Formation Of Adsorption Layer Research Articles

Impact of surfactant chain length on dynamic surface properties of alkyltrimethylammonium bromide/polyacrylic acid solutions

The dynamic surface properties of mixed solutions of polyacrylic acid (PAA) and alkyltrimethylammonium bromides (C nTAB) were measured by the oscillating ring method as a function of surface age and surfactant concentration. The concentration dependencies of the surface tension and dilational dynamic surface elasticity were similar to the corresponding results for other polyelectrolyte/surfactant solutions, which have been investigated earlier. The kinetic dependencies of the surface elasticity proved to be non-monotonic for all the investigated surfactants at n = 8, 10, 12, 14, 16 and displayed two local maxima at surfactant concentrations close to the critical micellar concentration (CMC). The first maximum was caused by an aggregate formation in the surface layer while the second maximum occurred simultaneously with a multilayer formation at the gas–liquid interface. The surface tension corresponding to the beginning of the aggregate formation decreased and the surface elasticity in the region of the first local maximum increased with the hydrophobicity of C nTAB/PAA complexes caused by the increasing hydrocarbon chain length of the surfactant. The hydrophobic interactions influenced also the height and position of the second local elasticity maximum. These effects were connected with changes in the rate of adsorption layer and aggregate structure formation. Comparable values of the real and imaginary parts of the dynamic surface elasticity at concentrations for aggregate formation in the surface layer indicated that the relaxation time of the mass exchange between the aggregates and the surrounding adsorption layer is comparable with the period of oscillations, i.e. ≤10 s.

Fluid States of Helium Adsorbed in Nanopores

We have studied helium adsorbed in new nanopores which have regular structures from nano-cage to three-dimensionally (3D) connected pores. Adsorption potential and layer formation of the adsorbed helium are observed by the vapor pressure for the adsorption. New paradigms of zero-D and 1D helium fluids are realized in nano-cages and nano-channels, respectively. The superfluid onsets (transitions) in the 1D and 3D nanopores show obvious dependence on the pore connections. The superfluid in the 3D pores has properties similar to the Bose-Einstein condensation of the 3D Bose atomic gas. The films of the 3He gas formed in the 4He preplated nanopores show the dimensional crossover depending on the pore connection: from the 2D Boltzmann gas to a 1D or 3D gas state with decreasing temperature. This gas changes to the degenerate state in each dimension at the lower temperatures. Extremely high frequency measurements of the helium adatoms on flat substrate determined the superfluid vortex parameters of the 4He films, and revealed a slippage (decoupling) of the helium adatoms in the non-superfluid state.

A method of investigation of interface between two immiscible liquids

Burst of the output power of radiation is recorded when the metal-coated conical point of an optical fiber crosses the interface of immiscible liquids. This phenomenon is caused by the resonance transfer of the wave energy from the inner channel into the outer; formation of a meniscus on the interface in the vicinity of the point promotes this transfer. This method of investigation provides information on the interface of immiscible liquids and on the process of formation of adsorption layers.

Kinetics of Adsorption Layer Formation in Solutions of Polyacid/Surfactant Complexes

The dynamic dilational elasticity of adsorption layers of the complexes between polyacids and dodecyltrimethyl ammonium bromide were measured by the oscillating ring method as a function of surface age and surfactant concentration. The concentration dependencies of surface tension and dilational surface elasticity are similar to the corresponding dependencies of other polyelectrolyte/surfactant solutions. At the same time, the kinetic dependencies of the dynamic surface elasticity differ significantly from the results for other systems and exhibit in respective concentration ranges one or two local maxima. The first maximum and the associated distortion of the harmonical surface tension oscillations are caused by an aggregate formation in the surface layer. The second maximum occurs simultaneously with a multilayer formation at the liquid surface, which probably results in a new relaxation mechanism of surface stresses. The hydrophobic interactions influence the height and position of the second elasticit...

