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No description available.

Luo Yun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / 论文摘要 --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vii / List of Tables --- p.xi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Conjugated Polymers --- p.1 / Chapter 1.1.1 --- Overview --- p.1 / Chapter 1.1.2 --- Conducting Polymers --- p.2 / Chapter 1.2 --- Electrochemical Doping of Conjugated Polymers --- p.5 / Chapter 1.2.1 --- Doping Conjugated Polymers --- p.7 / Chapter 1.2.2 --- Doping Level --- p.8 / Chapter 1.3 --- Charges in Conjugated Polymers --- p.10 / Chapter 1.3.1 --- Electronic and Geometric Configurations --- p.10 / Chapter 1.3.2 --- Charge Carriers --- p.10 / Chapter 1.4 --- Effects of Localization and Structural Disorder on Conductivity --- p.18 / Chapter 1.5 --- Cyclic Voltammetric Behavior of Conjugated Polymers --- p.18 / Chapter 1.6 --- PEDOT: PSS Systems --- p.21 / Chapter 1.7 --- Motivation --- p.25 / References --- p.27 / Chapter Chapter 2 --- Instrumentation --- p.32 / Chapter 2.1 --- X-ray Photoelectron Spectroscopy --- p.32 / Chapter 2.1.1 --- Introduction --- p.32 / Chapter 2.1.2 --- Basic Principles and Theory --- p.32 / Chapter 2.1.3 --- Qualitative Analysis Using XPS --- p.35 / Chapter 2.1.4 --- Angular Effect on XPS --- p.35 / Chapter 2.1.5 --- Chemical Shifts --- p.35 / Chapter 2.1.6 --- Valence Band Investigation --- p.37 / Chapter 2.1.7 --- Quantitative Analysis Using XPS --- p.37 / Chapter 2.1.8 --- Instrumental Setup for XPS --- p.40 / Chapter 2.2 --- Scanning Probe Microscopy --- p.40 / Chapter 2.2.1 --- General Introduction --- p.40 / Chapter 2.2.2 --- Atomic Force Microscopy and Conducting Atomic Force Microscopy --- p.40 / Chapter 2.2.3 --- Instrumental Setup for Conducting AFM --- p.44 / Chapter 2.3 --- Cyclic Voltammetry --- p.44 / Chapter 2.4 --- Kelvin Probe --- p.46 / Chapter 2.5 --- a-step Profilometer --- p.48 / References --- p.49 / Chapter Chapter 3 --- Cyclic Voltammetric Characterization of PEDOT:PSS --- p.51 / Chapter 3.1 --- Film Preparations --- p.51 / Chapter 3.2 --- Electrochemistry --- p.52 / Chapter 3.3 --- Results and Discussions --- p.53 / References --- p.56 / Chapter Chapter 4 --- Electronic Structure of Doped and Dedoped PEDOT:PSS Systems --- p.57 / Chapter 4.1 --- Introduction --- p.57 / Chapter 4.2 --- Sample Preparations --- p.58 / Chapter 4.3 --- Results and Discussions --- p.60 / Chapter 4.3.1 --- XPS of C 1s Core Level of PEDOT:PSS --- p.61 / Chapter 4.3.2 --- XPS of S 2p Core Level of PEDOT:PSS --- p.66 / Chapter 4.3.3 --- XPS of O Is Core Level of PEDOT:PSS --- p.71 / Chapter 4.3.4 --- XPS of Valence Band of PEDOT:PSS --- p.77 / Chapter 4.3.5 --- Further Explanations and Discussions --- p.77 / Chapter 4.4 --- Kevin Probe Measurement --- p.83 / Chapter 4.5 --- Conclusions --- p.83 / References --- p.85 / Chapter Chapter 5 --- Morphology and Nano-scale Electrical Properties of PEDOT:PSS Thin Film --- p.87 / Chapter 5.1 --- Introduction --- p.87 / Chapter 5.2 --- Sample Preparations --- p.87 / Chapter 5.3 --- Results and Discussions --- p.88 / Chapter 5.3.1 --- CAFM on as Prepared PEDOT.PSS and Ar+ Sputtered Thin Film --- p.88 / Chapter 5.3.2 --- CAFM on pH Dedoped PEDOT:PSS (pH=6.6) --- p.95 / Chapter 5.3.3 --- CAFM on Electrochemically Dedoped PEDOTrPSS --- p.98 / Chapter 5.4 --- Conclusions --- p.105 / References --- p.106 / Chapter Chapter 6 --- Concluding Remarks and Future Work --- p.107 / Chapter 6.1 --- Concluding Remarks --- p.107 / Chapter 6.2 --- Future Work --- p.108

