Photochromic performance and optics mechanism of single / double shell microcapsules

Polyurethane photochromic microcapsules and double shell photochromic microcapsules with polyurethane as inner wall material and chitosan as outer wall material have been prepared respectively by in situ polymerization. Comparing with unencapsulated azo photochromic compound, the prepared polyurethane photochromic microcapsules and polyurethane-chitosan double shell photochromic microcapsules showed advantages in the improved leakproofness of the applied photochromic compound and the irradiation intensity the photochromic compound accepted changed by double shell structure. It can be observed that,during coloration process,comparing with the time azo photochromic compound solution needed to reach the steady state during coloration process, polyurethane photochromic microcapsules and polyurethane-chitosan double shell microcapsules suspensions delayed the coloration process for 1. 6 s and 4. 8 s respectively. Moreover,during decoloration process,azo compound solution lost the steady state and decreased to the minimum absorbance at 20 s, and for polyurethane microcapsules and olyurethane-chitosan double shell microcapsules suspensions,it slowed down to 36%and 40%,respectively.