ma047991b_si_001.pdf (8.46 MB)
Controlled Foaming of Polymer Films through Restricted Surface Diffusion and the Addition of Nanosilica Particles or CO2-philic Surfactants
journal contribution
posted on 2005-03-22, 00:00 authored by Srinivas Siripurapu, Joseph M. DeSimone, Saad A. Khan, Richard J. SpontakSynergistic use of surface barriers and nanoscale additives is investigated as alternate means
by which to promote bubble nucleation in, and thus improve the porosity of, poly(methyl methacrylate)
(PMMA) thin films (i) constrained between impenetrable plates, (ii) modified with either nanosilica
particles, commercial short-chain fluorosurfactants, or designer CO2-philic block/graft copolymers, and
(iii) exposed to high-pressure CO2. Resultant foamed films exhibit a vast array of micro/mesocellular
morphologies in the presence of supercritical, as well as liquid, CO2 and demonstrate that copolymer
micelles afford better control over bubble nucleation (with pore cell densities, N, approaching 1012 cells/cm3) relative to hard nonporous nanoparticles, which alone increase N by more than 2 orders of magnitude
at low CO2 pressures. Incorporation of these nanoscale additives in a surface-constrained polymer matrix
serves to enhance foaming through concurrent restriction of CO2 diffusion, heterogeneous nucleation of
CO2 bubbles, and/or reduced interfacial tension between PMMA and CO2.