Foot, Peter

Kingston University Research Repository

Overview• Introduction • Conducting polymers• Polyaniline (PAni)• Limitations• Aim of study• Elastomers• Methodology - Discussion• Synthesis of polyaniline • Preparation and properties of blends – 1 : EO-EPI Elastomer• Preparation and properties of blends – 2 : NBR ElastomerConclusionsConducting Polymers• Conjugated organic macromolecules• Conduct electricity in the “DOPED” state  (i.e. when charged)POTENTIAL APPLICATIONS• Electrochromic and electro-luminescent devices• Anti-corrosion paints  & coatings• Radar absorbing materials• Printed circuits• AntistaticsPolyanilineWhy Polyaniline ?• Monomer inexpensive (aniline)• High yield polymerisation & low-toxicity polymer• High thermal and environmental stability • Good electrical and optical propertiesDrawbacks of PAni for industrial applications ? Low processability Poor mechanical propertiesPolyanilineConductivity=2.6x10-8 S/cm                              Conductivity=9.8S/cm • Electrical properties reversibly controlled via protonationNNNNn HHNNNNn HHHHX X+ +. .- -Low pHHigh pHAim of study• Synthesis, optimisation and analysis of conducting PAni• Blending solubilised PAni with elastomersConducting rubbers with good electrical & mechanical props.Elastomer 1Epichlorohydrin-ethylene oxide • Similar solubility parameter and H-bonding potential to polyanilines• Strong, flexible backbone • Good oil, fuel and solvent resistance.• Good heat resistance.CH2 n CHCH2ClOCH2 O m CH2Synthesis of Polyaniline Chemical polymerisation -- two-step route chosen:• Synthesis of PAni Hydrochloride salt• Deprotonation to prepare PAni base• Reprotonation (doping) of base with solubilisingagent, e.g. ionic surfactant or other sulfonic acid  NH2(NH4)2S2O8+N NNNn HHH HCl Cl++..- -Temp. 0 oCpH=0-0.51 M HClOxidative polymerisationPolyaniline - HClEffect of oxidant/monomer ratio on conductivity of Polyaniline.HCl( Optimum value is surprisingly sub-stoichiometric)0246810120 0.25 0.5 0.75 1 1.25 1.5 1.75Ratio of Oxidant/MonomerConductivity S/cm      0.75Polyaniline BaseN NNNn HHH HCl Cl++..- -NN NNn HHDeprotonation of the salt0.5 M NH4OHDoping (Re-protonating) PAni BaseN NHN NHnCH3SO3HSO3HC12H25SO3HCH3SO3HSOOOHO(DBSA)Conductivity and Solubility Parameters Only PAni.DBSA gave a reasonable match…PolymerConductivity (S.cm-1)Solubility parameters (J.cm-3)1/2Epi-EO 2x10-10 19.9PAni-DBSA 0.6 20.8PAni-CSA 0.9 22.9PAni-MeSA 2.7 23.9PAni-TSA 1.6 24PAni-NSA 1.5 25Preparation of BlendsBlends prepared by co-dissolution method• Polymers (PAni.DBSA & EPI.EO) dissolved in THF• Solvent evaporated on PTFE sheets to obtain conducting blend filmsPTFE sheetPAni.DBSABlended withEPI / EOUV-Vis Analysis of PANI.DBSA BLENDS Shows the dispersed polyaniline remains in conductive state 200 300 400 500 600 700 800 900Wavelength (nm) AbsorbancePani Base Pani-DBSA 20% Pani-DBSA773nm628nm-11-10-9-8-7-6-5-4-3-20 10 20 30 40 50 60Weight fraction of PAni-DBSA Log electrical conductivity (σ)                     Conductivity of Pani.DBSA Blends Percolation threshold apparently <1vol.%(Some elongated particles present, as well as larger “globules”) (a) Before percolation (b) After percolation (c) Totally connected1%GLASS TRANSITION OF PANI-DBSA BLENDS also indicate that the PAni.DBSA dissolves in the elastomerBlends PANI-DBSA Content (wt%)Tg oCEpi-EO 0 -40PAni-DBSA/Epi-EO 10 -37PAni-DBSA/Epi-EO 20 -36PAni-DBSA/Epi-EO 25 -35PAni-DBSA/Epi-EO 33.3 -33PAni-DBSA/Epi-EO 50 -23TGA analysis of PANI-DBSA BLENDS… reveals a compositional trend in the high-T degradation event0204060801000 100 200 300 400 500 600Temperature / oCWeight %100% Pani-DBSA 100% Rubber 10% Pani-DBSA 20% Pani-DBSA 33.3% Pani-DBSA 50% Pani-DBSA300-370oC290-355oC280-335oC270-320oC200-400oC10% Pani-DBSA 20.0% Pani-DBSA50.0% Pani-DBSABlend Morphology : Optical Microscopy (200x)Reveals PAni-rich and PAni-poor regions on the µm scale(both contribute to bulk conductivity)33.3% Pani-DBSASummary• Increasing oxidant ratio   higher concentration radical cationsshorter polymer chain  lower conductivity• Increased pH   decrease level of protonation  lower conductivity • PAni-DBSA