Properties Of Adsorbed Layers Research Articles

СВЯЗЬ СТРУКТУРЫ И ТРИБОЛОГИЧЕСКИХ ХАРАКТЕРИСТИК ДИАЛКИЛДИТИОФОСФАТОВ ЦИНКА

The article considers the dependence of the antiwear and antifriction action dialkyldithiophosphate zinc (ZDDP) from the value of hydrocarbon radicals. Experimentally studied the friction parameters in sliding contact, simulating a radial bearing. The value of the contact pressure, which implements a hydrodynamic modes depends on the roughness of the surfaces. Dedicated mode is boundary lubrication, which differs from the hydrodynamic and boundary friction regimes. This mode is characterized by a relatively constant coefficient of friction and a small amount of wear. As a criterion for evaluation of antiwear properties, used the value of contact pressure at which the transition from the boundary lubrication regime to the regime of boundary friction. It is found that the transition to the boundary friction regime occurs at different contact pressures for the same type of ZDDP with different length of hydrocarbon radicals. When using zinc dihexadecylnaphthalene the transition to boundary friction occurs at much larger values of contact pressure than when using dioctylphthalate zinc. The results are discussed taking into account the mechanism of adsorption of components of lubricating oils on metal surfaces. The dependence of the antiwear action of ZDDP from the length of the hydrocarbon radicals correspond to their influence on the parameters of a multi-molecular adsorption layer. The data on the influence of ancillary components on the structure and mechanical properties of adsorption layers, and on the rheological properties of lubricants in friction units. It is shown that the introduction of a hydrocarbon base oil ZDDP along with other components consisting of linear molecules with a sufficiently long hydrocarbon radicals, affects the range of contact pressures, which implements a hydrodynamic mode of friction. As an example, used hexadecanol diester and maleic acid. The inclusion of such components in the lubricating oil contributes to the implementation of the hydrodynamic regime, but does not affect the transition from boundary lubrication to boundary friction.

Surface properties of adsorption layers formed from triterpenoid and steroid saponins

Abstract Saponins are natural surfactants with non-trivial surface and aggregation properties which find numerous important applications in several areas (food, pharma, cosmetic and others). In the current paper we study the surface properties of ten saponin extracts, having different molecular structure with respect to the type of their hydrophobic fragment (triterpenoid or steroid aglycone) and the number of sugar chains (1 to 3). We found that the triterpenoid saponins Escin, Tea Saponin and Ginsenosides have area per molecule in the range between 0.5 and 0.7 nm2, and the adsorbed molecules are orientated perpendicularly to the interface. The comparison of the experimentally measured surface elasticities with theoretically estimated ones shows that the saponins with very high dilatational and shear elasticities (up to 2000 mN/m) have molecular interaction parameter in the adsorption layers which is above the threshold value for two-dimensional phase transition. In other words, the highly elastic layers are in surface condensed state, due to strong attraction between the adsorbed molecules. Furthermore, these adsorption layers have non-linear rheological response upon expansion and contraction, even at relatively small deformation. Layers from the other studied saponins (steroids and crude mixtures of triterpenoid saponins), which are unable to form strong intermolecular bonds within the adsorption layer, have zero shear elasticity and viscosity and low dilatational elasticity and viscosity, comparable in magnitude to those reported in literature for protein adsorption layers. The comparison of the results, obtained by several independent experimental methods, allowed us to formulate the conditions under which the results from different interfacial rheology tests could be compared, despite the complex non-linear response of the saponin adsorption layers.

Research highlights: probing adsorbed organic coatings on nanoparticle surfaces

We highlight three recent articles that probe interactions between ligands, polymers, and proteins on nanoparticles and demonstrate methodologies to characterize the adsorbed layer properties.

Pulse Height Spectral Studies of Ozonizer Discharges in Argon at a Moderate Pressure and the Associated Joshi Effect

The effect of light has been observed in the variation of discharge counts with pulse amplitude during d.c.. discharges through argon in a fresh and an aged Siemen's vessels. The pulse height spectra of the discharge for applied potentials of 1.75 and 1.82 kV (r.m.s.) have been measured in dark and under irradiation. The number of current pulses varies periodically with increasing amplitude both in the low and plateau-like intermediate amplitude regions; finally the number of pulse drops rapidly to negligible value in the high amplitude regions. The theoretical explanation for the various observed features in the plots has been attempted on the properties of adsorbed layers on the glass walls of the discharge tube.

