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Yu B, Li R, Segalman RA. Tuning the Double Gyroid Phase Window in Block Copolymers via Polymer Chain Conformation Near the Interface. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c00048] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Jiao S, DeStefano A, Monroe JI, Barry M, Sherck N, Casey T, Segalman RA, Han S, Shell MS. Quantifying Polypeptoid Conformational Landscapes through Integrated Experiment and Simulation. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c00550] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Segalman RA, Doherty MF. Introduction. Annu Rev Chem Biomol Eng 2021; 12:i-ii. [PMID: 34097847 DOI: 10.1146/annurev-ch-12-033021-100001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Oh S, Nikolaev A, Tagami K, Tran T, Lee D, Mukherjee S, Segalman RA, Han S, Read de Alaniz J, Chabinyc ML. Redox-Active Polymeric Ionic Liquids with Pendant N-Substituted Phenothiazine. ACS APPLIED MATERIALS & INTERFACES 2021; 13:5319-5326. [PMID: 33480673 DOI: 10.1021/acsami.0c20462] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Polymers that are elastic while supporting charge transport are desirable for flexible and soft electronics. Many polymers with bulky and conjugated redox-active pendant units have high glass transition temperatures (Tg) in their neutral form that will not lead to elasticity at room temperature. Their behavior in charged form in the solid state without an electrolyte has not been extensively studied. Here, the design strategy of polymeric ionic liquid where two weakly interacting ionic groups are used to maintain a low Tg is shown to lead to flexible redox active polymers. The use of a flexible ethylene backbone and redox-active phenothiazine (PTZ)-based pendant group resulted in polymers with relatively low Tg that are electrically conductive. PTZ that was N-substituted with 2-(2-ethoxyethoxy)ethoxy)ethyl was found to promote solubility of the polymer and lower the Tg of the neutral polymer by ∼150 °C relative to that of the Tg of a variant without the N-substituent. Doping with trifluoromethanesulfonimide leads to an electrically conductive polymer without significantly increasing the Tg. Physical characterization by UV-vis-NIR spectroscopy, electron spin resonance spectroscopy, and impedance spectroscopy verified that the molecular design leads to an efficient charge hopping between the PTZ groups.
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Nie H, Schauser NS, Self JL, Tabassum T, Oh S, Geng Z, Jones SD, Zayas MS, Reynolds VG, Chabinyc ML, Hawker CJ, Han S, Bates CM, Segalman RA, Read de Alaniz J. Light-Switchable and Self-Healable Polymer Electrolytes Based on Dynamic Diarylethene and Metal-Ion Coordination. J Am Chem Soc 2021; 143:1562-1569. [PMID: 33439016 DOI: 10.1021/jacs.0c11894] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Self-healing polymer electrolytes are reported with light-switchable conductivity based on dynamic N-donor ligand-containing diarylethene (DAE) and multivalent Ni2+ metal-ion coordination. Specifically, a polystyrene polymer grafted with poly(ethylene glycol-r-DAE)acrylate copolymer side chains was effectively cross-linked with nickel(II) bis(trifluoromethanesulfonimide) (Ni(TFSI)2) salts to form a dynamic network capable of self-healing with fast exchange kinetics under mild conditions. Furthermore, as a photoswitching compound, the DAE undergoes a reversible structural and electronic rearrangement that changes the binding strength of the DAE-Ni2+ complex under irradiation. This can be observed in the DAE-containing polymer electrolyte where irradiation with UV light triggers an increase in the resistance of solid films, which can be recovered with subsequent visible light irradiation. The increase in resistance under UV light irradiation indicates a decrease in ion mobility after photoswitching, which is consistent with the stronger binding strength of ring-closed DAE isomers with Ni2+. 1H-15N heteronuclear multiple-bond correlation nuclear magnetic resonance (HMBC NMR) spectroscopy, continuous wave electron paramagnetic resonance (cw EPR) spectroscopy, and density functional theory (DFT) calculations confirm the increase in binding strength between ring-closed DAE with metals. Rheological and in situ ion conductivity measurements show that these polymer electrolytes efficiently heal to recover their mechanical properties and ion conductivity after damage, illustrating potential applications in smart electronics.
