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Synthesizing polystyrene-block-poly(vinyl alcohol) (PS-b-PVA) via controlled radical polymerization of vinyl acetate, the traditional precursor to polyvinyl alcohol (PVA), is challenging due to the reactivity of the unconjugated α-acetoxy radical. We report the synthesis and characterization of PS-b-PVA block copolymers (BCPs) with tailorable PVA block lengths via RAFT polymerization of an alternative precursor, an aromatic organoborane comonomer BN 2-vinylnapthalene (BN2VN). RAFT homopolymerization of BN2VN (RB) using 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT) is described. Solid-state NMR, ATR-IR, SEC and thermogravimetric analysis reveal significant differences between PS-b-PVA and RS-b-RB. The fate of the trithiocarbonate end-group during oxidative conversion of the C–B side chain to a C–OH side chain was studied; while a hydrated aldehyde (e.g., gem-diol) was hypothesized, conclusive evidence was not found. 

We investigated the enhanced vapor responses and altered response ratios of a series of thiophene (co)polymers with oxygenated side chains (CH 2 OH, linear polyethylene glycol, and crown ether), including the novel poly(3-hydroxymethylthiophene) (PTOH) and other newly synthesized polymers. Hydroxymethyl-containing copolymers had higher mobility compared to poly(3-hexylthiophene) (P3HT). The larger crown ether moiety promotes transistor characteristics of P3HT while the smaller one impairs them. Incorporating different oxygen bearing functionalities increased responses of thiophene polymers to NO 2 , NH 3 , and acetone. For example a polyether side chain increases the NO 2 response sensitivity of copolymers of both P3HT and PTOH, but sensitivity towards gas analytes was more prominent for glycol-based functionalities rather than the crown ethers. PTOH is very sensitive to NO 2 and the response likely includes a contribution from conductive protons on the OH group. The lack of correlation among the rank-ordered gas sensitivities imparted by each functional group was found to be useful for designing a selective sensor array. We specifically showed high classification accuracy for all the polymer responses to NO 2 and acetone vapors, both of which gave increased device currents but with response ratios different enough to allow highly classifying discriminant functions to be derived. 

Polythiophenes with differently functionalized side chains (alkyl, oligoethylene oxide, ester, hydroxy, and carboxylic acid) and varied counterions of potassium salt electrolytes were investigated in organic electrochemical transistors (OECTs). In addition, mixed blends were investigated to evaluate any synergistic effects between functionalities. Depending on the functional moiety attached, a large shift to lower potentials of Vth, an increase in drain current, and increase in transconductance can be observed compared to the base combination of alkyl side chain and Cl-. The newly designed and synthesized hydroxy polymer displayed stability to large shifts in VTH, slight increase in drain current, and little or no increase in transconductance when an ionic radius of the dopant is increased until a much larger anion, large polarizability, and low hydration number such as TSFI- was used. The acid-functionalized polymer, on the other hand had the same magnitude in shift with respect to any anion that is larger than Cl-. The polymers were characterized by spectroscopy, x-ray diffraction, thermal analysis, and cyclic voltammetry. This work demonstrates that side-chain engineering can have substantial difference in the level of interaction in the electrolyte which would require tailoring the ion for specific polymer interactions. 

Organic electronics offer a route toward electronically active biocompatible soft materials capable of interfacing with biological and living systems. One class of promising organic electronic materials are π-conjugated peptides, synthetic molecules comprising an aromatic core flanked by oligopeptides, that can be engineered to self-assemble into elongated nanostructures with emergent optoelectronic functionality. In this work, we combine molecular dynamics simulations with electronic structure and charge transport calculations to computationally screen for high charge mobility π-conjugated peptides and to elucidate design rules linking aromatic core character with charge mobility. We consider within our screening library variations in the aromatic core chemistry and length of the alkyl chains connecting the oligopeptide wings to the core. After completing our computational screen we identify particular π-conjugated peptides capable of producing self-assembled biocompatible nanoaggregates with predicted hole mobilities of 0.224 cm^2/(Vs) and electron mobilities of 0.143 cm^2/(Vs), and uncover design rules that enhance understanding of the molecular determinants of charge mobility within π-conjugated peptide assemblies. 

This paper reports a new mechanism for particulate matter detection and identification. Three types of carbon particles are synthesized with different functional groups to mimic the real particulates in atmospheric aerosol. After exposing polymer‐based organic devices in organic field effect transistor (OFET) architectures to the particle mist, the sensitivity and selectivity of the detection of different types of particles are shown by the current changes extracted from the transfer curves. The results indicate that the sensitivity of the devices is related to the structure and functional groups of the organic semiconducting layers, as well as the morphology. The predominant response is simulated by a model that yielded values of charge carrier density increase and charge carriers delivered per unit mass of particles. The research points out that polymer semiconductor devices have the ability to selectively detect particles with multiple functional groups, which reveals a future direction for selective detection of particulate matter.

 

The improvement of conjugated polymer-based gas sensors involves fine tuning the backbone electronic structure and solid-state microstructure to combine high stability and sensitivity. We had previously developed a series of diketopyrrolopyrrole (DPP)-based polymer semiconductors by introducing a variety of fluorene linkers to study the trends and mechanisms governing gas sensitivities and electronic stability in air and under gate and drain bias stress. The proportional on-current change of organic field-effect transistors (OFETs) using a dithienyl DPP–fluorene polymer reached ∼600% for a sequential exposure from 0.5–20 ppm of NO 2 for 5 minutes and also a high response-to-drift ratio under dynamic bias stress. In the present work we specify the roles of static bias stress and traps in the sensing process for the first time. Apart from electronic structure, defects at the molecular and microstructural levels govern the ability to form and sustain traps and subsequent backbone dopability. A polymer with a twisted backbone was observed to be capable of creating an energetically broad trap distribution while a polymer with a high degree of solid-state order shows a tendency to form an energetically narrow trap distribution and a fast passivation of traps on exposure to air. The stability and energetic distribution of traps on subjecting the polymers to bias stress was related to electronic structure and solid-state packing; and the ability of NO 2 and NH 3 to fill/create traps further was evaluated. At a bias stress condition of V G = V D = −80 V, the polymers retain their NO 2 sensitivity both post NO 2 -aided recovery and air-aided recovery. In order to verify the ability of NH 3 to create traps, traps were erased from the OFET sensors by charging with the aid of a positive gate voltage leading to an increase in the NH 3 response when compared to air controls. This work demonstrates that the charge-trap filling and generation response mechanism is predominant and can even be leveraged for higher responses to vapors. Backbone dopability appears to be a minor contributor to responses in this category of polymeric semiconductors with engineered defects. Finally, bias stress generally does not preclude this category of OFET vapor sensors from recovering their original sensitivities.