Wetting Contact Angle Research Articles

Effects of femtosecond laser on hard dental tissues: A scoping review.

Traditional tooth preparation can cause patient discomfort, thermal damage to tissues, and occupational health risks for clinicians. Laser-based techniques, particularly femtosecond lasers, offer an alternative due to precise, non-invasive treatment without the thermal and mechanical drawbacks. The objective of this study was to assess available evidence on the effects of femtosecond laser treatment on enamel and dentin. The study design included in vitro or in vivo studies on human teeth reporting on qualitative and quantitative parameters of laser-dental tissue interaction. The review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) statement. The review was registered in the Open Science Framework registry. A comprehensive literature search of PubMed, Scopus, EMBASE/Ovid, Cochrane Library, DARE, LILACS and Pro Quest databases was conducted by three reviewers until 10th January 2024 and then updated on18th August 2024. Eligibility criteria included peer-reviewed articles published in English, focusing on human teeth, with available full text excluding reviews, conference proceedings and gray literature. The outcomes of interest were the quality of tooth preparation, surface characteristics, bond strength, thermal effects and damage to adjacent tissues with variables being laser parameters and tooth types. Methodological quality of studies was not conducted. The search yielded 48 articles after the removal of duplicates, irrelevant and non-retrievable articles. All were original in vitro studies investigating reporting on the outcomes of interest. Measurement methods included a range of microscopy, spectroscopy, optical coherence tomography, universal force testing and thermal imaging. Sapphire lasers were most commonly used with a wide range of parameters. Laser produced sharp-edged cavities with ablated surfaces free of melting (seen in approximately 10% of the craters), cracking, debris, with open dentinal tubules, increased wetting (Contact angle mean range 39.63 ̊(± 1.84 ̊) to 70.47 ̊(± 10.27 ̊) and roughness mean range 0.82 (± 0.05) to 4.20 (± 1.10)µm). Effects of femtosecond laser on bonding efficiency were inconsistent when compared to no treatment, conventional acid etching or Er:YAG laser. Femtosecond laser was shown to achieve precise tooth preparation with no or minimal thermal, mechanical and structural effects on adjacent tissue, however with variable bonding efficiency. Further research is needed to optimize laser parameters, investigate antibacterial effects, and establish long-term clinical outcomes and safety profiles.Date of registration: July 1st, 2024.Registration ID: OSF.IO/UQMNB.

Study on the mechanism of waterborne polyurethane modified ultrafine ground calcium carbonate and its properties in polypropylene plastics

AbstractGround calcium carbonate (GCC) has the effect of reducing the incremental cost and improving the application performance as a plastic filler. In this study, waterborne polyurethane (WPU) was employed as a novel modifier for the wet modification of GCC. Polypropylene (PP)‐based composites incorporating GCC were then prepared for mechanical properties testing. The oil absorption value, wetting contact angle, and settling time in kerosene indicated that the modified GCC achieved an excellent modification effect with a WPU dosage of 2.0 wt%. The X‐ray Diffraction, Fourier Transform Infrared Spectroscopy, and X‐ray Photoelectron Spectroscopy results indicate that WPU was successfully coated on the surface of the GCC. SEM images revealed improved wettability and compatibility of GCC in the composites after modification. The mechanical tests showed that the GCC‐WPU/PP composites exhibited enhanced properties, including a flexural strength of 107 MPa, impact strength of 9.54 kJ/m2, tensile strength of 29.7 MPa, and an elongation at break of 30.9%.Highlights WPU was innovatively used as a modifier of GCC. An optimal modification effect was gained at the low dosage (2.0 wt%). GCC has excellent compatibility and wettability in PP composites. The obtained PP‐based composites have better mechanical properties. The study has the potential to apply GCC in plastics and other industries.

