Properties Of Adsorbed Layers Research Articles

Adsorption Layer Properties and Foam Behavior of Aqueous Solutions of Whey Protein Isolate (WPI) Modified by Vacuum Cold Plasma (VCP)

For years, cold plasma processing has been used as a non-thermal technology in industries such as food. As interfacial properties of protein play a remarkable role in many processes, this study investigates the effect of cold plasma on the foaming and interfacial behavior of WPI. The objective of this study is to evaluate the effect of different gases (air, 1:1 argon–air mixture, and sulfur hexafluoride (SF6)) used in low-pressure cold plasma (VCP) treatments of whey protein isolate (WPI) on the surface and foaming behavior of aqueous WPI solutions. Dynamic surface dilational elasticity, surface tension isotherms, surface layer thickness, and the foamability and foam stability were investigated in this study. VCP treatment did not significantly affect the adsorption layer thickness. However, an increase in induction time, surface pressure equilibrium value, and aggregated size is observed after SF6VCP treatment, which can be attributed to the reaction of WPI with the reactive SF6 species of the cold plasma. The surface dilational elastic modulus increased after VCP treatment, which can be related to the increased mechanical strength of the protein layer via sulfonation and aggregate formation. VCP treatment of WPI increases the foam stability, while the average diameter of foam bubbles and liquid drainage in the foam depends on the gas used for the cold plasma.

Effect of NaCl concentration on the formation of high internal phase emulsion based on whey protein isolate microgel particles

At present, the effect of structural modification of microgel particles on high internal phase emulsions (HIPEs) is less studied. In this study, the structural modification effect of NaCl on whey protein isolate microgels (WPIMPs) was comprehensively characterized and applied to the construction of HIPEs. WPIMPs were prepared with NaCl (0–150 mM) and the structural changes were analyzed by measuring the particle size, Zeta-potential, and endogenous fluorescence spectra. The results showed that inducing WPIMPs by NaCl enhanced the surface hydrophobicity, decreased the Zeta potential, and elevated the degree of cross-linking. The interfacial behavior of WPIMPs was characterized by measuring interfacial tensions and adsorbed layer properties. The results showed that NaCl induction decreased the interfacial tension, increased the thickness of the adsorbed layer, and improved the viscoelasticity. The HIPEs were analyzed for micromorphology and particle sizes. The results indicated that NaCl-induced WPIMPs favored the formation of HIPEs with small particle sizes and provided HIPEs with superior environmental stability. This study provides a new idea for the structural modification of microgels and a new theoretical basis for the construction conditions of HIPE.

Insights into adsorption and diffusion behavior of shale oil in slit nanopores: A molecular dynamics simulation study

Nanoscale pores have been widely observed in shale plays. Within such a small scale pore, the interaction between fluid molecules and porewall surface becomes significant, and the adsorption state of shale fluids is quite different from that in conventional reservoirs. In this study, the method of molecular dynamics (MD) simulation is applied to address the adsorption and diffusion behavior of shale oil in slit nanopores. Firstly, two different models of organic graphene nanopore and inorganic quartz nanopore are constructed, and three typical components of alkanes (methane, propane, and n-octane) are selected to represent the shale oil fluids. Based on this model, the effects of fluid composition, nanopore type and porewall wettability on the adsorption and diffusion behavior of shale fluids are discussed. For the simulation method of hydrophilic porewall surface, in this study, a series of carbonyl functional group is grafted on graphene surface to enhance the hydrophilicity of porewall surface. Results indicate that the multicomponent alkanes in nanoscale pores can form a multilayer adsorption state. The heavy components will occupy the adsorption sites around the porewall surface. In contrast, the adsorbed amount of light components at porewall surface can be almost negligible. However, as the effect of multicomponent fluid is considered, a significant difference for the properties of adsorption layer and the mean square displacement (MSD) value can be observed compared with that of the pure component fluids. Similarly, shale fluids can also show a multilayer adsorption behavior of heavy components at the quartz nanopore wall surface, but the amount of adsorption is lower. Comparing the peak density of the first adsorption layer in organic matter pores with that in quartz nanopore, the former shows 1.87 times more than the latter for ternary mixture (C1-C3-C8). Furthermore, it can be also observed that the adsorption capacity of fluid in the nanopores with different wettabilities differs. As the O/C ratio in organic matter wall is above 15%, the peak density of adsorption layer is significantly increased with the carbonyl proportion increases. But this changing tendency is decreased as the O/C ratio reaches above 50.46%. Furthermore, from the simulation results, it is observed that with the carbonyl proportion increases, the fluid self-diffusion coefficient is gradually reduced. It indicates that the effect of rock wettability on the fluid diffusion behavior. This study can provide an important data support to understand the adsorption and diffusion behavior of shale oil in nanopores, which is important for the effective and efficient development of shale oil reservoirs.

