Controlling Surface Deformation and Feature Aspect Ratio in Photochemically Induced Marangoni Patterning of Polymer Films

Saurabh Shenvi Usgaonkar, Christopher J. Ellison, Satish Kumar

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Thin liquid polymer films can be topographically patterned when polymer/air interfaces are deformed by surface-tension gradients. Toward this end, a recently developed method first photochemically patterns surface-tension gradients along a solid, flat polymer film. On heating to the liquid state, the film initially develops topography reflecting the patterned surface-tension gradients. But capillary leveling and diffusion of the photoproduct oppose this causing the features to eventually decay back to a flat film upon extended thermal annealing. Intuitively, this interplay between competing mechanisms sets a limit on the maximum film deformation during the process. Prior studies show that the initial film thickness, photomask periodicity, and amount of photochemical conversion significantly affect the maximum film deformation. Here, we use a model based on lubrication theory to develop additional insights into this observation. We identify two regimes, capillary-leveling-dominated and photoproduct-diffusion-dominated, wherein the respective dominant mechanism determines the maximum film deformation that can be additionally related to various experimental parameters. Scaling laws for the variation of maximum film deformation and aspect ratio with film thickness and surface-tension pattern periodicity are also developed. Complementary experiments show good agreement with model predictions. Insights into the effect of surface-tension pattern asymmetry on the maximum film deformation are also provided. These findings reveal mechanistic detail and fundamental principles that are useful for controlling the process to form target patterns of interest.

Original languageEnglish (US)
Pages (from-to)7400-7412
Number of pages13
JournalLangmuir
Volume38
Issue number24
DOIs
StatePublished - Jun 21 2022

Bibliographical note

Funding Information:
This work was supported through the Industrial Partnership for Research in Interfacial and Materials Engineering at the University of Minnesota. S.S.U. acknowledges partial support through a fellowship awarded by the PPG Foundation.

Publisher Copyright:
© 2022 American Chemical Society.

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