Growth of micro-flowers behind hydrophobic polymer surface and impact of silver and tungsten oxide on the wetting characteristics

In this work, a simple and one-step process was demonstrated to develop hydrophobic polymer surfaces. Commercially available polycarbonate (PC) was treated to turn the front surface hydrophobic with an average wetting contact angle (WCA) as high as 110.5°. The formation of micro-flowers with a coverage density of 9.29 × 106/cm2 on the top of fine base nanostructures was confirmed by a high-resolution field emission scanning electron microscope (FESEM). Impact of typical metal and metal oxide such as silver (Ag) and tungsten oxide (WO3) deposited on such hydrophobic surfaces was demonstrated. Petals of micro-flowers and fine base nanostructures were well decorated with functional metals such as Ag and thus the front surface remained hydrophobic with an average WCA as high as 106.6°. Abundant sharp spikes on the top of narrow hills and dips as revealed in the high-resolution FESEM investigation, were speculated to be the reason behind this hydrophobic characteristic. On the other hand, the hydrophobic surface (WCA of ∼ 110.5°) turned hydrophilic (WCA of ∼11.7°) when the surface was decorated with functional metal oxides, such as WO3. Sessile drop tests were carried out to record average WCA and to understand the wetting characteristics of the specimens. A plausible mechanism for such hydrophobic characteristics as well as the transition from a hydrophobic state to a hydrophilic state has been elucidated.

Biodegradable polymer casting films for drug delivery and cell culture

In this work, for the first time, films were obtained based on biodegradable polyhydroxyalkanoates (PHAs) - a copolymer of 3-hydroxybutyrate-co-3-hydroxyvalerate P(3HB-co-3HV) and a copolymer of 3-hydroxybutyrate-co-4-hydroxybutyrate P(3HB-co-4HB), containing drugs of different chemical structure and action - antibiotics (ceftazidime, doripenem), antiseptic (chlorhexidine) and tissue regeneration stimulator (Actovegin) for drug delivery and cell culture. Using SEM, AFM and measuring the contact angles of water wetting, it is shown how PHAs composition and loading of films of P(3HB-co-3HV) and P(3HB-co-4HB) with drugs affect the porosity, roughness indicators and adhesive properties of the surface. The constructed films are a depot form of drug, the release of which in vitro is realized for a long time, without burst releases, corresponds to Korsmeyer-Peppas and Higuchi models with diffusion character. Films loaded with antibiotics have pronounced antibacterial activity and suppress the development of pathogens S. aureus and E. coli, without a pronounced negative effect on the adhesion and proliferation of epidermal cells. In the cultures of human keratinocytes HaCaT it was shown that the presence of actovegin, as well as ceftazidime in the films, exhibits a stimulating effect, increasing their number. The results demonstrate the suitability of the depot-films for cellular technologies and are promising for the reconstruction of tissues complicated by infection.

Study of lyophilic properties of pyrocarbon as a potential sorbent for cleaning water from oil and oil products

The lyophilic properties of pyrocarbon, obtained by pyrolysis of worn automobile tires, in relation to oil, gasoline, benzene, hexane, water, and water-oil and water-gasoline emulsions were studied. The research was carried out by the method of a lying drop on the surface formed by pyrocarbon particles of different dispersion, by determining the contact angle of wetting. The value of this angle was determined by analyzing images obtained photographically. It was established that organic substances and water have a significant contrast in terms of the wetting of pyrocarbon. Based on the determination of the contact angle, the work of adhesion in different systems was calculated depending on the temperature. Based on this, the conclusion was formulated that the selectivity of absorption of oil and oil products will increase with increasing temperature.

Immobilization of N,N‐diallyl‐N,N‐dimethylammonium chloride on polyethylene. Biocidal properties of the material

AbstractThe immobilization of N,N‐diallyl‐N,N‐dimethylammonium chloride (DADMAC) on low‐density polyethylene (LDPE) films was carried out by the method of postradiation grafting using x‐ray radiation. The introduction of polycation exchanger links provided the appearance of hydrophilicity of the surface of the modified film. By measuring the wetting contact angle, IR and SEM, the island‐type character of the coating from grafted polyDADMAC was detected. The death of Gram‐negative bacteria Pseudomonas aeruginosa, Gram‐positive bacteria Staphylococcus aureus, and yeast (eukaryotes) Yarrowia lipolytica on the surface of the film with grafted polyDADMAC was demonstrated.

Wetting Kinetics of Lithium-Sodium Orthoborate on Nickel and Stainless Steel under CO2-Lean and Saturated Conditions.

