UV Causes Dramatic Changes in Aggregation with Mixtures of Photoactive and Inert Surfactants

Abstract

Aqueous mixtures of photosensitive and inert surfactants have been prepared; photoreactions and changes in aggregation after irradiation have been characterized. The photosensitive component was a stilbene-containing gemini photosurfactant (E-SGP), and the inert surfactants were either DTAB (dodecyltrimethylammonium bromide) or one of two different gemini surfactants, 12-4-12 or 16-4-16 (butanediyl-1,4-bis(dodecyldimethylammonium bromide) or butanediyl-1,4-bis(hexadecyldimethylammonium bromide)). Small-angle neutron scattering (SANS) studies revealed that in general the initial nonirradiated mixed systems form vesicle-type aggregates (100-200 angstroms radius), in equilibrium with some smaller charged spheroidal or ellipsoidal micelles (approximately 20 angstroms radius). In all cases, UV irradiation resulted in disruption of these vesicles and the formation of charged micelles. 1H NMR showed that the main photoproduct is the cis, anti, cis dimer of E-SGP (ZEZ-DiSGP); hence, photochemically induced changes in the reactive SGP drive significant changes in the preferred aggregation structure. These results demonstrate the utility of photoactive surfactants in mixtures with inert analogues.

Surface and micelle properties of novel multi-dentate surfactants

“…[15][16][17][18]). Following standard procedures, raw data were treated to yield normalized scattering intensities I (Q) in cm −1 , where the momentum transfer Q = (4π/λ) sin(θ/2), with θ the scattering angle.…”

Tuning aggregation of microemulsion droplets and silica nanoparticles using solvent mixtures

“…The phase and structural studies of AOT-stabilized water-inoil microemulsions have been extensively reviewed [8]. Over the years there have been numerous studies of aggregation in microemulsion systems [9][10][11][12][13][14][15][16][17][18][19]. The approaches explored have ranged from pressure [9] and temperature [9,10] variation, electric field effects [11], to addition of various kinds of additives [12][13][14][15][16].…”

“…The approaches explored have ranged from pressure [9] and temperature [9,10] variation, electric field effects [11], to addition of various kinds of additives [12][13][14][15][16]. Photosensitive surfactants have been used [17][18][19], to demonstrate aggregation and phase destabilization induced by UV light. As far as is known there is no report of solvent-induced aggregation in microemulsion systems, employing blends of good and bad solvents.…”

Light-sensitive lamellar phases

“…While after UV irradiation, the effective domain size detected by DLS increases from 73 to 137 nm, this final state is still smaller than the original size (197 nm). On the basis of photochemical studies [15][16][17][18][19], the post-irradiation structures consist of mixed block co-polymer/hexylbenzene/hexylphenol/sodium hydrogen sulfate aggregates, where hexylbenzene is the dominant photoproduct. Thus, after irradiation the average domain size of L α -B might be expected to differ from the original L α -A phase.…”

“…This electrostatic effect can be eliminated by changing the ionic strength of the solution, through adding inert electrolyte. Recently, light has been used as a method to control vesicle stability [14][15][16][17][18]; this is an attractive approach because it is not necessary to change thermodynamic variables or the system chemical composition. Extensive studies involving an anionic photolyzable surfactant, sodium 4-hexylphenylazosulfonate (C 6 PAS), showed that UV light can provoke the breakdown of microemulsions formulated from mixtures with inert Aerosol-OT [19,20].…”