Total Interfacial Free Energy Research Articles

Highly efficient solid-liquid separation of anaerobically digested liquor of food waste: Conditioning approach screening and mechanistic analysis

Anaerobic digestion is known for its effectiveness and environmental friendliness in treating food waste. However, it produces anaerobically digested liquor (ADL). ADL usually has a high solid content and high concentrations of nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) carried by suspended solids (SS). Thus, when ADL with amounts of SS reaches the subsequent biochemical treatment units, they negatively impact the microbial stability of corresponding processes, causing unstable effluent qualities. For this reason, the solid-liquid separation of ADL acts as a crucial step for the wide application of anaerobic digestion. In this work, the typical sludge conditioning approaches, including flocculation/coagulation, coagulation, oxidation and advanced oxidation processes (AOPs), were systematically screened for their feasibility in enhancing the solid-liquid separation of ADL. The modified Fenton treatment combined with centrifugation was found to be the most effective approach, which realized the removal of 91.36% SS with FeSO4•7 H2O (5.96 g/L) and H2O2 (2.79 g/L) but without pH adjustment of ADL. The mechanism analysis showed that the modified Fenton promoted ADL colloidal aggregates to form looser medium-sized flocs with pores, increased the zeta potential to −17.6 mV, and highly reduced the total interfacial free energy. Also, extracellular polymeric substances (EPS) were released into liquid phase, which further eliminated the water-retaining properties of solid compositions. The analysis of surface chemical composition suggested that the modified Fenton decreased the hydrophilic component from 53.37% to 43.81% and the relative content of protein-N from 45.43% to 23.57%, while increased carbon chain and hydrocarbyl species. Furthermore, principal component analysis (PCA) suggested that SS, zeta potential, Lewis acid-base interfacial free energy, two-dimensional fractal index (2-Df) and C-(N, O) relative content were more sensitive to variations in conditioning approaches than protein-N relative content, and hydroxyl free radical (•OH) played the key role for the modified Fenton to improve SS removal from ADL.

Adhesion of Norovirus to Surfaces: Contribution of Thermodynamic and Molecular Properties Using Virus-Like Particles.

The aim of the study was to assess human norovirus and feline calicivirus (FCV) surface free energy, hydrophobicity, and ability to interact with fresh foods and food-contact surfaces. Virus-like particles (VLPs) of human norovirus (GI.1 and GII.4) and FCV were produced, purified, and analyzed for their surface free energy, hydrophobicity, and the total interfacial free energy of interaction [Formula: see text] with lettuce, strawberry, polyethylene, and stainless steel. GII.4 VLPs were further tested for adhesion at different pH, ionic strengths, and temperature. All the VLPs and the test materials showed low surface energies, as well as hydrophobic characters except for GI.1. Nearly all [Formula: see text] values were propitious for spontaneous adhesion. GII.4 VLPs adsorbed almost indifferently to stainless steel, polyethylene, and lettuce. Isoelectric point and high temperature generally promoted adhesion while ionic strength effect was surface-dependant. According to this study, all the materials assessed are of low-energy and hydrophobic nature except GI.1 VLPs. Interfacial free energies of interaction were favorable for spontaneous adhesion ([Formula: see text] < 0) of all VLPs to the test materials, except for GI.1 VLPs to both stainless steel and straweberry. It is also found that norovirus adhesion is more sensitive to physicochemical conditions than to surface character itself.

Antifouling performance of polytetrafluoroethylene and polyvinylidene fluoride ultrafiltration membranes during alkali/surfactant/polymer flooding wastewater treatment: Distinctions and mechanisms

Alkali/surfactant/polymer (ASP) flooding wastewater is highly caustic, and membrane fouling is the main obstacle during ASP ultrafiltration (UF) treatment. To maintain favorable filtration performance, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes were implemented here, and their antifouling properties and mechanisms were investigated based on the threshold flux theory. Compared with the PVDF membranes, the PTFE membranes exhibited superior antifouling properties with lower reductions in flux and smaller hydraulic resistance, and they presented a nearly identical pseudo-stable fouling rate at a later time point. In the fouling layers of the PTFE and PVDF membranes, anion polyacrylamide (APAM) was observed along with divalent/trivalent metal ions. The thermodynamic and molecular mechanisms of membrane fouling by APAM were elucidated using the Extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory and atomic force microscopy (AFM), respectively. The calculated total interfacial free energy (mJ/m2) of adhesion between the APAM and PTFE membranes was positive, and the value between the APAM and PVDF membranes was negative. Furthermore, the values and interaction distances of the measured intermolecular rupture and approaching forces were larger for APAM-PTFE than for APAM-PVDF. For the PTFE membranes, the positive free energies and smaller intermolecular interaction resulted in weaker APAM-PTFE adhesion and adsorption and therefore the lower levels of flux decline and the later achievement of the pseudo-stable fouling rate. Additionally, the total flux recoveries observed after physical cleaning reached 0.78–0.80 and 0.32–0.39 for the PTFE and PVDF membranes, respectively, which showed that the PTFE membranes can be cleaned easily. The PTFE membranes have considerable potential for extensive application in UF treatments for ASP wastewater. These results should promote understanding the essence of the threshold flux and the fouling control of UF membranes.

