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By Valentin KulikovRegensburg 08.06.2004 Automated System for Combinatorial Synthesis and High-throughput Characterization of Polymeric Sensor Materials.

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Presentation on theme: "By Valentin KulikovRegensburg 08.06.2004 Automated System for Combinatorial Synthesis and High-throughput Characterization of Polymeric Sensor Materials."— Presentation transcript:

1 by Valentin KulikovRegensburg Automated System for Combinatorial Synthesis and High-throughput Characterization of Polymeric Sensor Materials Application in development and optimizing of sensors for gaseous hydrogen chloride (cable fire alarms) Valentin Kulikov Munich 2004

2 by Valentin KulikovRegensburg Introduction to conducting polymers Electropolymerization concept and its realization Measurement concept and its realization Data analysis of experiment Influence of temperature to experiments Optimal thickness of polymer layer Representative results on HCl sensor based on aniline derivates Conclusion Outlook, application range of conducting polymers Outlook of the presentation

3 by Valentin KulikovRegensburg One has been taught that plastics, do not conduct electricity. Usually plastics are used as insulation around the copper wires in ordinary electrical cables. * Nobel Prize in Chemistry 2000 being awarded to Profs. A. J. Heeger, A. G. MacDiarmid and H. Shirakawa (MacDiarmid A.G., "Synthetic metals: A novel role for organic polymers (Nobel Lecture)", Angewandte Chemie, International Edition 40, , 2001) In 1977 three scientists Prof. A. J. Heeger, Prof. A. G. MacDiarmid and Prof. H. Shirakawa cointidentaly discowered and report conductive properties of the alternating-bond conjugated polymers (Polyacetylene). They found that the polymer could be (n- or p-) doped to the metallic state and thereby transformed into a good electrical conductor. Photo acknowledged from report of Nobel Prize in Chemistry 2000 History of conducting polymers

4 by Valentin KulikovRegensburg Conducting polymers Polymers are molecules formed of many identical units (monomers) bound to each other. For a polymer to be electrically conductive it must "imitate" a metal – the electrons in the bonds must be freely mobile and not bound fast to the atoms. One condition for this is that the polymer consists of alternate single and double bonds, termed conjugated double bonds: Example: Oxidation of Polyacetylene with iodine causes the electrons to be jerked out of the polymer, leaving "holes" in the form of positive charges that can move along the chain, thus leading to opening of an band gap and causes (semi)conductivity. (Nobel Prize in Chemistry 2000 ) - low weight - conductivity can be varied over a very broad area, from poor semi-conductors to metallic-level conductivity - Excellent tolerance to corrosion - large, flexible surfaces can be made relatively easily and cheaply

5 by Valentin KulikovRegensburg electrochemical devices (ion exchangers, catalysts, batteries...) - semiconductor electronics (wires, diodes, transistors, LEDs, displays, solar cells,...) - supercapacitors, whole integrated circuits...) - functional coatings (antistatic coating, electrochromic windows...) Wide application range of polymers Analytical devices: - chemical and biological sensors (immobilization of sensor components, electrical contact between electrode and enzyme or intermediator) - formation of molecularly imprinted polymers - gas sensors (HCl, NH3, O3, artificial nose...) - many others Target applications summary: - Flat displays for TVs, monitors, mobile phones, terminals, etc. - Cheap solar cells for energy conversion - Sensors (artificial nose - gas, chemo-, bio-) - Cheap semiconductors for general use - Corrosion protection and electrochromic windows - many others

6 by Valentin KulikovRegensburg Electropolymerization concept Serial synthesis EP sequence can be randomized to form a polymer layer or,multilayer structure. The electrodes are polymerized consequently. What can be varied? - chemical parameters (reagents, reagents ratio, additives,...) - physical parameters (temperature, EP potential, deposition time and charge....) - structural parameters (thickness, number of layers, sequence,...) What concept should cover? - Control of preparation and transport of target reagents - Control of addressation of electrodes - Control and synchronization of electropolymerization - Screening of EP kinetics Polymerization - Polymerization is process of building of blocks from monomers (mer - basic building block) - Depending on what element is added to the carbon backbone, different materials can be produced.