This research investigates the use of conducting polymer coatings on platinum (Pt) electrodes for use in neuroprostheses. Conducting polymers aim to provide an environment conducive to neurite outgrowth and attachment at the electrode sites, producing intimate contact between neural cells and stimulating electrodes. Conducting polymers were electropolymerised onto model Pt electrodes. Conventional polymers polypyrrole (PPy) and poly-3,4-ethylenedioxythiphene (PEDOT) doped with polystyrenesulfonate (PSS) and para-toluenesulfonate (pTS)were investigated. Improvement of material properties was assessed through the layering of polymers with multi-walled carbon nanotubes (MWNTs). The ability to incorporate cell attachment bioactivity into polymers was examined through the doping of PEDOT with anionic laminin peptides DCDPGYIGSR and DEDEDYFQRYLI. Finally, nerve growth factor (NGF), was entrapped in PEDOT during polymerisation and tested for neurite outgrowth bioactivity against the PC12 cell line. Each polymer modification was assessed for electrical performance over multiple reduction-oxidation cycles, conductivity and impedance spectroscopy, mechanical adherence and hardness, and biological response. Scanning electron microscopy was used to visualise film topography and x-ray photon spectroscopy was employed to examine chemical constitution of the polymers. For application of electrode coatings to neural prostheses, optimal bioactive conducting polymer PEDOT/pTS/NGF was deposited on electrode arrays intended for implantation. PC12s were used to assess the bioactivity of NGF functionalised PEDOT when electrode size was micronised. Flexibility of the design was tested by tailoring PEDOT bioactivity for the cloned retinal ganglion cell, RGC-5, differentiated via staurasporine. It was established that PEDOT films had superior electrical and cell growth characteristics, but only PPy was able to benefit from incorporation of MWNTs. Bioactive polymers were produced through inclusion of both laminin peptides and NGF, but the optimum film constitution was found to be PEDOT doped with pTS with NGF entrapped during electrodeposition. Application of this polymer to an implant device was confirmed through positive neurite outgrowth on vision prosthesis electrode arrays. The design was shown to be flexible when tailored for RGC-5s, with differentiation occurring on both PEDOT/pTS and PEDOT/DEDEDYFQRYLI. Conducting polymers demonstrate the potential to improve electrode-cell interactions. Future work will focus on the effect of electrical stimulation and design of bioactive polymers with improved cell attachment properties.

