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Surface characteristics of printing substrates are of the utmost importance to all types of paper that interact with ink. During all types of printing processes, the behaviour of the liquid phase (ink or dye) on the paper is directly defined by the paper cellulose-based surface. The printed ink spreads and penetrates more into paper fibres when the paper surface is rougher and more permeable. Contact angle measurements by sessile drop method are considered the most appropriate for determining the paper sheet surface energy. Paper as hydrophilic material has a high absorption rate resulting in a low contact angle. The objective of this study was to evaluate the surface free energy of laboratory-made papers containing straw pulp obtained from residues after the harvest of the most cultivated cereals in Croatia (wheat, barley and triticale). The obtained surface free energy results are promising for straw pulp usage in the manufacture of printing paper.

In this paper, temperature and concentration dependencies on density and surface tension of liquid Fe-C-O-Cr alloys (1.93 - 4.80 wt.% Cr) were investigated in high-temperature resistance observation furnace by a sessile drop method during heating from liquidus temperature to 1600 degrees C. The interfacial characteristics (interfacial tension, wetting angle, work of adhesion, and spreading coefficient) of liquid alloy/alumina system were also determined depending on temperature. The effect of temperature and chromium content on surface and interfacial properties was proven in case of all examined alloys. Based on the fact that the content of surface-active elements such as oxygen (up to 195 ppm) and sulfur (up to 545 ppm) was higher; the influence of activities of both mentioned elements on surface tension of alloy samples was assessed. Particular attention was paid to the dependence of the surface tension temperature coefficient on oxygen and sulfur activity. U ovom radu je ispitivana zavisnost gustine i površinskog napona od temperature i koncentracije kod legure Fe-C-O-Cr u tečnom stanju (1.93 - 4.76 wt.% Cr) u peći za ispitivanje na visokim temperaturama putem sessile drop metode prilikom zagrevanja od likvidus temperature do 1600 °C. Osobine na graničnoj površini ( napon na graničnoj površini, ugao kvašenja, adhezija i koeficijent širenja) legura sa sadržajem aluminijuma u tečnom stanju su utvrđene u zavisnosti od temperature. Uticaj temperature i sadržaja hroma na površinske osobine, kao i svojstva na graničnoj površini je dokazan kod svih ispitivanih legura. Na osnovu činjenice da je sadržaj aktivnih elemenata kao što su kiseonik (do 195 ppm) i sumpor (do 545 ppm) na površini bio viši, procenjen je i njihov uticaj na površinski napon kod uzoraka legura. Posebna pažnja je posvećena zavisnosti površinskog napona i koficijenta temperature od aktivnosti kiseonika i sumpora. Web of Science 56 2 151 143

Silicon-boron alloys have been recently pointed out as novel ultra-high temperature phase change materials for applications in Latent Heat Thermal Energy Storage (LHTES) and conversion systems. One of the emerging challenges related to the development of such devices is a selection of refractories applicable to build a vessel for storing molten Si-B alloys at high temperatures and under consecutive melting/solidification conditions. Previously, it has been documented that hexagonal boron nitride (h-BN) is the only one ceramic showing a non-wettability and limited reactivity with Si-B alloys at temperatures up to 1750 °C, what makes it a good candidate of the first selection for the predicted application. Nevertheless, pure h-BN shows a rather low mechanical strength that could affect a durability of the LHTES vessel. Therefore, the main purpose of this work was to examine high temperature behavior of commercial high strength h-BN composite having a nominal composition of h-BN-24ZrO2-6SiC (vol.%) in contact with a solid/liquid eutectic Si-3.2B alloy. Two types of sessile drop experiments were carried out: a step-contact heating up to 1750 °C, and a thermocycling at 1300 − 1450 °C composed of 15 cycles of the alloy melting/solidification. The obtained results showed a lack of wettability in the examined system at temperatures up to 1750 °C. The Si-3.2B alloy presented good repeatability of melting/solidification temperatures in consecutive thermal cycles, which was not affected by the interaction with the h-BN composite. However, due to reactions taking place between the composite’s components leading to structural degradation, it is not recommended to increase operational temperature of this material above 1450 °C.

