Langmuir,15 (22), 7546 -75501999.
Web Release Date: August 25, 1999
Copyright © 1999 American Chemical Society

Quantum-Chemical Calculations of the Charge Distribution in Ionic Surfactants

Paul D. T. Huibers

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307

Received March 30, 1999

In Final Form: June 29, 1999


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 alpha-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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