A new photosurfactant has been synthesized, and its photoreactions in water, interfacial properties, and changes in aggregation have been characterized. The compound is a stilbene-containing gemini photosurfactant (SGP), which is of interest because the headgroup spacer is a stilbene chromophore, and it may be prepared initially in the trans (E-SGP) form. Molecular simulations show that UV-induced reactions cause significant changes in molecular conformation and especially the relative orientation of hydrophobic chains. 1H nuclear magnetic resonance, UV−vis absorption, and liquid chromatography−mass spectroscopy results are consistent with photodimerization in aqueous solutions. Irradiation causes significant changes in surface tension (maximum Δγ = −12 mN m-1) and wettability (Δθ = −15° on hydrophobic glass). Furthermore, small-angle neutron scattering shows the initial E-SGP form is present as large vesicle-like aggregates whereas the UV-induced dimer gives small 20 Å spherical charged micelles. These results demonstrate the importance of molecular design for generating effective and efficient photosurfactants.

A photo-responsive organogel has been made by addition of a novel stilbene-containing photo-surfactant to toluene: exposure to UV light led to a gel-to-sol transition with spatial control.

Photoresponsive microemulsions have been made by addition of a photodestructible surfactant, sodium 4-hexylphenylazosulfonate (1), to AOT-stabilized water-in-heptane phases. Exposure of these samples to UV light led to changes in phase stability and droplet size, owing to breakdown of 1. Small-angle neutron scattering was used to follow this UV-induced shrinkage of the water nanodroplets: a maximum volume decrease was found to be in the order of 60%. Proton NMR of an UV-irradiated microemulsion shows that around 90% of the added 1 decomposes, to yield a mixture of 4-hexylphenol (∼37%) and hexylbenzene (52%).

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A photodestructible surfactant, sodium 4-hexylphenylazosulfonate (C6-PAS), has been introduced to AOT-stabilized water-in-heptane microemulsions. Proton NMR spectra show that C6-PAS undergoes UV-induced decomposition, to yield a mixture of 4-hexylphenol and hexylbenzene. The photostationary state was determined by 1H NMR, indicating that nearly 90% of the initial photosurfactant had been destroyed, yielding non-surface-active hexylbenzene as the main product. This phototriggered breakdown gives rise to changes in adsorption and aggregation properties of C6-PAS, representing a novel route to induce microemulsion destabilization. When a series of microemulsions containing different amounts of C6-PAS were exposed to UV light, part of the dispersed water phase-separated. Small-angle neutron scattering (SANS) was used to follow the resulting UV-induced shrinkage of the water nanodroplets: a maximum volume decrease was found to be in the order of 60-70%. Kinetic SANS studies were also carried out in order to follow the changes in aggregation as a function of UV irradiation time. Multicontrast SANS experiments gave further insight; for example, it was demonstrated that the shell thickness remained constant. This study represents the first example of light-induced microemulsion destabilization.

Stable vesicles are formed in a 1.4 wt % solution comprising a 1:3 mixture of the anionic photodestructible surfactant sodium 4-hexylphenylazosulfonate (C6PAS) and inert cationic cetyltrimethylamonium bromide (CTAB). UV irradiation drives an irreversible breakdown of the mixed C6PAS/CATB vesicles, owing to the selective degradation of C6PAS. A light-induced transition from small spherical-like polydisperse vesicles to long needle-like aggregation is observed.

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Gold particles have been formed in water-in-oil microemulsions doped with a photodestructible surfactant. UV light-induced nanoparticle flocculation has been achieved after photolysis of the photosurfactant, leading to a reduction in the steric stabilization provided by the surfactant layer.