Swelling-induced morphology in ultrathin supported films of poly(d,l-lactide).
In this study we describe a surface morphology that arises when ultrathin supported films of poly(d,l-lactide) are immersed in water. The films are initially flat with a rms roughness of approximately 2 nm. After immersion the surfaces of the films are covered with craters. The craters have a narrow distribution of sizes and are typically micrometers in diameter. They have depths in the 10-100 nm range. In situ atomic force microscopy shows that the craters occur as a result of a blistering process, which occurs when the films delaminate from the silicon substrate. The films buckle away from the substrate to give a nonzero initial diameter and then the blisters proceed to grow until they reach a maximum size. At any point during the growth process, the blisters can be made to collapse by removing the films from water. This phenomenon is explained in terms of a laterally confined swelling film, which has a buckling instability and releases excess strain energy by wrinkling. An expression for the initial buckling wavelength is extracted using the expressions for a buckling plate. Information about the mechanical properties of the films and the surface interaction between the film and substrate can also be obtained by considering the kinetics of blister growth.
Sharp
J S
JS
Department of Physics, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada, N2L 3G1. jssharp@sciborg.uwaterloo.ca
Jones
R A L
RA