Free Energy Of Adhesion Research Articles

Surface chemical composition and roughness as factors affecting the wettability of thermo-mechanically modified oak (Quercus robur L.)

Abstract European oak wood (W) was thermo-mechanically modified (TM) via densifying at 100 and 150°C and the surface properties of the TMW were investigated. The contact angle (CA) of the wood with the reference liquids water and diiodomethane was determined using the sessile drop method. The surface free energy of the TMW on tangential sections within the first 60 s after applying a drop was analyzed. The roughness parameters Ra and Rz parallel (‖) and perpendicular (⊥) to the grain were investigated. The wettability analysis showed that densified wood had a higher CA and lower work of adhesion and surface free energy than non-densified wood. An X-ray photoelectron spectroscopy [XPS or electron spectroscopy for chemical analysis (ESCA)] analysis showed that the oxygen to carbon atoms ratio (O/C ratio) of densified wood surface was lower than that of non-densified wood. The carbon C1-C2 atoms ratio (C1/C2 ratio) increased with increasing TM temperature. The results were interpreted as being that extractives migrate to the surface and amorphous and glassy polymers, i.e. lignin and hemicelluloses, in wood are rearranged. Increasing densification temperature makes TMW surfaces more hydrophobic.

Effects of physical and chemical aspects on membrane fouling and cleaning using interfacial free energy analysis in forward osmosis.

Natural organic matter (NOM) in micro-polluted water purification using membranes is a critical issue to handle. Understanding the fouling mechanism in the forward osmosis (FO) process, particularly identifying the predominant factor that controls membrane fouling, could have significant effects on exerting the advantages of FO technique. Cellulose triacetate no-woven (CTA-NW) membrane is applied to experiments with a high removal efficiency (> 99%) for the model foulant. Tannic acid (TA) is used as a surrogate foulant for NOM in the membrane fouling process, thus enabling the analysis of the effects of physical and chemical aspects of water flux, retention, and adsorption. The membrane fouling behavior is affected mainly by the combined effects of the osmotic dragging force and the interaction of the pH in the working solution, foulants, and calcium ions, as demonstrated by the water flux loss and the changes of membrane retention and adsorption. The fouled CTA-NW membrane (in PRO mode) could be flux-recovered by > 85% through physical cleaning methods. The interfacial free energy analysis theory was used to analyze the membrane fouling behavior with calculating the interfacial cohesion and adhesion free energies. The cohesion free energy refers to the deposition of foulants (TA or TA combined with calcium ions) on a fouled membrane. In addition, the adhesion free energy could be used to evaluate the interaction between foulants and a clean membrane.

Physicochemical characterization of Pseudomonas aeruginosa isolated from catering substratum surface and investigation of their theoretical adhesion

The physicochemical properties of six Pseudomonas aeruginosa isolated from catering environment surface at a health establishment and of different types of substratum surfaces were investigated. These physicochemical properties were determined by contact angles measurements via sessile drop technique. The strains of Pseudomonas aeruginosa (P3, P14, and P18) were hydrophobic, the others were hydrophilic. The results show also that all strains were predominantly electron donors (γ−) and weakly electron acceptors (γ+). Three types of marble (yellow, white and black), four types of granite (Bleu-Pearl, Rosa-Porrino, Galaxy and Green-Pinhel), corian, stainless steel 304 and polypropylene were studied. Except yellow marble and granite (Green-Pinhel) that classified as hydrophilic surfaces, the others were hydrophobic. The finding shows that yellow marble and Green-Pinhel granite were predominantly electron donating (γ−) and other substratum surfaces were weakly electron donating. Except yellow marble which has a high electron acceptor, the others have a weak electron acceptor character. The free energy of adhesion between the bacteria and substratum surface was calculated and used in this study to predict the adhesion of Pseudomonas aeruginosa on the studied substratum surface. For all studied the substratum, except P18, the adhesion of all Pseudomonas aeruginosa is thermodynamically favorable only to polyethylene. Moreover P11 has the ability to adhere to all substratum surfaces.

