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The adsorption and zeta potential of two series of cationic surfactants, i.e. alkyltrimethylammonium bromide and alkylpyridinium chloride, on rutile have been studied. The two series varied only in their hydrocarbon chain length. The effect of chain length on the lateral two-dimensional aggregation phenomena of surfactant molecules on the rutile surface has been explained by evaluating various thermodynamic parameters such as the effective number of CH 2 groups removed from the aqueous environment on to the solid surface (dn/d In C), the mean cohesive energy per CH 2 group (Φ) and the average mean aggregation number of the hemimicelle (nhm). The value of the mean cohesive energy in the case of alkyltrimethylammonium bromide (0.599 kcal/mol) is in very good agreement with literature values. It supports hemimicellar formation.