Title: Control over emergence and alignment of transient blisters in thermo-responsive gels using hierarchically patterned substrates

Abstract

Surfaces with tunable microscale textures are vital in a large variety of technological applications, including heat transfer, antifouling and adhesion. To facilitate such broad-scale use, there is a need to create surfaces that undergo reconfigurable changes in topology and thus, enable switchable functionality. To date, there is a relative dearth of methods for engineering surfaces that can be actuated to change topography over a range of length scales, and hence, form tunable hierarchically structured layers. Combining modeling and experiments, we design a geometrically patterned, thermo-responsive poly (N-isopropylacrylamide) gel film that undergoes controllable hierarchical changes in topology with changes in temperature. At the bottom, the film is covalently bound to a solid, curved substrate; at the top, the film encompasses longitudinal rectangular ridges that are oriented perpendicular to the underlying cylindrical curves. At temperatures below lower critical solution temperature (LCST), the swollen gel exhibits 3D variations in polymer density and thickness defined by the gel's top and bottom topography. As the temperature rises above LCST, the interplay between the upper ridges and lower curves in the gel drives non-uniform, directional solvent transport, the nucleation and propagation of a phase-separated higher-density skin layer, and the resulting pressure buildup within the film. Thesemore » different, interacting kinetic processes lead to an instability, which produces transient microscopic blisters in the film. Through simulations, we show how tuning the width of the ridges modifies the propagation of a skin layer and creates localized pressure build-up points, which enables control over the emergence, distribution, and alignment of the microscopic blisters. Futhermore, we provide a simple argument to predict the size of such microscopic features. Experiments confirm our predictions and further highlight how our computational model enables the rational design of topographical transitions in these tunable films. The development of actuatable, hierarchically structured films provides new routes for achieving switchable functionality in actuators, drug release systems and adhesives.« less

Authors:

Liu, Ya  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3903-502X"

Zhang, Cathy T. ^[2]; Aizenberg, Joanna  ^[2];

• Search DOE PAGES for author "Aizenberg, Joanna"
• Search DOE PAGES for ORCID "0000-0002-2343-8705"

Balazs, Anna C.  ^[1]

• Search DOE PAGES for author "Balazs, Anna C."
• Search DOE PAGES for ORCID "0000-0002-5555-2692"

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+ Show Author Affiliations

1. Univ. of Pittsburgh, PA (United States)
2. Harvard Univ., Cambridge, MA (United States). John A. Paulson School of Engineering and Applied Sciences (SEAS)

Publication Date:

Mon Jul 25 00:00:00 EDT 2022

Research Org.:

Northwestern Univ., Evanston, IL (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Bio-Inspired Energy Science (CBES)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1978912

Alternate Identifier(s):

OSTI ID: 1879765

Grant/Contract Number:  

SC0000989

Resource Type:

Accepted Manuscript

Journal Name:

Soft Matter

Additional Journal Information:

Journal Volume: 18; Journal Issue: 32; Journal ID: ISSN 1744-683X

Publisher:

Royal Society of Chemistry

Country of Publication:

United States

Language:

English

Subject:

42 ENGINEERING; Chemistry; Materials Science; Physics; Polymer Science