Conductive Polymers and Plastics in Industrial Applications Part 6 ppt

solubility. 13,14 The major drawback of such systems is that organic solvents such as dichloro- methane, m-cresol and N-methylpyrrolidone must be used, which are industrially undesirable. Two potential product areas can be explored for large scale electrochemical production of conducting polymers, these being aqueous colloidal dispersions or water soluble polymers. A brief description of these polymer technologies is discussed below. CONDUCTING POLYMER COLLOID PROCESSING To overcome the water solubility limitations of conducting polymers, aqueous dispersions that are sterically stabilized 15-21 have been prepared. More recent approaches involve the use of a core/shell approach where an inner inert colloidal core, such as SiO 2 or TiO 2 , is coated with the conducting polymer, in the presence of a steric stabilizer, in order to yield uniform colloid morphology and particle size distributions. 22-25 All of these approaches involve the production of the conducting polymer component via a chemical oxidative route. 26,27 This technique involves oxidizing the monomer using a chemical agent and has limitations as dis- cussed above. The electrochemical synthesis of conducting polymer colloids is based upon removing the polymer as it is formed above the electrode surface and stabilizing into colloidal particles with a polymeric surfactant (i.e., a steric stabilizer). In the early stages of electropolymerization, the process of oxidation and oligomerization is said to occur within the diffusion layer above the electrode surface. 28-31 As polymerization continues, the oligomer solubility (in the electrolyte solution) is exceeded and subsequently precipitates onto the electrode surface. If the electrolyte flows across the electrode surface fast enough, it is possible for the polymer to be swept away from the electrode before deposition occurs. 32-34 This process is further facilitated by the presence of the steric stabilizer. 35 The final product is a colloidal conducting polymer that is doped with the anion of the supporting electrolyte used during synthesis. ELECTROCHEMICAL REACTOR DESIGNS Two electrochemical cells designs were developed “in-house” at IPRI utilizing porous reticu- lated vitreous carbon (RVC – ERG Aerospace) foam electrodes. RVC is a three dimensional electrode material with a surface area to volume of 65.6 cm 2 /cm 3 at a porosity of 100 pores per inch (PPI). RVC was chosen as a replacement for the traditional plate electrode in order to maximize the electrode surface area and minimize the cell volume. The two designs consid- ered in this cell development study were either a facing anode/cathode design (Figure 1) or an sandwiched anode between two opposing cathodes configuration (Figure 2). Each cell com- partment is separated by an anion exchange membrane (Neosepta TM ) and protected by insert- 100 Conductive Polymers and Plastics ing filter paper between the membrane and electrode to minimize fouling. Electrolyte was flowed from separate catholyte and anolyte reservoirs. EVALUATION OF ELECTROCHEMICAL REACTORS In order to establish that the electrochemical cells were operating at optimal efficiency a se- ries of standardized tests have been developed so that different cells can be compared to one another. The theoretical and experimental details are discussed below. The cells were modelled as a Plug Flow Reactor type reactor. Equations exist for the de- sign and evaluation of each type of reactor. 36 Parameters valid for continuous flow reactors are based upon the assumption of mass transport limited conditions. The essential equations for this evaluation process are: Mass Transfer Coefficient (k m ) k m =i L /zFAC [1] i L limiting current z number of electrons of reaction F Faraday constant A electrode area Electrohydrodynamic Flow Cell 101 Figure 1. Parallel anode/cathode cell. Figure 2. Sandwiched anode configuration. C concentration of reactant In some cases it is preferable to use eq [1] as: k m A=i L /zFC [2] In general, and particularly for cells with plate electrodes, it is possible to use: k m A S =i L /zFCV R [3] A S = A/V R V R volume of reactor (containing electrode) For cells with three-dimensional electrodes: k m A e =i L /zFCV e [4] V e electrode volume Fractional Conversion (X A ) X A =(C (in) -C (out) )/C (in) or X A =1–(C (out) /C (in) ) [5] C (in) concentration of reactant IN C (out) concentration of