The adsorption of cationic surfactant dodecyltrimethylammonium bromide (C~1~2TAB) on polystyrene (PS) latex particles has been investigated by estimation of the hydrodynamic radius using dynamic light scattering measurements as well as by determination of the adsorption isotherm using a surface tension technique. The surface of the latex particle has a hairy characteristic and the pendant PS chains terminate in sulfate groups. Initially, C~1~2TA^+ ions were bound at the extremities of the PS chains through both electrostatic attraction between the quaternary ammonium head groups of C~1~2TA^+ ions and the terminal sulfate entities of the PS chains and hydrophobic interaction between the alkyl tails and the PS backbone. Combination of both forces led to L-type isotherm. At the stage I, adsorption yielded small aggregates with average aggregation number of 4.0 on the entities of PS chains. Further significant adsorption (the stage II) of C~1~2TA^+ ions subsequently occurred around the small aggregates formed initially through hydrophobic interaction between the hydrocarbons, finally leading to formation of globular micelles anchored at the extremities of PS chains with average aggregation number of 19.5 (the stage III). In comparison with the previous. SDS case, the present result indicated that the adsorption sites occupied initially are an important factor for determining the structure of surface micelles adsorbed on the pendant polymer chains. Whereas the initial adsorption sites are dominated by the interaction forces between the surfactant molecules/ions and the polymer chains.

Key words: QUATERNARY AMMONIUM COMPOUNDS, POLYSTYRENE, LATEX, ADSORPTION