Synthesis and tribological investigation of 4-vinyl guaiacol–based thioether derivatives as multifunctional additives and their interactions with the tribo surface using quantum chemical calculations

Novel 4-vinyl guaiacol based thioether derivatives were synthesized in a three-step reaction procedure by thiol-ene coupling as the key step. The synthesized compounds were characterised by spectroscopic techniques and evaluated for their tribological and antioxidant properties in two different base oils namely epoxy2-ethylhexyl esters of karanja fatty acids (EKE) and dioctyl sebacate (DOS). It was found that the synthesized products were exhibited superior antioxidant performance compared to butylated hydroxytoluene (BHT). All the three synthesized additives were improved the tribological properties of the base oil EKE and DOS. Dithio derivative at 0.75 wt% reduced the wear scar diameter by 36% and at 1 wt% improved the weld point by 33% of base oil EKE. Surface and elemental analysis result suggests that in the tribochemical process the synthesized thioether derivatives decompose and form an effective tribofilms on interacting surfaces. X-ray Photoelectron Spectroscopy (XPS) of the surface lubricated with base oil containing DMFD was evidence for the formation of tribofilm with FeS, FeSO₄ and Fe₂O₃. The antiwear behaviour of the additives was well correlated with quantum chemical calculations. Overall the dithio derivative is more effective as antiwear, extreme pressure and antioxidant bio lubricant additive than other thioether derivatives.     

High-pressure fluid phase equilibria: Experimental methods and systems investigated (1994–1999)

As a continuation of an earlier review, a compilation of systems for which high-pressure phase equilibrium data have been published between 1994 and 1999 is given. Vapor–liquid equilibria (VLE), liquid–liquid equilibria (LLE), vapor–liquid–liquid equilibria (VLLE), solid–liquid equilibria, solid–vapor equilibria, solid–vapor–liquid equilibria, critical points, the solubility of high-boiling substances in supercritical fluids and the solubility of gases in liquids (GLE) are included. For the systems investigated, the reference, the temperature and pressure range of the data, and the experimental method used for the measurements is given in 39 tables. Most of experimental data in the literature has been given for binary systems. Of the 824 binary systems, 350 have carbon dioxide as one of the components. Information on 135 pure components, 337 ternary systems and 120 multicomponent systems is given. Experimental methods for the investigation of high-pressure phase equilibria are classified and described.     

Partial miscibility in multicomponent polymer system

It has been shown, using the significant structure theory of liquids, that a lower critical solution temperature behavior as well as a upper critical solution temperature behavior can be expected for polymer–polymer systems and that a phase diagram of closed-loop-type in a polymer–polymer–solvent system can be possible. In this article the sublimation energy of a mixture was expressed as a quadratic form of segment surface fractions on pure components rather than that of mole fractions, and the effect of the segment surface fractions on critical compositions was explained. The calculated partial miscibilities were in good agreement with the experiment.     

Green Approaches to Field Nitrate Analysis: An Electroanalytical Perspective

The different approaches that have been taken in the development of analytical methods for the determination of nitrate within the field are reviewed. The emphasis has been placed on providing a critical appraisal of the chemistry that underpins current commercial systems and the need to remove the dependence on heavy metal and concentrated acid components. The search for more environmentally acceptable and user friendly systems has long been pursued and the present communication seeks to explore the recent development in portable testing technologies and how they might evolve in the future. In particular, the role of electrochemical techniques in the latter are investigated and their potential application compared and contrasted with the more traditional wet chemical detection strategies.     

Electron density topological properties are useful to assess the difference between hydrogen and dihydrogen complexes

B3LYP/6-31++G(d,p) and MP2/6-31++G(d,p) calculations for a series of hydrogen- and dihydrogen-bonded systems have been carried out in order to analyze the topology of the electron density and the energy densities at the respective energy-optimized bond critical points. Even though there are no significant differences when these properties are represented as a function of the dimerization energy, they can be separated into two well-defined sets if those properties are correlated with intermolecular distances. When analyzing the dependence of various properties with equilibrium bond lengths, the specific trends of dihydrogen bond systems consist of (a) lower electron density at the bond critical point, and (b) lower concentration/depletion of that density which can be translated in a different behavior for the Laplacian components. Furthermore, the sets of molecules form two different plots which allow for a valuable classification between hydrogen- and dihydrogen-bonded systems.     

Van der Waals model and equation of state of nitrobenzene-alkanes solutions near the critical consolute temperature

On the basis of the fluctuation theory of phase transitions a system close to the critical point is the ideal gas of order parameter fluctuations. An extended equation of state for binary solutions close to the critical consolute temperature has been proposed taking into account the properties of a real Van der Waals gas in this model. This equation has been used to analyze the temperature dependences of the concentrations of a series of nitrobenzene + alkane binary solutions in terms of different order parameters. It has been shown that the molar concentration of the solution should be used as an order parameter of the analyzed systems. It has been determined that the parameters of the extended equation of state are linear functions of (a) the number of carbon atoms in alkanes and (b) the compressibility factor of the solution components.     

