Triggered Structural Control of Dynamic Covalent Aromatic Polyamides: Effects of Thermal Reorganization Behavior in Solution and Solid States

Thermally rearrangeable aromatic polyamides (TEMPO-PA) and random copolyamides (TEMPO-PA-COOH) incorporating alkoxyamine moieties in the main chain were synthesized, and the effects of thermal reorganization behavior on their solution and solid-state structures were investigated. The hydrodynamic radius in solution decreased as the solution temperature increased because of the dissociation of the alkoxyamine unit. Additionally, the dry density of the thin films decreased as the fabrication temperature increased because of the suppression of polymer aggregation caused by the thermally induced radical crossover reaction. In addition, at the film surface of the random copolyamide containing hydrophobic TEMPO and hydrophilic 3,5-diaminobenzoic acid (DABA) units, the hydrophilicity decreased as the fabrication temperature increased. This is because hydrophobic TEMPO and hydrophilic DABA units tend to be discretely aggregated near the film surface to minimize the surface energy and suppress the hydrogen bonding via a radical crossover reaction during the thin-film fabrication process. The present study clearly shows that both the solution structure and the solid-state molecular aggregation structure of the dynamic covalent polymers can be easily controlled by a thermal trigger, and it provides a new method for controlling the higher-order structure of polymer solutions and solids

ESA-CF Synthesis of Linear and Cyclic Polymers Having Densely Appended Perylene Units and Topology Effects on Their Thin-Film Electron Mobility

A pair of topologically contrastive, linear and cyclic polymers having densely appended perylene diimide (PDI) units have been prepared by means of an electrostatic self-assembly and covalent fixation (ESA-CF) process, using an assembly composed of either linear or cyclic polyacrylate anions of different segment lengths (DP_n = 50, 93, and 128) accompanying countercations of a perylene diimide (PDI) derivative having a cyclic ammonium salt group (<b>II</b>_<b>L</b><b>/III</b> and <b>II</b>_<b>C</b><b>/III</b>, respectively). The subsequent heating treatment at 180 °C produced the covalently converted product, i.e., the linear <b>IV</b>_<b>L</b> and the cyclic <b>IV</b>_<b>C</b>, respectively, in which the PDI unit was introduced nearly quantitatively to the backbone acrylate units. The obtained linear and cyclic polymers having pendant PDI units were observed to form commonly spherical self-assemblies both in bulk and in solution states, while the solution viscosity was noticeably higher with the linear products than with the cyclic counterparts. The electron-only device (EOD) measurement by using thin-film samples of a series of cyclized products, <b>IV</b>_<b>C</b>, revealed consistently higher electron carrier mobilities in comparison with the corresponding linear counterparts, <b>IV</b>_<b>L</b>

Enhancing the Effect of the Nanofiber Network Structure on Thermoresponsive Wettability Switching

This letter reports the enhancing effects of a nanofiber network structure on stimuli-responsive wettability switching. Thermoresponsive coatings composed of nanofibers were prepared by electrospinning from thermoresponsive polymer poly(<i>N</i>-isopropylacrylamide) (PNIPAAm). The nanofiber coatings showed a large amplitude of thermoresponsive change in the wettability from hydrophilic to hydrophobic states compared to a smooth cast film. In particular, the combination of the surface chemistry and unique topology of the electrospun nanofiber coatings enables a transition from the Wenzel state to the metastable Cassie–Baxter state with an increase in temperature and consequently an enhanced amplitude of change in the water contact angles: the apparent contact angle differences between 25 and 50 °C are Δθ*_25–50 °C= 108 and 10° for the nanofiber coatings with a diameter of 830 nm and a smooth cast film, respectively. The fabrication of the 3D nanofiber network structure by electrospinning from stimuli-responsive materials is a promising option for highly responsive surfaces in wettability

New Semiconducting Polymers Based on Benzobisthiadiazole Analogues: Tuning of Charge Polarity in Thin Film Transistors via Heteroatom Substitution

