Quantifying Strain via Buckling Instabilities in Surface-Modified Polymer Brushes

Abstract

A compressive strain applied to bilayer films (e.g. thin film adhered to a thick substrate) can lead to buckled or wrinkled morphologies, which has many important applications in stretchable electronics, anti-counterfeit technology, and high-precision micro and nano-metrology. A number of buckling-based metrology methods have been developed to quantify the residual stress and viscoelastic properties of polymer thin films. However, in some systems (e.g. solvent-induced swelling or thermal strain), the compressive strain is unknown or difficult to measure. We present a quantitative method of measuring the compressive strain of wrinkled polymer films and coatings with knowledge of the "skin" thickness, wrinkle wavelength, and wrinkle amplitude. The derived analytical expression is validated with a well-studied model system, e.g., stiff, thin film (PS) bonded to a thick, compliant substrate (PDMS). After validation, we use our expression to quantify the applied swelling strain of previously reported wrinkled poly(styrene-alt-maleic anhydride) brush surfaces. Finally, the applied strain is used to rationalize the observed persistence length of aligned wrinkles created during atomic force microscopy (AFM) lithography and subsequent solvent exposure.

Advancements in Novel Mechano-Rheological Probes for Studying Glassy Dynamics in Nanoconfined Thin Polymer Films

“…Here h 1 is the polymer brush layer modified by cystamine so that it forms a cross-linked skin layer. [Reproduced from ref . Copyright 2020 ACS.…”

“…207 However, the strain applied during the wrinkling could not be easily obtained in such systems as the compression is applied through solventinduced swelling or thermal strain. Recently Reese et al 206 have introduced a methodology to quantify such strains that are applied on the polymer brushes by using the modification of the brushes to create a cross-linked skin layer (h 1 ) and unmodified substrate layer (h 2 ). Using an in situ AFM measurement system, when the strain is maintained as constant, the wavelength is obtained by 2-D fast Fourier transform power spectrum, and the amplitude is obtained from the cross-section of the AFM image using an analyzing software.…”

Wrinkled Interfaces: Taking Advantage of Anisotropic Wrinkling to Periodically Pattern Polymer Surfaces

“…According to an overview study carried out by the Fery's group, in general, metal coatings allow sub‐micron wrinkles to be produced, while rigid polymeric coatings allow wrinkles between 2 and 10 µm to be prepared. [ 121 , 122 ]…”

“…According to an overview study carried out by the Fery's group, in general, metal coatings allow sub-micron wrinkles to be produced, while rigid polymeric coatings allow wrinkles between 2 and 10 μm to be prepared. [121,122] Direct Surface Treatments: Some polymeric elastic substrates undergo direct oxidation typically using plasma treatment [62,123] or UV-ozone, [63,[124][125][126] a new skin is created on the substrate surface, thus forming a skin/substrate wrinkling system together with the original substrate. The oxidative method and the operating conditions allow surface wrinkles ranging from a few nanometers to several hundred microns to be obtained, their wavelength can be controlled by varying the duration of the oxidation and predicted according to the following equation [123] 𝜆 = 4.36t…”