Self-assembly behaviors of C₁₈ fatty acids in arginine aqueous solution affected by external conditions

The self-assembly properties of long-chain C₁₈ fatty acids salts have good application in the field of environmental protection, drug control relieve, renewable energy and so on. Their degree of unsaturation is varied from saturated, monounsaturated to polyunsaturated fatty acids, which influence their self-assembly behaviors. Moreover, different external stimuli can also affect different self-assembly behaviors. In this work, three different fatty acids (stearic acid, C_18:0; oleic acid, C_18:1; linoleic acid, C_18:2) were chosen as the building blocks to self-assemble with arginine, a basic amino acid. The phase behaviors of ion-pairing systems affected by pH, temperature and solvent were investigated based on diagrams in more detail. The rich phase transition was observed through the characterization by cryogenic-transmission electron microscopy (cryo-TEM), polarizing microscopy, particle size analysis and rheological properties. We hope that the phase transition (self-assembly behaviors) controlled by these external conditions may provide a good guide for many related fields.