Specific Surface Free Energy Research Articles

Физико-химические трансформации сапонитсодержащего материала при его активации измельчением

Structural-phase transformations on the surface of powder systems of saponite-containing material after mechanical dispersion have been studied. The degree of crystallinity, adsorption capacity and specific surface energy depending on the time mode of grinding were used as compared information characteristics. It has been established that, despite the fact of the constancy of the degree of crystallinity, mechanical grinding of saponite-containing raw materials leads to its activation, which is expressed by a proportional increase in the sorption capacity of the obtained powders, an increase in the concentration of active adsorption centers and the value of the specific free surface energy. An increase in the time of mechanical grinding of a saponite-containing material leads to the production of samples with an increased (compared to the initial material) surface hydrophilicity.

Daphnia-inspired dynamic slippery chemically bonded liquid surface for the active prevention of covalently attached foulant adhesion.

Engineering anti-adhesion coatings always focuses on a specific hierarchy and surface free energy, which passively endures water scouring to wash away the loosely attached foulants. Certain foulants, however, especially those that are highly adhesive or covalently attached on the coatings, cannot be removed off the designed surfaces easily. Inspired by the active self-hunting behavior of the filter-feeding animal Daphnia, herein, we propose a universal antifouling strategy with both passive and active adhesion repellency capabilities. The premise for this protocol is that the as-fabricated liquid-like surface is able to repel the settlement of general foulants upon static conditions. Under steady thermal stimuli, the dynamic liquid-like surface behaves like a boxer with an active prevention ability against highly adhesive foulant adhesion, e.g., proteins, crude oils, and even covalently adhered mussel species. The enhanced biocide-free anti-adhesion performance is attributed to the reversible non-covalent interactions of pollutants in the initial contact with the surface, which was innovatively proved by AFM tapping tests to elucidate the physicochemical interactions between the foulants and coating surfaces. We envision that such an active anti-covalent adhesion surface may have great potential in diverse fields, including marine antifouling, fluid handling and transportation, and energy-harvesting devices.

Hydrophobic-Hydrophilic Properties and Characterization of PIM-1 Films Treated by Elemental Fluorine in Liquid Perfluorodecalin.

A direct fluorination technique was applied for the surface treatment of PIM-1 films in a liquid phase (perfluorodecalin). The fluorinated samples were analyzed by various instrumental techniques. ATR-IR spectroscopy showed that the fluorination predominantly takes place in methylene- and methyl-groups. Cyano-groups, aromatic hydrogens and the aromatic structure of the PIM-1 repeat unit were shown to be relatively stable at the fluorination conditions. XPS confirmed that the concentration of fluorine, as well as oxygen, in the near surface layer (~1 nm) increases with fluorination time. C1s and O1s surface spectra of the fluorinated PIM-1 samples indicated an appearance of newly-formed C-F and C-O functional groups. Scanning electron microscopy and X-ray energy-dispersive spectroscopy of the fluorinated PIM-1 samples showed an increase of the fluorine concentration at the surface (~0.1-1 μm) with the treatment duration. Analysis of the slices of the PIM-1 films demonstrated a decline of the fluorine content within several microns of the film depth. The decline increased with the fluorination time. A model of fluorine concentration dependence on the film depth and treatment duration was suggested. A change in the specific free surface energy as a result of PIM-1 fluorination was revealed. The fluorination time was shown to affect the surface energy (γSV), providing its shift from a low value (25 mJ∙m-2), corresponding to tetrafluoroethylene, up to a relatively high value, corresponding to a hydrophilic surface.