Hydration film measurement on mica and coal surfaces using atomic force microscopy and interfacial interactions

The hydration film on particle surface plays an important role in bubble-particle adhesion in mineral flotation process. The thicknesses of the hydration films on natural hydrophobic coal and hydrophilic mica surfaces were measured directly by atomic force microscopy (AFM) based on the bending mode of the nominal constant compliance regime in AFM force curve in the present study. Surface and solid-liquid interfacial energies were calculated to explain the forming mechanism of the hydration film and atomic force microscopy data. The results show that there are significant differences in the structure and thickness of hydration films on coal and mica surfaces. Hydration film formed on mica surface with the thickness of 22.5 nm. In contrast, the bend was not detected in the nominal constant compliance regime. The van der Waals and polar interactions between both mica and coal and water molecules are characterized by an attractive effect, while the polar attractive free energy between water and mica (−87.36 mN/m) is significantly larger than that between water and coal (−32.89 mN/m), which leads to a thicker and firmer hydration layer on the mica surface. The interfacial interaction free energy of the coal/water/bubble is greater than that of mica. The polar attractive force is large enough to overcome the repulsive van der Waals force and the low energy barrier of film rupture, achieving coal particle bubble adhesion with a total interfacial free energy of −56.30 mN/m.

Simultaneous two drugs release form Janus particles prepared via polymerization-induced phase separation approach

Seeded emulsion polymerization of 2-dimethylaminoethylamino methacrylate (DMAEMA) was carried out using monodispersed poly(2-hydroxyehtyl methacrylate) (PHEMA) seeds to produce Janus particles. Three feeding approaches were used comprising one together, rest and continuous feeding methods to investigate different morphologies. However, FE-SEM results showed that all feeding approaches yielded dumbbell-like Janus particles. Furthermore, snowman-like Janus particles were obtained via seeded distillation precipitation polymerization (DPP). It is shown that minimizing the total interfacial free energy alongside difference in solubility parameters of Janus domains are responsible for obtained morphologies. Two different morphologies (dumbbell-like and snowman-like) were chosen as carriers of ibuprofen and DOX simultaneously. Also, simultaneous release of two drugs were investigated in different conditions. Dumbbell-like Janus particles showed higher ibuprofen loading whereas DOX was more loaded onto snowman-like Janus particles. Also, DOX was released more rapidly through Janus particles at different pH values and both types of Janus particles showed similar drugs release behaviors.

Topological changes in coarsening networks

Curvature driven grain growth proceeds by the motion of curved grain boundaries in polycrystals leading to a decrease in the total interfacial free energy. However, grain growth cannot occur without the so-called topological transitions. Indeed, it is a mathematical impossibility that a decrease in the number of grains per unit volume may take place without the topological transition that corresponds to the grain disappearance. Nonetheless, despite their importance, no previous work has studied the topological transitions in detail that take place during the transient as well as the self-similar state of coarsening. In the present work, the three classical topological changes are tracked during 2-d grain growth simulated by a Monte Carlo method. It is shown and discussed how topological transitions reach a self-similar state together with the grain size and the number of edges (faces) per grain distribution.

Silicone/vegetable oil Janus emulsion: Topological stability versus interfacial tensions and relative oil volumes

Several aspects were studied of the formation and destabilization in bulk of silicone/vegetable oil, SO/VO, Janus emulsions, stabilized by Tween 80. In the formation of the emulsions, it was unexpectedly found that the dispersions tended to contain both single and flocculated drops irrespective of the emulsification intensity. Microscopy of the emulsions with no cover glass revealed flocculated drops of a large (200–500μm) central SO drop with many small VO drops attached. Applying a cover glass did not significantly change the drop size; instead two-oil Janus drops of well-defined contact angle were found. The emulsions showed rapid creaming irrespective of the preparation method, but a few days storage did not significantly change the drop size in the creamed layer, nor was separation of the oils detected. The total interfacial free energy of the Janus drops at equilibrium was compared to the two relevant alternatives; engulfed and separate drops. The Janus drop free energies were found less for all volume ratios of the oils, when the surfactant concentrations in the aqueous phase was sufficient to prevent spreading of VO on SO. Changing the surfactant concentration to bring the interfacial tensions closer to the critical value for spreading gave declining interfacial free energy difference to that of engulfed drops.

