Chip-scale optical airflow sensor

Airflow sensors are an essential component in a wide range of industrial, biomedical, and environmental applications. The development of compact devices with a fast response and wide measurement range capable of in situ airflow monitoring is highly desirable. Herein, we report a miniaturized optical airflow sensor based on a GaN chip with a flexible PDMS membrane. The compact GaN chip is responsible for light emission and photodetection. The PDMS membrane fabricated using a droplet-based molding process can effectively transform the airflow stimuli into optical reflectance changes that can be monitored by an on-chip photodetector. Without the use of external components for light coupling, the proposed sensor adopting the novel integration scheme is capable of detecting airflow rates of up to 53.5 ms−1 and exhibits a fast response time of 12 ms, holding great promise for diverse practical applications. The potential use in monitoring human breathing is also demonstrated.

Glycidyl and Methyl Methacrylate UV-Grafted PDMS Membrane Modification toward Tramadol Membrane Selectivity

Pharmaceutical wastewater pollution has reached an alarming stage, as many studies have reported. Membrane separation has shown great performance in wastewater treatment, but there are some drawbacks and undesired byproducts of this process. Selective membranes could be used for pollutant investigation sensors or even for pollutant recovery. The polydimethylsiloxane (PDMS) membrane was first tested on separated and mixed antibiotic (ATB) water solutions containing sulfamethoxazole (SM), trimethoprim (TMP), and tetracycline (TET). Then, the bare and ultra-violet grafted (UV-grafted) PDMS membranes (MMA-DMAEMA 10, GMA-DMAEMA 5, and GMA-DMAEMA 10) were tested in tramadol (TRA) separation, where the diffusion coefficient was evaluated. Finally, the membranes were tested in pertraction with a mixture of SM, TMP, TET, and TRA. The membranes were characterized using the following methods: contact angle measurement, FTIR, SEM/EDX, and surface and pore analysis. The main findings were that TET was co-eluted during mixed ATB pertraction, and GMA-DMAEMA 5 was found to selectively permeate TRA over the present ATBs.

Oscillatory Reversible Osmotic Growth of Sessile Saline Droplets on a Floating Polydimethylsiloxane Membrane

We report a cyclic growth/retraction phenomena observed for saline droplets placed on a cured poly (dimethylsiloxane) (PDMS) membrane with a thickness of 7.8 ± 0.1 µm floating on a pure water surface. Osmotic mass transport across the micro-scaled floating PDMS membrane provided the growth of the sessile saline droplets followed by evaporation of the droplets. NaCl crystals were observed in the vicinity of the triple line at the evaporation stage. The observed growth/retraction cycle was reversible. A model of the osmotic mass transfer across the cured PDMS membrane is suggested and verified. The first stage of the osmotic growth of saline droplets is well-approximated by the universal linear relationship, whose slope is independent of the initial radius of the droplet. The suggested physical model qualitatively explains the time evolution of the droplet size. The reported process demonstrates a potential for use in industrial desalination.

Collagen fiber membrane-derived chemically and mechanically durable superhydrophobic membrane for high-performance emulsion separation

Developing high-performance separation membrane with good durability is a highly desired while challenging issue. Herein, we reported the successful fabrication of chemically and mechanically durable superhydrophobic membrane that was prepared by embedding UiO-66 as size-sieving sites within the supramolecular fiber structure of collagen fiber membrane (CFM), followed by the polydimethylsiloxane (PDMS) coating. The as-prepared CFM/UiO-66(12)/PDMS membrane featured capillary effect-enhanced separation flux and homogeneous porous channels guaranteed high separation efficiency. When utilized as double-layer separation membranes, this new type of composite membranes separated various surfactant stabilized water-in-oil microemulsions and nanoemulsions, with the separation efficiency high up to 99.993 % and the flux as high as 973.3 L m− 2 h− 1. Compared with commercial polytetrafluoro ethylene (PTFE) membrane, the advantage of the double-layer CFM/UiO-66(12)/PDMS membranes in separation flux was evident, which exhibited one order of magnitude higher than that of commercial PTFE membrane. The CFM/UiO-66(12)/PDMS membrane was acid-alkali tolerant, UV-aging resistant and reusable for emulsion separation. Notably, the CFM/UiO-66(12)/PDMS membrane was mechanically durable against strong mechanical abrasion, which was still capable of separating diverse water-in-oil emulsions after the abrasion with sandpaper and assembled as double-layer separation membranes. We anticipate that the combination of CFM and metal organic frameworks (MOFs) is an effective strategy for fabricating high-performance separation membrane with high mechanical and chemical durability. Graphical Abstract