Surface Free Energy Properties Research Articles

Improving the rheological behavior of alkali-activated slag pastes by using low surface free energy mineral admixtures

This study investigates the effect of low surface free energy mineral admixtures (CaF2-dominated fluorite (FL) and fluorine-containing lithium slag (LS)) on the rheological behavior of alkali-activated slag (AAS) pastes. The fluidity, rheological behavior, surface charge properties and surface free energy properties were tested. The interparticle forces based on extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were calculated to understand the mechanism for the rheological behavior improvement. The results revealed that both FL and LS could improve the fluidity and decrease the yield stress and plastic viscosity of AAS pastes. Furthermore, the attraction is manifested by the sum of electrostatic, van der Waals, and Lewis acid-base forces, and this value decreases with increasing LF or LS content, implying that the particle dispersion in AAS pastes is improved. Furthermore, observing flocculent structures captured by the metallographic microscope proves the better dispersion of AAS pastes after adding FL and LS. Moreover, incorporating LS or FL decreases the flexural and compressive strengths of AAS mortars.

Formulation of biocompatible microemulsions for encapsulation of anti-TB drug rifampicin: A physicochemical and spectroscopic study

Surfactant-based microemulsions have emerged as an advanced material for universal drug carriers for poorly soluble drugs. These microemulsions (MEs) are based on ionic liquid as oil in presence of traditional surfactants which have been receiving ample attention from research communities all over the world. In this study, we have reported oil-in-water MEs containing a hydrophobic ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) as oil phase, nonionic surfactants Brij35/Triton X100 and water. The microstructure of these BmimPF6-in-water (IL/w) MEs were identified by using UV-Vis and fluorescence spectroscopy. The breaks observed in the absorption spectra of both probe (p-nitroanaline) and drug (rifampicin) versus wt% of IL can be used to confirm the formation of MEs. Similar behavior has been observed in the emission spectra of fluorescence probe (pyrene) and drug in presence of varied wt% of IL which supported the results of the absorption spectroscopy. The results from dynamic light scattering (DLS) and scanning electron microscopy (SEM) measurements showed that the MEs had a nearly monodisperse droplet size distribution (PDI < 0.4) which indicates the homogeneity in distribution of the ME formulations. The incorporation of rifampicin-drug in the MEs shows notable changes which suggests the accumulation of drug in the palisade layers of the MEs. Further, the surface free energy properties of the MEs are explored from surface tension (γ) measurements. The changes in γ in these different MEs may be due to the changes in microstructures of the ME systems which can be helpful to recognize the transitions occurring in the ME structures. This study offers a better understanding of MEs features and paves path towards the potential applications of MEs in pharmaceutical industry.

Correlation between bond strength and surface free energy parameters of asphalt binder-aggregate system

The bonding potential is one of the imperative parameters of the asphalt binder-aggregate compositions and significantly affects the resistance of the asphalt mixtures against moisture damages. The properties of asphalt binder and aggregate have considerable effects on the moisture sensitivity and bond strength of the asphalt binder-aggregate composition. In the present study, the effects of the aging and stiffness of the asphalt binder, aggregate type, and their interactions on the bond strength and moisture susceptibility of the asphalt binder-aggregate systems were evaluated. The binder bond strength (BBS) test with a new approach of analyzing the failure pattern and the surface free energy (SFE) method were carried out to characterize the bond strength and bond energy parameters. The relationship between the bond strength, failure pattern in the BBS test, and SFE properties were presented. The results indicated strong and meaningful correlations between the SFE properties, failure patterns, and bond strength under dry and wet conditions. The meaningful and good correlations between the failure patterns and bond energies under dry and wet conditions demonstrate that the changes in the adhesive and cohesive failures in the asphalt binder-aggregate compositions highly depend on the SFE properties. Besides, according to SFE results and the failure patterns under dry and wet conditions, new energy parameters were introduced to evaluate the bond strength and moisture sensitivity.

