Vapor-Phase Polymerization of Nanofibrillar. Poly(3,4-Ethylenedioxythiophene) for

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1 Supporting Information for Vapor-Phase Polymerization of Nanofibrillar Poly(3,4-Ethylenedioxythiophene) for Supercapacitors Julio M. D Arcy,, Maher F. El-Kady,, Pwint P. Khine, Linghong Zhang, Sun H. Lee,, Nicole R. Davis,, David S. Liu,, Michael T. Yeung, Sung Y. Kim,,, Christopher L. Turner, Andrew T. Lech, Paula T. Hammond,,, * and Richard B. Kaner,, * Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States, The David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States, Department of Chemistry and Biochemistry, California NanoSystems Institute, University of California Los Angeles, Los Angeles, California 90095, United States, Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt, School of Mechanical Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu, South Korea , Department of Materials Science, University of California Los Angeles, Los Angeles, CA 90095, United States. *Address correspondence to hammond@mit.edu (P.T.H.), kaner@chem.ucla.edu (R.B.K.). 1

2 Common vapor-phase deposition strategies for non-nanostructured transparent PEDOT films Currently, two of the most common vapor-phase deposition strategies for fabricating a thinfilm of PEDOT are: oxidative chemical vapor deposition (ocvd) and vapor-phase polymerization (VPP). The vaporization of both oxidant and monomer makes ocvd a dry coating process that does not require any additives. 1, 2 When using iron(iii) chloride as the oxidant, sublimation can be carried out by heating a crucible between 240 and 320 o C. 3 By controlling synthetic parameters such as feed gases, temperature, pressure, and flow rates, thinfilms of ocvd PEDOT can be deposited on any type of substrate. 3 Alternatively, precoating a substrate with oxidant before exposure to monomer vapors leads to what is referred to as vaporphase polymerization (VPP). The homogeneity of a VPP PEDOT film is highly dependent on the evenness of the precoat; 4 the thickness of a VPP film is controlled by adjusting the feed of evaporated monomer. 5 This technique leads to conjugated organic electronics such as polypyrrole 6 and thiophene based backbones. 7 Droplet evaporation modes One-dimensional nanostructures deposit when molecules of the monomer 3,4- ethylenedioxythiophene carried in chlorobenzene vapor make contact with an evaporating aqueous droplet of FeCl 3 on a heated surface. The evaporation of an oxidant aqueous droplet proceeds by either of three possible routes, a constant contact area evaporation mode that diminishes the contact angle, or a constant contact angle evaporation mode that minimizes the contact area, 8 or a by a combination of the two. 9 This study involves a combination of both 2

3 evaporation modes, except on a gold surface where a constant contact area mode prevails due to pinning at the three-phase contact line. 10 Pinning of an oxidant droplet on a gold substrate results in a disk-shaped PEDOT film of homogeneous morphology comprised of vertically directed high aspect ratio one-dimensional nanostructures. In contrast, a contact line can retreat from its anchored point due to dewetting resulting in inward radial droplet compression during evaporation. Dewetting is a force that counteracts pinning and leads to a constant contact angle evaporation mode, 11 a small PEDOT film due to droplet compression, and ultimately makes the deposition of high aspect ratio one-dimensional nanostructures of EVPP-PEDOT difficult to control. The role of water in the synthesis of PEDOT The step-growth of PEDOT proceeds via oxidative radical polymerization when the monomer is oxidized by FeCl 3 resulting in EDOT radical cations that combine and dimerize. 3 Deprotonation of a dimer leads to stability and makes the incorporation of other cation units possible, thereby forming a conjugated backbone, a larger oligomer and eventually a polymer. 12, 13 The role of the proton scavenger is typically played by the oxidizing agent s anion or an additive such as pyridine although both perform poorly when compared to water. 14 Water is a better proton scavenger than the anion and results in conductive blue PEDOT; the arrival rate of water molecules to the oxidant surface initiates polymerization and determines the conjugation length. 15 Controlling both the level of embedded water as well as the arrival rate of additional water to the oxidant layer may provide an alternate route to the formation of PEDOT. 14 3