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Schauser NS, Nikolaev A, Richardson PM, Xie S, Johnson K, Susca EM, Wang H, Seshadri R, Clément R, Read de Alaniz J, Segalman RA. Glass Transition Temperature and Ion Binding Determine Conductivity and Lithium-Ion Transport in Polymer Electrolytes. ACS Macro Lett 2021; 10:104-109. [PMID: 35548991 DOI: 10.1021/acsmacrolett.0c00788] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Polymer electrolytes with high Li+-ion conductivity provide a route toward improved safety and performance of Li+-ion batteries. However, most polymer electrolytes suffer from low ionic conduction and an even lower Li+-ion contribution to the conductivity (the transport number, t+), with the anion typically transporting over 80% of the charge. Here, we show that subtle and potentially undetected associations within a polymer electrolyte can entrain both the anion and the cation. When removed, the conductivity performance of the electrolyte can be improved by almost 2 orders of magnitude. Importantly, while some of this improvement can be attributed to a decreased glass transition temperature, Tg, the removal of the amide functional group reduces interactions between the polymer and the Li+ cations, doubling the Li+ t+ to 0.43, as measured using pulsed-field-gradient NMR. This work highlights the importance of strategic synthetic design and emphasizes the dual role of Tg and ion binding for the development of polymer electrolytes with increased total ionic conductivity and the Li+ ion contribution to it.
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Moon JD, Sujanani R, Geng Z, Freeman BD, Segalman RA, Hawker CJ. Versatile Synthetic Platform for Polymer Membrane Libraries Using Functional Networks. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02414] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Nie H, Schauser NS, Dolinski ND, Geng Z, Oh S, Chabinyc ML, Hawker CJ, Segalman RA, Read de Alaniz J. The role of anions in light-driven conductivity in diarylethene-containing polymeric ionic liquids. Polym Chem 2021. [DOI: 10.1039/d0py01603a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The role of anion character in the photostationary state, magnitude of conductivity, and light-responsive properties of diarylethene-containing polymeric ionic liquids was investigated.
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Jones SD, Schauser NS, Fredrickson GH, Segalman RA. The Role of Polymer–Ion Interaction Strength on the Viscoelasticity and Conductivity of Solvent-Free Polymer Electrolytes. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c02233] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Sherck N, Webber T, Brown DR, Keller T, Barry M, DeStefano A, Jiao S, Segalman RA, Fredrickson GH, Shell MS, Han S. End-to-End Distance Probability Distributions of Dilute Poly(ethylene oxide) in Aqueous Solution. J Am Chem Soc 2020; 142:19631-19641. [DOI: 10.1021/jacs.0c08709] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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Moon JD, Freeman BD, Hawker CJ, Segalman RA. Can Self-Assembly Address the Permeability/Selectivity Trade-Offs in Polymer Membranes? Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01111] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Yu B, Danielsen SPO, Yang KC, Ho RM, Walker LM, Segalman RA. Insensitivity of Sterically Defined Helical Chain Conformations to Solvent Quality in Dilute Solution. ACS Macro Lett 2020; 9:849-854. [PMID: 35648517 DOI: 10.1021/acsmacrolett.0c00293] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The interplay between polymer-polymer and polymer-solvent interactions as well as interactions that impose secondary structures determines the conformation of polymer chains in dilute solution. Polypeptoids-poly(N-substituted glycines) have been shown to form helical secondary structures primarily driven by steric interactions from chiral, bulky side chains, while polypeptoids with a racemic mixture of the same side chains lead to unstructured coil chains with a shorter Kuhn length. Small-angle neutron scattering (SANS) of the polypeptoids in dilute solution reveals that the helical polypeptoids are only locally stiffer than the coil chains formed from the racemic analogue, but exhibit overall flexibility. We show that chain conformations of both helical and coil polypeptoids (in terms of radius of gyration, Rg) are insensitive to solvent quality (parametrized by the second virial coefficient, A2). Potential effects from the bulky, chiral/racemic side chains dominating chain conformations are excluded by comparison with an achiral polypeptoid lacking side chain chirality. The specific interactions between polypeptoid segments are likely dominating the chain conformations in this type of polypeptoids as opposed to polymer-solvent interactions or energetic contributions from the helical secondary structure.
