In this study, a series of π-conjugated block copolymers of regioregular poly(3-hexyl thiophene)-b-poly(2-vinyl pyridine) (P3HT–P2VP) was synthesized and their self-assembly behavior and the detailed thermodynamic phase diagram were explored. By a combination of TEM, SAXS, WAXS, and UV-VIS measurements, it was found that the π-conjugated P3HT in their various self-assembled nanodomains could be a rigid rod, or a semi-rigid chain, or even a fully flexible chain. With the P2VP volume fraction, ϕ, = 0.20, the P3HT–P2VP displays a nanowire structure with a fully extended all-transP3HT rod structure across the width of the nanowires, indicating a prevailing rod–rod interaction between P3HT blocks over the microphase separation interaction between the constituent blocks. With ϕ = ∼0.30 to 0.6, the P3HT–P2VPs show a highly ordered lamellar structure with the P3HT block exhibiting as a semirod-like chain composed of shorter rods connected by twisted 3HT units. With ϕ > 0.68, the π-conjugated block copolymers display self-assembling nanostructures of hexagonal close packed cylinders and spheres, indicating that P3HT adopts a fully coil-like structure that favors interfacial curvatures. In particular, for the P3HT–P2VP with ϕ = 0.68, a gyroid phase, the first of its kind for π-conjugated block copolymers, was observed upon heating. For the nanowire structured P3HT–P2VP, a liquid crystalline phase transition from the smectic-like crystalline state to a nematic structure was observed at ∼200 °C. The observed microstructures and transformations reveal the importance of the semirigid nature of π-conjugated P3HT chains and provide new guidelines for the organization of π-conjugated block copolymers for future optoelectronic applications.

Solution processing of π-conjugated polymers constitutes a major low-cost manufacturing method for the fabrication of many new organic optoelectronic devices. The solution self-assembly kinetics of π-conjugated rod-coil block copolymers of symmetric poly(3-hexyl thiophene)-b-poly(2-vinyl pyridine) (P3HT-P2VP) during drying and the phase transformations of the subsequently dried samples were studied by using a combination of TEM, SAXS, WAXS and DSC measurements. During solution drying in chlorobenzene, a good solvent for the copolymer, P3HT-P2VP first formed nanoseed aggregates followed by the directional growth of nanofibrils driven by the formation of prevailing form II P3HT crystals within its nanofibril core confined by the surrounding domain of P2VP blocks. This result was in sharp contrast when a similar molecular weight P3HT homopolymer was solution self-assembled in chlorobenzene, nearly free from confinement, in which case the resulting nanofibrils consisted of a mixture of majority form I and form II crystals. Solvent-cast films of P3HT-P2VP nanofibrils with form II crystals were heat-/cold-treated and showed solid-state phase transformations from form II crystals to form I crystals, both within nanofibrils with annealing, indicating the metastability of the form II crystals with temperature. A disordered state followed with increasing temperatures which, when cooled, induced the formation of a thermodynamically stable lamellar phase with only form I P3HT crystals. Correspondingly, the study provides new strategies for controlling polymorphs and nanostructures of π-conjugated block copolymers for future applications using solution processing and subsequent heat treatment.

We designed and fabricated a new sensing system which consists of two virtual impactors and two quartz-crystal microbalance (QCM) sensors for measuring particle mass concentration and size distribution. The virtual impactors utilized different inertial forces of particles in air flow to classify different particle sizes. They were designed to classify particle diameter, d, into three different ranges: d < 2.28 μm, 2.28 μm ≤ d ≤ 3.20 μm, d > 3.20 μm. The QCM sensors were coated with a hydrogel, which was found to be a reliable adhesive for capturing aerosol particles. The QCM sensor coated with hydrogel was used to measure the mass loading of particles by utilizing its characteristic of resonant frequency shift. An integrated system has been demonstrated.