Contact angle measurements were conducted on lithium-sodium orthoborate, an alkali-metal borate-based high-temperature carbon capture sorbent, in contact with nickel and stainless steel under air, N2, and CO2 atmospheres at 600 °C in order to assess the compatibility of this innovative sorbent with packed-bed reactors, typically used in the commercial carbon capture industry. On nickel, the results reveal the melt to be wetting (contact angle θ ≤ 90°), albeit with a contact angle reaching an apparent equilibrium over the experimental time considered. It was found that θ was lower under N2 than under CO2, which was explained as a consequence of the oxide-ion activity difference between the CO2-lean and saturated melts. On stainless steel, however, the melt rapidly spreads, tending toward complete wetting of the metal sheet (θ = 0°) in all atmospheres. For the two metals investigated, the results indicate high to very high wettability, hence the adequacy of using lithium-sodium orthoborate in conventional gas-liquid contactors, further backing this sorbent as a potential alternative to existing sorbents for CO2 capture.

Nanostructured thin films of TiO2 tailored by anodization

Although nanostructured TiO2 layers have been widely prepared by anodization, thin films with thicknesses under 1 μm, over substrate other than Ti foils, with structures beyond the nanopores, had remained a challenge. In this work, such nanostructured TiO2 thin films were synthesized by anodization of Ti films deposited by sputtering on FTO/glass substrates. Anodization was performed in an electrolyte based on 0.6 wt% of NH4F, a graphite cathode and the application of 30 V during lapses ranging from 3 to 14 min. The amorphous TiO2 structures acquired the crystal anatase phase after a post-annealing treatment at 450 °C/4 h. Porous morphologies were observed for anodizing times of 3 and 4 min, sponges were formed with 5 and 6 min and vertical tubular structures were achieved by using 7 up to 9 min; dissolution was observed for longer times. Pore diameters of the structures were in the range of 27 to 47 nm, lengths were within the 330 and 1000 nm interval, transmittance was in the visible range of 70 ± 10%, the energy gap was 3.37 ± 0.02 eV and the wet contact angle was between 20 to 27°. One major contribution of the findings herein developed, is that they can be extended to TiO2 thin films, with a specific nanostructure, grown on a wide gamma of substrates, relevant for particular applications.

Extraction and characterisation of cuticular waxes from Physalis peruviana calyx

SummaryWaxes play an important role in maintaining fruit quality and shelf‐life extension because they are naturally effective in blocking the migration of moisture. In this work, cuticular waxes from Physalis peruviana calyx (PPC) were extracted and characterised as potentially hydrophobic materials. Extraction was carried out using the Soxhlet technique with two non‐polar solvents, hexane and petroleum ether, and one polar solvent, ethanol. The extraction yield, lipid characterisation, and hydrophobic potential of cuticular waxes from PPC were analysed and compared using thin‐layer chromatography (TLC), attenuated total reflectance‐infrared spectroscopy (ATR‐IR), GC–MS chromatogram (FAMES), and wetting contact angle. Extraction using hexane was the most efficient method (yield of 9.61 ± 0.37%) for obtaining cuticular waxes with better hydrophobic properties, characterised by a contact angle of = 107.37 ± 1.0° and a hysteresis contact angle of 11° due mainly to the presence of functional groups desirable and characteristic of vegetable waxes. Greater texture homogeneity visualised using optical microscopy and the presence of capric acid (70.97%) as a major component of low‐molecular‐weight fatty acids were observed in this extract. Due to their biodegradable, potentially antifungal, and hydrophobic properties, cuticular waxes from PPC have the potential to replace synthetic waxes in industrial applications.

