Macroscopic Evidence of the Liquidlike Nature of Nanoscale Polydimethylsiloxane Brushes.

We report macroscopic evidence of the liquidlike nature of surface-tethered poly(dimethylsiloxane) (PDMS) brushes by studying their adhesion to ice. Whereas ice permanently detaches from solid surfaces when subjected to sufficient shear, commonly referred to as the material's ice adhesion strength, adhered ice instead slides over PDMS brushes indefinitely. When additionally methylated, we observe Couette-like flow of the PDMS brushes between the ice and silicon surface. PDMS brush ice adhesion displays a shear-rate-dependent shear stress, rheological behavior reminiscent of liquids, and is affected by ice velocity, temperature, and brush thickness, following scaling laws akin to liquid PDMS films. This liquidlike nature allows ice to detach solely by self-weight, yielding an ice adhesion strength of 0.3 kPa, 1000 times less than a low surface energy, perfluorinated monolayer. The methylated PDMS brushes also display omniphobicity, repelling essentially all liquids with vanishingly small contact angle hysteresis. Methylation results in significantly higher contact angles than previously reported, nonmethylated brushes, especially for polar liquids of both high and low surface tension.

Oleophobic textiles with embedded liquid and vapor hazard detection using differential planar microwave resonators.

Protective clothing must repel hazardous liquids such as oils, acids, and solvents, which often exhibit low surface tension. The low surface tension liquid repellency of textiles is currently characterized qualitatively, considering only the first thirty seconds of wetting. This study demonstrates that embedded sensors within protective fabrics can more fully characterize liquid repellency while simultaneously detecting the hazardous substance. The liquid repellency of oleophobic textiles was detected in-situ using differential planar microwave resonator structures. A differential split ring resonator was designed with resonant responses at 4.4 and 4.6 GHz with a sensitivity of 50 MHz per unit ε. Fabrics were rendered oleophobic by dip-coating. The liquid repellency was monitored in-situ using droplets of heptane, octane, decane, dodecane, and water. Wetting transitions and droplet evaporation were identified in real time. The 4.4 GHz resonance peak's shift was used to measure the liquid repellency, whereas the 4.6 GHz resonator monitored the liquid's vapor as it absorbed into a gas-sensitive elastomer. The microwave response was tracked over 10 h every 15 s, and this transient data could identify the liquids based on their wetting and evaporation rates. Such sensors could be readily embedded in oleophobic textiles and enhance personal protective equipment.

A high throughput tensile ice adhesion measurement system.

A prerequisite for designing materials with low adhesion to ice is to accurately measure the ice adhesion strength of the surface. The majority of studies in this field have typically focused on manipulating and measuring the adhesion strength of different materials under shear stress. Among them, elastomers have proven to be promising ice-phobic surfaces because they enable interfacial cavitation, a tension-driven surface instability. In this work, a high throughput, low cost device is designed to measure the tensile ice adhesion strength of different surfaces. The design and construction of the tensile ice adhesion measurement system is presented, along with the reasoning for the design decisions. The performance of the setup is characterized using experimental trials varying parameters such as temperature, pull-off speed, thickness of the substrate, and ice/substrate interfacial area, to verify the precision of the measurements.

Facile and rapid in-situ synthesis of chitosan-ZnO nano-hybrids applicable in medical purposes; a novel combination of biomineralization, ultrasound, and bio-safe morphology-conducting agent.

In this study, zinc oxide nanoparticle (ZnO-NPs) and also chitosan­zinc oxide (CS-ZnO-NPs) nano-hybrid were synthesized by a rapid ultrasound assisted co-precipitation method. The morphology, chemical bonding, crystal structure, UV absorption, toxicity and antibacterial properties of the CS-ZnO-NPs and ZnO-NPs were characterized. The FE-SEM (field emission scanning electron microscopy) micrographs and XRD (X-ray diffraction) analysis revealed that the used technique led to the preparation of homogeneous, ultra-thin (thickness of 20-30 nm) and highly pure ZnO sheets for the both kinds of nanoparticles. The obtained results also demonstrated a superior performance of CS-ZnO-NPs hybrid rather than ZnO-NPs in terms of antibacterial activity, cell viability and UV absorption. It was deduced that the designed biomineralization technique was a very fast and successful strategy to provide a ZnO hybrid with elevated bacterial growth inhibition and bio-safety. Furthermore, the experimental data of antibacterial analyses were compared with the curves obtained from modified Gompertz model and good accordance was observed.