Solute Adsorption and Gel Layer Formation during Ultrafiltration of Ovalbumin

To define the influence of osmotic pressure, solute adsorption, and gel layer formation on permeate flux during the ultrafiltration of an ovalbumin solution, the characteristics of the gel-like layer formed on the membrane surface were investigated and the adsorption rate of ovalbumin to membranes was measured under different conditions. Gel-like layer observed on the membrane surface was found to be a deposit layer formed by an aggregate of denatured ovalbumin which could be precipitated by centrifugation. This layer had a rejection ability for ovalbumin itself and little resistance for permeate flow. In both cases where there is a layer and where is not, the flux values during the ultrafiltration could be precisely predicted by the osmotic pressure and adsorption resistance model which took into account the influence of osmotic pressure and solute adsorption. The forced flow of solution into membrane pores shortened the time to reach adsorption equilibrium, suggesting a notable influence of solute adsorption into membrane pores.

Functionalization of solid surfaces with hyperbranched polyesters to control protein adsorption

Thin films of hyperbranched polyesters were studied in dry state and in aqueous buffer solution regarding their swelling behaviour and protein adsorption potential. The influence of the degree of branching, the backbone structure, flexibility as well as the polarity was varied. By changing the backbone structure from aromatic, aromatic–aliphatic to aliphatic the surface properties can be controlled from protein active to protein repelling. The higher adsorption potential observed in comparison to linear polyesters is the result of the large amount of end groups allowing the formation of hydrogen bonds, and the larger swellability of the more flexible linear polymers. The protein adsorption process was studied intensively by in-situ spectroscopic ellipsometry. Different approaches towards a proper optical model for the vis-ellipsometry data evaluation for the determination of the correct layer thickness and refractive index are discussed. IR-ellipsometric measurements using a new in-situ cell gave the full chemical evidence for the formation of thin protein adsorption layer on the polymer films in the aqueous buffer environment.

Codeposition of copper and tin from acidic sulfate solutions containing polyethylene glycols. Effect of length of the hydrocarbon chain

Voltammetry and electrochemical impedance spectroscopy technique were applied to study the effect of polyethylene glycols (PEG) with different molecular mass on Cu(II) and Sn(II) reduction kinetics in acidic sulfate solutions. Tetraethylene glycol was found to be the surface-active oligomer on both Cu and Sn substrates that holds the shortest (–CH2–CH2–O–)m chain. The exchange current density of the rate-limiting step Cu2+ + e → Cu+ falls drastically with an increase in the molecular mass of PEG. An addition of PEG into halide-free Sn(II) solutions results in the significant inhibition of Sn(II) reduction in the entire range of cathodic polarizations including the region of limiting current. Inhibition degree also increases with PEG molecular mass. In contrast with Cu|Cu(II) system, formation of adsorption layers on Sn electrodes proceeds significantly slower. Underpotential deposition of Sn(II) is observed in the region of Cu(II)-limiting current. The characteristic current minimum arises in the region where free Sn phase is thermodynamically stable. It deepens with the length of the hydrocarbon chain of PEG. The fall of current density seems to arise from the inhibitive PEG adsorption on tin atoms that are still not incorporated into general Cu–Sn lattice.

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.

Surface and bulk properties of aqueous binary mixtures of Pluronic F68 and low-molecular-weight cationic surfactants: 2. Wetting and modifying effects of mixed solutions

Wetting and adsorption modification of polystyrene surface with aqueous solutions of F68-cationic surfactant mixtures are studied. The synergism of wetting is revealed. It is established that the degree of synergism upon wetting is determined by the synergism of surfactant adsorption on a solid surface and peculiarities of the formation of mixed adsorption layers of surfactants. It is shown that low-molecular-weight cationic surfactants can be used to increase the efficiency of the modification of polymer surfaces with Pluronics.

