Highly stretchable or extremely soft silicone elastomers? One reaction to make them all - from easily available materials!

An easy curing reaction to prepare silicone elastomers is reported, in which a platinum catalyzed reaction of telechelic/multi-hydrosilane (Si-H) functional polydimethylsiloxane (PDMS) in the presence of oxygen and water leads to slow crosslinking. This curing chemistry allows versatile tailoring of elastomer properties, which exceed their intrinsic limitations. Both highly stretchable silicone elastomers and extremely soft silicone elastomers are prepared by creating highly entangled elastomers and bottle-brush elastomers from commercial precursor polymers, respectively. The highly stretchable elastomers can be uniaxially stretched to a maximum strain of 2800% and their areas can be biaxially extended 180-fold. The extremely soft silicone elastomers exhibit shear moduli of 1.2-7.4 kPa, depending on composition, values that are comparable to hydrogels and human soft tissues. The reported curing chemistry can be used to prepare a range of silicone elastomers with carefully tailored mechanical properties.

Combining Hyperbranched and Linear Structures in Solid Polymer Electrolytes to Enhance Mechanical Properties and Room-Temperature Ion Transport

Polyethylene oxide (PEO)-based polymers are commonly studied for use as a solid polymer electrolyte for rechargeable Li-ion batteries; however, simultaneously achieving sufficient mechanical integrity and ionic conductivity has been a challenge. To address this problem, a customized polymer architecture is demonstrated wherein PEO bottle-brush arms are hyperbranched into a star architecture and then functionalized with end-grafted, linear PEO chains. The hierarchical architecture is designed to minimize crystallinity and therefore enhance ion transport via hyperbranching, while simultaneously addressing the need for mechanical integrity via the grafting of long, PEO chains (Mn = 10,000). The polymers are doped with lithium bis(trifluoromethane) sulfonimide (LiTFSI), creating hierarchically hyperbranched (HB) solid polymer electrolytes. Compared to electrolytes prepared with linear PEO of equivalent molecular weight, the HB PEO electrolytes increase the room temperature ionic conductivity from ∼2.5 × 10–6 to 2.5 × 10−5 S/cm. The conductivity increases by an additional 50% by increasing the block length of the linear PEO in the bottle brush arms from Mn = 1,000 to 2,000. The mechanical properties are improved by end-grafting linear PEO (Mn = 10,000) onto the terminal groups of the HB PEO bottle-brush. Specifically, the Young’s modulus increases by two orders of magnitude to a level comparable to commercial PEO films, while only reducing the conductivity by 50% below the HB electrolyte without grafted PEO. This study addresses the trade-off between ion conductivity and mechanical properties, and shows that while significant improvements can be made to the mechanical properties with hierarchical grafting of long, linear chains, only modest gains are made in the room temperature conductivity.

Chemical characterization; Antimicrobial and Larvicidal activity of essential oil from Callistemon citrinus (Bottle brush) leaves

Mosquito-borne diseases are prevalent in more than 100 countries across the world. They are the major vectors for transmission of Malaria, dengue, yellow fever, filariasis, schistosomiasis, Japanese encephalitis etc. Many of the formerly employed insecticides in mosquito control have harmful effects on human health and other non-target populations, their non-biodegradable nature, the higher rate of bio-magnification in our ecosystem and increasing insecticide resistance on global scale are raising serious concerns. . Therefore, search for natural, eco-friendly alternatives such as bio-insecticides is imperative. In this study, Larvicidal activity of the essential oil obtained from the leaves of Callistemon citrinus was tested on Dengue vector mosquito Aedes aegypti & Chikungunya vector mosquito Culex sp. Also, the chemical composition of the essential oil was recorded using GC-MS analysis. The anti-microbial activity of the essential oil was checked against a few common bacteria and fungi. Callistemon citrinus comes out to be one of such bio-insecticides with many therapeutic active constituents, showing appreciable anti-microbial activity and 80-100% larvicidal activity.

Feeding Ecology, Behaviour and Habitat Utilization of Black Drongo (Dicrurus Macrocercus) in Pothwar Plateau, Pakistan

Black Drongo is an insectivorous bird native to Pakistan. The present study focused on its feeding preferences, behaviour, ecology and habitat relationships. The study was carried out from first week of December, 2019 to the second week of April, 2020 in the two villages of Rawalpindi named as Daultala (Location-I) and Nata Gujarmall (Location-II). Observations were made by point count method on foot using line transect method. Air (52.27%) was the most commonly used feeding substrate. Aerial feeding mode (52.27%) is preferred over plant or tree gleaning (n=58) and ground feeding (n=47). Most common perching site was man made obstacle, wire (37.72%). Thirteen indigenous tree species and two exotic trees including Eucalyptus (Eucalyptus camaldulensis) and Bottle brush (Callistemon citrinus) were used as perching site by Black Drongo throughout the study. Black Drongo remained solitary (36.36%) during feeding rituals and shared (63.63%) its intimate habitat with other birds. At Location-I and Location-II, habitat was shared with 12 and 16 bird species, respectively. The mean time of prey capturing attempt was lower at Location-I (1.93±0.17 min) than Location-II (2.16±0.16 min). The time range of prey capturing attempt was (0.1±0.16 min) to (11.5±0.17 min). Black Drongo captured prey successfully by first attempt (59.54%), maximum attempts noted were 6. After preying attempts Black Drongo came back to same perch site (67.27%); which is a representative of resource abundance.

A strain-adaptive, self-healing, breathable and perceptive bottle-brush material inspired by skin

A class of multi-skin-function mimetic bottle-brush elastomers with the integration of strain-adaptability, self-healing ability, breathability and ultra-sensitivity.