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Geng Z, Schauser NS, Lee J, Schmeller RP, Barbon SM, Segalman RA, Lynd NA, Hawker CJ. Role of Side-Chain Architecture in Poly(ethylene oxide)-Based Copolymers. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01116] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Sahu A, Russ B, Liu M, Yang F, Zaia EW, Gordon MP, Forster JD, Zhang YQ, Scott MC, Persson KA, Coates NE, Segalman RA, Urban JJ. In-situ resonant band engineering of solution-processed semiconductors generates high performance n-type thermoelectric nano-inks. Nat Commun 2020; 11:2069. [PMID: 32350274 PMCID: PMC7190739 DOI: 10.1038/s41467-020-15933-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2019] [Accepted: 04/01/2020] [Indexed: 11/25/2022] Open
Abstract
Thermoelectric devices possess enormous potential to reshape the global energy landscape by converting waste heat into electricity, yet their commercial implementation has been limited by their high cost to output power ratio. No single “champion” thermoelectric material exists due to a broad range of material-dependent thermal and electrical property optimization challenges. While the advent of nanostructuring provided a general design paradigm for reducing material thermal conductivities, there exists no analogous strategy for homogeneous, precise doping of materials. Here, we demonstrate a nanoscale interface-engineering approach that harnesses the large chemically accessible surface areas of nanomaterials to yield massive, finely-controlled, and stable changes in the Seebeck coefficient, switching a poor nonconventional p-type thermoelectric material, tellurium, into a robust n-type material exhibiting stable properties over months of testing. These remodeled, n-type nanowires display extremely high power factors (~500 µW m−1K−2) that are orders of magnitude higher than their bulk p-type counterparts. The design of solution-processed thermoelectric nanomaterials with efficient, stable performance remains a challenge. Here, the authors report an in-situ doping method based on nanoscale interface engineering to realize n-type thermoelectric nanowires with high performance and stability.
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Patterson AL, Yu B, Danielsen SPO, Davidson EC, Fredrickson GH, Segalman RA. Monomer Sequence Effects on Interfacial Width and Mixing in Self-Assembled Diblock Copolymers. Macromolecules 2020. [DOI: 10.1021/acs.macromol.9b02426] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Schauser NS, Grzetic DJ, Tabassum T, Kliegle GA, Le ML, Susca EM, Antoine S, Keller TJ, Delaney KT, Han S, Seshadri R, Fredrickson GH, Segalman RA. The Role of Backbone Polarity on Aggregation and Conduction of Ions in Polymer Electrolytes. J Am Chem Soc 2020; 142:7055-7065. [DOI: 10.1021/jacs.0c00587] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Nie H, Schauser NS, Dolinski ND, Hu J, Hawker CJ, Segalman RA, Read de Alaniz J. Light-Controllable Ionic Conductivity in a Polymeric Ionic Liquid. Angew Chem Int Ed Engl 2020; 59:5123-5128. [PMID: 31925869 DOI: 10.1002/anie.201912921] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 01/05/2020] [Indexed: 01/17/2023]
Abstract
Polymeric ionic liquids (PILs) have attracted considerable attention as electrolytes with high stability and mechanical durability. Light-responsive materials are enabling for a variety of future technologies owing to their remote and noninvasive manipulation, spatiotemporal control, and low environmental impact. To address this potential, responsive PIL materials based on diarylethene units were designed to undergo light-mediated conductivity changes. Key to this modulation is tuning of the cationic character of the imidazolium bridging unit upon photoswitching. Irradiation of these materials with UV light triggers a circa 70 % drop in conductivity in the solid state that can be recovered upon subsequent irradiation with visible light. This light-responsive ionic conductivity enables spatiotemporal and reversible patterning of PIL films using light. This modulation of ionic conductivity allows for the development of light-controlled electrical circuits and wearable photodetectors.
