Chemical-physical interaction

Pectins are longchain macromolecules. In aqueous solutions they form more or less stiff rods or coils, depending on their degree of branching and linking as well as their molecular weight. In addition interparticular or intermolecular physical-chemical interactions like Van-der-Waals forces, ionic interactions or hydrogen bonds influence the active volume of the molecule, the stiffness and the viscosity. 

Another important type of physical chemical interaction that may alter absorption is that of drug binding or adsorption onto the surface of another material. As with complexation and micellarization, adsorption will reduce the effective concentration gradient between gut fluids and the bloodstream, which is the driving force for passive absorption. While adsorption frequently reduces the rate of absorption, the interaction is often readily reversible and will not affect the extent of absorption. A major exception is adsorption onto charcoal, which in many cases appears to be irreversible, at least during the time of residence within the GIT. As a result, charcoal often reduces the extent of drug absorption. Indeed, this fact... 

Biosorption is a general phenomenon that can occur in either dead or living biomass. However, this process usually refers to a passive uptake mechanism carried out by nonviable microorganisms (dead yeasts). The biosorption process involves physical-chemical interactions between the yeast surface and the azo dyes, as well as possible passive diffusion inside dead cells. 

A Mechanistic Understanding of Bioavailability Physical-Chemical Interactions. Pellston, Michigan, 17 to 22 Aug 1992. Published as a SETAC Special Publication by Lewis Publishers, 1994. 

Recent experiments have shown that the non-specific, physical chemical interactions between small hydrophobic, water-insoluble molecules and the hydrocarbon chains of lipid membranes are important determinants of the rate at which these molecules enter cells and are metabolized (3.34). Cholesterol has the capability of modifying these interactions and also increases the affinity of vesicle surfaces for amphiphillic molecules (4) separating the lipid polar groups (35). 

The interaction between the counter-ion and the surface is not only physical chemical interaction may occur as well. Chemical interaction is not only influenced by the valence and size of the ions, but also by the chemical composition of the surface and the ion. This type of adsorption is called specific adsorption. 

Physical-Chemical Interactions Determining Particle Adhesion... 

It should be noted that this chapter has been limited to physical-chemical interactions between food macromolecules in model systems. The main reason is that in food systems, chemical protein-polysaccharide and protein-polyphenols interactions have not yet been sufficiently studied. A new trend in this area is covalent protein-polysaccharide hybrids (conjugates natural and synthetic) that are of great interest as functional additives and food ingredients... 

Taking into account physical-chemical interaction of alloying elements with A1 as well as with Sc, the following classification of alloying elements which includes 5 groups was proposed [7] ... 

A physical-chemical interaction through adsorption of the gas on the solid surface, which affects the resistance to breakage, attrition and abrasion. Thus the properties of the suspending gas have to be taken into account, or controlled, not just in the obvious applications where gas clearly plays a part like fluidization or pneumatic conveying but also in the not-so-obvious ones like grinding and discharge of powders from hoppers. 

The superficial phenomena of physical-chemical interaction of the liquid and solid phases and formation of the composite material microstructures proceed most intensively during rubber binder preparation. Therefore, the conditions under which the binder is prepared exert essential influence on the properties of composites. Uniformity of the prepared binder is defined by the intensity of the agitation process and depends on the process s speed and duration. 

Improvements of the physical properties include modifications to change the gross physical characteristics, such as texture, and to change the physical chemical interactions important to functional properties in cookery, such as foaming and whipping capabilities. Physical chemical laboratory methods and standards for assessing physical characteristics, unfortunately, are not well developed at this time (49). 

In order that the particles either repel or attract each other, they must be brought into sufficiently close encounters. This may be a consequence of Brownian motion or hydrodynamic transport. However, the solution stability is determined by the interactions during these encounters. We therefore first examine the nature of the physical-chemical interactions, followed by the transport phenomena that can bring about the encounters. Subsequent to these discussions we shall consider the combined effects of transport and surface interactions. 

Chemical reactions initiated in gas discharges and plasmas, in particular in low-temperature, nonequilibrium plasmas, have become indispensable for the advancement of many key technologies in the past 10-15 years (see, e.g Becker et al., 1992 Garscadden, 1992). The plasma-assisted etching of microstructures and the deposition of high-quality thin films with well-defined properties have become crucial steps in the fabrication of microelectronic devices with typical feature sizes of less than 0.5 /rm. The manufacture of state-of-the-art microchips now involves hundreds of process steps, most of them serial, to yield circuits with millions of discrete elements and interconnections in an area of a single square centimeter (Garscadden, 1992). Each step is a physical-chemical interaction that must be controlled. More than one-third of the process steps rely on plasma... 

