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This paper reviews the recent research and development of clay-based polymer nanocomposites. Clay minerals, due to their unique layered structure, rich intercalation chemistry and availability at low cost, are promising nanoparticle reinforcements for polymers to manufacture low-cost, lightweight and high performance nanocomposites. We introduce briefly the structure, properties and surface modification of clay minerals, followed by the processing and characterization techniques of polymer nanocomposites. The enhanced and novel properties of such nanocomposites are then discussed, including mechanical, thermal, barrier, electrical conductivity, biodegradability among others. In addition, their available commercial and potential applications in automotive, packaging, coating and pigment, electrical materials, and in particular biomedical fields are highlighted. Finally, the challenges for the future are discussed in terms of processing, characterization and the mechanisms governing the behaviour of these advanced materials.

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The structural and optical stability of nanoparticles directly influences their applications. The shape evolution of silver nanoplates synthesized in the presence of bis(2-ethylhexyl) sulfosuccinate (AOT) could be effectively frozen using thiols in aqueous solution. These thiols (e.g., 1-hexanethiol, 1-octanethiol, 1-dodecanethiol, and 1-hexadecanethiol) exhibit stronger surface affinity on the silver crystalline surfaces. This is evidenced from both the unchanged shape/size of nanoplates and their unshifted plasmon resonances in optical absorption. To quantitatively explain the thiol-frozen shape evolution mechanism of silver nanoplates at molecular scale, molecular dynamics simulation was performed. The results show that these thiols exhibit larger interaction energies than AOT molecules on the silver atomic surfaces and hence freeze the shape evolution of silver nanoparticles. This thiol-frozen strategy would not only be useful for stabilizing nanoparticles but would also allow the introduction of a wide range of surface chemical functionalities to the nanoparticles for potential applications in nanosensors.

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.

Two polymer–montmorillonite (MMT) nanocomposites have been synthesized by in situ intercalative polymerization. The styrene monomer is intercalated into the interlayer space of organically modified MMT, a layered clay mineral. Upon the intercalation, the complex is subsequently polymerized in the confinement environment of the interlayer space with a free radical initiator, 2,2-azobis isobutyronitrile. The aniline monomer is also intercalated and then polymerized within the interlayer space of sodium-and copper-MMT initiated by ammonium peroxodisulphate and interlayer copper cations respectively. X-ray diffraction indicates that the MMT layers are completely dispersed in the polystyrene matrix and an exfoliated structure has been obtained. The resulting polyaniline–MMT nanocomposites show a highly ordered structure of a single polyaniline layer stacked with the MMT layers. Fourier transform infrared spectra further confirm the intercalation and formation of both polymer–MMT nanocomposites.