Lisi Jia

Sugar alcohols are phase-change materials with various advantages but may suffer from leakage during applications. In this study, inositol nanocapsules were synthesized at various conditions, including the amount of precursors and the time for adding the precursors. The effects of synthesis conditions on the properties of the nanocapsules were studied. The morphology, chemical composition, microstructure, phase-change characteristics and size distribution of the nanocapsules were investigated by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), differential scanning calorimeter (DSC) and a zeta potential analyzer. The results confirm that inositol was well-encapsulated by an SiO₂ shell. The shell thickness increased, while the supercooling degree of the nanocapsules decreased with increasing time for adding the precursors. In order to obtain nanocapsules with good morphology and phase-change characteristics, the time for adding the precursors should increase with the amount of precursors. The nanocapsules with the best properties exhibited high melting enthalpy, encapsulation ratio and energy storage efficiency of 216.0 kJ/kg, 83.1% and 82.1%, respectively. The size of the nanocapsules was remarkably affected by the triethoxysilane (TES) amount.

In this study, a new type of functional hybrid suspension for solar energy conversion and thermal energy storage was prepared by adding carbon nanotube (CNT) and microencapsulated phase-change material (MEPCM) into deionized water. MEPCM with octadecane as the core material and titania (TiO₂) as the shell material was synthesized by the sol–gel method. The MEPCMs were spherical particles with diameters of 2–4 μm, and the thickness of the shell was about 100 nm. The MEPCM achieved better thermal stability and thermal conductivity than the pure octadecane due to the TiO₂ shell. The melting and solidification latent heats of the MEPCM were about 154.24 and 154.26 J/g, respectively. The encapsulation efficiency of octadecane was calculated to be 65.84%. Most of all, the novel hybrid CNT and MEPCM suspensions exhibited remarkable dispersion stability owing to the stable reticular structure composed of CNT in the suspension. Compared with pure water, the thermal conductivity, specific heat of the MEPCM/CNT suspension improved by 34.48 and 43.57%, respectively and the photo-thermal conversion efficiency reached a high value of 86.0%. This work provided a new type of hybrid functional suspension towards direct absorption solar collector for solar energy conversion and storage.

Nanoparticles, including Al2O3 and SiO2, and ultrasound were adopted to improve the solidification properties of water. The effects of nanoparticle concentration, contact angle, and ultrasonic intensity on the supercooling degree of water were investigated, as well as the dispersion stability of nanoparticles in water during solidification. Experimental results show that the supercooling degree of water is reduced under the combined effect of ultrasound and nanoparticles. Consequently, the reduction of supercooling degree increases with the increase of ultrasonic intensity and nanoparticle concentration and decrease of contact angle of nanoparticles. Moreover, the reduction of supercooling degree caused by ultrasound and nanoparticles together do not exceed the sum of the supercooling degree reductions caused by ultrasound and nanoparticles separately; the reduction is even smaller than that caused by ultrasound individually under certain conditions of controlled nanoparticle concentration and contact angle and ultrasonic intensity. The dispersion stability of nanoparticles during solidification can be maintained only when the nanoparticles and ultrasound together show a superior effect on reducing the supercooling degree of water to the single operation of ultrasound. Otherwise, the aggregation of nanoparticles appears in water solidification, which results in failure. The relationships among the meaningful nanoparticle concentration, contact angle, and ultrasonic intensity, at which the requirements of low supercooling and high stability could be satisfied, were obtained. The control mechanisms for these phenomena were analyzed.

Phase-change materials (PCM) with low supercooling degree (SD) are important in cold thermal energy storage (CTES) applications. The SD of nanosuspension PCM usually decreases with increasing nanoparticle concentration. However, the performance variation of nanosuspension PCM at high concentrations has been rarely studied, though it is important because nanoparticles tend to aggregate. In this paper, the SD and dispersion stability of nanosuspensions of TiO2, zirconium phosphate (ZrP), and TiO2 coupled with zirconium phosphate (TiO2-ZrP) were investigated at nanoparticle concentrations up to 5.0 wt %. Results show that the SD of TiO2 suspension did not remarkably varied with mass concentrations above 2.0 wt %. In contrast, the SD of TiO2-ZrP and ZrP were low and continuously decreased with increasing mass concentration of nanoparticles. The dispersion stability of TiO2-ZrP suspension improved compared with that of TiO2 suspension. Hence, TiO2-ZrP suspension provided more nucleation sites than TiO2 suspension to induce heterogeneous in water.

This study investigated the dispersion stability of aqueous TiO₂ nanofluids. The dispersion stability of binary nanofluids containing different concentrations of TiO₂ nanoplatelets (TiNP) and TiO₂ nanospheres (TiNS), either with or without dispersant sodium dodecyl sulfate (SDS), was evaluated by sedimentation observations and measurements of the Turbiscan stability index (TSI) values. The results revealed that the mixing of TiNS and TiNP nanofluids remarkably improved the dispersion stability than those of the individual TiO₂ nanoplatelets and nanospheres. Additionally, the binary nanofluids exhibited good dispersion stability up to 70% percentage of TiNP, after which the sedimentation increased. Moreover, the maximum total concentration of 0.8 wt.% TiO₂ binary nanofluids exhibited greater dispersion stability than those of the individual nanoparticles, but further increase to 0.9 wt.% resulted in the loss of dispersion stability. Furthermore, the addition of dispersant SDS further improved the dispersion stability of the TiO₂ nanofluids in case of the individual nanoparticles as well as that of binary nanofluids and retained good dispersion stability for increase in the maximum nanoparticle concentration from 0.9 to 4.0 wt.% of the TiO₂ nanofluids. The improved dispersion stability of TiO₂ nanofluids after combination with each other as well as with SDS offer potential applications for development of novel heat transport media and engineering research.

Dispersion stability has been extensively investigated because it significantly affects the properties of colloidal suspensions. However, for multi-component suspensions, the reported methods for stability evaluation are limited because several traditional methods are no longer appropriate, usually resulting in an unclear mechanism of dispersion stability. In this study, a novel nanocomposite was synthesized, exfoliated, and purified. The dispersion stability of binary suspensions comprising mixed and coupled titanium dioxide (TiO₂) and α-zirconium phosphate (ZrP) particles were compared with those of pure TiO₂ and ZrP suspensions by sedimentation observation, multiple light scattering, nuclear magnetic resonance, and dynamic light scattering measurements. The results obtained by the methods were consistent with one another, which indicated that the dispersion stability of the TiO₂ suspension was significantly improved by composite particles compared to mixed particles. The underlying mechanism for the improvement was also discussed. The improvement in dispersion stability could be attributed to controlled particle aggregation.