Determination of the Specific Free Surface Energy of Clinker-Free Composites on an Alkaline Activation Binder

Determination of the Specific Free Surface Energy of Clinker-Free Composites on an Alkaline Activation Binder

Critical Surface Tension and Specific Surface Free Energy of Clathrate Hydrate

Critical Surface Tension and Specific Surface Free Energy of Clathrate Hydrate

Investigation of the Impact of Cold Plasma Treatment on the Chemical Composition and Wettability of Medical Grade Polyvinylchloride

The impact of the Corona, dielectric barrier discharge, and low pressure radiofrequency air plasmas on the chemical composition and wettability of medical grade polyvinylchloride was investigated. Corona plasma treatment exerted the most pronounced increase in the hydrophilization of polyvinylchloride. The specific energy of adhesion of the pristine and plasma-treated Polyvinylchloride (PVC) tubing is reported. Plasma treatment increased markedly the specific free surface energy of PVC. The kinetics of hydrophobic recovery following plasma treatment was explored. The time evolution of the apparent contact angle under the hydrophobic recovery is satisfactorily described by the exponential fitting. Energy-dispersive X-ray spectroscopy of the chemical composition of the near-surface layers of the plasma-treated catheters revealed their oxidation. The effect of the hydrophobic recovery hardly correlated with oxidation of the polymer surface, which is irreversible and it is reasonably attributed to the bulk mobility of polymer chains.

Revealing the Surface Effect on Gas Transport and Mechanical Properties in Nonporous Polymeric Membranes in Terms of Surface Free Energy.

The contribution of surface roughness of nonporous polymeric membranes to their gas separation and mechanical properties was studied in terms of surface free energy. The membranes samples were prepared based on glassy polymers with different chain rigidity, namely polysulfone (PSU), cellulose triacetate (CTA), and poly(vinyl alcohol) (PVA). The results were obtained by atomic force and scanning electron microscopy (AFM and SEM) with individual gas permeation, wettability, and mechanical testing. The specific surface free energy (as well as its polar and dispersive components) for the polymers was calculated by the Owens-Wendt method. It was proven that the surface roughness of the polymer membranes affects both energy components; however, the degree of this influence depends on the chemical nature of the corresponding polymer. Moreover, it was assumed that the dispersive energy component is inversely correlated with any gases' total permeability. In contrast, the polar one is inversely correlated with the permeability by gases with the ability for site-specific interactions. The gas separation results confirmed this assumption. It was also shown that the mechanical properties of the polymer membranes are also influenced by the surface energy, namely, its dispersive component.

Changes in the Specific Charge Amount on the Surface of Cotton Fibres during the Alkali Pre-treatment Process

The aim of the pre-treatment process is to prepare cotton fabrics for subsequent technological operations, which are, in the majority, carried out in aqueous solutions. The pre-treatment processes modify, to some extent, the properties of cotton, resulting in a significant change in their zeta potential, the amount of specific surface charge or free energy surface. This study makes an assessment of the effect of the alkali pre-treatment process on changes in the amount of negative specific charges on cotton knitted surfaces, known as cationic demand. A “back-titration” method with the use of a Muetek PCD device was adopted for these experiments. It was found that the conventional process of alkali treatment of raw cotton knitted fabrics using sodium hydroxide in the presence of non-ionic surfactant reduced by nearly 50% the amount of negative specific surface charge. Also, changes in weight loss and improvements in the whiteness index, as well as the wettability of alkali pre-treated cotton knitwear, were observed.

The influence of hydrothermal brine on the short-term strength and elastic modulus of sandstones from exploration well EPS-1 at Soultz-sous-For\xeats (France)

Laboratory studies designed to provide the strength of rocks are typically performed on either dry- or water-saturated rock samples. To better understand the mechanical behaviour of rocks in a geothermal context, we provide here the short-term strength and static elastic modulus of sandstones from exploration well EPS-1 at the Soultz-sous-Forêts geothermal site (France) saturated in hydrothermal brine sourced from the adjacent production well GPK-2. We performed 59 uniaxial compressive strength experiments on samples of Buntsandstein sandstones sampled from six depths (1008, 1022, 1069, 1107, 1290, and 1414 m). Samples were deformed oven-dry (i.e., unsaturated), water-saturated (deionised water), or brine-saturated. Relative to the dry state, strength was reduced by between 24 and 39% and elastic modulus was reduced by between 9 and 19% when the samples were saturated with water. However, we observed no measurable difference in strength and elastic modulus between samples saturated in water and brine. These reductions in strength and elastic modulus in the presence of water or brine are considered the result of a reduction in specific surface-free energy. Changes to short-term strength and elastic modulus in the presence of hydrothermal brines likely require brines with higher salinities and/or lower values of pH than those typically found within the Upper Rhine Graben (the brine from GPK-2 has a salinity of ~ 10% and a pH of 5.5). These new data can be used to assist reservoir prospection, stimulation, and optimisation strategies at the geothermal sites within the Upper Rhine Graben.

