Surface Thermodynamic Properties Research Articles

The Effect of Temperature on the London Dispersive and Lewis Acid-Base Surface Energies of Polymethyl Methacrylate Adsorbed on Silica by Inverse Gas Chromatography

Inverse gas chromatography at infinite dilution was used to determine the surface thermodynamic properties of silica particles and PMMA adsorbed on silica, and more particularly, to quantify the London dispersive energy γsd, the Lewis acid γs+, and base γs− polar surface energies of PMMA/silica composites as a function of the temperature and the recovery fraction θ of PMMA. The polar acid-base surface energy γsAB and the total surface energy of the different composites were then deduced as a function of the temperature. In this paper, the Hamieh thermal model was used to quantify the surface thermodynamic energy of polymethyl methacrylate (PMMA) adsorbed on silica particles at different recovery fractions. A comparison of the new results was carried out with those obtained by applying other molecular models of the surface areas of organic molecules adsorbed on the different solid substrates. An important deviation of these molecular models from the thermal model was proved. The determination of γsd, γs+, γs−, and γsAB of PMMA in both the bulk and adsorbed phases showed an important non-linearity variation of these surface parameters as a function of the temperature. The presence of maxima in the curves of γsd(T) highlighted the second-order transition temperatures in PMMA showing beta-relaxation, glass transition, and liquid–liquid temperatures. These three transition temperatures depended on the adsorption rate of PMMA on silica. The proposed method gave a new relation between the recovery fraction of PMMA and its London dispersive energy, showing an important effect of the temperature on the surface energy parameters of the adsorption of PMMA on silica. A universal equation relating γsd(T,θ) of the systems PMMA/silica to the recovery fraction and the temperature was proposed.

Surface Thermodynamic Properties of Poly Lactic Acid by Inverse Gas Chromatography.

Poly lactic acid (PLA) is one of the most commonly used bio-derived thermoplastic polymers in 3D and 4D printing applications. The determination of PLA surface properties is of capital importance in 3D/4D printing technology. The surface thermodynamic properties of PLA polymers were determined using the inverse gas chromatography (IGC) technique at infinite dilution. The determination of the retention volume of polar and non-polar molecules adsorbed on the PLA particles filling the column allowed us to obtain the dispersive, polar, and Lewis's acid-base surface properties at different temperatures from 40 °C to 100 °C. The applied surface method was based on our recent model that used the London dispersion equation, the new chromatographic parameter function of the deformation polarizability, and the harmonic mean of the ionization energies of the PLA polymer and organic molecules. The application of this new method led to the determination of the dispersive and polar free surface energy of the adsorption of molecules on the polymeric material, as well as the glass transition and the Lewis acid-base constants. Four interval temperatures were distinguished, showing four zones of variations in the surface properties of PLA as a function of the temperature before and after the glass transition. The acid-base parameters of PLA strongly depend on the temperature. The accurate determination of the dispersive and polar surface physicochemical properties of PLA led to the work of adhesion of the polar organic solvents adsorbed on PLA. These results can be very useful for achieving reliable and functional 3D and 4D printed components.

Study on the Synthesis, Surface Activity, and Self-Assembly Behavior of Anionic Non-Ionic Gemini Surfactants.