Molecular dynamics analysis of the influence of Coulomb and van der Waals interactions on the work of adhesion at the solid-liquid interface

We investigated the solid-liquid work of adhesion of water on a model silica surface by molecular dynamics simulations, where a methodology previously developed to determine the work of adhesion through thermodynamic integration was extended to a system with long-range electrostatic interactions between solid and liquid. In agreement with previous studies, the work of adhesion increased when the magnitude of the surface polarity was increased. On the other hand, we found that when comparing two systems with and without solid-liquid electrostatic interactions, which were set to have approximately the same total solid-liquid interfacial energy, former had a significantly smaller work of adhesion and a broader distribution in the interfacial energies, which has not been previously reported in detail. This was explained by the entropy contribution to the adhesion free energy; i.e., the former with a broader energy distribution had a larger interfacial entropy than the latter. While the entropy contribution to the work of adhesion has already been known, as a work of adhesion itself is free energy, these results indicate that, contrary to common belief, wetting behavior such as the contact angle is not only governed by the interfacial energy but also significantly affected by the interfacial entropy. Finally, a new interpretation of interfacial entropy in the context of solid-liquid energy variance was offered, from which a fast way to qualitatively estimate the work of adhesion was also presented.

Design and mechanism of the formation of spherical KCl particles using cooling crystallization without additives

Potassium chloride crystals are cubic, which often leads to caking and greatly limits their applications. This caking can be overcome by modifying the crystal shape toward sphericity. Spherical particles have a high anti-caking ability and flowability. In this work, spherical KCl particles were prepared using a simple cooling crystallization process designed to function without additives. Among the four main processes in the crystallization of spherical particles, i.e., nucleation, growth, agglomeration, and attrition, agglomeration is the greatest contributor to the formation of spherical KCl particles, which were prepared following the principle that the adhesion force must be larger than the dispersion force. The adhesion free energy between KCl particles and solvents (i.e., water, n-hexane, formamide, diazomethane, methanol, ethanol, ethyl acetate, ethylene glycol, and dimethyl sulfoxide) was calculated using the Lifshitz–van der Waals acid–base approach, and water was found to be the most appropriate solvent because of its attractive interaction with the crystals. According to the relationship between the adhesion force and dispersion forces, we found that the stirring rate should be lower than 1300 rpm. Additionally, the effects of stirring rate and cooling rate on the KCl products were investigated and optimized, and the optimal conditions were found to be 400–500 rpm and 10–15 min/°C, respectively. All of the spherical KCl products prepared under the optimal conditions show a better morphology, flowability, and anti-caking performance than the original crystals.

Surface modification of glass fibers by oxidized plasma coatings to improve interfacial shear strength in GF/polyester composites

Plasma‐polymerized films (interlayers) of tetravinylsilane in mixture with oxygen gas (oxygen fraction 0‐0.71) were coated on glass fibers (GF) used as reinforcements in GF/polyester composite. Oxygen atoms of increased concentration (0‐18 at.%) were partly incorporated into the plasma polymer network, forming SiOC/COC bonding species and partly forming side polar (hydroxyl, carbonyl) groups with enhanced oxygen fraction. The amount of oxygen in plasma coatings influenced the Young's modulus, interfacial adhesion, and surface free energy of the interlayer. To determine the interfacial shear strength, a microindentation test was implemented for individual glass fibers on a cross‐section of GF/polyester composite. The interfacial shear strength for oxidized plasma coatings was up to 21% higher than that for the non‐oxidized interlayer, indicating a direct chemical effect of oxygen atoms on interphase properties. The interphase shear failure was controlled by the shear strength at the interlayer/fiber interface as follows from experimental and model data. POLYM. COMPOS., 40:E186–E193, 2019. © 2017 Society of Plastics Engineers

Investigating the Use of Nano Coating Over the Aggregate Surface on Moisture Damage of Asphalt Mixtures

One of the methods to improve adhesion between asphalt binder and aggregate and to reduce moisture susceptibility in asphalt mixtures is aggregate treatment using suitable coats which cause to change aggregate polarity. In this study, effect of nanomaterial coating on aggregate over moisture damage of HMA by means of thermodynamic and mechanical methods has been probed. Aggregates used in this study are granite and limestone that have been modified using iron oxide and aluminum oxide nanoparticles. Results illustrate that in comparing modified samples through nanoparticles with control samples, tensile strength ratio on moisture condition surpasses dry condition. Surface free energy result shows that aggregate coat with nanoparticles leads to decrease in differences between free energy of adhesion in moisture condition and dry condition, and thus, stripping event is diminished. Nanoparticles’ positive performance of iron oxide compared with aluminum oxide nanoparticles in decreasing the moisture sensitivity of asphalt mixtures built is more evident about either kind of aggregates.