The article presents original experimental data on surface tension of the Fe100 – xMnx (x = 4–13 wt %) melts. Surface tension and density of the melt were measured by the sessile drop method at heating from the liquidus temperature to 1780°C and subsequent sample cooling in the atmosphere of high-purity helium. Temperature and concentration dependences of surface tension and density of Fe–Mn melts were plotted. Manganese is a surface-active substance in iron melt. The value of surface tension coefficient of Fe–Mn melts decreases as Mn content increases. Experimental data on the surface tension of Fe–Mn melts is consistent with the theoretical dependences (the Pavlov–Popel’ equation and the Shishkovsky equation). During the investigation of Fe–Mn melt microheterogenity, correlation between the values of kinematic viscosity, surface tension, and density is revealed. Fluidity dependence of Fe–Mn melts on their density in the cooling mode has a linear character which indicates satisfaction of the Bachinskii law. Discrepancy in the melt viscosity ratios to the surface tension coefficient obtained from the experimental data and from the empirical formula is discovered. Using the experimental data on viscosity and surface tension of Fe–Mn melts, the entropy change in the melt’s bulk and the change in the melt’s surface entropy, respectively, are studied. The surface entropy and the bulk entropy in the melt decrease in their absolute value with its increasing Mn content. From the study results, it is concluded that there is no destruction of the microheterogeneous structure of Fe100 – xMnx (x = 4–13 wt %) melts when heated up to 1780°C. © 2020, Allerton Press, Inc. The reported study was funded by Russian Foundation for Basic Research, project no. 19-33-90198.

A facile method for the fabrication of colloidal photonic crystal coatings with tunable structural color on a wood surface was presented. The photonic crystal coatings were formed from monodisperse latex spheres composed of poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)). The latex spheres with a hard PSt core and elastomeric P(MMA-AA) shell were prepared using the emulsion polymerization method. The sessile drop method, a rapid single-step self-assembly method through simple evaporation of emulsion, was used to form three-dimensional colloidal crystals. Coatings with brilliant colors and uniform Bragg&rsquo, s diffraction covering the entire visible region were fabricated by controlling the sphere size. This simple method provided new insight into the development of wood color embellishment.

In this paper, the experimental performance of a new testing device designed for investigating the high temperature properties of molten Mg is presented. The newly developed device allows examining high temperature wetting behavior and thermophysical properties of molten Mg (and Mg alloys) by using various experimental procedures (e.g. classical sessile drop, pendant drop, dispensed drop and drop sucking). High temperature wettability tests at temperatures up to 1000 °C in an inert gas atmosphere or under high vacuum (up to 10−7 hPa) are now possible. It has been documented that the application of the classical sessile drop method combined with a capillary purification procedure successfully eliminates the problem of magnesium oxidation that traditionally affects obtained results. Selected examples of high temperature experiments carried out for molten Mg in contact with various refractories are presented in order to show a wide range of analytical possibilities of the new device. The results obtained by using the new device are important from both a high theoretical and practical perspective regarding liquid phase assisted fabrication and processing of Mg-based alloys and metal-matrix composites. Keywords: Equipment design, Sessile drop method, Reactivity, Mg composites, Mg alloys

In this work, we used a sessile drop experiment to assess a feasibility of novel processing design engaging liquid-phase assisted fabrication of multi-phase materials from Mo-Si-B system. For this purpose, binary eutectic silicon-boron alloy (Si-3.2B wt%) was subjected to contact heating with polycrystalline molybdenum substrate at temperature up to 1385 °C. It was in-situ observed that molten Si-3.2B alloy wets and rapidly spreads over the Mo surface. After the high temperature test, the solidified couple was subjected to structural characterization by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction methods. The obtained results revealed that the direct interaction between examined materials under applied testing conditions results in the reactively formed product layer having a thickness of ∼80 µm. The following structural features were recognized starting from the surface side: (I) the main product layer composed of columnar-like MoSi2 phase and Mo5Si3 phase; (II) an intermediate layer made of MoB and Mo5SiB2 phases. Although these results give the first indication for designing a novel liquid-assisted fabrication method of Mo-Si-B materials, an existence of porosity in the product layer clearly suggests that a further optimization of the process parameters is necessary.

Understanding the atomic-level phenomena occurring upon the wetting of graphene-coated Cu with liquid Ag is pivotal for the description of the wetting phenomenon and the role of graphene as a diffusion barrier. We have performed molecular dynamics (MD) simulations and confronted with our present experimental results to characterize wetting behavior of graphene coated Cu surfaces. Perfect and defected graphene layers covering Cu surface were wetted with liquid Ag droplet at 1273 K. Structural and topological aspects are discussed to characterize structure of the liquid Ag droplet and a product of wetting reaction occurring on Cu/Gn and Cu/Gndef substrates, also including perfect graphene layer and a pure Cu surface. The obtained results reveal the importance of defects in graphene structure, which play a key role in wetting mechanism and the formation of AgCu alloy. As a consequence, we observe a change of the wetting behavior and topology of both bulk and adsorbed Ag atoms by using Voronoi analysis (VA). Despite the differences in time scale, atomistic simulations allowed us to catch the early stages of wetting, which are important for explaining the final stage of wetting delivered from experiment. Our findings reveal also graphene translucency to metal-metal interactions, observed in previous papers.