Nanocomposite poly (ethylene oxide) films functionalized with silver nanoparticles synthesized with Acca sellowiana extracts

The development of nanoparticles synthesized using phenolic compounds and incorporated into biodegradable polymeric matrix brings as a new perspective to the production of nanocomposite films for application as food packaging. In this work, poly (ethylene oxide) (PEO) nanocomposite films containing silver nanoparticles (AgNPs) were produced using Acca sellowiana aqueous extract, and the physicochemical, morphological, antioxidant, and antimicrobial properties were evaluated. The synthesis of AgNPs was determined by the appearance of brownish color in the extract, accompanied by the UV–vis spectroscopy with a band around 400 nm. AgNPs presented a good colloidal stability by zeta potential, with low polidispersity index and particle size lower than 80 nm. PEO nanocomposite films presented antioxidant activity and the films containing AgNPs demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus. The incorporation of Acca sellowiana extract and AgNPs in PEO films was responsible to modify the mechanical properties, with decrease in tensile strength and increase in elongation at break. Beyond, was also observed an increase of the color parameter and decrease transmission of UV light thought the film, which are important parameters for food conservation. In the surface free energy properties, was observed an increase in the contact angle, due to the decrease in the films polarity. Based on the aforementioned, PEO nanocomposite films produced with Acca sellowiana extract and AgNPs is an active, antimicrobial and biodegradable material, and may be considered as an innovative packaging to promote the food conservation.

Engineering nanostructured cell micropatterns on Ti6Al4V by selective ion-beam inhibition of pitting

We have modified Ti6Al4V at the micro and nanoscale by using ion beam irradiation with 5 MeV Si+ ions through 1D micromasks. The passivation layer on irradiated areas inhibits hydrofluoric acid induced etching, leading to pitting contrasts. Surface microscopies and spectroscopies reveal that the nanotopographic modification correlates with a preferential titanium etching, and lead to dual surface free energy properties. The patterns are able to induce guidance of olfactory ensheathing glia cells, mainly through inhibition of adhesion on nanostructured areas, and could be attractive substrates for the induction of stimuli to neural cells under non voltaic polarization.

Wetting properties of poultry litter and derived hydrochar.

Detailed assessment of hydrochar wetting properties, which could provide an essential understanding of underlying mechanisms during its application to soils, is lacking. We characterized hydrochar produced from hydrothermal carbonization (HTC) performed on poultry litter at various temperatures and for different times in terms of hydrophobicity and surface free energy properties. Hydrochar was more hydrophobic than untreated poultry litter, and its hydrophobicity increased with increasing HTC temperature (contact angle > 130°). These changes were correlated with degradation of hemicellulose and cellulose. Hydrochar produced at 250°C contained mostly lignin and displayed high hydrophobicity over both prolonged wetting periods and repeated wetting cycles. Surface free energy was calculated using the Owens–Wendt–Rabel–Kaelble and Wu models, with the latter resulting in lower standard errors. The surface free energy decreased as HTC treatment severity increased from 26 mJ/m2 in the poultry litter to 8 mJ/m2 after treatment at 250°C for 60 min. The dispersive component fraction of the surface free energy increased with increasing treatment severity. This study demonstrated that changes in the physical composition of hydrochar due to increased treatment severity increase its hydrophobicity and decrease its surface free energy. Moreover, due to non-persistent hydrophobicity, hydrochar produced at temperatures lower than 250°C will likely not show adverse effects on soils.

Surfactant-Free Microemulsions of 1-Butyl-3-methylimidazolium Hexafluorophosphate, Diethylammonium Formate, and Water.

Surfactant-free microemulsions (SFMEs) are a unique kind of microemulsion, which form from immiscible fluids (i.e., oil and water phases) in the presence of amphi-solvents rather than traditional surfactants. In comparison with traditional surfactant-based microemulsions (SBMEs), SFMEs have received much less attention, and the current understanding of the unique system is very limited. Herein, we report a SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), the protic IL diethylammonium formate (DEAF), and water, in which the bmimPF6 and DEAF are used as the oil phase and amphi-solvent, respectively. Three kinds of microstructures, namely, water-in-bmimPF6 (W/IL), bicontinuous (BC), and bmimPF6-in-water (IL/W), are identified for the SFME, using cyclic voltammetry, cryo-TEM, and DLS techniques. Especially, the volumetric and surface free energy properties of the SFME are investigated by excess molar volume ( VmE) and surface tension (γ) measurements, and they are found to be similar to those of SBMEs. Discontinuous changes in VmE and γ with the system compositions are observed as the system microstructures change, which can be used to identify the structural transition of SFMEs. We think this study provides a better understanding of SFME features.

Effect of different cleaning methods of polyetheretherketone on surface roughness and surface free energy properties.