The use of surfactants in oil recovery can effectively improve crude oil recovery rate. Due to the enhanced salt and temperature resistance of surfactant molecules by non-ionic chain segments, anionic groups have good emulsifying stability. Currently, there are many studies on anionic non-ionic surfactants for oil recovery in China, but there is relatively little systematic research on introducing EOs into hydrophobic alkyl chains, especially on their self-assembly behavior. This article proposes a simple and effective synthesis method, using 3-aminopropane sulfonic acid, fatty alcohol polyoxyethylene ether, and epichlorohydrin as raw materials, to insert EO into hydrophobic alkyl chains and synthesize a series of new anionic non-ionic Gemini surfactants (CnEO-5, n = 8, 12, 16). The surface activity, thermodynamic properties, and self-assembly behavior of these surfactants were systematically studied through surface tension, conductivity, steady-state fluorescence probes, transmission electron microscopy, and molecular dynamics simulations. The surface tension test results show that CnEO-5 has high surface activity and is higher than traditional single chain surfactants and structurally similar anionic non-ionic Gemini surfactants. Additionally, thermodynamic parameters (e.g., ΔG°mic ΔH°mic ΔS°mic et al. indicate that CnEO-5 molecules are exothermic and spontaneous during the micellization process. DLS, p-values, and TEM results indicate that anionic non-ionic Gemini surfactants with shorter hydrophobic chains (such as C8EO-5) tend to form larger vesicles in aqueous solutions, which are formed in a tail to tail and staggered manner; Negative non-ionic Gemini surfactants with longer hydrophobic chains (such as C12EO-5, C16EO-5) tend to form small micelles. The test results indicate that CnEO-5 anionic non-ionic Gemini surfactants have certain application prospects in improving crude oil recovery.

Comparison of Forecasting Biases Over New York State Mesonet: A Wet Summer Versus a Dry Summer

AbstractExtreme weather events are occurring with increasing frequent due to the climate change. This increasing frequency may introduce more uncertainty in weather forecasting model performance, particularly when considering the intricate relationship of the land surface and atmosphere coupling system. In this study, we utilize data from the sophisticated New York State Mesonet to evaluate the performance of a forecasting system based on WRF Version 4 model, drawing insights from both dry and wet summers. Additionally, the model's performance is assessed on two land surface types: forest and farmland, to provide a comprehensive evaluation of impact of land surface heterogeneity. The surface meteorology, fluxes, and cloud development are assessed. The coupling between surface and atmosphere is diagnosed using a mixing diagram which serves to represent surface thermodynamic properties. The results reveal a systematic increase in warm season dry and warm biases, especially for forested sites during a drought year. The model exhibits heightened sensitivity to drought conditions, resulting in a substantial underestimation of latent heat fluxes during such period. During days with boundary layer clouds, the mixing diagram shows a notably slower growth of moist static energy in the model compared to observation. It is possible that these biases partly attribute to the underestimation of cloud optical depth due to not enough energy for the cloud development.

The Effect of Temperature on the Surface Energetic Properties of Carbon Fibers Using Inverse Gas Chromatography

This paper constitutes an original and new methodology for the determination of the surface properties of carbon fibers in two forms, namely, oxidized and untreated, using the inverse gas chromatography technique at infinite dilution based on the effect of temperature on the surface area of various organic molecules adsorbed on the carbon fibers. The studied thermal effect showed a large deviation from the classical methods or models relative to the new determination of the surface properties of carbon fibers, such as the dispersive component of their surface energy, the free surface energy, the free specific energy, and the enthalpy and entropy of the adsorption of molecules on the carbon fibers. It was highlighted that the variations in the London dispersive surface energy of the carbon fibers as a function of the temperature satisfied excellent linear variations by showing large deviations between the values of γsd (T), calculated using different models, which can reach 300% in the case of the spherical model. All models and chromatographic methods showed that the oxidized carbon fibers gave larger specific free enthalpy of adsorption whatever the adsorbed polar molecules. The obtained specific enthalpy and entropy of the adsorption of the polar solvents led to the determination of the Lewis acid–base constants of the carbon fibers. Different molecular models and chromatographic methods were used to quantify the surface thermodynamic properties of the carbon fibers, and the results were compared with those of the thermal model. The obtained results show that the oxidized carbon fibers gave more specific interaction energy and greater acid–base constants than the untreated carbon fibers, thus highlighting the important role of oxidization in the acid–base of fibers. The determination of the specific acid–base surface energy of the two carbon fibers showed greater values for the oxidized carbon fibers than for the untreated carbon fibers. An important basic character was highlighted for the two studied carbon fibers, which was larger than the acidic character. It was observed that the carbon fibers were 1.4 times more acidic and 2.4 times more basic. The amphoteric character of the oxidized fibers was determined, and it was 1.7 times more important than that of the untreated fibers This tendency was confirmed by all molecular models and chromatographic methods. The Lewis acid and base surface energies of the solid surface, γs+ and γs−, as well as the specific acid–base surface energy γsAB of the carbon fibers at different temperatures were determined. One showed that the specific surface energy γsAB of the oxidized fibers was 1.5 times larger than that of the untreated fibers, confirming the above results obtained on the strong acid–base interactions of the oxidized carbon fibers with the various polar molecules.

