The properties of aqueous solutions of poly(maleic acid/octyl vinyl ether), PMAOVE, were studied by
pyrene solubilization and fluorescence, solution viscosity, and phase separation induced by inorganic salts.
The results indicate the existence of hydrophobic intramolecular microdomains formed by the octyl side
groups. Pyrene solubilization and intramolecular alkyl chain association diminish sharply as the polymer
is neutralized and unfolds with increasing ionization. The saturation solubilization of pyrene by PMAOVE
corresponds to a ratio of 35 octyl side chains per pyrene at higher polymer concentrations for the un-neutralized polymer, and 42 at constant pH 4.0. Some hydrophobic solubilization averaging one pyrene
per polymer molecule persists up to complete neutralization. Besides pH, the polymer conformation is also
sensitive to solution ionic strength. A compact conformation is induced by the addition of 0.01 M NaCl,
as indicated by the low reduced viscosity at low pH. Further increase to about 0.1 M leads to the precipitation
of PMAOVE at concentrations of 500 ppm and above. Precipitation or phase separation of PMAOVE
solutions at pH 4 by bivalent cations occurs at much lower salt concentrations than with single-valent
cations. With barium in particular, the phase separation is not a simple precipitation. A very weak gel
phase separates from the solution. Only minor differences are detected with a range of anions of sodium
salts in precipitating PMAOVE at pH 11. In contrast to PMAOVE, the less hydrophobic lower homologue
poly(maleic acid/methyl vinyl ether), PMAMVE, shows no hydrophobic solubilization of pyrene and is not
precipitated by addition of NaCl up to saturation of the salt.
The interaction of hydrocarbon chains at aqueous interfaces is a
major factor in defining the interfacial
structures of monolayers and membranes formed by surfactants. The
intermolecular pair potentials which
can be expressed in the two-dimensional second virial coefficients
(B2(T)) are basic to understanding these
structures. In this report, measurements of the adsorption of
hexane vapor on water as a function of the
partial vapor pressure are reported for a static system in which the
vapor pressure is controlled by mixing
liquid hexane with either hexadecane or squalane. The
B2(T) for hexane at the water/vapor interface
is
approximately estimated at one temperature. The results confirm
that the extensive published data on
the adsorption of alkanes on water obtained in a vapor flow system are
incorrect, presumably due to
inadequate vapor saturation.
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