Crystal–liquid interfacial free energy and thermophysical properties of pure liquid Ti using electrostatic levitation: Hypercooling limit, specific heat, total hemispherical emissivity, density, and interfacial free energy

Thermophysical properties of liquid Ti are measured by a newly developed electrostatic levitation. In this study, we measure a hypercooling limit (ΔThyp), specific heat (Cp), total hemispherical emissivity (εT), and density (ρ) of liquid Ti. The ΔThyp of the liquid Ti is 341K. The Cp of the liquid Ti shows very weak temperature dependence during supercooling. The εT and ρ of the liquid Ti are given by 0.329 and ρ(T) (g/cm3)=(4.16−2.36)·10−4 (T−Tm). Finally, the interfacial free energy is estimated with the measured thermophysical parameters. The interfacial free energy is 0.164J/m2, and Turnbull’s coefficient is 0.48.

How do Quasi-Liquid Layers Emerge from Ice Crystal Surfaces?

Ice crystal surfaces melt at temperatures below 0 °C, and then quasi-liquid layers (QLLs) are formed. However, revealing the dynamic behavior of QLLs, which dominates the surface properties of ice crystals at temperatures near the melting point, remains an experimental challenge. Here, we demonstrate the similarities and differences in the generation mechanisms of two types of QLL phases, which show different morphologies and dynamics. We directly visualized the appearance of round liquidlike droplets (α-QLLs) and thin liquidlike layers (β-QLLs) on ice basal faces by advanced optical microscopy, which can allow visualization of the individual elementary steps on basal faces. We found that α-QLLs always appear at outcrops of dislocations, and that β-QLLs emerge from crystal surfaces where many microdefects are embedded. These results clearly demonstrate the similar function that strain induces the appearance of both types of QLLs. We also found that β-QLLs are spontaneously formed at interfaces between basal faces and α-QLLs, when the diameter of the α-QLLs becomes larger than several tens of micrometers. This result arose from the different structures of α- and β-QLLs: the β-QLLs probably have a structure intermediate between those of basal faces and α-QLLs, resulting in a reduction of the total interfacial free energy.

Effect of Polymer End Group on the Morphology of Polystyrene/Poly(methyl methacrylate) Composite Particles Prepared by the Solvent Evaporation Method

AbstractSummary: The effect of polymer end group on the morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA) composite particles was investigated on the basis of experimental observations and theoretical predictions. Both polymers with potassium persulfate (KPS)‐derived hydrophilic end group(s) and 2,2′‐azobis(isobutyronitrile) (AIBN)‐derived hydrophobic end group(s) were synthesized by emulsifier‐free emulsion polymerizations and solution polymerizations, respectively. Composite particles with the same end groups were prepared by release of toluene from PS/PMMA/toluene (1/1/24, w/w/w) droplets dispersed in an aqueous solution of sodium dodecyl sulfate (SDS). At a low SDS concentration, when the polymers with KPS‐derived end group(s) were employed, acornlike particles were formed. On the other hand, when the polymers with AIBN‐derived end group(s) were used, particles having a dimple were obtained. The interfacial tensions between toluene solutions of the polymers and SDS aqueous medium were lower for KPS‐derived end group(s) than for AIBN‐derived end group(s), and the difference was much larger for PS phase than PMMA phase. The predicted morphologies obtained from calculation of the minimum total interfacial free energy using the interfacial tensions agreed well with the experimentally observed morphologies in both cases. Moreover, the morphology of PS/PMMA composite particles with different end groups was also examined.

Quantifying the surface characteristics and flocculability of Ralstonia eutropha

The microbial surface and flocculability were qualitatively characterized through the combination of the surface thermodynamic and the extended DLVO approaches, with Ralstonia eutropha, a polyhydroxybutyrate-producing bacterium, as an example. The negativity of the zeta potential of R. eutropha decreased from the initial -19.5 to -11 mV in its cultivation with the consumption of glucose. The total interfacial free energy (DeltaGadh) was changed from -80 to 28.5 mJ m(-2) in its entire growth process. This suggests that the bacterial surface changed from hydrophobic into hydrophilic, resulting in an alteration of its surface characteristics and flocculability in its different growth phases. As a result, the stability ratio of suspensions increased with the increasing cultivation time, indicating that the cell particles became more repulsive with each other and led to a more stable suspension of R. eutropha in its cultivation. The obtained information in this work might be useful for better understanding the surface characteristics and the flocculability and even manipulating its flocculability in the microbial growth process.