Catechol-cation adhesion on silica surfaces: molecular dynamics simulations.

Understanding the interaction mechanism between catechol-cation and inorganic surfaces is vital for controlling the interfacial adhesion behavior. In this work, molecular dynamics simulations are employed to study the adhesion of siderophore analogues (Tren-Lys-Cam, Tren-Arg-Cam and Tren-His-Cam) on silica surfaces with different degrees of ionization and the effects of cationic amino acids and ionic strength on adhesion are discussed. Simulation results indicate that adhesion of catechol-cation onto the ionized silica surface is dominated by electrostatic interactions. At different degrees of ionization, the rank of the adhesions of three siderophore analogues on silica is different. Further analysis shows that the amino acid terminus has a large influence on the adhesion process, especially histidine adhesion on negatively charged surfaces. Tren-Lys-Cam (TLC) has a larger adhesion free energy than Tren-Arg-Cam (TAC) at a higher degree of ionization (18%); both the bulkier structure and delocalized charge of Arg decreased the cation's electrostatic interaction with the charged silica. In addition, the adhesion free energy on ionized silica surfaces decreased with increasing ionic strength of aqueous solutions. A linear correlation between the potential of mean force obtained from umbrella sampling and the rupture force via steered molecular dynamics simulations for siderophore analogue adhesion on silica surfaces is also found. This work may provide some guidance for developing the next generation underwater adhesives.

New garment proposal for prevention of spreading Gram-negative bacteria resistant to carbapenem antibiotic class under hospital settings

Sensitive skin diseases, including atopic dermatitis, skin inflammation and bedsores, leave patients vulnerable under hospital setting. It is important for the development of a hospital gown with “soft hand” properties and at the same time as a protector against nosocomial infections. Klebsiella pneumoniae has developed resistance to antibiotics in the carbapenem antibiotic class, known as carbapenem-resistant K. pneumoniae (CRKP). CRKP is resistant to nearly all antibiotics and can kill up to 50% of infected patients. This work consisted in the development of a washable recycled silk fibroin-based gown covalently linked with an amino acid l-Cysteine(l-Cys), focused on prevention of K. pneumoniae establishment, proliferation and spreading to community, for use under hospital settings. With the growing problem of resistance to antibiotics and few new therapies on the horizon, gowns adsorbed with L-Cys show to function as a barrier to the establishment and proliferation of microorganisms, providing user protection from infectious disease. This gown was knitted at a rectilinear needle loom with a Jersey knit structure. Then it was cross-linked with l-Cys, subjected to laundry, and subsequently characterized by energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, contact angle, free energy of adhesion, scanning electron microscopy and transmission electron microscopy. Results presented a bactericidal effect against K. pneumoniae of 94.92% after three rinses and 88.88% after five washing cycles, with the few adhered bacteria with an altered and compromised morphology.

Energy of Liposome Patch Adhesion to the Pipet Glass Determined by Confocal Fluorescence Microscopy.

The formation of the gigaseal in the patch clamp technique is dependent on the adhesion between the cell or liposome membrane and the glass pipet. The adhesion results in a capillary force causing creep of the patch membrane up the pipet. The membrane can be immobilized by counteracting the capillary force by positive pressure applied to the patch pipet. We use this phenomenon to develop a method for static measurement of the adhesion free energy of the lipid bilayer to the glass. Confocal fluorescent microscopy is used to track the bilayer creep inside the pipet and measure the immobilization pressure at various salt concentrations and pH. The adhesion energy is simply related to this pressure. For the studied phospholipid bilayers, its values were in the 0.3-0.7 mJ/m2 range, increased with salt concentration, and had a maximum as a function of pH. This method offers a way to measure bilayer-glass adhesion energy in patch clamp experiments that is more precise than dynamic methods.

