文獻名：Design and synthesis of an azobenzene–betaine surfactant for photo-rheological fluids

作者： Calum S.G. Butler^a ,Joshua P.King^a ,Luke W. Giles^a ,Joshua B. Marlow^a ,Mark Louis P. Vidallon^a ,Anna Sokolova^b ,Lilianade Campo^b ,Kellie L. Tuck^a ,Rico F. Tabor^a

^a School of Chemistry, Monash University, Clayton, VIC 3800, Australia

^b Australian Centre for Neutron Scattering, ANSTO, Lucas Heights, New South Wales 2234, Australia

摘要：

Hypothesis

Morphology of surfactant self-assemblies are governed by the intermolecular interactions and packing constraints of the constituent molecules. Therefore, rational design of surfactant structure should allow targeting of the specific self-assembly modes, such as wormlike micelles (WLMs). By inclusion of an appropriate photo-responsive functionality to a surfactant molecule, light-based control of formulation properties without the need for additives can be achieved.

Experiments

A novel azobenzene-containing surfactant was synthesised with the intention of producing photo-responsive wormlike micelles. Aggregation of the molecule in its cis and trans isomers, and its concomitant flow properties, were characterised using UV–vis spectroscopy, small-angle neutron scattering, and rheological measurements. Finally, the fluids capacity for mediating particle diffusion was assessed using dynamic light scattering.

Findings

The trans isomer of the novel azo-surfactant was found to form a viscoelastic WLM network, which transitioned to inviscid ellipsoidal aggregates upon photo-switching to the cis isomer. This was accompanied by changes in zero-shear viscosity up to 16,000

. UV–vis spectroscopic and rheo-SANS analysis revealed interactions of the trans azobenzene chromophore within the micelles, influencing aggregate structure and contributing to micellar rigidity. Particles dispersed in a 1 wt% surfactant solution showed a fivefold increase in apparent diffusion coefficient after UV-irradiation of the mixture.

關鍵詞：Wormlike micelles;Neutron scattering;Light responsive;Self-assembly;pi-pi interaction;Azobenzene;Rheology;Surfactant;Betaine