4 Removal of excess iron chloride using methanol and acid After multiple vigorous methanol washes, nanoribbons and nanofibers lose rigidity and become entangled. The oxidant serves as an in situ intrinsic template for the growth of nanoribbons and nanofibers and is partially soluble in methanol, and completely soluble in a hydrochloric acid solution, therefore washing results in the loss of structural rigidity for onedimensional EVPP-PEDOT architectures. Byproducts such as red catalytically inert FeCl 2 microcrystals are present at the interface between polymer and substrate and are also soluble. A low magnification sequence of tilted SEM images shows the surface topography of an EVPP- PEDOT film before (Figure S12a) and after (Figure S12b) methanol wash. An SEM image at higher magnification shows that overnight treatment in a 1M 6M HCl aqueous solution leads to complete structural relaxation of previously rigid one-dimensional nanostructures (Figure S12c). 4

5 Evaporative vapor-phase polymerization chamber Figure S1. A schematic diagram of the CVD reactor. (a) Perspective view of box-shaped reactor with lid. (b) Top view shows placement of substrate. (c) Front view of the cavities that house three cartridge heaters and a thermocouple. (d) Top view of the reactor. 5

6 Ramping temperature profile Figure S2. Ramping temperature versus time profile of a typical experiment. 6

7 Wrinkled topography of vertically directed one-dimensional architectures Figure S3. Close-up sequence of SEM images of an EVPP-PEDOT film. (a) A film is comprised of a wrinkled topography. (b-c) Images of higher magnification show that the surface of wrinkles is coated by vertically directed one-dimensional nanoribbons and nanofibers. 7

8 Large-scale coverage of one-dimensional architectures Figure S4. Close-up sequence of SEM images of an EVPP-PEDOT film. (a) The entire surface is homogeneously coated by vertically directed one-dimensional nanostructures. (b) Nanoribbons 8

9 preferentially nucleate throughout the film. (c-d) The morphology of an EVPP-PEDOT film is comprised of an entangled architecture of both nanoribbons as well as nanofibers. (e-f) A micrograph sequence shows that nanoribbons are comprised of nanobundles of high aspect ratio nanofibers possessing aspect ratio of 250. Evolution of one-dimensional architectures Figure S5. Growth of oxidant crystallites. (a) Initially, low aspect-ratio crystallites protrude out of a hardened polymer shell and these (b) continue to grow into high aspect ratio crystallites that serve as intrinsic templates for the deposition of high aspect ratio one-dimensional EVPP- PEDOT architectures. 9

10 Cross-section of an EVPP-PEDOT film Figure S6. Morphology, structure, and composition of an EVPP-PEDOT film before and after washing. Before washing: (a) cross-sectional SEM image shows vertically directed rigid nanoribbons ranging between 10 and 35 µm in length growing out of a polymer film, (b) the bottom of the polymer film is comprised of a red colored 20 µm layer of FeCl 2 microcrystals and, (c) x-ray powder diffraction patterns indicate that these reduced oxidant microcrystals are a mixture of hydrated phases of FeCl 2. After washing: (d) reduced oxide and the bottom layer of 10

11 microcrystals are removed resulting in a cross-sectional morphology characterized by (e) a porous and nanofibrillar architecture supported by a 2 µm thick EVPP-PEDOT polymer film. Deposition of EVPP-PEDOT on gold coated substrate Figure S7. A view inside the CVD chamber after polymerization is complete. Recently deposited disk-shaped EVPP-PEDOT film remains adhered to a gold-coated substrate. 11

12 Radial inward deposition of nanostructures Figure S8. Polymerization progresses radially inward. The direction of polymerization is studied by quenching a reaction during deposition. The blue arrow shows the direction of growth and propagation of anisotropic one-dimensional architectures. (a) Typically, nucleation first takes place at the edge. (b) Nanostructures sprout radially inward toward the center of the droplet. 12

13 Nascent morphologies of EVPP-PEDOT Figure S9. Hollow structures deposit during the initial stages of polymerization. These hollow one-dimensional EVPP-PEDOT microstructures are found in a sample that is still wet, typically within the first 20 min of polymerization. These grow in size from (a) small to (b-c) large, as polymerization proceeds. 13

14 Control of EVPP-PEDOT nanostructures via water concentration Figure S10. Scanning electron micrograph of EVPP-PEDOT deposited with excess water present inside the CVD chamber. (a) The surface of this film is comprised of a wrinkled topography that (b) lacks nanofibers. 14

15 Templated growth of one-dimensional architectures of EVPP-PEDOT Figure S11. Energy dispersive spectroscopy (EDS) mapping of EVPP-PEDOT collected utilizing a 15 kev accelerating voltage. (a) SEM image shows nanoribbons and nanofibers of EVPP-PEDOT. (b-e) EDS elemental maps show an atomic composition that is characteristic of PEDOT's chemical structure. (f) An underlying iron scaffold is present beneath the polymer skin. 15