The swelling phenomenon in the rehumidification path should be distinguished from that observed under a perfect saturation case. The previous one is mainly due to variations in suction pressure, and the second one is due to the reorganisation of clay minerals resulting from the complex physical-chemical interactions (Ghoreychi 1997). 

Plastic containing Cl is in its essence a composite material. Inhibitors and special additives, which also have a function regulating physical-chemical interactions between the polymer and inhibitor, are spread within the polymer component of the composite at a given degree of cohesion with the polymer. Compatibility of the Cl with the polymer binder should not be too high as the inhibitor would not be released from the composite. In the case of low compatibility the release rate of the inhibitor will be too high and the life of the plastic as an inhibitor carrier would be unacceptably low. 

Metal corrosion is a physical-chemical interaction between a metal and a medium leading to degradation of service properties of the metal and the medium or a technical system they constitute. A chemical reaction between a metal and a medium, or their components, at their interface lies at the base of metal corrosion. 

Transfer of aqua electrolytes in polymers has characteristics [22] that distinguish it from the transfer of other low-molecular-weight matter. The presence of water in the medium sorbed may result in formation of aqua associates and electrolyte in the polymer. Depending on the amount of sorbed water, the polymers are subdivided into three groups (i) hydrophobic, i.e. slightly swelling in water (water concentration in the polymer below 0.5%), (ii) mildly hydrophilic (water concentration 0.5-10%), (iii) hydrophilic (water concentration above 10%). This subdivision is very conventional since the permeability mechanism depends not only on water concentration in the polymer but on the nature of their physical-chemical interactions with electrolyte ions and macromolecular active centers as well [23]. 

As long as mechanical properties of CM are governed chiefly by the mechanical and physical-chemical interactions of the ingredients at the interfaces, it can be regulated by changing the conditions of these interactions. Compatihility can be regulated by the following methods ... 

P, M and L are the pol3mier, metal and lubricating medium P, 1/, Cl are the frictional factors, i.e. pressure, velocity and the presence of Cl in the friction zone TCRP are the tribochemical reaction products. The latter can fulfill the function of wear inhibitors (WI) during physical-chemical interactions with the inhibitor on the metal friction surface or form neutral wear products (NWP) affecting neither corrosion nor friction. The task is how to transform these products into useful ones during friction. 

Thus, FO are acting as adhesion promoters and corrosion inhibitors, whose mechanism can be explained as follows. In the course of thermal molding of powder polymer coatings filled by FO the oxides enter into physical-chemical interactions with the polymer melt. As a result, the oxides are reduced in the surface layer of the particles to metals. This fact is confirmed by... 

In its true sense, any component of a tribosystem promoting suppression of unfavorable tribochemical processes in the friction zone, irrespective of whether it was impregnated or formed internally, can be related to WI [34]. WI can be formed both as a result of physical-chemical interactions of polymers and metals, or physical fields and energy effects on a part or friction joint. This can be, e.g. thermochemical or radiation-thermal treatment, ion implantation, superposition of electrical and magnetic fields, shifts of electrode potentials, passage of electrical current, etc. 

As suggested by the above paragraph, other types of phenomena affect the previously described transport mechanisms of the contaminants toward the electrodes. These are the physical-chemical interactions, both between different compounds in the aqueous phase and between these aqueous species and the sohd phases of the soil system. Some of these interactions are precipitation, acid-base, complex formation and redox reactions, adsorption, and ion exchange and surface complexation reactions. 

Natural polymers such as starch and protein are potential alternatives to petroleum-based polymers for a number of applications. Unfortunately, their high solubility in water limit their use for water sensitive applications. To solve this problem thermoplastic starches have been laminated using water-resistant, biodegradable polymers. For example, polylactic acid and P(3HB-co-3HV) were utilised as the outer layers of the stratified polyester/PWS (plasticized wheat starch)/polyester film strucmre in order to improve the mechanical properties and water resistance of PWS which made it useful for food packaging and disposable articles [65]. Moreover, improved physic-chemical interactions between P(3HB-CO-3HV) and wheat straw fibres were achieved with high temperature treatment. It resulted in increased P(3HB-co-3HV) crystallization, increased Young s moduli and lowered values of stress and strain to break than the neat matrix of P(3HB-co-3HV). There was no difference in the biodegradation rate of the polymer [66]. 

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