title: Dielectric-spectroscopy approach to ferrofluid nanoparticle clustering induced by an external electric field.
abstract: An experimental study of magnetic colloidal particles cluster formation induced by an external electric field in a ferrofluid based on transformer oil is presented. Using frequency domain isothermal dielectric spectroscopy, we study the influence of a test cell electrode separation distance on a low-frequency relaxation process. We consider the relaxation process to be associated with an electric double layer polarization taking place on the particle surface. It has been found that the relaxation maximum considerably shifts towards lower frequencies when conducting the measurements in the test cells with greater electrode separation distances. As the electric field intensity was always kept at a constant value, we propose that the particle cluster formation induced by the external ac electric field accounts for that phenomenon. The increase in the relaxation time is in accordance with the Schwarz theory of electric double layer polarization. In addition, we analyze the influence of a static electric field generated by dc bias voltage on a similar shift in the relaxation maximum position. The variation of the dc electric field for the hysteresis measurements purpose provides understanding of the development of the particle clusters and their decay. Following our results, we emphasize the utility of dielectric spectroscopy as a simple, complementary method for detection and study of clusters of colloidal particles induced by external electric field.
authors.affiliation: Institute of Experimental Physics SAS, Watsonova 47, 04001 Košice, Slovakia.
authors.forename: Michal
authors.initials: M
authors.lastname: Rajnak
authors.affiliation: Faculty of Electrical Engineering and Informatics, Technical University of Košice, Letná 9, 04200 Košice, Slovakia.
authors.forename: Juraj
authors.initials: J
authors.lastname: Kurimsky
authors.affiliation: Faculty of Electrical Engineering and Informatics, Technical University of Košice, Letná 9, 04200 Košice, Slovakia.
authors.forename: Bystrik
authors.initials: B
authors.lastname: Dolnik
authors.affiliation: Institute of Experimental Physics SAS, Watsonova 47, 04001 Košice, Slovakia.
authors.forename: Peter
authors.initials: P
authors.lastname: Kopcansky
authors.affiliation: Institute of Experimental Physics SAS, Watsonova 47, 04001 Košice, Slovakia.
authors.forename: Natalia
authors.initials: N
authors.lastname: Tomasovicova
authors.affiliation: Laboratory of Magnetic Fluids, Center for Fundamental and Advanced Technical Research, Romanian Academy-Timisoara Branch, Bv. M. Viteazu 24, Timisoara RO-300223, Romania and National Institute of Research-Development in the Pathology Domain and Biomedical Science "Victor Babes," Splaiul Independentei Street 99-101, sector 5, Bucharest RO-050096, Romania.
authors.forename: Elena Alina
authors.initials: EA
authors.lastname: Taculescu-Moaca
authors.affiliation: Institute of Experimental Physics SAS, Watsonova 47, 04001 Košice, Slovakia.
authors.forename: Milan
authors.initials: M
authors.lastname: Timko
mesh_terms: D058266:Dielectric Spectroscopy; D004560:Electricity; D004566:Electrodes; D059346:Magnets / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*