A novel eco-friendly strategy for removing phenanthrene from groundwater: Synergism of nanobubbles and rhamnolipid

Nanobubbles (NBs), given their unique properties, could theoretically be paired with rhamnolipids (RL) to tackle polycyclic aromatic hydrocarbon contamination in groundwater. This approach may overcome the limitations of traditional surfactants, such as high toxicity and low efficiency. In this study, the remediation efficiency of RL, with or without NBs, was assessed through soil column experiments (soil contaminated with phenanthrene). Through the analysis of the two-site non-equilibrium diffusion model, there was a synergistic effect between NBs and RL. The introduction of NBs led to a reduction of up to 24.3 % in the total removal time of phenanthrene. The direct reason for this was that with NBs, the retardation factor of RL was reduced by 1.9 % to 15.4 %, which accelerated the solute replacement of RL. The reasons for this synergy were multifaceted. Detailed analysis reveals that NBs improve RL's colloidal stability, increase its absolute zeta potential, and reduce its soil adsorption capacity by 13.3 %–19.9 %. Furthermore, NBs and their interaction with RL substantially diminish the surface tension, contact angle, and dynamic viscosity of the leaching solution. These changes in surface thermodynamic and rheological properties significantly enhance the migration efficiency of the eluent. The research outcomes facilitate a thorough comprehension of NBs' attributes and their relevant applications, and propose an eco-friendly method to improve the efficiency of surfactant remediation.

Theoretical study on tin oxide surface chemistry mechanism and thermodynamic properties for atomic layer deposition equipment optimization

Theoretical study on tin oxide surface chemistry mechanism and thermodynamic properties for atomic layer deposition equipment optimization

Study of surface thermodynamic properties of some boron compounds by inverse gas chromatography at infinite dilution

This paper is devoted to the determination of the dispersive component of the surface energy of two boron materials such as h-BN and BPO4 surfaces by using the inverse gas chromatography (IGC) at infinite dilution. The specific interactions and Lewis’s acid-base parameters of these materials were calculated on the light of the new thermal model concerning the dependency of the surface area of organic molecules on the temperature, and by using also the classical methods of the inverse gas chromatography as well as the different molecular models such as Van der Waals, Redlich-Kwong, Kiselev, geometric, Gray, spherical, cylindrical and Hamieh models. It was proved that h-BN surface exhibits higher dispersive surface energy than BPO4 material.The specific properties of interaction of the two boron materials were determined. The results obtained by using the new thermal model taking into account the effect of the temperature on the surface area of molecules, proved that the classical IGC methods, gave inaccurate values of the specific parameters and Lewis’s acid base constants of the solid surfaces. The use of the thermal model allowed to conclude that h-BN surface has a Lewis basicity twice stronger than its acidity, whereas, BPO4 surface presents an amphoteric character.

Preparation and characterization of phase change capsules containing waste cooking oil for asphalt binder thermoregulation

