Thermal hysteresis induced by ammonium polyacrylate as antifreeze polymer

摘要

Growth and melting rates of a single crystal of ice in ammonium polyacrylate (NH_4PA) aqueous solutions were measured at different solution temperatures, and the morphology of the ice crystals was observed. Thermal hysteresis, defined as the difference between the melting temperature and the non-equilibrium freezing temperature of ice, was confirmed in NH_4PA solutions at concentrations below 25.0 mM. The higher the NH_4PA concentration, the larger the thermal hysteresis, although the thermal hysteresis induced by NH_4PA was much smaller than that induced by antifreeze proteins, antifreeze glycoproteins, or poly(vinyl alcohol). A single crystal of ice grown in the NH_4PA solutions at temperatures within the thermal hysteresis region exhibited the basal faces. When the solution temperature was below the non-equilibrium freezing temperature, the ice crystal grew faster in the a-axis direction than in the c-axis direction, while retaining the basal faces.