Molecular Mechanisms of Interphase Evolution in the Liquid Polystyrene−Glassy Poly(phenylene oxide) System

A study of polymer chain diffusion by surface enhanced Raman: effects of plasmonic substrate topology

We report on a new methodology to track chain interdiffusion between polymer slabs based on Raman enhanced by plasmonic substrates. Diffusion is studied in a deuterated-polystyrene/polystyrene (dPS/PS) polymer pair, designed to provide a well-characterized diffusion behavior. The bilayer, 160 nm thick in total, is supported on a plasmonic substrate that provides local amplification of Raman signals in sample regions of close proximity to it. Gold-based substrates with structures of inverted pyramids, spherical nanoparticles and tipped pillars were investigated. Interdiffusion between dPS and PS is promoted upon annealing and followed in situ by dynamic spectral acquisition. A simple model that describes the coupling between the sampled region arising from the plasmonic effect and the diffusion process is employed to interpret spectral evolution data. It is shown that a highly regular topology and surface continuity are key features of the plasmonic substrate in order to provide reliable results. With pyramidal substrates, the most suitable substrates for this application, data are consistent with diffusion coefficients in the range 10-13-10-15 cm2 s-1 and dimensions of sampled regions below 40 nm. The strategy provides a reliable labeling-free technique to investigate polymer interdiffusion on the nanoscale.

Balancing Segregation and Complexation in Amphiphilic Copolymers by Architecture and Confinement

Segregation is a well-known principle for micellization, as solvophobic components try to minimize interactions with other entities (such as solvent) by self-assembly. An opposite principle is based on complexation (or coacervation), leading to the coassembly/association of different components. Most cases in the literature rely on only one of these modes, though the classical micellization scheme (such as spherical micelles, wormlike micelles, and vesicles) can be enriched by a subtle balance of segregation and complexation. Because of their counteraction, micellar constructs with unprecedented structure and behavior could be obtained. In this feature, systems are highlighted, which are between both mechanisms, and we study concentration, architecture, and confinement effects. Systems with inter- and intramolecular interactions are presented, and the effects of polymer topology and monomer sequence on the resulting structures are discussed. It is shown that complexation can lead to altered micellization behavior as the complex of one hydrophobic and one hydrophilic component can have a very low surface tension toward the solvent. Then, the more soluble component is enriched at the surface of the complex and acts as a microsurfactant. Although segregation dominates for amphiphilic copolymers in solution, the effect of the complexation can be enhanced by branching (change of architecture). Another possibility to enhance the complexation is by confining copolymers in a (pseudo-) 2D environment (like the one available at liquid-liquid interfaces). These observations show how new structural features can be achieved by tuning the subtle balance between segregation and complexation/solubilization.

Atomic Force Microscopy Nanomechanics Visualizes Molecular Diffusion and Microstructure at an Interface

Here we demonstrate a simple, yet powerful method, atomic force microscopy (AFM) nanomechanical mapping, to directly visualize the interdiffusion and microstructure at the interface between two polymers. Nanomechanical measurements on the interface between poly(vinyl chloride) (PVC) and poly(caprolactone) (PCL) allow quantification of diffusion kinetics, observation of microstructure, and evaluation of mechanical properties of the interdiffusion regions. These results suggest that nanomechanical mapping of interdiffusion enables the quantification of diffusion with high resolution over large distances without the need of labeling and the assessment of mechanical property changes resulting from the interdiffusion.