P. Kekicheff et al., MEASUREMENT OF DEPLETION INTERACTION IN SEMIDILUTE SOLUTIONS OF WORM-LIKE SURFACTANT AGGREGATES, Journal de physique. II, 4(5), 1994, pp. 735-741
The force as a function of separation is measured beween two mica surf
aces coated with adsorbed bilayers of cetyltrimethylammonium bromide (
CTAB) and immersed in aqueous solutions of elongated and semi-flexible
micelles of CTAB. For the range of concentrations studied, where the
ionic strength is kept constant, the worm-like micelles form a transie
nt network similar to an entangled polymer solution (semi-dilute regim
e). The electrical double-layer repulsion between the adsorbed bilayer
s is preceded at larger separations by an attraction with two distinct
regimes. The first one is the strongest and is attributed to a comple
te depletion of micelles. As predicted by the theory, the range of the
interaction is reduced while the strength is increased as the volume
fraction is increased. The second regime appears at larger separations
where an oscillation-like shape is superimposed on a weak attractive
background. It is suggested that the attraction results from an orient
ation depletion of the anisotropic micelles aligning along the surface
s. The oscillatory behavior is further evidenced with measurement of t
he structure factor by SANS.