Thermally Switchable Liquid Crystals Based on Cellulose Nanocrystals with Patchy Polymer Grafts.

A thermally "switchable" liquid-crystalline (LC) phase is observed in aqueous suspensions of cellulose nanocrystals (CNCs) featuring patchy grafts of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM). "Patchy" polymer decoration of the CNCs is achieved by preferential attachment of an atom transfer radical polymerization (ATRP) initiator to the ends of the rods and subsequent surface-initiated ATRP. The patchy PNIPAM-grafted CNCs display a higher colloidal stability above the lower critical solution temperature (LCST) of PNIPAM than CNCs decorated with PNIPAM in a brush-like manner. A 10 wt% suspension of the "patchy" PNIPAM-modified CNCs displays birefringence at room temperature, indicating the presence of an LC phase. When heated above the LCST of PNIPAM, the birefringence disappears, indicating the transition to an isotropic phase. This switching is reversible and appears to be driven by the collapse of the PNIPAM chains above the LCST, causing a reduction of the rods' packing density and an increase in translational and rotational freedom. Suspensions of the "brush" PNIPAM-modified CNCs display a different behavior. Heating above the LCST causes phase separation, likely because the chain collapse renders the particles more hydrophobic. The thermal switching observed for the "patchy" PNIPAM-modified CNCs is unprecedented and possibly useful for sensing and smart packaging applications.

Enhanced Alignment of Water-Soluble Polythiophene Using Cellulose Nanocrystals as a Liquid Crystal Template.

Cellulose nanocrystals (CNCs) are bioderived, rodlike particles that form a chiral nematic liquid crystal (LC) in water. In this work, CNCs were used to induce long-range order in a semiconducting polymer, poly[3-(potassium-4-butanoate) thiophene-2,5-diyl] (PPBT). When mixed with CNCs, it was found that PPBT was incorporated into the liquid crystal "template" to form ordered structures with highly birefringent domains, as observed under polarized light. We show that the π-π interactions between polymer chains, which contribute considerably to the energetics of the semiconducting system, are directly influenced by the presence and packing of the liquid crystal phase. Upon increasing the concentration of CNCs from the isotropic to chiral nematic regime, we observe a bathochromic shift in the UV-vis spectra and the emergence of the 0-0 vibrational peak, suggesting enhanced π-π stacking leading to chain coplanarization. Furthermore, the chiral nature of the PPBT/CNC mixture was evidenced by a negative peak in circular dichroism (CD) spectroscopy, promoting the notion that the polymer chains followed the helicoidal twist of the chiral nematic liquid crystal host. At high temperatures, the peak height ratios and overall intensities of the UV-vis and CD spectra associated with PPBT decreased as the chiral nematic pitch grew larger in size.

A Commentary on Co-Processed API as a Promising Approach to Improve Sustainability for the Pharmaceutical Industry.

Pharmaceutical products represent a meaningful target for sustainability improvement and emissions reduction. It is proposed here that rethinking the standard, and often linear, approach to the synthesis of Active Pharmaceutical Ingredients (API) and subsequent formulation and drug product processing will deliver transformational sustainability opportunities. The greatest potential arguably involves API that have challenging physico-chemical properties. These can require the addition of excipients that can significantly exceed the weight of the API in the final dosage unit, require multiple manufacturing steps to achieve materials amenable to delivering final dosage units, and need highly protective packaging for final product stability. Co-processed API are defined as materials generated via addition of non-covalently bonded, non-active components during drug substance manufacturing steps, differing from salts, solvates and co-crystals. They are an impactful example of provocative re-thinking of historical regulatory and quality precedents, blurring drug substance and drug product operations, with sustainability opportunities. Successful examples utilizing co-processed API can modify properties with use of less excipient, while simultaneously reducing processing requirements by delivering material amenable to continuous manufacturing. There are also opportunities for co-processed API to reduce the need for highly protective packaging. This commentary will detail the array of sustainability impacts that can be delivered, inclusive of business, regulatory, and quality considerations, with discussion on potential routes to more comprehensively commercialize co-processed API technologies.

Characterization of Submicron Bubbles Formed by the Hydrophobin Cerato-ulmin.

Cerato-ulmin is a fungal hydrophobin protein with a high surface activity due to its amphipathic nature. When aqueous dispersions are gently agitated by hand, cerato-ulmin (CU) assembles into cylindrical bubbles visible in an optical microscope. After approximately 1 h the larger micron-sized bubbles rise out of the solution, leaving only submicron particulates, which persist indefinitely. Dynamic light scattering experiments show that these persistent particles shrink when positive air pressure is applied to the suspension and expand when vacuum is applied. Small-angle X-ray scattering at ambient pressure suggests an extended core-shell structure, consistent with small air-filled bubbles stabilized by a protein film. A comparison between the SAXS of the persistent submicron bubbles and AFM of the buoyant larger bubbles found immediately after agitation show that both have similar film thickness of 13-15 nm or five protein molecules. The extended shapes confirm the solid-like properties of these CU membranes, even in submicron particulate structures, consistent with microtensiometry results on interfacial CU membranes.