has good compatibility with Epi-EO elastomer• Level of conductivity of the blends can be modified according todesired application• Percolation threshold of blends  ~1% w/w• UV-visible spectrometry shows PAni-DBSA remains in the doped form upon blending with Epi-EO copolymer.INTRODUCTION Elastomer-intrinsically conducting polymer blends were prepared by: Solution mixing, i.e. by using a shared solvent Mechanical mixing,  using an internal mixer Criteria for selection of main components: High chemical attack resistance (elastomer). Good solubility and miscibility with selected partner-polymer (for elastomer and conductive polymer). Good thermal stability (both polymers). Good electrical conductivity (conductive polymer). Both polymers were blended by using solution mixing, with chloroform as the shared solvent NBR (with 48 wt% acrylonitrile content) and PAni.DBSA were chosen as the elastomer and conducting polymer respectivelySolubility Parameter Values Calculated by using Equation 1 and molar attraction constant s  calculated by Hoy.Equation 1 :      δp = (ρ x ΣFi) / Mowhere δp = solubility parameter for polymer , ρ = density of polymer , Σfi = sum of group molar attraction constants of polymer repeat unit & Mo = formula weight of the polymer repeat unitPolymer Solubility Parameter Value (J.cm-3)1/2NBR (48 wt% ACN content)PAni.DBSA20.820.8FT-IR Spectroscopy Spectra of blend films resemble a superposition of spectra for NBR and PAni.DBSA but a few notable peak shifts provide evidence of molecular-scale interaction between the two polymersPure material/ blend (wt% NBR:wt% PAni.DBSA)Peak assignment (cm-1). Indication of peak intensity: W, weak; M, medium=N-HstretchingS=Ostretching-CΞNstretchingPAni.DBSANBRBlends90:1050:503447W-3411W3437W1030M-1081W1029W-2237M2237W2236WDSC Analysis Samples of pure NBR, pure PAni.DBSA and their blends (with 10, 20, 30, 40 and 50 wt% of added PAni.DBSA) analyzed by DSC (-30oC to 400oC, heating rate 20oC/min).  DSC thermograms of all blends show some degree of temperature shifting for their thermal processes (based on the onset value of endotherm or exotherm) Blends with 10 to 30% PAni.DBSA showed largest shifts. Other evidence showed good miscibility for these blendsDC Electrical Conductivity 100 µm films of pure NBR, pure PAni.DBSA and their blends were cast onto glass slides for this purpose Electrical conductivity measured by van der Pauw 4-probe technique, except for films with low conductivity (<10-7 S/cm) which were measured by using a 2-probe technique Apparently two stages of conductivity percolation, with thresholds < 1 vol.% and ~16 vol.% of PAni.DBSAElectrical Conductivity of NBR-PAni.DBSA Blends as a Function of PAni.DBSA Content( 2 stages of percolation apparent)-16-14-12-10-8-6-4-200 10 20 30 40 50PAni.DBSA loading (wt%)Log conductivity (S/cm)Optical Microscopy All blends studied by optical microscopy (200 x magnification) and images captured digitally As before, the observed bright green regions are well-blended regions of both components (rich in NBR).  TEM reveals nano-sized particles & in these regions. The dark green regions (rich in PAni.DBSA) are large particles or agglomerates of PAni. DBSAOptical Micrographs for Blends: (a) with 5 wt% of Added PAni.DBSA and (b) with 40 wt% of Added PAni.DBSA(a) (b)125 µm125 µmThermal Mixing/Cross-Linking of NBR Blends Polymers  blended in an internal mixer (Brabender) Cross-linked by dicumyl peroxide Vulcanisation studied by MDR Samples characterised as for solvent-cast blends Anisotropic mechanical & electrical properties  (i.e. parallel & perpendicular to flow) also measuredMean Glass Transition Temperatures (Tg) for Peroxide-Vulcanised NBR and NBR-PAni.DBSABlendsComposition(wt% NBR : wt% PAni.DBSA*)Glass transition temperature (Tg), oCVulcanised NBR (48.2 wt% ACN)Vulcanised blends90:1080:2070:3060:4050:50-10-7-7-5-8-8Tensile Strength of Blends vs. Composition PAni gives some initial reinforcement, then weakens the rubber1111.51212.51313.5140 1020 30 40 50Added PAni.DBSA (wt%)TeTensile strength (MPa)Test pieces parallel to flow directionTest pieces perpendicular to flow