論文 - 堀田　篤

Thermally Reversible Gel-Sol Transition of Hydrogels via Dissociation and Association of an Artificial Protein Nanocage

Nasu E., Kawakami N., Takamura S., Hotta A., Arai R., Miyamoto K.

Biomacromolecules （Biomacromolecules）  25 （ 4 ） 2358 - 2366 2024年04月

ISSN  15257797

　概要を見る

Oligomeric protein nanocages often disassemble into their subunits and reassemble by external stimuli. Thus, using these nanocages as cross-linkers for hydrogel network structures is a promising approach to allow hydrogels to undergo stimuli-responsive gel-sol transitions or self-healing. Here, we report hydrogels that show a reversible gel-sol transition resulting from the heat-induced dissociation and reassociation of protein nanocages. The hydrogel contained the 60-mer artificial protein nanocage, TIP60, as a supramolecular cross-linker for polyethylene glycol network structures. The hydrogel showed a gel-to-sol transition upon heating at a temperature above the melting point of TIP60 and immediately returned to a gel state upon cooling to room temperature. During the heating and cooling treatment of the hydrogel, small-angle X-ray scattering analysis suggested the dissociation and reassociation of TIP60. Furthermore, we demonstrated redox-responsive cargo release from TIP60 in the hydrogel. These results showed the potential of TIP60 as a component of multi-stimuli-responsive hydrogels.

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Contact-Killing Antibacterial Polystyrene Polymerized Using a Quaternized Cationic Initiator

Jitsuhiro A., Maeda T., Ogawa A., Yamada S., Konoeda Y., Maruyama H., Endo F., Kitagawa M., Tanimoto K., Hotta A., Tsuji T.

ACS Omega （ACS Omega）  9 （ 8 ） 9803 - 9812 2024年02月

　概要を見る

Contact-killing antibacterial materials are attracting attention owing to their ability for sustained antibacterial activity. However, contact-killing antibacterial polystyrene (PS) has not been extensively studied because its chemically stable structure impedes chemical modification. In this study, we developed an antibacterial PS sheet with a contact-killing surface using PS synthesized from 2,2′-azobis-[2-(1,3-dimethyl-4,5-dihydro-1H-imi-dazol-3-ium-2-yl)]propane triflate (ADIP) as a radical initiator with cationic moieties. The PS sheet synthesized with ADIP (ADIP-PS) exhibited antibacterial activity in contrast to PS synthesized with other azo radical initiators. Surface ζ-potential measurements revealed that only ADIP-PS had a cationic surface, which contributed to its contact-killing antibacterial activity. The ADIP-PS sheets also exhibited antibacterial activity after washing. In contrast, PS sheets containing silver, a typical leachable antibacterial agent, lost all antibacterial activity after the same washing treatment. The antibacterial ADIP-PS sheet demonstrated strong broad-spectrum activity against both Gram-positive and Gram-negative bacteria, including drug-resistant bacteria. Cytotoxicity tests using L929 cells showed that the ADIP-PS sheets were noncytotoxic. This contact-killing antibacterial PS synthesized with ADIP thus demonstrated good prospects as an easily producible antimicrobial material.

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Blending Bottlebrush Polymers for Compensation of Orientation Birefringence of Polystyrene for Use as an Optical Polymer

Tamura M., Kurokawa N., Hotta A.

ACS Applied Polymer Materials （ACS Applied Polymer Materials）  5 （ 12 ） 10245 - 10255 2023年12月

　概要を見る

For optical applications, including lenses, widely used polystyrene (PS) has not received much attention due to its considerably high birefringence. In this study, an efficient method was introduced to compensate for the orientation birefringence of PS through bottlebrush polymers with well-controlled PS graft chains (PS-BBP). PS-BBP were synthesized by ring-opening metathesis polymerization of norbornene-terminated PS macromonomers produced via atom transfer radical polymerization. Blend-film samples were then prepared by mixing linear PS and PS-BBP. One of the blend samples with a specific ratio of linear PS to PS-BBP (30:70) demonstrated extremely low orientation birefringence of |Δn| ∼3.9 × 10-4 even under 120% strain. In addition, the blend samples preserved almost the same refractive indices as linear PS, possessing the transparency required for optical polymers across the visible-wavelength range. The obtained PS blend could be utilized as an optical material with excellent optical properties.

