Weak-anchoring effects in a thin pinned ridge of nematic liquid crystal.

A theoretical investigation of weak-anchoring effects in a thin two-dimensional pinned static ridge of nematic liquid crystal resting on a flat solid substrate in an atmosphere of passive gas is performed. Specifically, we solve a reduced version of the general system of governing equations recently derived by Cousins et al. [Proc. R. Soc. A 478, 20210849 (2022)10.1098/rspa.2021.0849] valid for a symmetric thin ridge under the one-constant approximation of the Frank-Oseen bulk elastic energy with pinned contact lines to determine the shape of the ridge and the behavior of the director within it. Numerical investigations covering a wide range of parameter values indicate that the energetically preferred solutions can be classified in terms of the Jenkins-Barratt-Barbero-Barberi critical thickness into five qualitatively different types of solution. In particular, the theoretical results suggest that anchoring breaking occurs close to the contact lines. The theoretical predictions are supported by the results of physical experiments for a ridge of the nematic 4^{'}-pentyl-4-biphenylcarbonitrile (5CB). In particular, these experiments show that the homeotropic anchoring at the gas-nematic interface is broken close to the contact lines by the stronger rubbed planar anchoring at the nematic-substrate interface. A comparison between the experimental values of and the theoretical predictions for the effective refractive index of the ridge gives a first estimate of the anchoring strength of an interface between air and 5CB to be (9.80±1.12)×10^{-6}Nm^{-1} at a temperature of (22±1.5)^{∘}C.

Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface.

A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis during sub-millisecond wrinkle formation and decay, after abruptly increasing or reducing the voltage, respectively. The decay time constant closely followed the film thickness dependence expected for surface tension driven viscous levelling. Modelling of the system using numerical solution of the Stokes flow equations with electrostatic forcing predicted that wrinkle formation was faster than decay, in accord with observations.

Relationship between molecular association and re-entrant phenomena in polar calamitic liquid crystals.

The relationship between molecular association and re-entrant phase behavior in polar calamitic liquid crystals has been explored in two families of materials: the 4'-alkoxy-4-cyanobiphenyls (6OCB and 8OCB) and the 4'-alkoxy-4-nitrobiphenyls. Although re-entrant nematic phase behavior has previously been observed in the phase diagram of 6OCB/8OCB, this is not observed in mixtures of the analogous nitro materials. As there is no stabilization of the smectic A phase in mixture studies, it was conjectured that the degree of association for the nitro systems is greater than that for the cyano analogues. This hypothesis was tested by using measured dielectric anisotropies and computed molecular properties to obtain a value of the Kirkwood factor, g, which describes the degree of association of dipoles in a liquid. These computed values of g confirm that the degree of association for nitro materials is greater than that for cyano and offer a useful method for quantifying molecular association in systems exhibiting a re-entrant polymorphism.

Fabrication and evaluation of a micro(bio)sensor array chip for multiple parallel measurements of important cell biomarkers.

This report describes the design and development of an integrated electrochemical cell culture monitoring system, based on enzyme-biosensors and chemical sensors, for monitoring indicators of mammalian cell metabolic status. MEMS technology was used to fabricate a microwell-format silicon platform including a thermometer, onto which chemical sensors (pH, O2) and screen-printed biosensors (glucose, lactate), were grafted/deposited. Microwells were formed over the fabricated sensors to give 5-well sensor strips which were interfaced with a multipotentiostat via a bespoke connector box interface. The operation of each sensor/biosensor type was examined individually, and examples of operating devices in five microwells in parallel, in either potentiometric (pH sensing) or amperometric (glucose biosensing) mode are shown. The performance characteristics of the sensors/biosensors indicate that the system could readily be applied to cell culture/toxicity studies.

Molecular bridging of silicon nanogaps.

The highly doped electrodes of a vertical silicon nanogap device have been bridged by a 5.85 nm long molecular wire, which was synthesized in situ by grafting 4-ethynylbenzaldehyde via C-Si links to the top and bottom electrodes and thereafter by coupling an amino-terminated fluorene unit to the aldehyde groups of the activated electrode surfaces. The number of bridging molecules is constrained by relying on surface roughness to match the 5.85 nm length with an electrode gap that is nominally 1 nm wider and may be controlled by varying the reaction time: the device current increases from ≤1 pA at 1 V following the initial grafting step to 10-100 nA at 1 V when reacted for 5-15 min with the amino-terminated linker and 10 µA when reacted for 16-53 h. It is the first time that both ends of a molecular wire have been directly grafted to silicon electrodes, and these molecule-induced changes are reversible. The bridges detach when the device is rinsed with dilute acid solution, which breaks the imine links of the in situ formed wire and causes the current to revert to the subpicoampere leakage value of the 4-ethynylbenzaldehyde-grafted nanogap structure.

Nanoscale aryleneethynylene molecular wires with reversible fluorenone electrochemistry for self-assembly onto metal surfaces.

[structure: see text] Two rigid-rod conjugated molecules (11 and 12) of ca. 4 and 7 nm length, respectively, bearing protected terminal thiol groups have been synthesized via multistep Sonogashira coupling reactions and shown to possess reversible cathodic solution electrochemistry arising from reduction of the fluorenone units.