Harnessing Surface Wrinkle Patterns in Soft Matter

Abstract

Mechanical instabilities in soft materials, specifi cally wrinkling, have led to the formation of unique surface patterns for a wide range of applications that are related to surface topography and its dynamic tuning. In this progress report, two distinct approaches for wrinkle formation, including mechanical stretching/releasing of oxide/PDMS bilayers and swelling of hydrogel fi lms confi ned on a rigid substrate with a depth-wise modulus gradient, are discussed. The wrinkling mechanisms and transitions between different wrinkle patterns are studied. Strategies to control the wrinkle pattern order and characteristic wavelength are suggested, and some efforts in harnessing topographic tunability in elastomeric PDMS bilayer wrinkled fi lms for various applications, including tunable adhesion, wetting, microfl uidics, and microlens arrays, are highlighted. The report concludes with perspectives on the future directions in manipulation of pattern formation for complex structures, and potential new technological applications.

Phase Diagrams of Instabilities in Compressed Film-Substrate Systems

“…Similarly, various instabilities in film-substrate systems under biaxial compression have also been analyzed individually but still require a systematic understanding [6,7,9,11,13,14,30,[65][66][67][68][69][70][71]. Furthermore, it is expected that the systematic understanding and phase diagrams of instabilities can guide future design of new materials and structures for practical applications [2,5,21,36,38,72]. Fig.…”

“…Compressive membrane stresses can be frequently induced in films bonded on substrates due to various reasons, such as growth and swelling of the films [1][2][3][4][5][6][7], thermal expansion mismatch between the films and the substrates [8][9][10][11][12], ion irradiation treatment [13,14], electric fields applied on the films [15][16][17], relaxation of prestretches in the substrates [18][19][20][21][22][23], and mechanical compression on the substrates [24][25][26][27]. As the compressive stresses in the films reach critical values, the homogeneous deformation of the film-substrate systems becomes unstable, switching into states of inhomogeneous deformation with nonflat configurations of the films.…”

Controlled fabrication of nanoscale wrinkle structure by fluorocarbon plasma for highly transparent triboelectric nanogenerator

“…Meanwhile, we noticed that the wrinkle profile on Solaris was closer to a sinusoidal shape. In the region of low deformation, assuming a homogeneous film and bulk materials with perfect adhesion at the interface, λ can be described by 8 :…”

“…Thereby, selfassembled patterns for large-area patterning, which generally employ physical-chemical or mechanical instabilities within a constrained system to form highly ordered structures, have attracted great attention for many years [2][3][4][5][6][7] . Among these methods, mechanically inducing a wrinkle structure on a bilayer system is especially suited to creating highly ordered microstructures across a large surface and features convenient fabrication and a tunable wavelength by adjusting the thickness of the stiff layer and the prestrain [8][9][10][11][12] . As a result, wrinkle structures have been used in various applications, such as smart adhesion, liquid/cell shaping, particle assembly, optical surfaces, flexible electronic devices, and energy harvesters [13][14][15][16][17][18][19][20] .…”

Catastrophic Thinning of Dielectric Elastomers

“…tunable adhesion, wetting, open-channel microfluidics, etc. [22,23] and on-demand fluorescent patterning [24]. By re-defining and furthering the concept of electromechanical instability of dielectric films, the paper essentially implies that new experimental campaigns and new analytical studies based on formula (2) are now required to generate a finer physical picture of the catastrophic thinning phenomenon.…”