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Electric Fields for Surface Design and Chemical Analysis
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology. (Tillämpad fysik)
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the use of electric fields for evaluation and control of chemical systems. An electric field can result in the flow of charge across an interface between a metal and a solution, by means of chemical reactions. This interplay between electricity and chemistry, i.e. electrochemistry, is a field of crucial importance both within research and industry. Applications based on electrochemical principles encompass such diverse areas as batteries and fuel cells, pH electrodes, and the glucose monitor used by people suffering from diabetes.A major part of the present work concerns the use of static electric fields in solutions containing a non-contacted metal surface. In such a setup it is possible to control the extent of electrochemical reactions at different positions on the metal. This allows the formation and evaluation of various types of gradients on electrodes, via indirectly induced electrochemical reactions. This approach is a new and simple way of forming for instance molecular gradients on conducting surfaces. These are very advantageous in biomimetic research, because a gradient contains a huge amount of discrete combinations of for example two molecules. The basis for the technique is the use of bipolar electrochemistry. Briefly, a surface can become a bipolar electrode (an electrode that acts as both anode and cathode) when the electric field in the solution exceeds a certain threshold value, thereby inducing redox reactions at both ends. In our experiments, the driving force for these reactions will vary along the electrode surface. Since the result of an electrochemical reaction can be the deposition or removal of material from an electrode, bipolar electrochemistry can be used to create gradients of that material on a surface. In order to gain a deeper understanding of these processes, the potential and current density distributions at bipolar electrodes were investigated with different methods. Especially the use of imaging techniques was important for the visualization and analysis of the gradients. Using this knowledge, the formation of more complex gradients was facilitated, and the results were further compared to simulations based on simple conductivity models. These simulations also provided us with means to predict the behavior of new and interesting setup geometries for pattering applications.The other major part is more application driven and deals with the use of alternating electric fields for chemical analysis, a technique known as electrochemical impedance spectroscopy (EIS). In this work, EIS has been applied for the analysis of engine oils and industrial cutting fluids. Emphasis was placed on practical aspects of the measurement procedure, and on the evaluation of the results using statistical methods. It was for example shown that it was possible to simultaneously determine the amount of different contaminants in low conducting solutions. Generally, EIS is used to measure the impedance of a solution or a solid, often as a function of the frequency of the alternating electric field. The impedance of a system is closely correlated to its complex dielectric constant, and EIS can therefor be used to examine many chemical and physical processes. It is further well suited for characterizing low conducting media with little or no redox-active species. The evaluation of impedance data is often a quite complex task, which is why we have made use of statistical methods that drastically reduce the effort and quickly reveal significant intrinsic parameters.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 50 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1206
Keyword [en]
Electric fields, Surface design, Chemical analysis, Bipolar electrodes, Impedance spectroscopy
National Category
Inorganic Chemistry Physical Chemistry Physical Chemistry Physical Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-12485ISBN: 978-91-7393-819-8 (print)OAI: oai:DiVA.org:liu-12485DiVA: diva2:214
Public defence
2008-10-02, Planck, Fysikhuset, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-09-29 Created: 2008-09-08 Last updated: 2009-05-18Bibliographically approved
List of papers
1. Formation of Molecular Gradients on Bipolar Electrodes
Open this publication in new window or tab >>Formation of Molecular Gradients on Bipolar Electrodes
2008 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 47, no 16, 3034-3036 p.Article in journal (Refereed) Published
Keyword
Bipolar electrodes, electrochemistry, imaging, molecular gradients, surface chemistry
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-14881 (URN)10.1002/anie.200705824 (DOI)
Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2017-12-13Bibliographically approved
2. Potential and Current Density Distributions at Electrodes Intended for Bipolar Patterning
Open this publication in new window or tab >>Potential and Current Density Distributions at Electrodes Intended for Bipolar Patterning
2009 (English)In: Analytical Chemistry, ISSN 0003-2700, Vol. 81, no 1, 453-459 p.Article in journal (Refereed) Published
Abstract [en]

This paper deals with the use of reaction gradients on bipolar electrodes for the patterning of electrode surfaces. More specifically, the potential and current density distributions in two setups containing bipolar electrodes were investigated to optimize and design specific gradient geometries. Comparisons with simulations based on simple conductivity models showed a good qualitative agreement, demonstrating that these models could be used to predict bipolar behavior in more complex setups. In conjunction with imaging surface plasmon resonance (iSPR) experiments, the reaction gradients on bipolar electrodes could further be visualized. It was, for example, found that the gradient in potential difference was approximately linearly distributed in the center of the bipolar electrode and that these potential differences could be determined using an ordinary Ag/AgCl reference electrode. The present results thus provide a better understanding of the processes relevant for bipolar patterning. This approach was finally used to generate a circular gradient region in a self-assembled monolayer, thereby showing the possibilities to create interesting substrates for biosensors and microarray applications.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16423 (URN)10.1021/ac801871c (DOI)
Available from: 2009-01-23 Created: 2009-01-23 Last updated: 2009-05-18
3. Imaging SPR for detection of local electrochemical processes on patterned surfaces
Open this publication in new window or tab >>Imaging SPR for detection of local electrochemical processes on patterned surfaces
2008 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 134, no 2, 545-550 p.Article in journal (Refereed) Published
Abstract [en]

Imaging surface plasmon resonance (iSPR) was used in conjunction with voltammetry to investigate the possibility of detecting local electrochemical processes in situ on chemically modified electrodes. More specifically, a pattern of self-assembled monolayers (SAMs) of thiocholesterol and 1-hexadecanethiol was microcontact printed on gold substrates, and the blocking characteristics on different parts of the pattern were investigated. The SPR images reflected the changes in the refractive index over the working electrode due to electrochemical processes, which in the present case showed the ability of the SAMs to impede faradaic reactions. The results show that differences in packing densities or porosity of SAMs in different regions of a patterned surface can be visualized as electrochemical images using iSPR. The strength of utilizing an optical detection method for electrochemical characterization lies in the ability to achieve lateral resolution in real-time. Electrochemical reactions can also be used to enhance the contrast in SPR images of thin layers of components with similar thicknesses and refractive indices.

