The surge of interest in and scientific publications on the structure and properties of nanocomposites has made it rather difficult for the novice to comprehend the physical structure of these new materials and the relationship between their properties and those of the conventional range of composite materials. Some of the questions that arise are: How should the reinforcement volume fraction be calculated? How can the clay gallery contents be assessed? How can the ratio of intercalate to exfoliate be found? Does polymerization occur in the clay galleries? How is the crystallinity of semi-crystalline polymers affected by intercalation? What role do the mobilities of adsorbed molecules and clay platelets have? How much information can conventional X-ray diffraction offer? What is the thermodynamic driving force for intercalation and exfoliation? What is the elastic modulus of clay platelets? The growth of computer simulation techniques applied to clay materials has been rapid, with insight gained into the structure, dynamics and reactivity of polymer-clay systems. However these techniques operate on the basis of approximations, which may not be clear to the non-specialist. This critical review attempts to assess these issues from the viewpoint of traditional composites thereby embedding these new materials in a wider context to which conventional composite theory can be applied. (210 references).

ObjectiveVaping may increase the cytotoxic effects of e-cigarette liquid (ECL). We compared the effect of unvaped ECL to e-cigarette vapour condensate (ECVC) on alveolar macrophage (AM) function.MethodsAMs were treated with ECVC and nicotine-free ECVC (nfECVC). AM viability, apoptosis, necrosis, cytokine, chemokine and protease release, reactive oxygen species (ROS) release and bacterial phagocytosis were assessed.ResultsMacrophage culture with ECL or ECVC resulted in a dose-dependent reduction in cell viability. ECVC was cytotoxic at lower concentrations than ECL and resulted in increased apoptosis and necrosis. nfECVC resulted in less cytotoxicity and apoptosis. Exposure of AMs to a sub-lethal 0.5% ECVC/nfECVC increased ROS production approximately 50-fold and significantly inhibited phagocytosis. Pan and class one isoform phosphoinositide 3 kinase inhibitors partially inhibited the effects of ECVC/nfECVC on macrophage viability and apoptosis. Secretion of interleukin 6, tumour necrosis factor α, CXCL-8, monocyte chemoattractant protein 1 and matrix metalloproteinase 9 was significantly increased following ECVC challenge. Treatment with the anti-oxidant N-acetyl-cysteine (NAC) ameliorated the cytotoxic effects of ECVC/nfECVC to levels not significantly different from baseline and restored phagocytic function.ConclusionsECVC is significantly more toxic to AMs than non-vaped ECL. Excessive production of ROS, inflammatory cytokines and chemokines induced by e-cigarette vapour may induce an inflammatory state in AMs within the lung that is partly dependent on nicotine. Inhibition of phagocytosis also suggests users may suffer from impaired bacterial clearance. While further research is needed to fully understand the effects of e-cigarette exposure in humans in vivo, we caution against the widely held opinion that e-cigarettes are safe.

Preparation of industrially useful clay−polymer nanocomposite materials often requires the dispersal of clay particles within a polymer matrix. The degree to which the clay particles may be dispersed has an effect on the resultant properties of the material, and the clay is often rendered organophilic using alkylammonium species to facilitate incorporation of polymer. The use of a low molecular weight poly(propylene) oxide diamine is investigated as a reagent for controlling the separation between layers in smectite clays and therefore the extent to which the clay tactoid may be dispersed. The arrangement and interactions of the amine species in the interlayer region are investigated through analysis by both experimental methods and computer simulation, which gives insight into coordination mechanisms within the organoclay. Infrared spectroscopy indicates the presence of extensive hydrogen bonding within the amine−clay interlayer. Some of the amine species were found to intercalate in a nonprotonated state, resulting in strong hydrogen-bonding interactions between amine and ammonium groups. Large-scale classical molecular dynamics simulation shows that the amine groups do not interact strongly with the clay sheets, in contradistinction to ammonium groups. The effect of simulation cell size was considered, and in the limit of zero finite size effects, physically realistic undulations are observed within the individual clay sheets.

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We have synthesized a range of montmorillonite-based clay-polymer nanocomposites by intercalation of a variety of functionalized molecules having poly(ethylene oxide) and poly(propylene oxide) backbones from aqueous solution using a facile batch process. We focus on montmorillonite clays charge-balanced by cation exchange with Li + and K + , but otherwise unmodified. Analysis by X-ray diffraction and thermal methods showed that intercalation occurred in all cases and that the composites displayed a range of interlayer spacings and organic content, from monolayer arrangements to pseudo-trilayer arrangements. Intercalated K + -montmorillonites had a propensity to exfoliate, in marked contrast to their resistance to swelling by water. Large-scale molecular dynamics simulations of selected composites were used to elucidate possible interlayer arrangements of the composites. Materials property studies showed that these clay-polymer composites had significantly increased Young's moduli compared to the unfilled polymer.