Naslov
Dielectric relaxation of nanosized particles dispersed in water

Autori
Vuletić, Tomislav ; Frka-Petešić, Bruno ; Tomić, Silvia ; Sondi, Ivan

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
4th Symposium of Science and Technology of Nanomaterials, / Dragan Mihailovič - Ljubljana : Institut Jožef Stefan, 2005, 35-36

Skup
4th Symposium of Science and Technology of Nanomaterials,

Mjesto i datum
Ljubljana, Slovenija, 24.10.2005. - 25.10.2005

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
dielectric spectroscopy; colloids; soft matter; latex

Sažetak
Electrical signaling and complex dynamics in soft-matter systems are of the fundamental interest in life sciences and biotechnology. We investigate dielectric relaxation in colloids, in aqueous environment of varying ionic strength and pH. The one system under study - polystyrene latex [Interfacial Dynamics Co.] is a model colloidal system, since the latex particles are monodisperse, ideally spherical (diameters range 56-1000 nm), surfactant-free and suspended in low-ionic strength electrolytes. Latex colloid is charge-stabilized, since the particle surface is modified by -COOH groups. This surface charge, along with the well-defined counterion atmosphere (H+, Na+), leads to the well-determined polarization response. This response we investigated with low-frequency dielectric spectroscopy. LFDS is application specific and non-destructive technique allowing detection and quantification of polarization response of charged systems in polar and non-polar solvents [Nandi et al., Chem. Rev. 100, 2013 (2000) ; Zoltowski, J. Electroanal. Chem. 443, 149 (1998)]. We used LFDS setup of our design and construction, based on a simple two-plate electrode cell, for measurement of aqueous/liquid samples. By experimental design and proper data processing we achieve a high sample throughput and a broad measurement range of 0.5 kHz - 50 MHz with a single instrument, Agilent 4294A precision impedance analyzer. In colloids two different relaxations are expected theoretically [Dukhin & Shilov Adv.Coll. Interface Sci. 13, 153 (1980) ; O’ Brien, J. Colloid Interface Sci. 113, 81 (1986)], as well as reported experimentally [Schwann et al., J. Phys. Chem. 66, 2626 (1962) ; Roldán-Toro & Solier, J. Colloid Interface Sci. 274, 74 (2004)]. Accordingly, we have observed the low-frequency, LF mode, in the kHz range, and the high-frequency, HF mode, in the MHz range. However, using our advanced experimental setup, we have undertaken to quantitatively relate the experiment with theory. The observed relaxations were interpreted with generalized Debye equation (dashed lines in the figure). One of the obtained parameters, the central relaxation time,  can be related to the characteristic length scale, L, of the counterion atmosphere polarization, through the diffusion equation L2≈  D. We found that the LF mode length scale is similar to the particle size, as expected by Dukhin & Shilov, only if the diffusion constant, D of the H+ ions is considered - meaning that only this ionic species is found in the Stern layer close to the particle surface, while other species prevail in the bulk solution. For the HF mode, we found that it can not be related to the thickness of the Gouy-Chapman diffuse layer, as was expected by O'Brien. HF mode may be speculated to be due to cooperative relaxation [Swenson et al., 5th IDMRC, Lille], when ionic atmospheres (diffuse layers) of particles come into contact. Corresponding length-scale will be much smaller than particle size, as, indeed, we observed. Our further studies are concentrated on the relationship of the dielectric strength,   and of concentrations of ions and surface charge densities.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemija

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