The green utilization of waste is of great significance to the sustainable development of human society. In this work, a new kind of capsule with the phase change heat storage function was prepared using waxy components extracted from waste cooking oil (WCO) as core material for the thermoregulation of asphalt binder. The differences in waxy components before and after hydrolysis treatment were studied including functional groups, phase transition temperature, and phase transition enthalpy. Meanwhile, the surface morphology, thermodynamic properties, and mechanical properties of the phase change capsules (PCCs) were also characterized comprehensively. Additionally, the effect of PCCs on asphalt thermoregulation was also examined in the laboratory. The results indicate that the waxy components after hydrolysis treatment are more suitable for asphalt binder thermoregulation in terms of the phase transition temperature, phase transition enthalpy, and thermal stability. According to the results of differential scanning calorimeter and thermogravimetric experiments, it can be calculated that the ratio of wall material and core material in PCCs is about 1:1, which endows the capsule with excellent heat storage properties (125 J/g), mechanical properties (>13 N), and thermal stability (>190 ℃). With the help of the temperature sensor, it is found that PCCs can delay the change rate of asphalt temperature with the environment by undergoing a phase transition to mitigate the damage of asphalt pavement in extremely hot climates. However, the performance of PCCs in asphalt mixtures still needs to be further explored. Overall, the findings of this research can further promote the green utilization of WCO and the functionalization of construction and building materials.

Thermal modeling for anionic surfactant using Inverse gas chromatography and image processing techniques

Anionic surfactants are one of the necessary ingredients demanded in extensive bio-and pharmaceutical industry. Their concern on human health and environmental safety get increase and is originated from its surface thermodynamic properties. Surface thermodynamic properties have severely an effect on thermodynamic and kinetic parameters in the chemical reaction. However, there is a kind of serious differences between theoretical calculation and experimental result because of lacks of understanding on complex surface thermodynamic properties. Inverse gas chromatography (IGC) is an analytic chemistry tool providing information on physicochemical and thermodynamic parameters. Herein, a thermal modeling of surface thermodynamic properties is suggested. Net retention volume, VN, of n-alkanes and polar probes upon sodium lauryl sulfate surface properties as an anionic surfactant are analyzed at diverse temperatures range from 363.15 to 433.15 K using IGC. VN of n-alkane values are employed to assess the London dispersive surface free energy, γSL by comprehensive thermodynamic models and results into the Guttmann Lewis acid-base parameters and acid-base constants. The results reveal that an excellent linear correlation coefficient value closer to 1. The current work demonstrates how to approach surface thermodynamic characteristics of anionic surfactant and suggests a new thermal model as an advanced model. Additionally, scanning electron microscopy image analysis regarding the surface morphology has been carried out using image processing techniques. Current comprehensive approach enables to analyze and apply for an effective understanding on surfactant molecules.

New Physicochemical Methodology for the Determination of the Surface Thermodynamic Properties of Solid Particles

The study of the surface thermodynamic properties of solid materials is primordial for the determination of the dispersive surface energy, polar enthalpy of adsorption and Lewis’s acid base properties of solid particles. The inverse gas chromatography technique (IGC) at infinite dilution is the best surface technique for the determination of the surface physicochemical properties of materials. (1) Background: This paper was devoted to studying the surface properties of solid materials, such as alumina, titania and silica particles, using the IGC technique. (2) Methods: Different methods and molecular models, such as the spherical, cylindrical, Van der Waals, Redlich–Kwong, Kiselev and geometric models, were used to determine the London dispersive surface energy of solid surfaces. The Hamieh model was also used and highlighted the thermal effect on the surface area of solvents. (3) Results: The variations of the dispersive surface energy and the free energy of adsorption were determined for solid particles as a function of the temperature, as well as their Lewis’s acid base constants. Alumina surfaces were proved to exhibit a strong Lewis amphoteric character three times more basic than acidic, titanium dioxide more strongly basic than acidic and silica surface exhibited the stronger acidity. (4) Conclusions: The new methodology, based on the Hamieh model, gave the more accurate results of the physicochemical properties of the particle surfaces.