16 Intrinsic template removal during purification Figure S12. SEM images of EVPP-PEDOT nanoribbons before and after washing with methanol and acid. (a) The sample's pristine morphology is comprised of vertically-directed and rigid nanoribbons as well as nanofibers. (b) Methanol wash leads to partial removal of reduced oxidant (FeCl 2 ) and to partial slackening of both nanoribbons and nanofibers. (c) Further treatment using a hydrochloric acid solution results in complete removal of the oxidant/scaffold and to total relaxation of one-dimensional nanoscale architectures. 16

17 REFERENCES AND NOTES 1. Chelawat, H.; Vaddiraju, S.; Gleason, K. Conformal, Conducting Poly(3,4- Ethylenedioxythiophene) Thin Films Deposited Using Bromine as the Oxidant in a Completely Dry Oxidative Chemical Vapor Deposition Process. Chem. Mater. 2010, 22, Lock, J. P.; Lutkenhaus, J. L.; Zacharia, N. S.; Im, S. G.; Hammond, P. T.; Gleason, K. K. Electrochemical Investigation of PEDOT Films Deposited Via CVD for Electrochromic Applications. Synth. Met. 2007, 157, Im, S. G.; Gleason, K. K. Systematic Control of the Electrical Conductivity of Poly(3,4- Ethylenedioxythiophene) Via Oxidative Chemical Vapor Deposition. Macromolecules 2007, 40, Yang, X.-M.; Shang, S.-M.; Li, L.; Tao, X.-M.; Yan, F. Vapor Phase Polymerization of 3,4- Ethylenedioxythiophene on Flexible Substrate and Its Application on Heat Generation. Polym. Adv. Technol. 2011, 22, Jang, K.-S.; Kim, D. O.; Lee, J.-H.; Hong, S.-C.; Lee, T.-W.; Lee, Y.; Nam, J.-D. Synchronous Vapor-Phase Polymerization of Poly(3,4-Ethylenedioxythiophene) and Poly(3- Hexylthiophene) Copolymer Systems for Tunable Optoelectronic Properties. Org. Electron. 2010, 11, Subramanian, P.; Clark, N.; Winther-Jensen, B.; MacFarlane, D.; Spiccia, L. Vapour-Phase Polymerization of Pyrrole and 3,4-Ethylenedioxythiophene Using Iron(III) 2,4,6- Trimethylbenzenesulfonate. Aust. J. Chem. 2009, 62, Winther-Jensen, B.; Chen, J.; West, K.; Wallace, G. Vapor Phase Polymerization of Pyrrole and Thiophene Using Iron(III) Sulfonates as Oxidizing Agents. Macromolecules 2004, 37,

18 8. Cai, Y. Chemical Template Directed Iodine Patterns on the Octadecyltrichlorosilane Surface. Langmuir 2008, 24, Dugas, V.; Broutin, J.; Souteyrand, E. Droplet Evaporation Study Applied to DNA Chip Manufacturing. Langmuir 2005, 21, Tarasevich, Y. Y. Simple Analytical Model of Capillary Flow in an Evaporating Sessile Drop. Phys. Rev. E 2005, 71, Deegan, R. D. Pattern Formation in Drying Drops. Phys. Rev. E 2000, 61, Martin, D. C.; Wu, J.; Shaw, C. M.; King, Z.; Spanninga, S. A.; Richardson-Burns, S.; Hendricks, J.; Yang, J. The Morphology of Poly(3,4-Ethylenedioxythiophene). Polym. Rev. 2010, 50, Baxamusa, S. H.; Im, S. G.; Gleason, K. K. Initiated and Oxidative Chemical Vapor Deposition: A Scalable Method for Conformal and Functional Polymer Films on Real Substrates. Phys. Chem. Chem. Phys. 2009, 11, Fabretto, M.; Zuber, K.; Hall, C.; Murphy, P. High Conductivity PEDOT Using Humidity Facilitated Vacuum Vapour Phase Polymerisation. Macromol. Rapid Commun. 2008, 29, Fabretto, M.; Zuber, K.; Hall, C.; Murphy, P.; Griesser, H. J. The Role of Water in the Synthesis and Performance of Vapour Phase Polymerised PEDOT Electrochromic Devices. J. Mater. Chem. 2009, 19,