To determine the effect of different individual, laboratory and professional cleaning methods on the surface-roughness (SR) and surface free energy (SFE) of polyetheretherketone (PEEK), PMMA-based (PMMA) and composite (COMP) materials. 330 specimens of PEEK, PMMA and COMP (N = 990) were prepared and divided into the following cleaning protocols (n = 30/group): (i) individual prophylaxis using (ST) soft, (MT) medium-hard and (SOT) sonic toothbrushes, (ii) in-lab cleaning protocols consisting of (SY) Sympro cleaning system, (SS) SunSparkle, (UB) ultrasonic bath and (AP) Al2O3-powder device and (iii) professional prophylaxis applying (PS) Perio Soft-Scaler, (SO) Sonicsys, (AFC) Air Flow Comfort, and (AFP) Air Flow Plus. After each protocol SR (profilometer), SFE (contact angle devise) and surface topography (SEM) were measured. Data were analyzed using multivariate analysis, Kruskal-Wallis-H- and Mann-Whitney-U-test (p&lt;0.05). No impact of material on SR was observed (p = 0.443). Cleaning using conventional air-abrasion and powders (AP), followed by AFC produced higher SR values than the remaining methods (p&lt;0.001). Within SFE, the cleaning method exerted the highest influence on SFE values (p&lt;0.001, ηP2 = 0.246), closely followed by the polymer material (p&lt;0.001, ηP2 = 0.136). PMMA and PEEK presented after cleaning lower SFE than COMP. PS, UB and SO showed lower SFE than specimens cleaned using SS, ST and SY. Cleaning using SY led to the highest SFE. With regard to SR, all methods - with exception of conventional air-abrasion - can be recommended to clean PEEK. According to the SFE, PEEK may be an acceptable material providing even lower plaque accumulation rates than COMP. The field for more research is now open for scrutiny.

Rheological and Chemical Characterization of Biobinders from Different Biomass Resources

The increasing costs and strong worldwide demand for petroleum and the adverse environmental impact of the consumption of nonrenewable energy sources have encouraged the development of alternative sources of renewable energy. One source of renewable energy can be developed in biorefineries, where biomass feedstocks can be converted to biocrude oil through thermochemical processes. Biocrude oil can replace petroleum-based transportation fuels and can be used to build and maintain transportation infrastructure, which requires an energy-intensive process that consumes natural resources, including mineral aggregates, steel, cement, and petroleum-based binder. This study aimed to characterize biocrude oil as an alternative binder material, which is referred to here as biobinder. The hydrothermal liquefaction technique was used to produce biobinder from spirulina algae (microalgae), swine manure, and nanoalgae. A chemical analysis was performed with the saturates, aromatics, resins, and asphaltenes technique to characterize the percentage of different components present in the biobinder. A rheological characterization of biobinders was conducted to evaluate their feasibility for use in pavement construction and to predict their performance during the service life of a pavement. Surface free energy properties of biobinders also were determined with the use of a sessile drop device to characterize adhesion properties. The results indicated that biobinder had significantly different rheological and chemical properties than conventional asphalt binder. When blended with conventional binder, biobinder showed the potential to reduce the stiffness of original binder. As a result, it might be used to rejuvenate mixes with recycled asphalt materials or find an application under low-temperature conditions.

Application of surface free energy techniques to evaluate bitumen-aggregate bonding strength and bituminous mixture moisture sensitivity

This paper presents a combination of surface free energy testing techniques for aggregates and bitumen, with mechanical moisture-sensitivity assessment techniques for identification of compatible bitumen–aggregate combinations. Results from the surface free energy measurements and calculations were compared with data from the rolling bottle test and the saturation ageing tensile stiffness test in order to establish relationships amongst the three techniques. The mineralogical composition and microstructure of the aggregates were characterised using a mineral liberation analyser. For the same bitumen type, moisture sensitivity of mixtures containing limestone aggregates were found to be lower than mixtures containing granite aggregates. The presence of high amounts of quartz and feldspar (up to 50%) in the granite compared with almost none in limestone, and the significant amount of calcite in limestone (96% or more) versus none in granite were cited as possible reasons for the differences in performance of the two aggregate types. The porosity of the worst performing aggregates was higher than the best performing aggregate. The study concludes that moisture damage in the bituminous mixture is a function of the physico-chemical surface free energy properties of bitumen and aggregates as well as the mineralogical composition of aggregates.

Spatial Patterns of Microbial Retention on Polymer Surfaces

Microbial adhesion and retention on surfaces are complex phenomena, critical to the formation and development of biofilms. Recently, the focus of research has been more and more on the importance of retention of bacteria under fluctuating high shear forces in biofilm formation. The aim of the present work was to carry out a comparative study of the retention process of different bacterial and yeast species using: (1) a range of surfaces with different surface free energy properties and (2) a number of different bacterial cell physiological states. It was found for the first time that once a threshold cell number is retained on the surface, microbial retention patterns are formed following a power law, i.e., not stochastic. Our results demonstrated that the overall spatial patterns of microbial retention observed for the different substrates are similar for the all investigated cell types and that the drastic modification of the surface free energy does not affect this spatial organization. On the other hand, the microbial retention patterns appear to be significantly affected by the physiological state of the cells. Finally, the experimental retention patterns have been well simulated by a general agent-based model, confirming that the typical fractal distribution of retained cells is the result of a self-organization process.

