Understanding the Swelling Behavior of Modified Nanoclay Filler Particles in Water and Ethanol

Abstract

Clay−polymer nanocomposite materials have gained much attention owing to their low weight ratio of filler to reinforcement properties, delivering lightweight yet resilient materials with excellent barrier properties to gas diffusion. An important process in their production is clay exfoliation, as maximum reinforcement and improvement of barrier properties occur when the clay mineral platelets are fully separated and dispersed through the polymer matrix with a preferred orientation. In this study we examine clay swellingthe first step leading to exfoliationusing molecular dynamics to generate solvation energetics, swelling curves, and atomic density profiles of three types of clay mineralsmontmorillonite, vermiculite, and hectoritewith interlayer Na + cations and/or three quaternary ammonium surfactants in water and ethanol. Analysis based on the provided simulations can help to distinguish between favorable and unfavorable swelling profiles of mineral/surfactant/solvent systems and therefore guide further research into this complex field. ■ INTRODUCTIONSince the early 1990s, when first introduced by Toyota, clayreinforced plastics, or clay−polymer nanocomposite (CPNC) materials, have attracted much attention owing to their superior performance and additional properties relative to conventionally filled (e.g., glass fiber) plastics. The term "nanocomposites" arises owing to the clay filler particles having at least one size domain in the nanometer region. Clay minerals are defined by Guggenheim and Martin as "phyllosilicate minerals and minerals which impart plasticity to clay and which harden upon drying or firing". 1 This typically refers to the fraction of soils with particle size of a layer thickness lower than 2 μm. As individual montmorillonite clay mineral layers are only 10 Å (1 nm) thick, these kind of clay minerals have a very high aspect (breadth to thickness) ratio. At relatively low filler loadings, polymers reinforced with clay minerals gave rise to similar mechanical properties for CPNCs as composites with much higher conventional filler loadings. 2 Initially, it was considered that the nanoscale size of these clay minerals conferred unique properties to the CPNC material. However, in time it became apparent that the strongly bound polymer interfacial layers on the clay mineral allowed CPNC materials to be placed within conventional composite theory. 3 In addition, owing to the preferred orientation and overlap of the highly anisotropic clay mineral platelets, CPNC materials were found to have far superior barrier properties to gas diffusion and better thermal stability compared to the pure polymers, or conventional composites, accelerating their deployment in packaging applications. The dramatically increased usage of plastic-based packaging materials over the last few decades together with future consumption predicted to increase even further 4 have served to stimulate the industry to provide new, more efficient barrier solutions 5−7 with the potential to further extend the usage of CPNC mate...

Swelling Pressure in Systems with Na-Montmorillonite and Neutral Surfaces: A Molecular Dynamics Study

“…This means a severe restriction to the dynamics because the expansion from one hydration state to the next higher state only occurs if a there is a coordinated influx of water. 61 The transition in the Mt-Mt system from 1WL to 2WL…”

“…This means a severe restriction to the dynamics because the expansion from one hydration state to the next higher state only occurs if a there is a coordinated influx of water. 61 The transition in the Mt−Mt system from 1WL to 2WL involves the transfer of 150 water molecules from bulk to interlayer. From Figure 10 it is clear that the influx of water into the interlayer was rapid and took place immediately after the load was reduced to 14 MPa.…”

Enhanced intercalation of organo-muscovite prepared via hydrothermal reaction at low temperature

“…The aim of organic ion exchange treatment is to alter their surface property into hydrophobic. Basically, quaternary ammonium ions are the common organic cations used in organic ion exchange treatment [23]. One of the organic cations that are frequently used to modify the muscovite surface property is cetyltrimethylammonium ions (CTA + ).…”

Nanoclays‐Incorporated Thin‐Film Nanocomposite Membranes for Reverse Osmosis Desalination

“…However, with further increase in NC‐LAP loading to 0.4 wt%, an abrupt drop in salt rejection is observed possibly due to the formation of defects at higher NC‐LAP loadings. In other words, since NC‐LAP are coated and attached onto the PSf surface through van der Waals interactions and its particle size can swell up by sorbing water molecules in the aqueous solution, [ 44,48 ] this may induce voids among particles. [ 49 ] For thinner NC‐LAP layers, the grown polyamide during the thin‐film polymerization could penetrate the NC‐LAP layers and anchor the nanoclays onto the substrate and polyamide through hydrogen bond interactions.…”