Molecular Dynamics Simulation of Organic−Inorganic Nanocomposites:  Layering Behavior and Interlayer Structure of Organoclays

Abstract

Isothermal−isobaric (NPT) molecular dynamics simulation has been performed to investigate the layering behavior and structure of nanoconfined quaternary alkylammoniums in organoclays. This work is focused on systems consisting of two clay layers and a number of alkylammoniums, and involves the use of modified Dreiding force field. The simulated basal spacings of organoclays agree satisfactorily with the experimental results in the literature. The atomic density profiles in the direction normal to the clay surface indicate that the alkyl chains within the interlayer space of montmorillonite exhibit an obvious layering behavior. The headgroups of long alkyl chains are distributed within two layers close to the clay surface, whereas the distributions of methyl and methylene groups are strongly dependent on the alkyl chain length and clay layer charge. Monolayer, bilayer, and pseudo-trilayer structures are found in organoclays modified with single long alkyl chains, which are identical to the structural models based on the measured basal spacings. A pseudo-quadrilayer structure, for the first time to our knowledge, is also identified in organoclays with double long alkyl chains. In the mixture structure of paraffin-type and multilayer, alkyl chains do not lie flat within a single layer but interlace, and also jump to the next layer in pseudo-trilayer as well as next nearest layer in pseudo-quadrilayer.

Molecular Simulation of the Interlayer Structure and the Mobility of Alkyl Chains in HDTMA+/Montmorillonite Hybrids

“…In our opinion, it is a transition structure between lateral-bilayer and paraffin-monolayer. Furthermore, both our simulation for MO-II-19 and other reports 22,29 also demonstrate the existence of a mixed structure in organoclays. The existence of the mixed structure can well explain the broad reflections in the XRD patterns of organoclays.…”

“…These charge parameters proved to work well with the systems of hydrated clays and surfactant-modified clays. 22,23,[25][26][27][28] Accordingly, there are two different unit cells built in this study. The unit cell formula for MMT-I is Na 0.5 (Al 3.5 Mg 0.5 )Si 8 O 20 (OH) 4 and that for MMT-II is Na 1 -(Al 3 Mg 1 )Si 8 O 20 (OH) 4 .…”

Interlayer Structure and Dynamics of HDTMA+-Intercalated Rectorite with and without Water: A Molecular Dynamics Study

“…10 As shown in Rec1 (Figure 2c), the two peaks of N are dissymmetrical, which is different from the symmetrical distribution of ammonium N in organointercalated smectites. 32,35 A much higher charge amount of the illite part than the semctite part is responsible for this phenomenon.…”

Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR

“…The ordered (all-trans) conformation would be predominant when amine chains radiate away from the clay surface with the increase of amine concentration [7][8][9]. More recently, molecular modeling provided some critical information about the structure of organic clay and interaction of surfactant-clay and surfactant-surfactant [10], which was not elucidated by previous experimental results.…”