Air-liquid interfacial self-assembly of conjugated block copolymers into ordered nanowire arrays

The ability to control the molecular packing and nanoscale morphology of conjugated polymers is important for many of their applications. Here, we report the fabrication of well-ordered nanoarrays of conjugated polymers, based on the self-assembly of conjugated block copolymers at the air-liquid interface. We demonstrate that the self-assembly of poly(3-hexylthiophene)-block-poly(ethylene glycol) (P3HT-b-PEG) at the air-water interface leads to large-area free-standing films of well-aligned P3HT nanowires. Block copolymers with high P3HT contents (82-91%) formed well-ordered nanoarrays at the interface. The fluidic nature of the interface, block copolymer architecture, and rigid nature of P3HT were necessary for the formation of well-ordered nanostructures. The free-standing films formed at the interface can be readily transferred to arbitrary solid substrates. The P3HT-b-PEG films are integrated in field-effect transistors and show orders of magnitude higher charge carrier mobility than spin-cast films, demonstrating that the air-liquid interfacial self-assembly is an effective thin film fabrication tool for conjugated block copolymers.

Aggregation behavior of rod-coil-rod triblock copolymers in a coil-selective solvent

Recent experiments have reported that the self-assembly of conjugated polymers mimicking rod-coil-rod triblock copolymers (BCPs) in selective solvents exhibits unique aggregate morphologies. However, the nature of the arrangement of the polymers within the aggregates and the spatial organization of the aggregates remain an unresolved issue. We report the results of coarse-grained Langevin dynamics simulations, which investigated the self-assembly behavior of rod-coil-rod BCPs in a coil-selective solvent. We observe a rapid formation of cylindrically shaped multichain clusters. The initial stages of formation of the aggregates was seen to be independent of the strength of the solvent selectivity. However, for higher solvent selectivities, the clusters were seen to merge into larger units at later stages. A reduction in rod to coil block ratio was observed to decrease the size and number of clusters. In the limit of a highly concentrated solution, we observe the formation of a networked system of distinct clusters, which however retain the cylindrical arrangement observed at lower polymer concentrations.

Synthesis, self-assembly and photophysical properties of oligo(2,5-dihexyloxy-1,4-phenylene vinylene)-block-poly(ethylene glycol)

We describe the synthesis and characterization of a family of diblock copolymers with 5 units of a dihexyloxy-phenylenevinylene block (OHPV) connected to a series of poly(ethylene glycol) (PEG) chains of different average lengths (12, 45 and 115 PEG units: OHPV5-b-PEG12, OHPV5-b-PEG45, OHPV5-b-PEG115). All three polymers underwent self-assembly in ethanol, a good solvent for the PEG units, but poor for the OHPV segment. The nature of the structures formed depends sensitively on the length of the PEG block. OHPV5-b-PEG115 formed long fiber-like micelles of uniform width, whereas OHPV5-b-PEG45 formed fragile broad ribbons. We also obtained thin ribbons with OHPV5-b-PEG12 but they tend to fold and twist upon themselves. The structures obtained were characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM), as well as by wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC). In addition, their photophysical properties were examined by UV-vis, steady state fluorescence and fluorescence decay measurements. The results of these experiments indicate that the OHPV groups pack differently in the fiber-like micelles of OHPV5-b-PEG115 than in the lamellar structures formed by OHPV5-b-PEG45.

Supramolecular Chemistry in the Formation of Self-Assembled Nanostructures from a High-Molecular-Weight Rod-Coil Block Copolymer

The self-assembled nanostructures of a high-molecular-weight rod-coil block copolymer, poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS), in p-xylene are studied. The cylindrical micelles, long segmental cylindrical micelle associates, spherical micelles, and spherical micelle associates are observed with increased copolymer concentration. The high molecular weight of PS leads to the entanglement between PS chains from different micelles, which is the force for supramolecular interactions. Short cylindrical micelles are connected end-to-end via this supramolecular chemistry to form long segmental cylindrical micelle associates, analogue to the condensation polymerization process, with direction and saturation. On the other hand, spherical micelles assemble via supramolecular chemistry to form spherical micelle associates, yet without any direction due to their isotropic properties.

Block copolymer self-assembly controlled by the “green” gas stimulus of carbon dioxide

CO₂ can act as a “green” stimulus to precisely tune the self-assembly of block copolymers.

pH-responsive inorganic–organic hybrid supramolecular hydrogels with jellyfish-like switchable chromic luminescence

A novel hybrid hydrogel, based on electrostatic co-assembly of polyoxometaltate and the ABA triblock copolymers shows both sol–gel transition and luminescence variation in response to pH change.