Patterned crystal growth and heat wave generation in hydrogels

The crystallization of metastable liquid phase change materials releases stored energy as latent heat upon nucleation and may therefore provide a triggerable means of activating downstream processes that respond to changes in temperature. In this work, we describe a strategy for controlling the fast, exothermic crystallization of sodium acetate from a metastable aqueous solution into trihydrate crystals within a polyacrylamide hydrogel whose polymerization state has been patterned using photomasks. A comprehensive experimental study of crystal shapes, crystal growth front velocities and evolving thermal profiles showed that rapid growth of long needle-like crystals through unpolymerized solutions produced peak temperatures of up to 45˚C, while slower-crystallizing polymerized solutions produced polycrystalline composites and peaked at 30˚C due to lower rates of heat release relative to dissipation in these regions. This temperature difference in the propagating heat waves, which we describe using a proposed analytical model, enables the use of this strategy to selectively activate thermoresponsive processes in predefined areas.

Mesoscopic metastable liquid in congruent vapor-liquid diagram of argon from about zero up to boyle`s temperature (review of FT-model)

Such paradigms of the coupled classical metastability and nonclassical criticality as the existence of a unified EOS (common for both gas and liquid phases) with its mean-field (mf), so-called Andrews-van der Waals’ critical point (CP) should be questioned to recognize the realistic stratified structure of a mesoscopic liquid phase. It exists supposedly in the wide range of temperatures located between about zero , K and up to the singular first Boyle’s point . Its opposite, also singular second Boyle’s point corresponds to the alternative origin for the crossover continuous bounds separating the specific structural strata of a mesoscopic liquid. The region of a heterogeneous l-phase spanning the whole temperature range can be termed the non-Gibbsian phase (due to its discrete cluster-like structure) without any appeals to the concept of a spinodal decomposition. The respective metastable liquid stratum is formed by three segments of supercritical , subcritical and sublimation metastable states of a formally incompressible liquid constrained by the pair of fixed extensive parameters (N,V). Its location on the CVL-diagram is restricted by the new introduced here ml-bound and by the known Zeno-line (ZL) bound. Thus, all above-mentioned strata belong to the region of soft fluid with the dominance of interparticle attraction. The remaining parts of CVL-diagram are spanned either by the real gas state-points and solid state-points (crystalline and/or amorphous) or by the region of hard fluid in the classification proposed by Ben-Amotz and Herschbach.

Correlation between kinetic fragility and Poisson's ratio from analysis of data for soft colloids

We consider the link between fragility and elasticity that follows from the analysis of the data for a set of soft colloid materials consisting of deformable spheres reported by [Mattsson et al., Nature, 2009, 462, 83]. The present work makes a quantitative analysis through an explicit definition for fragility index m in terms of density dependence, extending the corresponding formula of m for molecular systems in terms of temperature dependence. In addition, we fit the data for the high-frequency shear modulus for the respective soft-colloid to a corresponding theoretical expression for the same modulus. This expression for the elastic constant is in terms of the corresponding pair correlation function for the liquid treated as of uniform density. The pair correlation function is adjusted through a proper choice of the parameters for the two body interaction potential for the respective soft-colloid material. The nature of correlation between the fragility and Poisson ratio observed for the soft colloids is qualitatively different, as compared to the same for molecular glasses. The observed link between fragility of a metastable liquid and its elastic coefficients is a manifestation of the effects of structure of the fluid on its dynamics. The present work thus analyses the data on soft colloids and by introducing definitions from statistical mechanics obtains a correlation between kinetic fragility and Poissons's ratio for the soft material.

Second critical point in two realistic models of water

The hypothesis that water has a second critical point at deeply supercooled conditions was formulated to provide a thermodynamically consistent interpretation of numerous experimental observations. A large body of work has been devoted to verifying or falsifying this hypothesis, but no unambiguous experimental proof has yet been found. Here, we use histogram reweighting and large-system scattering calculations to investigate computationally two molecular models of water, TIP4P/2005 and TIP4P/Ice, widely regarded to be among the most accurate classical force fields for this substance. We show that both models have a metastable liquid-liquid critical point at deeply supercooled conditions and that this critical point is consistent with the three-dimensional Ising universality class.