Study on the synthesis and properties of cardanol sulfonate

Abstract In this work, using the natural product cardanol and chlorosulfonic acid as the main raw materials, the anionic surfactant cardanol sulfonate (CDS) was synthesised and investigated for its surface properties and thermodynamic properties using surface tension, conductivity and fluorescence methods. In addition, the application properties of CDS, such as foaming and cleaning ability were investigated and compared with those of sodium dodecylbenzene sulfonate (SDBS). The structure of the surfactant was characterised by FTIR, 1H NMR and MS. The Krafft point of the surfactant was below 25 °C, indicating good water solubility. The CMC values were determined by surface tension, conductivity and micropolarity measurements. The obtained CMCs agreed well within the measuring accuracy. The CMC increased with increasing temperature. As a function of temperature, the following CMC values were obtained: 5.13 × 10−3 mol L−1 (25 °C), 5.63 × 10−3 mol L−1 (35 °C) and 5.77 × 10−3 mol L−1 (45 °C). The values of surface tensions at the respective CMCs were γ CMC = 44.47 mN m−1 (25 °C), 43.53 mN m−1 (35 °C), and 42.45 mN m−1 (45 °C). The application property results showed that the foaming capacity, foam stabilisation and cleaning ability of CDS and SDBS were similar to each other, indicating that CDS can be used as a raw material for commercial detergent production.

Insights into the membrane biofouling behavior of planktonic anammox bacteria: Effect of solution pH and ionic strength

Understanding the effect of solution pH and ionic strength on membrane biofouling of anammox bacteria is essential for the widespread application of anammox MBRs. To provide an original elucidation, this study combined interfacial thermodynamics analysis and filtration experiments with an established planktonic anammox MBR to explore the biofouling behavior of anammox bacteria under varying solution pH and ionic strengths. Preliminary results showed that variation in solution pH and ionic strength has critical impacts on the thermodynamic properties of planktonic anammox bacteria and membrane surfaces. The further interfacial thermodynamics analysis and filtration experiments indicated that an increased pH and a decreased ionic strength could reduce membrane fouling by planktonic anammox bacteria. More specifically, a higher pH or lower ionic strength resulted in a stronger repulsive energy barrier due to the larger interaction distance covered by the dominant electrostatic double layer (EL) component compared to the Lewis acid-base (AB) and Lifshitz–van der Waals (LW) components, which corresponded to a reduction in the normalized flux (J/J0) decline and the accumulation of cake resistance (Rc) during the filtration process. Furthermore, the aforementioned effect mechanism was verified by a correlation analysis of the thermodynamic properties and filtration behavior. These findings have generalized significance for understanding the biofouling or aggregation behavior of anammox bacteria.

Synthesis and properties of alkyl glyceryl ether sulfonate

Abstract In this work, alkyl glyceryl ether sulfonates with two alkyl chain lengths were synthesised by etherification and sulfonation. The structures of these sulfonates were characterised by FTIR, 1H NMR and MS. Their characterisations were investigated for their surface properties and thermodynamic properties by surface tension, conductivity and fluorescence methods. The critical micelle concentration (CMC) of surfactants increases with increasing temperature and decreases with increasing alkyl chain length. The micellation process of alkyl glyceryl ether sulfonates is spontaneous and driven by entropy.

Water sorption properties of brewer's spent grain: A study aimed at its stabilization for further conversion into value-added products

Due to its high moisture content and perishability, the water adsorption isotherms, and thermodynamic properties of brewer's spent grain obtained from barley malt (BSGL) and wheat malt based (BSGW) were evaluated under storage and drying conditions. Chemically characterized BSGs were subjected to the static gravimetric method to experimentally obtain the water adsorption isotherms at ten temperatures (5–90 °C). As the best-fitted model (R2adj > 0.9928 e χ2 ≤ 0.0001), the GAB parameters were used to determine the adsorption surface area, spreading pressure, and thermodynamic properties. At temperatures from 5 to 50 °C, the adsorption isotherms of BSGL and BSGW showed convex curves, typical of type III isotherms. However, at temperatures above 60 °C, the curves started to present typical type II isotherms with sigmoid-shaped sorption behavior. The equilibrium moisture content of BSGs increased with increasing relative humidity and/or decreasing temperature. The spreading pressure increased as the water activity and temperature increased, contrary to that observed for the adsorption surface area. Thermodynamic analysis showed that the net isosteric heat of adsorption, enthalpy, and differential entropy decreased as the equilibrium moisture increased. The compensation theory was confirmed, and its results indicated that the adsorption processes were enthalpy-driven. The positive values for Gibbs free energy indicated that the adsorption processes were not spontaneous, which may be related to the composition of BSGs in terms of lipids and proteins. From an energy and stability point of view, a water activity of 0.4 is the ideal condition for the storage of BSGs.

