3D Printed Reactors and Kessil Lamp Holders for Flow Photochemistry: Design and System Standardization

A low-cost 3D printed standardized flow-photochemistry setup has been designed and developed for use with a pressure-driven flow system using photochemistry lamps available in most laboratories. In this research, photochemical reactors were 3D printed from polypropylene which facilitated rapid optimization of both reactor geometry and experimental setup of the lamp housing system. To exemplify the rapidity of this approach to optimization, a Kessil LED lamp was used in the bromination of a range of toluenes in the 3D printed reactors in good yields with residence times as low as 27 seconds. The reaction compared favorably with the batch photochemical procedure and was able to be scaled up to a productivity of 75 mmol h-1.

Interplay of Active Stress and Driven Flow in Self-Assembled, Tumbling Active Nematics

Lyotropic chromonic liquid crystals (LCLCs) are a special type of hierarchical material in which self-assembled molecular aggregates are responsible for the formation of liquid crystal phases. Thanks to its unusual material properties and bio compatibility, it has found wide applications including the formation of active nematic liquid crystals. Recent experiments have uncovered tumbling character of certain LCLCs. However, how tumbling behavior modifies structure and flow in driven and active nematics is poorly understood. Here, we rely on continuum simulation to study the interplay of extensile active stress and externally driven flow in a flow-tumbling nematic with a low twist modulus to mimic nematic LCLCs. We find that a spontaneous transverse flow can be developed in a flow-tumbling active nematic confined to a hybrid alignment cell when it is in log-rolling mode at sufficiently high activities. The orientation of the total spontaneous flow is tunable by tuning the active stress. We further show that activity can suppress pressure-driven flow of a flow-tumbling nematic in a planar-anchoring cell but can also promote a transition of the director field under a pressure gradient in a homeotropic-anchoring cell. Remarkably, we demonstrate that the frequency of unsteady director dynamics in a tumbling nematic under Couette flow is invariant against active stress when below a threshold activity but exhibits a discontinuous increase when above the threshold at which a complex, periodic spatiotemporal director pattern emerges. Taken together, our simulations reveal qualitative differences between flow-tumbling and flow-aligning active nematics and suggest potential applications of tumbling nematics in microfluidics.

Label-Free, Color-Indicating, Polarizer-Free Dye-Doped Liquid Crystal Microfluidic Polydimethylsiloxane Biosensing Chips for Detecting Albumin

We reveal a novel design for dye-doped liquid crystal (DDLC) microfluidic biosensing chips in the polydimethylsiloxane material. With this design chip, the orientation of DDLCs was affected by the interface between the walls of the channels and DDLCs. When the inside of a channel was coated with an N,N-dimethyl-n-octadecyl-3-aminopropyltrimethoxysilyl chloride (DMOAP) alignment layer, the DDLCs oriented homeotropically in a homeotropic (H) state under cross-polarized microscopy. After immobilization of antigens with antibodies on the alignment layer-coated microchannel walls, the optical intensity of the DDLC change from the dark H state to the bright planar (P) state. Using pressure-driven flow, the binding of antigens/antibodies to the DDLCs could be detected in an experimental sequential order. The microfluidic DDLCs were tested by detecting bovine serum albumin (BSA) and its immune-responses of antigens/antibodies. We proved that this immunoassay chip was able to detect BSA antigens/antibodies pairs with the detection limit about 0.5 µg/mL. The novel DDLC chip was shown to be a simple, multi-detection device, and label-free microfluidic chips are presented.

Diffusion and flow across shape-perturbed plasmodesmata nanopores in plants

Plasmodesmata are slender nanochannels that link neighboring plant cells and enable the exchange of nutrients and signaling molecules. Recent experiments have demonstrated significant variability in the concentric pore shape. However, the impact of these geometric fluctuations on transport capacity is unknown. Here, we consider the effects on diffusion and advection of two ideal shape perturbations: a radial displacement of the entire central desmotubule and a harmonic variation in the cytoplasmic sleeve width along the length of the pore. We use Fick’s law and the lubrication approximation to determine the diffusive current and volumetric flow rate across the pore. Our results indicate that an off-center desmotubule always increases the pressure-driven flow rate. However, the diffusive current is only enhanced for particles comparable in size to the width of the channel. In contrast, harmonic variations in the cytoplasmic sleeve width along the length of the pore reduce both the diffusive current and the pressure-driven flow. The simple models presented here demonstrate that shape perturbations can significantly influence transport across plasmodesmata nanopores.