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Proceedings of the 90th JSCM Anniversary Conference
J. Jpn. Soc. Colour Mater., 91〔3〕，85–88（2018）

Organogel-in-Water Emulsions as Thermal-Energy Storage and Heat Transfer Fluids
Toshio Sakai＊,†, Kosuke Iijima＊ and Kei Suzuki＊＊ Department of Materials Chemistry, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan†Corresponding Author, E-mail: tsakai@shinshu-u.ac.jp(Received November 28, 2017; Accepted January 28, 2018)
Abstract
We report here on the potential of organic phase-change material gel-in-water (OPCMG/W) emulsions as thermal-energy storage and heattransfer fluids. Gelation of OPCM droplets in OPCM/W emulsions enhanced the colloidal stability against temperature change in the rangeof －1 to 40℃ and prevented the supercooling of OPCM droplets in the emulsions. Furthermore, the thermal properties of OPCMG particles
in OPCMG/W emulsions were similar to those of OPCM alone.
Key-words: Organic phase-change material, Organogel-in-water emulsion, Thermal-energy storage, Heat transfer fluid,
Supercoolingthermal-energy storage and heat transfer fluids. We consider
that the gelation of OPCM droplets in OPCM/W emulsions
should enhance the colloidal stability of OPCM/W emulsions
because the gelation of OPCM droplets in emulsions isexpected to prevent the coalescence ( fusion) of OPCM
droplets even upon collision of OPCM droplets due to thehigher viscoelasticity than liquid droplets. Also, the gelationof OPCM droplets in OPCM/W emulsions should preventthe supercooling of OPCM droplets in OPCM/W emulsions
because 3D network formed in OPCM droplets should act asnuclei for solidification of OPCM droplets in emulsions.

1．Introduction
Organic phase-change materials ( OPCMs ) such asparaffin have attracted attention as effective thermal-energy
storage materials because of their high energy storage
density afforded by the latent heat of OPCM during thephase change process, the tunability of phase-transition
temperature by OPCM type and mixing of different
OPCMs above 0℃ and the reusability of OPCMs due tothe chemical stability1-7). The OPCM-in-water (OPCM/W ) emulsions are also attracting attention as thermalenergy storage and heat transfer fluids because of their
thermal conductivity and thermal-energy transport due to thefluidity of the OPCM/W emulsions even below solidifyingtemperature of OPCM, the heat-transfer rates to the OPCM
enhanced due to large specific surface area of OPCM andthe tunability of temperature change of whole OPCM/Wemulsions by combining latent heat of OPCM with sensible
heat of water1-7). In order to apply the OPCM/W emulsions
as thermal-energy storage and heat transfer fluids to thepractical thermal management system, higher colloidal
stability of OPCM/W emulsions and control of supercoolingof OPCM droplets in the emulsions are required7-21). Then,
we have investigated the effect of surfactant on the colloidal
stability of OPCM/W emulsions and supercooling of OPCM
droplets in the emulsions. We found that surfactants withlonger hydrocarbon chain as a hydrophobic group areeffective to enhance the colloidal stability of OPCM/Wemulsions and prevent the supercooling of OPCM droplets inthe emulsions22).
In this work, we examine the potential of organic phasechange material gel-in-water (OPCMG/W) emulsions as

2．Experimental
OPCMG/W emulsions ( OPCM content in water =30 vol%) were prepared by mixing of OPCM containing anorganic gelator (N-Lauroyl-L-glutamic acid di-n-butylamide;LGBA, AJINOMOTO Co., Inc. ) and ethanol (C2H5OH,Wako ) with water using a rotor-stator homogenizer( CLEARMIX CLM-0.8S, M-Technique ) at 60℃ ( seeFig. 1 ) . Hexadecane ( C 16H 34, 99.2%, Tokyo Chemical
Industry Co., Ltd) was used as an OPCM in this experiment.
Colloidal stability and fluidity of hexadecane gel-in-water(HDG/W) emulsions were confirmed by monitoring theemulsion state before and after cooling (from 40℃ to －1℃)
and heating (from －1℃ to 40℃). Solidifying-temperature(Ts) and -period (ts) of HDG particles in HDG/W emulsions
were determined from the temperature stagnation causedby phase transition from liquid to solid and the period thattemperature reached to 2℃, respectively, during the coolingprocess of HDG/W emulsions from 40℃ to －1℃ (see upper
panel of Fig. 2). The melting-temperature (Tm) and -period(tm) of HDG particles in HDG/W emulsions were determined－5－© 2018 Journal of the Japan Society of Colour Material