reactant OUT For a PFR operated in single pass mode, and assuming first order mass controlled kinet- ics, the following relationship will hold: C (out) =C (in) exp[-(k m A e /Q v )] [6] Q v volumetric flow rate X A = 1-exp[-(k m A e )/Q v ] [7] 102 Conductive Polymers and Plastics X A = 1-exp[-{k m A e /V R } τ ] or ln (C (out) /C (in) ) = -{k m A e /V R } τ [8] τ residence time (V R /Q V or V e /Q V for three dimensional porous electrode) For a PFR operated in recirculation mode: X At PFR , = 1-exp[-(t X A PFR T / τ ] [9] t time τ T residence time in holding tank FIGURES OF MERIT Space-time Yield ( ρ st ) ρ st = m/V R t [10] m mass of product In terms of k m , at 100% current efficiency, φ ρ st =k m A e MC (in) [11] M molecular weight of reactant Current Efficiency ( φ ) φ =Q p /Q T [12] Q p charge required to produce product Q T total charge used EXPERIMENTAL CHEMICALS Potassium hexacyanoferrate (II) and sodium nitrate were used as supplied from Ajax (Analar). Milli-Q grade water was used in all experiments. Electrohydrodynamic Flow Cell 103 EQUIPMENT A PAR 363 potentiostat/galvanostat was used in all efficiency tests. All potentials were mea- sured versus a Ag/AgCl reference electrode. A Shimadzu UV-1601 UV-Visible spectrophotometer was used for all concentration determinations. Data acquisition was made using a Maclab™ (AD Instruments) interface using Chart V3.3.5 software. PROCEDURES Each Cell design was tested by preparinga1Lanolyte solution consisting of 2 mM K 4 Fe(CN) 6 .3H 2 0 (aq) and 0.5 M NaN0 3(aq) .A1Lcatholyte solution of 0.5 M NaNO 3(aq) . The anolyte and catholyte solutions were then flowed through their respective compartments at 20, 40 and 60 mL/min by peristaltic pumps. Efficiency tests were carried out at a constant po- tential of +0.8Vinsingle pass mode. A chronoamperogram at the applied potential was recorded for both the duration of cell flushing and sample collection. Initially, 1 to 3 cell volumes were passed through the cell at +0.8 V, at the flow rate being investigated, and discarded to waste. With the potential still be- ing applied, a minimum of 1 cell volume was then collected. The collection time (sec) and actual volume collected (mL) were also determined. The charge passed was then determined by integrating the area under the curve from the end of the data acquisition and back for the to- tal collection time (t sec). The concentration of Fe(CN) 6 3- produced from Fe(CH) 6 4- test solution was determined by UV-Vis Spectroscopy. RESULTS AND DISCUSSION Analysis of the current efficiency parameters for both cell designs in- dicated that at + 0.8 V both cells de- signs had efficiencies of 99 % or better. The dependence of the mass transfer coefficient is shown in Fig- ure 3. At large residence times, or low flow rates, the mass transfer process in the sandwich configura- tion is slightly higher. At shorter residence times, higher flow rate, both cell designs have similar mass transfer characteristics due to greater turbulence induced with in 104 Conductive Polymers and Plastics Figure 3. Effect of sandwich and parallel configuration on the mass transfer coefficient (K m A e /V R ). the RVC electrodes at higher flow rates. The effect of this turbulence is characterized by the rapid increase in mass transport at lower residence times (or higher flow rates). The relationship of space time yield, ρ st , to residence time, Figure 4, shows that the sandwich configura- tion is most efficient at all flow rates investigated. The sandwich configu- ration has higher ρ st values due to minimizing the effect of electrode shielding and thereby utilizing more of the available anode surface. In the sandwich configuration, ρ st decreases as the electrolyte residence time with in the cell is also reduced. This is in- dicative of insufficient electrolyte contact with the electrode at shorter residence times, but also shows that the cell was operating near its optimal at the lowest flow rate. Increasing the flow rate from 20 to 60 mL/min re- duces the space time yield by 15%. In the case of the parallel configuration, the space time yield was at a maxi- mum at shorter residence times. This result gives further evidence that this cell design was far less efficient than the sandwich configuration. The fractional conversion, Fig- ure 5, of Fe(CH) 6 4- to Fe(CN) 6 3- was better than 99% for both cell designs. The sandwich configuration was again a more efficient cell design. Interestingly, fractional