Photodirected Wrinkle Formation via ‘Click’ Chemistry

Material wrinkling/buckling on an elastomer is a cost effective method to generate long range surface topography and has led to numerous proposed applications ranging from antifouling coatings,^{1, 2} tunable microarray lenses/optical coatings,^{3, 4} enhancements in solar cell efficiency,^{5, 6} and substrates for directed cell growth.^{7, 8}  Despite a large body of work in this area, however, the precise control over wrinkle confinement and orientation necessary to engineering textured surface remains a challenge.

Photopolymerizable click chemistry offers an attractive new medium to spatiotemporally direct wrinkle formation.⁹  To generate wrinkles, a base elastomer, embedded with photoinitiator and photoabsorber, is formed using off-stoichiometric amounts of thiols and enes through Michael type addition.  The elastomer is then strained and irradiated with UV light to induce a second polymerization of the excess functional groups.  While the photoinitiator initiates the second polymerization, the photoabsorber confines the UV light to a thin skin layer, creating the necessary conditions for the wrinkle formation upon release of the strain.  Through photomasked UV light, these wrinkles can be selectively confined and oriented, facilitating the formation of complex patterns with multiple distinct wavelengths as well as the formation of gradients containing a continuum of wrinkle wavelengths. Current work includes design and synthesis of new multi-functional monomers capable of undergoing orthogonal click chemistries, allowing wrinkle formation under ambient conditions. With the wide selection of commercially available and synthesizable monomers, photoinitiators, photomasks and stoichiometric control, we present an alternative system to wrinkle formation that is highly versatile, further enabling the a priori design and engineering of textured surfaces.

References

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(2) Efimenko, K., et al.  J. Nature Mater. 2005, 4, 293-297

(3) Chandra, D., Yang, S. and Lin, P.-C. Appl. Phys. Lett. 2007, 91,

(4) van den Ende, D., et al.  Adv Mater 2013, 25, 3438-3442

(5) Kim, J. B., et al.  Nat Photonics 2012, 6, 327-332

(6) Xie, K. Y. and Wei, B. Q. Adv Mater 2014, 26, 3592-3617

(7) Guvendiren, M. and Burdick, J. A. 2010, 31, 6511-6518

(8) Guvendiren, M. and Burdick, J. A. 2013, 2, 155-164

(9) Ma, S. J., Mannino, S. J., Wagner, N. J. and Kloxin, C. J. Macro Letters 2013, 2, 474-477

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