annealing temperature and molecular weight of PS (96 and 6850 kg/mol). We focused on the competition between dewetting, occurring as a result of unfavorable intermolecular interactions at the PNVP/PS interface, and spontaneous cross-linking of PNVP, occurring during thermal annealing, as we recently reported (Telford, A. M.; James, M.; Meagher, L.; Neto, C. ACS Appl. Mater. Interfaces 2010, 2, 23992408). Using optical microscopy, we studied how the dewetting morphology and dynamics at different temperatures depended on the relative viscosity of the top PNVP film, which increased with cross-linking time, and of the bottom PS film. In the PNVP/PS96K system, cross-linking dominated over dewetting at temperatures below 180 C, reducing drastically nucleated hole density and their maximum size, while above 180 C the two processes reversed, with complete dewetting occurring at 200 C. On the other hand, the PNVP/PS6850K system never achieved advanced dewetting stages as the dewetting was slower than cross-linking in the investigated temperature range. In both systems, dewetting of the PNVP films could be avoided altogether by thermally annealing the bilayers at temperatures where cross-linking dominated. The cross-linking was characterized quantitatively using neutron reflectometry, which indicated shrinkage and densification of the PNVP film, and qualitatively through selective removal of the bottom PS film. A simple model accounting for progressive cross-linking during the dewetting process predicted well the observed hole growth profiles and produced estimates of the PNVP cross-linking rate coefficients and of the activation energy of the process, in good agreement with literature values for similar systems.

Item Details

Item Type:Refereed Article
Research Division:Chemical Sciences
Research Group:Physical Chemistry (incl. Structural)
Research Field:Colloid and Surface Chemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Chemical Sciences
Author:Thickett, SC (Dr Stuart Thickett)
ID Code:99400
Year Published:2011
Web of Science® Times Cited:7
Deposited By:Chemistry
Deposited On:2015-03-23
Last Modified:2017-10-24
Downloads:0

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