Victor Multanen

Physical mechanisms of interaction of cold plasma with polymer surfaces

Physical mechanisms of the interaction of cold plasmas with organic surfaces are discussed. Trapping of plasma ions by the CH2 groups of polymer surfaces resulting in their electrical charging is treated. Polyethylene surfaces were exposed to the cold radiofrequency air plasma for different intervals of time. The change in the wettability of these surfaces was registered. The experimentally established characteristic time scales of the interaction of cold plasma with polymer surfaces are inversely proportional to the concentration of ions. The phenomenological kinetic model of the electrical charging of polymer surfaces by plasmas is introduced and analyzed.

Plasma treatment switches the regime of wetting and floating of pepper seeds

Cold radiofrequency plasma treatment modified wetting and floating regimes of pepper seeds. The wetting regime of plasma-treated seeds was switched from the Wenzel-like partial wetting to the complete wetting. No hydrophobic recovery following the plasma treatment was registered. Environmental scanning electron microscopy of the fine structure of the (three-phase) triple line observed with virgin and plasma-treated seeds is reported. Plasma treatment promoted rapid sinking of pepper seeds placed on the water/air interface. Plasma treatment did not influence the surface topography of pepper seeds, while charged them electrically. Electrostatic repulsion of floating plasma-treated seeds was observed. The surface charge density was estimated from the data extracted from floating of charged seeds and independently with the electrostatic pendulum as σ≈1-2μC/m2.

Probing properties of cold radiofrequency plasma with polymer probe

The probe intended for the characterization of cold plasma is introduced. The probe allows estimation of the Debye length of the cold plasma. The probe is based on the pronounced modification of surface properties (wettability) of polymer films by cold plasmas. The probe was tested with the cold radiofrequency inductive air plasma discharge. The Debye length and the concentration of charge carriers were estimated for various gas pressures. The reported results coincide reasonably with the corresponding values established by other methods. The probe makes possible measurement of characteristics of cold plasmas in closed chambers.

Friction, Free Axes of Rotation and Entropy

Friction forces acting on rotators may promote their alignment and therefore eliminate degrees of freedom in their movement. The alignment of rotators by friction force was shown by experiments performed with different spinners, demonstrating how friction generates negentropy in a system of rotators. A gas of rigid rotators influenced by friction force is considered. The orientational negentropy generated by a friction force was estimated with the Sackur-Tetrode equation. The minimal change in total entropy of a system of rotators, corresponding to their eventual alignment, decreases with temperature. The reported effect may be of primary importance for the phase equilibrium and motion of ubiquitous colloidal and granular systems.

Biofilm formation on agricultural waste pretreated with cold low-pressure nitrogen plasma and corona plasma discharges

Agricultural waste (AW) was pretreated with cold low-pressure nitrogen plasma (LPD) and corona atmospheric plasma discharges (CAPD), in an attempt to increase the bacterial attachment and biofilm formation. Biofilm formation was examined in the presence of exogenously added P. putida and B. cereus as well as in a sterile medium where only the indigenous bacteria which grow naturally on the wood surface could form biofilm. The exposure of AW to (LPD) led to a 3.5-fold increase in biofilm formation of the exogenously add P. putida F1 in MMT (minimal medium supplied with toluene) and a 1.6-fold increase in MMG (minimal medium supplied with glucose) compared to the untreated AW. The increase in biofilm formation was also observed with the exogenously added B. cereus or with indigenous bacteria that grow naturally on the AW. The effect of the CAPD on biofilm formation was weak. SEM analysis of the LPD-treated AW showed an increase in surface roughness, which we assume is one of the reasons for the enhancement of the biofilm formation. The apparent contact angle of a sessile drop on the surface of LPD-treated AW as well as on the bacterial layer showed their hydrophilic nature. In conclusion, the increase in biofilm formation of the exogenously added P. putida or B. cereus was due to the LPD treatment. Importance To the best of our knowledge, this is the first study to describe the effect of wood plasma treatment on biofilm formation. This technology can be further implemented for bioremediation of contaminated soils.

Camphor-Engine-Driven Micro-Boat Guides Evolution of Chemical Gardens

A micro-boat self-propelled by a camphor engine, carrying seed crystals of FeCl3, promoted the evolution of chemical gardens when placed on the surface of aqueous solutions of potassium hexacyanoferrate. Inverse chemical gardens (growing from the top downward) were observed. The growth of the “inverse” chemical gardens was slowed down with an increase in the concentration of the potassium hexacyanoferrate. Heliciform precipitates were formed under the self-propulsion of the micro-boat. A phenomenological model, satisfactorily describing the self-locomotion of the camphor-driven micro-boat, is introduced and checked.