Storing Solar Energy in Sodium Acetate-Based Hand Warmers Using Light-Absorbing Particles

Abstract

We have fabricated an eco-friendly, affordable, and recyclable heat-releasing chemical bag (hence forth termed as hand warmers), which melts when exposed to solar radiation and can be suitable for warming the hands and feet of mountain dwellers, hikers, and motorbike/vehicle riders during winter. Our hand warmer uses sodium acetate trihydrate (CH3COONa·3H2O, SAT)-based composites consisting of a suitable photothermal-responsive additive to shorten the melting time of the hand warmer for practical applications. Under simulated solar radiation, activated charcoal powder, graphite powder, graphene flakes, and copper nanoparticles (Cu-NPs) were tested as photothermal-responsive additives, which reduced the melting time of the hand warmer by a factor of 0.68, 0.65, 0.63, and 0.57 respectively, when compared to the sample without any additives. Moreover, the stability of the hand warmer was maintained for two–three months (at which point the samples were deliberately discharged) by incorporating 9 mL of extra water (8% wt) in the SAT composites, which demonstrates the long-term heat storage capacity of the hand warmer.

Innovative Development of Programmable Phase Change Materials and Their Exemplary Application

“…This enthalpy has a maximum ∆G crit , which must be overcome for crystal growth. ∆G c results from the lower dependency of the required surface energy ∆G s (~r 2 ) compared to the volume energy released by crystal growth ∆G v (~r 3 ). ∆G v is also dependent on the temperature of the melt T and the degree of the supercooling ∆T sup .…”

“…A switchable PCM has already been implemented in different applications. The material is used in hand-warming pouches [3] or even in larger heat storage modules for domestic heat supply, as described in [4][5][6]. The material is then combined with a mechanical switch that is triggered manually or by a sensor-based electronic control.…”

Normal-to-Supercooled Liquid Transition in Molecular Glass-Formers: A Hidden Structural Transformation Fuelled by Conformational Interconversion

“…For centuries, supercooled liquids have played a vital role in science, industry, and the day-to-day life of human beings. − They develop when their chemical components fail to create crystallization nuclei below the freezing point. Consequently, the formation of supercooled liquids is often related to the manufacturing of glasses (including the molecular ones) via the vitrification process, in which progressive lowering of the temperature results in dramatic slowing down of molecular motions from nanoseconds to hundreds of seconds around the glass-transition temperature ( T g ). ,, This process takes place in both the nonergodic and ergodic dynamic domains of the ultraviscous liquid, which intersect at the crossover temperature T B . , However, well above T g and T B , there is another characteristic point at which intermolecular organization, molecular motion, and transport coefficients (e.g., diffusivity, viscosity) undergo significant changes. − These transformations delineate collectively the inflection point which is often referred to as the Arrhenius crossover. − …”