Wrinkling of a thin film on a nematic liquid-crystal elastomer (original) (raw)

Surface wrinkling in liquid crystal elastomers

Soft Matter, 2012

Structured surfaces give rise to novel and potentially useful properties such as controllable wettability and structural colour. Here, we demonstrate structured surfaces via reversible surface wrinkling in liquid crystal elastomers (LCEs). A thin polymer film deposited on top of a shape-responsive LCE exhibits a reversible, periodic surface wrinkling pattern in response to temperature changes. The orientation of the wrinkles depends on the orientation of the nematic director and the temperature at which the bilayer is prepared, and the wrinkles can be re-oriented in a single sample by heating or cooling the sample above or below the preparation temperature. We show that this bilayer system can be used to measure the modulus of nanoscale thin poly(styrene) films deposited on the LCE. Additionally, when a micron-thick polymer film is deposited on top of an LCE, the bilayer exhibits reversible curling with temperature. This system provides a simple method for measuring the mechanical properties of thin polymer films without the need for clamping and mechanical stretching and provides a new approach to generate reversible, microstructured surfaces.

Strain dependence of the nematic fluctuation relaxation in liquid-crystal elastomers

Physical Review E, 2010

Dynamic light scattering on a nematic liquid-crystal elastomer was performed as a function of deformation perpendicular to the director and along the director. We show that the relaxation rate of the nematic director fluctuations increases with strain along the director, as expected from the theory of semisoft elasticity. Deformation applied perpendicular to the director, on the other hand, decreases the relaxation rate to a very small value at the onset of the soft elastic response, revealing the existence of a dynamic soft mode. The results are in complete agreement with the theory of semisoft elasticity and allow us to determine all the constants of the model.

Elastomeric patterns probed by a nematic liquid crystal

Molecular Crystals and Liquid Crystals, 2017

Soft Janus elastomers have two surfaces with diverse characteristics. In this work, by tuning the chemical composition and the surface roughness we were able to vary the wettability of thin films (thickness of 100-200 µm) and spheres (diameters in the order of 200 µm to 2 mm) and evidence the multifunction of the opposite sides. We also describe a simple and inexpensive method to reveal the wrinkledlabyrinthine patterns that appear in the Janus particles by means of a nematic liquid crystal (LC). LC contact angle measurements associated with the swelling and anchoring characteristics of the surfaces were used to image the Janus particles opening new platforms for sensor applications from flexible free-standing LCs containers.

Evolution of wrinkles in hard films on soft substrates

2004

A compressively strained film on a substrate can wrinkle into intricate patterns. This Rapid Communication studies the evolution of the wrinkle patterns. The film is modeled as an elastic nonlinear plate and the substrate a viscoelastic foundation. A spectral method is developed to evolve the nonlinear system. When the initial film strains are isotropic, the wrinkles evolve into a pattern with a motif of zigzag segments, in random orientations.

Nematic fluctuations and semisoft elasticity in swollen liquid-crystal elastomers

Physical review. E, Statistical, nonlinear, and soft matter physics, 2015

Dynamic light scattering (DLS) experiments were performed on stretched sheets of liquid crystal elastomers (LCEs) swollen with a nematic solvent with different swelling ratios. We show that the obtained stress-strain curve and DLS data can still be explained with the concepts of semisoft elasticity. The stress-strain curve shows a typical semisoft response with a threshold strain and a plateau region where stress increases only a little with the applied strain. The width of the plateau decreases with the increase of the swelling ratio because the polymer backbone anisotropy reduces during the swelling. The relaxation rate of thermally excited director fluctuations, however, still shows a typical response, and our measurements indicate the presence of a soft dynamic director-shear mode, as predicted by the theory of semisoft elasticity.

Observation of a Soft Mode of Elastic Instability in Liquid Crystal Elastomers

Physical Review Letters, 2009

In monodomain liquid crystal elastomers a symmetry-breaking locked-in anisotropy causes a semisoft elastic response characterized by a plateau in the stress-strain curve. We show by dynamic light scattering performed as a function of deformation that the relaxation rate of the nematic director fluctuations decreases with strain to a very small value at the onset of the soft elastic response, revealing the existence of a dynamic soft mode. The results are in complete agreement with the theory of semisoft elasticity and allow us to determine all the constants of the model.

Semisoft elasticity and director reorientation in stretched sheets of nematic elastomers

2002

A two-dimensional effective model for the semi-soft elastic behavior of nematic elastomers is derived in the thin film limit. The model is used to investigate numerically the force-stretch curves, the deformed shape, and to resolve the local patterns in the director orientation in a stretching experiment. From the force-stretch curves we recover the two critical stretches which mark the transition from hard to soft and back to hard response. We present an analytical model for their dependence on the aspect ratio of the sample, and compare with numerical results.

Study of the optical, thermal, and mechanical properties of nematic liquid crystal elastomers

Journal of Information Display, 2016

In the present study, the optical, thermal, and mechanical properties of liquid crystal elastomers (LCEs) were investigated using various techniques. The presence of functional groups in LCE was studied using Fourier transform infrared spectroscopy. The phase transition temperatures were confirmed via polarizing optical microscopy and Fabry-Perot scattering studies. The differential thermal analysis was used for investigating the thermal behavior. A dynamic mechanical analysis was used to study the mechanical properties of LCE. The significant mechanical changes with a considerable reversible effect were observed for this soft material. The changes in the mechanical shape with the temperature are attributed to the change in the phase of the LCE material.