Tuning and Erasing Surface Wrinkles by Reversible Visible‐Light‐Induced Photoisomerization

Abstract

Periodic wrinkling across different scales has received considerable attention because it not only represents structure failure but also finds wide applications. How to prevent wrinkling or create desired wrinkling patterns is non-trivial because the dynamic evolution of wrinkles is a highly nonlinear problem. Herein, we report a simple yet powerful method to dynamically tune and/or erase wrinkling patterns with visible light. The light-induced photoisomerization of azobenzene units in azopolymer films leads to stress release and consequently to the erasure of the wrinkles. The wrinkles in unexposed regions are also affected and oriented perpendicular to the exposed boundary during the stress reorganization. Theoretical models were developed to understand the dynamics of the reversible photoisomerization-induced wrinkle evolution. This method can be applied for designing functional materials/devices, for example, for the reversible optical writing/erasure of information as demonstrated here.

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

“…The optimal wavelength does not only generate a high cis conversion level, it also triggers a considerable dynamic effect with the help of the enhanced cis absorbance. This result corroborates recent experiments in which not an UV but a higher wavelength light source was selected to trigger azobenzene-embedded systems, such as blue-green light [23,24] and other illumination scenarios [4,[25][26][27].…”

Patterning Surfaces on Azo‐Based Multilayer Films via Surface Wrinkling Combined with Visible Light Irradiation

“…Evidently, the wrinkle evolution in the unexposed D 2 region of the as‐wrinkled PDMS/PDO 3 /PS system is basically similar with that in the wrinkled PDMS/PDO 3 system, while for the wrinkle evolution in the exposed D 1 region, the two wrinkling systems are distinct from each other. In the latter case, the wrinkle wavelength in the exposed D 1 region is kept constant, and the wrinkle amplitude decreases increasingly until the wrinkles are fully erased during the light irradiation . These comparison results demonstrate that different mechanisms are responsible for the phototunable wrinkle patterns in the PDMS/PDO 3 and PDMS/PDO 3 /PS systems, which will be discussed subsequently.…”

“…The repeated photoisomerization between the “trans” and “cis” states requires an increase in the spatial volume of the polymer matrix for the local transition/movement of the azobenzene chromophores and the concomitant segmental motion of the polymer chains . Owing to the increase in the free volume of the polymer matrix induced by the “trans/cis” photoisomerization, the thickness of the PDO 3 film increases ≈4% according to the AFM characterization . This result reveals that the photoinduced increase in the thickness of the PDO 3 film plays a reversed role in the notable reduction of the wrinkle wavelength.…”

“…The influences of experimental parameters (e.g., the film thickness of the photosensitive intermediate layer and the photoinert outmost layer, selective exposure size, and geometry) on the resultant patterns and the involved mechanism of the photo‐modulated wrinkle patterns have been systematically investigated. Evidently, this wrinkle wavelength‐decreasing evolution in the PDO 3 ‐based multilayer film/substrate system upon light irradiation is distinct from the amplitude‐decreasing evolution in the corresponding PDO 3 /PDMS (film/substrate) bilayer system . In the latter bilayer system, it has been identified that the stress release instead of the photosoftening effect of PDO 3 plays the predominant role .…”

Compliance‐Mediated Topographic Oscillation of Polarized Light Triggered Liquid Crystal Coating

“…Examples showing stress releases in coatings typically show wrinkling, as two layers of different modulus are deposited on one another. [15][16][17] In this work, we present an approach to bridge the effects observed in freestanding films and the applicability of The ability to induce oscillating surface topographies in light-responsive liquid crystal networks on-demand by light is interesting for applications in soft robotics, self-cleaning surfaces, and haptics. However, the common height of these surface features is in the range of tens of nanometer, which limits their applications.…”