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Multifunctionality of Iodinated Halogen-Bonded Polymer: Biodegradability, Radiopacity, Elasticity, Ductility, and Self-Healing Ability

Oyama Y., Kurokawa N., Hotta A.

ACS Biomaterials Science and Engineering （ACS Biomaterials Science and Engineering）  9 （ 11 ） 6094 - 6102 2023年11月

　概要を見る

A polymer with high contents of ester bonds and iodine atoms was synthesized, exhibiting sufficient biodegradability and radioactivity for biomedical applications. The iodine moieties of the synthesized polyester can generate halogen bonding between molecules, which may develop additional functional properties through the bonding. In this study, poly(glycerol adipate) (PGA) was selected and synthesized as a polyester, which was then adequately conjugated with three different types of iodine compounds via the hydroxy groups of PGA. It was found that the iodine compounds could effectively work as donors of halogen bonding. The thermal analysis by differential scanning calorimetry (DSC) revealed that the glass transition temperature increased with the increase in the strength of interactions caused by π-π stacking and halogen bonding, eventually reaching 49.6 °C for PGA with triiodobenzoic groups. An elastomeric PGA with monoiodobenzoic groups was also obtained, exhibiting a high self-healing ability at room temperature because of the reconstruction of halogen bonding. Such multifaceted performance of the synthesized polyester with controllable thermal/mechanical properties was realized by halogen bonding, leading to a promising biomaterial with multifunctionality.

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Measurements of the Dissociation Heats of Tetrabutylammonium Acetate and Tetrabutylammonium Hydroxide Ionic Semiclathrate Hydrates

Iwai T., Takamura S., Hotta A., Ohmura R.

International Journal of Thermophysics （International Journal of Thermophysics）  44 （ 3 ）  2023年03月

ISSN  0195928X

　概要を見る

Ionic semiclathrate hydrates mainly consist of water typically together with tetrabutylammonium and tetrabutylphosphonium salts. Since ionic semiclathrate hydrates have the large dissociation heat under ambient pressure and temperature conditions, various ionic semiclathrate hydrates have been studied as safety and eco-friendly phase change materials. In this study, tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates were proposed as thermal energy storage media for air conditioning and cooling lithium-ion batteries. The dissociation heat, which was a significant thermophysical property to design thermal energy storage systems, were measured at various mass fractions. The largest dissociation heats of tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates were 212.9 ± 0.9 kJ⋅kg−1 and 200.4 ± 2.2 kJ⋅kg−1. As a result of the comparison of the dissociation heats of tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates with those of other ionic semiclathrate hydrates, it was found that tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates had the promising thermophysical properties as thermal energy storage media for air conditioning and cooling lithium-ion batteries, respectively.

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Thermophysical Properties of Ionic Semiclathrate Hydrate Formed with Tetrabutylphosphonium Malonate

Iwai T., Oguro S., Ota I., Hiraga K., Hotta A., Ohmura R.

International Journal of Thermophysics （International Journal of Thermophysics）  44 （ 2 ）  2023年02月

ISSN  0195928X

　概要を見る

Ionic semiclathrate hydrate is a crystalline compound mainly composed of water, which can dissociate at ordinary pressure and temperature. Ionic semiclathrate hydrates have been widely studied to develop prospective green and safety phase change materials utilized in a thermal energy storage system to cool batteries, in air conditioning, and in a cold chain system. The thermophysical properties, such as equilibrium temperature and dissociation heat, and the mass fraction dependence of such properties need to be carefully investigated to design such systems. In this study, the equilibrium temperature and the dissociation heat of tetrabutylphosphonium malonate ionic semiclathrate hydrates were experimentally determined at various mass fractions through an established method: the maximum value of the dissociation heat was 179.70 kJ·kg−1 at w = 0.357 and the equilibrium temperature was 8.9 °C at w = 0.357. By comparing tetrabutylphosphonium malonate ionic semiclathrate hydrates with other media in terms of the measured equilibrium temperature and the dissociation heat, the usability of the hydrates as thermal energy storage media for general air conditioning was discussed.