Impact of Amphiphilic Nanostructures on Formation and Rheology of Interfacial Layers and on Foam Film Drainage

The aim of the present studies is to clarify how the surfactant adsorption layer properties are related to the course of the drainage parameters of microscopic foam films in the special case of aqueous solutions containing premicellar amphiphilic nanostructures. The scope of the research covers the adsorption dynamics, construction of equilibrium adsorption isotherms, surface rheology of interfacial layers, and foam film drainage kinetics. It is established that, in the premicellar domain, there are concentration intervals, where the considerable irregularities of adsorption layerproperties are observed: several plateau regions in the surface tension isotherms, unusual changes of the surface rheological characteristics, etc. The systematic investigation of the drainage of foam films obtained from these solutions show that the dependences of basic kinetic parameters of the films on the amphiphile concentration run in synchrony with changes in the adsorption layer properties. Thus, the presence of smaller loose aggregates (premicelles) plays a significant role for the kinetic stability of films. The importance of this research is related toproviding a better insight into the initial stages of self-assembling phenomena and into the factors determining thedrainage and the stability of thin liquid films. The results have implications for the understanding and the correct prediction of properties of foam systems.

Triallyl ammonium amphiphiles: self-assembly and complexation with bovine serum albumin

Currently, the investigation on the interaction of cationic surfactants with proteins attract the wide attention of researchers. Proteins participate in the majority of important biological processes; therefore, they are essential for a living organism. The addition of proteins to a surfactant solution can significantly modify the adsorption layer properties at liquid/fluid interfaces. In turn, surfactants can markedly affect the conformational behaviour of proteins. Therefore, in this study, the cationic amphiphiles triallyldodecylammonium bromide and triallyltetradecylammonium bromide have been synthesised. Their aggregation behaviour in an aqueous solution, solubilisation capacity towards the hydrophobic azo dye and complexation with bovine serum albumin (BSA) were evaluated. The lower homologue has demonstrated an unusual two-step aggregation behaviour, controlled morphology aggregates and various solubilisation capacities for Orange OT. The increase in the length of the hydrocarbon tail from dodecyl to tetradecyl has resulted in the disappearance of the second critical point and the enlargement of the particle size. Both of the amphiphiles that were investigated effectively interacted with BSA and were bound to the tryptophan amino acid residue of the protein. For surfactants/BSA systems, it was shown that by varying the length of the hydrophobic tail, the dominance of the various types of interactions can be achieved.

Kinetics and Thermodynamics of Hemicellulose Adsorption onto Nanofibril Cellulose Surfaces by QCM-D.

The adsorption of hemicellulose derived from bagasse onto nanofibril cellulose has been studied in terms of kinetics and thermodynamics. In situ monitoring of bagasse hemicellulose with different molecular weights onto the nanofibril cellulose surfaces has been investigated using quartz crystal microbalance and dissipation. Then, the adsorption kinetics and thermodynamic properties were analyzed. Also, the sorption behavior and the adsorption layer properties were quantified in aqueous solutions. The maximum adsorption mass was 2.8314 mg/m2 at a concentration of 200 mg/L. Also, compared with that of the low-molecular-weight hemicellulose, the adsorption capacity of the high-molecular-weight hemicellulose was higher, and the adsorption rate changed faster and could reach an equilibrium in a shorter time. The intraparticle diffusion kinetic model represented the experimental data very well. Therefore, the kinetics of hemicellulose on the fiber adsorption was commonly described by a three-stage process: mass to transfer, diffusion, and equilibrium. The Gibbs energy change of the adsorption of hemicellulose was found to range from −20.04 to −49.75 kJ/mol at 25 °C. The entropy change was >0. It was found that the adsorption was spontaneous, and the adsorbed mass increased with the increase in temperature. This strengthened the conclusion that the adsorption process of the bagasse hemicellulose on the NFC was driven by the increase in entropy caused by the release of water molecules due to hydrophobic interaction or solvent reorganization.