Impact of ionic liquid-type imidazolium surfactant addition on dynamic properties of BSA adsorption layers at different pH.

The dynamic interfacial properties of mixed solutions of bovine serum albumin (BSA) and the ionic liquid-type imidazolium surfactant ([C16mim]Br) were measured as a function of the interface age, surfactant concentration and solution pH. Three BSA conformers were investigated: the normal N form as well as the fast F and aged A forms, corresponding to the different solution pH, respectively. The interfacial tension and the interfacial dilational elasticity isotherms for the mixed adsorption layers indicate that the addition of [C16mim]Br to the different structures of BSA isomers influences the properties of the adsorption layer at the decane/water interface. The addition of [C16mim]Br does not influence the structure of the protein at pH below the isoelectric point of BSA, but at higher solution pH, the addition of surfactants significantly influences the dynamic interfacial properties of BSA solutions due to the electrostatic interaction between the components.

Effect of surface potential on extracellular matrix protein adsorption.

Extracellular matrix (ECM) proteins, such as fibronectin, laminin, and collagen IV, play important roles in many cellular behaviors, including cell adhesion and spreading. Understanding their adsorption behavior on surfaces with different natures is helpful for studying the cellular responses to environments. By tailoring the chemical composition in binary acidic (anionic) and basic (cationic) functionalized self-assembled monolayer (SAM)-modified gold substrates, variable surface potentials can be generated. To examine how surface potential affects the interaction between ECM proteins and substrates, a quartz crystal microbalance with dissipation detection (QCM-D) was used. To study the interaction under physiological conditions, the ionic strength and pH were controlled using phosphate-buffered saline at 37 °C, and the ζ potentials of the SAM-modified Au and protein were determined using an electrokinetic analyzer and phase analysis light scattering, respectively. During adsorption processes, the shifts in resonant frequency (f) and energy dissipation (D) were acquired simultaneously, and the weight change was calculated using the Kelvin-Voigt model. The results reveal that slightly charged protein can be adsorbed on a highly charged SAM, even where both surfaces are negatively charged. This behavior is attributed to the highly charged SAM, which polarizes the protein microscopically, and the Debye interaction, as well as other short-range interactions such as steric force, hydrogen bonding, direct bonding, charged domains within the protein structure, etc., that allow adsorption, although the macroscopic electrostatic interaction discourages adsorption. For surfaces with a moderate potential, proteins are not significantly polarized by the surface, and the interaction can be predicted through simple electrostatic attraction. Furthermore, surface-induced self-assembly of protein molecules also affects the adsorbed structures and kinetics. The adsorbed layer properties, such as rigidity and packing behaviors, were further investigated using the D-f plot and phase detection microscopy (PDM) imaging.

Interfacial layer properties and foam film drainage kinetics of aqueous solutions of hexadecyltrimethylammonium chloride

Comparative studies of adsorption layer properties at the air/solution interface – dynamic and equilibrium surface tension measurements, surface dilatational rheology – and the drainage behaviour of microscopic foam films of aqueous solutions of hexadecyltrimethylammonium chloride (cetyltrimethylammonium chloride, CTAC), are performed within a broad surfactant concentration range. Two different concentrations of the added electrolyte (sodium chloride, NaCl) are investigated: 0.1M and 0.5M. The interfacial layer characteristics are studied using profile analysis tensiometer (PAT-1). The foam film drainage kinetics is investigated by the microinterferometric technique of Scheludko–Exerowa. Concerted onset of specific peculiarities is established for both adsorption layer properties and the foam film parameters. A remarkably good correlation is established between the run of the dynamic and equilibrium surface tension isotherms, the course of the surface dilatational elasticity and the peculiarities of drainage kinetics and film stability against the surfactant concentration within each of these concentration intervals. The obtained results shed additional light on the important role of the surfactant adsorption layers for understanding the details of microscopic foam film drainage and stability characteristics.

