Preparation And Properties Of Organic Reversible Thermochromic Materials Microcapsules

Fluorane,as the third generation of heat-sensitive dyes,has become the main body of thermochromic materials.The organic reversible thermochromic materials composed of fluorane as leuco have been widely used in various fields,such as anti-counterfeiting,temperature indicating,textile and daily life.Encapsulation of organic reversible thermochromism materials by microencapsulation technology can solve the problems of thermal stability,poor acid and alkaline resistance,and greatly expand the application field of organic reversible thermochromism materials.Firstly,an important fluorane thermal-sensitive dye intermediate,2-carboxy-4-diethylamino-2-hydroxydibenzophenone（KETO）,was synthesized with m-diethylaminophenol and phthalic anhydrideas raw materials,with a yield of 69.8%;Using KETO and p-hydroxydiphenylamine as raw materials,2-aniline-6-diethylamino fluorane（thermosensitive green）was synthesized under the action of concentrated sulfuric acid as a catalyst and dehydrating agent,and the yield was 55.1%;3,6-dimethoxy fluorane（thermosensitive yellow）was obtained with p-toluene sulfonic acid catalyzed by phthalic anhydride and methoxy phenol,with a yield of 45.8%.Secondly,the organic reversible thermochromic material microcapsules were prepared by the method of in situ polymerization with three components of thermosensitive green-bisphenol AF-twelve alcohol as core material and urea formaldehyde resin as wall material.Through the analysis of the morphology,particle size and distribution of the microcapsules,the optimum conditions for the preparation of the microcapsules were as follows:emulsification speed 2000 rpm,emulsification time 30 min,emulsifier concentration 3%,emulsifier dosage 5 times of core material;the discoloration temperature of the microcapsule is 16°C,the color change interval is12°C to 26°C,and it has good cycle of discoloration;The organic reversible thermochromism compound was encapsulated by microencapsulation,which greatly improved its thermal stability and storage capacity at room temperature,as well as solvent resistance and acid and alkaline resistance.Then,nano-SiO₂ modified urea-formaldehyde resin/dodecanol microcapsules were prepared by in-situ polymerization,and the influence of various factors on the permeability of microcapsules was discussed.The optimum preparation conditions of microcapsules were as follows:the core-wall ratio is1:2,curing end pH value is 1.5²,dosage of NH4Cl and PVA are 5%and 4%respectively,amount of nanosilica is5%.The prepared microcapsules were smooth and regular spheres with with the diameter of 1.85⁵μm,core material content of 79.3%,encapsulation efficiency of62.5%,and latent heat of phase change of 148.4J/g.The permeability of nano SiO₂modified microcapsules decreased by 45.9%compared with that of unmodified microcapsules prepared under the conditions of sample preparation.Finally,the organic reversible thermochromic material microcapsules were prepared by the method of interfacial polymerization with three components of thermosensitive green-bisphenol AF-twelve alcohol as core material.The process conditions were optimized.The prepared microcapsules have good discoloration properties but poor dispersibility,and further optimization of the preparation process is required to improve the dispersibility of the microcapsules.