A Multistate Adsorption Model for the Adsorption of C14EO4 and C14EO8 at the Solution/Air Interface

The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (CnEOm) can be well described by the reorientation model. In its classical version, it assumes two adsorption states; however, there are obviously surfactants that can adsorb in more than two possible conformations. The experimental data for C14EO4 and C14EO8 (dynamic and equilibrium surface tensions and surface dilational visco-elasticity as measured by bubble profile analysis tensiometry) are used to verify if a reorientation model with more than two possible adsorption states can better describe the complete set data of CnEOm adsorption layers at the water/air interface. The proposed refined theoretical model allows s different states of the adsorbing molecules at the interface. The comparison between the model and experiment demonstrates that, for C14EO4, the assumption of s = 5 adsorption states provides a much better agreement than for s = 2, while for C14EO8, a number of s = 10 adsorption states allows an optimum data description.

Impact of Adsorption Layer Properties on Drainage Behavior of Microscopic Foam Films: The Case of Cationic/Nonionic Surfactant Mixtures

Aqueous mixtures of cationic hexadecyltrimethylammonium chloride (CTAC) and nonionic pentaethyleneglycol monododecyl ether (C12E5) are investigated. Adsorption layer properties are systematically studied within a wide concentration range for a 1:1 molar ratio of the surfactants. Surface tension and dilatational rheology measurements are conducted by profile analysis tensiometry. The interfacial data are juxtaposed to drainage kinetics and stability results for microscopic foam films, investigated by microinterferometric thin liquid film instrumentation. The obtained results give experimental evidence of synergistic interactions in the studied solutions, as compared to the corresponding single surfactant systems. Specific runs of dynamic and equilibrium surface tension curves are registered against the total surfactant quantity; the surface dilatational elasticities for the mixtures are systematically higher. A clear correlation is established between adsorption layer performance and foam film characteristics. The maxima of the film lifetimes are well outlined, and the respective values are shifted towards lower overall concentrations. The reported results substantiate the key role of the adsorption layers, and the surface dilatational properties in particular, for foam film drainage kinetics and stability. The well-expressed synergy observed in adsorption layer and foam film properties suggests the substantial benefits of using mixed surfactant systems in the design and fine-tuning of foam systems for innovative applications.

Dynamic properties of adsorption layers of pulmonary surfactants. Influence of matter exchange with bulk phase

The dynamic surface properties of solutions of pulmonary surfactant (PS) were investigated at various temperatures and in a broad range of surface tensions. The efficient dynamic surface elasticity was determined for the first time in case when the characteristic adsorption time is comparable with the period of surface area oscillations. The mechanical relaxation in the PS adsorption layer is accelerated strongly not only in the course of compression, but also in the course of expansion due to the formation of a sublayer. The harmonic oscillations of the surface area induce stationary oscillations of the surface tension if the characteristic adsorption time does not exceed the oscillation period and the sublayer formation is sufficiently fast. The information on the dynamic properties of the PS adsorption layer allows estimation of the PS efficiency in medical applications.

Viscoelastic characterization of the crosslinking of β-lactoglobulin on emulsion drops via microcapsule compression and interfacial dilational and shear rheology

HypothesisInterfacial rheology provides insight into the mechanical properties of adsorption layers on liquid–liquid interfaces, which mediates the stability of emulsion droplets. The use of capsule compression at the scale of an emulsion droplet to probe the interfacial rheology may open up the possibility of testing the interfacial rheological properties of droplets with complex histories and extremely small volumes found in many applications. ExperimentsThe time dependent interfacial rheological behavior of β-lactoglobulin adsorption layers on an oil/water interface in the native and crosslinked state was extracted using small oscillatory indentation with atomic force microscopy (AFM). The results of this novel model and experimental approach were compared to the well-established techniques of interfacial shear rheology (ISR) and dilational pendant drop tensiometry that were performed on analogous interfaces. FindingsThe tan δ measured between the ISR and AFM measurements provide similar results in an overlapping frequency range, but the viscoelastic moduli G’ and G’’ differ by several orders of magnitude. This is most likely the result of the different flow fields and the low deformation of the AFM measurements compared to dilational and shear flow fields.