Liquid mixtures of xenon with fluorinated species: xenon + sulfur hexafluoride

The vapor-liquid equilibrium of binary mixtures of xenon + SF6 has been measured at nine temperatures from 235.34 to 295.79 K and pressures up to 6.5 MPa. The mixture critical line is found to be continuous between the critical points of the pure components, and hence, the system can be classified as type I phase behavior in the scheme of van Konynenburg and Scott. The excess Gibbs free energies have been calculated, and the experimental results have been interpreted using the statistical associating fluid theory for potentials of variable range (SAFT-VR). Additionally, the SAFT-VR equation has been used to model other systems involving SF6 and alkanes, illustrating the predictability of the approach and further demonstrating the transferability of parameters between binary mixtures involving alkanes and xenon.     

Hydrodynamic instability in a three-component electrochemical system

The Raleigh-Benard thermodynamic instability in electrochemical systems containing three types of univalent ionic components is considered for the case of a galvanostatic electrolysis. Dimensionless parameters characterizing the stability threshold and their critical values are found. Influence of an indifferent-electrolyte type and its concentration on the system stability is analyzed. A procedure is suggested for calculating the critical current from the dimensionless parameters at fixed physical characteristics of the system and initial concentrations of components     

Biomaterials in total joint replacement

The current state of materials systems used in total hip replacement is presented in this paper. An overview of the various material systems used in total hip replacement reported in literature is presented in this paper. Metals, polymers, ceramics and composites are used in the design of the different components of hip replacement implants. The merits and demerits of these material systems are evaluated in the context of mechanical properties most suitable for total joint replacement such as a hip implant. Current research on advanced polymeric nanocomposites and biomimetic composites as novel materials systems for bone replacement is also discussed. This paper examines the current research in the materials science and the critical issues and challenges in these materials systems that require further research before application in biomedical industry.     

Micellar behavior of some amphiphilic block polyurethanes in aqueous/nonaqueous media

Amphiphilic polyether block polyurethanes based on Pluronic type macrodiol and polyethylene glycol as co-segment have been prepared. Their micellar behavior in N,N-dimethylformamide solution, aqueous solvent mixtures and with added inorganic salts or urea was investigated by employing fluorescence spectroscopy and tensiometry techniques. Increased values of the critical micelle concentration were found for the more soluble block copolyurethane. The structural components have a strong influence on micellar characteristics of the studied systems.     

Micellisation behaviour of mixtures of sodium dodecylsulphate and sodium lauroylsarcosinate in water

The critical micelle concentrations of binary mixtures of sodium dodecylsulphate (SDS) and sodium lauroylsarcosinate (SLAS) have been determined in water by conductivity measurements at different mole fractions for each of the components. The critical micelle concentrations were slightly lower than that predicted from ideal mixing theory indicating positive synergistic interactions in mixed micelle formation. The results of the mixed systems were analysed using the Regular Solution Theory and the approach based on the Gibbs–Duhem equation which allowed for the determination of the composition of the mixed micelle, the activity coefficients and the pair-wise molecular interaction parameter β. The β values were all negative at all mole fractions investigated, showing a slight deviation from ideality, with an average value of –0.27. The excess free energy of the mixed systems was also calculated and the values were all negative for the mixed systems studied, an indication that the mixed micelles are thermodynamically stable relative to the individual component. This thermodynamic parameter also exhibits symmetrical behaviour with respect to micellar composition suggestive of a regular solution behaviour of the mixed surfactant system.     

Phase separation in solutions of polyelectrolyte complexes: The decisive effect of a host polyion

Boundaries of the existence of insoluble polyelectrolyte complexes in solutions of nonequimolar mixtures of quaternary polyamines and polycarboxylates of various degrees of polymerization have been determined with turbidimetric titration. It has been shown that in salt-free media the position of critical points expressed as the ratio between the charge numbers of polymer components in a mixture depends on the chemical nature of the host polyelectrolyte (polycation or polyanion) but does not depend on either the nature of the guest polyelectrolyte or the degree of polymerization of mixture components. Upon addition of a low-molecular-mass polyelectrolyte, the heterogeneous region widens. The shorter the host polyelectrolyte relative to the guest polyelectrolyte, the more pronounced this effect. Based on the thermodynamic state of the systems under examination, an explanation of this effect is confirmed by the velocity sedimentation data.     

Membrane separation in flow injection systems

A critical review of membranes for on-line separations in flow-through dialysers is given. Historical perspectives are briefly outlined. The fundamental aspects of dialysis as the selective separation of species through a semi-permeable membrane are discussed. Work done on theoretical principles by a number of authors is described and a simplified model is given. The basic components, locations thereof and the influence of various parameters on dialysis efficiency are highlighted. The value of dialysis as sampling preparation system for chromatography and reactor systems is outlined and the suitability of dialyser/flow injection systems in dilution, preconcentration and multicomponent analysis is evaluated. The review is concluded with a brief look at the use of dialysis in proteinligand binding studies and microdialysis.     