Adsorption layer properties of alkyltrimethylammonium bromides at interfaces between water and different alkanes

We measured the interfacial tensions of aqueous solutions against different oil phases using drop profile analysis tensiometry (PAT-1, Sinterface Technologies, Germany) for decyl- and dodecyltrimethylammonium bromide (C10TAB and C12TAB) in phosphate buffer (10mM, pH7). The following alkanes were used as oil phases: hexane, heptane, octane, nonane, decane, dodecane and tetradecane. The obtained equilibrium interfacial tension isotherms were fitted by the Frumkin Ionic Compressibility model (FIC). The surfactants adsorb at the water/oil interface in competition with the oil molecules. At high surfactant surface coverage this competitive adsorption is manifested in two ways. First, for short chain surfactants, the oil molecules are embedded into the adsorption layer. Second, for long chain surfactants, the short alkane chains of the oil molecules are squeezed out from the adsorption layer due to strong mutual interaction between surfactants’ chains.

Remarkably high surface visco-elasticity of adsorption layers of triterpenoid saponins

Saponins are natural surfactants, with molecules composed of a hydrophobic steroid or triterpenoid group, and one or several hydrophilic oligosaccharide chains attached to this group. Saponins are used in cosmetic, food and pharmaceutical products, due to their excellent ability to stabilize emulsions and foams, and to solubilize bulky hydrophobic molecules. The foam and emulsion applications call for a better understanding of the surface properties of saponin adsorption layers, including their rheological properties. Of particular interest is the relation between the molecular structure of the various saponins and their surface properties. Here, we study a series of eight triterpenoid and three steroid saponins, with different numbers of oligosaccharide chains. The surface rheological properties of adsorption layers at the air–water interface, subjected to creep-recovery and oscillatory shear deformations, are investigated. The experiments showed that all steroid saponins exhibited no shear elasticity and had negligible surface viscosity. In contrast, most of the triterpenoid saponins showed complex visco-elastic behavior with extremely high elastic modulus (up to 1100 mN m−1) and viscosity (130 N s m−1). Although the magnitude of the surface modulus differed significantly for the various saponins, they all shared qualitatively similar rheological properties: (1) the elastic modulus was much higher than the viscous one. (2) Up to a certain critical value of surface stress, τC, the single master curve described the dependence of the creep compliance versus time. This rheological response was described well by the compound Voigt model. (3) On increasing the surface stress above τC, the compliance decreased with the applied stress, and eventually, all layers became purely viscous, indicating a loss in the layer structure, responsible for the elastic properties. The saponin extracts, showing the highest elastic moduli, were those of Escin, Tea saponins and Berry saponins, all containing predominantly monodesmosidic triterpenoid saponins. Similarly, a high surface modulus was measured for Ginsenosides extracts, containing bidesmosidic triterpenoid saponins with short sugar chains.

S111053 境界潤滑性能を支配する吸着膜のナノ物性評価([S111-05]第19回卒業研究コンテスト(5))

Additives are components of lubricants. According to the required function, additives have a lot of species. Oiliness additives belong to one of these species. The required function for oiliness additives is the friction reduction under boundary lubrication. It is considered that the friction reduction is derived from adsorption layers which are constructed by the molecules of the oiliness additives. Huge amount of previous papers reported that there is the relationship between the friction reducing effect and the molecular properties. However, the evidence of that relationship was the results from macro-scale friction tests, in spite of that the scales of adsorption layer and molecules are nano-scale or angstrom-scale. Hence, we think that the discussion about the effects of the mechanical properties of adsorption layers on the friction reduction is insufficient. In this study, the relationship between friction behavior in micro-scale and nano tribological properties about the adsorption layers was investigated. Stearic acid and Decanonic acid were used for the oiliness additives. The adsorption of the oiliness additives was measured by Quartz Crystal Microbalance (QCM). Atomic Force Microscope (AFM) was used for observation of the several properties about the adsorption layer and the nano-tribological behavior. And the nano-tribological behavior was compared with the results of the micro scale friction test. From these results, it was observed that the stearic acid constructed the adsorption layer, and the layer of the stearic acid had the friction reducing effect. Finally, correlation of the tribological properties between the micro-scale and nano-scale was found. Similar behavior about friction force was shown in nano- and micro-scale.

