Patterning Of Cholesteric Liquid Crystal Microcapsules By Using Contact Printing Method And Their Applications As Temperature Indicator In Biomedical Devices

Cholesteric liquid crystals(CLCs)possess some unique properties as compared to other materials.Thermochromism is one of the well-known characteristic which is base of many applications such as CLCs radiations sensors,temperature indicators,chemical sensors etc.The transition temperature range can be tuned by mixing CLCs materials in specific proportions.But the problem of concern is that the thermochromic characteristics of CLCs can be easily disturbed by environmental factors like light,chemicals,radiations and temperature.The problem of sensitivity can be overcome by microencapsulation of CLCs in polymeric materials.The outer shell of CLCs microcapsules act as protective and controlling layer of the properties related to environmental sensitivity.In our present work,five different CLCs materials are mixed in different proportions to get the basic color change with response to temperature.For our final product,the weight ratio of cholesteryl acetate(CA),cholesteryl benzoate(CB),cholesteryl chloride(CC),cholesteryl nonanoate(CN)and cholesteryl oleyl carbonate(COC)is 1:2:3:2:1 and transition temperature range is 40?70 ? which is suitable for anti-counterfeit applications.The mixtures of CLC materials are microencapsulated in NOA61 by using photo-polymerization induced phase separation method.Many factors affecting on the microencapsulation process and properties of microcapsules like core/shell weight ratio,emulsification rate,emulsification time,stirring rate,emulsifier content and UV exposure time are studied thoroughly.Emulsification rate,emulsifier content and stirring rate have significant impact on the microcapsules size,shell thickness and size distribution.The optimized conditions for microencapsulation are the core/shell mass ratio 7:1;emulsifier content 3 wt%;emulsification rate 1500 rpm and UV exposure for 2 hours.CLCs microcapsules were successfully patterned by contact printing method using PDMS stamps.PDMS stamps were prepared by soft lithography and treated with oxygen plasma for better printing results of CLCs microcapsules.The printed CLCs microcapsules can be used as temperature indicators.On the other part of the work,a flameless heating patch is designed,fabricated and used in biomedical applications.The heat was generated by exothermic reaction of iron powder with oxygen and controlled by wax and sodium acetate trihydrate(phase change materials).By optimized quantities of the materials,heat in the range of 30?40 ? can be obtained for about 3 hours which is required for intravenous tube.