Dilational visco-elasticity of polyelectrolyte/surfactant adsorption layers at the air/water interface: Poly(vinyl pyridinium chloride) and sodium dodecylsulfate

The dilational dynamic surface elasticity of mixed aqueous polyvinylpyridinium chloride/sodium dodecyl sulfate solutions (PVPmCl/SDS) was measured as a function of time and surfactant concentration. This system represents a typical example of polyelectrolyte/surfactant complex formation and subsequent aggregation on the nano-scale. The concentration dependence of the real part of the dynamic surface elasticity for the mixed PVPmCl/SDS solutions in 0.1M NaCl and without added NaCl qualitatively agreed with the corresponding results for some previously studied polyelectrolyte/surfactant solutions. This similarity indicates that strong changes of the surface visco-elasticity in a narrow concentration range can be explained by the formation of microparticles in the surface layer. The addition of 0.1M NaCl to PVPmCl/SDS solutions led to an almost two times decrease of the surface elasticity at low concentrations and to the acceleration of the adsorption layer formation. At the same time the imaginary part of surface elasticity of PVPmCl/SDS solutions was significantly higher than the corresponding results for the earlier studied systems and the adsorption layers proved to be visco-elastic in a broad concentration range. The application of the Maxwell rheological model in this case allowed the calculation of the main relaxation time. The main relaxation process is the surfactant exchange between the surface layer and the bulk phase or in the surface layer between free surfactant molecules and those bound in aggregates. The distinction of the surface visco-elasticity of PVPmCl/SDS solutions from the previously studied systems can be explained by the lower stability of polyelectrolyte/surfactant complexes in the adsorption layer.

Molecular stratification nanotechnology in antiadhesive modification of fabric fibres

The dependence of the oil-repellent effect on the structure of a modifying layer of fluorocarbons was established. Formation of a nanosize monomolecular adsorption layer is optimum for attaining the greatest effect. It is useful to conduct molecular stratification from chlorocarbon medium (perchloroethylene) for the necessary orientation of the molecules of the fluorocarbon amphiphilic substance. Cationization of the surface of textile fibres is required for forming a nanosize layer from aqueous solution.

DFT and electrochemical studies of tris(benzimidazole-2-ylmethyl)amine as an efficient corrosion inhibitor for carbon steel surface

The corrosion inhibition properties of tris(benzimidazole-2-ylmethyl)amine (TBMA) were analyzed by DFT and electrochemical techniques such as polarization curves and electrochemical impedance spectroscopy (EIS). DFT results clearly show that TBMA posses corrosion inhibition properties by having a delocalization region (N 1 C 2 N 3) in the benzimidazole ring that gives up their π electron density through its HOMO orbital to the metal LUMO to form a adsorption layer over the metallic surface; this has been proved by interacting the TBMA and its protonated structures with the surface of Fe 13 cluster, showing that the protonated moiety adsorbs strongly on the iron surface than that of the neutral structure. Electrochemical impedance data demonstrate that the interface between the electrode and the TBMA solution decreases the charge capacitance and simultaneously increases the function of the charge/discharge of the interface, facilitating the formation of adsorption layer over the iron surface.

The influence of pyrocarbon modification on the physicochemical characteristics of the surface of pores and transport properties of inorganic membranes

The structure of pyrocarbon crystallites deposited on the surface of the pore channels of TRUMEM composite inorganic membranes (TiO2 on porous steel) was studied by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. According to the X-ray data, the lattice of pyrocarbon crystallites of size Lc=40.0 nm has hexagonal symmetry with d002=3.368 A. The deposition of pyrocarbon crystallites with Lc up to 1.5 nm was identified by X-ray photoelectron spectroscopy and scanning electron microscopy. Coating the pore channels of membranes with pyrocarbon decreased the density of the electric charge on their surface by a factor of ∼5.5. The temperature dependences of the hydrodynamic permeability coefficient were obtained for the initial and pyrocarbon-modified membranes when polar and nonpolar fluids flowed through them. The electrostatic force and energy of the interaction of ethanol molecules with each other and the surface of pores were calculated; the results were compared with the O-H···O H-bond energy. The main reason for the formation of alcohol adsorption layers was the formation of H-bonds between its molecules and O-H···O atoms on the surface of pores.

