AbstractThe solvent effect of D2O on the thermochromic sensitivity of a polydiacetylene (PDA) vesicle system was characterized and estimated numerically in this study. Three types of diacetylene compounds (10,12‐pentacosadiynoic acid,N‐[2‐(2‐hydroxyethoxy)ethyl]pentacosa‐10,12‐diynamide, andN‐(4‐aminophenyl)pentacosa‐10,12‐diynamide) were used to form the vesicle solution by sonication in H2O and D2O. This was followed by polymerization using UV irradiation to form a PDA vesicle system. The solvent effect of D2O on the physical properties of the PDA vesicles was estimated. The physical properties investigated herein were PDA vesicle size, critical vesicle concentration, and thermochromic change rate. The thermochromic change rate was measured using the relative degree of blue color (RBC), which was obtained from the UV spectrum data. The rate constants (kHand kD) of the thermochromic change were measured by plotting RBC against temperature. The solvent effect of D2O was estimated via the ratio kD/kH. Finally, the solvent effect of D2O on three physical properties of the PDA vesicles (vesicle size, critical vesicle concentration, and thermochromic change rate) was characterized numerically.