@article{MTMT:1401799, title = {Electrolyte diodes with weak acids and bases. II. Numerical model calculations and experiments}, url = {https://m2.mtmt.hu/api/publication/1401799}, author = {Iván, Kristóf and Gyökérné Wittmann, Mária and Simon L., Péter and Noszticzius, Zoltán and Snita, D}, doi = {10.1063/1.2085049}, journal-iso = {J CHEM PHYS}, journal = {JOURNAL OF CHEMICAL PHYSICS}, volume = {123}, unique-id = {1401799}, issn = {0021-9606}, abstract = {This is the second part of our work dealing with electrolyte diodes with weak acids and bases. In the first part an approximative analytical solution was derived for the steady-state current-voltage characteristic (CVC) of a reverse-biased diode (a quasi-one-dimensional gel connecting an acidic and an alkaline reservoir), applying either strong or weak electrolytes. An approximative analytical solution is compared here with a numerical solution free of any approximations and with CVCs measured experimentally with both strong and weak electrolytes. It is shown that the deviations between the numerical and analytical solutions are mostly due to assumptions made for the fixed charge concentration profiles. The concept of optimal analytical solution is introduced which does not use such assumptions and applies only the quasielectroneutrality and quasiequilibrium approximations. It is proven that the slope of the CVC based on the optimum analytical solution can be calculated without the complicated derivation of that solution itself. The calculation of that slope is based on the fact that in the optimum analytical solution all currents are inversely proportional to the length if the boundary conditions are held constant and realizing that in the middle part of the gel the only mobile counterions of the fixed ionized groups are hydrogen ions. In the experimental part the apparatus and the preparation of the gel are described together with the CVCs measured with strong and weak electrolytes. From these CVCs the fixed ion concentration in the middle part of the gel can be determined. That fixed ion concentration is 1.96 X 10(-4)M measured with weak electrolytes and 3.48 X 10(-4)M measured with strong electrolytes. The deviation indicates that the strong base causes some hydrolysis of the gel. Finally, possible applications of weak acid-weak base diodes are discussed. (c) 2005 American Institute of Physics.}, year = {2005}, eissn = {1089-7690}, orcid-numbers = {Iván, Kristóf/0000-0003-3637-3979; Simon L., Péter/0000-0002-2183-1853} } @article{MTMT:1401798, title = {Electrolyte diodes with weak acids and bases. I. Theory and an approximate analytical solution}, url = {https://m2.mtmt.hu/api/publication/1401798}, author = {Iván, Kristóf and Simon L., Péter and Gyökérné Wittmann, Mária and Noszticzius, Zoltán}, doi = {10.1063/1.2085047}, journal-iso = {J CHEM PHYS}, journal = {JOURNAL OF CHEMICAL PHYSICS}, volume = {123}, unique-id = {1401798}, issn = {0021-9606}, abstract = {Until now acid-base diodes and transistors applied strong mineral acids and bases exclusively. In this work properties of electrolyte diodes with weak electrolytes are studied and compared with those of diodes with strong ones to show the advantages of weak acids and bases in these applications. The theoretical model is a one dimensional piece of gel containing fixed ionizable groups and connecting reservoirs of an acid and a base. The electric current flowing through the gel is measured as a function of the applied voltage. The steady-state current-voltage characteristic (CVC) of such a gel looks like that of a diode under these conditions. Results of our theoretical, numerical, and experimental investigations are reported in two parts. In this first, theoretical part governing equations necessary to calculate the steady-state CVC of a reverse-biased electrolyte diode are presented together with an approximate analytical solution of this reaction-diffusion-ionic migration problem. The applied approximations are quasielectroneutrality and quasiequilibrium. It is shown that the gel can be divided into an alkaline and an acidic zone separated by a middle weakly acidic region. As a further approximation it is assumed that the ionization of the fixed acidic groups is complete in the alkaline zone and that it is completely suppressed in the acidic one. The general solution given here describes the CVC and the potential and ionic concentration profiles of diodes applying either strong or weak electrolytes. It is proven that previous formulas valid for a strong acid-strong base diode can be regarded as a special case of the more general formulas presented here. (c) 2005 American Institute of Physics.