Interfaces physico-chemical characteristics

Buffle, J., R. R. De Vitre, D. Perret, and G. G. Leppard. 1989. Physico-chemical characteristics of a colloidal iron phosphate species formed at an oxic-anoxic interface of a eutrophic lake. Geochimica et Cosmochimica Acta 53 399-408. 

Interfacial physico-chemical characteristics of food emulsifiers at fluid interfaces. 

In summary, the formation, stability, and mechanical properties of food dispersed systems depend on the way in which the constituent particles and macromolecules adsorb and interact at fluid-fluid interfaces (Figure 14.1). Thus, the optimum use of emulsifiers depends on our knowledge of their interfacial physico-chemical characteristics — such as surface activity, structure, stability, superficial viscosity, etc. — and the kinetics of film formation at fluid-fluid interfaces. 

An activated carbon in contact with a salt solution is a two-phase systan consisting of a solid phase that is the activated carbon surface and a liquid phase that is the salt solution containing varying amounts of different ionic and molecular species and their complexes. The interface between the two phases acts as an electrical double layer and determines the adsorption processes. The adsorption capacity of an activated carbon for metal cations from the aqueous solutions generally depends on the physico-chemical characteristics of the carbon surface, which include surface area, pore size distribution, electro-kinetic properties, the chemistry of the carbon surface, and the nature of the metal ions in the solution. Activated carbons are invariably associated with acidic and basic carbon-oxygen surface groups. 

From the obtained results it can be seen, that the difference in physico-chemical characteristics of the surfactants, and therefore different emulsifying properties, affect the size of the droplets. In all cases, the decrease in the amount of surfactant leads to larger droplets and a broader size distribution. Generally, the size of droplets was varied between 240 and 400 nm. Droplets with the smallest size were obtained with Span 80 regardless to its concentration indicating that the minimum droplet size for this system is reached. The addition of Tween 80 to Span 80 in a ratio 3 2 increases the stability of miniemulsions and improves the monodispersity of the droplets. In this case, both surfactants are involved in the process of the droplet stability. Hydrophobic molecules of Span 80 are oriented at the oil-droplet interface, whereas hydrophilic molecules of Tween 80 preferably stays in an aqueous phase, and... 

Studies of uranium transport through gel membranes reported by other researchers (58,59) revealed that a change in the physico-chemical characteristics of the plasticizer in the polymer matrix does not lead to an unambiguous relationship between the transmembrane flux and the extraction equilibrium at die interface. 

In the experiments on the Jt-A characteristics, it has been usually assumed that thermal equilibrium will be attained easily if the experiment is performed using a slow rate of compression of thin film at the interface. Measurements under thermal equilibrium are, of course, the necessary condition to obtain the physico-chemical properties of the individual "phase" of the lipid ensemble. 

The authors of this book have a scientific perspective that is strongly influenced by thermodynamics, and a conviction that the thermodynamic approach still has continuing relevance and importance. Our aim is to demonstrate how an understanding of the thermodynamic basis of the interactions of food biopolymers in aqueous solution and at interfaces can be used by food scientists and engineers to design colloidal systems with novel or improved characteristics — physico-chemical, nutritional, or sensory. The book is arranged in four parts. 

A very significant characteristic of colloidally dispersed particles is their large specific surface area, which may be as large as 10 to 10 cm cm . This value increases with decreasing size of colloidal particles. Due to their internal as well as external active surface, the colloidal particles affect many important characteristics of the soil, such as its ability to bind ions, water, gases and its tendency to swelling and adhesion. This results from the fact that the most important chemical, physico-chemical and physical processes occur on phase interfaces formed between the active surface of the colloid and liquid phase, i.e. soil water. 

This book presents coverage of the dynamics, preparation, application and physico-chemical properties of polymer solutions and colloids. It also covers the adsorption characteristics at and the adhesion properties of polymer surfaces. It is written by 23 contemporary experts within their field. Main headings include Structural ordering in polymer solutions Influence of surface Structure on polymer surface behaviour Advances in preparations and appUcations of polymeric microspheres Latex particle heterogeneity origins, detection, and consequences Electrokinetic behaviour of polymer colloids Interaction of polymer latices with other inorganic colloids Thermodynamic and kinetic aspects of bridging flocculation Metal complexation in polymer systems Adsorption of quaternary ammonium compounds art polymer surfaces Adsorption onto polytetrafluoroethylene from aqueous solutions Adsorption from polymer mixtures at the interface with solids Polymer adsorption at oxide surface Preparation of oxide-coated cellulose fibre The evaluation of acid-base properties of polymer surfaces by wettability measurements. Each chapter is well referenced. 

In this framework, in the specially designed mortars consisting of binders of either lime and metakaolin or natural hydraulic lime and fine aggregates of carbonate nature, nano-titania of anatase (90 per cent) and rutile (10 per cent) form has been added (4.5-6% w/w of binder). The aim was to study the effect of nano-titania in the hydration and carbonation of the above binders and to compare the physico-chemical properties of the nano-titania mortars with those mortars without nano-titania, used as reference. Thermal analysis (DTA-TG), infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed to investigate the evolution of carbonation, hydration and hydraulic compound formation during a six-month curing period. Furthermore, the stone-mortar interfaces, the adhesion resistance to external mechanical stress, relative to the physicochemical characteristics of the stone-mortar system and the role of the nano-titania as additive, were reported and are discussed in this chapter. 

Regarding the accelerated leaching potential of acidic precipitation, several aspects have to be considered, if the effective leaching flux is to be assessed they may be categorized as follows i) physico-chemical properties of the precipitation, ii) physico-chemical conditions of the interface precipitation-leaf surface, iii) biological characteristics of the leaves and in particular of their surfaces. Some of these aspects will be addressed up on later to point out their crucial role in determining the quantity and quality of the leachates. 

The test aims to determine whether the rate measured is written as a product of a function of only physico-chemical variables (temperature, concentrations, partial pressure, etc.) by a function of the morphological characteristics of a medium (surface-to-volume ratio, area of interfaces, volumes of the phases, etc.). 

The main characteristic of a composite system is its heterogeneity, expressed by the existence of the interface between components, which concentrates the most important transformations that are responsive for the obtaining of a material with superior properties. The adhesion, mechano-chemical and thermo-chemical reactions, etc., initiated in the interfacial (of transition) layers between layers, which occur by specific mechanisms, will determine or not the increase of physico-mechanical properties. 

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