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Publications (51)
Photothermal conversion using plasmonic nanomaterials for
reversible epoxies based on the Diels-Alder reaction is a promising
approach for targeted self-healing materials and recyclable 3D
printing materials. In the presentation, reversible epoxies was
synthesized and their recycle processes were studied. Recycle
processes were carried out by a the...
Additive manufacturing of thermoset is attractive due to their superior stiffness, chemical resistance, and thermal stability. However, the slow curing rate of thermoset such as epoxy poses challenge in layer by layer printing. Traditionally, photoinitiators are incorporated in epoxy to enhance the curing rate using UV light. However, photo initiat...
We used FTIR and 1H-NMR to confirm that the predominant side reaction near and above the retro Diels-Alder temperatures was due to maleimide homopolymerization. Then, we explored strategies to minimize the maleimide homopolymerization, including: reduced maleimide concentration, use of a free radical inhibitor, and functionalization of maleimides o...
We studied the effect of side reactions on the reversibility of epoxy with thermoreversible Diels–Alder (DA) cycloadducts based on furan and maleimide chemistry. The most common side reaction is the maleimide homopolymerization which introduces irreversible crosslinking in the network adversely affecting the recyclability. The main challenge is tha...
Non-fullerene acceptor-based polymer solar cells (NFA-PSCs) can exhibit high morphological stability under thermal stress, often resulting in the fabrication of thermally stable NFA-PSCs. Here, our stability study with systematic steps shows that high morphological stability of active layers does not necessarily guarantee high thermal stability for...
Thermoset epoxy polymers are non-recyclable due to their irreversible crosslinked structure. We develop thermally reversible epoxies by incorporating dynamic covalent bonds like diene-dienophile linkages initiating Diels’ Alder reaction chemistry. However, the lack of localized heating precision and low thermal conductivity of epoxies can make the...
The relationship between Kuhn length lk, Kuhn monomer volume v0, and plateau modulus GN⁰, initially proposed by Graessley and Edwards for flexible polymers, and extended by Everaers, has a large gap in experimental data between the flexible and stiff regimes. This gap prevents the prediction of mechanical properties from the chain structure for any...
Rheology, DSC, and drop tests of thermally reversible Diels-Alder polymers were detailed, which were synthesized using a bismaleimide and tetra- and hexa-furan functionalized polyetheramines. These were further modified with a TiN nanoparticles, which strongly absorb visible light.
A block copolymer with discotic liquid crystalline behavior was synthesized using Grignard metathesis polymerization (GRIM) and initiators for continuous activator regeneration atom transfer radical polymerization (ICAR-ATRP). A novel discotic liquid crystalline mesogen, 6-(pyren-1-yloxy)hexyl methacrylate (PyMA), comprises a block that is attached...
The glass transition temperature (Tg) is a key property that dictates the applicability of conjugated polymers. The Tg demarks the transition into a brittle glassy state, making its accurate prediction for conjugated polymers crucial for the design of soft, stretchable, or flexible electronics. Here we show that a single adjustable parameter can be...
Fully conjugated donor-acceptor block copolymers can serve as the active layer in organic photovoltaics and other organic electronic devices. Self-assembly into periodic domains and crystallization of the constituent blocks are crucial to enable control of the multiscale structure and consequently electronic properties. Resonant soft X-ray scatteri...
Synthesis of two conducting polymers containing 3‐hexylthiophene and 3‐[2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy]thiophene is demonstrated. In thin‐film transistors, the high‐molecular‐weight polymer shows an average mobility of 4.2 × 10−4 cm2 V−1 s−1. Most importantly, the polymers have high conductivity upon doping with iodine and also have high stabi...
Fully conjugated donor–acceptor block copolymers are established as model systems to elucidate fundamental mechanisms of photocurrent generation in organic photovoltaics. Using analysis of steady‐state photoluminescence quenching, exciton dissociation to a charge transfer state within individual block copolymer chains is quantified. By making a sma...
Despite significant recent progress, much about the mechanism for charge photogeneration in organic photovoltaics remains unknown. Here, we use conjugated block copolymers as model systems to examine the effects of energetic and entropic driving forces in organic donor-acceptor materials. The block copolymers are designed such that an electron dono...