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β to α Form Transition Observed in the Crystalline Structures of Syndiotactic Polystyrene (sPS)

Ouchi T., Nagasaka S., Hotta A.

AIChE Annual Meeting, Conference Proceedings （AIChE Annual Meeting, Conference Proceedings）  2023-November   2112 - 2119 2023年

　概要を見る

A solid-solid crystalline transition from β to α forms in syndiotactic polystyrene (sPS) was found during the mechanical deformation in the temperature range of 130-218 °C, studied by X-ray and infrared spectroscopy. α and β forms, in contrast to the other two crystalline structures (γ and δ forms) in sPS, are two major crystalline forms manufactured through a concise molding process which is industrially readily accessible. There have been a number of structural transitions found between two crystalline structures among the four different crystalline forms of sPS. In this work, β to α form transition at well below the melting temperature of sPS (~270 °C) was found by mechanical deformation, which became more pronounced as temperature increased. The structural transition was intimately related to the crystallization temperature and the densities of α and β forms.

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Synthesis and thermophysical properties of Tetrabutylammonium picolinate hydrate as an energy storage phase change material for cold chain

Yamamoto K., Iwai T., Hiraga K., Miyamoto T., Hotta A., Ohmura R.

Journal of Energy Storage （Journal of Energy Storage）  55 2022年11月

　概要を見る

Ionic semiclathrate hydrates, the water-based phase change materials (PCMs) have potential for thermal energy storage media. There are a number of hydrates, reported in the literature, which are suitable as PCMs for air conditioning system of the required temperature range 10–15 °C. In this study, Tetrabutylammonium picolinate hydrate (TBAPi hydrate) was newly synthesized as a PCM for the cold chain, which has a lower phase equilibrium temperature than the previously reported hydrates. Thermophysical properties of TBAPi hydrate were experimentally measured. The hydrate dissociation heat was determined using a differential scanning calorimeter (DSC). The phase equilibrium temperature was measured by visually observing system with a CMOS camera and microscope. Also, the cycling test was conducted to confirm the long-term stability of thermophysical properties. The largest dissociation heat was 157.7 ± 4.9 kJ・kg−1 at a mass fraction of TBAPi aqueous solution, wTBAPi of 0.37. The highest phase equilibrium temperature of TBAPi hydrate was 5.5 °C at 0.34 ≤ wTBAPi ≤ 0.36. These thermophysical properties did not change even after 200 cycles of hydrate formation and dissociation. Based on the experimental results, TBAPi hydrate can be applied to the transport and storage of vaccines, blood packs, and perishable foods.

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Measurements of phase equilibrium temperature and dissociation heat of tetrabutylphosphonium glutarate ionic semiclathrate hydrate

Iwai T., Ohta I., Hiraga K., Kashima K., Hotta A., Ohmura R.

Fluid Phase Equilibria （Fluid Phase Equilibria）  562 2022年11月

ISSN  03783812

　概要を見る

Thermophysical properties such as phase equilibrium temperature and dissociation heat are important to determine the performance of phase change materials targeting thermal energy storage. The phase equilibrium temperature and dissociation heat of tetrabutylphosphoniumglutarate ionic semiclathrate hydrate were measured in this study. The highest phase equilibrium temperature of tetrabutylphosphoniumglutarate hydrate was experimentally determined 287.4 K at the mass fraction 0.347 and 0.357. The largest dissociation heat was 193.3 ± 1.6 kJ/kg at the mass fraction 0.357. The measurement results in this work show that the dissociation heat can be utilized in the suitable temperature range targeting general air conditioning and data center.

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Numerical simulation of non-linear loading–unloading hysteresis behavior of blood clots

Tashiro K., Shobayashi Y., Hotta A.

