The transition between the Cassie and Wenzel wetting regimes has been observed under vertical vibration of a water drop placed on a rough micrometrically scaled polymer pattern. The transition takes ...place under the constant force per unit length of the triple contact line, not under constant pressure. A study of the vibrating drop deposited on the rough surface supplied valuable information concerning the Cassie−Wenzel wetting transition.
Wetting properties of lycopodium-based surfaces are reported. The surfaces demonstrate high apparent contact angles accompanied by high adhesion of water droplets, similar to the recently reported ...biological interfaces (rosea Rehd) showing the “petal effect”. Apparent contact angles depended strongly on the droplet volume. Vertical vibration of droplets deposited on the lycopodium-based reliefs promoted wetting transition. Semiquantitative analysis of the observed wetting transition taking into account the hierarchical topography of the relief is presented. We relate the high adhesion of droplets to the partial filling of pores constituting the relief.
The motion of ferrofluidic marbles on flat polymer substrates is reported. Nanopowders of polyvinylidene fluoride and γFe2O3 were used for the preparation of ferrofluidic marbles. The marbles are ...activated easily with an external magnetic field. A microfluidic device based on ferrofluidic marbles (the ferrofluidic bearing) is described. Velocities of marbles as high as 25 ± 3 cm/s were registered. The sliding of ferrofluidic drops on superhydrophobic surfaces was studied. It was demonstrated that the threshold magnetic force necessary for the drop displacement depends linearly on the drop radius, thus the motion of the drop is defined by the processes occurring in the vicinity of the triple line only.
A superhydrophobic surface is produced from industrial grade polymer materials. The surface comprises partly disordered triple-scaled arrays of polyvinylidene fluoride (PVDF) globules. An inherently ...superhydrophobic metallic surface is produced with polymer template. The mathematical model based on the Cassie−Baxter hypothesis of air trapping under a water drop is built, which gives the apparent contact angle on the manifold-scaled interface. The presence of several scales itself is not a sufficient condition of hydrophobicity of inherently wettable surfaces. The geometrical features favoring the increase of the vapor-water interface fraction are necessary for this phenomenon.
The surface of water “marbles” obtained with hydrophobic lycopodium and polyvinylidene fluoride particles was investigated first with environmental scanning electron microscopy. The shape of water ...marbles was studied both experimentally and theoretically. The mathematical model describing the deformation of marbles by gravity is proposed. The model allowed the calculation of the effective surface tension of marbles and gives 0.09 J/m2 for marbles coated with PVDF and 0.06 J/m2 for marbles coated with lycopodium. The effective surface tensions of marbles calculated independently by the horizontal vibration of marbles were in semiquantitative agreement with the above values (0.07 J/m2 for marbles coated with PVDF and 0.055 J/m2 for marbles coated with lycopodium).
We report electrically controlled membranes which become permeable when an electrical field is exerted on a droplet deposited on the membrane. Micro-porous polycarbonate membranes are obtained with ...the breath-figures assembly technique, using micro-scaled stainless steel gauzes as supports. The membranes demonstrate pronounced Cassie-Baxter wetting. Air cushions trapped by the droplet prevent water penetration through the membrane. We demonstrate two possibilities for controlling the permeability of the membrane, namely contact and non-contact scenarios. When an electrical field is exerted on a droplet deposited on the membrane, the triple-line is de-pinned and the wetting transition occurs in the non-contact scheme. Thus, the membrane becomes permeable. The contact scheme of the permeability control is based on the electrowetting phenomenon.
Pulsed electric fields (PEFs) technology was reported to be useful as a disinfection method in the liquid food industry. This technology may lead to membrane permeabilization and bacterial death. ...However, resuscitation of viable but non-culturable cells and sublethally injured microorganisms in food was reported to be associated with foodborne outbreaks. The main aim of this study was to investigate the possible recovery of injured PEF-treated bacteria. The PEF treatment of
and
led to a reduction of 3.2 log
and 4.8 log
, respectively. After 5 h, no colony forming units (CFUs) were observed when the bacteria were suspended in phosphate buffer saline (PBS); and for 24 h, no recovery was observed. The PEF-treated
in brain-heart infusion (BHI) medium were maintained at 1.84 × 10
CFU mL
for about 1.5 h. While
decreased to zero CFU mL
by the 4th hour. However, after that, both bacteria recovered and began to multiply. Flow cytometry analysis showed that PEF treatment led to significant membrane permeabilization. Mass spectrometry analysis of PEF-treated
which were suspended in BHI revealed over-expression of 22 proteins, where 55% were related to stress conditions. Understanding the recovery conditions of PEF-treated bacteria is particularly important in food industry pasteurization. To our knowledge, this is the first comprehensive study describing the recovery of injured PEF-treated
and
bacteria.
The possibility of forming a hydrophobic metallic interface is shown when it is micrometrically textured. On such surface obtained by gold coating the polymer honeycomb template, the apparent contact ...angle of water was observed to be close to or greater than 90°. The metal hydrophobicity is explained by trapping air inside pores of pattern according to the Cassie–Baxter wetting model. The agreement between calculated and observed values of the apparent contact angle justifies the applicability of this model in the present case. Formation of the acute local (Young) angle on the pore surface is provided by its concave form.
The wetting of rough honeycomb micrometrically scaled polymer substrates was studied. A very strong dependence of the apparent contact angle on the drop volume has been established experimentally. ...The environmental scanning electron microscopy study of the fine structure of the triple line is reported first. The triple line is not smooth and prefers grasping the polymer matrix over air holes. The precursor rim surrounding the drop has been observed. The revealed dependence of the apparent contact angle on the drop volume is explained by the transition between the pure Cassie and combined Wenzel−Cassie wetting regimes, which is induced by capillarity penetration of water into the holes of relief.
One of the promising technologies that can inactivate microorganisms without heat is pulsed electric field (PEF) treatment. The aim of this study was to examine the influence of PEF treatment (2.9 kV ...cm−1, 100 Hz, 5000 pulses in trains mode of 500 pulses with a pulse duration of 10 µs) on Saccharomyces cerevisiae eradication and resealing in different conditions, such as current density (which is influenced by the medium conductivity), the sort of medium (phosphate buffered saline (PBS) vs. yeast malt broth (YMB) and a combined treatment of PEF with the addition of preservatives. When the S. cerevisiae were suspended in PBS, increasing the current density from 0.02 to 3.3 A cm−2 (corresponding to a total specific energy of 22.04 to 614.59 kJ kg−1) led to an increase of S. cerevisiae eradication. At 3.3 A cm−2, a total S. cerevisiae eradication was observed. However, when the S. cerevisiae in PBS was treated with the highest current density of 3.3 A cm−2, followed by dilution in a rich YMB medium, a phenomenon of cell membrane resealing was observed by flow cytometry (FCM) and CFU analysis. The viability of S. cerevisiae was also examined when the culture was exposed to repeating PEF treatments (up to four cycles) with and without the addition of preservatives. This experiment was performed when the S. cerevisiae were suspended in YMB containing tartaric acid (pH 3.4) and ethanol to a final concentration of 10% (v/v), which mimics wine. It was shown that one PEF treatment cycle led to a reduction of 1.35 log10, compared to 2.24 log10 when four cycles were applied. However, no synergic effect was observed when the preservatives, free SO2, and sorbic acid were added. This study shows the important and necessary knowledge about yeast eradication and membrane recovery processes after PEF treatment, in particular for application in the liquid food industry.
PDF