directionElectrical Conductivity Un-strained samples: surprisingly little effect of thermal treatment or cross-linking-16-14-12-10-8-6-4-200 10 20 30 40 50Added PAni.DBSA (wt%)Log Conductivity (S.cm-1)-16-14-12-10-8-6-4-200 10 20 30 40 50Added PAni.DBSA (wt%)Log Conductivity (S.cm-1)Non-vulcanised Peroxide-VulcanisedElectrical Conductivity: Effect of Strain - 1 10% Pani.DBSA Blend  - 3rd cycle (shows little fatigue)-5.53-5.525-5.52-5.515-5.51-5.505-5.5-5.495-5.490 20 40 60 80 100Elongation in Length (%)Log Conductivity (S.cm-1)Loading Unloading-5.542-5.54-5.538-5.536-5.534-5.532-5.53-5.528-5.5260 20 40 60 80 100Elongation in Length (%)Log Conductivity (S.cm-1)Loading UnloadingStrain parallel to flow (milling) directionStrain perpendicular to flowElectrical Conductivity: Effect of Strain - 2 30% Pani.DBSA-NBR Blend  (3rd cycle again)-2.6-2.55-2.5-2.45-2.4-2.35-2.30 20 40 60 80 100Elongation in Length (%)Log Conductivity (S.cm-1)Loading Unloading-2.568-2.566-2.564-2.562-2.56-2.558-2.5560 20 40 60 80 100Elongation in Length (%)Log Conductivity (S.cm-1)Loading UnloadingStrain parallel to flow directionStrain perpendicular to flowCONCLUSION Polyaniline-nitrile rubber blends with reasonable miscibility and useful electrical properties have been prepared. (Miscibility between both polymers could be further improved by using a coupling agent.) Intermolecular interactions revealed by IR peaks and DSC transition temperatures shifts Two stages of conductivity percolation threshold observed. The earlier one corresponds to the well-blended phase and the later one to the separated phase. Thermal blends:  conducting polymer appears to have both reinforcing or plasticising effects on NBR  Conductivity of strained samples is anisotropic; samples strained in the flow direction show  a repeatable increase in conductivity under tension. Mechanism still under analysis .AcknowledgementsPEO-ECH  Blends:• Dr Zaid Abbas• Dr. S. Barton• Dr Ahmed Farid (London Metropolitan University)NBR and ENR Blends:Malaysian Rubber BoardDr. Stuart Cook (TARRC,Hertford)Dr. Huda MorganDr. Andrew Tinker (Director of R&D, TARRC)Dr  K-C Yong (on study leave from MRB)Some Relevant Publications1. The Effects of Composition and Processing Variables on the Properties of Thermoplastic Polyaniline Blends and Composites.   H Morgan, PJS Foot and NW Brooks, J Mater. Sci. 36, 5369-77 (2001).2. The Electronic Properties of Metal-Complexed Poly(3-Alkylthiophene) Films. PJS Foot, M Miah, V Montgomery and I Youngs, Mater. Res. Bull. 37, 2055-66 (2002).3. Thermal Doping of Polyaniline by Sulfonic Acids. D Poussin, H Morgan and PJS Foot, Polymer International 52, 433-38 (2003).4. Synthesis and properties of a novel thiophene conducting copolymer with mesogenic groups attached parallel to the polymer backbone.  J W Brown, G J Lambe, P J S Foot and J A Clipson.  Macromol. Rapid Commun. 25, 1000 (2004).5. Synthesis of Liquid Crystalline Conducting Polymers for Laser Alignment. J W  Brown, P J S Foot, L Gabaston, P Ibison and A Prevost. Macromolecular Chemistry & Physics 205, 1823 (2004).6. Conductive Poly(Butadiene-co-Acrylonitrile)-Polyaniline Dodecylbenzenesulfonate [NBR-PAniDBSA] Blends prepared in Solution.  K C Yong, P J S Foot, S J Cook and A J Tinker, European Polymer J.  42, 1716-27 (2006)7. Conductive Polyaniline/Poly (Epichlorohydrin-co-Ethylene Oxide) Blends Prepared in Solution.  Z K Abbas, S J Barton, P J S Foot and H Morgan.   Polymers and Polymer Composites 15, 1-8 (2007).8. Electrically-Conductive Epoxidised Natural Rubber-Polyaniline DBSA Blends. KC Yong, PJS Foot, H Morgan, S Cook, A Tinker, M Ahmad, J Rubb. Res. 11, 59-77 (2008).9. Synthesis and Characterisation of Polyaniline/Montmorillonite Nanocomposites. A Shakoor, T Z Rizvi and P J S Foot, Polym. Polym. Comp. 17 (6), 347-52 (2009).10. Properties of  Thermally-Mixed Poly(Butadiene-co-Acrylonitrile)-PolyanilineDodecylbenzenesulfonate Blends.  Submitted to J. Appl. Polym. Sci.

Conductive polymer-elastomer blends

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Conductive polymer-elastomer blends

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