7 by Valentin KulikovRegensburg Addressation of electropolymerization Electrical addressation + Simplest addressation technique + No moving parts involved + High reliability + Electropolymerization is performed in single electrochemical cell - Constant relatively large volume of reagents required (given by size of electrochemical cell) Mechanical addressation - Required expensive robotic systems - Required continuous user inspection - Low reliability - High instrumentation requirements (multi-channel systems) + Low volume of reagents involved + Not limited amount of electrodes

8 by Valentin KulikovRegensburg polymerized electrode Concept of combinatorial electrochemical synthesis and high-throughput investigation of their electrical properties

9 by Valentin KulikovRegensburg Electropolymerization set-up

10 by Valentin KulikovRegensburg Dosing station

11 by Valentin KulikovRegensburg Electropolymerization set-up

12 by Valentin KulikovRegensburg Electrochemical cell General - Three electrode system - Sat. Ag/AgCl KCL ref. electrode - central Aux and Ref. electrode - limit applications to high conduct. electrolytes Fluidic system - One input, two outputs - Sensors of liquid level not required - Only single, one directional peristaltic pump required - driven by underpressure

13 by Valentin KulikovRegensburg Electrochemical cell and its practical realization

14 by Valentin KulikovRegensburg Electrode Array dimensions: 60,8 x 60,8 mm 384 Contact pins 96 interdigital electrodes IDT4 for four-point conductance measurement Single IDT4 electrode Electrode detail SiO2 layers: ~1 um Pt layer: ~0,5 um Pitch 0,5 mm Pt Si support SiO 2 Pt

15 by Valentin KulikovRegensburg Reproducibility of electropolymerization (possible effects of cell geometry and polymerization order) 2) Influence of electropolymerization order - observed no effect of the electropolymerization order 1) Influence of distance among work electrodes and reference electrode - observed no effect of the cell geometry on polymerization rate Experiment: Aniline 0,1 M in 1M H2SO4 Conditions: 40°C, Vp = 0,9V vs. sat. Ag/AgCl EP time app. 100 sec.

16 by Valentin KulikovRegensburg Electropolymerization set-up

17 by Valentin KulikovRegensburg Electrical addressation, Multiplexer 96 - High impedance (due to reed relays) - Multifunctional computer controlled device - Addressation of 96 work el. - special 4A + 2B switch configuration polymerized el. protected el. - Time synchronization

18 by Valentin KulikovRegensburg electrodes involved during experiment in one electrochemical cell How to prevent undesirable electropolymerization on neighboring electrodes? Possible protection techniques: 1) application of Vx potential close to the reference level (not working) 2) application of Vx close to the auxiliary electrode potential level (working) 3) application of the potential of Aux. electrode to the semiconducting array support (working) 4) combination 2 and 3 Electrical addressation visual test of protected electrodes Protected electrodes

19 by Valentin KulikovRegensburg Electropolymerization set-up electropolymerization circuit

20 by Valentin KulikovRegensburg Electropolymerization circuit - protected electrodes connected to Aux. potential - two diodes limits the potential difference between Ref. and Aux. level to prevent undesirable electrochemical processes - Dosing station controlled by Multiplexer 96 device - Electropolymerization synchronized by clock generator 2Hz

21 by Valentin KulikovRegensburg Measurement concept polymerized electrode

22 by Valentin KulikovRegensburg Measurement set-up DC conductance - The same instrumentation as in EP set-up involved - Additionally high impedance voltmeter K2000 for simultaneous 4p and 2p measurements

23 by Valentin KulikovRegensburg Simultaneous two- and four-point measurement DC conductance four long strip electrodes the most effective using of the surface area folding four point technique involved - eliminates contact effects - measurement of bulk conductance - required special topology of electrodes - improvement for simultaneous four - and two- point measurement

24 by Valentin KulikovRegensburg Simultaneous two- and four-point measurement DC conductance - possible to separate bulk and contact resistance - according to the designed geometry of the electrode, the ideally R2/R4 ratio is approximately 3

25 by Valentin KulikovRegensburg Measurement set-up

26 by Valentin KulikovRegensburg Multiplexer 96, addressation during measurement - Addressation of 96 electrodes - four-pint configuration - auto zero offsetting mode - auto calibration mode