Dynamic surface tension and dilational viscoelasticity of adsorption layers of alkylated chitosans and surfactant–chitosan complexes

The kinetics of the adsorption at the air-water interface and the processes of the structure formation inside the adsorption layers of hydrophobically modified systems [alkylated chitosans and sodium dodecyl sulfate (SDS)–chitosan (Ch) complexes] have been studied by the tensiometric method based on the axisymmetric rising-bubble-shape analysis as a function of the bulk concentration of polymers and the ageing time of their adsorption layers. The kinetics of the adsorption of chitosan, alkylated chitosans (ChC3, ChC8, and ChC12), and surfactant–polyelectrolyte (PE) complexes formed by the chitosan and the polysoaps with oppositely charged anionic surfactant SDS is characterized by an induction time (the so-called lag time), τlag, corresponding to the diffusion stage of the formation of adsorption layers. During this time, the decrease in the surface tension (or the increase in the surface pressure π) does not exceed several millinewtons per meter that corresponds to the “gaseous” state of adsorption layers. The postlag stage of the formation of the adsorption layer is characterized by the remarkable rate of increase in the surface pressure π that corresponds to the conformational rearrangement of PEs inside the adsorption layer by increasing the number of hydrophobic groups (adsorbing centres) in contact with the non-polar phase at the interface. It has been found that during the lag time, the adsorption of alkylated chitosans (cationic polysoaps) increases with increasing alkyl chain length, whereas during the postlag time, the adsorption of the ChC3 is maximal with regard to other polysoaps. It has been confirmed that at equal content of alkyl groups in the system, the surface activity of the SDS–Ch complexes is much higher with regard to that of the polysoaps. The viscoelasticity of adsorption layers of individual PEs and their complexes continuously increases with the ageing time, giving evidence for the interaction between the polymers inside the adsorption layers. It has been found that the rate of increase in the dilational storage module E′ of the adsorption layers of SDS–Ch complexes is much higher than for the polysoaps that correlates with the higher surface activity of the former with regard to the latter. For the mentioned systems, the module E′ is much higher than the loss module E″ that confirms the solid-like properties of their adsorption layers. On the other hand, the adsorption layers of the chitosan are liquid-like, while E′<<E′′.

Effect of the interface with solid on the interfacial region in the blends of linear polymers formedin situ

Blends of polyurethane and poly (methyl methacrylate) of various compositions were synthesized in situ in presence of various amounts of nanoparticles (fumed silica). From thermo- physical measurements it was found that the reaction is accompanied by the phase separation and evolution of two phases. The temperature transitions in the systems and their positions depend on the blend composition and on the filler amount. Using scanning differential calorimetry, the fraction of an intermediate region between two main phases has been estimated from the changing of heat capacity increments. It was observed that in filled polymer blends in the temperature region between two main relaxation transitions, there appears the third transition. This transition is supposed to be the result of the formation of adsorption layer at the interface with solid. The appearance of such an intermediate regions increases essentially the total fraction of an interfacial region in the system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4646–4651, 2006

Study on adsorption and reaction mechanism of preparation of TiO 2/SiO 2 by adsorption phase reactor technique

This paper approaches the evolution of adsorption layer with temperature under different water concentrations. EDX and X-ray diffraction (XRD) indicated that under low water concentration (LWC), there was a sharp decrease in TiO 2 quantity curve and grain size curve between 40 °C and 60 °C. But under high water concentration (HWC), TiO 2 quantity and grain size both rose continually. In transmission electron microscopy (TEM) picture, the characteristic of samples of LWC and HWC at low temperature were similar, whereas they became quite different at high temperature. These phenomena manifest that the effects of adsorption and reaction alter at different conditions. Under LWC, adsorption mechanism dominates the process. Under HWC, the chief mechanism at low temperature was similar to that of LWC and at high temperature the major reaction region switches from adsorption to alcohol bulk. Based on the characteristics of adsorption on silica surface, the phenomenology theory dealt with formation of adsorption layer and its evolution with temperature was proposed.

