(397b) Photodirected Control of Topography using Thiol-ene “Click!” Chemistry

Photodirected
Control of Topography using Thiol-ene 
?Click!?  Chemistry

Stephen J. Ma1, Dr. Norman J.
Wagner1,2, Dr. Christopher J. Kloxin1,2,3

1)   University of Delaware,
Department of Chemical and Biomolecular Engineering

2)   Center for Molecular and
Engineering Thermodynamics

3)   University of Delaware,
Department of Materials
Science and
Engineering

Wrinkling/buckling on elastomers represent a cost-effective approach
to creating
surface topography, leading to a broad range of applications in antifouling coatings,1,2  optical coatings and tunable lenses3,4, substrates for directed cell growth5,6, and enhancements in solar cell efficiency.7,8    One of the ongoing challenges of wrinkling is
the
limited ability to confine
and orient the wrinkles toward
the development of performance materials.

Using an acrylate-rich thiol-ene elastomer, embedded with
photoinitiator and photoabsorber, we have developed a rapidly curing wrinkling system.9 Upon irradiating the strained elastomers with UV light, the photoinitiator will induce radical polymerization of
the excess acrylates while
the
photoabsorber confines the light to a
thin skin
layer at the surface, creating the necessary conditions for

wrinkle formation on
the
order of seconds.
In
conjunction with photomasked UV light,
these wrinkles can be easily confined and oriented to
generate complex patterns
of multiple distinct wrinkle wavelengths and wrinkle gradients.
 With the addition of a
photoorthogonal 
 photoinitiator,   we  
can also ?lock' the shape of the elastomer through further bulk radical polymerization.

365 nm

Figure
1. Photopatterning is a very fast, inexpensive way to confine and orient wrinkles.

Beyond the ability to easily orient and align wrinkles through photopatterning, our wrinkle system is also
highly versatile.
 The ?click' nature of thiol-ene chemistry ensures high tunability of elastic modulus,
network architecture and surface functionality of the elastomer, through the types of monomers used and careful stoichiometric
control.  The presence of
excess acrylates also
enables post-functionalization
of various moieties
at
the surface
of
the films.

Additionally, recent advances in particle synthesis through thiol-ene chemistry,10,11,12 has opened up new avenues
in wrinkle
formation. By
covalently
attaching these particles atop strained thiol-ene elastomers,
it is possible to
form wrinkles with an additional level of surface roughness on the size-scale of the particles themselves, thereby enhancing the surface properties of the materials. More interestingly, these particles offer new
potential platforms for generating surface
topography on 3D objects, enabling, for the first time, the
experimental study of wrinkle formation on spheres.

References

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297

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

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(9) Ma, S. J., Mannino, S. J., Wagner, N. J.
and
Kloxin, C. J. Macro Letters 2013, 2,
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(10) Durham, O.Z., Krishnan, S., Shipp, D.A. Macro Letters 2012, 1, 1134-1137

(11) Wang, C., Podgorski, M., Bowman, C.N. Materials Horizons 2014, 1,
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(12) Amato, D.V., Amato, D.N., Flynt, A.S., Patton, D.L. Polymer Chemistry, 2015, Advance Article