Preparation And Properties Research Of Microencapsulated Phase Change Materials

Phase change materials(PCMs)can be used for energy storage and utilization through the phase change latent heat during their phase change process,which is helpful to improve energy efficiency.Organic solid-liquid PCMs possess the advantages of high phase change latent heat,wide phase transition temperature range and no phase separation,but there are also some problems such as volume change and liquid leakage.These deficiencies can be compensated by the application of microencapsulation techniques.Polyaniline(PANI)is considered as one of the most promising conductive polymer because of its good environmental stability,unique doping mechanism,easy preparation and cost-effective raw materials.It could also be a suitable shell material for microencapsulated phase change materials(MicroPCMs)due to its good thermal stability plus its merits mentioned above.In this paper,Palmitic acid(PA)and Tetradecanol(TD)were selected as core materials and PANI was selected as shell material,MicroPCMs were prepared via in situ polymerization method and the thermal performance,morphology,thermal stability,chemical and crystal structure of the MicroPCMs were characterized.The effects of preparation conditions on the properties and morphology of the MicroPCMs were systematically studied.1.MicroPCMs with PA as core material and PANI as shell material was prepared via in situ polymerization method and its performance was characterized.The effects of core/shell mass ratio,polymerization temperature,polymerization time,dosage of oxidant and polymerization agitation rate on the heat storage performance,morphology and thermal stability of MicroPCMs were investigated by single factor method.The results show that the core/wall mass ratio,polymerization temperature and dosage of oxidant have direct influence on the morphology of the product.The encapsulation ratio of core material increased first and then decreased with the increase of polymerization time,but decreased with the increase of polymerization agitation rate.The optimum conditions were as follows:The core/shell mass ratio was 4.0:6.0.The polymerization was initiated at 75 ℃ for 2 h and then completed at 30℃ for 7 h with the oxidant(ammonium persulfate,APS)/aniline(ANI)molar ratio of 0.75 under low-speed agitation.The phase transition temperature of the prepared MicroPCMs with good capsule morphology and better thermal stability is 60.86℃,with the phase change enthalpy of 126.5 J g-1 and the encapsulation ratio of 55.92%.2.Five different proton acids were applied to dop PANI.PA/PANI MicroPCMs were prepared under the optimum conditions mentioned above.The effects of the type and the dosage of the acid dopants on the heat storage performance,morphology and thermal stability of the PA/PANI MicroPCMs were investigated.The results show that spherical MicroPCMs could be obtained when taurine was applied as dopant,while granular,lamellar or block composite rather than MicroPCMs would be obtained when the other acids were applied as dopants.The encapsulation ratio of increased at first and then decreased with the increase of taurine dosage.The taurine-doped PA/PANI MicroPCMs with the best morphology and stable thermal performance could prepared when the mole ratio of taurine to aniline was 0.4.The phase transition temperature was 60.4℃,while the phase change enthalpy was 122.3 J g-1 and the encapsulation ratio was 54.07%.But the morphology of the optimum conditions was still worse than the undoped MicroPCMs,which was due to that the electrostatic repulsion between the protonated polyaniline molecules is not conducive to the wall deposition around the PA droplets.3.Different emulsifiers were utilized to prepare PA/PANI MicroPCMs.The effects of the type and dosage of emulsifiers on the heat storage performance,morphology and thermal stability of the PA/PANI MicroPCMs were studied.The results showed that when SDBS was applied as emulsifier,the morphology and thermal stability of the prepared MicroPCMs are the best.The dosage of emulsifier has little effect on the heat storage performance and thermal stability of the product.When the amount of emulsifier was 6%,MicroPCMs with the best morphology could be prepared.The phase transition temperature was 60.5℃,the phase change enthalpy was 149.2 J g-1,and the encapsulation ratio was 65.96%.4.MicroPCMs with TD as core material and PANI as shell material was prepared via in situ polymerization method according to the optimum conditions mentioned above.The effects of the types of emulsifiers and core/wall mass ratio on the thermal storage properties and morphology of the TD/PANI MicroPCMs were investigated.Emulsifier would result in excessive emulsification of the system,which is detrimental to the encapsulated TD and form capsules.The encapsulation ratio of core material increased first and then decreased with the increase of core/wall mass ratio without emulsifier.When the core/wall mass ratio was 4.8:5.2,the encapsulated effect and morphology was the best result and the prepared TD/PANI MicroPCM showed stable thermal performance.The phase transition temperature of the prepared TD/PANI MicroPCM was 32.44 ℃,while the phase change enthalpy is 102.3 J g-1 and the encapsulation ratio is 46.42%.