Fault-Tolerant Electro-Responsive Surfaces for Dynamic Micropattern Molds and Tunable Optics

Abstract

Electrically deformable surfaces based on dielectric elastomers have recently demonstrated controllable microscale roughness, ease of operation, fast response, and possibilities for programmable control. Potential applications include marine anti-biofouling, dynamic pattern generation, and voltage-controlled smart windows. Most of these systems, however, exhibit limited durability due to irreversible dielectric breakdown. Lowering device voltage to avoid this issue is hindered by an inadequate understanding of the electrically-induced wrinkling deformation as a function of the deformable elastic film thickness. Here we report responsive surfaces that overcome these shortcomings: we achieve fault-tolerant behavior based on the ability to self-insulate breakdown faults, and we enhance fundamental understanding of the system by quantifying the critical field necessary to induce wrinkles in films of different thickness and comparing to analytical models. We also observe new capabilities of these responsive surfaces, such as field amplification near local breakdown sites, which enable actuation and wrinkle pattern formation at lower applied voltages. We demonstrate the wide applicability of our responsive, fault-tolerant films by using our system for adjustable transparency films, tunable diffraction gratings, and a dynamic surface template/factory from which various static micropatterns can be molded on demand.Dynamic control of surface topography and roughness is highly desired for its potential to accomplish what is difficult for traditional static surfaces to achieve, such as adjustable wettability 1 , smart adhesion 2 , antifouling abilities 3 , tunable light diffraction 4 , e-skin and stretchable devices 5,6 . Depending on the material's mechanical properties, such surfaces can show a variety of topographies during deformation, including wrinkling (or buckling), formation of localized ridges, period-doubling, creasing, and delamination 7,8 . Several methods have been used to induce such surface deformation, such as in-plane mechanical compression 9-11 , relaxation after depositing thin films on pre-stretched substrates [12][13][14][15][16][17] , thermal expansion mismatch after cooling thin films deposited on hot substrates [18][19][20][21][22] , ion irradiation 23,24 , differential swelling of film layers 2,[25][26][27][28][29] , and electric-field-induced deformation [30][31][32] . Among these various approaches, electric-field-induced deformation is particularly attractive due to its ability to reversibly actuate at high frequency and its potential for miniaturization and programmable control 33 . This type of deformation relies on the concept of voltage-induced electromechanical instability 34-39 , a phenomenon frequently observed in dielectric elastomer actuators (DEAs) [40][41][42][43][44][45] . Wang and Zhao, for example, have produced creased/cratered/wrinkled structures by immobilizing a DEA on a rigid substrate 32,46 . This DEA-like system is composed of four layers from top to bottom: a conductive li...

The Evolution of Self-Wrinkles in a Single-Layer Gradient Polymer Film Based on Viscoelasticity

“…Wrinkles widely exist in nature, and the phenomenon has been a focus in recent years − from avoiding performance penalties to exploiting surface morphology and properties. The wrinkles have found broad applications in electronic device diffraction gratings, functional surfaces, microlens arrays, dry adhesives, smart windows, stretchable electronics, and advanced optical devices. ,− Many works have been performed on the strategies for wrinkle fabrication and mechanisms in layered systems, achieving significant progress in the elaboration of functional and micro/nanostructured surfaces. The underlying mechanism of wrinkling is the instability of the energy and mechanical properties. − The widely studied representative system is the typical bilayer system with a rigid top layer on a soft elastic substrate. ,, The surface wrinkles appear when the residual stresses exceed a critical value induced by the external stimulus, ,− such as heating, light, solvent swelling, mechanical stretching/compression, and applying an electric field.…”

Electrically tunable directional light scattering from soft thin membranes

“…The most used technologies for such optical devices consist of electrochromic materials [4][5][6] and polymerdispersed liquid crystals (PDLC) [7][8][9][10]. Recently, so-called dielectric elastomer actuators (DEAs) have been reported as a promising alternative technology to obtain voltage-induced large and continuous changes of the transparency of a soft surface [11][12][13][14][15][16][17][18][19]. Unlike electrochromic materials, where the operation is based on electrochemical reactions, the DEA technology relies on an electrostatic effect, which is therefore intrinsically faster [11][12][13][14][15][16][17][18][19].…”

“…Recently, so-called dielectric elastomer actuators (DEAs) have been reported as a promising alternative technology to obtain voltage-induced large and continuous changes of the transparency of a soft surface [11][12][13][14][15][16][17][18][19]. Unlike electrochromic materials, where the operation is based on electrochemical reactions, the DEA technology relies on an electrostatic effect, which is therefore intrinsically faster [11][12][13][14][15][16][17][18][19]. In comparison with PDLC materials, which only offer on-off switching capabilities, DEA-based devices allow for the transparency to be controlled over continuous ranges [11][12][13][14][15][16][17][18][19].…”

“…Unlike electrochromic materials, where the operation is based on electrochemical reactions, the DEA technology relies on an electrostatic effect, which is therefore intrinsically faster [11][12][13][14][15][16][17][18][19]. In comparison with PDLC materials, which only offer on-off switching capabilities, DEA-based devices allow for the transparency to be controlled over continuous ranges [11][12][13][14][15][16][17][18][19].…”

“…The second strategy combines the previous concept with a compression of the membrane by an outer annular DEA, so as to obtain a dual-operation device, whose transparency can be both increased and decreased, depending on whether the electrical activation is used to generate a membrane expansion or contraction [14]. The third strategy uses transparent electrodes that cover a DE membrane fixed to a rigid glass substrate, whose transparency can be reduced by very high electric fields, which create microscopic craters on the surface, due to electromechanical instabilities [15][16][17][18]. The fourth strategy uses electric field-induced alignments of liquid crystals encapsulated within a DE membrane sandwiched between transparent electrodes, so as to switch the membrane's appearance from opaque to transparent [19].…”