Molecular dynamics insight into the cointercalation of hexadecyltrimethyl-ammonium and acetate ions into smectites

Abstract

Classical molecular dynamic simulations are performed to investigate the microscopic properties of hexadecyltrimethylammonium (HDTMA) intercalated smectites with and without the cointercalation of acetate groups. Three model smectites with distinct layer-charge characteristics are selected as the frameworks and their HDTMA intercalates correspond to the representative monolayer, bilayer, and paraffin configurations of the aliphatic chains. In the organoclays without cointercalation, all trimethylammonium headgroups of HDTMA are fixed firmly above the center of the surface six-member rings through electrostatic attractions with surface oxygen, whereas the alkyl chains are a little more mobile. It is found that the cointercalations can significantly increase the basal spacings of the pure HDTMA intercalated smectites. The distributions and mobility of the HDTMA headgroups are not affected by the acetate ions because of the overwhelming attractions coming from the clay sheets. The acetate groups are fixed by the HDTMA headgroups through ion pairing. This simulation study provides a molecular level basis to understand the effects of cointercalation on properties of organoclays.

Structure and dynamic properties of water saturated CTMA-montmorillonite: molecular dynamics simulations

“…The low mobility of the ammonium N of CTMA + is in accordance with the density distribution, both of which indicate that most of the ammonium N are closely related to the surface six-member rings. The self-diffusion coefficient of alkyl chains in previous simulation which used dry A-Mt model for 1.00 CEC case is 0.86 × 10 − 11 m 2 /s (Liu et al, 2009). Compared to that value, the self-diffusion coefficient for alkyl chain in the interlayer space of A-Mt-1.00 system is higher (1.40 × 10 − 11 m 2 /s), indicating that the alkyl chain in the middle of interlayer space undergoes faster motions under the water saturated condition.…”

Combined experimental and theoretical investigation of interactions between kaolinite inner surface and intercalated dimethyl sulfoxide

“…In our simulation cases, the recently developed INTER-FACE force field [30,31] was adopted, which has already been proven quite successful in describing many inorganic-organic and inorganic-bimolecular interfaces, especially for clays, in quantitative agreement with available experimental data [30,[32][33][34][35][36][37][38][39][40][41][42]. The force field parameters of our systems were summarized in detail in Ref.…”

“…The spatial distribution of intercalated DMSO is represented by the atom concentration profiles along the z direction (normal to the kaolinite basal surface), by which the interlayer structure of DMSO between kaolinite layers can be concluded [33,51]. The DMSO molecules in the simulated kaolinite-DMSO intercalation complex form a monolayer with a basal spacing of 1.20 nm.…”

Acidities of confined water in interlayer space of clay minerals

“…For example, according to numerous experimental and theoretical studies, it has been well recognized that in interlayer spaces, water can form integer-number molecular layers and organic ions (e.g. alkylammoniums) can form layering or paraffin configurations depending on the layer-charge characteristics (Mooney et al, 1952a,b;Bérend et al, 1995;Boek et al, 1995;Skipper et al, 1995a,b;Karaborni et al, 1996;Cases et al, 1997;Chang et al, 1998;Skipper, 1998;Smith, 1998;Sutton and Sposito, 2001;Tambach et al, 2004a,b;Lagaly et al, 2006;Liu and Lu, 2006;Skipper et al, 2006;Liu et al, 2007Liu et al, , 2008aLiu et al, , 2009Cygan et al, 2009;Suter et al, 2009;Anderson et al, 2010).…”