Tuning Polymer Nanocomposite Morphology: AC Electric Field Manipulation of Epoxy–Montmorillonite (Clay) Suspensions

Abstract

Over the last decade, the utility of inorganic nanoparticles as additives to enhance polymer performance has been established and now provides numerous commercial opportunities, ranging from advanced aerospace systems to commodity plastics.[1] Low-volume additions (1±5 wt.-%) of highly anisotropic nanoparticles, such as layered silicates or carbon nanotubes, provide property enhancements with respect to the neat polymer that are comparable to those achieved by conventional loadings (15±40 wt.-%) of traditional fillers. The lower loadings facilitate processing and reduce component weight. In addition, unique value-added properties not normally possible with traditional fillers are also observed, such as reduced permeability, tailored biodegradability, optical clarity, self-passivation, electrical conductivity, electrostatic discharge, remoteactuated shape recovery, and flammability, oxidation, and ablation resistance.[2] Many references to this technology utilize the moniker nanocomposites', which invokes parallels to traditional fiber-reinforced composite technology and the ability to spatially engineer, design, and tailor' materials performance for a given application. However, development of chemical and processing procedures to disrupt the low-dimensional crystallites (tactoids and ropes) and achieve uniform distribution of the nanoelement (layered silicate and single wall carbon nanotube, respectively) is system specific and, in general, inadequate. Even less developed are approaches to provide spatial and orientational control of the hierarchical morphology with precision comparable to that conventionally obtained through fiber plies and weaving. Herein, we demonstrate the utility of AC electric fields to direct the morphology of polymer±inorganic nanocomposites, specifically epoxylayered silicate systems, through dielectrophoretic effects. [3] This provides an unprecedented ability to tailor physical properties of bulk nanocomposites such as modulus, thermal expansivity, and optical clarity and to develop detailed structure±property relationships through tuning of the nanoscale orientational distribution of nanoelements. Previous morphology±processing studies of polymer± layered silicate nanocomposites have focused on the influence of shear and elongational forces on nanoelement orientation. For example, Krishnamoorti and co-workers have extensively examined and correlated the impact of layered silicate dispersion on melt rheometry and relaxation dynamics.[4] In parallel, recent studies have indicated that shear-induced orientation of these semi-rigid plates, even in simple shear flows, is highly complex, potentially exhibiting tumbling and kayaking behavior reminiscent of the behavior of complex fluids such as liquid crystals and block copolymers. [5] This complexity restricts the general utility of shear forces for precision morphology to uniaxial in-plane alignment, for applications such as ultra-high barrier films. Optimization for other potential applications, such as dielectric under-fills for electro...

Synthesis and characteristics of polystyrene–clay nanocomposites via in situ intercalative polymerization in a direct current electric field

“…[2][3][4][5][6] However, few approaches are developed to control the spatial and oriented morphology of nanomaterials when compared with the conventional ways with fiber and weaving as additives. For example, with tuning effects of electric field, epoxy-layered silicate nanocomposite, [7][8][9][10] styrene-acrylonitrile copolymer/clay nanocomposite, 11 and polypropylene/layered silicate nanocomposites 12 have been recently prepared under an applied electric field.…”

Geomaterials: their application to environmental remediation

“…Such properties are related to the volume fraction, shape and size of the filler particles. Following the pioneering work of Toyota researchers on a nylon 6-clay nanocomposite in the early 1990s [43,47,48], well-exfoliated nanocomposites have been produced in various nylons [44,[49][50][51], polystyrene [52], certain polyimides [53], polypropylene [54][55][56][57], polylactide [58,59] and epoxies [60][61][62]. These studies showed that the improvement in the mechanical performances of nanocomposites mainly originated from the nanosize dimensions of silicates (as this results in an extremely large aspect ratio) and from strong polymer-filler interactions that might affect the effectiveness of the load transfer between the silicate layers and polymer matrix.…”

Cobalt hydroxide colloidal particles precipitation on nanoclay layers for the formation of novel nanocomposites of carbon nanotubes/nanoclay

“…In addition, the degraded layered structure of nanoclay as a result of the CNTs growth within its interlayer spaces will be beneficial for future formation of exfoliated nanoclay in a polymer matrix. Compared to conventional micro-sized fillers, the addition of nanoclay and CNTs in a polymer matrix led to nanocomposite exhibiting markedly improved physicochemical properties at lower loading [22][23][24][25][26]. Since the present novel CNTs-nanoclay composite structure could be directly incorporated into a polymer matrix without the traditional removal of the support material, the resulting composite can be expected to exhibit greatly enhanced mechanical properties due to the mechanical interlocking between CNTs and nanoclay layers as well as the combination of the advantages of both CNTs and nanoclay.…”