Long-lived electrets and lack of ferroelectricity in methylammonium lead bromide CH3NH3PbBr3 ferroelastic single crystals

Accumulation of CH3NH3+ and Br− ionic species at the ferroelastic domain boundaries creates a polar electret state in the hybrid perovskite CH3NH3PbBr3 that mimics a ferroelectric P(E) hysteresis loop.

The Development and the Study of the Properties of Hydrosorption Material Based on a Blended Thermoplastic Vulcanisate

Hydrosorption thermoplastic vulcanisates (TPVs) with a controllable swelling rate have been developed. They contain low-density polyethylene (LDPE), nitrile butadiene rubber (NBR), and sodium carboxymethyl cellulose (Na-CMC) – a water-soluble polymer (WSP). They were mixed on a laboratory mill in two stages and vulcanised at a temperature of 170°C. At the first stage, the NBR with a vulcanising system and carbon black were mixed with the WSP at 50°C, and at the second stage this composite was mixed with the polyethylene (PE) at 140°C. The hydrosorption, deformation and strength, and electret properties of the obtained TPVs were studied. The study of the sorption properties under conditions of limited and unlimited access of water showed that composites consisting of 25% polyethylene and 75% WSP swell in water by ∼28%, and here processes of migration of the WSP out of the composites are absent. The deformation and strength properties were determined on an Inspekt Mini TR-3 kN tensile testing machine. The level of deformation and strength characteristics of the obtained TPVs is not high, which is due to the low adhesion between the PE and the polar NBR, and also between the NBR and the WSP. However, for seals and gaskets, the achievable level of strength properties is quite adequate. An electret state of the TPVs was obtained in a negative corona discharge as they cooled down after heating to 90°C. Washers were manufactured from the developed TPVs, and they were tested for their sealing capacity. It was shown that the electret state inhibits the process of swelling of the TPVs in water, which is due to the negative effect of the electric field on the rate at which wetting, dissolution, and diffusion processes take place. However, during service, the electret state of articles manufactured from the developed TPVs rapidly relaxes, after which the swelling process occurs at a steady rate. This makes it possible to carry out assembly work involving the fitting or replacement of seals made of the hydrosorption TPVs.