148 research outputs found
Optical Waveguide-Enhanced Diffraction for Observation of Responsive Hydrogel Nanostructures
Optical diffraction measurements are reported for in situ observation of swelling and collapsing of responsive hydrogel nanostructures. The optical signal is enhanced by probing the surface carrying periodic arrays of hydrogel nanostructures by resonantly excited optical waveguide modes. UV-nanoimprint lithography is employed for the preparation of the arrays of nanopillars from photo-crosslinked N-isopropylacrylamide (pNIPAAm)-based hydrogel that are covalently tethered to a gold surface. The thermo-responsive properties of such pNIPAAm nanopillars that swell in 3D are compared to those of a thin film prepared from the identical material and that is allowed to swell predominantly in 1D. The nanopillars with a diameter of ≈100 nm and aspect ratio of 2 swell by a factor of ≈6 as determined by optical measurements supported by simulations that are compared to morphological characteristics obtained from atomic force microscopy. Bending of nanopillars above the lower critical solution temperature (LCST), erasure of the topographic structure by drying at temperature below the LCST, and recovery by subsequent swelling below the LCST and drying at temperature above the LCST are observed
Tack energy and switchable adhesion of liquid crystal elastomers
The mechanical properties of liquid crystal elastomers (LCEs) make them
suitable candidates for pressure-sensitive adhesives (PSAs). Using the nematic
dumbbell constitutive model, and the block model of PSAs, we study their tack
energy and the debonding process as could be measured experimentally in the
probe-tack test. To investigate their performance as switchable PSAs we compare
the tack energy for the director aligned parallel, and perpendicular to the
substrate normal, and for the isotropic state. We find that the tack energy is
larger in the parallel alignment than the isotropic case by over a factor of
two. The tack energy for the perpendicular alignment can be 50% less than the
isotropic case. We propose a mechanism for reversibly switchable adhesion based
on the reversibility of the isotropic to nematic transition. Finally we
consider the influence of several material parameters that could be used to
tune the stress-strain response
Deformation and adhesion of a periodic soft–soft nanocomposite designed with structured polymer colloid particles
Adhesion and anisotropic friction enhancements of angled heterogeneous micro-fiber arrays with spherical and spatula tips
Recent advances in gecko adhesion and friction mechanisms and development of gecko-inspired dry adhesive surfaces
Design of biomimetic fibrillar interfaces: 1. Making contact.
This paper explores the contact behaviour of simple fibrillar interfaces designed to mimic natural contact surfaces in lizards and insects. A simple model of bending and buckling of fibrils shows that such a structure can enhance compliance considerably. Contact experiments on poly(dimethylsiloxane) (PDMS) fibrils confirm the model predictions. Although buckling increases compliance, it also reduces adhesion by breaking contact between fibril ends and the substrate. Also, while slender fibrils are preferred from the viewpoint of enhanced compliance, their lateral collapse under the action of surface forces limits the aspect ratio achievable. We have developed a quantitative model to understand this phenomenon, which is shown to be in good agreement with experiments
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