Microbial  Cellulose  (MC)  is  a highly  porous  macromolecule  with  intrinsic  properties  that  make  it  a  useful  substrate  for  conductive  materials  within  ultracapacitors.  MC  has  the  potential  to  increase  capacitance  by  serving  as  a  high  surface  area  substrate  for  conductive  polymers  and  carbonaceous  materials.  Electrode  surface  area  is  a  critical  parameter  in  ultracapacitors  because  capacitance  depends  on  the  available  active  sites  that  are  accessible  to  counter  ions.  Commercial  ultracapacitors  increase  electrode  surface  area  by  adding  micro­size  carbonaceous  materials.  Most  commercial  devices  also  require  adhesive  compounds  to  bind  the  conductive  material  to  the  substrate.  Adhesive  compounds  increase  sheet  resistance  and  hinder  overall  capacitance.  MC  membranes  possess  highly­ordered  surface  hydroxyl  groups  that  readily  bind  to  different  types  conductive  materials  and  reduce  the  need  for  additive  adhesive  compounds.  This  thesis  investigates  three  unique  methods  for  converting  a  MC  membrane  into  a  working  ultracapacitor electrode. In  the  first  method,  polypyrrole  and  carbon  nanotubes  (CNTs)  are  added  to  a  medium  of  Acetobacter  that  incorporates  the  material  into  a  homogeneous  crystalline  matrix of beta­1,4 glucan chains. The resulting MC is a fully integrated membrane  with a  homogeneous  embedded  layer  of  conductive  material.  SEM  imaging  shows  the  conductive  material  is  incorporated  primarily  at  the  core  of  the  membrane.  As  a  result,  this  electrode  suffered  from  high  sheet  resistance  and  did  not  generate  any  significant  capacitance.  In  the  second  method,  a  conductive  ink  consisting  of  CNTs,  carboxymethyl  cellulose  (CMC),  polypyrrole,  and  DI  water  was  used  to  coat  the  surface  of  a  dried  cellulose  membrane.  After  1­2  hours,  the  ink  dries  and  leaves  a  shiny  black  conductive  layer  on  the  membrane’s  surface.  CMC’s  role  in  the  ink  is  to  increase  viscosity  and  help  bind  the  conductive  material  to  the  membrane  surface.  CMC  is  also  a  dielectric  material  that  acts  as  an  insulator  to  the  polypyrrole  and  CNTs,  and  ultimately  impedes  electrical  energy  storage.  In  the  final  method,  a  MC  membrane  was  soaked  in  aqueous  and  non­ aqueous  pyrrole  solutions,  and  polymerized  with  FeCl3  and  Fe2(SO4)3.  Single  and  double  membrane  device  configurations  were  also  investigated.  Surface  polymerization  of  pyrrole  monomers  proved  to  be  the  best  method  for  converting  microbial  cellulose  into  a  working electrode with good capacitance and cyclability. / text

The majority of conjugated polymers are more stable as p-doped materials than n-doped materials. Stable n-doped polymers are still desirable and for all polymer OPVs, pLEDS, n-channel FETs, and other polymeric electronic devices. The use of donor-acceptor architectures has led to improvements in n-type polymer performance. The approach taken here has been to include a metal-coordination site within a donor-acceptor polymer backbone in order to explore the effect of redox matching between the conjugated polymer backbone and the transition metal center. Conducting polymers have shown promise as polymeric actuators for prosthetics, robotics, and dynamic braille displays. For the majority of conducting polymers, the actuation mechanism is a bulk phenomenon related to the uptake and expulsion of counterions. This performance may be improved by incorporating monomers which display geometry changes as a function of oxidation state into the polymer backbone. The molecular-level actuation should additively yield a macroscopic actuation that would surpass as well as compliment the bulk mechanism discussed above. We have synthesized a conjugated polymer which incorporates the sym-dibenzocyclooctatetraene moiety, which is known to undergo a change in geometry from a tub-shaped neutral structure to a planar radical anion, into the polymer backbone. The solution processability of conjugated polymers promises large-scale roll-to-roll processing for organic photovoltaics. However, the use of thin active layers in the majority of high efficiency devices reported to date prohibits this. The recently reported donor-acceptor copolymer KP115 shows high efficiencies in polymer-fullerene blend bulk heterojunction devices even with very thick active layers. This has been reported to be unrelated to the morphology of the blends. By further characterizing this material and preparing derivatives of this polymer, we aim to relate the unique performance of these devices to a structural feature of the polymer. It is proposed that the low recombination rates observed for these blends may be due to the presence of discrete donor and acceptor units in the polymer backbone. In order to further explore this idea, we have a prepared a derivative of KP115 in which a conjugation-breaking meta-phenyl linkage has been introduced between the silolodithiophene unit and the dithienylthiazolo[5,4-d]thiazole unit. / text

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No description available.

