Jr. Charron et Rd. Tilton, A SCANNING ANGLE REFLECTOMETRY INVESTIGATION OF BLOCK-COPOLYMER ADSORPTION TO INSOLUBLE LIPID MONOLAYERS AT THE AIR-WATER-INTERFACE, Journal of physical chemistry, 100(8), 1996, pp. 3179-3189
We modified the technique of scanning angle reflectometry to measure t
he surface excess concentration as water-soluble polystyrene-poly(ethy
lene oxide) (PS-PEO) diblock copolymers adsorb from solution to dipalm
itoylphosphatidylcholine (DPPC) monolayers spread at the air-water int
erface. Polymers adsorb by penetrating the lipid monolayer. Surface pr
essure data and fluorescence microscopy indicate that PS-PEO adsorptio
n drives the liquid expanded-to-liquid condensed phase transition in t
he DPPC monolayer by decreasing the available area per lipid. PS-PEO a
dsorption is therefore functionally equivalent to mechanical compressi
on of the monolayer. Accordingly, the extent of PS-PEO adsorption acco
mmodated by DPPC monolayers in different regimes of the surface pressu
re-area isotherm correlates with the compressibility of the penetrated
monolayers. Polymer adsorption to Liquid expanded monolayers increase
s the interface compressibility to equal that of the phase transition
regime. Polymer segments that adsorb to monolayers in the phase transi
tion and the liquid expanded regimes force lipids from the expanded to
the condensed state, thereby creating accessible interfacial area for
the polymer. Polymer surface concentrations in those monolayer regime
s are indistinguishable from those attained at the air-water interface
in the absence of a spread monolayer. Liquid condensed monolayers can
not accommodate polymer segments in this way, and as a result, the ext
ent of polymer adsorption is diminished.