Wettability between liquid Ag and graphene-coated SiC single crystal has been investigated by dispensed drop method at T = 970 C under vacuum accompanied with subsecond recording of the drop/substrate images (100 frames per second) by high-speed high-resolution CCD camera. Non-contact heating method coupled with capillary purification of the Ag drop procedure has been applied. Scanning electron microscopy combined with EDS analysis and scanning probe microscopy combined with Raman spectroscopy techniques has been utilized for microstructure and surface characterization of samples before and after high-temperature wetting tests. Immediately after its detachment from the capillary, the Ag drop showed non-wetting behavior (h > 90) forming a high contact angle of h = 114. Surface characterization of the drop surface after wettability tests evidenced the presence of graphene and Si transferred from the substrate to the top of Ag drop. These findings suggest chemical interaction phenomena occurring at the interface. Locally, an intimate contact between liquid Ag and SiC substrate was allowed by the appearance of discontinuities in the graphene layer basically produced by thermomechanical stress. Local dissolution of carbon into liquid Ag and its reorganization (by segregation, nucleation and growth) as secondary graphene layer at the Ag surface was also observed.

Research of the last years pointed out that most soils are neither completely hydrophilic nor hydrophobic, but exhibit a subcritical level of water repellency (i.e. contact angle, CA > 0° and < 90°). Soil water repellency (SWR) is mainly caused by organic compounds of different origin and structure, showing the relevance of biofilms and organic coatings present at many particle surfaces. Despite the importance of SWR for hydraulic processes like preferential flow phenomena, generation of heterogeneous moisture patterns, or surface run-off generation, detailed investigations on the spatial variability of SWR at various scales have rarely been carried out. We introduce a new and easy-to-apply operation for measuring the spatial distribution of SWR using a modified sessile drop method for direct optical assessment of CA at a small scale. The specific objectives of this paper are to apply a sampling and preparation technique that preserves the original spatial arrangement of soil particles and to characterize soil wettability in terms of CA at a high spatial resolution. Results revealed that the sampling and preparation technique allows determination of CA at the millimeter scale using droplets of 1 μL volume. Direct measurement on grain surfaces of the sand fraction is possible for grain sizes > 300 μm using drop volumes down to 0.1 μL. Geostatistical evaluation showed that the measurement grid scale is below the range of spatial dependency for droplets of 1 μL volume, but not for measurements on single grains (pure nugget effect). Results show further that the small-scale differences in wettability, especially for CA < 90°, cannot be detected by the conventional WDPT test. From these findings it can be concluded that the proposed technique allows the identification of small-scale variations in wettability that may promote the formation of heterogeneous flow fields and moisture patterns in soil under unsaturated conditions.

Surface tension and density measurements of liquid Ag-Sb-Sn alloys were carried out over a wide temperature range by using the sessile drop method. The surface tension experimental data were analyzed by the Butler thermodynamic model in the regular solution approximation. The wetting characteristics of these alloys on Cu and Ni substrates have been also determined. The new experimental results were compared with the calculated values as well as with data available in the literature.

Non-wetting behavior of liquid Zn alloy sometimes occurs on high-tensile strength steels that usually contain Si and Mn. Many studies have been undertaken to improve the wettability of liquid Zn. In this work, we applied the sessile drop method to measure the change in contact angle and diameter of liquid Zn droplets wetted on steels containing Si and Mn with time. We could then quantitatively evaluate the wettability of those steels using liquid Zn. Si weakens the work of adhesion and spreading velocity of liquid Zn on steels. Mn, however, has a small effect on the contact angle and the work of adhesion but occasionally increases the spreading velocity even when Si content is high in steels.

Since it has been pointed out that liquid Zn alloy sometimes exhibits non-wetting behavior on high-tensile strength steels usually containing Si and Mn, there have been several studies to improve the wettability of liquid Zn. Although those studies evaluated the wettability qualitatively by observation of the surface of galvanized steels or exfoliation testing of Zn on steel substrates, it is further required to evaluate the wettability of liquid Zn on steels by measuring the contact angle, work of adhesion, spreading velocity etc. which are usually used to assess the general wetting behavior. In the present work, we applied a sessile drop method to measure the change in contact angle and diameter of liquid Zn droplets wetted on steels containing Si and Mn with time to evaluate quantitatively the dynamic wetting behavior of liquid Zn on steel substrates.

Surface Free Energy (SFE) of solids should be calculated using theoretical models. The contact angle (CA) measurement on a surface is considered the most practical way to obtain the SFE. The results of five methods based in the models are compared: the method of Zisman (ZI), the geometric mean (GM), the harmonic mean (HM), the Lifshitz-van der Waals / Acid-Base (LW/AB) and the equation of state (ES). The SFE calculated with GM, HM and LW/AB methods change with the amount and type of liquid used, however, when water, glycerol and dimethyl sulfoxide are used together the SFE and its dispersive and polar components are similar in value for the three methods. In the case of the ES model the values of SFE change with the liquid used; finally using the ZI method the SFE values are 20% lower than the values of SFE obtained with the other methods. Fil: Schuster, Jonathan Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina Fil: Schvezov, Carlos Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina Fil: Rosenberger, Mario Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina. Board of Development and Technological Innovation; Estados Unidos