Protruding organic surfaces triggered by in-plane electric fields

Coatings with a dynamic surface topography are of interest for applications in haptics, soft robotics, cell growth in biology, hydro- and air dynamics and tribology. Here we propose a design for creating oscillating surface topographies in thin liquid crystal polymer network coatings under an electric field. By applying an alternating electric field, the coating surface deforms, and pre-designed local corrugations appear. The continuous AC electric field further initiates oscillations superimposed on the formed topographies. This effect is based on microscopic free volume creation. By exciting the liquid crystal network at its resonance frequency, maximum free volume is generated and large surface topographies are formed. Molecular simulation is used to examine this behaviour in microscopic detail as a function of oscillation frequency. Surface topography formation is fast and reversible. Excess free volume is energetically unfavourable, thus the surface topographies disappear within seconds once the electric field is removed.OLD ChemE/Organic Materials and Interface

3D Helix Engineering in Chiral Photonic Materials

Engineering the helical structure of chiral photonic materials in three dimensions remains a challenge. 3D helix engineered photonic materials are fabricated by local stratification in a photopolymerizable chiral nematic liquid crystal. The obtained chiral photonic materials reflect both handedness of circular polarized light and show super-reflectivity. Simulations match the experimentally observed photonic properties and reveal a distorted helical structure. 3D engineered polymer films can be made that reflect both left- and right handed circular and linear polarized light dependent and exhibit a changing color contrast upon altering the polarization of incident light. Hence, these 3D engineered photonic materials are of interest for new and emerging applications ranging from anti-counterfeit labels and data encryption to aesthetics and super-reflective films.ImPhys/Imaging Physic

High-Frequency Surface Dynamics at an Electroactive Polymer Producing Underwater Soundwaves

Coatings with dynamic surface structures are appealing to many applications like haptics and soft robotics. Restrictively, the speed of the surface dynamics in these coatings is often limited to frequencies below 1 kHz, which makes them unsuitable for applications like acoustics and communication optics. This work describes a method to create high-frequency surface dynamics controlled by alternating electric fields on a substrate-contact-modulated coating that consists of an elastic poly(dimethyl siloxane) network supported by SU-8 microstructures. The principle is based on the global application of Maxwell stress that is locally resisted by the supporting SU-8 microstructures. In-between the microstructures the elastic material is stretched, causing a large deformation of the surface topography, which is supported by the authors’ finite element method models. By applying a high-frequency alternating field, they discovered resonance effects at frequencies up to 230 kHz, where the surface of the coating vibrates at high speeds and large amplitudes. At these high frequencies, the coatings can produce and detect ultrasound waves underwater, indicating their potential for ultrasound transducers in the future.ImPhys/Medical ImagingBUS/TNO STAF