Amphiphilic nanostructures in aqueous solutions of triethyleneglycol monododecyl ether

The aim of the present study is to relate the surfactant adsorption layer properties at air/solution interface to the drainage parameters of microscopic foam films in the case of aqueous solutions of the non-ionic amphiphile triethyleneglycol monododecyl ether (C12E3). The scope of the research covers adsorption dynamics, construction of equilibrium surface tension isotherm, studies on dilational rheology of the interfacial layers and foam film drainage kinetics. It is established that in the premicellar concentration domain (for surfactant concentrations higher than the range where the Henry’s law is operative but one–two orders of magnitude lower than the conventional CMC-values) there are considerable irregularities of the adsorption layer properties: two plateau regions and a kink are registered in the experimental surface tension isotherm, unusual changes of the surface rheological characteristics. The systematic investigations of the microscopic foam films reveal that the courses of basic kinetic parameters against the amphiphile concentration run in synchrony with the changes in the adsorption layer anomalies. This fact is related to the presence of premicellar surfactant aggregates. The results are juxtaposed to previously obtained characteristics of aqueous solutions of the non-ionic amphiphile tetraethyleneglycol monododecyl ether under similar experimental conditions (Colloids & Surfaces A, 392 (2011) 233–241).

Adsorption of Lipid Liquid Crystalline Nanoparticles on Cationic, Hydrophilic, and Hydrophobic Surfaces

Investigation of nonlamellar nanoparticles formed by dispersion of self-assembled lipid liquid crystalline phases is stimulated by their many potential applications in science and technology; resulting from their unique solubilizing, encapsulating, and space-dividing nature. Understanding the interfacial behavior of lipid liquid crystalline nanoparticles (LCNPs) at surfaces can facilitate the exploitation of such systems for a number of potentially interesting uses, including preparation of functional surface coatings and uses as carriers of biologically active substances. We have studied the adsorption of LCNP, based on phosphatidylcholine/glycerol dioleate and Polysorbate 80 as stabilizers, at different model surfaces by use of in situ ellipsometry. The technique allows time-resolved monitoring of the layer thickness and the amount adsorbed, thereby providing insights into the restructuring of the lipid nanoparticle upon adsorption. The effects of solvent condition, electrolyte concentration, particle size, and surface chemistry on adsorbed layer properties were investigated. Furthermore, the internal structures of the particles were investigated by cryo-transmission electron microscopy and small angle X-ray diffraction on the corresponding liquid crystalline phases in excess water. LCNPs are shown to form well-defined layers at the solid-liquid interface with a structure and coverage that are determined by the interplay between the self-assembly properties of the lipids and lipid surface interactions, respectively. At the hydrophobic surface, hydrophobic interaction results in a structural transition from the original LCNP morphology to a monolayer structure at the interface. In contrast, at cationic and hydrophilic surfaces, relaxation is a relatively slow process, resulting in much thicker adsorbed layers, with thickness and adsorption behavior that to a greater extent reflect the original bulk LCNP properties.

S115022 中性子反射率測定を用いた固液界面における油性剤吸着層の厚さと密度に関する研究

Boundary lubrication is one of the most interesting topics in the field of tribology. Under the boundary lubrication, oiliness additives mixed in a base oil are expected to form adsorption layers on a sliding surface and then achieve low friction and high wear durability. Many classical reports confirmed that the adsorptive performance of an additive to the surface greatly affects the friction coefficient of surface. However, quantitative analysis for the physical and chemical properties of adsorption layers had not been done until recent years because the adsorption layers are very thin, less than several nanometers. To clarify the phenomena under boundary lubrication, thickness and density of an adsorption layer of oiliness additives formed on a metal surface under the lubricating oil were directly measured by neutron reflectometry that is one of in-situ analytical methods. A copper surface on ultra-flat silicon block was formed by physical deposition. The poly-alpha-olefin was used as base oil, and some kinds of deuterated acids were used as additives. The reflectivity profiles for such sample were acquired by neutron reflectometer in air, in PAO and in PAO mixed with additive. Fitting operation based on Parratt's theory showed that the thickness of the additive adsorption layer on the metal surface was very thin, approximately 2.3-2.4 nm and its density was 42-100% of bulk acid. Neutron reflectometry is a quite useful tool for in-situ analysis for the interface between the metal surface and lubricant.

