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Self-assembly of isoporous membranes of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) involves many parameters: the block copolymer composition, the solvent and its interactions with the respective blocks, composition of the casting solution, solvent evaporation, and immersion into a water bath. We characterized the self-assembly of PS-b-P4VP in solution in nearly neutral or P4VP-selective solvent and on the surface of a cast film. We used a combination of room temperature (RT) and cryogenic high-resolution scanning electron microscopy (cryo-HR-SEM) to study copolymer micellization in dried films, in solution, and on the membrane surface during evaporation. The solutions, with and without addition of small water amounts, were investigated by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). We have shown that the starting point for membrane formation is a microphase-separated copolymer solution with the P4VP within the micelle core. As water is introduced, this structure is preserved as long as the system is far from equilibrium. Closer to equilibrium the PS blocks form the micelles core.

Preparation of organic structures on the nanometer scale by the spontaneous self-assembly of molecular species is a very active field of research in materials science. Among the various morphologies reported, tubular architectures are of particular interest since they may find applications in catalysis, selective separation, drug release, sensors, containers, and conducting devices in nano-, opto-, or ionoelectronics. A brief review of the topic is given in our previous report in this journal.[1] It has been previously reported that organic nanotubes with strikingly monodisperse diameters can be very easily obtained from the alkaline salt of the naturally occurring lithocholic bile acid (LCA).[1] Cryo-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS) techniques were used to characterize the structures, which appear as very uniform tubes with 52 nm outer diameters and internal cavities 49 nm in diameter. Nevertheless, some TEM images showed additional morphologies such as twisted and helical ribbons, and thin, long, and semi-rigid fibers (ªfibrilsº). At the same time, theoretical descriptions of the formation of tubes through such metastable intermediates have also been proposed. [2,3] For a complete description of the sodium lithocholate (SLC) nanotubes, it is now important to investigate the kinetics of their formation with different and complementary techniques. We report here such a study, taking advantage of the relations between structural information gained from both reciprocal-and real-space. For that purpose, SAXS experiments and cryo-TEM imaging were performed.For both SAXS and cryo-TEM techniques, there is a minimum time (ªdead timeº, t d ) required to disperse the LCA powder into NaOH aqueous solution before starting a measurement. The t d for the cryo-TEM samples was ca. 80 s. Figure 1A shows the evolution of the SAXS scattering profile versus time for a 1.01 wt.-% SLC suspension. The first curve is recorded at the SAXS t d of 160 s, and others are accumulated up to ca. 48 000 s, i.e., more than 13 h. For comparison, a scattering curve obtained from an aged suspension (Dt~270 000 s, over 3 days) is also shown as a reference scattering signature obtained with a stabilized suspension (curve R).As shown in Figure 1A, the scattering curve of the reference sample shows eight well-defined oscillations confirming ).

Reversible addition-fragmentation chain transfer (RAFT) polymerization along with benzyl dithiobenzoate chain transfer agent was employed for the controlled preparation of four diblock copolymers of styrene (St, less polar monomer) and 2-or 4-vinyl pyridine (2VP or 4VP, more polar monomers): St 161-b-2VP 48 , St 161-b-2VP 121 , St 161-b-4VP 76 and St 161-b-4VP 107 , where the subscripts indicate the experimentally determined degrees of polymerization for each block. These diblock copolymers and their common homopolySt precursor were characterized in terms of their molecular weights and compositions using gel permeation chromatography and 1 H-NMR spectroscopy, respectively. All four diblock copolymers self-assembled in dilute toluene solutions to form reverse spherical micelles, which were characterized using atomic force microscopy and cryogenic transmission electron microscopy. Both microscopy techniques revealed that the 4VP-bearing diblock copolymers formed larger micelles than the 2VP-bearing ones, a result of the greater 4VP-toluene incompatibility as compared to the 2VP-toluene one. Finally, films cast from chloroform solutions of the diblocks were investigated in terms of their bulk morphologies using transmission electron microscopy. While the 2VP-containing block copolymer self-assembled into a spherical morphology, the 4VP-containing one with comparable composition and molecular weight formed a cylindrical structure, manifesting the greater 4VP-St incompatibility as compared to that of the 2VP-St pair.

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