Biocybernetics and Biomedical Engineering （Biocybernetics and Biomedical Engineering）  42 （ 4 ） 1205 - 1217 2022年10月

ISSN  02085216

　概要を見る

The stress–strain characteristics of a clot during loading/unloading mechanical cycles are significant features to assess the underlying mechanisms of thrombectomy, especially when multiple thrombectomy attempts are required. We investigated a damage model to predict loading/unloading response of clots. To study the validity of the model, we tested theoretical models to reproduce the experimentally obtained mechanical characteristics of clots under various conditions. Three types of clot analogs with different red blood cell (RBC) compositions were prepared. Cylindrical clot analogs were formed for the tensile and compression tests. Loading/unloading tests at 80% of strain were conducted, where the material parameters were determined by fitting the results to a theoretical curve combining the damage model and the elasto-plastic constitutive model. Through the computation for theoretical curves, unique characteristics of clots were revealed such that the hysteresis loss rate did not change by varying RBC contents, except for the clot created with 0% RBC composition, under compressive loading. In addition, the plastic strain decreased as the RBC content decreased under tensile loading, whereas it increased as the RBC content decreased under compressive loading. A three-dimensional finite element method (FEM) was employed with the determined parameters. The FEM could accurately reproduce the experimental stress–strain curves for all types of clot analogs and for both loading types up to a strain of 80%. The results indicate that the theoretical model which incorporates and combines the damage model and the elasto-plastic constitutive model is applicable to predict the non-linear stress–strain behavior of clots under loading and unloading.

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Synthesis and evaluation of green phase change materials for efficient air conditioning by tetrabutylphosphonium phosphate ionic semiclathrate hydrate

Iwai T., Miyamoto T., Kurokawa N., Hotta A., Ohmura R.

Journal of Energy Storage （Journal of Energy Storage）  52 2022年08月

　概要を見る

A tetrabutylammonium bromide (TBAB) hydrate is the only ionic semiclathrate hydrate that has been commercialized as a medium for efficient thermal energy storage targeting general air conditioning. However, TBAB is an environmental pollutant, while liquid water and ice that have been widely used as conventional media, also have difficulty in increasing the thermal energy storage density as well as the coefficient of performance (COP) of a refrigerator to form solid. In this study, a tetrabutylphosphonium phosphate ((TBP)3PO4) hydrate was proposed as an alternative green medium. The dissociation heat and the phase equilibrium temperature, which were both crucial factors to evaluate the thermal energy storage density, and COP was experimentally determined. It was found that the maximum dissociation heat was 154.1 ± 2.0 kJ・kg−1 at the mass fraction of 0.309. The highest phase equilibrium temperature was 10.0 °C at the mass fractions of 0.290, 0.299, and 0.309. The thermal energy storage density of (TBP)3PO4 hydrates was 3.7 times larger than that of water. (TBP)3PO4 hydrates increased the COP of a refrigerator to form solid by 42% as compared with ice, indicating the potential size-reduction of conventional devices with the decrease in the power consumption of a refrigerator. The effective balance between environmental protection and the system performance through (TBP)3PO4 hydrates was also discussed.

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Pinacol hydrate as a novel thermal energy storage medium for electric vehicles

Kiyokawa H., Kondo Y., Koyama R., Kurokawa N., Atsushi H., Alavi S., Ota I., Ohmura R.

Journal of Energy Storage （Journal of Energy Storage）  51 2022年07月

　概要を見る

Movement towards the gradual replacement of gasoline combustion vehicles to electrical vehicles is occurring on a global scale. Heat management of lithium-ion batteries (LIB) is necessary for long-term operation and safety of the power sources of electrical vehicles. This research suggests pinacol hydrate as a phase change material (PCM) for use as an alternative cooling media for LIB. The pinacol hydrate crystallizes under atmospheric pressure and temperatures around 45 °C, which are compatible with LIB operating conditions. Its dissociation enthalpy can control the excessive heating of the battery. The equilibrium phase transition temperature of pinacol hydrate was reported about a decade ago, but its thermal storage capacity has not been reported yet and updated quantitative measurements are required. Hence, in this study the equilibrium temperatures and dissociation enthalpies are experimentally measured for pinacol aqueous solutions prepared with mass fractions between 0.40 and 0.85. The maximum thermal storage capacity is measured by differential scanning calorimetry to be 301.9 kJ/kg for mass fraction of 0.50 which is compatible with operating conditions of up to 45.6 °C. A minimization of reservoir tank mass by 35% of that needed for conventional technologies may be possible by using pinacol hydrate.

