This review covers recently reported polymer composites that show a thermoelectric (TE) effect and thus have potential application as thermoelectric generators and Peltier coolers. The growing need for CO2-minimizing energy sources and thermal management systems makes the development of new TE materials a key challenge for researchers across many fields, particularly in light of the scarcity or toxicity of traditional inorganic TE materials based on Te and Pb. Recent reports of composites with inorganic and organic additives in conjugated and insulating polymer matrices are covered, as well as the techniques needed to fully characterize their TE properties.

In the past decade, reports detailing the preparation, characterization, and application of deep eutectic solvents (DESs) have grown in number significantly, showing signs of increased interest and attention. Indeed, these systems provide tunable polar environments attractive for their ease of synthesis and lack of need for purification. DESs are homogeneous systems composed of two or more components having a significantly depressed melting point compared to either constituent material. As interest and application of DESs grow, the need for a common understanding of their preparation and characterization is required. In this Perspective, we discuss metal-free DESs, focusing on their preparation, characterization of physical properties, and considerations for their application. We highlight inconsistencies or omissions in literature reports as well as factors for researchers to consider when investigating these systems.

We report wavelength and time-resolved photoluminescence studies of isolated extended (1-10 μm length) poly(3-hexylthiophene) (P3HT) nanofibers (xNFs) cast on glass from suspension. The PL spectra of xNFs show multiple vibronic replicas that appear to be associated with the existence of both H- and J-type aggregates. The PL spectra of xNFs made from regioregular (rr)- (93%) and highly regioregular (hrr)-P3HT (98%) both show similarities in PL spectra suggestive of common chain packing features, as well as subtle differences that can be attributed to higher long-range order in the hrr-xNFs. Specifically, PL spectral measurements on isolated xNFs made from highly regioregular (>98%) P3HT showed a red-shifted electronic origin (≈30 meV) and increased 0-0/0-1 PL intensity ratio for the J-type species, suggestive of enhanced structural coherence length and intrachain order.

Ionic liquids (ILs) have received attention for a diverse range of applications, but their liquid nature can make them difficult to handle and process and their high viscosities can lead to suboptimal performance. As such, encapsulated ILs are attractive for their ease of handling and high surface area and have potential for improved performance in energy storage, gas uptake, extractions, and so forth. Herein, we report a facile method to encapsulate a variety of ILs using Pickering emulsions as templates, graphene oxide (GO)-based nanosheets as particle surfactants, and interfacial polymerization for stabilization. The capsules contain up to 80% IL in the core, and the capsule shells are composed of polyurea and GO. We illustrate that capsules can be prepared from IL-in-water or IL-in-oil emulsions and explore the impact of monomer and IL identity, thereby accessing different compositions. The spherical, discrete capsules are characterized by optical microscopy, scanning electron microscopy, infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and 1H NMR spectroscopy. We illustrate the application of these IL capsules as a column material to remove phenol from oil, demonstrating ≥98% phenol removal after passage of >170 column volumes. This simple method to prepare capsules of IL will find widespread use across diverse applications.

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Janus particles have recently garnered significant attention for their distinct properties compared to particles that are homogeneously functionalized. Moreover, high aspect ratio Janus particles that are rod-like or planar (i.e., nanosheets) are especially intriguing considering their interfacial properties as well as their ability to assemble into higher order and hybrid structures. To date, major challenges facing the exploration and utilization of 2D Janus particles are scalability of synthesis, characterization of tailored chemical functionalization, and ability to introduce a diverse set of functionalities. Herein, a facile method to access Janus 2D graphene oxide (GO) nanosheets by combining a Pickering-type emulsion and grafting-from polymerization via ATRP is reported. Janus GO nanosheets bearing PMMA on one face as well as the symmetrically functionalized analogue are prepared, and the chemical, thermal, structural, surface, and interfacial properties of these materials are characterized. Time-of-flight secondary ion mass spectrometry coupled with Langmuir-Blodgett films is shown to be an ideal route to conclusively establish asymmetric functionalization of 2D materials. This work not only provides a facile route for the preparation of Janus nanosheets but also demonstrates the direct visualization of polymer grown from the surface of GO.

Mechanically robust, highly compressible, and conductive thermoplastic polyurethane/carbon black foams were successfully fabricated via 3D printing. Thixotropic inks were formulated by dispersing nanoclay, carbon black, and polymer in an organic solvent, and then 3D multifunctional sensors were prepared by direct ink writing (DIW). Sequential removal of solvent and nanoclay yielded a porous polymer/carbon black structure, which maintained excellent elasticity and compression cyclability. The presence of carbon black in the foams led to good electrical conductivity and stable piezoresistive sensing signals at a strain of up to 80%, including the ability to distinguish human motions. Complementary to a decrease in resistance upon compression, the foam can be used as a gas sensor device, as exposure to volatile organic compounds causes the polymer to swell and an increase in resistance. The printed conductive foams can be easily recycled and reprocessed by dissolution in an organic solvent and subsequent re-3D printing, with little detriment to performance.

The task-specific ionic liquid (IL), 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM]­[2-CNpyr]), was encapsulated with polyurea (PU) and graphene oxide (GO) sheets via a one-pot Pickering emulsion, and these capsules were used to scrub CO2 (0–5000 ppm) from moist air. Up to 60 wt % of IL was achieved in the synthesized capsules, and we demonstrated comparable gravimetric CO2 capacities to zeolites and enhanced absorption rates compared to those of bulk IL due to the increased gas/liquid surface-to-volume area. The reactive IL capsules show recyclability upon mild temperature increase compared to zeolites that are the conventional absorber materials for CO2 scrubbing. The measured breakthrough curves in a fixed bed under 100% relative humidity establish the utility of reactive IL capsules as moisture-stable scrubber materials to separate CO2 from air, outperforming zeolites owing to their higher selectivity. It is shown that thermal stability, CO2 absorption capacity, and rate of uptake by IL capsules can be further modulated by incorporating low-viscosity and nonreactive ILs to the capsule core. This study demonstrates an alternative and facile approach for CO2 scrubbing, where separation from gas mixtures with extremely low partial pressures of CO2 is required.