Effect of Modulation and Functionalization of UiO-66 Type MOFs on Their Surface Thermodynamic Properties and Lewis Acid–Base Behavior

In this study, we investigated the surface thermodynamic properties of four MOF structures of the UiO-66 series, by employing seven molecular models, a thermal model, and three other methods using the inverse gas chromatography (IGC) technique at infinite dilution. We first determined the effect of the modulation of UiO-66 by an acid (e.g., formic acid and acetic acid) and on the other hand, we studied the effect of the functionalization of the organic linker by an amine group (NH2) on their dispersive component of the surface energy and on their Lewis acid–base properties. We found that all the studied MOFs presented an amphoteric character with a strong acidity whose acidity/basicity ratio is greater than 1 using all the models and methods in IGC. Moreover, the introduction of a modulator such as acetic acid or formic acid in the synthesis of these MOFs increased the number of structural defects and therefore increased the acidity of these MOFs. Similarly, the functionalization of the MOF by the NH2 group leads to an increase in the basicity constant of the functionalized MOF while remaining smaller than their acidity constant. In addition, the use of acids as modulators and amine groups as functional groups resulted in an increase in the dispersive component of the surface energy of the MOFs. Finally, comparing the results obtained by the different models and methods and based on the increasing order of the acidity of each MOF, it was clear that the thermal model resulted in more exact and precise values than the others. Our findings pave the way for the design and development of new acid catalysts based on UiO-66 structures.

Theoretical and Experimental Studies on the Critical Size Effect on Surface Heat Capacity Using In Situ Microcalorimetry: During the Solid–Liquid Reactions of Cu2O Nanocubes

Phase transition, energy storage, and other activities depend critically on the size variations of nanomaterials for their heat capacity. The size variation of the nanomaterial is also equally important to the thermodynamic properties for chemical reaction processes. Based on this, it will be fascinating to examine how the surface heat capacity of nanomaterials changes with size. Herein, we used an in situ microcalorimeter to report a general approach to obtaining the regular patterns of numerical changes in the surface heat capacity at different sizes and temperatures when the chemical reactions of cuprous oxide (Cu2O) take place in the liquid phase. We synthesized four Cu2O nanocubes with uniform size distributions, which range from 40 to 120 nm, by using the liquid-phase reduction method. Combined with the principle of thermodynamic cycle and transition state theory, the effects of size and temperature changes on the standard molar formation thermodynamic properties, surface thermodynamic properties, and specific surface thermodynamic properties of Cu2O nanocubes were calculated and analyzed. The calculated results are in agreement with the established thermodynamic model. It is inspiring that we find that Cu2O nanocubes also have a critical size in the range of 55–67 nm, and their molar surface heat capacity and specific surface heat capacity are 59.35 and 59.31 nm, respectively. This property allows them to exhibit differences in thermal resistance from bulk materials within an acceptable range of error. This work has important scientific significance and values for enriching and developing the surface physical chemistry and understanding the energy storage and other processes of nanomaterials.

TChem: A performance portable parallel software toolkit for complex kinetic mechanisms