As one of the most effective molecular design strategies in organic electronics, heteroatom substitution was employed for the first time to study the acceptor variation effects on the optical, electrochemical, molecular assembling, and charge-transport properties of novel semiconducting polymers containing benzobisthiadiazole (BBT)-related heterocycles, namely, poly­(dithiazolfluorene-<i>alt</i>-thiadiazolo­benzotriazole) (PSN), poly­(dithiazolfluorene-<i>alt</i>-selenadiazolo­benzotriazole) (PSeN), and poly­(dithiazol­fluorene-<i>alt</i>-selenadiazolo­benzothiadiazole) (PSeS). The effect of the heteroatom substitution was clearly shown in the UV–vis–NIR absorption spectra in which the substitution of the sulfur (S) and/or nitrogen (N) atoms in PSN with the selenium (Se) and sulfur (S) atoms led to a red-shift in the absorption profile. In addition, the energy levels of these polymers, determined from cyclic voltammetry (CV) measurements and density functional theory (DFT) calculations, also varied due to the hetroatom substitution effect. Accordingly, thin film transistors (TFTs) based on these polymers showed different charge transport properties. For example, PSN displayed p<i>-</i>type unipolar performances with a high hole mobility up to 0.65 cm² V^–1 s^–1. In contrast, PSeS showed n-type dominant charge transport properties with an electron mobility up to 0.087 cm² V^–1 s^–1. Intriguingly, PSeN exhibited ambipolar charge transport properties with balanced μ_h and μ_e values. These different charge polarities in the TFTs were correlated to the energy levels, π–π stacking distances, and polymer crystallinities evaluated by their grazing-incidence wide-angle X-ray scattering (GIWAXS) patterns and atomic force microscopy (AFM) images. We believe that this simple and effective approach will guide the way to developing high-performance ambipolar and/or n-channel semiconducting polymers for TFTs

Ionic Liquid-Based Electrolytes Containing Surface-Functionalized Inorganic Nanofibers for Quasisolid Lithium Batteries

In the present study, surface amino-functionalized silica nanofibers (<i>f</i>-SiO₂NFs, average diameter = 400 and 1000 nm) are used as one-dimensional (1-D) fillers of ionic liquid (IL)-based quasisolid electrolytes. On adding <i>f</i>-SiO₂NFs to an IL (1-ethyl-3-methylimidazolium bis­(trifluoromethanesulfonyl)­amide, EMITFSA) containing lithium bis­(trifluoromethanesulfonyl)-amide (LiTFSA), the well-dispersed 1-D nanofillers easily form a three-dimensional network structure in the IL, function as physical cross-linkers, and increase the viscosity of the composites, consequently providing a quasisolid state at a 3.5 wt % fraction of the NFs. Rheological measurements demonstrate that the prepared composites exhibit “gel-like” characteristics at 40–150 °C. All prepared composites show high ionic conductivities, on the order of 10^–3 S cm^–1, around room temperature. To investigate the additive effect of <i>f</i>-SiO₂NFs in the composites, the lithium transference numbers are also evaluated. It is found that thinner NFs enhance the transference numbers of the composites. In addition, quasisolid lithium-ion cells containing the prepared composites demonstrate relatively high rate characteristics and good cycling performance at high temperature (125 °C)

Electrospun Composite Nanofiber Yarns Containing Oriented Graphene Nanoribbons

The graphene nanoribbon (GNR)/carbon composite nanofiber yarns were prepared by electrospinning from poly­(acrylonitrile) (PAN) containing graphene oxide nanoribbons (GONRs), and successive twisting and carbonization. The electrospinning process can exert directional shear force coupling with the external electric field to the flow of the spinning solution. During electrospinning, the well-dispersed GONRs were highly oriented along the fiber axis in an electrified thin liquid jet. The addition of GONRs at a low weight fraction significantly improved the mechanical properties of the composite nanofiber yarns. In addition, the carbonization of the matrix polymer enhanced not only the mechanical but also the electrical properties of the composites. The electrical conductivity of the carbonized composite yarns containing 0.5 wt % GONR showed the maximum value of 165 S cm^–1. It is larger than the maximum value of the reported electrospun carbon composite yarns. Interestingly, it is higher than the conductivities of both the PAN-based pristine CNF yarns (77 S cm^–1) and the monolayer GNRs (54 S cm^–1). These results and Raman spectroscopy supported the hypothesis that the oriented GONRs contained in the PAN nanofibers effectively functioned as not only the 1-D nanofiller but also the nanoplatelet promoter of stabilization and template agent for the carbonization