Juraj Kurimský

Electric Field-Driven Assembly of Sulfonated Polystyrene Microspheres

A designed assembly of particles at liquid interfaces offers many advantages for development of materials, and can be performed by various means. Electric fields provide a flexible method for structuring particles on drops, utilizing electrohydrodynamic circulation flows, and dielectrophoretic and electrophoretic interactions. In addition to the properties of the applied electric field, the manipulation of particles often depends on the intrinsic properties of the particles to be assembled. Here, we present an easy approach for producing polystyrene microparticles with different electrical properties. These particles are used for investigations into electric field-guided particle assembly in the bulk and on surfaces of oil droplets. By sulfonating polystyrene particles, we produce a set of particles with a range of dielectric constants and electrical conductivities, related to the sulfonation reaction time. The paper presents diverse particle behavior driven by electric fields, including particle assembly at different droplet locations, particle chaining, and the formation of ribbon-like structures with anisotropic properties.

Ticks and radio-frequency signals: behavioural response of ticks ( Dermacentor reticulatus ) in a 900 MHz electromagnetic field

Abstract The electromagnetic field (EMF) is present in the environment throughout the world and encompasses both natural and human-made sources of electromagnetic fields. It has been shown that EMF influences a variety of biological systems, including the behavioural responses of both vertebrates and invertebrates. As such, determining the effects of the EMF on the ecosystem in detail may be important for understanding the ecology and biology of organisms, particularly those, such as ticks, that are important in disease transmission. Our main goal was to determine if the tick, Dermacentor reticulatus, interacts with the EMF. An experimental behavioural test of tick sensitivity to radio frequency power radiation was performed under laboratory conditions. Tests were performed in an electromagnetic compatibility laboratory in a radio frequency electromagnetic field (RF-EMF) anechoic chamber. Ticks were irradiated using a Double-Ridged Waveguide Horn Antenna with 900 MHz RF-EMF. The applied radio-frequency power was tuned below the proposed limit for public exposure to mobile phone base stations. We found that exposure induces an immediate tick locomotor response manifested either in a previously unreported jerking movement of the whole body or in jerking of the first pair of legs. Overall, ticks exhibited significantly greater movement in the presence of the RF-EMF. Significant sex differences relative to RF-EMF exposure were observed in both response variables. In the presence of RF-EMF, body jerking by females was greater than in males and vice versa for leg jerks. This study represents the first experimental evidence of a behavioural response of D. reticulatus ticks to exposure to RF-EMF.

Assembly of 1D Granular Structures from Sulfonated Polystyrene Microparticles

Being able to systematically modify the electric properties of nano- and microparticles opens up new possibilities for the bottom-up fabrication of advanced materials such as the fabrication of one-dimensional (1D) colloidal and granular materials. Fabricating 1D structures from individual particles offers plenty of applications ranging from electronic sensors and photovoltaics to artificial flagella for hydrodynamic propulsion. In this work, we demonstrate the assembly of 1D structures composed of individual microparticles with modified electric properties, pulled out of a liquid environment into air. Polystyrene particles were modified by sulfonation for different reaction times and characterized by dielectric spectroscopy and dipolar force measurements. We found that by increasing the sulfonation time, the values of both electrical conductivity and dielectric constant of the particles increase, and that the relaxation frequency of particle electric polarization changes, causing the measured dielectric loss of the particles to shift towards higher frequencies. We attributed these results to water adsorbed at the surface of the particles. With sulfonated polystyrene particles exhibiting a range of electric properties, we showed how the electric properties of individual particles influence the formation of 1D structures. By tuning applied voltage and frequency, we were able to control the formation and dynamics of 1D structures, including chain bending and oscillation.