The static and dynamic properties of polymer-layered silicate nanocomposites are discussed, in the context of polymers in confined spaces and polymer brushes. A wide range of experimental techniques as applied to these systems are reviewed, and the salient results from these are compared with a mean field thermodynamic model and non-equilibrium molecular dynamics simulations. Despite the topological constraints imposed by the host lattice, mass transport of the polymer, when entering the galleries defined by adjacent silicate layers, is quite rapid and the polymer chains exhibit mobilities similar to or faster than polymer self-diffusion. However, both the local and global dynamics of the polymer in these nanoscopically confined galleries are dramatically different from those in the bulk. On a local scale, intercalated polymers exhibit simultaneously a fast and a slow mode of relaxation for a wide range of temperatures, with a marked suppression (or even absence) of cooperative dynamics typically associated with the glass transition. On a global scale, relaxation of polymer chains either tethered to or in close proximity (<1nm as in intercalated hybrids) to the host surface are also dramatically altered. In the case of the tethered polymer nanocomposites, similarities are drawn to the dynamics of other intrinsically anisotropic fluids such as ordered block copolymers and smectic liquid crystals. Further, new non-linear viscoelastic phenomena associated with melt-brushes are reported and provide complementary information to those obtained for solution-brushes studied using the Surface Forces Apparatus.

The static and dynamic properties of polymer-layered silicate nanocomposites are discussed in the context of polymers in confined media. Despite the topological constraints imposed by the host lattice, mass transport of the polymer into the silicate layers (at least in the case of essentially non-polar polystyrene) appears to be unhindered and exhibits mobility similar to that of the pure polymer. However, both the local and global dynamics of the polymer in the hybrids are dramatically different from those in the bulk. On a local scale, intercalated polymer chains exhibit higher flexibility along their backbone along with a marked suppression (or even absence) of cooperative dynamics typically associated with the glass transition. On a global scale, relaxation of polymer chains either tethered to or in close proximity (<1 nm as in intercalated hybrids) to the host surface are dramatically altered and parallel those of other intrinsically anisotropic materials such as block copolymers and liquid crystals.

The rheology of end-tethered polymer layered silicate nanocomposites is investigated using linear viscoelastic measurements in oscillatory shear with small strain amplitudes. Two systems consisting of poly( -caprolactone) and nylon-6 with varying amounts of layered silicate (montmorillonite) are examined. The storage (G′) and loss (G′′) moduli increase at all frequencies with increasing silicate loading, consistent with previous findings with conventionally filled polymer systems. However, the powerlaw dependence of G′ and G′′ in the terminal zone is different from that observed in homopolymers and decreases with increasing silicate loading. At low frequencies the rheological response becomes almost invariant with frequency, suggestive of a solid-like response. Comparisons are drawn with rheology of other intrinsically anisotropic materials, and an attempt is made to explain phenomenologically their rich-rheological behavior.

The melt-state linear viscoelastic properties for a series of intercalated nanocomposites are examined. The nanocomposites are based on a short disordered polystyrene-polyisoprene diblock copolymer and varying amounts of dimethyldioctadecylammonium modified montmorillonite. The linear dynamic oscillatory moduli and the stress relaxation moduli are in quantitative agreement and suggest that at short times the relaxation of the nanocomposites is essentially unaffected by the presence of the layered-silicate. However, at long times (or equivalently low frequency), the hybrids exhibit dramatically altered viscoelastic behavior. Hybrids with silicate loadings in excess of 6.7 wt % exhibit pseudo-solidlike behavior, similar to that observed in previous studies of exfoliated end-tethered nanocomposites. On the basis of simple phenomenological arguments, the long time behavior is attributed to the presence of anisotropic stacks of silicate sheets randomly oriented and forming a percolated network structure that is incapable of relaxing completely. These arguments are further supported by the ability of largeamplitude oscillatory shear to orient these nanocomposites and to increase their liquidlike character.

Polystyrene nanocomposites with functionalized single-walled carbon nanotubes (SWNTs), prepared by the in-situ generation and reaction of organic diazonium compounds, were characterized using melt-state linear dynamic viscoelastic measurements. These were contrasted to the properties of polystyrene composites prepared with unfunctionalized SWNTs at similar loadings. The functionalized nanocomposites demonstrated a percolated SWNT network structure at concentrations of 1 vol % SWNT, while the unfunctionalized SWNT-based composites at twice the loading of SWNT exhibited viscoelastic behavior comparable to that of the unfilled polymer. This formation of the SWNT network structure for the functionalized SWNT-based composites is because of the improved compatibility between the SWNTs and the polymer matrix and the resulting better dispersion of the SWNT.