Regularities of the Two-Layer Adsorption of Anionic Surfactant and Cationic Polyelectrolyte on the Fused Quartz Surface

The adsorption of sodium dodecyl sulfate (SDS) on the quartz capillary surface that was preliminarily covered with a layer of cationic polyelectrolyte (CPE) is studied. The charge sign change of the modified quartz surface and subsequent increase of negative surface charge observed upon the adsorption of SDS indicate the formation of the second adsorption layer composed of surfactant molecules. It is shown that the surfactant layer is stronger attached to the surface at a higher charge of the CPE adsorption layer. Upon the formation of the surfactant layer on a looser CPE adsorption layer, the desorption of SDS molecules decreases, which can be associated with the partial penetration of these molecules into the CPE layer.

Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

Kinetics and mechanism of gold electrooxidation in sulfuric acid solutions of thiocarbamide (TCA) are studied by measuring voltammograms (VA) of gold and glassy carbon (GC) electrodes. In a potential (E) range from −0.2 to 1.2 V (SCE), VA of a gold electrode demonstrate three peaks. The first and the second peaks correspond to gold electrooxidation to [AuTCAads] + and [Au(TCAads)3]3+ ions at E of 0.152 and 0.554 V, while the third one corresponds to TCA electrooxidation. The electrooxidation of TCA on GC electrodes is characterized by two VA peaks at 0.983 and 1.437 V. The first peak corresponds to the formation of formamidine disulfide (FADS) (ka1 = 6.40 × 10−4 cm/s), while the second peak corresponds to TCA oxidation to sulfides and hydrosulfides (ka2 = 7.78 × 10−5 cm/s). The composition of adsorption layers formed at the Au electrode is analyzed by Auger spectroscopy. The introduction of sodium sulfide into TCA solutions eliminates the formation of adsorption layers and accelerates Au oxidation in such solutions. The rate constants of gold electrooxidation ka = 6.31 × 10−3 cm/s and Au(I) electroreduction kc = 5.46 × 10−4 cm/s in TCA solutions are estimated. Kinetic parameters (charge transfer coefficients, reactions orders in carbamide) are determined and the mechanisms of Au and TCA oxidation in sulfuric acid solutions are proposed.

Numerical Solution of Binary Liquid-Phase Adsorption onto Porocel Clay Using Linear, Freundlich and Langmuir Isotherms

A generalized mathematical model is presented to describe the process of multi-component adsorption onto porous media in fixed beds. The model was applied to the binary adsorption, without reaction, of aromatics and sulphur compounds onto a fixed bed of Porocel clay for kerosene deodorization using linear, Freundlich and Langmuir isotherms independently. A computational scheme for the solution of the model equations is presented. The scheme is based on orthogonal collocation for spatial discretization of the resulting set of coupled hyperbolic and parabolic partial differential equations for the macro-and micro-system, respectively. Michelsen's modified third-order semi-implicit Runge-Kutta method combined with step-size adjustment strategy was used to integrate the resulting 4N ordinary differential equations. Excellent agreement between the simulated results and pilot plant data was obtained for the breakthrough profiles for the non-linear adsorption isotherms of Freundlich and Langmuir. No agreement was obtained for the linear isotherm. Also, using the Freundlich and Langmuir isotherms, the exit concentration of the less preferentially adsorbed component (aromatics) exceeded its inlet concentration to the adsorption column for a certain period. This is indicative of the behaviour of competitive multi-component adsorption: relative to aromatics, sulphur compounds are selectively adsorbed onto Porocel clay. The relationship between solid- and liquid-phase concentration profiles for the Freundlich isotherm revealed the formation of multiple adsorption layers upon the primary mono-molecular layer. Again, for the Freundlich isotherm, the structure of the profiles exhibited a highly pronounced maximum for sulphur. An experimental breakthrough time of 8 h was also predicted for both aromatics and sulphur compounds using the non-linear Freundlich and Langmuir isotherms.

Molecular dynamics of ≡SiOC·O radicals “grafted” onto the Aerosil surface in adsorption layers of carbon dioxide

As the formation of adsorption layers of carbon dioxide on the Aerosil surface proceeds, the character of rotational mobility of grafted radicals ≡SiOC·O changes from the anisotropic Brownian motion in vacuo to Brownian motion in a potential of 1.7–1.9 kcal mol−1. The ≡SiOC·O radicals were proposed for use as probes to study the dynamic characteristics of adsorbates on the Aerosil surface.