Interfacial properties and electron structure of Al/B4C interface: A first-principles study

This research aims at investigating the structural, mechanical and electronic properties of the Al (111)/B4C (0001) interface by first-principles calculations. This model geometry Al (111)/B4C (0001) is chosen because the close-packed planes of Al and B4C have the (111) and (0001) orientation, respectively, and the lattice mismatch is only ∼2.1%. Among four B4C (0001) surfaces with different terminations, our calculation of surface free energies predicted that C-terminated B4C (0001) surface is the most stable one. Relaxed atomic geometries, the work of adhesion and interfacial free energies were calculated for three C-terminated B4C (0001)/Al (111) interfaces with different stacking sequences (top-site, hollow-site, and bridge-site). Results reveal that the relaxed top-site (hollow-site-like) Al/B4C interface has the best adhesion force and also be the most stable. The interfacial electron structure including charge density difference, Bader charge and density of states (DOS) is analyzed to determine the nature of metal/carbide bonding and we find the formation of AlC bond and possibly the formation of Al4C3 in the interface.

Mechanism and inhibition of trisodium phosphate particle caking: Effect of particle shape and solubility

We investigated the influence of particle shape and solubility on the caking behavior of trisodium phosphate by considering the adhesion free energy and crystal bridge theory. Caking of trisodium phosphate during the drying process under static conditions is a two-step process: adhesion followed by crystal bridge formation between particles. The adhesion free energy plays an important role in adhesion. Trisodium phosphate particles cannot adhere to each other and cake when the adhesion free energy is greater than a critical value, which varies with particle shape. Compared with granular particles, cylindrical particles have larger contact area between particles, which results in more crystal bridges forming and a higher caking ratio. Thus, the critical value is about 100mJ/m2 for cylindrical particles, but 60mJ/m2 for granular particles at 25°C. Concerning the solubility, when particles are similar shapes and soluble in the rinsing liquid, the caking ratio has a linear relationship with adhesion free energy. However, if the particles are insoluble in the rinsing liquid, caking can be completely prevented regardless of adhesion free energy because no crystal bridges form during the growth process. Hence, caking of trisodium phosphate particles could be inhibited by screening rinsing liquids, and optimizing the particle shape and size distribution.

Use of aggregate nanocoating to decrease moisture damage of hot mix asphalt

In this research, the effect of using nanocoating on the surface of aggregates on moisture damage of the hot mix asphalt has been studied with thermodynamic and mechanical methods. Aggregates used in this research are granite and limestone which have been modified with nano calcium carbonate (CaCO3) and nano zinc oxide (ZnO). The obtained results in this research show that tensile strength ratio of samples made with modified aggregate has improved in comparison to the control samples. Results of surface free energy indicate that coating of aggregates with nanoparticles reduces the difference between the free energy of adhesion in wet and dry conditions which reduces the stripping tendency of asphalt mixtures. Also, coating of the aggregates with nanoparticles caused better wettability of the aggregates’ surface by asphalt binder. The aggregates treated with nano CaCO3 showed better resistance against moisture damage in both the methods that were used in this study.

Interfacial bonding of fine aggregate concrete to low modulus fibers

The present work describes the feasibility of using cost effective and low modulus polymeric fibers including Nylon 6,6 and Acrylic fibers as reinforcement of fine aggregate cementitious composites. For this purpose, the pullout energy and interfacial bonding strength of fibers to the different matrix compositions where evaluated using a pullout test. Surface free energy of the fibers and different fine aggregate composites were also evaluated using the sessile drop method. Fiber to cement bonding strength, thermodynamic work of adhesion and surface free energy (wetting affinity) were assessed by changing maximum aggregate size, water to cement (binder) ratio, using fly ash as supplementary cementing materials (SCMs) and fiber type. Both chemical and mechanical interfacial interactions were measured and it was found that the Nylon 6,6 fiber showed highest pullout energy and flexural toughness due to more mechanical interlocking to the matrix.

