In honour of the 65th birthday of Valentin B. Fainerman

This Honorary Note is dedicated to the 65th birthday of Valentin Fainerman and summarizes some of his contributions to the field of interfacial dynamics. First of all, he made the maximum bubble pressure tensiometry the most frequently used methodology in the short time range of surfactant adsorption at liquid surfaces. This work allows us now to use experimental data down to the time range of sub-milliseconds for analyzing adsorption mechanisms of surfactants and polymers and their mixtures. The contributions of V.B. Fainerman to the quantitative understanding of the thermodynamics of adsorption represent a significant step ahead and describe adsorption layers even of rather complex nature, such as mixed protein–surfactant layers. These models consider molecular interfacial reorientation and aggregation. His thermodynamic approach is able to explain various interfacial systems which includes for example also phase transitions in insoluble monolayers. Based on diffusional transport and the proposed thermodynamic models, the adsorption kinetics and dilational rheology of liquid interfacial layers have reached a new level of understanding.     

Adsorption complexes ‘zeolite–cationic surfactant’: properties and surface activity in a polymer composite material based on ultra-high-molecular-weight polyethylene

We investigated the adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) to zeolite from premicellar and micellar solutions, as well as some properties of the organically modified zeolite surface and the nature of its interfacial interaction with ultra-high-molecular-weight polyethylene (UHMWPE) in a UHMWPE-based polymer composite material (PCM). The formation mechanism of mono- and bimolecular adsorption layers of cetyltrimethylammonium cation and bromide anion to the clinoptilolite (Cli) surface was proposed, and the thermodynamic and kinetic characteristics of adsorption were determined. The surface texture of organically modified zeolite was studied by instrumental methods; the thermal stability limits of CTAB adsorption layers to zeolite surface and their decomposition behavior in inert and oxidizing media were established. The evaluation of the deformation and strength properties, the study of the supramolecular structure, and the calculation of the thermodynamic and kinetic parameters of the PCM crystallization process revealed that the filing with organically modified Cli increases the UHMWPE surface activity and improves their compatibility.     

Thermodynamics, adsorption kinetics and rheology of mixed protein-surfactant interfacial layers

Depending on the bulk composition, adsorption layers formed from mixed protein/surfactant solutions contain different amounts of protein. Clearly, increasing amounts of surfactant should decrease the amount of adsorbed proteins successively. However, due to the much larger adsorption energy, proteins are rather strongly bound to the interface and via competitive adsorption surfactants cannot easily displace proteins. A thermodynamic theory was developed recently which describes the composition of mixed protein/surfactant adsorption layers. This theory is based on models for the single compounds and allows a prognosis of the resulting mixed layers by using the characteristic parameters of the involved components. This thermodynamic theory serves also as the respective boundary condition for the dynamics of adsorption layers formed from mixed solutions and their dilational rheological behaviour. Based on experimental studies with milk proteins (β-casein and β-lactoglobulin) mixed with non-ionic (decyl and dodecyl dimethyl phosphine oxide) and ionic (sodium dodecyl sulphate and dodecyl trimethyl ammonium bromide) surfactants at the water/air and water/hexane interfaces, the potential of the theoretical tools is demonstrated.The displacement of pre-adsorbed proteins by subsequently added surfactant can be successfully studied by a special experimental technique based on a drop volume exchange. In this way the drop profile analysis can provide tensiometry and dilational rheology data (via drop oscillation experiments) for two adsorption routes — sequential adsorption of the single compounds in addition to the traditional simultaneous adsorption from a mixed solution. Complementary measurements of the surface shear rheology and the adsorption layer thickness via ellipsometry are added in order to support the proposed mechanisms drawn from tensiometry and dilational rheology, i.e. to show that the formation of mixed adsorption layer is based on a modification of the protein molecules via electrostatic (ionic) and/or hydrophobic interactions by the surfactant molecules and a competitive adsorption of the resulting complexes with the free, unbound surfactant. Under certain conditions, the properties of the sequentially formed layers differ from those formed simultaneously, which can be explained by the different locations of complex formation.     

