Alternative TitleVoltammetric current in viscous sodium alginate solutions
Note (General)Whether mass transport rates in viscous sodium alginate (SA) are dependent of viscosity is a controversial issue because few data reported on the size of network. This thesis considered the mass transport behavior of three different species in viscous SA solutions by means of voltammetry, dynamic light scattering (DLS) and time-evolution of diffusing dye. Applications were also explored in the light of its unique mass transport property. This thesis consists of five chapters. Chapter 1 is devoted to introduction of the sodium alginate, determining of diffusion coefficient, slow scan voltammetry and cylindrical electrode. The experimental procedures are described in chapter2. Chapter 5 is the conclusions. Chapter 3 deals with the effects of viscosity on the voltammetric current of FcTMA. Voltammograms were almost independent of the increasing viscosity of the SA solution even in a solid-like state. The diffusion coefficient of the FcTMA did not vary with the viscosity evaluated by a viscometer. Because change in redox charge may cause complications on the value of diffusion coefficients by means of electrochemical measurement, the variation of conductivity with viscosity was also measured. The conductivity was not only independent of D but also of redox species. The independence was confirmed by means of time-evolution of diffusing dye experiment. The result showed the D-values were close to the value of organic molecular in water regardless of the viscosity. The intrinsic viscosity was evaluated. The value 15 dm3g-1 equivalent to the volume as large as 3m3 of water in which one mole of the unit of SA polymer generates the viscosity. In contrast, diffusion coefficients of the latex particle which was 0.84μm and 0.42μm in diameter by DLS and Stokes-Einstein equation respectively, decreased with the increasing of the viscosity of SA. It demonstrated molecules bigger than that volume would exhibit viscous effects by blocking diffusion with the network of SA. As an application, it can use for long long-term chronoamperometry experiments. The reproducible current of different angle of electrode surface against the horizon (0, 60) got with the time even of 1500s without any effect of nature convection, whereas it was irreproducible for times longer than 20s. Consequently, SA works as stabilization of diffusion currents by blocking the nature convection. Because the electrodeposition of silver in aqueous often shows granular, spongy and dendritic morphology owing to the nonuniform current distributions caused by nature convection, that unique property can be used for deposition of silver. The silver film deposited in SA solution exhibited no morphology even on an optical microscopy scale. Chapter 4 focus on the slow scan voltammetry in SA solutions. For a voltammetry experiment at a stationary, constant-area electrode, the charging current always exist since the potential is continuously changing in a potential sweep experiment. The diffusion current must always be measured from a baseline of charging current. While capacitive current is proportional to the square root of scan rate and Faradaic diffusion current varies with square root of scan rate, so that capacitive current is relatively more important at high scan rates, especially in low concentrations. Voltammetry at low scan rate has always been used for extracting Faradaic diffusion current from capacitive one in determining lower concentration solutions. It is necessary to avoid unexpected nature convection because it is a long-term experiment. The linear sweep voltammograms of two redox species, FcTMA and potassium hexacyanoferrate in KCl solution with SA at platinum disc electrode were clear , reproducible and propotional to the square root of scan rate, whereas that in aqueous solution were complicatedly wave-like variations at lower scan rate. The peak currents with SA were almost the same as those without SA, whereas they were smaller than those without SA at low scan rate. The ratio of the peak currents with SA to that without SA was increased with decreasing of scan rate. The similar variation of voltammograms and peak current happened at platinum wire electrode 0.1mm in diameter and 10mm in length, but a wire electrode were more strongly affected by natural convection than a disc electrode at low scan rate. Irreproducible and larger chronoamperometric currents at the wire electrode were noticeable earlier than that at the disk electrode. Slow scan voltammetry is suitable for detection of redox species with low concentrations. A wire electrode in SA solution was demonstrated to be a powerful tool for determining concentrations up to 0.5μM at 0.1 mV s-1. The faradaic current waves were obtained clearly and reproducibly even at 0.01 mV s-1.
Collection (particular)国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
Date Accepted (W3CDTF)2020-01-16T18:57:33+09:00
Data Provider (Database)国立国会図書館 : 国立国会図書館デジタルコレクション