POLY(ETHYLENE GLYCOL) AMPHIPHILE ADSORPTION AND LIPOSOME PARTITION

Surface localized poly(ethylene glycol) (PEG) amphiphiles of type C-16 :0-EO(151) and C-18:2-EO(1.51) were studied via ellipsometry at macros copic, hat methylated silica (MeSi), phosphatidic acid (PA), and phosp hatidylcholine (PC) surfaces. At these surfaces the amphiphiles adsorb similarly, in a non-cooperative manner, achieving a plateau (approxim ate to 0.1 PEG chains/nm(2)) well below amphiphile critical micelle co ncentration (CMC). The resultant PEG-enriched layers were 10-15 nm thi ck, with a polymer concentration (approximate to 0.07 g/cm(3)) greater than the PEG-enriched phase of many dextran, PEG aqueous two-phase sy stems. PEG-amphiphile adsorption (mg/m(2)) at hydrophobic and phosphol ipid flat surfaces correlated with changes in the partition (log K) of PC liposomes in such two-phase systems. PEG-amphiphile adsorption at macroscopic surfaces appears to represent a balance between hydrophobi c attraction and repulsive intra-chain interactions which promote chai n elongation normal to the surface.