We present TChem, a performance portable software toolkit to enable the analysis of complex kinetic mechanisms. The software provides tools for gas-phase and surface chemistry, thermodynamic properties, and implements formulations for several canonical reactor models. Analytical derivatives necessary to construct Jacobian matrices corresponding to all implemented functionalities are available through automatic differentiation. TChem uses the Kokkos framework to achieve portability across multiple heterogeneous computing platforms with a single version of the code. We implement a hierarchical parallelism framework to enable efficient chemical source term and thermodynamic property evaluations over the number of samples assigned to the local computing device. We analyze parallel efficiency results extracted from test cases for thermodynamic properties, source terms, and Jacobians evaluations on Intel Xeon CPUs and NVIDIA Volta GPUs. Program summaryProgram Title: TChemCPC Library link to program files:https://doi.org/10.17632/25prt5g35w.1Developer's repository link:https://github.com/sandialabs/TChemLicensing provisions: BSD 2-clauseProgramming language: C++Nature of problem: TChem seeks efficient solutions of models that involve complex chemical kinetic mechanisms, which are essential for various applications areas such as combustion modeling, atmospheric chemistry and catalysis. In general, a detailed chemical kinetic mechanism involves a number of species and associated elementary reactions. The system of governing equations is typically highly non-linear and stiff, involving a large range of time scales.Solution method: TChem provides source term functions and numerical/analytic Jacobians for canonical reactor models. In particular, the analytic Jacobian is computed using automatic differentiation techniques implemented in the SACADO library. For solving stiff time ODE/DAE systems, TChem uses the Tines implementation of an adaptive 2nd-order backward difference formula to obtain efficient solutions that evolve on a range of time scales. The software employs batch parallelism to exploit massively parallel modern computing devices. Target workflows correspond to reactive flow problems or uncertainty quantification studies, which require the solutions of many samples corresponding to different grid points or input conditions. The software provides performance portable implementations aiming to use modern heterogeneous computing platforms i.e., multi/many core host processors with external GPU accelerators. We achieve the performance portability using the Kokkos parallel programming model that enables translation of a single Kokkos implementation to multiple device-specific backend codes.

Augmented scaled particle theory for a hard disk fluid

The success of scaled particle theory (SPT) can be certainly ascribed to the appealing physical idea embedded in it, i.e., accounting for the work needed to insert a particle into a liquid by a bulk contribution and a surface contribution. So, it can describe bulk and surface thermodynamic properties in the same framework. The surface tension term in SPT involves one flat-surface contribution and two additional contributions due to surface curvatures. High-order curvature terms (also called non-Hadwiger terms) were evidenced. Recently, we have developed an augmented scaled particle theory (ASPT) by adding one high-order curvature term for a hard sphere fluid. Here, we extend ASPT to a two-dimensional hard disk fluid. As for the 3D case, our 2D ASPT allows for improving both bulk and surface thermodynamic properties of a hard disk fluid with respect to the original SPT.

Disentangling the size-dependent redox reactivity of iron oxides using thermodynamic relationships

Nanoparticles often exhibit size-dependent redox reactivities, with smaller particles being more reactive in some cases, while less reactive in others. Predicting trends between redox reaction rates and particle sizes is often complicated because a particle's dimensions can simultaneously influence its aggregation state, reactive surface area, and thermodynamic properties. Here, we tested the hypothesis that interfacial redox reaction rates for nanoparticles with different sizes can be described with a single linear free-energy relationship (LFER) if size-dependent reactive surface areas and thermodynamic properties are properly considered. We tested this hypothesis using a well-known interfacial redox reaction: the reduction of nitrobenzene to aniline by iron-oxide-bound Fe2+. We measured the reduction potential (EH) values of nano-particulate hematite suspensions containing aqueous Fe2+ using mediated potentiometry and characterized the size and aggregation states of hematite samples at circumneutral pH values. We used the measured EH values to calculate surface energies and reactive surface areas using thermodynamic relationships. Nitrobenzene reduction rates were lower for smaller particles, despite their larger surface areas, due to their higher surface energies. When differences in surface areas and thermodynamic properties were considered, nitrobenzene reduction kinetics for all particle sizes was described with a LFER. Our results demonstrate that when Fe2+ serves as a reductant, an antagonistic effect exists, with smaller particles having larger reactive surface areas but also more positive reduction potentials. When Fe3+ serves as an oxidant, however, these two effects work in concert, which likely explains past discrepancies regarding how iron oxide particle sizes influence redox reaction rates.