Relationship between Energy Characteristics of Surface of Polymeric Membranes and Their Transport Properties

Molecular theory of wetting was used to calculate the specific free surface energy of membranes based on amorphous polymers of varied chemical structure from experimental wetting angles obtained for test fluids. A relationship was found between the dispersion component of the surface energy of a membrane, its gas permeability, and free volume of the polymer. This makes it possible to employ the wetting method to prognosticate the transport properties of polymeric membranes. In wetting of membranes with aqueous solutions of alcohols, the concentration of an alcohol corresponding to the onset of its sorption into the membrane was determined. The correlation of the value obtained with the alcohol concentration that corresponds to the onset of sorption and is determined independently by the gravimetric method enables use of wetting angles for optimizing the conditions of experiments on nanofiltration and pervaporation.

Hydrophobic Properties of Thin Films of Comb-Shaped Perfluorohexylethyl Methacrylate-Polydimethylsiloxane Copolymers Deposited from Supercritical Carbon Dioxide Solutions

Comb-shaped copolymers of perfluorohexylethyl methacrylate and methacryloxypropyl-terminated polydimethylsiloxane are synthesized by radical polymerization in supercritical carbon dioxide, solubility of the copolymers in supercritical carbon dioxide is studied, and hydrophobic properties of thin films obtained via precipitation of the copolymers from trifluorotrichloroethane and supercritical carbon dioxide solutions on substrates are examined. On the basis of water and dimethyl sulfoxide contact angle measurements, the specific free surface energy of the formed films is calculated. It is shown that the thin films of the copolymers have a lower surface energy and are characterized by a smaller water contact angle hysteresis than the films based on homopolymer poly(perfluorohexylethyl methacrylate). A comparative testing of coatings based on the homopolymer and copolymer deposited from solutions in supercritical carbon dioxide on the surface of nylon fabrics is performed. It is found that copolymer-coated fabrics have on average higher water contact angles.

Energy characteristics of finely dispersed rock systems

In their genesis, rocks accumulate their energy potential – free energy of rock-forming minerals and the rock in general that is an important criterion of raw material genetic classification for construction materials production. The free energy value for the macrostate of a substance (rock) is atomization energy. The critical surface tension value can be used as an energy characteristic for destroyed rock in a finely dispersed state. If condensed phase surfaces carry no significant electrostatic charge, then main surface forces that determine the interaction between solids are dispersion ones evaluated by the Hamaker constant value. These energy parameters can enable forecasting various physical and mechanical properties of minerals and rocks and thereby increase the efficiency of construction materials production where synthesis is based on the complete rock destruction. Since compared chemical compositions of minerals forming rocks revealed a predominant silicon dioxide content in them, the aim of this paper was to establish a possible relationship between the silicon dioxide content and energy characteristics for finely dispersed rock systems of various genetic types. The selected objects of research were different genesis rocks typically used in the construction materials industry and quartz as a main rock-forming mineral. Test samples of rocks in a finely dispersed state were obtained by dry milling. It is established that an increase in silicon dioxide content in the limestone – quartz series leads to higher atomization energy, specific mass atomization energy and free surface energy with intensified dispersion interaction between particles evaluated by an increase in the Hamaker constant.

