Secondary surface properties

Attachment of molecules to the surface of a solid filler in polymeric biocomposites affects a variety of innate properties, particularly those related to the surface of (he filler material. An overview of the surface modification techniques and how they alter specific filler properties is outlined in Table 3.3. The attachment of molecules affects the immediate physical and chemical composition of a surface, which can alter secondary surface properties related to surface interactions, such as wetting, zeta potential, suiface solution reactions including dissolution/degradation, as well as cellular interactions. These primary and secondary properties do not necessarily alter how the filler interacts with polymer binders in a biocomposite setting, but these properties can change the inherent overall properties of the resultant filler. 

Separation depends on the selection of a process in which the behaviour of the material is influenced to a very marked degree by some physical property. Thus, if a material is to be separated into various size fractions, a sieving method may be used because this process depends primarily on the size of the particles, though other physical properties such as the shape of the particles and their tendency to agglomerate may also be involved. Other methods of separation depend on the differences in the behaviour of the particles in a moving fluid, and in this case the size and the density of the particles are the most important factors and shape is of secondary importance. Other processes make use of differences in electrical or magnetic properties of the materials or in their surface properties. 

Another interesting modification of glass surfaces was introduced by Beier and Hoheisel.23 They synthesized a flexible, dendritic linker system that enables covalent immobilization of oligonucleotides and PNAs with high loading capacity in a controlled manner. This method facilitates the modulation of surface properties such as hydrophobicity and charge. The synthesis of the linker system involves two consecutive reactions an acylation of surface-bound amine groups with acid chloride (4-nitrophenyl-chloroformate or acryloylchloride) and subsequent reaction with an amine. A bis-amine results in a linker system, while a polyamine produces a dendritic structure (Fig. 14.3). Because polyamines possess primary and secondary amine... 

Surface Properties of lUDs. Most lUDs currently in use cause only minimum changes in the uterine endometrium (19). Excessive menstrual bleeding, intermenstrual spotting, and bleeding between menstrual periods have been noted as sources of annoyance, and they constitute a major reason for removal of lUDs. Such bleeding is probably secondary to local hyperemia, edema, pressure necrosis, and sometimes endometritis (20). After lUDs are inserted into the uterus, some patients complain of pain and low backache, but pain is a minor reason for discontinuing intrauterine contraception. 

Crystal shape, size, and density all affect the physical properties of the final solid fat matrix. Crystal growth, primary nucleation, and secondary nucleation in fat systems are influenced by many factors, including diffusion, molecular compatibility, TAG structure, nuclei composition and surface properties, number of nuclei, and processing conditions (temperamre and/or shear) (38, 39). It is during the crystallization process of fats that the template for the final physical properties of the material is created. 

The modification of zeolites mainly relies on secondary synthesis methods. The aim of modification is to reprocess the zeolites using suitable techniques to improve the properties and functions such as (1) acidity, (2) thermal and hydrothermal stability, (3) catalytic performance such as redox catalytic and coordination catalytic properties, etc., (4) channel structures, (5) surface properties and microporous frameworks and charge-balancing ions. Modification is also called secondary synthesis and can lead to new properties that cannot be achieved through direct synthesis. Let us consider the case of faujasite (FAU), the main component of the cracking catalyst, and its catalytic performance (represented by the catalytic activity K/K Std for n-hexane cracking). From Table 6.1 it is seen that the secondary synthesis affects the catalytic performance to a considerable degree. 

A variety of techniques and apparatus have been developed to study and measure surface properties of pol5uners and other materials. Three of the most useful techniques for such measurements are electron spectroscopy for chemical analysis (ESCA) also known as x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and ion scattering spectroscopy (ISS). Table 10.8 shows a comparison of the sampling depth of traditional methods and the new techniques. These analyses can focus on a much shallower thickness of the surface and virtually yield analyses of the outermost layers of a polymer article. Some of these methods and examples of their application to fluoroplastics are discussed below. 

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