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Nie H, Schauser NS, Dolinski ND, Hu J, Hawker CJ, Segalman RA, Read de Alaniz J. Light‐Controllable Ionic Conductivity in a Polymeric Ionic Liquid. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201912921] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Danielsen SPO, Davidson EC, Fredrickson GH, Segalman RA. Absence of Electrostatic Rigidity in Conjugated Polyelectrolytes with Pendant Charges. ACS Macro Lett 2019; 8:1147-1152. [PMID: 35619444 DOI: 10.1021/acsmacrolett.9b00551] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The delocalization of electrons in conjugated polymers impacts their chain shape, affecting their local ordering, self-assembly, and ultimately charge transport. Conjugated polyelectrolytes introduce electrostatic interactions as a molecular design parameter to potentially tune chain rigidity by combining the π-conjugated polymer backbone with pendant ionic groups. In conventional polyelectrolytes, the self-repulsion of the bound charges induce extended rod-like chain configurations. Here, we leverage small-angle neutron scattering to measure the chain shapes of model conjugated polymers in dilute solution with controlled fractions of randomly distributed pendant charges. We find these model polythiophenes are semiflexible, with a persistence length of approximately 3 nm, regardless of charge fraction, suggesting the effective absence of electrostatic rigidity in conjugated polyelectrolytes. While the overall persistence length is negligibly impacted by pendant charges, optical spectroscopy indicates that the pendant charges increase the backbone torsion between thiophene rings without significantly impacting the π-conjugation length (the length of electron delocalization along a nearly planar backbone) in dilute solution. These results indicate the effective decoupling of the pendant ionic charges from the overall chain conformation with implications for solution processing of organic semiconductors.
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Zhang Y, D'Ambra CA, Katsumata R, Burns RL, Somervell MH, Segalman RA, Hawker CJ, Bates CM. Rapid and Selective Deposition of Patterned Thin Films on Heterogeneous Substrates via Spin Coating. ACS APPLIED MATERIALS & INTERFACES 2019; 11:21177-21183. [PMID: 31117458 DOI: 10.1021/acsami.9b05190] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The selective deposition of polymer thin films can be achieved via spin coating by manipulating interfacial interactions. While this "spin dewetting" approach sometimes generates spatial localization on topographic and chemical patterns, the connection between material selection, process parameters, and resulting film characteristics remains poorly understood. Here, we demonstrate that accurate control over these parameters allows incomplete trichlorosilane self-assembled monolayers (SAMs) to induce spin dewetting on both homogeneous (SiO2) and heterogeneous (Cu/SiO2 or TiN/SiO2) surfaces. Glassy polymers undergo a sharp transition from uniform wetting to complete dewetting depending on spin speed, solution concentration, polymer molecular weight, and SAM chemistry. Under optimal conditions, spin dewetting on line-space patterns results in the selective deposition of polymer over regions not functionalized with SAM. The insights described herein clarify the importance of different variables involved in spin dewetting and provide access to a versatile strategy for patterning polymeric thin films.
