Surfactant diffusion through bicontinuous micellar networks: a case study of the C9G1/C10G1/H2O mixed surfactant system

Scientific Results and Economic Effects from the Centre for Surfactants Based on Natural Products (SNAP)

This review article will give a broad overview of the synthesized and characterised surfactants within the competence centre SNAP (Centre for Surfactants Based on Natural Products). The surfactants differ within their hydrophilic groups, hydrophobic groups as well as the linkage between these groups. The main focus was put on sugar-based surfactants and surfactants containing polyhydroxyl groups so this part will be the most extensive in the review. Interactions between surfactants and polymers have also been investigated and will be described in the final part of the review. SNAP resulted in the publication of 239 scientific articles and 22 PhD degrees.

Micelle structures in aqueous solutions of glucose-based surfactants having an isoprenoid-type hydrophobic chain

Surfactant self-diffusion coefficients have been measured on a binary system of 1-O-beta-3,7-dimethyloctyl-D-maltopyranoside (beta-Mal(2)(Ger))/water and a mixed surfactant system of beta-Mal(2)(Ger)/1-O-beta-3,7-dimethyloctyl-D-glucopyranoside (beta-Glc(Ger))/water at 25 degrees C. For comparison, measurements have also been made on 1-O-beta-decyl-D-maltopyranoside (beta-Mal(2)C(10))/water and beta-Mal(2)C(10)/1-O-beta-decyl-D-glucopyranoside (beta-GlcC(10))/water. The hydrodynamic radius of beta-Mal(2)(Ger) micelles obtained from the micellar diffusion coefficient is around 3 nm and nearly equal to that of beta-GlcC(10) micelles within experimental error. In the mixed surfactant systems, the hydrodynamic radii for both systems increase with increasing X(G) (the mole fraction of beta-Glc(Ger) or beta-GlcC(10) in the total mixed solute) above X(G) congruent with 0.4 when the total surfactant concentration is kept constant at 2 wt%. The R(H) of beta-Glc(Ger)/Mal(2)(Ger) micelles increases more rapidly than beta-GlcC(10)/beta-Mal(2)C(10) micelles, and then phase separation occurs at X(G) congruent with 0.65. On the other hand, the R(H) of beta-GlcC(10)/beta-Mal(2)C(10) micelles continues to increase until the phase separation occurs at X(G) congruent with 0.92. Measurements have also been performed as a function of total surfactant concentration at constant X(G) (=0.6). The CMC of the beta-Glc(Ger)/Mal(2)(Ger) system is larger than that of the beta-GlcC(10)/beta-Mal(2)C(10) system as expected from the results of the pure surfactant systems published previously. The R(H) increases with increasing total surfactant concentration for both systems. At higher concentrations, the R(H) of beta-Glc(Ger)/Mal(2)(Ger) micelles increases more rapidly than beta-GlcC(10)/beta-Mal(2)C(10) micelles. These results can be explained by the fact that the geranyl and decyl chains have the same volume but different chain lengths.

The water/n-octane/octyl-β-d-glucoside/1-octanol system: Phase diagrams and phase properties

The partial phase diagram of D2O/n-octyl-beta-D-alkyl-glucoside(C8G1)/n-octane has been determined at T=25 degrees C. The diagram contains a funnel-shaped micellar phase originating from the water corner of the phase diagram D2O/C8G1 with the stem forming a narrow three-phase region, in which the three phases in equilibrium are two microemulsions of similar composition and an excess oil phase. The microemulsions have been characterized with NMR self-diffusion measurements. At high surfactant concentration and no or low n-octane content, branched micelles exist. As the n-octane content is increased, discrete micelles are formed. Upon further addition of n-octane, the phase separation into two microemulsion phases is induced. Possible mechanisms causing the phase separation are discussed. The phase diagram of D2O/(C8G1)/1-octanol has been determined at 25 degrees C. Ten different phase regions were identified. The phases have been characterized with SAXS and deuterium heavy water NMR, and the swelling of the lamellar phase was investigated with SAXS.

Interactions between n-octyl and n-nonyl β-d-glucosides and α- and β-cyclodextrins as seen by self-diffusion NMR

In this work (1)H NMR self-diffusion experiments have been performed to determine the self-diffusion coefficients of n-octyl beta-d-glucoside and n-nonyl beta-d-glucoside in alpha-cyclodextrin and beta-cyclodextrin solutions at 25 degrees C. Two questions are addressed. The first concerns the general influence on nonionic surfactant transport properties when cyclodextrins are present in solution. The second question concerns the influence of surfactant-chain length and cyclodextrin cavity volume on the association constant. The self-diffusion coefficients of the alkyl glucosides, in cyclodextrin-containing solutions, depend on the cyclodextrin concentration on account of the formation of complexes. The cyclodextrin diffusion is only mildly influenced, since the complex has similar diffusion coefficients as the free cyclodextrin. There are some obstruction effects at the highest surfactant concentrations which decrease the cyclodextrin diffusion. A set of equations to model the self-diffusion coefficients of the surfactant and cyclodextrin was developed and is presented. On the basis of such equations, properties such as association constants, and micelle and complex diffusion coefficients can be estimated.