Polymer–nanoparticle interfacial interactions in polymer nanocomposites: Confinement effects on glass transition temperature and suppression of physical aging

Abstract

The effects of confinement on glass transition temperature (T g ) and physical aging are measured in polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(2-vinyl pyridine) (P2VP) nanocomposites containing 10-to 15-nm-diameter silica nanospheres or 47-nm-diameter alumina nanospheres. Nanocomposites are made by spin coating films from sonicated solutions of polymer, nanofiller, and dye. The T g s and physical aging rates are measured by fluorescence of trace levels of dye in the films. At 0.1-10 vol % nanofiller, T g values can be enhanced or depressed relative to neat, bulk T g (T g,bulk ) or invariant with nanofiller content. For alumina nanocomposites, T g increases relative to T g,bulk by as much as 16 K in P2VP, decreases by as much as 5 K in PMMA, and is invariant in PS. By analogy with thin polymer films, these results are explained by wetted P2VP-nanofiller interfaces with attractive interactions, nonwetted PMMA-nanofiller interfaces (free space at the interface), and wetted PS-nanofiller interfaces lacking attractive interactions, respectively. The presence of wetted or nonwetted interfaces is controlled by choice of solvent. For example, 0.1-0.6 vol % silica/PMMA nanocomposites exhibit T g enhancements as large as 5 K or T g reductions as large as 17 K relative to T g,bulk when films are made from methyl ethyl ketone or acetic acid solutions, respectively. A factor of 17 reduction of physical aging rate relative to that of neat, bulk P2VP is demonstrated in a 4 vol % alumina/ P2VP nanocomposite. This suggests that a strategy for achieving nonequilibrium, glassy polymeric systems that are stable or nearly stable to physical aging is to incorporate well-dispersed nanoparticles possessing attractive interfacial interactions with the polymer.

A review on the role of interface in mechanical, thermal, and electrical properties of polymer composites

“…The absence of strong interfacial interaction of wetted fillers have no substantial impact on T g [182,204]. This phenomenon was explained by the thermomechanical similarities of planar polymer films and polymer nanocomposites [223].…”

“…The presence of strong interaction between the matrix and the fillers (e.g., H-bonding [30,220], electrostatic interaction [220,221], and covalent bonding [222]) increase the T g while the free space at the interface of nonwetted fillers lead to reduced T g [204,223]. The absence of strong interfacial interaction of wetted fillers have no substantial impact on T g [182,204].…”

“…This phenomenon was explained by the thermomechanical similarities of planar polymer films and polymer nanocomposites [223]. If the interaction between the fillers and surrounding matrix is the same as the interfacial interaction between ultrathin layer of the bulk polymer and the substrate, T g will be invariant [204]. Additionally, it was reported that there may be more than one T g in polymer nanocomposites with strong interactions between the fillers and polymer chains [196].…”

“…T g was determined using dynamic mechanical spectroscopy [195][196][197][198][199], calorimetry [191,[200][201][202], and dilatometry [184,203] techniques. Since the mobility of the polymer chains around the fillers is related to the interfacial interaction, the presence of the interaction and their strength can be estimated by measuring T g and relaxation time [11,204]. For example, stronger interactions will cause reduction of the dynamic loss, decrement of thermal expansion coefficient and increment of T g [205].…”

Preparation and characterization of poly(hydroxyurethane) /halloysite nanocomposites via in-situ polymerization

“…In the reported works, polyamide/silica nanocomposites [4], poly(ethylene terephthalate)/silica nanocomposites [5], phenolicformaldehyde resin/silica nanocomposites [6], hyperbranched polymer/silica nanocomposites [7], polyurethane/silica nanocomposites [8][9][10], etc, the silica nanoparticles had been organo-modified before the step polymerization of various monomers. It is well known that surface modification by grafting of polymers onto inorganic nanoparticles is an effective way to improve its dispensability in an organic polymeric matrix and its compatibility with the polymeric matrix, thus enhancing the properties of the composite materials [11][12][13]. Clays have attracted considerable attention because of their specific structure architecture, unique chemical and physical properties, such as zeolites, montmorillonite, vermiculite, attapulgite and other mica-type silicates.…”