Adsorption of Model Perfumes at the Air–Solution Interface by Coadsorption with an Anionic Surfactant

Abstract

The adsorption of the model perfumes phenyl ethanol, PE, and linalool, LL, at the air-solution interface by coadsorption with the anionic surfactant sodium dodecyl 6-benezene sulfonate, LAS-6, has been studied primarily by neutron reflectivity, NR. The variation in the mixed surface adsorption with solution composition is highly nonideal, and the more hydrophobic LL is more surface active. At a LAS-6 concentration of 0.5 mM the adsorption of PE and LL is broadly similar but with the LL systematically more surface active, and at 2 mM the LL completes more effectively for the surface than the PE. The variation in surface composition with solution composition and concentration reflect the greater hydrophobicity and hence surface activity of LL, and the greater solubility of PE in aqueous solution. Changing the geometry of the LAS isomer, from the symmetrical LAS-6 geometry to the more asymmetrical LAS-4, results in the LL competing more effectively for the surface due to changes in the packing constraints associated with the hydrophobic region. The results provide insights into the factors that affect coadsorption that can be more broadly applied to the surface delivery of a wide range of molecules other than perfumes.

Enhanced perfume surface delivery to interfaces using surfactant surface multilayer structures

“…The more hydrophilic phenylethanol is predominantly solubilized into the headgroup region. These different locations are consistent with the observations associated with surfactant self-assembly and perfume solubilization [9,26,35]. The differences in location result in the surface multilayer structures existing over a wider range of surfactant/perfume compositions for phenylethanol than for linalool.…”

“…Taking average values from the data for solution compositions of 30/70, 20/80 and 10/90 mol ratio gives a total adsorption (LAS-6 + LL) $5 Â 10 À10 mol cm À2 and a surface composition (mole fraction of LL) $0.45, and this is broadly similar to that previously reported for LL rich compositions in LAS-6/LL mixtures [35].…”

“…Taking an average value for Dq of 0.4 Â 10 À6 Å À2 (from Table 2) this gives an adsorbed amount/bilayer of $1.25 Â 10 À10 mol cm À2 . This amount is broadly consistent with coadsorption of PE in the absence of CaCl 2 where only monolayer adsorption occurs [35]. Furthermore, assuming that the perfume is equally distributed within the whole bilayer stack, then the total adsorption is $40 Â 10 À10 mol cm À2 .…”

“…The calculations (see earlier) based on the NR data for h-LAS-6/d-perfume show substantial adsorption of perfume into the multilayer structure. Within a single bilayer the amount of perfume coadsorbed is comparable to those observed in the co-adsorption with a LAS-6 monolayer at the surface, in the absence of CaCl 2 [26,35]. However, the number of bilayers in the surface structure means that the total amount of perfume within the surface region is substantially enhanced.…”

Modulation of partition and localization of perfume molecules in sodium dodecyl sulfate micelles

“…Further understanding of the aggregate structures and the interaction in surfactant/perfume mixtures has been achieved by investigating the localization of perfume molecules in surfactant micelles, [16][17][18][19][20][21][22][23][24][25] and by obtaining more precise size or shape of surfactant/perfume aggregates. 20-22 Mahapatra 16 and Fischer et al 17 pursued the partition and localization of different perfume molecules in surfactant micelles by 1 H NMR and Pulsed Field Gradient (PFG)-NMR.…”