Co-harvesting Solar Energy with Ambient Heat and On-Demand Release of Thermal Energy Below 0 oC Through Visible-Light-Controlled Photochemical Phase Transitions of Azopyrazoles

Photochemical crystal-to-liquid transition generally needs UV light as a stimulus and it is even more challenging to carry out below 0 oC. Here, we design a series of 4-alkylthioarylazopyrazoles as molecular solar thermal batteries, which show bidirectional visible-light-triggered photochemical trans-crystal ↔ cis-liquid transitions below ice point (-1 oC). Through co-harvesting visible-light energy and low-temperature ambient heat, high energy density (0.25 MJ kg-1) is achieved. Further, the rechargeable solar thermal batteries devices are fabricated, which can be charged by blue light (400 nm) at -1 oC. Then, the charged devices can release energy on demand in the form of high-temperature heat. Under green light (532 nm) irradiation, the temperature difference between the charged devices and the ice-cold surrounding is up to 13.5 oC. This study paves the way for the design of advanced molecular solar thermal batteries that store both natural sunlight and ambient heat over a wide temperature range.

On Structural Rearrangements Near The Glass Transition Temperature in Amorphous Silica

The formation of clusters was analyzed in a topologically disordered network of bonds of amorphous silica (SiO2) based on the Angell model of broken bonds termed configurons. It was shown that a fractal-dimensional configuron phase was formed in the amorphous silica above the glass transition temperature Tg. The glass transition was described in terms of the concepts of configuron percolation theory (CPT) using the Kantor-Webman theorem, which states that the rigidity threshold of an elastic percolating network is identical to the percolation threshold. The account of configuron phase formation above Tg showed that (i) the glass transition was similar in nature to the second-order phase transformations within the Ehrenfest classification and that (ii) although being reversible, it occurred differently when heating through the glass–liquid transition to that when cooling down in the liquid phase via vitrification. In contrast to typical second-order transformations, such as the formation of ferromagnetic or superconducting phases when the more ordered phase is located below the transition threshold, the configuron phase was located above it.

Influence of Liquid Inclusions to Explosive Instability of Ice

The influence of the nuclei of the liquid phase arising during mechanical deformations of polycrystalline ice at temperatures below -40 ... -45 C on its explosive instability is considered. The nucleus of the liquid phase appear in ice when part of the hydrogen bonds are broken when high pressure is applied to ice crystals. The resulting clusters can have characteristics close to those of bulk metastable water. It is known that such water in the region of negative temperatures has anomalous thermodynamic characteristics. In particular, at a temperature of -60 C and a pressure of 100 MPa, there is a second critical point of water for the liquid-liquid transition. It was found that the transition occurs between the two types of water LDL (low density water) and HDL (high density water), with the Widom line coming out into the one-component region of the water phase diagram. This line is the locus of increased fluctuations in entropy and density. Near atmospheric pressure, the temperature on the Widom line is -45 C. If the pressure inside the ice and its temperature turn out to be close to the line of coexistence of LDL and HDL, then liquid inhomogeneities can become a source of mechanical instability of the medium due to the growth of fluctuations in the energy of molecules and destruction of the ice structure. Such conditions can occur at temperatures below -45 C and pressures above 100 MPa.

The Water Polymorphism and the Liquid–Liquid Transition from Transport Data

NMR spectroscopic literature data are used, in a wide temperature-pressure range (180–350 K and 0.1–400 MPa), to study the water polymorphism and the validity of the liquid–liquid transition (LLT) hypothesis. We have considered the self-diffusion coefficient DS and the reorientational correlation time τθ (obtained from spin-lattice T1 relaxation times), measured, respectively, in bulk and emulsion liquid water from the stable to well inside the metastable supercooled region. As an effect of the hydrogen bond (HB) networking, the isobars of both these transport functions evolve with T by changing by several orders of magnitude, whereas their pressure dependence become more and more pronounced at lower temperatures. Both these transport functions were then studied according to the Adam–Gibbs model, typical of glass forming liquids, obtaining the water configurational entropy and the corresponding specific heat contribution. The comparison of the evaluated CP,conf isobars with the experimentally measured water specific heat reveals the full consistency of this analysis. In particular, the observed CP,conf maxima and its diverging behaviors clearly reveals the presence of the LLT and with a reasonable approximation the liquid–liquid critical point (LLCP) locus in the phase diagram.