Phase diagrams of metal systems with highly volatile components: Simulation and experiments

A critical analysis is performed of existing literature data on the melting diagrams of systems whose components are a low-volatile metal and a high-volatile component. Models for the р–Т phase diagrams of binary systems are developed, and characteristic isobaric sections (partial state diagrams) are presented that correspond to the experimental data for real systems.     

Vapor-liquid equilibrium in selected aromatic binary systems: m-xylene-hydrogen sulfide and mesitylene-hydrogen sulfide

Huang, S.S.-S. and Robinson, D.B., 1984. Vapor—liquid equilibrium in selected aromatic binary systems: m-xylene—hydrogen sulfide and mesitylene—hydrogen sulfide. Fluid Phase Equilibria, 17: 373–382.Vapor and liquid equilibrium phase compositions have been determined for the m-xylene-hydrogen sulfide and mesitylene—hydrogen sulfide binary systems at temperatures of 310.9, 352.6, 394.3 and 477.6 K and at several pressures from the vapor pressure of the less volatile component to the vapor pressure of hydrogen sulfide or to the critical pressure for the system, whichever was higher. The data have been used to calculate equilibrium ratios for each of the components in the binary systems. The results of Eakin and DeVaney (1974) for the mesitylene—hydrogen sulfide system at 310.9 and 477.6 K are also included for comparison.The data presented are useful in evaluating the properties of condensate reservoir fluids containing hydrogen sulfide and aromatic compounds.     

Mixed micelles of structurally related antidepressant drugs

 The composition of micelles in a binary mixture of the amphiphilic antidepressant drugs imipramine hydrochloride and clomipramine hydrochloride has been determined from an analysis of the variation of the critical micelle concentration from conductivity techniques as a function of solution composition. The equilibrium distribution of components between micelle and monomer phases was evaluated using a theoretical treatment based on excess thermo-dynamic quantities. The nonideality of mixing, expressed in terms of the interaction parameter β, was appreciable in systems containing low imipramine mole fractions, suggesting differences in the packing characteristics within micelles of these two drugs. Received: 7 July 1997 Accepted: 10 August 1997     

State diagrams of perfluorocarbon/solvent systems

The phase behaviour of perfluorocarbons in various solvents has been investigated. In case of perfluorohexadecane the state diagrams with trichlorotrifluoroethylene (CF₂Cl-CFCl₂) known also as Freon F113 and hexafluorobenzene (C₆F₆) as solvents could be determined in the total concentration range and also at temperatures far below the melting temperatures of the pure components. Beside the normal melt transitions in this binary systems some not yet known intramolecular phase transitions were found. From the course of the liquidus curve the Flory-Huggins interaction parameter of these systems could be determined. So statements about the quality of these solvents can be made. The investigated substances are suitable solvents for all perfluorocarbons which are actually available. The high molecular polytetrafluoroethylene (PTFE) cannot entirely be dissolved by these solvents, although traces are soluble. The reason is that the boiling points and critical temperatures of the solvents lie below the temperatures of the liquidus curve of the polymer of the considered system.     

Landau-type theory applied to mixtures of liquid crystals of opposite diamagnetic anisotropies

An application of Landau-type theory to interpret the orientation of mixed liquid crystals of opposite diamagnetic anisotropies has been made. Experimental NMR results on three systems containing benzene and acetonitrile as the probe molecules have been interpreted. The computed order parameters are in agreement with those obtained experimentally in several systems. The switching transition at a critical concentration and temperature and the coexistence of two types of orientations have been explained.     

Encapsulation,protection, and release of hydrophilic active components: Potential and limitations of colloidal delivery systems

There have been major advances in the development of edible colloidal delivery systems for hydrophobic bioactives in recent years. However, there are still many challenges associated with the development of effective delivery systems for hydrophilic bioactives. This review highlights the major challenges associated with developing colloidal delivery systems for hydrophilic bioactive components that can be utilized in foods, pharmaceuticals, and other products intended for oral ingestion. Special emphasis is given to the fundamental physicochemical phenomena associated with encapsulation, stabilization, and release of these bioactive components, such as solubility, partitioning, barriers, and mass transport processes. Delivery systems suitable for encapsulating hydrophilic bioactive components are then reviewed, including liposomes, multiple emulsions, solid fat particles, multiple emulsions, biopolymer particles, cubosomes, and biologically-derived systems. The advantages and limitations of each of these delivery systems are highlighted. This information should facilitate the rational selection of the most appropriate colloidal delivery systems for particular applications in the food and other industries.     

Thermotropic liquid crystalline glycolipids

Are the liquid crystalline properties of the materials of living systems important in biological structures, functions, diseases and treatments? There is a growing consciousness that the observed lyotropic, and often thermotropic liquid crystallinity, of many biological materials that possess key biological functionality might be more than curious coincidence. Rather, as the survival of living systems depends on the flexibility and reformability of structures, it seems more likely that it is the combination of softness and structure of the liquid-crystalline state that determines the functionality of biological materials. The richest sources of liquid crystals derived from living systems are found in cell membranes, of these glycolipids are a particularly important class of components. In this critical review, we will examine the relationship between chemical structure and the self-assembling and self-organising properties of glycolipids that ultimately lead to mesophase formation.