Interfacial Dilational Properties of Novel Crosslinking Phenol-Amine Resin Block Polyether Demulsifiers at Decane-Water Interfaces

Nine novel crosslinking phenol-amine resin block polyether (PARPEmn) as demulsifier were synthesized for Shengli Oil Field. And the dilational rheological properties of absorbed film of nine different structural demulsifiers were investigated by longitudinal wavesmethod (the Langmuir trough-Wilhelmy plate technique) at the decane-water interfaces. The results show that demulsifier concentration is an important factor in controlling the dilational properties of adsorption layer. The dilational elasticity for all demulsifiers appeared a maximum value with the increasing concentration. Most important of all, the relations between interface dilational properties and demulsifier structures have been studied. It demonstrates that the interfacial dilational modulus increase with the increase the HLB value of demulsifiers.

Adsorption layer properties and foam film drainage of aqueous solutions of tetraethyleneglycol monododecyl ether

The aim of the present study 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 of the non-ionic amphiphile tetraethyleneglycol monododecyl ether (C 12E 4), containing premicellar nanostructures. The scope of the research covers adsorption dynamics, construction of equilibrium adsorption isotherms, studies on surface rheology of the interfacial layers and microscopic foam film drainage kinetics. It is established that in the premicellar concentration domain considerable irregularities of the adsorption layer properties are observed: two plateau regions are registered in the experimental surface tension isotherm along with unusual changes of the surface rheological characteristics. The systematic investigation of the drainage of microscopic foam films obtained from these solutions show that the dependencies of basic kinetic parameters of the films on the amphiphile concentration run in synchrony with the changes in the adsorption layer properties. This fact is related to the presence of smaller surfactant aggregates (premicelles). They are presumed to be organized as Platonic bodies. The premicelles play also a significant role in the kinetic stability of the films. The importance of this research is in providing better insight into the initial stages of self-assembling phenomena and into the factors determining the adsorption layer properties and the drainage behaviour of thin liquid films.

Temperature-dependent adsorption of cellulose ethers on silica and hydrophobized silica immersed in aqueous polymer solution

The influence of temperature on adsorption and the adsorbed layer properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) were investigated on silica and hydrophobized silica surfaces immersed in aqueous polymer solution. To achieve a concise understanding a quartz crystal microbalance with dissipation, ellipsometry, and atomic force microscopy imaging were employed. These techniques provide complimentary information on the structure, mass and viscoelastic properties of the polymer layers. Adsorption was first allowed at 25 °C. Next, the temperature was increased step-wise up to 50 °C and then decreased again. This procedure highlights the temperature dependence of the adsorbed material, as well as the hysteresis in the adsorption due to temperature cycling. A change in temperature not only affects the adsorbed amount, but also the properties of the layer as illustrated by measurements of its water content, thickness and viscoelasticity.

Surface-Induced Rearrangement of Polyelectrolyte Complexes: Influence of Complex Composition on Adsorbed Layer Properties

The adsorption characteristics of two different types of polyelectrolyte complexes (PECs), prepared by mixing poly(allylamine hydrochloride) and poly(acrylic acid) in a confined impinging jet (CIJ) mixer, have been investigated with the aid of stagnation point adsorption reflectometry (SPAR), a quartz crystal microbalance with dissipation (QCM-D), and atomic force microscopy (AFM) using SiO(2) surfaces. The two sets of PEC were prepared by combining high molecular mass PAH/PAA (PEC-A) and low molecular mass PAH/PAA (PEC-B). The PEC-A showed a higher adsorption to the SiO(2) surfaces than the PEC-B. The adsorption of the PEC-A also showed a larger change in the dissipation (ΔD), according to the QCM-D measurements, suggesting that the adsorbed layer of these complexes had a relatively lower viscosity and a lower shear modulus. Complementary investigations of the adsorbed layer using AFM imaging showed that the adsorbed layer of PEC-A was significantly different from that of PEC-B and that the changes in properties with adsorption time were very different for the two types of PECs. The PEC-A complexes showed a coalescence into larger block of complexes on the SiO(2) surface, but this was not detected with the PEC-B. The size determinations of the complexes in solution showed that they were very stable over time, and it was therefore concluded that the coalescence of the complexes was induced by the interaction between the complexes and the surface. The results also indicated that polyelectrolytes can migrate between the different complexes adsorbed to the surface. The results also give indications that the preparation of PEC-B leads to the formation of two different types of polyelectrolyte complexes differing in the amount of polymer in the complexes; i.e., two populations of complexes were formed with similar sizes but with totally different adsorption structures at the solid-liquid interface.