Hydraulic irreversibility of ultrafiltration membrane fouling by humic acid: Effects of membrane properties and backwash water composition

Five commercially available ultrafiltration (UF) membranes: polyethersulfone (PES, 100kDa), polyvinylidene fluoride (PVDF, 100kDa) and cellulose acetate (CA, 100, 30 and 10kDa), were fouled with humic acid (HA) solutions and cleaned using various compositions of backwash water including ultrapure water, monovalent cations (Na+), divalent cations (Ca2+), an organic compound (HA) and UF permeate. The hydraulically irreversible fouling and the hydraulic cleaning efficiency (HCE) for each combination of membrane and backwash water composition were analyzed. In summary, both the membrane properties and the backwash water composition affected hydraulically irreversible fouling. The membrane properties significantly affected the total fouling, and the HCE was primarily affected by the backwash water composition. Further, the adhesive free energy between HA and the membranes correlated well with the total fouling. Ultrapure water was superior to UF permeate for backwashing, and the presence of appropriate components (e.g., Na+ or HA) further improved the HCE; however, Ca2+ exerted detrimental impacts on the HCE. In addition, the removal of the deposited HA was consistent with the amount of Ca2+ released from the fouling layer during backwashing. Mechanistic analysis suggested that the backwashing process involves fouling layer swelling, ion exchange, electric double layer release and competitive complexation.

Caking and adhesion free energy of maltitol: Studying of mechanism in adhesion process

Caking is a common phenomenon of maltitol that causes problems of separation, processing and transportation. To study the mechanism of caking, method of capillary rise was used to measure the contact angles between maltitol particles and relevant liquids. Based on the calculation of adhesion free energy of maltitol particles in different liquids by Lifshitz–van der Waals acid-base theory, the relationship between adhesion free energy and the maltitol particles size has been established. It is concluded that the adhesion free energy of maltitol with rinsing liquid plays a key role in caking. When the adhesion free energy is higher than a critical value (about 60mJ/m2), the repulsion between the particles can avoid caking. In general, the adhesion free energy depends on the rinsing liquid used and maltitol particles size. The adhesion free energy increases with increasing the particles size of maltitol and type of liquids (water, ethyl acetate, formamide, ethylene glycol, ethanol, methanol in sequence). Hence, controlling particles size distribution and screening of rinsing liquid are crucial factors to avoid caking.

Effects of Regular-Sized and Nanosized Hydrated Lime on Binder Rheology and Surface Free Energy of Adhesion of Foamed Warm Mix Asphalt

Although foamed warm mix asphalt (WMA) offers many potential benefits, there are some performance concerns. Researchers are making efforts to study the usage of different additives as modifiers to meet standard specifications of asphalt mixes for paving applications; however, selection of an appropriate modifier is extremely important to better performing asphalt. In recent years, there has been a dramatic interest in research, technology, and production of nanoparticles (nanomaterials). The current study was conducted with the objective of addressing the potential benefits of using nanosized hydrated lime (NHL) compared with regular-sized hydrated lime (RHL) as a modifier to the WMA produced using an additive. This paper documents the findings of the effect of NHL and RHL on the asphalt binder rheology and provides an insight into their effect on the free energy of adhesion of the asphalt binder-aggregate system. The rheology of asphalt binder was investigated based on the dynamic shear rheometer (DSR) test, whereas the free energy of adhesion was quantified based on the surface free energy (SFE) measurements of the asphalt binders and aggregate. Rheology results showed that the addition of NHL in smaller amounts can provide improved characteristics as compared with RHL. In concurrence with the rheology results, the free energy of adhesion showed that the NHL is more competitive compared with the RHL. Foaming the asphalt binder adversely affects the asphalt binder-to-aggregate adhesion.

Characterizing dissolved organic matter fouling of nanofiltration membranes and evaluating effects of naproxen retention