Formation of “Snowmanlike” Polystyrene/Poly(methyl methacrylate)/Toluene Droplets Dispersed in an Aqueous Solution of a Nonionic Surfactant at Thermodynamic Equilibrium

"Snowmanlike" polystyrene (PS)/poly(methyl methacrylate) (PMMA) composite particles were prepared by evaporation of toluene from PS/PMMA/toluene droplets dispersed in an aqueous solution of polyoxyethylene nonylphenyl ether surfactant (Emulgen 911). Partitioning experiments revealed that the Emulgen 911 concentration was higher in the droplets than in the aqueous solution during toluene evaporation. As a consequence, the interfacial tensions between the polymer phases (PS and PMMA) and the aqueous phase (gammaP-T/W) were extraordinarily low (approximately 10(-1) mN/m). The interfacial tension between the PS and PMMA phases containing toluene (gammaPS-T/PMMA-T) measured by the spinning drop method was not affected by the presence of Emulgen 911. Based on minimization of the total interfacial free energy at a polymer weight fraction in the toluene droplet of 0.17, the formation of spherical droplets is expected, in agreement with experiment. The subsequent morphology change of the PS/PMMA/toluene droplets from spherical to snowmanlike during toluene evaporation under thermodynamic equilibrium is attributed to (i) the low values of gammaP-T/W, which explains the increase in the interfacial area between the droplets and the aqueous phase, and (ii) the increase in gammaPS-T/PMMA-T with increasing polymer weight fraction.

DLVO Approach to the Flocculability of a Photosynthetic H2-Producing Bacterium, Rhodopseudomonas acidophila

The DLVO theory was used to explore the flocculation characteristics of a H2-producing photosynthetic bacterium, Rhodopseudomonas acidophila. The relationship between the surface characteristics of this strain and itsflocculability was evaluated. Its flocculability was governed by both electrolyte concentration and pH, and the appropriate electrolyte concentration and pH were found to be 0.1 M NaCl solution and pH 7.0, respectively. In addition, the extracellular polymeric substances produced by R. acidophila were observed to have a significant effect on its flocculation. The effective Hamaker constant between R. acidophila and water was only 2.27 x 10(-23) J, suggesting that the contribution of van der Waals interaction energy to the total interaction energy could be neglected. As a result, the bacterial particles could not overcome the total energy barrier to flocculate effectively. Otherwise, because the repulsive total interfacial free energy between the bacterial cells and water was positive, the cell particles of R. acidophila repelled each other, resulting in a great stability of the cell suspensions.

Revisiting the Morphology Development of Solvent-Swollen Composite Polymer Particles at Thermodynamic Equilibrium†

Morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA)/toluene droplets, in which phase separation proceeds, dispersed in SDS aqueous solution was examined. It changed from ex-centered PS-core/PMMA-shell to hemisphere with increasing SDS concentration. At low polymer weight fraction (wp), PS and PMMA phases contained non-negligible amount of PMMA and PS, respectively. The small amount of PS and PMMA in PMMA and PS phases, respectively, affected significantly the interfacial tension between polymer/toluene and aqueous solutions. Interfacial tension between PS and PMMA phases at low wp was measured by the spinning drop method, showing a quite low value ( approximately 10-2 mN/m). Predicted morphology obtained from calculation of minimum total interfacial free energy of the droplets using the interfacial tensions agreed well with the experimental observation.

Melting of embedded anisotropic particles: PbIn inclusions in Al

Small particles embedded in the solid state can assume facetted shapes that indicate the anisotropy in interfacial free energy between the particle and the embedding phase. Previous in situ transmission electron microscopy (TEM) of Al–In has shown that such facetted nanoparticles with cubic symmetry embedded in a solid can produce a series of complex melt configurations. To determine the dependence of melt configuration on solid–solid facet energies, this work numerically calculates the equilibrium melt trajectory for a family of cuboctahedral particles parameterized by the ratio of matrix–particle interfacial free energies for orientations taken with respect to the crystal axes of the matrix, ϒ = γ100/γ111. The calculations assume that equilibrium occurs with the minimization of the total interfacial free energy to determine the stable internal melt configuration for a fixed volume of melt confined within a member of the cuboctahedral family. At particular melt volume fractions, abrupt transitions in shape occur when a stable configuration reaches a touching or necking instability. In situ TEM of a dilute Al alloy containing embedded nanosized PbIn inclusions that gradually melt as the temperature is increased from 230 to 260°C is consistent with the results calculated for ϒ = 1.245.

