Wrinkling-to-delamination transition in thin polymer films on compliant substrates

Abstract

Compressing a thin, stiff film attached to a thick, compliant substrate can lead to a number of different modes of mechanical deformation depending upon the material properties of the system. In this article we explore direct transitions from surface wrinkling to buckle delamination, and provide a theoretical framework for understanding the conditions under which such transitions take place, as well as the resulting dimensions of the wrinkling-induced delamination. A key conclusion of this work is that the width of the delamination blister formed from a wrinkled film is relatively strain-independent, suggesting that delaminations can be used in such systems to measure the adhesion energy at the film-substrate interface. In addition, we demonstrate how the length and width of delaminations can be tailored through straightforward control of the substrate and film properties in the system, illustrating how wrinkling delaminations can be used for both thin film metrology and patterning applications.

Fig. 1

(a) A thin film on a compliant substrate undergoes either surface wrinkling or buckle delamination in response to in-plane compression. (b) An instability “map” that predicts the preferred mode for a given system. Upon in-plane compression, the film will prefer to either wrinkle or delaminate from the substrate per the system parameters. The circles indicate the approximate locations for three specific systems obtained from the references as indicated.

Fig. 2

(a) Delamination in a wrinkled film-substrate system. The formation of a delaminated region of width, L, results in the relaxation of compressive strain in the film over a region with characteristic width, R, which in turn causes a significant decrease in wrinkle amplitude within the relaxation region. (b) An optical micrograph showing a wrinkled PS film (E_f ≈ 4 GPa, h ≈ 300 nm) on PDMS (E_s ≈ 0.5 MPa) following delamination. The strain in the film at delamination was ≈ 2 %. (c) Modeled relationship demonstrating the profiles of the delamination, relaxation zone, and wrinkled regions. (d) Scanning electron micrograph showing oblique angle of delamination and relaxation zone. (c–d) Used with permission from Mechanics of Materials and Proceedings of the National Academy of Sciences.

Fig. 3

Relaxation length (R) (right y-axis, red solid circles) and buckle delamination length (L) (left y-axis, black open circles) as a function of strain for a PS film (h ≈ 100 nm) on PDMS. R is inversely proportional to strain, while L is essentially constant. The line is a power law fit to the R data with the exponent constrained to a value of −1. The error bars represent one standard deviation of the data, which is taken as the experimental uncertainty of the measurement.

Fig. 4

Scaling relationships for L and R. Samples 1–4 (high E_s) are plotted with solid circles, and samples 6–10 (low E_s) with open circles. In (b), data from Fig. 3 are plotted as solid triangles. The error bars represent one standard deviation of the data, which is taken as the experimental uncertainty of the measurement.

Fig. 5

A PS film bonded to a selectively UVO-treated PDMS, showing the initiation of buckle delaminations on the untreated region (low G) and their arrest at the boundary between the treated (high G) and untreated (low G) regions.