Resonant soft x-ray scattering (RSoXS) leverages chemical specificity to characterize thin films but is limited near the nitrogen edge. The challenge is that commercially available x-ray transparent substrates are composed of Si3N4 and thereby absorb incident x-rays and generate incoherent fluorescence. To overcome this challenge, we designed and f...
Recently, small molecule non-fullerene acceptors have been rapidly developed and are now being incorporated in the top-performing organic photovoltaic devices. These non-fullerene acceptors typically consist of ~ 10 aromatic rings arranged in an alternating electron-rich/electron-deficient architecture reminiscent of push-pull polymers, making them...
Despite tremendous progress in using additives to enhance the power conversion efficiency of organic photovoltaic devices, significant challenges remain in controlling the microstructure of the active layer, such as at internal donor–acceptor interfaces. Here, we demonstrate that the addition of low molecular weight poly(3-hexylthiophene)s (low-MW...
Triplet population dynamics of solution cast films of isolated polymorphs of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pn) provide quantitative experimental evidence that triplet excitation energy transfer is the dominant mechanism for correlated triplet pair (CTP) separation during singlet fission. Variations in CTP separation rates are c...
Conjugated block copolymers simultaneously control the mesoscale morphology and interfacial structure of the active layer in organic electronic devices. Fully conjugated block copolymers, where both backbones are conjugated, are commonly synthesized in two steps. First, poly(3-alkylthiophene-2,5-diyl) (P3HT) is synthesized by Kumada catalyst transf...
The stiff backbones of conjugated polymers can lead to a rich phase behavior that includes both crystalline and liquid crystalline phases, making measurements of the glass transition challenging. In this work, the glass transitions of regioregular poly(3-hexylthiophene-2,5-diyl) (RR P3HT), regiorandom (RRa) P3HT, and poly((9,9-bis(2-octyl)-fluorene...
Fluorinating conjugated polymers is a proven strategy for creating high performance materials in polymer solar cells, yet few studies investigated the importance of the fluorination method. We compare the performance of three fluorinated systems: a poly(benzodithieno-dithienyltriazole) (PBnDT-XTAZ) random copolymer where 50% of the acceptor units a...
The control of the bulk-heterojunction (BHJ) morphology in polymer/polymer blends remains a critical hurdle for optimizing all-polymer solar cells (all-PSCs). The relationship between donor/acceptor phase separation, domain size, and the resulting photovoltaic characteristics of PDFQx3T and P(NDI2OD-T2)-based all-PSCs was investigated. We varied th...
The electronic properties of organic semiconductors are strongly influenced by intermolecular packing. When cast as thin films, crystalline π-conjugated molecules are strongly textured, potentially leading to anisotropic charge transport. Consequently, it is hypothesized that the orientation of crystallites in the active layer plays an important ro...
We investigate the influence that covalent linkage of electron donating and accepting blocks in high performance fully conjugated block copolymer photovoltaics has on charge generation and recombination using ultrafast mid-infrared transient absorption spectroscopy. We show that block copolymer architectures containing a conjugated bridge between t...
Solvent vapor annealing treatments are used to control the orientation of nanostructures produced in thin films of a poly(styrene)-block-poly(isoprene)-block-poly(styrene)-block-poly((±)-lactide) (PS-PI-PS-PLA) and its blends with PLA homopolymer. The PS-PI-PS-PLA tetrablock terpolymer, previously determined to adopt a core(PLA)-shell(PS) cylindric...
Fully conjugated block copolymers that covalently link donor and acceptor units within the molecular structure have the potential to simultaneously control the mesoscale assembly and interfacial structure. As a consequence, utilizing block copolymers as the active layer provides a unique opportunity to tune charge and energy transfer processes whil...
Improving the performance of organic electronic devices depends on exploiting the complex nanostructures formed in the active layer. Current imaging methods based on transmission electron microscopy provide limited chemical sensitivity, and thus the application to materials with compositionally similar phases or complicated multicomponent systems i...