conversion in- creased with decreasing residence time, or increasing flow rate, due to enhanced electrolyte turbulence. Electrohydrodynamic Flow Cell 105 Figure 5. Effect of sandwich and parallel configuration on Fractional Conversion. Figure 4. Effect of sandwich and parallel configuration on the space time yield, ρ st . EXAMPLES OF POLYMERS SYNTHESIZED USING THESE CELL DESIGNS A number of conducting polymer colloids have been syn- thesized using these cell designs. Colloids such as polypyrrole-nitrate, 2-4 polypyrrole-lactoferrin, 37 polyaniline-polystyrene sulfonate/camphorsulfonic acid 38 have been successfully synthesized. A TEM, Fig- ure 6, of a typical polypyrrole nitrate colloid shows typi- cal colloid morphologies achieved when using these cells. A major feature of this synthesis technique is that the colloids formed have a controllable and uniform size distributions. CONCLUSIONS In this paper we have presented a method of characterizing the efficiency and performance of electro- chemical flow cells utilizing three-dimensional reticu- lated vitreous carbon foam electrodes. Cell design characterization is critical for the successful implementa- tion and scale up of electrochemical cell, especially with respect to the scale up from laboratory to prototype and commercial conducting polymer syn- thesis. REFERENCES 1 J.N. Barisci, P.C. Innis, L.A.P. Kane-Maguire, I.D. Norris and G.G. Wallace., Synth. Met., 1997, 84, 181-182. 2 J.N. Barisci, C.Y. Kim, D.Y. Kim, J.Y. Kim, J. Mansouri, G.M. Spinks and G.G. Wallace., Colloids and Surfaces A., 1997, 126, 129-135. 3 J. Barisci, J. Mansouri, G. Spinks, G. Wallace, D.Y. Kim and C.Y. Kim, Synth. Met., 1997, 84, 361-362. 4 V. Aboutanos, J.N. Barisci, P.C. Innis and G.G. Wallace., Colloids and Surfaces A., in press. 5 W-P. Hsu, K. Levon, K-S. Ho, A.S. Myerson and T.K. Kwei., Macromolecules, 1993, 26, 318-1323. 6 R.M. McCullough, R.D. Lowe, M. Jayaraman and D.L. Anderson., J. Org. Chem., 1993, 58, 904-912. 7 Y. Wei and J. Tian., Polymer, 1992, 33, 4872-4874. 8 H. Masuda and K. Kaeriyama., Synth. Met., 1992, 13, 461-465. 9 S. Rapi, V. Bocchi and G.P. Gardini., Synth. Met., 1988, 24, 217-221. 10 D. Delabouglise and F. Garnier., New J. of Chem., 1991, 15, 233-234. 11 S-A. Chem and G-W. Hwang., J. Am. Chem. Soc., 1994, 116, 7939-7940. 12 E.E Havinga, W. ten Hoeve, E.W. Meijer, and H. Wynberg., Chem. Mater., 1989, 1, 650-659. 13 Y. Cao, P. Smith and .J. Heeger., Synth. Met., 1992, 48, 91. 14 Y. Cao, P.Smith and A.J. Heeger., App. Phys. Lett., 1992, 60, 2711. 15 H. Eisazadeh, G. Spinks and G.G. Wallace., Mater. Forum, 1992, 16, 341-344. 16 C. DeArmitt and S.P. Armes., Langmuir, 9(1993)652-654. 17 B. Vincent., Polym. Adv. Tech., 1995, 6, 356-361. 106 Conductive Polymers and Plastics Figure 6. TEM of Polypyrrole-nitrate colloids. 18 M. Aldissi and S.P Armes., Prog. Org. Coatings, 1991, 19, 21-58. 19 H. Eisazadeh, G.Spinks and G.G. Wallace., Mater. Forum, 1993, 17, 241-245. 20 S.Y. Luk, W. Lineton, M. Keane, C. DeArmitt and S.P. Armes., J. Chem. Soc., Faraday Trans., 1995, 91, 905-910. 21 S.P. Armes and B. Vincent., J. Chem. Soc., Faraday Trans., 1987, 228-290. 22 S.P. Armes, S. Gottesfeld, J.G. Beery, F. Garzon, Agnew., Polym., 1991, 32, 2325-2330. 23 R. Flitton , J. Johal, S. Maeda and S.P. Armes., J. of Colloid and Interfacial Sci., 1995, 173, 135- 142. 24 S. Maeda and S.P. Armes., Synth. Met.,1995, 69, 499-500. 25 S. Maeda and S.P. Armes., Chem. Mater., 1995, 7, 171-178. 26 German Patent P 37 29 566.7 Zipperling Kessler & Co. 27 US Patent Application 823416, 823511 and 823512 Allied-Signal, Zipperling Kessler & Co. and Americhem Inc. 28 R. John and G.G. Wallace., J. Electroanal. Chem., 1991, 306, 157. 29 B.R. Scharifker and D.J. Fermin., J. Electroanal. Chem., 1994, 365, 35. 30 B.R. Scharifker, E. Garcia-Pastoriza and W. Marino., J. Electroanal. Chem., 1991, 335, 85. 31 D.E. Raymond and D.J. Harrison., J. Electroanal. Chem., 1993, 355, 115. 32 A.F. Diaz and B.J. Bargon in Handbook of Conducting Polymers, T.A. Skotheim Ed., Vol 1, Marcel Dekker, New York, 1986, 81. 33 C.K. Baker and J.R. Reynolds., J. Electroanal.Chem., 1988, 251, 307. 34 C. Lee, J. Kwak and A.J. Bard., J. Electrochem. Soc., 1989, 136, 3720. 35 H. Eisazadeh, G. Spinks and G.G. Wallace., Mater. Forum, 1992, 16, 341. 36 F. Walsh., “A First Course in Electrochemical Engineering”, The Electrochemical Consultancy, England, 1993. 37 V. Aboutanos, J.N. Barisci, G.R. Harper and G.G. Wallace, submitted ANTEC 98. 