Fabrication of fine-pored polydimethylsiloxane using an isopropyl alcohol and water mixture for adjustable mechanical, optical, and thermal properties.

Porous polydimethylsiloxane (PDMS) has garnered interest owing to its large inner surface area, high deformability, and lightweight, while possessing inherent properties, such as transparency, flexibility, cost-effectiveness, ease of fabrication, chemical/mechanical stability, and biocompatibility. For producing porous PDMS, gas foaming, sacrificial template, and emulsion template techniques have been used extensively. However, the aforementioned methods have difficulty in achieving submicron-sized inner pores, which is advantageous for improving flexibility and transparency. This study demonstrates a simple fabrication method for obtaining porous PDMS with fine pores partially down to the sub-micron scale. This is possible by the use of cheap, volatile, and easily accessible isopropyl alcohol (IPA) as a co-solvent in water and pre-PDMS emulsion. IPA shows an affinity towards both water and prepolymer, resulting in an increased distribution of small water particles inside PDMS before curing. These water particles evaporate while curing the prepolymer emulsion, thereby generating fine pores. The fine size and number density of pores are controlled by water and the added amount of IPA, resulting in adjustable mechanical, optical, and thermal properties of porous PDMS.

Highly Sensitive Detection of Benzene, Toluene, and Xylene Based on CoPP-Functionalized TiO2 Nanoparticles with Low Power Consumption.

Among various metal oxides, titanium dioxide (TiO2) has received considerable interest as a gas-sensing material owing to its high reliability at high operating temperatures. Nonetheless, TiO2 generally has low sensitivity to target gases. In particular, TiO2-based sensors have difficulty in sensitively detecting benzene, toluene, and xylene (referred to as BTX). Moreover, the reported TiO2-based sensors have not simultaneously satisfied the demand for tens of ppb BTX detection and operation with low power consumption. This work proposes a BTX sensor using cobalt porphyrin (CoPP)-functionalized TiO2 nanoparticles as a sensing material on a suspended microheater fabricated by bulk micromachining for low power consumption. TiO2 nanoparticles show an enhanced sensitivity (245%) to 10 ppm toluene with CoPP functionalization. The proposed sensor exhibits high sensitivity to BTX at concentrations ranging from 10 ppm down to several ppb. The high reliability of the sensor is also explored through the long-time operation with repeated exposure to 10 ppm toluene for 14 h.