Polymer Engineering Faculty Research

Title

Structure and cleavage energy of surfactant-modified clay minerals: Influence of CEC, head group and chain length

Document Type

Article

Publication Date

4-13-2010

Abstract

The interlayer structure and cleavage energy of surfactant-modified clay minerals at the molecular level were determined for 50 different alkylammonium-modified montmorillonites of different cation exchange capacity (CECs of 91 meq/100 g and 143 meq/100 g), head group structure, and chain length using molecular dynamics simulation with specifically developed sampling techniques. The interlayer density and the cleavage energy are lower for partially packed, flat-on alkyl multilayers in the interlayer space and higher for densely packed, flat-on alkyl multilayers in the interlayer space, in agreement with trends in gallery spacing and molecular conformation. Particularly high cleavage energies, in excess of 60 mJ m−2, are found when charged head groups of surfactants are not vertically separated between the clay mineral layers at equilibrium distance due to strong contributions from Coulomb energy. A widely tunable range of cleavage energies between 25 and 210 mJ m−2 was identified by simulation, whereas experimental data on the separation of modified layered clay minerals remain difficult to obtain. Alkylammonium-modified clay minerals with the lowest cleavage energy are of particular interest as additives for nanocomposites with increased potential for exfoliation without further chemical functionalization.

Publication Title

Philosophical Magazine

Volume

90

Issue

17-18

First Page

2415

Last Page

2424