Laurent Germanaud

Micellar properties of zwitterionic phosphobetaine amphiphiles in aqueous solution: Influence of the intercharge distance

Zwitterionic amphiphiles of the general formula H(CH2)y+ N(CH3)2(CH2)n PO2C6H5−, where the number of intercharge methylenesn is varied, were studied in dilute aqueous solution. Their critical micellar concentrations show a peculiar variation withn, first increasing asn varies from 1 to 4 and then slowly decreasing as methylenes are added up to 10. This behavior is interpreted as being the consequence of two opposite contributions. The first is the classical CMC lowering due to the increase of hydrophobic character with the total number of methylene groups in the surfactant molecule. The second contribution is the increase in the dipole moment of the zwitterionic headgroup withn, leading to stronger dipole-dipole repulsions between headgroups at the micellar surface. Experimental results suggest that the dipole moment does not increase linearly withn because of the polymethylene chain flexibility. This is supported by13C NMR relaxation experiments.

Mesomorphic structure of neutral amphiphilic phosphotobetaines having different interionic distances. II: Phenylphosphinatobetaines

Abstract A set of amphiphilic phenylphosphinatobetaines having different interionic distances and two lengths of paraffinic chain were studies by X-ray diffraction. It has been shown that phenylphosphobetaines behave as lyotropic liquid crystals and exhibit, in concentrated water solutions, mesophases with a hexagonal structure. The respective influences of the water concentration, the interionic distance, and the length of the paraffinic chain on the geometrical structure parameters have been established. The structural behavior of the phenylphosphobetaines is compared to that of ethoxyphosphobetaines; it shows the influence of the organic substituent bound to the phosphorus atom.