Functionalized Cellulose Nanocrystal-Mediated Conjugated Polymer Aggregation.

Inducing the self-assembly of π-conjugated polymers into semicrystalline aggregates has been a topic of substantial interest in the field of organic electronics and is typically achieved using energy-intensive solution processing or postfilm deposition methods. Here, we demonstrate the ability of bioderived cellulose nanocrystals (CNCs) to act as structure-directing agents for the conjugated semiconducting polymer, poly(3-hexylthiophene) (P3HT). CNCs were grafted with polystyrene, P3HT or poly(N-isopropylacrylamide), and subsequently blended with P3HT in solution to study the effect on conjugated polymer self-assembly. The presence of polymer-grafted CNCs resulted in an increase in P3HT semicrystalline aggregate formation, the degree of which depended on the surface free energy of the grafted polymer. The time-dependent P3HT aggregation was characterized by UV-vis spectroscopy, and the resulting data was fit to the Avrami crystallization model. The surface energies of each additive were calculated via contact angle measurements and were used to elucidate the mechanism of P3HT aggregation in these blended systems. P3HT aggregation was enhanced by unfavorable polymer-polymer interactions at the CNC surface, and spatial confinement effects that were imposed by phase separation. Finally, films were cast from the P3HT/CNC solutions and their electronic performance was characterized by organic field-effect transistor device measurements. Films containing polymer-grafted CNCs exhibited higher charge-carrier mobilities, in some cases, up to a 6-fold increase. These bioderived particles constituted a significant volume fraction of the deposited P3HT thin films with an increase in performance, showing promise as a method for reducing costs and improving the sustainability of organic electronics.

Control of Nucleation Density in Conjugated Polymers via Seed Nucleation.

The development of processing methods to precisely control the solution state properties of semiconducting polymers in situ have remained elusive. Herein, a facile solution seed nucleation processing method is presented in which nucleated poly(3-hexylthiophene) (P3HT) solutions are blended with well-solvated, non-nucleated counterparts as a means to promote the formation of interconnected polymer networks. Nucleation and growth of these networks was induced by preprocessing the solution with UV irradiation and subsequent solution aging prior to deposition via blade-coating. This process was adopted for both batch and continuous flow processing. Superior charge carrier (hole) mobilities were observed in samples with nucleated seeds compared to controls with 0% nucleated P3HT and 100% nucleated P3HT. UV-vis spectral analysis identified that an intermediate degree of solution aggregation (15-20%) is most conducive to enhanced charge transport. The role of intrachain and interchain ordering and alignment on the mesoscale and macroscale is characterized via X-ray scattering, atomic force microscopy, and optical microscopy techniques. The results presented here provide a framework to enable in situ control of the nucleation and growth process to achieve targeted solution state properties resulting in reliable and reproducible performance when the solutions are used for device fabrication.

High-Throughput Image Analysis of Fibrillar Materials: A Case Study on Polymer Nanofiber Packing, Alignment, and Defects in Organic Field Effect Transistors.

High-throughput discovery of process-structure-property relationships in materials through an informatics-enabled empirical approach is an increasingly utilized technique in materials research due to the rapidly expanding availability of data. Here, process-structure-property relationships are extracted for the nucleation, growth, and deposition of semiconducting poly(3-hexylthiophene) (P3HT) nanofibers used in organic field effect transistors, via high-throughput image analysis. This study is performed using an automated image analysis pipeline combining existing open-source software and new algorithms, enabling the rapid evaluation of structural metrics for images of fibrillar materials, including local orientational order, fiber length density, and fiber length distributions. We observe that microfluidic processing leads to fibers that pack with unusually high density, while sonication yields fibers that pack sparsely with low alignment. This is attributed to differences in their crystallization mechanisms. P3HT nanofiber packing during thin film deposition exhibits behavior suggesting that fibers are confined to packing in two-dimensional layers. We find that fiber alignment, a feature correlated with charge carrier mobility, is driven by increasing fiber length, and that shorter fibers tend to segregate to the buried dielectric interface during deposition, creating potentially performance-limiting defects in alignment. Another barrier to perfect alignment is the curvature of P3HT fibers; we propose a mechanistic simulation of fiber growth that reconciles both this curvature and the log-normal distribution of fiber lengths inherent to the fiber populations under consideration.