Residence Time Distribution in an Asymmetrical Twin-Screw Extruder

Residence time distribution (RTD) is an important parameter for characterizing axial conveying and mixing in a twin-screw extruder (TSE). This work studies the RTD and flow patterns in an asymmetrical TSE (ATSE) using a transparent barrel for visualization. The RTD of an aqueous solution of sodium carboxymethyl cellulose is measured by using red fine sand particles as tracers, collecting them by a moving thin film at the die exit, and counting them for further statistical calculation. The effects of the screw configuration, screw speed, and feed rate are considered. When the geometrical dimensions and operating parameters are identical, the mean residence time t̅ in the ATSE is larger than those in a classical (symmetrical) TSE. This is a signature of backflow occurring in the intermeshing regions through the radial gaps between the low flight and the inner wall of the barrel. It is confirmed by particle image velocimetry. Moreover, a response surface model is developed to quantify the effects of the screw configuration and operating parameters on t̅

One-Pot Synthesis of Arylketones from Aromatic Acids via Palladium-Catalyzed Suzuki Coupling

A palladium-catalyzed one-pot procedure for the synthesis of aryl ketones has been developed. Triazine esters when coupled with aryl boronic acids provided aryl ketones in moderate to excellent yields (up to 95%) in the presence of 1 mol % Pd­(PPh₃)₂Cl₂ for 30 min

Coherent Random Lasing in Colloidal Quantum Dot-Doped Polymer-Dispersed Liquid Crystal with Low Threshold and High Stability

High-concentration (2–10 wt %) ZnCdSeS/ZnS alloyed quantum dot-doped polymer-dispersed liquid crystals (QD-PDLCs) were prepared via ultraviolet (UV) curing. The QD-PDLC morphology and resonance characteristics of a coherent random laser were investigated. The doping concentration of the liquid crystal and quantum dots was varied to investigate its effect on the lasing threshold, line width, and stability with respect to the density and grain size of the liquid crystal droplets inside the PDLC structure. Furthermore, the QD-PDLC laser performance was influenced by the pump position and area because of spatial localization of the random resonators. Moreover, the QD-PDLC showed good long-term stability; after 15 days of laser excitation (3 h/day), the laser output was maintained at 92% of the original emission intensity. The random laser threshold was as low as 50 μJ/cm2 with the optimized preparation process, which suggested strong potential for applications in polymer random fiber lasers, sensors, and displays