Abstract:We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.

The hierarchical assemblies of supramolecules, which consisted of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with 3-pentadecylphenol (PDP) hydrogen-bonded to the 4VP, were investigated in thin films after solvent annealing in a chloroform atmosphere. The synergistic coassembly of PS-b-P4VP and PDP was utilized to generate oriented hierarchical structures in thin films. Hierarchical assemblies, including lamellae-within-lamellae and cylinders-within-lamellae, were simultaneously ordered and oriented from a few to several tens of nanometers over macroscopic length scales. The macroscopic orientation of supramolecular assembly depends on the P4VP(PDP) fraction and can be tailored by varying the PDP to P4VP ratio without interfering with the supramolecular morphologies. The lamellar and cylindrical microdomains, with a periodicity of ∼40 nm, could be oriented normal to the surface, while the assembly of comb blocks, P4VP(PDP), with a periodicity of ∼4 nm, were oriented parallel to the surface. Furthermore, using one PS-b-P4VP copolymer, thin films with different hierarchical structures, i.e., lamellae-withinlamellae and cylinders-within-lamellae, were obtained by varying the ratio of PDP to 4VP units. The concepts described in these studies can be potentially applied to other BCP-based supramolecular thin films, thus creating an avenue to functional, hierarchically ordered thin films.

The demand for an efficient method to clean spreading oil on water is increasingly urgent due to the frequent occurrence of oil spill accidents around the world. In this work, we used a simple one-step electrospinning technique without the requirement of post-treatments to fabricate polystyrene (PS) fibrous sorbents that show exceptional oil adsorption capability. This method involves the dissolution of PS in cosolvents composed of a good solvent, chlorobenzene, and a nonsolvent, DMSO, for electrospinning. The size of the PS fibers electrospun from the cosolvents is rather uniform, and more importantly, the nonsolvent induces a highly porous structure throughout the fibers during the drying process. The porous structure imparts superhydrophobic surface to the fibrous mats, and thus the fibers can selectively adsorb oils while repel water. Furthermore, both the capacity and the rate of oil adsorption are greatly enhanced for the sorbents made of the porous fibers, in contrast to pore-free ones. The oil adsorption capability is closely dependent on the fiber size and the porous morphology, which can be simply controlled by adjusting the compositions of polymer solutions.

Wormlike micelles are flexible polymerlike chains formed by the self-assembly of amphiphilic molecules either in water ("normal" worms) or in oil ("reverse" worms). Normal and reverse worms have both been studied extensively and have generally been found to exhibit analogous rheological properties (e.g., Maxwell fluidlike behavior). Here, we report a hitherto unexplored difference between these two classes of micelles pertaining to the effect of temperature on their rheological properties. For normal worms, the plateau modulus remains constant as the sample is heated while the relaxation time exponentially decreases. For reverse worms, however, both the plateau modulus and the relaxation time decrease exponentially upon heating. Consequently, the zero-shear viscosity of reverse worms decreases more rapidly with temperature than for normal worms. To explain these differences, we propose that increasing the temperature weakens the driving force for micellization in reverse worms whereas it only accelerates the dynamics of surfactant exchange in normal worms.

We report a strategy that combines supramolecular assembly and solvent annealing to manipulate the microdomain orientation in block copolymer thin films. In supramolecular thin films formed by polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with 3-pentadecylphenol (PDP) hydrogen-bonded onto P4VP blocks, where PS blocks phaseseparate into cylindrical microdomains, we found that the orientation of PS cylinders can be controlled by using different types of solvents to anneal the films. As films are annealed under the vapors of solvents bearing no oxygen atoms, such as chloroform, PS cylinders are perpendicular to the surface, while under those of solvents bearing oxygen, such as THF, PS cylinders are parallel to the surface. Furthermore, the orientation is switchable upon the alternate use of different types of solvents. The 1 H NMR measurements showed that the strengths of hydrogen bonds between PDP and P4VP are greatly weakened in oxygen-bearing solvents due to the competition of the highly electronegative oxygen atoms. We thus suggest that the binding capability of PDP onto P4VP is the key to determine whether the supramolecules can be assembled in the vapors of different types of solvents, which in turn, regulates the orientation of PS cylinders.

Organic small molecule semiconductors have many advantages over their polymer analogues. However, to fabricate organic semiconductor-based devices using solution processing, it is requisite to eliminate dewetting to ensure film uniformity and desirable to assemble nanoscopic features with tailored macroscopic alignment without compromising their electronic properties. To this end, we present a modular supramolecular approach. A quaterthiophene organic semiconductor is attached to the side chains of poly(4-vinylpyridine) via noncovalent hydrogen bonds to form supramolecular assemblies that act as p-type semiconductors in field-effect transistors. In thin films, the quaterthiophenes can be readily assembled into microdomains, tens of nanometers in size, oriented normal to the surface. The supramolecules exhibited the same field-effect mobilities as that of the quaterthiophene alone (10−4 cm2/(V·s)). Since the organic semiconductors can be readily substituted, this modular supramolecular approach is a viable method for the fabrication of functional, nanostructured organic semiconductor films using solution processing.

We report the synthesis, morphology, and applications of conjugated rod-coil-coil triblock copolymers, polyfluorene-block-poly(N-isopropylacrylamide)-block-poly(N-methylolacrylamide) (PF-b-PNIPAAm-b-PNMA), prepared by atom transfer radical polymerization first and followed by click coupling reaction. The blocks of PF, PNIPAAm, and PNMA were designed for fluorescent probing, hydrophilic thermo-responsive and chemically cross-linking, respectively. In the following, the electrospun (ES) nanofibers of PF-b-PNIPAAm-b-PNMA were prepared in pure water using a single-capillary spinneret. The SAXS and TEM results suggested the lamellar structure of the PF-b-PNIPAAm-b-PNMA along the fiber axis. These obtained nanofibers showed outstanding wettability and dimension stability in the aqueous solution, and resulted in a reversible on/off transition on photoluminescence as the temperatures varied. Furthermore, the high surface/volume ratio of the ES nanofibers efficiently enhanced the temperature-sensitivity and responsive speed compared to those of the drop-cast film. The results indicated that the ES nanofibers of the conjugated rod-coil block copolymers would have potential applications for multifunctional sensory devices.

Fully bio-based epoxy thermosets can be achieved by the reaction of active esters and epoxide in eugenol-derived epoxy compounds.