Smart emulsion system driven by light-triggered ionic liquid molecules and its application in eco-friendly water-saving dyeing.

The smart emulsification and demulsification system with the light response is a useful tool in various industries, including green chemistry, catalytic reaction, pharmaceuticals, and environmental remediation. Herein, an ionic liquid crystal compound with a light triggered switch based on the azobenzene group [(4-{3-methyl-1-[3-(8-octyloxyoctyl)oxy-4-oxobutanoyl]imidazo-lium-1-yl}octyl)oxy] -N-(4-methylphenyl)benzene-1,2-diazene bromide (MOIAzo), was designed and synthesized, which could cause reversible transition between emulsification and demulsification through the light trigger. The ionic liquid has an efficient photoinduced liquefaction process, which dramatically lowers the melting point of ionic liquids from 79 to 9.2 oC. This significantly broadens the liquid state temperature of the ionic liquid crystal. The ionic liquid crystal MOIAzo exhibits both photoinduced and thermally induced nematic liquid crystal properties. The smart emulsion system was effectively employed in an eco-friendly water-saving dyeing process of cationic dyes for cationic dyeable polyester (CDP) fabrics, which used only half the amount of water compared with the conventional water bath dyeing method. After dyeing, the oil and water phases can be efficiently separated through the light irradiation, and the oil phase can be reused for the subsequent dyeing process. This novel smart emulsion dyeing method greatly reduces the water consumption and wastewater discharge. MOIAzo as a light-triggered ionic liquid molecule opens up new dimensions in green chemistry.