Microencapsulation Of Cholesteric Liquid Crystals By Interfacial Polymerization And Its Thermochromic Characteristics

Cholesteric liquid crystal (CLC) with excellent thermochromiccharacteristics and wide temperature domain has an important role indisplay, security, information recording and other fields. Because of itssensitivity, CLC is easily disturbed by external factors, which would lowerthe performance. The microencapsulation of CLC can prevent the externalinfluences and broaden its use range.A kind of cholesteric liquid crystal (CLC) mixture containing fivecholesteryl additives, which can successively reflected circularly polarizedlight from red to blue with temperature increase, was prepared. The ratioof cholesteryl acetate (CA), cholesteryl chloride (CC), cholesteryl azelaicacid ester (CN), cholesteryl benzoate (CB) and cholesteryl oleyl carbonate(COC) was2:2:2:3:1. Reflection spectra and displaying color wouldchange with different proportion of CLC content. Microcapsulation of the CLC mixture was achieved by usinginterfacial polymerization in which isophorone diisocyanate (IPDI) andwater were used to form a thin impermeable polyurea shell. The factorsaffecting the microcapsule preparation were studied. The mass ratio ofliquid crystal and IPDI plays a very important role in thinning shellthickness. Particle size and distribution were mainly affected by theemulsification rate, agitation rate and emulsifier content.Thermochromic characteristics of CLC/microcapsule membrane areaffected by many factors, such as the properties of the CLC microcapsules,PVA content, coating thickness, etc. After a series of experiments inoptimizing thermochromism, the thickness of the membrane displayingthe best color was about15μm. The conditions of microencapsulationwere confirmed to be the mass ratio of liquid crystal and IPDI5:1,emulsifier content3wt%, emulsification rate5000rpm and agitation rate1000rpm. So the size and shell thickness of microcapsule were about9μmand200nm, respectively.