INTERFACIAL BEHAVIOR OF BLOCK POLYELECTROLYTES .6. PROPERTIES OF SURFACE MICELLES AS A FUNCTION OF R AND X IN P(S260-B-VP240/RX)

The interfacial properties of AB diblock polyelectrolytes P(S260-b-VP240/RX), where PS = polystyrene, PVP = poly(4-vinylpyridinium), R = C1 to C18, and X = I and Br, have been studied in detail at the air-water interface using the Langmuir film balance technique. Previous studies1,2 have been extended to explore the scope of the surface micellization phenomenon by varying the length of the pyridinium alkylating agent (R), studying the temperature dependence of surface pressure vs mean molecular area (i.e., pi-A), and controlling the speciation and concentration of the counterion (Z-) in the aqueous subphase. Surface micelle formation is a general phenomenon for all the materials measured, as shown using transmission electron microscopy (TEM) of the corresponding Langmuir-Blodgett(LB)films. It is shown that both the counterion and the hydrophobicity of R affect the relative balance between a surface micelle whose polyelectrolyte chains are surface-adsorbed (starfish morphology) and a surface micelle whose polyelectrolyte chains are subphase-solubilized (jellyfish morphology). Plateaus observed in pi-A curves for diblocks with moderate to strong hydrophobic R groups are associated with a compression-induced solubilization of the alkylated polyelectrolyte chains. The balance between surface-adsorbed and solubilized PVP/R+ chains can be readily altered by changing the counterion from Cl- to Br- to I- or by changing the concentration of the counterion. The size, aggregation number, and conformation of the surface micelles derived from P(S260-b-VP240/RX) diblocks are shown to be readily tunable by a judicious choice of R, X, and the experimental conditions.