The kinetics of phase separation in thin polymer blend films of polystyrene and polybutadiene on a silicon substrate is examined by optical microscopy of the free film boundary. Our observations on 1000 and 200 Å films are consistent with a crossover from three-to two-dimensional spinodal decomposition kinetics in the (off-critical) viscous hydrodynamic regime. In this stage of phase separation the exponent n, characterizing the scale R͑t͒ ϳ t n of the coarsening pattern, is predicted to change from 1 to a value near 0.46 upon lowering the dimensionality. [S0031-9007(96)00326-2]

The adsorption of a series of nonionic surfactants, C n H2 n +1(OC2H4) m OH (C n E m ), from aqueous solution onto a self-assembled monolayer (SAM) before and after chemical modification has been studied by neutron reflection. On a SAM consisting of a layer of undecenyl trichlorosilane with the ethylenic group at the aqueous interface all the surfactants adsorbed to form a monolayer whose thickness compared with the length of the molecule suggests that the molecules are tilted at angles in the region of 60° away from the surface normal. There was some penetration of the SAM layer by the alkyl chains of the surfactants. When the SAM was hydroxylated, the pattern of adsorption was found to be quite different and, for all the surfactants, the layer was only about 4 Å thick with a segmental surface density constant within experimental error, and there was no penetration of the SAM. The structure of this layer is attributed to hydrogen bonding between the ethylene glycol groups in the surfactant and the OH groups on the surface of the SAM. For comparison the adsorption of the same set of surfactants was studied on the bare silica surface. In all cases the adsorption was in the form of a defective bilayer, quite different again from the adsorption pattern on the two SAMs.

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Concomitant with the development of polymer nanocomposite (PNC) technologies across numerous industries is an expanding awareness of the uncertainty with which engineered nanoparticles embedded within these materials may be released into the external environment, particularly liquid media. Recently there has been an interest in evaluating potential exposure to nanoscale fillers from PNCs, but existing studies often rely upon uncharacterized, poor quality, or proprietary materials, creating a barrier to making general mechanistic conclusions about release phenomena. In this study we employed semiconductor nanoparticles (quantum dots, QDs) as model nanofillers to quantify potential release into liquid media under specific environmental conditions. QDs of two sizes were incorporated into low-density polyethylene by melt compounding and the mixtures were extruded as free-standing fluorescent films. These films were subjected to tests under conditions intended to accelerate potential release of embedded particles or dissolved residuals into liquid environments. Using inductively-coupled plasma mass spectrometry and laser scanning confocal microscopy, it was found that the acidity of the external medium, exposure time, and small differences in particle size (on the order of a few nm) all play pivotal roles in release kinetics. Particle dissolution was found to play a major if not dominant role in the release process. This paper also presents the first evidence that internally embedded nanoparticles contribute to the mass transfer, an observation made possible via the use of a model system that was deliberately designed to probe the complex relationships between nanoparticle-enabled plastics and the environment.

Multiwall carbon nanotubes (MWCNTs) are nanofillers used in consumer and structural polymeric products to enhance a variety of properties. Under weathering, the polymer matrix will degrade and the nanofillers may be released from the products potentially impacting ecological or human health. In this study, we investigated the degradation of a 0.72 % (by mass) MWCNT/amine-cured epoxy nanocomposite irradiated with high intensity ultraviolet (UV) light at various doses, the effects of UV exposure on the surface accumulation and potential release of MWCNTs, and possible mechanisms for the release resistance of the MWCNT surface layer formed on nanocomposites by UV irradiation. Irradiated samples were characterized for chemical degradation, mass loss, surface morphological changes, and MWCNT release using a variety of analytical techniques. Under 295 nm to 400 nm UV radiation up to a dose of 4865 MJ/m2, the nanocomposite matrix underwent photodegradation, resulting in formation of a dense, entangled MWCNT network structure on the surface. However, no MWCNT release was detected, even at very high UV doses, suggesting that the MWCNT surface layer formed from UV irradiation of polymer nanocomposites resist release. Four possible release resistance mechanisms of the UV-induced MWCNT surface layer are presented and discussed.