Introducing inverse gas chromatography as a method of determining the surface heterogeneity of minerals for flotation

New Progress on London Dispersive Energy, Polar Surface Interactions, and Lewis's Acid-Base Properties of Solid Surfaces

The determination of the polar surface free energy, polar properties, and Lewis's acid base of solid materials is of capital importance in many industrial processes, such as adhesion, coatings, two-dimensional films, and adsorption phenomena. (1) Background: The physicochemical properties of many solid particles were characterized during the last forty years by using the retention time of injected well-known molecules into chromatographic columns containing the solid substrates to be characterized. The obtained net retention time of the solvents adsorbed on the solid, allowing the determination of the net retention volume directly correlated to the specific surface variables, dispersive, polar, and acid-base properties. (2) Methods: Many chromatographic methods were used to quantify the values of the different specific surface variables of the solids. However, one found a large deviation between the different results. In this paper, one proposed a new method based on the London dispersion equation that allowed the quantification of the polar free energy of adsorption, as well as the Lewis's acid-base constants of many solid surfaces. (3) Results: The newly applied method allowed us to obtain the polar enthalpy and entropy of adsorption of polar model organic molecules on several solid substrates, such as silica, alumina, MgO, ZnO, Zn, TiO2, and carbon fibers. (4) Conclusions: our new method based on the separation between the dispersive and polar free surface energy allowed us to better characterize the solid materials.

Regulating Chemistry Composition on a Crystal Surface by Introducing a Cation Trapping Agent: A Novel Strategy to Tune Moisture Sensitivity of Crystals

The crystal moisture sensitivity can be tuned by the chemical composition on the crystal surface. Ammonium dinitramide (ADN) crystal is a promising oxidizer for solid propellants. However, its strong moisture sensitivity greatly limits its practical applications. Here, we report a novel strategy to reduce moisture sensitivity by trapping ammonium cations with montmorillonite (MMT) to modulate the chemistry composition on the ADN crystal surface. An extraordinary phenomenon can be found: the crystal surface of the recrystallized ADN with 1% MMT (ADN-1% MMT) is rearranged with more low-surface-energy -NO₂ groups (65.84%) and less high-surface-energy NH₄⁺ groups (4.8%). In addition, ADN-1% MMT presents a more homogeneous low surface energy feature with a narrower surface energy distribution. As a result, ADN-1% MMT exhibits a noticeably lower hygroscopicity at 20 °C and 60% RH, which is accordant with the simulated hygroscopicity based on XRD and moisture sensitivity prediction based on surface energy. This study brings out a novel modification idea to adjust crystal moisture sensitivity by tuning the chemistry composition on the crystal surface based on trapping cations.

New Methodology to Study the Dispersive Component of the Surface Energy and Acid-Base Properties of Silica Particles by Inverse Gas Chromatography at Infinite Dilution

A new methodology was proposed to determine the dispersive component of the surface energy ${\gamma}_s^d$ of a solid taking into account the effect of the temperature on the surface area of n-alkanes, methylene group (${a}_{- CH2-}$) and polar molecules, thus defeating the method used by Dorris-Gray Schultz et al. We determined the correct ${\gamma}_s^d$ of the surface energy, the specific free energy, enthalpy and entropy of adsorption of polar molecules as well as the acid base constants of silica particles with an excellent accuracy. We confirmed the dependence of the dispersive component of the surface energy on the variations of the surface areas of organic molecules used in IGC technique at infinite dilution. The specific properties of interactions of silica particles were determined. The new proposed model took into account this thermal effect. Obtained results proved that the other used IGC methods gave inaccurate values of the specific parameters of silica surface, except for the vapor pressure method that led to excellent results of the specific free energy, enthalpy and entropy of adsorption, and the acid-base constants of the silica particles.

Surface Chemical Heterogeneity of Low Rank Coal Characterized by Micro-FTIR and Its Correlation with Hydrophobicity

Micro-Fourier transform infrared (micro-FTIR) spectroscopy was used to correlate the surface chemistry of low rank coal with hydrophobicity. Six square areas without mineral impurities on low rank coal surfaces were selected as testing areas. A specially-designed methodology was applied to conduct micro-FTIR measurements and contact angle tests on the same testing area. A series of semi-quantitative functional group ratios derived from micro-FTIR spectra were correlated with contact angles, and the determination coefficients of linear regression were calculated and compared in order to identify the structure of the functional group ratios. Finally, two semi-quantitative ratios composed of aliphatic carbon hydrogen, aromatic carbon hydrogen and two different types of carbonyl groups were proposed as indicators of low rank coal hydrophobicity. This work provided a rapid way to predict low rank coal hydrophobicity through its functional group composition and helped us understand the hydrophobicity heterogeneity of low rank coal from the perspective of its surface chemistry.

Absorbable Hemostatic Aggregates

Topical absorbable hemostats are routinely utilized in surgical procedures to assist in controlling intraoperative bleeding. SURGICEL Original Absorbable Hemostat, one of the most frequently used adjunctive hemostats, is composed of oxidized regenerated cellulose (ORC). We report here that a novel powdered form of ORC, composed of aggregates of ORC fine fibers, provides additional valuable hemostatic performance characteristics and retains the biochemical and bactericidal profile of the parent ORC fabric. The ORC aggregates are more effective in promoting coagulation than their constituent ORC fine fibers because of more favorable surface energetics and surface area. Aggregates with similar particle size distributions that have higher sphericity values exhibit better coagulation efficacy. Finally, ORC aggregates more effectively promote clot formation than starch-based hemostatic particles. The results of this investigation indicate that the efficacy of this novel powdered hemostat is based on its chemical composition, morphology, and particle surface energetics.

Inverse gas chromatography applications: a review

Inverse gas chromatography (IGC) is a versatile, powerful, sensitive and relatively fast technique for characterizing the physicochemical properties of materials. Due to its applicability in determining surface properties of solids in any form such as films, fibres and powders of both crystalline and amorphous structures, IGC became a popular technique for surface characterization, used extensively soon after its development. One of the most appealing features of IGC that led to its popularity among analytical scientists in early years was its similarity in principle to analytical gas chromatography (GC). The main aspect which distinguishes IGC experiments from conventional GC is the role of mobile and stationary phases. Contrary to conventional GC, the material under investigation is placed in the chromatographic column and a known probe vapour is used to provide information on the surface. In this review, information concerning the history, instrumentation and applications is discussed. Examples of the many experiments developed for IGC method are selected and described. Materials that have been analysed include polymers, pharmaceuticals, minerals, surfactants, and nanomaterials. The properties that can be determined using the IGC technique include enthalpy and entropy of sorption, surface energy (dispersive and specific components), work of co/adhesion, miscibility and solubility parameters, surface heterogeneity, glass transition temperature, and specific surface area.