ПОВЕРХНОСТНО-АКТИВНЫЕ СВОЙСТВА АЛКАНОЛАМИДОВ

The indicators of the wetting ability of surfaces with aqueous solutions of the studied alkanolamides based on distilled fatty acids of rapeseed (DKRMA) and sunflower (DKPMA) oils were studied and monoethanolamide. The sizes of surfactant components were diagnosed using high-precision instruments: a DataPhysics DCAT 21 tensiometer and a 90Plus/BI-MAS particle size analyzer. The contact angles of wetting of glass (hydrophilic) and paraffin (hydrophobic) surfaces with DCPMA solutions at concentrations above the critical micelle concentration (CMC) (1.5-2.0 g/dm3) reached values of 33.0-34.0º. For DKRMA, the contact angles were 34.0-35.0º for the glass surface and 36.0-37.0º for the paraffin surface. It was found that before CMC (at a surfactant concentration of 0.5-1.0 g/dm3), the hydrodynamic radii of the components are in the range of 120.7 - 121.1 nm. Outside the CMC, the hydrodynamic radii of particles of surfactant micelles reach values of 221.3 - 221.6 nm. It was revealed that the synthesized alkanolamides belonged to the category of monodisperse systems according to the fractional composition of the particles of the dispersed phase. The latter is regulated by the uniformity of dispersed particle sizes. The latter is regulated by the uniformity of dispersed particle sizes. Depending on the average size of dispersed particles, the surfactants under study are highly dispersed systems (divided by particle size of the dispersed phase). The surfactants under study are highly dispersed systems, in accordance with the classification by particle size of the dispersed phase depending on the average size of the dispersed particles. It has been proven that the products take an intermediate position between nano- and microparticles. The cloud point temperature (81-83ºС) was measured and the hydrophilic-lipophilic balance (HLB) (11.8-11.9) of the surfactants under study was calculated. The obtained HLB values mean that alkanolamides belong to the group of “oil in water” emulsions. The pH of aqueous solutions of surfactants at a concentration of 10.0 g/dm3 was 7-8. Neonol AF 9-12 was used as a control surfactant.

ВЛИЯНИЕ УЛЬТРАЗВУКА НА ИЗМЕНЕНИЕ ОБЪЕМНОЙ ДОЛИ ЖИДКОСТИ В ПЕНЕ И ЕЕ УСТОЙЧИВОСТЬ

The wave method of acting on matter has long been an area of intense scientific and technological research. Ultrasonic dispersion allows to obtain various highly dispersed, homogeneous and chemically pure suspensions of solid particles in liquids; accelerates and improves the process of obtaining emulsions; ultrasonic waves of different frequencies create conditions for obtaining the structure of the material, which is characterized by isotropy of certain properties. However, the mechanism of action on dispersed systems, namely Pickering systems, is not well understood today. In this work, a study of the variation of liquid volume fraction and stability of bulk foam and its monolayers has been carried out to determine the features and nature of the failure of this dispersed system under wave action. The dependence of foam multiplicity and stability on the concentration and nature of solid particle-stabilizers (titanium oxide, clay, Aerosil-380), as well as on the content and structure of surfactant modifiers (anionic surfactant sodium decyl sulfate, cationic surfactants hexylamine and cetyltrimethylammonium bromide) is shown. The increase in the concentration of solid particles led to an increase in the resistance of foams to ultrasonic actions. The study of changes in the multiplicity and stability of foams at changing the concentration of water repellent showed that the maximum resistance to ultrasonic impacts was observed not at the maximum concentration of surfactant, but at the concentration corresponding to the maximum contact angle of wetting of particles (540). The use of long-chain surfactant cetyltrimethylammonium bromide increased the stability of the foam layer to ultrasonic action at a lower (compared to hexylamine) degree of modification of the surface of solid particles.

Crude oil sorbent based on cellulose nanofibrils-methacrylate grafted copolymers

Hydrophobic composites of cellulose nanofibrils (CNF) with acrylic polymers are obtained by methyl methacrylate (MMA) and butyl methacrylate (BMA) polymerization in Pickering emulsion, stabilized with cellulose nanofibrils. Successful modification of CNF surface by grafting MMA or BMA was confirmed by infrared spectroscopy, gel permeation chromatography, and scanning electron microscopy. The obtained composites were also characterized by simultaneous thermal analysis and wetting contact angle measurement. Composites based on CNF exhibit good thermal and oil sorption properties.

Characterization of Natural and Synthetic Fabrics for the Treatment of Complex Wastes.

