The influence of the water-soluble surfactant sodium dodecyl sulfate (SDS) on the self-assembly of amphiphilic block copolymers through hydrodynamic instabilities of organic solvent/water interfaces was studied. Micropipette aspiration measurements performed on evaporating chloroform droplets containing polystyrene-b-poly(ethylene oxide) (PS-PEO) revealed that interfacial instabilities were correlated to an approach of the organic/water interfacial tension to zero. The addition of SDS to the aqueous phase lowered the interfacial tension, thereby facilitating the onset of instability at lower concentrations of PS-PEO within the droplets. Further, increased amounts of SDS led to qualitatively different mechanisms of interfacial instability and correspondingly different morphologies of the resulting copolymer/surfactant assemblies. Similar, though less pronounced, effects were obtained using poly(vinyl alcohol) (PVOH) as a water-soluble surfactant, reflecting its more weakly concentration-dependent surface activity. These results enabled a single PS-PEO or polybutadiene-PEO block copolymer of fixed composition to be processed into aggregates that could be easily tuned from multi-vesicular particles to wormlike micelles and to spherical micelles.

The mechanical properties and thermal stability of several grades of poly(aryletherketone)s (PAEKs) were investigated using thermal, rheological, and dynamic mechanical characterization. Detailed rheological characterization revealed that several grades of poly(etheretherketone) (PEEK) exhibit relaxation behavior characteristic of a long-chain branched structure. The potentially branched PEEKs showed greater mechanical damping behavior than the linear-chain PEEKs. The molecular weight dependence on zero-shear viscosity for several linear-chain polymers indicates that the PEEKs behave as rigid chains in the melt. Differences in chain structure do not significantly influence dynamic mechanical behavior in the solid state but affect stability at elevated temperatures. The poten-

Superhydrophobic surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large-and small-scale channels. In this paper, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from polydimethylsiloxane with well-defined micron-sized patterns of surface roughness. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction, the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. Thus, in this paper we demonstrate that vortex shedding dynamics is very sensitive to changes of feature spacing, size and orientation along superhydrophobic surfaces.