Interlayer structure of organically modified montmorillonites: Effect of surfactant loading

The surfactant cetyltrimethylammonium ion (CTA⁺) was confined within the galleries of montmorillonite (MMT) to obtain a series of organo-montmorillonites (C16-MMTs) through an ion-exchange intercalation reaction. The C16-MMT formed a single precipitate layer when CTA⁺ loading was 18.3 wt% but stratified at high loadings. The conformational disorder increased with increasing CTA⁺ loading. The upper precipitate was characterized by a larger gallery height and a higher surfactant loading in comparison with lower precipitate. The confined methylene chains adopted a lateral monolayer with a small percentage of conformation freedoms at CTA⁺ loading of 18.3 wt%. The intercalated methylene chains were arranged either in a lateral monolayer or in a tilted interdigitated bilayer at CTA⁺ loading of 24.7 wt% while in either a tilted interdigitated bilayer or a lateral bilayer at high CTA⁺ loadings. The different arrangements of methylene chains intercalated in the MMT galleries are believed to be the reason for the stratification.