In the present study, nine fabrics have been tested for brackish water treatment with the aim of industrial application under the concept of zero liquid discharge (ZLD). Moisture content was determined, where it was observed that the lignocellulosic fabrics had a moisture content ranging from 2.5 to 8.5%. The wetting contact angle showed that the flax with polylactic acid (LPLA) was the most hydrophobic. The determination of the liquid absorption capacity showed that, of the synthetic fabrics, the one with the highest absorption, both in distilled water and in brackish water, was the polyester (PES) fabric with an absorption of 816% compared to its initial weight. In the natural fabrics, the highest absorption capacity was shown by the wet-laid without treatment (WL-WT) fabric for both distilled water and brackish water, although it required several cycles of operation to maintain this stable absorption. Exposure to brackish water improved the absorption capacity of all samples. Mechanical and thermal characterization showed that the synthetic fabrics were more resistant than the natural fabrics, although they may compete in terms of applicability. The capillarity study showed that the most hydrophilic fabrics completed the test the fastest. Finally, the composting degradation test showed that those fabrics with polylactic acid (PLA) content degraded faster in the first 14 days and thereafter the degradation of the lignocellulosic content showed a slower degradation until 112 days. The Bam fabric did not degrade during the course of the experiment.

Influence of the Porphyrin Structures on the Contact Angle of Water Wetting by Langmuir-Schaefer Films

Studying the contact angle of water droplets on the surfaces of thin films formed by organic compounds allows to establish hydrophilic/hydrophobic properties of the films. Knowledge of hydrophilicity/hydrophobicity makes it possible to optimize the composition and increase the adhesive properties of films, improving their functionality. In this study, the dependence of the contact angle of Langmuir-Schaefer films (LS-films) of three compounds: 5,10,15,20-tetraphenylporphyrin (I), 2-aza-21-carba-5,10,15,20-tetraphenyl-porphyrin (II), and 5,15-bis(2,6-bis(dodecycloxy)phenyl)porphyrin (III) was examined. Contact angle data were obtained for LS-films with different transfer numbers of floating layers of the studied porphyrins and different surface roughness. It was found that LS-films of compounds I and II are hydrophobic and their hydrophobicity increases with an increasing of transfer number. In addition, an increase in the surface roughness of the LS film of compound I compared to compound II reduces the value of the contact angle. Unlike porphyrins I and II, LS-films of compound III displayed hydrophilic properties. The obtained data can be used for the targeted design of compounds to create thin film materials of various purposes.

Sensing Properties of Metamaterials Utilized as Self-Cleaning Coating for Solar Mirrors

In this work the experimental activity conducted on self-cleaning sensitive metamaterial coatings for solar mirrors is described. The aim of the research activity is the modulation of solar mirrors wettability in order to reduce water consumption in ordinary cleaning operation and, consequently, maintenance costs, as well as the addition of sensoring properties to the mirrors for the remote acquisition of their performance. In particular, cermet metamaterials and hybrid polymers have been selected as matrices and doped with conductive particles. Considering that in the most part of solar mirrors architectures the external layer consists of an amphiphobic alumino-silicate, which has a wetting contact angle (WCA*) of around 50°, in this work different “silica-like” based coatings have been fabricated by means of sputtering deposition (for inorganic cermet metamaterials) and spraying (for polymers ) with the aim of obtaining a more hydrophobic behavior (WCA > 90° can halve the amount of water required for mirrors cleaning), preserving mirrors optical properties and exhibiting, at the same time, electrical properties suitable to sensoring purpose.

Експериментальне визначення зміни капілярної утримної здатності сітчастих розділювачів фаз