β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 4. Impact on the Stability of Foam Films and Foams

The complexity and high sensitivity of proteins to environmental factors give rise to a multitude of variables, which affect the stabilization mechanisms in protein foams. Interfacial and foaming properties of proteins have been widely studied, but the reported unique effect of pH, which can be of great interest to applications, has been investigated to a lesser extent. In this paper, we focus on the impact of pH on the stability of black foam films and corresponding foams obtained from solutions of a model globular protein—the whey β-lactoglobulin (BLG). Foam stability was analyzed utilizing three characteristic parameters (deviation time, transition time and half-lifetime) for monitoring the foam decay, while foam film stability was measured in terms of the critical disjoining pressure of film rupture. We attempt to explain correlations between the macroscopic properties of a foam system and those of its major building blocks (foam films and interfaces), and thus, to identify structure-property relationships in foam. Good correlations were found between the stabilities of black foam films and foams, while relations to the properties of adsorption layers appeared to be intricate. That is because pH-dependent interfacial properties of proteins usually exhibit an extremum around the isoelectric point (pI), but the stability of BLG foam films increases with increasing pH (3–7), which is well reflected in the foam stability. We discuss the possible reasons behind these intriguingly different behaviors on the basis of pH-induced changes in the molecular properties of BLG, which seem to be determining the mechanism of film rupture at the critical disjoining pressure.

SuSMoST: Surface Science Modeling and Simulation Toolkit.

We present to the scientific community the Surface Science Modeling and Simulation Toolkit (SuSMoST), which includes a number of utilities and implementations of statistical physics algorithms and models. With SuSMoST it is possible to predict or explain the structure and thermodynamic properties of adsorption layers. SuSMoST automatically builds formal graph and tensor-network models based on atomic description of adsorption complexes and helps to do ab initio calculations of interactions between adsorbed species. Using methods of various nature SuSMoST generates representative samples of adsorption layers and computes its thermodynamic quantities such as mean energy, coverage, density, and heat capacity. From these data one can plot phase diagrams of adsorption systems, assess thermal stability of self-assembled structures, simulate thermal desorption spectra, and so forth.

Studies on interfacial interactions between petroleum sulfonate and sulfobetaine molecules by rheological measurements

The dilational rheological properties of aqueous solutions of anionic surfactant petroleum sulfonate (KPS), zwitterionic surfactant alkyl sulfobetaine (ASB) and their mixtures have been investigated at the kerosene-water interface by the oscillating drop method. The influences of time, dilational frequency, bulk concentration and interfacial pressure on the dilational properties have been expounded. The experimental results show that the nature of film containing anionic surfactant KPS molecules is determined by the diffusion-exchange process between the bulk and the interface. On the other hand, the in-film process, such as the orientation change of hydrophilic groups, controls the properties of adsorption layers formed by betaine ASB molecules. The dilational rheological behaviors of KPS-ASB mixtures are close to those of ASB. In addition, the complex system gets the largest dilational modulus at higher bulk concentration, due to a synergistic effect between KPS and ASB caused by electrostatic attraction. The mixed adsorption of KPS and ASB may lead to more compact films and result in higher interfacial dilational modulus at optimum ratio of adsorbed KPS to ASB molecules. The mixed adsorption of KPS and ASB molecules may lead to more compact film and result in larger interfacial dilational elasticity at higher concentration.

Physical and Mechanical Properties of Asphalt Concrete Modified with Activated Mineral Powders

The study of the properties of asphalt concrete modified with activated mineral powders is described. Mineral powders were exposed to physicochemical activation by the joint grinding of limestone with oil sludge in a ball mill in order to produce asphalt concrete samples. Modification of mineral powder grains surface can improve adsorption layer properties. This leads to sharp increase in the adhesion between bitumen and mineral powder grains. Activated mineral powders are characterized by lower porosity, bitumen capacity and swelling. Water resistance of such samples is higher than that of non-activated powders. It has been determined that production of asphalt concrete with activated mineral powders requires 57% less bitumen than production of control samples. At the same time, the physicomechanical properties of asphalt concrete samples fully satisfy the requirements of regulatory documents.

Correction to "Equilibrium Contact Angle and Adsorption Layer Properties with Surfactants".

The last line in eq 27 on page 7213 should read (Formula Presented) In the caption for Figure 2a on page 7213 it should read (a) In the macroscopic approach, the equilibrium contact angle is determined by the solid-liquid interfacial tension γsl and the liquid-gas and solid-gas interfacial tensions γ and γ sg that depend on the respective surfactant concentrations Gd and Ga on the droplet and the adsorption layer. (Formula Presented).

