Altering surface characteristics

The most widely used thermoplastic polymer is the ethylene—vinyl acetate copolymer, which is obtainable in a wide range of molecular weights as well as in a variety of compositions. Often flexibilizers or plasticizers are added in order to improve both the mechanical shock resistance and the thermal properties of the adhesive. Polybutenes, phthalates, and tricresyl phosphate have been used as plasticizers. Tackifying agents can also be added. Because hot-melt adhesives are frequendy ethylene-based, they are subject to oxidation if, as in a typical situation, the adhesive sits in an applicator for long periods before use. Thus, antioxidants such as hindered phenols are often used, as are fillers. Fillers are added to opacify or to modify the adhesive s flow characteristics, as well as to reduce cost. Wax is also a very important component. Wax alters surface characteristics by decreasing both the liquid adhesive s surface tension and its viscosity in the melt. Upon solidification, however, the wax acts to increase the strength of the adhesive. Both paraffin and microcrystalline wax are used (see Waxes). 

In this study, the tribological behaviour of the HTOZ-on-UHMWPE sliding pair for cementless knee joint prostheses was evaluated using unidirectional pin-on-disk tests and multidirectional pin-on-plate tests. Results were compared to the friction and wear properties of the TZP-on-UHMWPE sliding pair and the effects of the altered surface characteristics were examined. 

Under Irradiation. Under illumination, the surface characteristics can undergo dramatic changes, altering the nature of the adsorption sites. Thus, dark adsorption—desorption events are altered, and additional events arising from photoadsorption—photodesorption equiUbria take place. 

Water uptake causes a host of problems in drug products and the inactive and active ingredients contained in them. Moisture uptake has been shown to be an important factor in the decomposition of drug substances [1-8]. Moisture has also been shown to change surface properties of solids [9,10], alter flow characteristics of powders [11,12], and affect the compaction properties of solids [13]. This chapter discusses various mathematical models that can be used to describe moisture uptake by deliquescent materials. 

Adsorption of (bio)polymers occurs ubiquitously, and among the biopolymers, proteins are most surface active. Wherever and whenever a protein-containing (aqueous) solution is exposed to a (solid) surface, it results in the spontaneous accumulation of protein molecules at the solid-water interface, thereby altering the characteristics of the sorbent surface and, in most cases, of the protein molecules as well (Malmsten 2003). Therefore, the interaction between proteins and interfaces attracts attention from a wide variety of disciplines, ranging from environmental sciences to food processing and medical sciences. 

One can drastically alter the properties of polymers by suitable reactor design during forming of the polymer into its final shape. As examples, crystallinity, anisotropy, and surface characteristics can be tailored by ... 

The emulsifier is a surface-active agent which alters the characteristics of the water-oil interface. 

Adsorption and/or transformation of appropriately selected molecules can alter the surface characteristics of metal catalysts thereby affecting both activities and selectivities. 

An example is the reproducible formation of a strain variant in a thermophilic Bacillus [36,70]. The variant was first detected by its altered surface layer (S-layer) protein, which differed from the wild type in molecular mass and crystalline structure, as observed by electron microscopy. In continuous cultivation, the event of variant formation was accompanied by a characteristic pattern of changes in several process variables (Fig. 2), and the kinetics of variant formation could be followed by quantified SDS-PAG electrophoresis (Fig. 3). 

As cells start to adhere to the surface, the uniformity in its characteristics is disturbed. The altered spots on the surface, which consist of adhering cells, present new characteristics concerning the surface potential and Hamaker s constant, and consequently, the rate of cellular deposition is not uniform over the surface. The present model is based on the simplified assumption that the overall rate of deposition is the arithmetic sum of two contributions deposition on the bare surface and deposition on the altered surface. Each of them has its own time constant and depends also on the fraction of the area which is already covered, X. Therefore, by extending equation (19), the overall rate of deposition is given by ... 

Considerable improvement in wear resistance can be achieved when dissimilar metals are coupled, and this is especially true for steels coupled with silicon bronze and Stellite alloys. The wear data further suggest that improvement in wear resistance can be achieved by altering the surface characteristics, such as by surface treatment or by adding a coating.75... 

A characteristic of immobilized enzymes that is often ignored is the potential partitioning of ions and substrates and/or products due to electrostatic potentials or hydrophobic moments. This factor could be used to advantage, for example, if the optimal conditions for enzyme activity do not match those of the process stream. To use the example cited earlier, a succinamidopropyl surface was shown by electrostatic partitioning of ions and independent chemical analysis to have 96 ymol charged groups/g dry beads (25). Attachment of 2 ymol trypsin/g did not significantly alter this characteristic. 

Lee, V. H., and Carson, L. W. (1986), Ocular disposition of inulin from single and multiple doses of positively charged multilamellar liposomes Evidence for alterations in tear dynamics and ocular surface characteristics,/. Ocul. Pharmacol, 2, 353-364. 

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