The subject of this study is the process of loss of capillary holding capacity (CHC) as a result of a violation of the balance of external and internal forces on the phase interface (PI) "liquid - gas" of the capillary in the cell of the mesh phase separator (MPS) of the capillary means for ensuring the integrity of the fuel (CMEIF) with a long service life in chemically aggressive fuel components (FP): nitrogen tetroxide (NT) and asymmetric dimethylhydrazine (NDMH). The goal is to improve the selection of design parameters of the CMEIF through the refinement of traditional approaches to the calculation of the CHC MPS depending on the term of their operation. Task: to determine the rate of corrosion of the main structural material of the MPS - steel nets of the twill weave type, and its effect on the structural and geometric characteristics of the nets; to perform an experimental determination of the change in the MPS CHC; to improve the mathematical model for determining the MPS CHC, considering the term of their operation as part of the fuel system of space flight vehicles (SFV). The methods used are as follows: to determine the rate of corrosion - metallographic studies and measurement of the geometric dimensions of mesh samples; to determine the change in CHC - the bubble method. The following results were obtained. The coefficient of the maximum corrosion rate was determined. A new, refined dependence of the average value of Bo cr on the temperature of the FP was obtained. Linear regressions of changes in the approximated values of CHC MPS depending on the duration of their operation were obtained. An increase in the average arithmetic value of the wetting contact angle θ in the NDMG over 31 years of MPS operation was determined. An improved mathematical model for determining the CHC of MPS was obtained, considering the period of their operation in JSC and NDMH. Conclusions. The scientific novelty of the obtained results is as follows: for the first time, comprehensive studies were carried out to determine the rate of corrosion of the main structural material of MPS after a long period of their stay (from 14 to 31 years) in FP (NT and NDMG) and under their pairs, the results of which revealed regularities of flow corrosion processes in the liquid and gas phase, established corrosion rates and deduced coefficients, the application of which improves the engineering methods of calculating the main parameters of MPS; the physical model for calculating Bo kr received further development; the physical model for calculating the CHC has been improved, which makes it possible to calculate the value of the static CHC of the MPS with greater accuracy than it was before and to make the final design of the designed CMEIF more perfect and reliable.

A numerical study on the effect of wall wettability on film formation in liquid–liquid slug flow

This study numerically investigates the effect of the contact angle on the hydrodynamics of liquid–liquid slug flow in a capillary with an internal diameter of 2.4 mm. The finite volume method is used to solve the Navier–Stokes equation, and the volume-of-fluid method is employed for interface capturing. The contact angle varies from 13° to 169°. The aqueous phase is observed as a continuous medium, the organic phase is in a dispersed phase at low contact angles, and the aqueous phase is dispersed as a medium at high contact angles. The slug velocity is lower at partial wetting contact angles than at fully wetting or non-wetting contact angles. The vorticity inside the slug is higher at extreme contact angles (169°/13°) and becomes very pronounced near the interface. At the Weber number Weslug>0.135, fully developed film is observed. The thickness of this film increases as the interfacial tension decreases. Additionally, the pressure within the slug rises with an increase in interfacial tension.

Protective and water-repellent properties of alkylcarboxylic and alkylphosphonic acid films on technically pure magnesium

The formation of superhydrophobic coatings using low‑toxicity corrosion inhibitors is a promising method for corrosion protection of metals and alloys. In this study, the effects of surface roughness and the of the adsorbed substance structure on wettability and corrosion resistance of commercially pure magnesium were investigated. Surface roughness was created by three different methods: paper grinding, etching in nitric acid solution and laser treatment. Oleic, stearic and octadecylphosphonic acids were investigated as potential surface modifiers for the formation of corrosion resistant superhydrophobic coatings. It has been shown that the protective and hydrophobic properties of acid films on magnesium, as well as their stability, are determined by both the initial surface morphology and the nature of the inhibitors. Experimentally, the laser treatment was found to be preferable to mechanical and chemical surface preparation and the best hydrophobic agent among the studied acids is phosphonic acid. The most stable films with excellent superhydrophobic and protective properties in atmospheres of high humidity and salt spray clamber are formed in a solution of 0.001 M octadecylphosphonic acid on the surface of magnesium with high roughness. In addition, the effect of vinyltrimethoxysilane on the protective and hydrophobic properties of stearic acid and octadecylphosphonic acid films was investigated. The results of direct corrosion tests and wetting contact angle degradation kinetics studies showed that the protective and hydrophobic properties of stearic acid can be enhanced by its layer-by-layer adsorption with silane. They practically reach the parameters of octadecylphosphonic acid.

