A quantitative structure-property relationship study was performed on the critical micelle concentration (cmc) of nonionic surfactants using the CODESSA program. A known correlation between the logarithm of the cmc and counts of linear alkane carbon atoms and ethoxy groups in linear alkyl ethoxylates was improved (R 2) 0.996) by adding cross terms of these molecular descriptors. A general three-parameter structure-property relationship was developed for a diverse set of 77 nonionic surfactants (R 2) 0.984) employing topological descriptors calculated for the hydrophobic fragment of the surfactant molecule. The three descriptors represent contributions from the size of the hydrophobic group, the size of the hydrophilic group, and the structural complexity of the hydrophobic group.

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The charge distribution in common ionic surfactant molecules is estimated using quantum chemical methods. Calculations are compared for four widely accepted semiempirical methods (MINDO/3, AM1, PM3, and MNDO/d). The atomic partial charges are calculated for surfactants with linear alkyl tails and common headgroups, including anionic (sulfate, sulfonate, carboxylate), cationic (trimethylammonium, pyridinium), and amphoteric (betaine, dimethylamine oxide) classes. The headgroup charges are shown to distribute to the rest of the molecule, with significant partial charge on the α-methylene group (3−40%) and a partial charge on the remaining alkyl tail (4−11%). The partial charge distribution influences surfactant self-assembly and physical properties.

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Thermally reversible gelation in 1% aqueous solutions of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(sodium acrylate) has been observed. The transition that occurs as the temperature is increased through the gelation threshold (T gel) is clearly observable by rheological and small-angle neutron scattering (SANS) measurements. SANS measurements suggest that within the hydrogel there exists an unusually uniform matrix of scattering centers, attributed to close packing of micelle-like aggregates surrounded by highly hydrated poly(sodium acrylate) and unassociated ethylene oxide/propylene oxide copolymer. The physical cross-linking caused by these scattering centers induces gelation. Direct model fits to the SANS data suggest that the scattering centers are similar in structure, but somewhat smaller than micelles of the poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) component, with a dehydrated poly(propylene oxide) core of radius 30 Å surrounded by a hydrated PEO corona of outer radius 60 Å.

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The aqueous solubilities of a set of 109 hydrocarbons and 132 halogenated hydrocarbons (total 241) are correlated by a three term equation using descriptors calculated solely from molecular structure, with a correlation coefficient (R) of 0.979 and a standard error (s) of 0.386 log units. This equation allows the estimation of aqueous solubilities of hydrocarbons and halogenated hydrocarbons (including polychlorinated biphenyls). The key descriptor is the molecular volume, modified by topological and electrostatic terms. The use of descriptors calculated only from molecular structure eliminates the need for experimental determination of properties for use in the correlation and allows for the estimation of aqueous solubility for molecules not yet synthesized or isolated.