Topological Paths and Transient Morphologies during Formation of Mesoporous Block Copolymer Membranes

We systematically investigated the structure formation pathways and transient morphologies involved in the formation of mesoporous membranes by the self-assembly of block copolymers during nonsolvent-induced phase separation. Using AFM, SEM, and in situ synchrotron SAXS, we mapped the topological paths and characteristic transient structures into a ternary phase diagram. We focused on the stability region of an ordered pore phase which is relevant for the generation of integral asymmetric isoporous membranes. We could identify several characteristic morphologies, i.e., spinodal networks, sphere percolation networks, ordered pore structures, and disordered and ordered cylinder arrangements together with transient structures connecting their stability regions. With given evaporation rates for the pure solvents, we calculated the corresponding composition trajectories in the phase diagram to identify suitable experimental conditions in terms of initial polymer volume fraction, solvent composition, and immersion time to trap the desired pore structure

Thermal transport in binary colloidal glasses: Composition dependence and percolation assessment

The combination of various types of materials is often used to create superior composites that outperform the pure phase components. For any rational design, the thermal conductivity of the composite as a function of the volume fraction of the filler component needs to be known. When approaching the nanoscale, the homogeneous mixture of various components poses an additional challenge. Here, we investigate binary nanocomposite materials based on polymer latex beads and hollow silica nanoparticles. These form randomly mixed colloidal glasses on a sub-μm scale. We focus on the heat transport properties through such binary assembly structures. The thermal conductivity can be well described by the effective medium theory. However, film formation of the soft polymer component leads to phase segregation and a mismatch between existing mixing models. We confirm our experimental data by finite element modeling. This additionally allowed us to assess the onset of thermal transport percolation in such random particulate structures. Our study contributes to a better understanding of thermal transport through heterostructured particulate assemblies

Homogeneous Nucleation of Ice Confined in Hollow Silica Spheres

Ice nucleation is studied in hollow silica (HS) spheres. These hierarchical materials comprise ∼3 nm pores within the silica network, which are confined to a ∼20 nm shell of a hollow sphere (with diameters in the range ∼190–640 nm). The multiple length scales involved in HS spheres affect the ice nucleation mechanism. We find homogeneous nucleation inside the water filled capsules, whereas heterogeneous nucleation prevails in the surrounding dispersion medium. We validate our findings for a series of hollow sphere sizes and demonstrate the absence of homogeneous nucleation in the case of polystyrene–silica core–shell particles. The present findings shed new light on the interplay between homogeneous and heterogeneous nucleation of ice with possible implications in undercooled reactions and the storage of reactive or biologically active substances

The effect of morphology and particle–wall interaction on colloidal near-wall dynamics

We investigated the near-wall Brownian dynamics of different types of colloidal particles with a typical size in the 100 nm range using evanescent wave dynamic light scattering (EWDLS). In detail we studied dilute suspensions of silica spheres and shells with a smooth surface and silica particles with controlled surface roughness. While the near wall dynamics of the particle with a smooth surface differ only slightly from the theoretical prediction for hard sphere colloids, the rough particles diffuse significantly slower. We analysed the experimental data by comparison with model calculations and suggest that the deviating dynamics of the rough particles are not due to increased hydrodynamic interaction with the wall. Rather, the particle roughness significantly changes their DLVO interaction with the wall, which in turn affects their diffusion