Nanofiltration (NF) membrane fouling caused by two types of natural dissolved organic matter (DOM), namely Qingcaosha reservoir (QCS) DOM and Taihu Lake (TH) DOM, on naproxen (NPX) retention, were assessed. The results indicated that NPX retention could be interpreted with respect to the DOM molecular weights (MW) and the fouling characteristics. Organics with medium- and low-MW, e.g. less than 10 kDa, significantly affected NPX retention and resulted in membrane fouling. DOMs with medium MW (1.5–10 kDa) mainly had strong hydrophobic characteristics, and adhered well to the NF membrane surface to form a fouling layer, which altered the hydrophobicity and negative charge of the membrane surface. The hydrophobicity and electronegativity of the adhered DOM fouling layer was responsible for the decreased membrane flux and the change in NPX retention. TH DOM contained more hydrophobic organics with MW 1.5–10 kDa than QCS DOM, and the cohesion free energy and adhesion free energy between the membrane and foulants were more negative for TH DOM, which caused more severe membrane fouling. The surface free energy between membranes and foulants is a useful parameter for membrane fouling analysis, and a mechanism of influencing NPX retention in the presence of DOM was proposed. The increased NPX removal by QCS DOM-fouled membrane was mainly attributed to electrostatic repulsion, whereas the decreased NPX rejection by TH DOM-fouled membrane was mainly attributed to cake-enhanced concentration polarization.

The effects of leaf roughness, surface free energy and work of adhesion on leaf water drop adhesion.

The adhesion of water droplets to leaves is important in controlling rainfall interception, and affects a variety of hydrological processes. Leaf water drop adhesion (hereinafter, adhesion) depends not only on droplet formulation and parameters but also on the physical (leaf roughness) and physico-chemical (surface free energy, its components, and work-of-adhesion) properties of the leaf surface. We selected 60 plant species from Shaanxi Province, NW China, as experimental materials with the goal of gaining insight into leaf physical and physico-chemical properties in relation to the adhesion of water droplets on leaves. Adhesion covered a wide range of area, from 4.09 to 88.87 g/m2 on adaxial surfaces and 0.72 to 93.35 g/m2 on abaxial surfaces. Distinct patterns of adhesion were observed among species, between adaxial and abaxial surfaces, and between leaves with wax films and wax crystals. Adhesion decreased as leaf roughness increased (r = −0.615, p = 0.000), but there were some outliers, such as Salix psammophila and Populus simonii with low roughness and low adhesion, and the abaxial surface of Hyoscyamus pusillus and the adaxial surface of Vitex negundo with high roughness and high adhesion. Meanwhile, adhesion was positively correlated with surface free energy (r = 0.535, p = 0.000), its dispersive component (r = 0.526, p = 0.000), and work of adhesion for water (r = 0.698, p = 0.000). However, a significant power correlation was observed between adhesion and the polar component of surface free energy (p = 0.000). These results indicated that leaf roughness, surface free energy, its components, and work-of-adhesion for water played important roles in hydrological characteristics, especially work-of-adhesion for water.

Fouling effects of algogenic organic matters during nanofiltration of naproxen

This work investigated the effects of two types of algogenic organic matter (AOM), namely Anabaena AOM and Chlorella AOM, on the removal of naproxen using three different nanofiltration (NF) membranes. The effects of AOM membrane fouling on the rejection of naproxen were interpreted with respect to the AOM molecular weights (MW) and the fouling characteristics. Organics with medium and low molecular weights, e.g., less than the 10kDa of the Anabaena AOM and Chlorella AOM, significantly affected the naproxen removal and resulting membrane fouling. Anabaena AOM and Chlorella AOM with large and medium MW (>1.5kDa) adhered well to the NF membranes to form a fouling layer, which enhanced the hydrophobicity and negative charge of the membrane surface. The hydrophobicity and electronegativity of the adhered AOM fouling layer was responsible for the decreased membrane flux and the increased naproxen removal. During the filtration process, AOMs with low MW could enter the membrane pores, which also affected the naproxen removal and resultant membrane fouling. Anabaena AOM contained more hydrophobic organics than Chlorella AOM, whose cohesion free energy and adhesion free energy between the membrane and foulants were more negative and caused more severe membrane fouling and a higher naproxen removal effect, or, more specifically, the degree of membrane flux declined from 7.0% to 18.8% and naproxen retention increased from 7.3% to 15.1% in the presence of Anabaena AOM, while which from 3.0% to 15.4% and from 3.9% to 12.3% in the presence of Chlorella AOM, respectively. The surface free energies of the membranes and foulants is a useful parameter for membrane fouling analysis, and a mechanism for the enhanced naproxen removal in the presence of AOM was also proposed.