Leaching kinetics of mechanically activated boron concentrate in a NaOH solution

Mechanical activation is an effective pretreatment method that can change the properties of boron concentrates, thus promoting B2O3 leaching from samples. Four boron concentrate samples were milled for 0, 10, 30, and 60 min and leached in a NaOH solution at various leaching temperatures and initial NaOH concentrations. We investigated the main control steps for leaching and obtained the kinetic parameters. We discuss the influences of the specific surface area and surface free energy on the apparent rate constants. During the early-stage leaching (0–20 min), the leaching process was controlled by a combination of the surface chemical reaction and diffusion through the product layer; however, the surface chemical reaction was the main controlling step with an apparent activation energy of 29.37–39.77 kJ/mol. During the late-stage leaching (>40 min), the leaching process of the milled samples was controlled by a combination of the surface chemical reaction and diffusion through the product layer; in contrast, that of the unmilled sample was controlled by the surface chemical reaction and showed a high apparent activation energy of 69.14 kJ/mol. With increasing milling time, the apparent activation energy and reaction order decreased, thus reducing the dependence on temperature and NaOH concentration. The leaching rate constants were related to the specific surface area, surface free energy, and other properties, such as crystal amorphization and chemical bonds stability. After milling for 60 min, the surface free energy increased from 26.88 to 33.99 mJ/m2, and the Lewis acid component increased from 0 to 3.31 mJ/m2, promoting the absorption of the solvent and OH– in the leaching solution, which also accelerated the leaching rate.

Inverse gas chromatography as a method for determination of surface properties of binding materials

Inverse gas chromatography (IGC) is a promising measurement technique for investigating the surface properties of binding materials, which are the major influence element for the adsorption performance of superplasticizer. In this work, using the IGC method, blast furnace slag (BFS), sulphoaluminate cement (SAC) and portland cement (P·O) are employed to systematically evaluate the corresponding dispersive component (γsd), specific surface free energy (γsab), and acid-base properties. The obtained results show that γsd contributes to a major section of the surface free energy in the three binding materials, suggesting they are of a relatively low polarity. Compared to the two kinds of cements, the BFS possesses the highest dispersive and specific surface free energies (the values are 45.01 mJ/m2 and 11.68 mJ/m2, respectively), and also exhibits a wider distribution range of γsd, indicating their surfaces are heterogeneous. For acid-base properties, the results indicate the surfaces of three samples are basic in nature. In addition, the adsorption investigation shows that per unit surface of BFS adsorbs the most superplasticizer molecules, which indicates the higher surface free energies is beneficial to the superplasticizer adsorption.

Adhesive properties of gamma-irradiated polyketone

The effect of polyketone (PK) γ-irradiation dose on the energy characteristics of the PK surface, the specific free surface energy, and the interfacial energy at the boundary between polar (water) and nonpolar (octane) liquids has been studied for the first time. The most significant changes in the energy characteristics of the surface occur at doses up to 100 kGy, and improvement in PK adhesion to the polar and nonpolar phases is observed at doses above 75 and 200 kGy, respectively.

Specific surface free energy component distributions and flotabilities of mineral microparticles in flotation—An inverse gas chromatography study

In fundamental flotation studies often the contact angle with water is used to describe wettability of a mineral surface and it is correlated with flotability. A more fundamental parameter however is the specific surface free energy related to the contact angle via Young’s equation. Inverse gas chromatography (iGC) has recently been proven to be a suitable method to determine specific surface free energy components and their distributions of particulate surfaces. In this study the pure minerals quartz (SiO2), fluoro-apatite (Ca5[F,(PO4)3]), and magnetite (Fe3O4) are examined for flotabilities and surface energy component distributions considering different methods of sample treatment and the effect of the collectors sodium oleate and dodecyl ammonium acetate. The parameter of specific net free energy of interaction between bubbles and particles immersed in water ΔGpwb resulting from the complex surface energy analyses is introduced and used to evaluate the hydrophobicity of the mineral surface in correlation to microflotation recoveries. The results lead to the hypothesis that only small fractions of the surface and their change of wettability by flotation reagent adsorption will inherently define the flotability of minerals. Consequently, the main purpose of the amphiphilic collector molecules seems to be the reduction of high specific surface free energies of small fractions of the surface that lead to a strong attraction between particle surface sites and water molecules rather than the hydrophobization of the entire mineral surface, a new paradigm in flotation science.

