Organic Semiconductor Micro/Nanocrystals for Laser Applications

Organic semiconductor micro/nanocrystals (OSMCs) have attracted great attention due to their numerous advantages such us free grain boundaries, minimal defects and traps, molecular diversity, low cost, flexibility and solution processability. Due to all these characteristics, they are strong candidates for the next generation of electronic and optoelectronic devices. In this review, we present a comprehensive overview of these OSMCs, discussing molecular packing, the methods to control crystallization and their applications to the area of organic solid-state lasers. Special emphasis is given to OSMC lasers which self-assemble into geometrically defined optical resonators owing to their attractive prospects for tuning/control of light emission properties through geometrical resonator design. The most recent developments together with novel strategies for light emission tuning and effective light extraction are presented.

Amphiphilic random and random block terpolymers with PEG, octadecyl, and oleyl pendants for controlled crystallization and microphase separation

Amphiphilic random and random block terpolymers bearing PEG chains, crystalline octadecyl groups, and amorphous oleyl groups were designed to control crystallization and microphase separation in the solid state.

Can molecular flexibility control crystallization? The case of para substituted benzoic acids

Little is known about the relationship between the kinetic process of nucleation and the molecular and crystal structures of a crystallizing solute. Here we compare the behaviour of a series of benzoic acids with a focus on conformational effects.

Feedback regulation of crystal growth by buffering monomer concentration

Crystallization is a ubiquitous means of self-assembly that can organize matter over length scales orders of magnitude larger than those of the monomer units. Yet crystallization is notoriously difficult to control because it is exquisitely sensitive to monomer concentration, which changes as monomers are depleted during growth. Living cells control crystallization using chemical reaction networks that offset depletion by synthesizing or activating monomers to regulate monomer concentration, stabilizing growth conditions even as depletion rates change, and thus reliably yielding desired products. Using DNA nanotubes as a model system, here we show that coupling a generic reversible bimolecular monomer buffering reaction to a crystallization process leads to reliable growth of large, uniformly sized crystals even when crystal growth rates change over time. Buffering could be applied broadly as a simple means to regulate and sustain batch crystallization and could facilitate the self-assembly of complex, hierarchical synthetic structures.

Pembrolizumab microgravity crystallization experimentation

Crystallization processes have been widely used in the pharmaceutical industry for the manufacture, storage, and delivery of small-molecule and small protein therapeutics. However, the identification of crystallization processes for biologics, particularly monoclonal antibodies, has been prohibitive due to the size and the flexibility of their overall structure. There remains a challenge and an opportunity to utilize the benefits of crystallization of biologics. The research laboratories of Merck Sharp & Dome Corp. (MSD) in collaboration with the International Space Station (ISS) National Laboratory performed crystallization experiments with pembrolizumab (Keytruda®) on the SpaceX-Commercial Resupply Services-10 mission to the ISS. By leveraging microgravity effects such as reduced sedimentation and minimal convection currents, conditions producing crystalline suspensions of homogeneous monomodal particle size distribution (39 μm) in high yield were identified. In contrast, the control ground experiments produced crystalline suspensions with a heterogeneous bimodal distribution of 13 and 102 μm particles. In addition, the flight crystalline suspensions were less viscous and sedimented more uniformly than the comparable ground-based crystalline suspensions. These results have been applied to the production of crystalline suspensions on earth, using rotational mixers to reduce sedimentation and temperature gradients to induce and control crystallization. Using these techniques, we have been able to produce uniform crystalline suspensions (1–5 μm) with acceptable viscosity (<12 cP), rheological, and syringeability properties suitable for the preparation of an injectable formulation. The results of these studies may help widen the drug delivery options to improve the safety, adherence, and quality of life for patients and caregivers.

Improvement of Transparencies and Mechanical Properties of Poly(cyclohexylene dimethylene cyclohexanedicarboxylate) Parts Using a Compounding Nucleating Agent to Control Crystallization

Poly(cyclohexylene dimethylene cyclohexanedicarboxylate) (PCCE) is a kind of copolyester polymer with excellent toughness and outstanding flexibility. However, the opacity caused by crystallization limits the widespread application of PCCE in products that have transparency requirements. The effects of 1,3:2,4-Di-p-methylbenzylidene sorbitol (MDBS) on the crystallization behavior, transparency, and mechanical properties of a PCCE melt were investigated via differential scanning calorimetry (DSC), spectrophotometry, and tensile testing. The results suggest that the transparency and mechanical properties of PCCE drastically improve and that its crystallization behaviors are obviously influenced by the addition of MDBS. PCCE with 0.6 wt% MDBS was then selected as a representative sample, and its thermal behavior and crystal morphology were further investigated by DSC, hot-staged polarizing microscopy (HSPLM), and scanning electron microscopy (SEM). The quantitative results suggest that, compared to neat PCCE resin, PCCE/MDBS has a lower isothermal and nonisothermal crystallization activation energy, which indicates a rapid crystallization process. The results also show that, compared to the pure PCCE melt, the PCCE/MDBS melt experiences a greater increase in the number of crystals and a greater decrease in the crystal size during cooling. The acceleration of the crystallization process and reduction in crystal size can be both attributed to the nucleation effect of the MDBS. In conclusion, because the addition of the nucleating agent improves the transparency and tensile properties of PCCE by adjusting and controlling its thermal and crystallization behaviors, the proposed technique of using a compounding nucleating agent to control crystallization is therefore suitable for PCCE.

Controlled Assembly of Nanorod TiO2 Crystals via a Sintering Process: Photoanode Properties in Dye-Sensitized Solar Cells

We present for the first time a synthetic method of obtaining 1D TiO2 nanorods with sintering methods using bundle-shaped 3D rutile TiO2 particles (3D BR-TiO2) with the dimensions of around 100 nm. The purpose of this research is (i) to control crystallization of the mixture of two kinds of TiO2 semiconductor nanocrystals, that is, 3D BR-TiO2 and spherical anatase TiO2 (SA-TiO2) on FTO substrate via sintering process and (ii) to establish a new method to create photoanodes in dye-sensitized solar cells (DSSCs). In addition, we focus on the preparation of low-cost and environmentally friendly titania electrode by adopting the “water-based” nanofluids. Our results provide useful guidance on how to improve the photovoltaic performance by reshaping the numerous 3D TiO2 particles to 1D TiO2-based electrodes with sintering technique.

Tailoring the physicochemical properties of zeolite catalysts

Here we summarize our recent findings in the area of zeolite synthesis, focusing on pathways to control crystallization in the absence of organics, tailoring crystal habit with growth modifiers, and pioneering techniques in zeolite surface science to elucidate the mechanisms of growth.