38 P.C. Innis, G.Spinks, G.G. Wallace., submitted ANTEC 98. Electrohydrodynamic Flow Cell 107 Hydroxyethyl Substituted Polyanilines: Chemistry and Applications as Resists Maggie A.Z. Hupcey Dept. of Materials Science and Engineering, Cornell University, Ithaca, NY Marie Angelopoulos, and Jeffrey D. Gelorme IBM T.J. Watson Research Center, Yorktown Heights, NY Christopher K. Ober Dept. of Materials Science and Engineering, Cornell University, Ithaca, NY INTRODUCTION In the field of conducting polymers, solubility of the polymer is a highly desirable quality. One method that has been widely used to enhance the solubility of conducting polymers is the incorporation of ring substituents on the polymer backbone. 1-3 However ring substituents have generally resulted in a decrease in the conductivity of the polymer. Steric constraints im- posed by the substituents disrupt the coplanarity of the polymer chains as well as increase the interchain distance. Both factors reduce the mobility of the carriers and as a result lower con- ductivity is exhibited. In this work, we wish to report a new series of polyaniline copolymers possessing a hydroxyethyl substituent that improves the solubility of the conducting polymer and yet retains a high conductivity. In the field of microlithography, conducting polymers have potentially many uses. 4-6 For example, it is thought that damage to the gate oxide and to the resist sidewalls during plasma etching is due to the charging of the insulating resist layer. In SEM metrology of devices and masks using a conventional insulating resist, charging of the resist yields errors in the mea- surement, a problem conducting resists have been shown to alleviate. 7 Conducting polymers have also been proven useful in electron beam (e-beam) lithography, where the exposing radi- ation is a beam of electrons. Excess electron charge builds up at the surface of an insulating resist causing severe pattern distortion; with a conducting resist the excess charge is dissi- pated. 8 With these new hydroxyethyl substituted polyanilines, a simple derivitization to make a crosslinkable conducting resist is possible. EXPERIMENTAL The polyaniline copolymers were synthesized following a well-known procedure. 9 Copoly- mer compositions were determined via integration on a 300 MHz Varian 1 H NMR. Molecular weights were measured via GPC eluted with NMP with 0.5% LiCl added to each sample. For UV-Visible spectra and conductivity measurements, films were spun coat from 5% (wt/wt) NMP solutions filtered through 5 µ m filters onto polished quartz discs, then baking the sam- ples in an 85 o C oven for 15min. Conductivities were measured via four point probe. Doping with camphorsulfonic acid (CSA) and acrylamidomethyl-propanesulfonic acid (Aampsa) was done by adding the dopant in the ratio of 2 mole acid per mole repeat unit to a 5% (wt/wt) NMP solution of the base polymer, and processed as for the undoped. For HCl doping, the undoped spun coat films were immersed in 1M HCl overnight and dried under light vacuum. The methacrylate functionalization was achieved by dissolving the poly(o-hydroxyethyl)aniline homopolymer in cyclohexanone at 3 wt%, adding isocyanoethylmethacrylate (IEM) and stirring for 48 hours until complete disappearance of the isocyanate peak in the IR spectrum. RESULTS AND DISCUSSION COPOLYMERIZATION Seven copolymers were synthe- sized by varying the molar amount of o-hydroxyethylaniline mono- mer in the polymerization (Figure 1). It was found that the incorpo- rated functionality always ex- ceeded the feed (Table 1). The GPC results show that the molecu- lar weight decreased from a high of M n =22K and leveled off at around M n =12K for feeds larger than 30%. ELECTRONIC PROPERTIES In the undoped or base form, the hydroxyethyl substituted polymers exhibit a red shift in the exciton absorption in the UV-Visible spectrum as compared to the unsubstituted emeraldine base. A λ max of 609 nm is observed for the thin film of the unsubstituted polyaniline base whereas a λ max of 629 nm is observed for the fully substituted poly(o-hydroxyethyl)aniline. The fully substituted 110 Conductive Polymers and Plastics Figure 1. Poly(o-hydroxyethyl)aniline copolymer synthesis. [...]