An experimental and molecular-statistical study of the adsorption of the iodobenzene, 2-iodothiophene, and isomeric iodoadamantane molecules on the graphite basal face surface

The thermodynamic characteristics of adsorption of iodobenzene, 2-iodothiophene, and 1- and 2-iodoadamantanes on the surface of graphitized thermal carbon black were determined experimentally. The influence of the special features of the molecular structure of the adsorbates on the thermodynamic characteristics of adsorption was studied. The atom-atom approximation of the semiempirical molecular-statistical theory of adsorption was used to calculate the thermodynamic characteristics of adsorption of the adsorbates using the newly determined potential function parameters of pair intermolecular interaction (φ(r)) of I with C atoms of the basal graphite face. For the example of isostructural monohalogenated benzenes, thiophenes, and adamantanes, a comparative analysis of the contributions of the F, Cl, Br, and I atoms to the thermodynamic characteristics of adsorption was performed for the nonspecific adsorption of these compounds on a plane graphitized carbon black surface.     

Interfacial rheology of mixed layers of food proteins and surfactants

Mixed protein–surfactant adsorption layers at liquid interfaces are described including the thermodynamic basis, the adsorption kinetics and the shear and dilational interfacial rheology. It is shown that due to the protrusion of hydrophobic protein parts into the oil phase the adsorption layers at the water–hexane interface are stronger anchored as compared to the water-air surface. Based on the different adsorption protocols, a sequential and a simultaneous scheme, the peculiarities of complexes between proteins and added surfactants are shown when formed in the solution bulk or at a liquid interface. The picture drawn from adsorption studies is supported by the findings of interfacial rheology.     

介孔碳CMK-3对苯酚的吸附动力学和热力学研究

研究了介孔碳CMK-3对苯酚的吸附性能, 与传统商用活性碳(CAC)进行了比较, 结果表明, CMK-3比CAC的吸附量大、吸附速率快、达到平衡时间短, 是一种较好的吸附剂. 同时探讨了介孔碳CMK-3对苯酚的吸附热力学和动力学特征. CMK-3对苯酚的吸附行为可用Langmuir和Freundlich等温式进行描述, 相关性都较好, 但更符合Freundlich经验公式. 分别采用模拟一阶反应和二阶反应模型考察了吸附动力学, 并计算了这些动力学模型的速率常数. 模拟二级反应模型和实验数据之间有较好的相关性. 分别计算了热力学参数ΔG0, ΔS0和ΔH0, 结果表明, CMK-3对苯酚的吸附过程是吸热和自发的.     

The effects of energy sites on adsorption of Lennard-Jones fluids and phase transition in carbon slit pore of finite length a computer simulation study

A Monte Carlo simulation method is used to study the effects of adsorption strength and topology of sites on adsorption of simple Lennard-Jones fluids in a carbon slit pore of finite length. Argon is used as a model adsorbate, while the adsorbent is modeled as a finite carbon slit pore whose two walls composed of three graphene layers with carbon atoms arranged in a hexagonal pattern. Impurities having well depth of interaction greater than that of carbon atom are assumed to be grafted onto the surface. Different topologies of the impurities; corner, centre, shell and random topologies are studied. Adsorption isotherms of argon at 87.3 K are obtained for pore having widths of 1, 1.5 and 3 nm using a Grand Canonical Monte Carlo simulation (GCMC). These results are compared with isotherms obtained for infinite pores. It is shown that the surface heterogeneity affects significantly the overall adsorption isotherm, particularly the phase transition. Basically it shifts the onset of adsorption to lower pressure and the adsorption isotherms for these four impurity models are generally greater than that for finite pore. The positions of impurities on solid surface also affect the shape of the adsorption isotherm and the phase transition. We have found that the impurities allocated at the centre of pore walls provide the greatest isotherm at low pressures. However when the pressure increases the impurities allocated along the edges of the graphene layers show the most significant effect on the adsorption isotherm. We have investigated the effect of surface heterogeneity on adsorption hysteresis loops of three models of impurity topology, it shows that the adsorption branches of these isotherms are different, while the desorption branches are quite close to each other. This suggests that the desorption branch is either the thermodynamic equilibrium branch or closer to it than the adsorption branch.     

Statistical physics modeling of water vapor adsorption isotherm into kernels of dates: Experiments,microscopic interpretation and thermodynamic functions evaluation

In this paper, water sorption isotherms into date kernels give interesting insights about the sorption mechanism. The equilibrium adsorption data expressing the change in moisture content of date kernels were collected at three different temperatures using the static gravimetric technique. The adsorption isotherm profiles demonstrated that this process was performed via an infinite number of layers. A modified form of the Brunauer, Emett and Teller (BET) model is obtained based on the use of the real gas law and statistical physics treatment so the interaction between molecules is considered. This advanced model is used to fit experimental isotherms by numerical simulation. The sorption mechanism is theoretically explained by the parameters that could be related to the water adsorption process. Based on fitting results, we find that the number of molecules per site (parameter n) has a linear tendency with temperature thanks to the thermal agitation effect. A deeper analysis of adsorption energy demonstrates that the water vapors are physisorbed in the date kernels. Through the exploitation of our model, three classic thermodynamic functions are investigated to interpret the macroscopic aspect of the adsorption mechanism.     