Simulated Annealing as a Method for the Determination of the Spatial Distribution of a Condensable Adsorbate in Mesoporous Materials

The simulated annealing algorithm is employed for the determination of the spatial distribution of a condensable adsorbate in reconstructed digital domains of mesoporous materials. The optimum configuration for a given degree of saturation is derived assuming that in equilibrium the total interfacial free energy reaches a global minimum value. The suggested approach is applied to reconstructed matrixes of Vycor and random sphere packs. Furthermore, the effective diffusivities of inert gases in the Knudsen regime are calculated in the resulting “dry” and “wet” images with a step-by-step random walk method. The predicted gas relative permeability curves are in satisfactory agreement with experimental results, confirming that the suggested combination of digital reconstruction and simulated annealing is a useful tool for the determination of the spatial distribution of a condensable sorbed phase in mesoporous solids.

Thermodynamic analysis of the morphology of monomer-adsorbed, cross-linked polymer particles prepared by the dynamic swelling method and seeded polymerization

Thermodynamic simulation of the morphology of monomer-adsorbed, cross-linked polymer particles prepared by the dynamic swelling method which the authors proposed was conducted to clarify its thermodynamic stability from the viewpoint of the total interfacial free energy. By comparing it with experimental results reported in previous articles, it was found that the morphology was controlled thermodynamically. Snowman-shaped composite polymer particles having different morphologies were prepared by seeded polymerization of the monomer-adsorbed, cross-linked polymer particles, in which the polymer particles had different cross-linking densities.

Impact of carbon and nitrogen conditions on E. coli surface thermodynamics

Escherichia coli cultured under different carbon and nitrogen conditions was measured for growth and surface thermodynamics to examine the impact of C/N ratio on E. coli growth and its surface thermodynamics. Among the three carbon sources, glucose grown cultures had the greatest specific growth rate (0.67 and 0.44 h −1 with ammonia and nitrate serving as the nitrogen source, respectively, and no carbon or nitrogen limitation), and yielded the least hydrophilic surface (31.49 and 22.23 mJ m −2 of the total interfacial free energy of interaction); propionate grown cultures had the greatest stoichiometric yield coefficient (0.61 and 0.49 g biomass per g substrate), lipopolysaccharide production efficiency (0.161 and 0.149 g per g biomass), and yielded the most hydrophilic surface (46.32 and 39.32 mJ m −2 of the total interfacial free energy of interaction). For the same carbon source, ammonia-grown cultures yielded a greater specific growth rate, growth yield and lipopolysaccharide production efficiency, and a more hydrophilic surface than nitrate grown cultures. In carbon-limited cultures, a smaller specific growth rate and lipopolysaccharide production efficiency and greater growth yield were observed as compared with cultures grown with no carbon and nitrogen limitation. In addition, under carbon-limited growth, the cells exhibited a less hydrophilic surface. When nitrogen was the limiting factor, E. coli displayed a smaller specific growth rate and growth yield, greater lipopolysaccharide production efficiency and a more hydrophilic surface as compared with cultures grown with no carbon and nitrogen limitation.

Prediction and manipulation of the phase morphologies of multiphase polymer blends: II. Quaternary systems

We have applied our model concerning the phase structures of multiphase polymer blends to quaternary blends of polyethylene, polypropylene, polystyrene and poly(methyl methacrylate) of different overall compositions. Predictions of the phase morphologies of such multicomponent blends are based on minimization of the total interfacial free energy of the system. We compare predictions of the model with experimental observations, and show agreement in every case between the predicted and experimental morphologies. Furthermore, we show that the phase structure of a quaternary blend can be converted from one type of phase morphology to another, e.g. from an encapsulation type to the dispersion type, by using an interfacially active block copolymer. This shows the possibility of adjusting the phase morphologies of multicomponent systems as desired.

Substrate curvature resulting from the capillary forces of a liquid drop

The difference between interfacial tension and interface stress is illustrated by considering a hemispherical liquid drop on a solid substrate. The equilibrium shape is determined by minimizing the total interfacial free energy, which leads to the Young equation for balance of the interfacial tensions. The curvature of the substrate is determined by the interfacial stresses. Two contributions are calculated: one arising from the hydrostatic pressure in the drop, the other from the imbalance of the interfacial stresses.