Dilation and Shear Rheology of Mixed β-Casein/Surfactant Adsorption Layers

The present study deals with dilational and shear rheological properties of adsorption layers of the milk protein beta-casein (BCS) mixed with the nonionic dodecyl dimethyl phosphine oxide (C12DMPO) and the positively charged dodecyl trimethyl ammonium bromide (DoTAB), respectively. The drop profile analysis tensiometer PAT-1 was applied for the dilational rheological studies at low frequency harmonic relaxations. A special modification of the setup, consisting of a coaxial capillary combined with a double dosing system, provides exchange of the drop volume during experiments. This arrangement offers a unique protocol for studies of mixed surface layers, formed by sequential adsorption of the individual compounds. The dilational viscoelastic modulus and the dilational viscosity of the mixed layers, built-up in the two different ways, were investigated and compared. The features of the mixed surface layers drawn from the dilational rheology are qualitatively confirmed by the shear rheological parameters measured by torsion shear rheometry ISR-1. Recently derived theoretical models were used for a quantitative description of the equilibrium state and dilational rheology of the surface layers formed by the single components and their mixtures.

Interactions between Adsorbed Layers of αS1-Casein with Covalently Bound Side Chains: A Self-Consistent Field Study

The effect on the adsorbed layer properties of the modification of alpha S1-casein by covalent bonding with an uncharged polysaccharide side chain has been investigated using lattice-based self-consistent field (SCF) theory. Interactions between two hydrophobic planar surfaces coated by a layer of adsorbed modified alpha S1-casein have been studied as a function of pH and ionic strength. While the interactions of the unmodified alpha S1-casein layers become attractive at high ionic strength, it has been shown that the presence of polysaccharide attachment to the alpha S1-casein molecule can confer net repulsive interactions over a wide range of salt concentration. The disordered protein is represented as a linear flexible polyampholyte with a sequence of hydrophobic, polar, and charged units based on the known alpha S1-casein primary structure. The hydrophilic side chain is attached at various fixed positions along the casein backbone. Different lengths and locations of the attached polysaccharide side chain are examined. Interfacial structures and colloidal stability properties of the system are determined, including the surface-surface interaction potential, the extent of protein bridging, and the distribution of protein segments from the surface under different conditions of pH and ionic strength. It has been found that the covalent bonding of short hydrophilic chains may not only enhance but can also worsen the colloidal stabilizing properties of the modified protein, depending on the position of the attachment.

Layer-to-layer adsorption of oppositely charged polyelectrolytes: The effect of molecular mass: 1. Formation of the first layer

The formation and properties of adsorption layers of poly(dimethyldiallylammonium chloride) with different molecular masses on the surface of fused quartz are studied by the capillary electrokinetics method. It is shown that the value of ζ potential depends on the flow rate of liquid determined by the pressure drop. Such behavior can be explained by the deformation of the adsorption layer. At low rates of liquid flow, constant values of adsorption and time needed to achieve these values decrease for the samples of lower molecular masses, which is probably related to the more closely packed structure and, hence, to the lower deformability of the adsorption layers, as well as to the shortest times during which conformational rearrangements proceed in the layer. The time of conformational changes in the adsorption layer significantly exceeds the time of adsorption. The adsorption of cationic polyelectrolyte is irreversible. It is found that the compaction of adsorption layers increases with time; the rate of compaction of layers of a low-molecular-mass polyelectrolyte is higher and the layers of a high-molecular-mass polyelectrolyte retain the residual deformability even for six days. The measurements of the filtration of polyelectrolyte solutions through thin quartz capillaries allow the thickness of adsorption layers and their deformation under pressure to be estimated.