CPS L 946

A thermodynamic inequality, providing the possibility of calculating the limiting number of adsorbed layers from the excess adsorption data, is discussed. For identical cross-sectional areas of molecules of both components this inequality simplifies considerably and defines the limiting value of the surface phase capacity. Therefore, it may be used as criterion of the accuracy of the surface phase capacity value evaluated by other methods. Taking this criterion into account a method is proposed to determine the surface phase capacity and number of adsorbed layers from the excess adsorption data. It is verified by using the excess adsorption data available from the literature.     

Thermodynamic pressure of simple fluids confined in cylindrical nanopores by isothermal-isobaric Monte Carlo: influence of fluid/substrate interactions

The thermodynamic pressure or grand potential density is calculated by isobaric-isothermal Monte Carlo algorithm for simple Lennard-Jones fluid confined in cylindrical pores presenting chemical heterogeneities along their axis. Heuristic arguments and simulation results show that the thermodynamic pressure of the confined fluid contains two contributions. The first term is the usual pressure of the bulk fluid for a density equal to the confined fluid density defined as the total number of confined particles divided by the accessible volume due to thermal agitation. A second term has to be added, which is empirically shown to be proportional to the fluid/wall interface area and almost constant along the adsorption and desorption branches. This interfacial contribution, calculated for various pore models, has small variations reminiscent of the fluid adsorption/desorption properties calculated in the various pores. In particular, it is shown that this interfacial quantity is maximum for a fluid/substrate interaction intensity of the same order as the fluid/fluid one, while the thermodynamic pressure at which rapid desorption occurs presents a minimum. Stronger or weaker fluid/wall affinity favors gas state nucleation on the desorption of confined fluids.     

Influence of solid surface on equilibria in polymer mixtures

The influence of solid disperse particles (aerosil) on phase equilibria in ternary (polymer-polymer-solvent) and binary (polymer-polymer) systems has been investigated using adsorption and gas chromatography techniques. The change in position and shape of the binodal for the ternary systems has been established. The region of thermodynamic compatibility of two polymers in a common solvent is broadened due to the selective adsorption of high molecular weight fraction of one of the polymers, this effect being dependent on the amount of solid particles introduced into the system. For binary systems, the thermodynamic interaction parameters χ₂₃ have been determined and increasing thermodynamic stability of the mixture in the presence of the solid phase has been discovered. The complicated dependences of the interaction parameters on mixture composition are connected with differences in selectivity of adsorption for various compositions. It is supposed that increased thermodynamic stability of a mixture of two incompatible polymers in the presence of solid is due to the transition of both polymers into adsorption and border layers.     

Adsorption of crystal violet dye from aqueous solution using mesoporous materials synthesized at room temperature

In this work, batch adsorption experiments are carried out for crystal violet dye using mesoporous MCM-41 synthesized at room temperature and sulfate modified MCM-41 prepared by impregnation method using H₂SO₄ as sulfatising agent. The surface characteristics, pore structure, bonding behavior and thermal degradation of both the MCM-41 samples are characterized by nitrogen adsorption/desorption isotherms, X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectroscopy and thermo gravimetric analysis (TGA). The adsorption isotherm, kinetics and thermodynamic parameters are investigated for crystal violet (CV) dye using the calcined and sulfated MCM-41. Results are analysed using Langmuir, Freundlich and Redlich-Peterson isotherm models. It is found that the Freundlich model is an appropriate model to explain the adsorption isotherm. The highest adsorption capacity achieved is found to be 3.4×10⁻⁴ mol g⁻¹ for the sulfated MCM-41. The percentage removal of crystal violet dye increases with increase in the pH for both the MCM-41 adsorbents. Kinetics of adsorption is found to follow the second-order rate equation. From the thermodynamic investigation, it is evident that the adsorption is exothermic in nature.     