... trends in chip integration have increased requirements for both the density of interconnections and heat dissipation In addition, the proliferation of semiconductors in mobile computer and communication devices has added size and weight limitations These trends towards increased integration and miniaturization show no signs of abating; and thus, it is clear that the requirements of interconnection and. .. produced in solution from which it can be easily spin coated into thin films 112 Conductive Polymers and Plastics Figure 3 PaniIEM e-beam exposure: 0.075 µm equal lines and spaces Sample: PaniEtOH 100% methacrylated, CSA doped Exposure: 250 µC/cm2 at 25 keV Develop: 1 min ethyl lactate This new substituted polyaniline, PaniIEM, is useful as a new negative-tone resist Upon e-beam and broad band UV light... unsubstituted polyaniline The high conductivity exhibited by the poly(o-hydroxyethyl) aniline is due to the altered interchain hydrogen bonding as well as improved polymer/solvent interactions resulting in a more expanded coil conformation In agreement with this is the highly delocalized free carrier tail extending into the near-infrared that is observed for the poly(o-hydroxyethyl)aniline LITHOGRAPHY The... the dominant form of device protection, starting with the dual inline package from the early days of microelectronics Because of its dominance in packaging the huge volume of memory chips, plastic packaging has had a solid technology base from which the requirements of more specialized applications have been met by incremental improvements Plastic packaging has continued to thrive by increasing the... of interconnections (I/Os) that can be handled and by reducing the thickness of the package The latter has helped overcome some of the thermal limitations of encasing the chip in epoxy, a poor thermal conductor, as well as meeting requirements for miniaturization A continuing attractive feature of plastic packaging is the fact that the packaged chips are easily handled individually both for test and. .. compared to emeraldine base and poly(o-hydroxyethyl) aniline The ethoxy functionality and the hydroxyethyl substituent basically pose similar geometric constraints on the polymer However, the hydroxy functionality provides a means for hydrogen bonding between chains thereby reducing the interchain distance In addition the hydroxy group provides a means of hydrogen bonding with the processing solvent which... further improvement in this regard Two other inter-related packaging considerations directly impacted by the choice of device protection are chip test and burn -in and reworkability of the assemblies These aspects will be touched on in this overview as well, including a brief description of one approach to achieving reworkability without using molded plastic packaging PLASTIC PACKAGING Molded plastic... Epstein, A.J., Synth.Met., 1997, 84, 35 Electroformation of Polymer Devices and Structures G G Wallace, J N Barisci, A Lawal, D Ongarato, and A Partridge Intelligent Polymer Research Laboratories, University of Wollongong, Australia INTRODUCTION Table 1 Inherently conductive polymers The discovery of inherently conducting polymers (see Table 1) just 17 years ago has led to the widespread use of polymers. .. resulting polymer composite still retaining high (>90%) water content, but also having electronic conductivity and electroactivity These conducting polymer containing materials can be grown to large dimensions with the final shape determined by that of the gel at the time of gelation Spatial distribution of conducting polymers throughout the hydrogel networks is Figure 1: Schematic representation showing... even more tightly integrated into the device protection technology in order to achieve functional, reliable, compact and cost-effective semiconductor packaging for the future For the remainder of this paper, a cursory evaluation of the main device protection technologies will be given in terms of how well they integrate interconnection and heat dissipation with device protection and what potential . 9(1993 )65 2 -65 4. 17 B. Vincent., Polym. Adv. Tech., 1995, 6, 3 56- 361 . 1 06 Conductive Polymers and Plastics Figure 6. TEM of Polypyrrole-nitrate colloids. 18 M. Aldissi and S.P Armes., Prog. Org. Coatings, 1991,. (Neosepta TM ) and protected by insert- 100 Conductive Polymers and Plastics ing filter paper between the membrane and electrode to minimize fouling. Electrolyte was flowed from separate catholyte and anolyte. charging of the insulating resist layer. In SEM metrology of devices and masks using a conventional insulating resist, charging of the resist yields errors in the mea- surement, a problem conducting