The evaluation of the surface free energy of liquids and solids in concrete technology

This paper presents initial results from an extensive study on the calculation of the surface free energy of mineral materials. The usefulness of such evaluation is demonstrated through the technological operation of casting and moulding concrete. Surface interactions will firstly act on the dispersion of particles inside the concrete mix and the viscosity of the fresh material; the specific effect of superplasticizers and Modifying Viscosity Agent is presented through the determination of surface free energy properties. The second analysis is dealing with the interactions between mineral and vegetal oils applied on the wooden or steel formwork and fresh concrete. The evaluation of contact angle and interfacial forces help to efficiently select the most appropriate material.

Surface Characterization of Poly(l-lactic acid)−Methoxy Poly(ethylene glycol) Diblock Copolymers by Static and Dynamic Contact Angle Measurements, FTIR, and ATR-FTIR

The surface composition and surface free energy properties of two types of amphiphilic and semicrystalline diblock copolymers consisting of poly(L-lactic acid) coupled to (methoxy poly(ethylene glycol) (PLLA-MePEG) having differing block lengths of PEG were investigated by using static and dynamic contact angle measurements, transmission Fourier infrared spectroscopy (FTIR), and attenuated total reflection spectroscopy (ATR-FTIR) and compared with results obtained from PLLA and MePEG homopolymers. The contact angle results were evaluated by using the van Oss-Good method (acid-base method), and it was determined that the Lewis base surface tension coefficient (gamma-) of the copolymers increased with an increase of the PEG molar content at the copolymer surface. This result is in good agreement with the transmission FTIR and ATR-FTIR results but not proportional to them, indicating that the surfaces of the copolymers are highly mobile and that the molecular rearrangement takes place upon contact with a polar liquid drop. The dynamic contact angle measurements showed that the strong acid-base interaction between the oxygen atoms in the copolymer backbone of the relatively more hydrophilic PEG segments with the Lewis acidic groups of the polar and hydrogen-bonding water molecules enabled the surface molecules to restructure (conformational change) at the contact area, so that the PEG segments moved upward, whereas the apolar methyl pendant groups of PLLA segments buried downward.

Use of surface free energy properties to predict moisture damage potential of Asphalt concrete mixture in cyclic loading condition

The synergistic effects of microdamage due to repeated loading in Asphalt-Aggregate system at a high temperature (40°C) and moisture damage analysis based on surface free energy theory are presented in this paper. The introduction of moisture in either a liquid or vapor state during cyclic loading may well be more damaging than simply moisture conditioning an asphalt concrete sample prior to testing. This difference may be due to the presence of a dynamic “network” of adhesive fracture, which potentially provides a channel for moisture movement within the sample. The percentage of the surface area of aggregate that has been exposed to water was used as a significant index to quantify the level of adhesive fracture. This index is calculated with the surface free energies of aggregate and asphalt which are measured by two methods, the universal gas adsorption and the Wilhelmy plate, respectively. The relation between the percentage of the surface area of the aggregate exposed to water and the number of cycles of loading assists in quantifying adhesive fracture in the asphalt-aggregate mixture.

The Maximum Peel Strength of Pressure-Sensitive Styrene-Butadiene Emulsion Polymers

Peel strengths of five pressure-sensitive styrene-butadiene emulsion polymers, having different amounts of gel and different glass transition temperatures, have been determined as a function of temperature and peel rate. For each peel rate, the peel strength reaches a maximum at a particular temperature, and this maximum peel strength is associated with the change of the mode of failure from cohesive to adhesive. The maximum peel strength is found to be largely independent of the gel level and possibly of the glass transition temperature of the polymer within the domain of pressure-sensitive polymeric properties. The maximum peel strength appears to be dependent on the kind of substrates and the stabilization system of the emulsion polymers (surface free energy properties of the bonded interfaces).

Monte Carlo Calculations of Effective Surface Tension for Small Clusters

In this study we have calculated configurational Helmholtz free energy differences between n and n – 1 molecule water clusters and nand n – 1 atom argon clusters using classical effective atom-atom pair potentials and the Bennett–Metropolis Monte Carlo technique. When plotted versus n–1/ 3 the slope of the free energy differences yields an effective surface tension, σ. It is found that these slopes display a universal (material independent) property related to the excess surface entropy / κ per molecule (or atom), Ω. For most materials (in the bulk liquid state) the latter quantity is about 2. The results indicate that clusters as small as n = 10 display bulk surface free energy properties. The temperature dependence of the effective surface tension for the model water clusters is also investigated and is consistent with a simple scaled form, σ / κTρ2/3liquid ≈ Ω(Tc /T – 1), where Tc = 647 K and Ω = 1�9.

