Contact elastomeric

Compatibility and Corrosion. Gas turbine fuels must be compatible with the elastomeric materials and metals used in fuel systems. Elastomers are used for O-rings, seals, and hoses as well as pump parts and tank coatings. Polymers tend to swell and to improve their sealing abiUty when in contact with aromatics, but degree of swell is a function of both elastomer-type and aromatic molecular weight. Rubbers can also be attacked by peroxides that form in fuels that are not properly inhibited (see Elastomers, synthetic Rubber, natural). 

Proper compounding and formulation are critical to the successful uses of most elastomeric materials. The suppHers should be contacted for information. 

Fluoiocaibon elastomeis aie synthetic, noncrystaUine polymers that exhibit elastomeric properties when cross-linked. They are designed for demanding service appHcations in hostile environments characterized by broad temperature ranges and/or contact with chemicals, oils, or fuels. 

However, conductive elastomers have only ca <10 of the conductivity of soHd metals. Also, the contact resistance of elastomers changes with time when they are compressed. Therefore, elastomers are not used where significant currents must be carried or when low or stable resistance is required. Typical apphcations, which require a high density of contacts and easy disassembly for servicing, include connection between Hquid crystal display panels (see Liquid crystals) and between printed circuit boards in watches. Another type of elastomeric contact has a nonconducting silicone mbber core around which is wrapped metalized contacts that are separated from each other by insulating areas (25). A newer material has closely spaced strings of small spherical metal particles in contact, or fine soHd wires, which are oriented in the elastomer so that electrical conduction occurs only in the Z direction (26). 

V-clamp joints (Fig. 10-140) are attached to the pipe by butt-weld or expanded joints. Theoretically, there is only one relative position of the parts in which the conical surfaces of the clamp are completely in contac t with the conical surfaces of the stub ends. In actual practice, there is considerable flexing of the stub ends and the clamp also complete contact is not required. This permits use of elastomeric gaskets... 

The finite size effects in the contact between a spherical lens of polyurethane and a soft flat sheet of crosslinked polyfdimethyl siloxane) (PDMS) has been addressed by Falsafi et al. [37]. They showed that for deformations corresponding to contact diameters larger than the sheet thickness, the compliance of the system was affected by the glass substrate supporting the soft sheet. In order to minimize the finite size effects in the adhesion measurement of small elastomeric lenses, Falsafi et al. [38] and Deruelle et al. [39] used relatively thick elastic sheets to support their samples. 

Mangipudi et al. [63,88] reported some initial measurements of adhesion strength between semicrystalline PE surfaces. These measurements were done using the SFA as a function of contact time. Interestingly, these data (see Fig. 22) show that the normalized pull-off energy, a measure of intrinsic adhesion strength is increased with time of contact. They suggested the amorphous domains in PE could interdiffuse across the interface and thereby increase the adhesion of the interface. Falsafi et al. [37] also used the JKR technique to study the effect of composition on the adhesion of elastomeric acrylic pressure-sensitive adhesives. The model PSA they used was a crosslinked network of random copolymers of acrylates and acrylic acid, with an acrylic acid content between 2 and 10%. 

The study of acid-base interaction is an important branch of interfacial science. These interactions are widely exploited in several practical applications such as adhesion and adsorption processes. Most of the current studies in this area are based on calorimetric studies or wetting measurements or peel test measurements. While these studies have been instrumental in the understanding of these interfacial interactions, to a certain extent the interpretation of the results of these studies has been largely empirical. The recent advances in the theory and experiments of contact mechanics could be potentially employed to better understand and measure the molecular level acid-base interactions. One of the following two experimental procedures could be utilized (1) Polymers with different levels of acidic and basic chemical constitution can be coated on to elastomeric caps, as described in Section 4.2.1, and the adhesion between these layers can be measured using the JKR technique and Eqs. 11 or 30 as appropriate. For example, poly(p-amino styrene) and poly(p-hydroxy carbonyl styrene) can be coated on to PDMS-ox, and be used as acidic and basic surfaces, respectively, to study the acid-base interactions. (2) Another approach is to graft acidic or basic macromers onto a weakly crosslinked polyisoprene or polybutadiene elastomeric networks, and use these elastomeric networks in the JKR studies as described in Section 4.2.1. 

Some rubber base adhesives need vulcanization to produce adequate ultimate strength. The adhesion is mainly due to chemical interactions at the interface. Other rubber base adhesives (contact adhesives) do not necessarily need vulcanization but rather adequate formulation to produce adhesive joints, mainly with porous substrates. In this case, the mechanism of diffusion dominates their adhesion properties. Consequently, the properties of the elastomeric adhesives depend on both the variety of intrinsic properties in natural and synthetic elastomers, and the modifying additives which may be incorporated into the adhesive formulation (tackifiers, reinforcing resins, fillers, plasticizers, curing agents, etc.). 

Such polymers are as hydrophobic as poly(tetrafluoroethylene) (Teflon), with water contact angles in the range of 107°. But, unlike Teflon, polyphosphazenes of this type are easy to fabricate, are flexible or elastomeric, and can be used as coatings for other materials. ... 

An elastomeric closure is a packaging component that is, or may be, in direct contact with a drug product. Elastomer selection for parenteral packaging principally involves consideration of chemical, physical, and biological properties, with emphasis on the stability profile of the drug/container system. Typical elastomeric closure compositions are listed in Tables 1 1. Although certain packaging applications frequently call to mind certain elastomer types, it is not feasible to prescribe specific... 

Ferguson, G. S. Chaudhury, M. K. Sigal, G. B. Whitesides, G. M. 1991. Contact adhesion of thin gold-films on elastomeric supports—Cold welding under ambient conditions. Science 253 776-778. 

Antwerp, Belgium, 22nd-23rd Nov. 1999, paper 17 ELASTOMERIC COMPOUNDS FOR CONTACT WITH FOOD... 

Many published results on electronic transport properties of organic materials, where metal contacts are usually made by evaporation of metals, do not describe the quality of the organic/metal interface, and some exotic observed features may perhaps be ascribed to extrinsic effects such as metal diffusion. The relatively simple contact lamination technique may become an alternative, since it provides a means for establishing electrical contacts without the potential disruption of the organic material associated with metal evaporation. The method consists in bringing the organic layer into mechanical contact with an elastomeric element coated with a thin metal film, which can also be patterned. The contacts are robust and reversible... 

The compatibility of LP with materials that they may contact can create hazard problems. Hollister (Ref 19) reviews the compatibility of several LP systems in contact with elastomeric materials... 

The irradiated components can be placed adjacent to sulfur-containing unvulcanized elastomeric compounds and, when necessary, coated with suitable adhesive between the contacting surfaces to ensure good bond after final cure of the tire. ... 

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