Colloids and Surfaces A: Physicochemical and Engineering Aspects 183 – 185 (2001) 715 – 724 Structural properties of cationic surfactant/pentanol/water systems and their interaction with negatively charged layer silicates Rita Patakfalvi, Imre De ´ka ´ ny * Department of Colloid Chemistry and Nanostructured Materials Research Group of the Hungarian Academy of Sciences, Uniersity of Szeged H-6720 Szeged, Aradi .t. 1, Hungary Abstract Hexadecyltrimethylammonium bromide/pentanol/water and hexadecylpyridinium chloride/pentanol/water liquid crystalline systems were investigated. We studied the influence of water and pentanol on the swelling and rheological properties of lamellar liquid crystalline systems. We studied the possibility of inserting negatively charged layer silicates in these cationic surfactant/pentanol/water systems. Combining the adsorption data from X-ray diffraction, the composition of adsorption layer was calculated. After addition of Na-montmorillonite to the liquid crystalline system, the silicate lamellae were built up into the ordered liquid crystalline structure. Therefore, in the case of adsorption from aqueous solution, ordered liquid crystalline structure appears in the adsorption space between the silicate layers, and this structure determines the degree of swelling and the adsorption layer composition on the solid silicate surface. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Clay minerals; Adsorption; Liquid crystalline system; Cationic surfactants; X-ray diffraction; Rheology www.elsevier.nl/locate/colsurfa 1. Introduction Liquid crystalline systems formed by cationic surfactants have been described in numerous pub- lications. The structural characteristics of liquid crystalline mesophases, the arrangement of the molecules and the globular, cylindrical or lamellar structure of the associations are revealed by the analysis of the phase diagrams of surfactant/co- surfactant/water systems, presented by Ekwall et al. and Friberg et al. [1–3]. Heinz Hoffmann analyzed micelles formed by cationic and anionic surfactants in solutions of various concentrations and studied the properties of the different phases by rheological and X-ray diffraction methods [4]. Friberg and Venable [3] studied tetrade- cyltrimethylammonium bromide/pentanol/water systems and established that the interlamellar dis- tance is dependent on the water/surfactant ratio but the presence of the cosurfactant also affects (reduces) the extent of the swelling of the liquid crystalline system. The microstructure and the rheological properties of lamellar liquid crystals * Corresponding author. Tel.: +36-62-321347; fax: +36- 62-454210. E-mail address: i.dekany@chem.u-szeged.hu (I. De ´ka ´ny). 0927-7757/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0927-7757(01)00498-8