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Compensation for Orientation Birefringence of PMMA by Blending Bottlebrush Polymers Composed of Well-Controlled Graft Chains

Tamura M., Kurokawa N., Hotta A.

ACS Macro Letters （ACS Macro Letters）  11 （ 6 ） 799 - 804 2022年06月

　概要を見る

The birefringence of optical polymers is a great issue in optical devices, inhibiting major applications of polymers to optical lenses and films. In this study, we have synthesized effective bottlebrush polymers with which we could attain almost zero birefringence when mixed with optical poly(methyl methacrylate) (PMMA). In detail, the PMMA bottlebrush polymers (PMMA-BBP) were synthesized by the ring-opening metathesis polymerization (ROMP) of norbornene-terminated PMMA macromonomers prepared via atom transfer radical polymerization (ATRP). Linear PMMA and PMMA-BBP were mixed to fabricate blend-film samples (PMMA/PMMA-BBP), which were uniaxially drawn to introduce molecular orientations. Linear PMMA possessed a negative value for its orientation birefringence, while the value of PMMA/PMMA-BBP increased as the PMMA-BBP content increased, whose orientation birefringence could reach almost zero when the ratio of the linear PMMA to PMMA-BBP became 73:27, regardless of the magnitude of the strain. The results reveal that the orientation birefringence of PMMA can be effectively controlled and removed by blending the appropriate content of PMMA-BBP.

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Highly-toughened and dimensionally-stable TEMPO cellulose nanofiber/bio-PBSA nanocomposites fabricated via Pickering emulsion process

Kurokawa N., Matsumoto K., Hotta A.

Composites Science and Technology （Composites Science and Technology）  223 2022年05月

ISSN  02663538

　概要を見る

Bioplastic poly(butylene succinate-co-adipate) (PBSA) has several advantages because of its flexibility and high biodegradability. PBSA, however, possesses poor mechanical properties and dimensional instability. To overcome this, PBSA composites with TEMPO-oxidized cellulose nanofibers (TOCN/PBSA) were fabricated via the Pickering emulsion method. Porous bio-nanocomposite TOCN/PBSA mediums were made by the Pickering emulsion method, followed by the subsequent lyophilization to obtain TOCN/PBSA films by compression molding. It was confirmed that the Pickering-emulsion condition was a key factor to control the TOCN dispersion state in composite films. The Young's modulus of TOCN/PBSA composite films increased to 305 MPa at the TOCN concentration of 5 wt%, which was almost twice as high as that of pure PBSA. The studies on the morphology and tensile testing also revealed that the dispersion state of TOCNs was important to achieve excellent reinforcement effects and to suppress the fracture of composite films caused by stress concentration. The coefficient of thermal expansion at the TOCN concentration of 5 wt% was reduced to ∼25 × 10−5 K−1, half the value of pure PBSA. It was concluded that compounding TOCNs via the Pickering emulsion method was a very effective reinforcement method to improve the mechanical properties and the dimensional stability of PBSA.

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Morphology and mechanical property of quenched poly(L-lactide)/N,N-dimethylacetamide gels

Inukai S., Kurokawa N., Endo F., Maeda T., Hotta A.

Polymer （Polymer）  242 2022年03月

ISSN  00323861

　概要を見る

Mechanically tough poly(L-lactide) (PLLA)/N,N-dimethylacetamide (DMAc) gels by rapid quenching using liquid nitrogen (LN) were synthesized. PLLA/DMAc solution at 110 °C was cooled at room temperature (PLLA-RT), or quenched by LN before keeping at RT (PLLA-LN). PLLA-RT with the PLLA concentrations of 5, 8, and 11 wt% did not form gel, while PLLA-RT with 14 and 17 wt% could form brittle gel exhibiting coarse structures. In contrast, PLLA-LN could form stable gel regardless of the PLLA concentration. The storage modulus of the gel with the PLLA concentration of 17 wt% increased from 78.7 kPa (PLLA-RT) to 563.7 kPa (PLLA-LN) at the strain of 0.1%. From the structural analysis, PLLA-RT formed spherulites (100–200 μm in diameter), whereas PLLA-LN formed relatively uniform network structures with continuous microporous skeletons without spherulites. The structural changes significantly contributed to the formation of stable, re-moldable, biodegradable, and biocompatible physical gels with ecofriendly and enhanced mechanical properties.

