ISSN:
1435-1536
Keywords:
Zwitterionicamphiphiles
;
phenylphosphinatobetaines
;
micelles
;
13CNMR relaxation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Zwitterionic amphiphiles of the general formula H(CH2)y + N(CH3)2(CH2)n PO2C6H 5 − , 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01457261
Permalink