A series of 12-, 13-, and 14-membered crown ether rings bearing polymerisable side-chains has been synthesised. The crown ethers were attached to a methacrylate or acrylate polymerisable group either via a short link (Ring-CH(_2)-O-Polymer) or via a spacer group. Both hydrocarbon and ethylene oxide spacer groups were used, giving structures of the form (Ring-CH(_2)-O-(CH(_2))(_6)-O-Polymer) and (Ring-CH(_2)-O-((CH(_2)CH(_2))(_2)O)-Polymer). The ethylene oxide chain can potentially bind to a Li(^+) dopant ion. The relative Li(+) binding affinity of 12-, 13-, and 14-membered mono- and disubstituted crown ethers has been assessed by variable temperature (^13)c and (^7)Li NMR. The crown ether bearing monomers were polymerised using standard free-radical polymerisation methods to yield amorphous materials whose glass transition temperature (T(_g)) was controlled principally by the nature of the spacer group. On doping with lithium triflate (LiCF(_3)SO(_3)), the polymers exhibit high ionic conductivity. The conductivity was primarily dependent on polymer T(_g), but was also found to be higher for 12-crown-4 based systems than for 13-crown-4 and 14-crown-4 based analogues. This behaviour was consistent with the results of the NMR studies, which showed that Li(^+) exchange occurs more readily between 12-crown-4 rings than 13- or 14-crown-4 rings. The NMR studies also showed that 12-crown-4 systems have a higher tendency to form 2:1 (ring : Li(^+)) complexes. Within a polymer matrix, the presence of 2:1 complexes allows Li(^+) migration via an association-disassociation mechanism, avoiding the high energy intermediate state of a free or weakly bound Li(^+) ion. The greater encapsulation provided by 2:1 complexation may also aid in ion pair separation.

This research investigates the use of conducting polymer coatings on platinum (Pt) electrodes for use in neuroprostheses. Conducting polymers aim to provide an environment conducive to neurite outgrowth and attachment at the electrode sites, producing intimate contact between neural cells and stimulating electrodes. Conducting polymers were electropolymerised onto model Pt electrodes. Conventional polymers polypyrrole (PPy) and poly-3,4-ethylenedioxythiphene (PEDOT) doped with polystyrenesulfonate (PSS) and para-toluenesulfonate (pTS)were investigated. Improvement of material properties was assessed through the layering of polymers with multi-walled carbon nanotubes (MWNTs). The ability to incorporate cell attachment bioactivity into polymers was examined through the doping of PEDOT with anionic laminin peptides DCDPGYIGSR and DEDEDYFQRYLI. Finally, nerve growth factor (NGF), was entrapped in PEDOT during polymerisation and tested for neurite outgrowth bioactivity against the PC12 cell line. Each polymer modification was assessed for electrical performance over multiple reduction-oxidation cycles, conductivity and impedance spectroscopy, mechanical adherence and hardness, and biological response. Scanning electron microscopy was used to visualise film topography and x-ray photon spectroscopy was employed to examine chemical constitution of the polymers. For application of electrode coatings to neural prostheses, optimal bioactive conducting polymer PEDOT/pTS/NGF was deposited on electrode arrays intended for implantation. PC12s were used to assess the bioactivity of NGF functionalised PEDOT when electrode size was micronised. Flexibility of the design was tested by tailoring PEDOT bioactivity for the cloned retinal ganglion cell, RGC-5, differentiated via staurasporine. It was established that PEDOT films had superior electrical and cell growth characteristics, but only PPy was able to benefit from incorporation of MWNTs. Bioactive polymers were produced through inclusion of both laminin peptides and NGF, but the optimum film constitution was found to be PEDOT doped with pTS with NGF entrapped during electrodeposition. Application of this polymer to an implant device was confirmed through positive neurite outgrowth on vision prosthesis electrode arrays. The design was shown to be flexible when tailored for RGC-5s, with differentiation occurring on both PEDOT/pTS and PEDOT/DEDEDYFQRYLI. Conducting polymers demonstrate the potential to improve electrode-cell interactions. Future work will focus on the effect of electrical stimulation and design of bioactive polymers with improved cell attachment properties.