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Thermoset poly(2-methoxyethyl acrylate)-based polyurethane synthesized by RAFT polymerization and polyaddition

Tazawa S., Maeda T., Hotta A.

Materials Chemistry and Physics （Materials Chemistry and Physics）  278 2022年02月

ISSN  02540584

　概要を見る

A solid poly(2-methoxyethyl acrylate) (PMEA)-based polyurethane (PU) has been synthesized through reversible addition−fragmentation chain transfer (RAFT) polymerization followed by polyaddition. PMEA with four hydroxyl-groups (PMEA-(OH)4) synthesized using RAFT reagents with 4 hydroxyl groups works as an effective prepolymer and crosslinker. The thermoset PMEA-based PU can be obtained by mixing PMEA-(OH)4 and diisocyanate without additional agents for the synthesis. The temperature-independent mechanical property of the thermoset PMEA-based PU due to the chemical crosslinking points is confirmed by dynamic mechanical analysis (DMA) at temperatures ranging from 25 °C to 110 °C. The mechanical property at room temperature is also evaluated by tensile testing: The Young's modulus of PMEA-based PU increased from 454 ± 31 kPa to 574 ± 54 kPa by decreasing Mn of the PMEA prepolymer from 14,000 to 7,600. It is concluded that our synthesized PMEA-based PU exhibits sufficiently elastomeric characteristics as compared with conventional crosslinked PMEA, which may be used as a durable and more stretchable biomedical material.

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Thermogelling Nanocomposite Hydrogel: PLGA Molecular Weight in PLGA-b-PEG-b-PLGA Affecting the Thermogelling Behavior

Maeda T., Tanimoto K., Hotta A.

Macromolecular Chemistry and Physics （Macromolecular Chemistry and Physics）  223 （ 1 ）  2022年01月

ISSN  10221352

　概要を見る

Thermoresponsive gelation of the nanocomposites consisting of poly(lactic acid-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic acid-co-glycolic acid) (PLGA-b-PEG-b-PLGA) triblock copolymers and LAPONITE (LAPONITE/PLGA-b-PEG-b-PLGA nanocomposites) is investigated by decreasing the molecular weights of PLGA as 1130, 900, and 470 g mol−1. As for the pure triblock copolymers, it is confirmed by UV–vis and SANS that a micellar structure with a hydrophobic core is formed even in the case of PLGA-b-PEG-b-PLGA with the lowest PLGA molecular weight of 470 g mol−1 (Triblock0.5k). As for the nanocomposites with LAPONITE, it is found that the gelation temperature (Tgel) becomes less dependent on the PLGA-b-PEG-b-PLGA concentration and more stable as the PLGA molecular weight decreases, and that Tgel of the nanocomposites almost linearly decreases as the LAPONITE concentration increases. Eventually, the nanocomposite with Triblock0.5k reaches Tgel between room temperature and physiological temperature. In addition, gradual degradation behavior is observed for the nanocomposite with Triblock0.5k. Considering the monomeric molecular weights of LA and GA at the LA/GA ratio of ≈2.0, it is concluded that the PLGA-b-PEG-b-PLGA with the lower PLGA molecular weight (i.e., Triblock0.5k) can be effectively used for thermoresponsive and degradable hydrogels targeting biomedical applications.

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Synthesis and thermophysical property evaluation of ionic semiclathrate hydrate formed with tetrabutylphosphonium glycine as a chilling temperature phase change material

Miyamoto T., Kurokawa N., Ota I., Hotta A., Ohmura R.