}, keywords = {DIFFUSION; REACTOR; hydrogel; TRANSISTORS; IONIC SYSTEMS}, year = {2005}, eissn = {1089-7690}, orcid-numbers = {Iván, Kristóf/0000-0003-3637-3979; Simon L., Péter/0000-0002-2183-1853} } @article{MTMT:1401891, title = {Electrolyte diodes and hydrogels: Determination of concentration and pK value of fixed acidic groups in a weakly charged hydrogel}, url = {https://m2.mtmt.hu/api/publication/1401891}, author = {Iván, Kristóf and Gyökérné Wittmann, Mária and Simon L., Péter and Noszticzius, Zoltán and Vollmer, J}, doi = {10.1103/PhysRevE.70.061402}, journal-iso = {PHYS REV E STAT NONLIN}, journal = {PHYSICAL REVIEW E - STATISTICAL NONLINEAR AND SOFT MATTER PHYSICS (2001-2015)}, volume = {70}, unique-id = {1401891}, issn = {1539-3755}, abstract = {Current-voltage (CV) characteristics of polyvinyl alcohol (PVA) - glutardialdehyde hydrogel cylinders were measured in aqueous KCl solutions. To this end a new special apparatus was constructed where the gel cylinder connects two electrolyte reservoirs. The measured quantities are the electric current flowing through the gel and the potential difference between the two reservoirs. Concentration polarization near the gel-liquid interfaces is decreased considerably by applying an intense mechanical stirring in both reservoirs. Under these conditions below 1 V concentration polarization is negligible, and the CV curves are nearly straight lines. It was found that the gel applied here is a weakly charged anionic hydrogel. Concentration of fixed anions was determined from the slope of these lines measured in 0.001 and 0.01 molar KCl solutions. Fixed anion concentration of the same piece of gel was measured also with a different method, when the gel was used in an acid-base diode. In this case one reservoir contained 0.1 molar HCl, and the other 0.1 molar KOH. From the results of the two measurements, the concentration (4.45x10(-3) M) and the pK value (4.03) of the fixed acid groups responsible for the anionic character of the gel was calculated. The pK value is compatible with fixed carboxylic acid groups contaminating the PVA gel. Furthermore, concentration polarization phenomena in the boundary layers nearby the gel were studied in 0.001 M KCl solutions, measuring the diodelike CV characteristic of a gel cylinder, when stirring was applied only at one side of the gel. Boundary layers facing the cathode or the anode responded in a different way to stirring. The difference cannot be explained completely with the hypothesis of electroconvection suggested previously.}, keywords = {REACTOR; TRANSISTORS; SOLUTE DIFFUSION; IONIC SYSTEMS}, year = {2004}, eissn = {1550-2376}, orcid-numbers = {Iván, Kristóf/0000-0003-3637-3979; Simon L., Péter/0000-0002-2183-1853} } @article{MTMT:1036728, title = {A dynamic light scattering study on aggregation of rodlike colloidal particles}, url = {https://m2.mtmt.hu/api/publication/1036728}, author = {Brunner, R and Gall, S and Wilke, W and Zrínyi, Miklós}, doi = {10.1016/S0378-4371(97)00014-9}, journal-iso = {PHYSICA A}, journal = {PHYSICA A - STATISTICAL MECHANICS AND ITS APPLICATIONS}, volume = {239}, unique-id = {1036728}, issn = {0378-4371}, year = {1997}, eissn = {1873-2119}, pages = {477-485}, orcid-numbers = {Zrínyi, Miklós/0000-0002-9362-3199} } @article{MTMT:1036729, title = {Direct observation of abrupt shape transition in ferrogels induced by nonuniform magnetic field}, url = {https://m2.mtmt.hu/api/publication/1036729}, author = {Zrínyi, Miklós and Barsi, L and Szabo, D and Kilian, H G}, doi = {10.1063/1.473589}, journal-iso = {J CHEM PHYS}, journal = {JOURNAL OF CHEMICAL PHYSICS}, volume = {106}, unique-id = {1036729}, issn = {0021-9606}, year = {1997}, eissn = {1089-7690}, pages = {5685-5692}, orcid-numbers = {Zrínyi, Miklós/0000-0002-9362-3199} }