All-conjugated block copolymers bring together hole- and electron-conductive polymers and can be used as the active layer of solution-processed photovoltaic devices, but it remains unclear how molecular structure, morphology, and electronic properties influence performance. Here, the role of the chemical linker is investigated through analysis of t...
Nanoporous poly(styrene)-b-poly(isoprene)-b-poly(styrene) (PS–PI–PS) was prepared from PS–PI–PS–PLA (PLA = poly(d,l-lactide)) tetrablock terpolymer precursors. Hydroxy end-functionalized PS–PI–PS was synthesized by sequential anionic polymerizations and used to initiate the ring-opening polymerization of d,l-lactide. A combination of small-angle X-...
Renewable ABA triblock copolymers were prepared by sequential polymerization of the plant-based monomers menthide and α-methylene-γ-butyrolactone (MBL or tulipalin A). Ring-opening transesterification polymerization of menthide using diethylene glycol as an initiator gave α,ω-dihydroxy poly(menthide) (HO-PM-OH), which was converted to α,ω-dibromo e...
Star-shaped polystyrene-block-poly(methyl methacrylate) copolymer
(PS-b-PMMA) was synthesized by utilizing α-cyclodextrin
(α-CD) as a junction point of the star-shaped block copolymer.
Eighteen hydroxyl groups on α-CD were substituted with bromine by
the reaction with α-bromoisobutyryl bromide for atom transfer
radical polymerization. We found that...
Block copolymers have received considerable attention as a promising platform for the synthesis of nanomaterials and fabrication of nanostructures because of their self-assembling nature to form periodically ordered structures in the nanometer-scale range. By controlling the composition and architecture of individual block components, a variety of...
Photovoltaic devices of end-functionalgroup-modified poly 3-(hexylthiophene)/ [6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM; see figure) are fabricated with thermal annealing. The surface energies between donor and acceptor were matched by varying the end group, which can be used to control vertical and horizontal phase separation in the ac...
We synthesized coil-rod-coil triblock copolymers composed of regioregular poly(3-hexyl thiopene) (P3HT) block via anionic coupling reaction. Two different coil blocks (poly(2-vinyl pyridine) (P2VP) and polyisoprene (PI)) were selected. P2VP-b- P3HT-b-P2VP copolymer was synthesized in a polar solvent of tetrahydrofurane, while PI-b-P3HT-b-PI copolym...
We investigated the effects of microstructural (crystallization and molecular orientation) and morphological alternation (grain boundary) of poly(3-hexylthiophene) (P3HT) films on the field-effect mobility (mu) before (as-spun P3HT) and after (melt-crystallized P3HT) melting of P3HT films. Although grazing incidence X-ray scattering shows that melt...
We introduced a facile synthetic strategy of coil−rod−coil triblock copolymers containing regioregular poly(3-hexylthiophene) (P3HT) block via anionic coupling reaction. Two different coil blocks (poly(2-vinylpyridine) (P2VP) and polyisoprene (PI)) were selected. P2VP-b-P3HT-b-P2VP copolymer was synthesized in a polar solvent of tetrahydrofuran, wh...
Phase diagrams of blends consisting of poly(3-n-alkylthiopene) having four different n-alkyl side chain lengths (n = 4, 6, 8,12) and polystyrene (PS) were obtained by turbidity measurement. All of the P3AT/PS blends employed in this study exhibited the upper critical solution temperature (UCST) type phase behavior. From n=4 [poly(3-butylthipene)] t...
A study was conducted to investigate the occurrence of side reactions during the synthesis of well defined poly(3-hexythiophene) (P3HT) microinitiators, using standard procedures. The study also demonstrated the preparation of high purity macroinitiators and P3HT-block-polymethylacrylate copolymers (P3HT-b-PMA). 2,5-dibromo-3-HT was synthesized by...
An antireflection film was prepared by spin-coating of poly(methyl methacrylate) (PMMA) solution in chloroform in the presence of small amounts of nonsolvent alkanes. When the vapor pressure of a nonsolvent was lower than that of chloroform, a dense skin layer was formed because of the rapid solvent evaporation during spin-coating, whereas increasi...