27 by Valentin KulikovRegensburg Measurement protocol Multi-parameter High-Throughput Characterization of HCl-sensitive Materials - The minimal amount of most informative measurements is required to provide the most comprehensive characterization of polymer libraries within reasonable time Measurement procedure and protocol - comprehensive meas. + reversibility + reproducibility + response + drifts + concentration depend. + fitting models - reasonable invest. time (12:15 for one library) Fast kinetic ( two consequent cycles ) + analyte concentration sweep Parameter extraction: reversibility and reproducibility of gas effect, fitting to Langmuir or Henry model Slow kinetic ( two consequent cycles ) Parameter extraction: reversibility and reproducibility of gas effect

28 by Valentin KulikovRegensburg Measurement protocol, definition of parameters Multi-parameter High-Throughput Characterization of HCl-sensitive Materials

29 by Valentin KulikovRegensburg Data analysis one of 96 IDT4 electrodes

30 by Valentin KulikovRegensburg Analysis of sensors

31 by Valentin KulikovRegensburg Reproducibility of electropolymerization (current kinetic) Current kinetics for subsequent electropolymerization of aniline at 96 electrode groups: the first experiments The similar experiment with several Improvements: - equilibrium of the EP system - application of protection potential - thermo-stabilization - nitrogen atmosphere

32 by Valentin KulikovRegensburg Thermo-stabilization of electropolymerization and measurement Electropolymerization - influence of temperature on polymerization ratio - thermo-stabilization required - thermostat with proportional (P) and continual current output - temperature range from room temperature up to 80°C Measurement - observed influence of temperature on during adsorption and desorption - temperature range from room temperature up to 125°C - Thermo-desorption, improvement of sensors reversibility

33 by Valentin KulikovRegensburg Application in conductometric polymer gas sensors (Sensors for gaseous hydrogen chloride) Why the sensor for gaseous HCl is needed? polyvinylchloride (PVC) + O2 -> HCl +... Application in fire alarm systems for cable burning - PVC cables - PVC interior details in cars, planes, trains, etc. Prevention of fire disasters caused by burning of cable isolation, PVC (in buildings, transport, and others)

34 by Valentin KulikovRegensburg Optimization of HCl gas sensors, Influence of chemical content, representative results The best relative sensitivity The best desorption rate The best absolute sensitivity The best reversibility* The best response linearity The best reproducibility* The best response time The best contact with electrodes * of gas effect

35 by Valentin KulikovRegensburg Conclusion - Developed and realized: - concept for combinatorial electropolymerization (including hardware, fluidic system and control software) - concept for high-throughput screening (including hardware and control software) - Developed comprehensive measurement protocol for characterization of gas sensors - Developed analysis software, which simplifies work with results, calculates, visualizes and exports all defined parameters such reversibility, reproducibility, response, desorption ratio, allows fitting to Langmuir and Henry model, etc... - This combinatorial set-up was used for optimization of sensors for gaseous hydrogen chloride based on aniline derivates - The representative results illustrates the wide range of application of the developed tool

36 by Valentin KulikovRegensburg Outlook - Application in chemo-sensors

37 by Valentin KulikovRegensburg Outlook - Application in organic electronics Organic field- effect transistors (OFETs) - Schottky diodes - MSM detectors organic light-emitting diodes and displays (OLEDs) Philips announced luminiscent flat TV based on organic polymers available on the market in 2006 organic coatings (corrosion protectors, electrochromic windows), solar cells and many others

38 by Valentin KulikovRegensburg Prof. Alexander Koch Prof. Otto. S. Wolfbeis PD. Dr. Vladimir M. Mirsky Prof. Daniel Donoval Dr. Qingli Hao and others Acknowledgment This work was supported by the project "KOMBISENS" from German Ministry for Science and Technology.

39 by Valentin KulikovRegensburg Thank you for your attention

40 by Valentin KulikovRegensburg Gas addition and gas flow system c (HCl) is a required concentration (in ppm), C o (HCl) is the initial HCl concentration in cylinder (about 200 ppm), fr TOTAL is total flow rate (600 mL/min) and fr(HCl) is the flow rate of HCl in range mL / minute

41 by Valentin KulikovRegensburg Practical realization of electronic thermostat

42 by Valentin KulikovRegensburg Optimization of HCl gas sensors, Influence of the polymerization charge, example - above 1,5 mC modification of polymer layer - optimal EP charge found 0,2 mC for PANI -to thin layer: not overgrowing

43 by Valentin KulikovRegensburg Sweep and pulse technique

44 by Valentin KulikovRegensburg Thermo-desorption


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