Keyword
Imaging surface plasmon resonance, Microcontact printing, Local electrochemical analysis, Surface analysis
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-14884 (URN)10.1016/j.snb.2008.05.042 (DOI)
Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2017-12-13
4. Current oscillations during chronoamperometric and cyclic voltammetric measurements in alkaline Cu(II)-citrate solutions
Open this publication in new window or tab >>Current oscillations during chronoamperometric and cyclic voltammetric measurements in alkaline Cu(II)-citrate solutions
2008 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 53, no 5, 2188-2197 p.Article in journal (Refereed) Published
Abstract [en]

It is demonstrated that current oscillations can be observed during chronoamperometric and cyclic voltammetric experiments in solutions containing 0.4 M CuSO4 and 1.2 M citrate at pH 11 and 50 °C. The oscillations, which are shown to originate from local variations in the pH, result in the deposition of nanostructured Cu and Cu2O materials. It is concluded that the current oscillations are analogous to the previously described potential oscillations obtained under controlled current conditions in alkaline Cu(II)-lactate, -tartrate and -citrate solutions. Rotating disk electrode results clearly show that the reduction of the Cu(II)-complexes is kinetically controlled and that the rate of the reduction increases with increasing pH and temperature. It is also shown that the presence of a cathodic peak on the anodic scan in the cyclic voltammograms can be used to identify the experimental conditions leading to the spontaneous current (or potential) oscillations. Electrochemical quartz crystal microbalance results indicate that the cathodic peak stems from an increased rate of the reduction of the Cu(II)-citrate complexes due to a rapid increase in the local pH. This causes Cu2O rather than Cu to be deposited which, however, results in a decrease in the local pH and a decreasing current. In situ ellipsometry data confirm that Cu2O deposition replaces that of Cu in the potential region of the cathodic peak. The present findings should facilitate syntheses of nanolayered materials based on spontaneous potential or current oscillations.

Keyword
Current oscillations, Cu; Cu2O, Nanolayers, Local pH variations, Citrate
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-14885 (URN)10.1016/j.electacta.2007.09.032 (DOI)
Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2017-12-13
5. Simultaneous estimation of soot and diesel contamination in engine oil using electrochemical impedance spectroscopy
Open this publication in new window or tab >>Simultaneous estimation of soot and diesel contamination in engine oil using electrochemical impedance spectroscopy
Show others...
2007 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 127, no 2, 613-618 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we explore the combination of electrochemical impedance spectroscopy and multivariate data analysis to simultaneously predict the concentrations of soot and diesel in engine oil. For this purpose, we use a well defined measurement set-up to minimize interference from ambient noise, and to obtain a large amount of data in a short period of time. An imperative requirement is that soot and diesel affect the impedance in different ways over the employed frequency range. It was, for example, found that diesel had a larger influence at lower frequencies. Using partial least squares modelling we show that it is possible to simultaneously predict the concentrations of both soot and diesel in engine oil. Since the temperature in an engine varies, the influence of the oil temperature is investigated in a preliminary experiment. This study is a part of the development of an electrochemical on-board sensor for real-time monitoring of engine oil.

Keyword
Electrochemical impedance spectroscopy, Multivariate data analysis, Engine oil; Diesel, Soot
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-14886 (URN)10.1016/j.snb.2007.05.014 (DOI)
Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2017-12-13
6. Evaluation of industrial cutting fluids using electrochemical impedance spectroscopy and multivariate data analysis
Open this publication in new window or tab >>Evaluation of industrial cutting fluids using electrochemical impedance spectroscopy and multivariate data analysis
Show others...
2012 (English)In: Talanta: The International Journal of Pure and Applied Analytical Chemistry, ISSN 0039-9140, E-ISSN 1873-3573, Vol. 97, 468-472 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we explore the combination of electrochemical impedance spectroscopy (EIS) and multivariate data analysis to evaluate the concentration and pH of an industrial cutting fluid. These parameters are vital for the performance of for instance tooling processes, and an on-line monitoring system would be very beneficial. It is shown that both the total impedance and the phase angle contain information that allows the simultaneous discrimination of the concentration and the pH. The final evaluation was made with a regression model, namely partial least squares (PLS). This approach provided a way to quickly and simply find the correlation between EIS data and the sought parameters. The results from the measurements showed the possibility to predict the concentration and pH level, indicating the potential of this method for on-line measurements.

Place, publisher, year, edition, pages
Elsevier, 2012
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-14888 (URN)10.1016/j.talanta.2012.05.001 (DOI)000308268800071 ()
Note

funding agencies|Carl Trygger Foundation (CTS)||Swedish Sensor Center (S-SENCE)||

Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2017-12-13

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