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Yu B, Danielsen SPO, Patterson AL, Davidson EC, Segalman RA. Effects of Helical Chain Shape on Lamellae-Forming Block Copolymer Self-Assembly. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b00211] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Mazaheripour A, Thomas EM, Segalman RA, Chabinyc ML. Nonaggregating Doped Polymers Based on Poly(3,4-Propylenedioxythiophene). Macromolecules 2019. [DOI: 10.1021/acs.macromol.8b02389] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Patterson AL, Danielsen SPO, Yu B, Davidson EC, Fredrickson GH, Segalman RA. Sequence Effects on Block Copolymer Self-Assembly through Tuning Chain Conformation and Segregation Strength Utilizing Sequence-Defined Polypeptoids. Macromolecules 2019. [DOI: 10.1021/acs.macromol.8b02298] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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Danielsen SPO, Nguyen TQ, Fredrickson GH, Segalman RA. Complexation of a Conjugated Polyelectrolyte and Impact on Optoelectronic Properties. ACS Macro Lett 2019; 8:88-94. [PMID: 35619414 DOI: 10.1021/acsmacrolett.8b00924] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Electrostatic assembly of conjugated polyelectrolytes, which combine a π-conjugated polymer backbone with pendant ionic groups, offer an opportunity for tuning materials properties and a new route for formulating concentrated inks for printable electronics. Complex coacervation, a liquid-liquid phase separation upon complexation of oppositely charged polyelectrolytes in solution, is used to form dense suspensions of π-conjugated material. A model system of a cationic conjugated polyelectrolyte poly(3-[6'-{N-butylimidazolium}hexyl]thiophene) bromide and sodium poly(styrenesulfonate) dissolved in tetrahydrofuran-water mixtures was used to investigate this complexation behavior of conjugated polyelectrolytes in terms of electrostatic strength, solvent quality, and polymer concentration. The balance of electrostatic interaction between the oppositely charged polyelectrolytes together with their charge compensating counterions and solvent quality for the hydrophobic π-conjugated backbone leads to a rich phase diagram of soluble complexes, precipitates, and complex coacervates. The conjugated polyelectrolyte in the polyelectrolyte complexes has an increased π-conjugation length and enhanced emissivity, with ideal chain configurations due to the reduction of kink sites and torsional disorder. The advantageous photophysical properties in the dense liquid phases makes the scheme attractive for the large-scale processing of optoelectronic devices, chemical sensors, and bioelectronics components.
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Thomas EM, Davidson EC, Katsumata R, Segalman RA, Chabinyc ML. Branched Side Chains Govern Counterion Position and Doping Mechanism in Conjugated Polythiophenes. ACS Macro Lett 2018; 7:1492-1497. [PMID: 35651223 DOI: 10.1021/acsmacrolett.8b00778] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Predicting the interactions between a semiconducting polymer and dopant is not straightforward due to the intrinsic structural and energetic disorder in polymeric systems. Although the driving force for efficient charge transfer depends on a favorable offset between the electron donor and acceptor, we demonstrate that the efficacy of doping also relies on structural constraints of incorporating a dopant molecule into the semiconducting polymer film. Here, we report the evolution in spectroscopic and electrical properties of a model conjugated polymer upon exposure to two dopant types: one that directly oxidizes the polymeric backbone and one that protonates the polymer backbone. Through vapor phase infiltration, the common charge transfer dopant, F4-TCNQ, forms a charge transfer complex (CTC) with the polymer poly(3-(2'-ethyl)hexylthiophene) (P3EHT), a conjugated polymer with the same backbone as the well-characterized polymer P3HT, resulting in a maximum electrical conductivity of 3 × 10-5 S cm-1. We postulate that the branched side chains of P3EHT force F4-TCNQ to reside between the π-faces of the crystallites, resulting in partial charge transfer between the donor and the acceptor. Conversely, protonation of the polymeric backbone using the strong acid, HTFSI, increases the electrical conductivity of P3EHT to a maximum of 4 × 10-3 S cm-1, 2 orders of magnitude higher than when a charge transfer dopant is used. The ability for the backbone of P3EHT to be protonated by an acid dopant, but not oxidized directly by F4-TCNQ, suggests that steric hindrance plays a significant role in the degree of charge transfer between dopant and polymer, even when the driving force for charge transfer is sufficient.
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