By Gaea Marelle Miranda, M.Sc.Feb 14 2019.jpg)
Image Credits: science photo/shutterstock.com
Research on surface instabilities is continuously being facilitated as a means to understand their formation and use in organizing or measuring the properties of materials at the micro and nanoscale. One instability that has been the focus of contemporary research is surface wrinkling, especially on its applications in measuring thin-film properties.
Surface wrinkling is a morphological effect of the constrained shrinking or swelling of materials. In thin-film properties, surface wrinkling poses effects on particle assembly, mechanical characterization, surface patterning, and smart adhesion.
Wrinkling manifests in varied forms depending on the substance or material. In an elastic substrate, energetics and equilibrium are primarily responsible for the wrinkle amplitude or wavelength. In a viscous substrate, kinetics determines the rate at which wrinkles would grow. Surface wrinkling should be perceived as a primary response to film-substrate and stress.
Measuring Thin-Film Properties
Relative to other methods of measuring the property of thin films, surface wrinkling is considered as a simple yet well-established process. Wrinkling provides a means to assess a thin-film’s mechanical properties. In particular, the geometric properties formulated by the wrinkling process are measured through a variety of processes.
These processes include measuring thickness in terms of fingering instabilities, residual stress in dewetting, Poisson’s ratio in elastic thin sheets, and thickness and modulus in floating thin films. Recent findings on the use of surface wrinkling suggest that the method could also be used to determine material thin film properties.
Recent Studies on Surface Wrinkling
There are numerous contemporary findings on the applications of surface wrinkling in measuring thin-film properties. For instance, one study sought to develop a wrinkling-based method aimed at measuring the mechanical properties of polymeric films that are exposed to high viscosity levels and inability to reach mechanical equilibrium. Results suggest that critical strains are influenced by the liquid substrate thickness and compression strain rate.
Another study found that a film’s lateral dimension could significantly affect the surface wrinkling of a thin film. Using finite element (FE) simulations, an analytical expression of shear tractions at the film–substrate interface was measured. Results suggest that surface wrinkling, and even post-wrinkling, is controlled by the size of the lateral dimensions of the thin film in a particular moduli ratio.
Moreover, modern approaches to surface wrinkling propose that a non-wettable Si substrate preparation of polymeric thin films, treated using plasma irradiation, could produce competitive surface structures that are applicable as membranes. These new findings on surface wrinkling provide a more expansive approach to its applicability.
Sources and Further Reading
- “Surface Wrinkling: A Versatile Platform for Measuring Thin-Film Properties”, Advanced Materials, https://ws680.nist.gov/publication/get_pdf.cfm?pub_id=902425.
- “Competitive concurrence of surface wrinkling and dewetting of liquid crystalline polymer films on non-wettable substrates”, Soft Matter, https://pubs.rsc.org/en/content/articlelanding/2017/sm/c7sm01668a#!divAbstract.
- “A Kinetics Approach to Surface Wrinkling of Elastic Thin Films”, Mechanical Self-Assembly, https://link.springer.com/chapter/10.1007%2F978-1-4614-4562-3_5.
- “Effect of lateral dimension on the surface wrinkling of a thin film on compliant substrate induced by differential growth/swelling”, Journal of the Mechanics and Physics of Solids”, Journal of the Mechanics and Physics of Solids, https://www.sciencedirect.com/science/article/pii/S0022509615001520.
- “Surface wrinkling of nanostructured thin films on a compliant substrate”, Computational Materials Science, https://www.sciencedirect.com/science/article/pii/S0927025610003678.
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