Journal of Energy Storage （Journal of Energy Storage）  45 2022年01月

　概要を見る

Ionic semiclathrate hydrate, which is formed under atmospheric pressure with sustainably safe properties, has a potential for solid-liquid phase change materials(PCMs). In this study, the thermophysical property of tetrabutylphosphonium glycine(TBPGly) hydrate containing no halogen guest compound, glycine (aminoacetic acid), was investigated to evaluate the availability as an eco-efficient thermal energy storage medium. The phase equilibrium temperature was obtained through visual observation method. The heat flow rate curve behavior and dissociation heat were measured via differential scanning calorimetry(DSC). In the dissociation process, a single hydrate dissociation peak emerged, indicating TBPGly hydrate has one type of crystallographic structure. The concentration dependency of the TBPGly aqueous solution on the equilibrium temperature and the dissociation heat was confirmed. The highest equilibrium temperature of 5.8 °C was confirmed at the fraction range wTBPGly =0.368 or xTBPGly =0.0306, and the largest dissociation heat was 177.7 kJ·kg−1 at the fraction range wTBPGly =0.377or xTBPGly =0.0318. The estimated hydration number in the congruent composition was found to be in 31.2 to 32.5. In addition, based on the measured physical property, the optimum operating temperature and volume fraction of TBPGly hydrate was evaluated to determine the concentration for the practical cooling system. These data revealed TBPGly hydrate is available as a solid or slurry PCM under the operating temperature range 2 °C to 5.8 °C. The experimental data as well as the illustrative calculations contribute to accelerate the expansion in the application range, and provide the prospect in selecting the suitable composition toward the actual hydrate-based cooling system.

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Thermophysical Properties of a Promising Material for Thermal Energy Storage Synthesized by Tetrabutylphosphonium Malonate and Water

Iwai T., Oguro S., Ohta I., Hotta A., Ohmura R.

Proceedings of IEEE Asia-Pacific Conference on Computer Science and Data Engineering, CSDE 2022 （Proceedings of IEEE Asia-Pacific Conference on Computer Science and Data Engineering, CSDE 2022）  2022年

　概要を見る

Thermal energy storage for air conditioning is increasingly becoming important because the fluctuating output of renewable energy and the growing cooling demand will need to be addressed. In this study, we proposed tetrabutylphosphonium malonate hydrate as an environment friendly thermal energy storage medium for air conditioning. Equilibrium temperature and dissociation heat, which were significant thermophysical properties for commercialization, were experimentally determined at three mass fractions of tetrabutylphosphonium malonate aqueous solution. The maximum value of equilibrium temperature was determined to be 8.9 °C. The largest dissociation heat was measured to be 148.1 kJ/kg. These results indicate that tetrabutylphosphonium malonate hydrate has appropriate thermophysical properties for a thermal energy storage medium.

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Investigation of the thermodynamic properties of hydrates as cooling phase change materials for their implementation in electric vehicles

Kiyokawa H., Miyamoto T., Takeya S., Ota I., Iwai T., Hotta A., Ohmura R.

New Journal of Chemistry （New Journal of Chemistry）  2022年

ISSN  11440546

　概要を見る

Electric vehicles (EVs) play key roles in realizing a sustainable society. Lithium-ion batteries (LIBs) implemented in EVs deteriorate due to significant temperature changes. To maintain LIBs in an appropriate temperature range, a competitive thermal energy storage (TES) medium is needed. Phase change materials (PCMs) that can utilize their latent heat have great potential. In this study, we focused on piperazine hexahydrate as a promising candidate for a PCM and investigated its thermodynamic properties that are essential for practical design. The equilibrium temperature and dissociation enthalpy were determined in the mass fraction range of 0.250 to 0.550. The results showed that piperazine hexahydrate had a maximum equilibrium temperature of 42.9 °C and a maximum dissociation enthalpy of 250.0 ± 3.7 kJ kg−1 at a mass fraction of 0.443, which is the congruent point of piperazine hexahydrate. Piperazine hexahydrate can be utilized as a PCM in the temperature range of 34.4 °C to 42.9 °C. By utilizing piperazine hexahydrate instead of a conventional water-cooling system, the volume of the TES tank may be reduced by 31% approximately. The crystal system of the piperazine hexahydrate prepared in the present study was determined to be pseudomonoclinic by powder X-ray diffraction (PXRD) measurements, which is the same as that reported in the literature.

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