Wettability of denture soft-lining materials

Data on the wettability of long-term resilient denture base lining materials have previously been obtained by static methods. This study determined the dynamic contact angle of a range of long-term resilient lining materials and the surface free energy properties of these materials. This method was a rapid and convenient method for determining wettability parameters. The equilibrium contact angle revealed the Flexor and Novus materials to be the least wetted with the Molloplast-B material, and CoeSuper-Soft material was wetted similarly to Trevalon material. The contact angle hysteresis indicated that all the soft-lining materials tested would improve denture stability under dislodgment forces. The surface-free energies appeared to be similar for all the soft-lining materials but were significantly lower than that of Trevalon.

Surface Free Energy Components of Clay-Synthetic Humic Acid Complexes from Contact-Angle Measurements

AbstractThe surface free energy components of clay-organic complexes were determined to assess to what extent an organic adsorbate modified the surface properties of the mineral, insofar as the stability of soil aggregates is concerned. Adsorption isotherms for two synthetic, humic acid-like polymers were determined on a Ca-montmorillonite. From contact-angle measurements performed on dry surfaces, the surface free energy properties of the clay-organic complexes were determined using the two-liquid-phases method (water and hydrocarbons). This method allows both the dispersive and nondispersive components of the solid surface free energy, γDS and γPS, to be determined. The results show that a very small amount of polymer (1% by weight) adsorbed on the external surfaces of the montmorillonite decreased markedly the surface free energy components of the clay: γDS decreased from 75 to 28 mJ/m2 for polycondensate catechol (PC) and from 75 to 30 mJ/m2 for polycondensate catechol triglycine (PCT), whereas γPS ranged from 35 to 16 mJ/m2 (PC) and from 35 to 17 mJ/m2 (PCT). Although their chemical compositions were different, both polymers similarly modified γDS and γPS. Increasing the amount of polymer adsorbed (from 1% to 3.5% by weight) affected mostly γPS, which became as low as 5 mJ/m2; meanwhile, γDS decreased from 30 to 23 mJ/m2. Possibly, the molecular orientation of the adsorbate changed in the process of dehydration. Following adsorption of synthetic humic acid-like polymers, dry Ca-montmorillonite complexes displayed γS values &lt; 50 mJ/m2, which were consistent with the solid-water contact angles measured in air.

Oxygen permeability and surface free energy properties of silicone-containing copolymers of methyl methacrylate

Novel organofunctional siloxanes from γ-methacryloxypropyltrimethoxysilane (MPTMS) were synthesized by transesterification reactions with high monohydric alcohols, branched alcohols, ether alcohols, phenol, and mandelic acid. The factors effecting the substitution ratios were determined. Copolymers of these siloxanes with methyl methacrylate (MMA) were prepared by bulk copolymerization in glass molds and their swelling, thermal, oxygen permeability, and surface free energy characteristics were investigated in order to determine the effect of the substituted group on the produced copolymer. The changes in these properties by the crosslinking of the copolymer with ethylene glycol dimethacrylate (EGDM) were also investigated. The copolymers containing branched, nonpolar, and lengthy pendant groups were found to be highly oxygen permeable possibly due to the introduction of larger free volume by these groups. The surface energy analysis showed that the main variation was found to be in γ values rather than γ values and only ether alcohol substitution increased γ values to a greater extent.

Oxygen transport and surface active properties of silicone containing copolymers of methyl methacrylate II

AbstractNew organofunctional siloxanes from γ‐methacryloxypropyltrimethoxysilane (MPTMS) were synthesized by transesterification of methoxy groups with linear high alcohols, ether alcohols, and α‐hydroxyacids. The factors affecting the substitution ratios were determined.These siloxanes were copolymerized with methyl methacrylate (MMA), crosslinked with ethylene glycol dimethacrylate (EGDM) in order to examine the effect of substituted groups to the oxygen permeability coefficient (Pd) and surface free energy properties of the resultant copolymers.The substitution of the oxygen containing polar groups decreased the oxygen permeability due to the interactions between polar groups decreasing the free volume. However, these groups increased the polar component of surface free energy (γ) and thus total surface free energy (γS). The hydrophilicity of the carbitol and 2‐ethoxyethanol containing siloxane‐MMA copolymers was found to be suitable for biomedical applications.