Influence of hydrophilic silica nanoparticles on the adsorption layer properties of non-ionic surfactants at water/heptane interface

There is a notable paucity of studies investigating the impact of charged nanoparticles on the interfacial behavior of nonionic surfactants, assuming that the interactions are negligible in the absence of electrostatic forces. Here, we argue about our observations and the existence of a complex interfacial behavior in such systems depending on the type and chemical structure of surfactant. This study set out to investigate the effects of interactions between hydrophilic silica nanoparticles (NP) and non-ionic surfactants on water/heptane dynamic interfacial properties using drop profile analysis tensiometry (PAT). Three surfactants were studied, namely Triton X-100 (significantly soluble in water phase), C12DMPO (well soluble in both phases) and SPAN 80 (oil-soluble). The different chemical structures and partition coefficients of the surfactants enabled us to cover possible interactions and differentiate between bulk and interfacial interactions. We observed that hydrophilic silica NPs had a negligible effect on the interfacial behavior of Triton X-100, that they increased the surface activity of C12DMPO when both compounds are initially in the aqueous phase. Most interestingly is that the added NPs generated unstable interfacial NP-surfactant complexes and reduced the pseudo-equilibrium interfacial tension of oil-soluble surfactant, Span 80, even though NPs and surfactants were in different bulk phases.

Dynamic properties of adsorption layers of heptadecafluoro-1-nonanol. Effect of surface phase transitions

The dilational surface rheology was applied to study the properties of adsorbed layers of a fluorinated surfactant (heptadecafluoro-1-nonanol) with a surface phase transition at the water – air interface. At relatively low surface tensions (<~57 mN/m) the dynamic surface elasticity reached anomalously high values (~200 mN/m) and exhibited a local minimum at higher surface tensions in the region of a two-dimensional phase transition. A mathematical model was developed to describe dilational properties of the adsorbed layer in the region of coexistence of two surface phases. The application of this model to solutions of the fluorinated surfactant allowed estimation of the kinetic parameters of the relaxation processes in the surface layer.

Adsorption phenomena in systems containing complexes of cucurbit[7]uril with organic compounds

The aim of this study is to consider the adsorption phenomena at the electrode/solution interface in systems containing complexes of cucurbit[7]uril (CB7) with organic compounds: adamantanol‑1, ferrocene and organic dye 3,3′‑diethylthiocarbocyanine iodide. These guests form exclusively stable inclusive complexes with CB7. Experimental dependences of differential capacitance C as a function of potential were used in calculating the adsorption parameters characterizing the most important properties of adsorption layers formed by compounds under study at the electrode/solution interface. For all the systems studied here, as for those studied earlier, adsorption parameters for negative and positive charges of the electrode surface differ. Obviously this points to deep changes in the properties of adsorption layers depending on the electrode potential.

Interfacial dilational rheology of fatty acid methyl ester and alkyl benzene sulfonate mixed solutions

The dilational rheological properties of aqueous solutions of anionic surfactant sodium 3,4-diheptylbenzene sulfonate (C7C7phS), nonionic surfactant oxyethylated fatty acid methyl esters (C18=E10) and their mixtures have been investigated at the kerosene-water interface by the oscillating drop method. The influences of time, dilational frequency, bulk concentration and interfacial pressure on the dilational properties have been expounded. The experimental results show that the in-film process, such as the orientation change of EO chain, controls the properties of adsorption layers formed by nonionic surfactant C18=E10 molecules. On the other hand, the diffusion-exchange process plays the crucial roles in determining the nature of film containing anionic surfactant C7C7phS molecules. The dilational rheological behaviors of C18=E10/C7C7phS mixtures in the presence of 1 × 10−5 mol·L−1 C7C7phS are close to those of C18=E10. At the same time, mixtures at mole ratio 1:1 show similar behaviors with C7C7phS. The mixed adsorption of C18=E10 and C7C7phS may lead to more compact films and result in higher interfacial elasticity.

Equilibrium Contact Angle and Adsorption Layer Properties with Surfactants.

The three-phase contact line of a droplet on a smooth surface can be characterized by the Young equation. It relates the interfacial energies to the macroscopic contact angle θe. On the mesoscale, wettability is modeled by a film-height-dependent wetting energy f( h). Macro- and mesoscale descriptions are consistent if γ cos θe = γ + f( ha), where γ and ha are the liquid-gas interface energy and the thickness of the equilibrium liquid adsorption layer, respectively. Here, we derive a similar consistency condition for the case of a liquid covered by an insoluble surfactant. At equilibrium, the surfactant is spatially inhomogeneously distributed, implying a nontrivial dependence of θe on surfactant concentration. We derive macroscopic and mesoscopic descriptions of a contact line at equilibrium and show that they are consistent only if a particular dependence of the wetting energy on the surfactant concentration is imposed. This is illustrated by a simple example of dilute surfactants, for which we show excellent agreement between theory and time-dependent numerical simulations.