No abstract

Operation of a flat slot die with rollers for the extrusion foaming of polymers, which has been originally designed by Benkreira et al. (Int. Polym. Proc., 19, 111 (2004)), is considered. The rotation of rollers makes it possible to independently control shear rate inside the die, in the bubble nucleation zone, thus influencing the cell density. In experimental studies of low‐density polyethylene foaming, the influence of the roller rotation speed on the cell density at variable isobutane and talc concentrations and die outlet area has been determined. Based on the fluctuational nucleation theory, a simple model is proposed for estimating the number density of supercritical nuclei formed at the nucleation stage and evaluating the cell density in the foam with allowance for bubble coalescence effects. POLYM. ENG. SCI., 54:96–109, 2014. © 2013 Society of Plastics Engineers

No abstract

Active matter contains self-propelled units able to convert stored or ambient free energy into motion. Such systems demonstrate amazing features related to the phenomenon of self-organization and phase transitions and can be used for the development of artificial materials and machines that operate away from equilibrium. Significant advances in the fabrication of active matter were achieved when studying low-density gas and small crystallites. However, the technique of preparation of active matter, where one can observe the formation of stable crystals, is extremely challenging. Here, we describe the novel method to obtain a stable 2D crystal in the active octane-in-water emulsion during the process of heterogeneous crystallization. Active motion is driven by the Marangoni flow emerging at the interface of the droplet. It is established that the crystal volume increases linearly in time in the process of crystallization. Moreover, the dependence of the crystal growth rate on the average velocity of droplets motion in the emulsion has a maximum. The kinetics of crystal growth is defined by a competition between the processes of attachment and detachment of droplets from the crystal surface. Crystallization proceeds via condensation of droplets from the gas phase through the formation of liquid as an intermediate phase, which covers the crystal surface with a thin layer. Inside the liquid layer the bond-orientational order of droplets decreases from the crystal surface toward the gas phase. We anticipate our study to be a starting point for the development of new materials and technologies on the basis of nonequilibrium droplet systems.

No abstract