The structures of complexes of a vermiculite intercalated by cationic surfactants, a mixture of cationic surfactants, and a mixture of cationic and nonionic surfactants

We have used neutron diffraction in conjunction with isotopic labeling to determine the structures of complexes of a vermiculite (Eucatex) with the two single-chain surfactants dodecyl trimethylammonium bromide (C(12)TAB) and hexadecyl trimethylammonium bromide (C(16)TAB). We have also determined the structure of the mixed chain complex prepared from a 1:1 solution Of C12TAB and C16TAB. The interlamellar spacing appears from the value of the d-spacing to be determined by the longer chain and this has been confirmed by neutron diffraction. The composition of the mixed compound indicates that the longer chain, C(16)TA(+), accounts for most of the charge neutralization, with the C12TAB presumably present as ion pairs. The structure of a series of complexes formed by intercalating the vermiculite with a mixture Of C12TAB and oligoethylene glycol monododecyl (C12Em) or monohexadecyl ethers showed that the ion pairs Of C12TAB could be replaced by a nonionic surfactant. In particular, the stoichiometry of the intercalation Complex Of C12TAB and C12E5 was found to contain 1.4 C12TAB molecules to I C12E5, corresponding to complete replacement of the ion pairs by the nonionic surfactant. The uptake of other nonionic surfactants decreases with the size of the ethylene oxide head group in such a way that the number of ethylene oxide groups in the interlayer space is approximately constant, which suggests that hydrophilic interactions as well as hydrophobicity play a part in determining the uptake of organic material into the interlamellar space. (C) 2002 Elsevier Science (USA).