Elastic properties of the (001) face of xenon crystals

In this work we investigated the elastic properties of the (001) face of xenon crystal. The slabs (twodimensional crystals) defined by (001) planes are generated, their structures are optimized and the slabs thermodynamic functions in excess to the crystal bulk calculated. The calculations are based on the Lennard-Jones 6−12 force field, classical elasticity theory and surface thermodynamics. In this work, the number of planes undergoing relaxation is not a priori constrained but it follows from the minimization of the free energy of the slabs and of the bulk, in respect to atomic positions. The value of the surface free energy is calculated as a function of the homogeneous strain of the 2D (001) cell measured relatively to the cell of the stable 3D crystal. At 0 K, when strain is not applied, the specific surface free energy is about 0.064 Jm-2 and decreases by about 6% at 50 K. The surface stress is positive amounting to 0.010 Jm-2 at 0 K, and it decreases by about 50% at 50 K. We find that the surface stress can be released by a reorganization of the interatomic distances at the crystal surfaces. The surface excess mean value of the slab elastic constants at 0 K is small (0.012 GPa) and it decreases by about 35% at 50 K. The method proposed can be alternative to molecular dynamics simulations in order to assess the excess surface properties of materials having a complex structure.

Thermal stability of self-assembled surfaces and micropatterns made of ladder polysilsesquioxanes

Self-assembled films made of ladder [2-(carboxymethylthio)ethyl]-polysilsesquioxanes adsorbed on mica are stable within a wide temperature range (293–373 K). A thermally induced transformation, resulting in a significant decrease of free surface energy but not in a collapse of macromolecules in the adsorbed film was observed only at 393 K. The unique behaviour has been ascribed to a specific rearrangement of hydrogen bonds between COOH groups. It is irreversible under ambient conditions, but the structural features and properties of the self-assembled film can be reverted to the primary state if the sample is kept in humid atmosphere (steam). Wetting angle measurements as well as microscopic (AFM) and spectroscopic (ATR FTIR, ARXPS) studies were carried out to evaluate changes in the surface morphology and its physiochemical properties. The studied [2-(carboxymethylthio)ethyl]-polysilsesquioxanes were also used as a printing ink on native mica. The micropatterns exhibited all the characteristic properties of the self-assembled films, which can be exploited for the formation of precisely localized surface textures of specific chemical composition and specific free surface energy.

Polymer Nanocomposites Development and Research for Petrochemical and Oil and Gas Production Equipment

The research and development results of new anti-friction polymer nanocomposites based on polytetrafluoroethylene characterized with an increased wear resistance due to the polymer matrix with complex fillers-modifiers modification are presented in the paper. Fillers include micro- and nanoscale components of different nature and the particles geometry having specific surface and surface free energy high values. These factors provide the polymer matrix high-performance structural modification and significant increase in nanocomposites wear resistance in dry boundary friction.

Interactions between aminated cellulose nanocrystals and quartz: Adsorption and wettability studies

Abstract Cellulose nanocrystals (CNCs) are potential high-performance, biodegradable, and environmentally-friendly alternatives to the oil-derived chemicals currently used in mineral processing. For this purpose, the understanding of phenomena associated with interactions between CNCs and minerals is crucial. In the present study, aminated CNCs with varying crystal sizes and crystal size distributions were examined in terms of their adsorption properties on quartz and the wetting properties of quartz surfaces after CNC adsorption. CNCs with varying alkyl chain lengths were obtained from consequent periodate oxidation and reductive amination, followed by mechanical high-intensity homogenisation. The adsorption of CNCs was studied based on polyelectrolyte titration. An enhanced interaction between CNCs and the quartz surface, including decreasing CNC surface charges, was obtained. Subsequently, wetting studies of CNC-coated quartz were performed using the sessile drop method. The specific surface free energies of both the rough and smooth surfaces were obtained and compared to determine the effects of roughness on wetting properties. The results showed that smooth surfaces possess a low specific surface free energy due to the absence of surface heterogeneities. For rough surfaces, the specific surface free energy was decreased as the extended alkyl chains of adsorbed CNCs modified the wetting properties of the surface.