Preparation and characterization of a form-stable phase change hydrogel for heat-protective clothing

Wang, Yanfei; Zhang, Jichen; Han, Xuelian; Jiang, Yong

doi:10.1039/d2nj05096j

Cited by 4 publications

(7 citation statements)

References 53 publications

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“…Table compares hybrid salogels reported in this work with other systems reported in the literature for CCH and its eutectics based on the amount of PCM in the shape-stabilizing matrix and heat of fusion retained. Compared to impregnation of inorganic PCMs in porous matrices, − encapsulation in polymer capsules, thickening with cellulosic and superabsorbent polymer thickeners, and entrapment in covalently crosslinked PAAm, the hybrid salogel developed in this work demonstrated more efficient entrapment of the salt hydrate, achieving more than 95% PCM content in the salogel. Due to the ability to trap a large amount of PCM with a small amount of polymer, the hybrid salogels showed the best heat of fusion retention of the pristine salt hydrate PCM.…”

Section: Resultsmentioning

confidence: 99%

“…Salogel preparation flowchart is shown in Scheme 1 in the Supporting Information. Because of the known supercooling effect that is significant in the case of CCH, no crystallization occurred in the salogel systems at room temperature. However, crystallization occurred at refrigeration temperature of 4 °C in a few hours in contrast to CNH salogels reported in our previous work which required freezing temperatures for several hours …”

Section: Methodsmentioning

confidence: 99%

“… − In contrast, covalently crosslinked polymer gels, which also often require large polymer amounts (5%–60% by weight), provide shape stabilization (Figure S1). − However, the permanent nature of the crosslinks renders these materials irreversible, making filling and removal from thermal energy storage modules impossible. In contrast to these previous strategies, our group introduced temperature-responsive polymer salogels (polymer gels in inorganic salt hydrates) based on hydrogen bonding polymers such as poly(vinyl alcohol) (PVA), for reversible shape stabilization of liquid salt hydrates. , The on-demand reversibility of gelation by heating above a gel-to-sol transition temperature ( T gel ) allows filling and removal of the salogels from thermal energy storage devices, whereas gelation below T gel provides shape stabilization above the melting temperature of the salt hydrate ( T m ).…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we explore salogel systems in a different, chloride-based PCM: calcium chloride hexahydrate (CaCl 2 ·6H 2 O, CCH). CCH has low toxicity and is economical compared to lithium-based salt hydrates as it is generated as a waste byproduct in chemical processes such as soda ash production, and is also naturally abundant. ,, In addition, a melting temperature of 29 °C and heat of fusion of 190 J/g make this salt hydrate ideal for thermal energy storage applications in waste heat recovery, textiles, and buildings. ,, Shape stabilization of CCH by impregnation in a porous matrix − or encapsulation , has been demonstrated, but these approaches lack temperature-triggered reversibility and also result in a significantly reduced heat of fusion compared to that of neat CCH. Similarly, the use of polymer thickeners for CCH, , or permanently cross-linked networks for the CCH-MgCl 2 ·6H 2 O eutectic, lacks the desired shape stabilization and temperature reversibility.…”

Section: Introductionmentioning

confidence: 99%

“… 10 − 23 In contrast, covalently crosslinked polymer gels, which also often require large polymer amounts (5%–60% by weight), provide shape stabilization ( Figure S1 ). 24 − 40 However, the permanent nature of the crosslinks renders these materials irreversible, making filling and removal from thermal energy storage modules impossible. In contrast to these previous strategies, our group introduced temperature-responsive polymer salogels (polymer gels in inorganic salt hydrates) based on hydrogen bonding polymers such as poly(vinyl alcohol) (PVA), for reversible shape stabilization of liquid salt hydrates.…”

Section: Introductionmentioning

confidence: 99%

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Hybrid Polymer Salogels for Reversible Entrapment of Salt-Hydrate-Based Thermal Energy Storage Materials

Rajagopalan,

Haney,

Shamberger

et al. 2023

ACS Appl. Eng. Mater.

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One of the challenges preventing wide use of inorganic salt hydrate phase change materials (PCMs) is their low viscosity above their melting point, leading to leakage, phase segregation, and separation from heat exchanger surfaces in thermal management applications. The development of a broad strategy for using polymers that provide tunable, temperaturereversible shape stabilization of a variety of salt hydrates by using the lowest possible polymer concentrations is hindered by differences in solubility and gelation behavior of polymers with change in the type of ion. This work addressed the challenge of creating robust, temperature-responsive shape-stabilizing polymer gels (i.e., salogels) using a low cost PCM, calcium chloride hexahydrate (CaCl 2 •6H 2 O, CCH). Due to the extremely high (9 M) concentration of chloride ions and the tendency to salting-out polymer chains, the previous strategy of using single-polymer salogels was not successful. Thus, this work introduced a strategy of using two polymers, poly(vinyl alcohol) and ultrahigh molecular weight polyacrylamide (PVA and PAAm, respectively), along with borax as a cross-linker to achieve temperature-reversible, shape-stable salogels. This system resulted in robust salogels whose gel-to-sol transition temperature (T gel ) was tunable within an applicationrelevant range of gelation temperature (30−80 °C). This behavior was enabled by a synergistic combination of dynamic covalent cross-links between PVA units and entanglements of PAAm chains which were combined into a single hybrid network. The hybrid salogels had <5 wt % polymer content, maintaining ∼95% of the heat of fusion of the pure PCM. Importantly, the noncovalent nature of gelation supported thermo-reversibility of gelation, shape stability, and retention of thermal properties over 50 melting/ crystallization cycles.

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