Displacement processes on hydrophilic/hydrophobic surfaces in 1-propanol-water mixtures

Selective adsorption of 1-propanol-water mixtures was investigated on adsorbents of various surface character. The enthalpy of displacement of 1-propanol by water was studied on graphitized PRINTEX-80, K-60 silicagel, and n-alkylammonium vermiculites. The free enthalpy and entropy isotherms of displacement were derived. The adsorption between the silicate layers of hydrophobic vermiculites was followed by x-ray measurements, and thermodynamic functions were calculated for the structural changes in the adsorption layers. Formation of alcohol-water clusters on the surfaces plays an important role.     

The standard free energy of surfactant adsorption at air/water and oil/water interfaces: Theoretical vs. empirical approaches

The standard free energy of surfactant adsorption represents the work of transfer of a surfactant molecule from the bulk of solution to an infinitely diluted adsorption layer. This quantity can be determined by non-linear fits of surface-tension isotherms with the help of a theoretical model of adsorption. Here, the models of Frumkin, van der Waals and Helfand-Frisch-Lebowitz are applied, and the results are compared. Irrespective of the differences between these models, they give close values for the standard free energy. The results from the theoretical approach are compared with those from the most popular empirical approach. The latter gives values of the standard free energy, which are considerably different from the respective true values, with c.a. 10 kJ/mol for nonionic surfactants, and with c.a. 20 kJ/mol for ionic surfactants. These differences are due to contributions from interactions between the molecules in dense adsorption layers. It is concluded that the true values of the standard free energy can be determined with the help of an appropriate theoretical model. For the processed sets of data, the van der Waals model gives the best results, especially for the determination of the standard adsorption enthalpy and entropy from the temperature dependence of surface tension. The results can be useful for the development of a unified approach to the thermodynamic characterization of surfactants.     

Beta-casein bilayer adsorption at the solution/air interface: experimental evidences and theoretical description

Ellipsometric and surface pressure studies of beta-casein adsorption layers at the water/air interface support the idea of a model that assumes the formation of a second layer adjacent to the primary adsorption layer. A thermodynamic model describes the concentration behavior of the surface pressure and the adsorbed amount with one and the same set of model parameters over the entire concentration range studied.     

Molecular statistical calculations of the adsorption of proline and its hydroxy derivatives on graphitized thermal carbon black

The thermodynamic characteristics of adsorption of proline and its hydroxy derivatives on the surface of graphitized thermal carbon black (GTCB) were calculated. The arrangement of hydroxyl groups in the amino acid molecule was shown to influence their adsorption on GTCB. The influence of internal rotation angles in proline and its hydroxy derivative molecules on their adsorption on GTCB was studied.     

The influence of an intramolecular H-bond on the adsorption of sulfur-containing amino acids on graphitized thermal carbon black

The thermodynamic characteristics of adsorption of sulfur-containing amino acids and their derivatives on the surface of graphitized thermal carbon black were calculated by the molecular statistical method. The parameters of the atom-atom potential function of intermolecular interaction between the S atom in amino acids and the graphite C atom were determined. It was shown that an intramolecular H-bond influenced the adsorption of amino acids on the surface of graphitized thermal carbon black.     

Using solvents to control hydrogen adsorption on skeletal nickel

The results from adsorption-calorimetric studies of hydrogen adsorption on skeletal nickel are generalized. The thermodynamic characteristics of adsorbed hydrogen are calculated according to the model of an ideal surface with discrete heterogeneity. It is shown that the states of surface layers in solutions, formed upon hydrogen adsorption on skeletal and porous nickel, depend on the nature and composition of the solvent. Based on the resulting data, the possibility of using a solvent to control adsorption in a skeletal nickel-hydrogen system is confirmed.     

Interaction of isoniazid drug with the pristine and Ni-doped of (4, 4) armchair GaNNTs: a first principle study

In this research, the interaction of isoniazid drug (INH) with the pristine and Ni-doped Gallium nitride nanotubes (GaNNTs) is investigated by using density function theory. The adsorption energy, deformation energy, natural bond orbital (NBO), quantum parameters, molecular electrostatic potential (MEP) and thermodynamic parameters of all adsorption models are calculated from optimized structures. The values of adsorption energy, enthalpy and Gibbs free energy of all adsorption models are negative and all adsorption process are favorable in view of thermodynamic points. It is notable that Ni-doped decrease adsorption strength and it is not suitable for INH adsorption on the GaNNTs surface. The MEP, NBO and maximum amount of electronic charge ΔN results demonstrate that the negative potential are localized around adsorption position and the positive potential are localized around INH molecule. The calculated results indicate that the GaNNTs is a good candidate to making absorber and sensor for detecting INH drug.