Bubble Behavior and Anode Effect on Different Carbon Anode Designs in Cryolite Melt Applying a See-through Furnace

Anodic CO2 gas evolution is one of the main processes in the Hall-Héroult electrolysis cell for primary aluminium production. This work is a laboratory scale study of the effect of anode geometry, anode orientation and carbon anode material on bubble behavior and bubble properties in cryolite melt. Increased knowledge of the bubble behavior is important for improved design of industrial cells, but also for laboratory‐scale experiments. The anodes studied in this work are frequently applied for investigation of reaction kinetics and mass transport, anode effect, current efficiency, anode quality properties, etc. It is therefore of interest to study the bubble dynamics of these anodes in more detail because bubble evolution is relevant for all the above-mentioned phenomena.The anode potential has been shown to be highly dependent on anode geometry and orientation. For this study four different anode designs were made: horizontal (downward-facing), inverted horizontal (upward-facing), vertical, rod (with both vertical and horizontal surface). For most of the designs, characteristics such as bubble noise, bubble size, and wetting were obtained as a function of current density or anode potential/cell voltage. The bubble noise normally went through a maximum, while the bubble size decreased in the whole current density range. The wetting contact angle showed little variation with current density. It was assumed that the current density had a stronger effect on the contact angle through its effect on the bubble size than the polarization and associated surface roughening.Also, phenomena like nucleation, growth, coalescence, bubble detachment and anode effect were studied for both graphite and industrial carbon as anode material. The nucleation was more pronounced at the industrial carbon due to more active sites confirmed by CT analysis. The coalescence process was found to be independent of current density/potential and carbon anode material and was in the range 16-24 msec. On increased currents anode effect occurred on both anodes, the current being lower for the graphite anode at onset. Video recordings and electrochemical measurements showed more abrupt initiation of the anode effect on the graphite and a strong de-wetting of the anode. With the existence of a (C – F) surface compound on the anode, as long as the anode effect gas could escape the electrode surface, the anode seems to be electrochemically active towards both CO/CO2 and PFC formation during anode effect.In addition to the bubble characteristics and phenomena described, the impact of the results for better anode design for laboratory scale studies is discussed.

Interaction of surfactants with Prunus laurocerasus leaf surfaces: time-dependent recovery of wetting contact angles depends on physico-chemical properties of surfactants

BackgroundSurfactants are added to spray solutions because they significantly improve foliar uptake of active ingredients (AIs) into the leaves. It was intended to investigate whether surfactant solutions forming a dried deposit on Prunus leaf surfaces after they were sprayed, lead to structural and functional changes of the cuticle/atmosphere interface. This could potentially result in irreversibly enhanced leaf surface wetting, which should be of major disadvantage. Enhanced wetting could promote leaching of ions and promote leaf surface colonization with microorganisms.ResultsPrunus laurocerasus leaf surfaces were sprayed with aqueous solutions of non-ionic alcohol ethoxylates, a cationic, an anionic and one large polar surfactant. Directly after spraying and drying of the different surfactant solutions, wetting contact angles of deionized water (without surfactant) were significantly lower (between 6 and 54°) compared to wetting contact angles on untreated leaves (77°). Leaf surface wettability with deionized water was more pronounced with non-ionic alcohol ethoxylates (wetting contact angles ranging between 6 and 22°) compared to the other 3 surfactants (wetting contact angles ranging between 42 and 54°). Wetting contact angles of deionized water on leaf surfaces treated with non-ionic alcohol ethoxylates continuously increased again over time resulting in final wetting contact angles not different from untreated leaf surfaces. The time-dependent recovery of wetting contact angles was dependent on the degree of ethoxylation of the non-ionic alcohol ethoxylates. The wetting contact angle recovery rate was lower the higher the degree of ethoxylation of the alcohol ethoxylates was. With the cationic, anionic and large polar surfactant a recovery of wetting contact angles was not observed. In addition, on fully dehydrated and dead leaves wetting contact angle recovery was not observed for any of the tested surfactants after spraying and drying. Analytical determinations of the amounts of alcohol ethoxylates on the leaf surfaces after spraying and drying showed that amounts of alcohol ethoxylates decreased over time on the surface (24–72 h).ConclusionOur results indicate that non-ionic alcohol ethoxylates diffused within hours from the leaf surface into the leaf over time and thus fully disappeared from the leaf surface. This was not the case with the cationic, anionic and the large polar surfactants remaining on the leaf surface.Graphical