A Study On The Thermal Properties Of Nano Composite Phase Change Material Microcapsules

As energy shortage is more serious and environmental crisis of mankind is moreconcerned, phase change materials and related technologies have gained more attentionnowadays. Microencapsulation of phase change material is one of these application formsof energy storage technology. This study focus on the Nano composite phase changematerial microcapsules (NC--MicroPCMs), the hydrophobic treatment of nano-materials,and the relations between the thermal properties of NC--MicroPCMs and the content ofnanoparticles uptake.Two hydrophobic agents (silane) are chosen, they are phenyltrimethoxysilane (PTMS)and octyltrimethoxysilane (OTMS) by measuring the contact angle with the core phasechange material (bromo-hexadecane). The optimal processing parameters of thehydrophobic treatment are determined by using statistical software Minitab15.0. Theeffectiveness of the processing parameters, e.g., reaction time, temperature and the amountof silane coupling agent are also discussed. The physical and chemical properties of thesamples are analyzed by FTIR, laser particle analyzer. The effect of treatment of TiO2arealso valued by activation rate in the study, which is widely accepted in the study field ofsurface modification of nano particles.The results have shown that:1The best hydrophobic treatment agent is OTMS.2As the reaction time is20min, the amount of hydrophobic treatment agent is5%(w/w), temperature80℃, the effect of hydrophobic of nano-TiO2particles is thebest, and the contact angle is120°.3The average particle size of unmodified nano-TiO2is0.35μm, with a narrowparticle size distribution; the modified nano-TiO2particle sizes are between0.31μm-0.35μm.4Activation rate of nano-TiO2are increased as the contact angle increas; as contactangle is120°, the activation rate is up to96.7%.5OTMS had been grafted onto the nano-TiO2particles by the evidence of FTIR andRaman spectroscopy.This study choose four nano-TiO2particle samples which different contact angles of51.5°,91.6°,109°,120°. Four different NC-MicroPCMs are prepared with melamine-formaldehyde as shell and bromohexadecane as core, by using in-situpolymerization of microencapsulation. The ratio of Core/shell is5:1, the molar ratio offormaldehyde/melamine is1.8:1, the amount of nano-TiO2particles are6%by the weightof core (w/w). The properties of NC-MicroPCMs are studied by using scientificinstruments of scanning electron microscope (SEM), infrared spectroscopy (FTIR), Ramanspectroscopy, laser particle size analysis, differential scanning calorimetry (DSC) andthermogravimetric (TG).The results have shown that:1The amounts of nano-particles uptake on NC-MicroPCMs of EMP0, EMP1,EMP11, EMP5respectively are0.79%,1.94%,3.65%,4.61%.2The temperatures of thermal decomposition are TMPCM201℃, TEMP0219℃,TEMP1283℃, TEMP11286℃, TEMP5306℃respectively.3The more the amount of nano-TiO2particles in the NC-MicroPCMs, thebetter the thermal stability, the lower super-cooling and higher enthalpy ofthe NC-MicroPCMs.4Four NC-MicroPCMs and one MicroPCM are spherical, non-blocking welldispersion by the observation of SEM. Nanoparticles are observedembedding on the sample EMP5(the one which the contact angle is themaximum120°) and forming a cross-linkage structure around it.5The more the amount of nano-TiO2, the smaller the particle size ofNC-MicroPCMs. The particle sizes of one MicroPCMs and fourNC-MicroPCMs from high to low are8.719μm,6.738μm,6.694μm,6.317μm,5.932μm.6FTIR and Raman spectroscopy data show that the greater thehydrophobicity of nano-TiO2particles, the more the amount of nano-TiO2particles embedded on the microcapsules.