Surfaces/interfaces, fluoropolymer

Extremely low interaction forces in monomolecular adsorption layers on liquids, Langmuir Blodgett films or in solid interfaces are the precondition for low energy surfaces. Perfluorocarbons or terminal fluorinated parts in amphiphilic molecules and fluoropolymers meet these demands. 

Fig. 3. Interfacial slip of an entangled melt at a non-adsorbing perfectly smooth surface, where the dots represent an organic surface (e.g., obtained by a fluoropolymer coating), which invites little chain adsorption. Lack of polymer adsorption produces an enormous shear rate jiat the entanglement-free interface between the dots and the first layer of (thick) chains. y-x=vs/a is much greater than the shear rate y present in the entangled bulk. This yields an extrapolation length b, which is too large in comparison to the chain dimensions to be depicted here...

New additives based on fluoropolymers have been introduced by DuPont and by Dyneon, to promote free flowing in polyolefins for extrusion and blown film production. They appear to act by coating the interior surface of the extrusion die with a microscopically thin non-stick film, which reduces friction at the resin/die interface and allows the extrusion compound to flow freely and more rapidly through the die opening. The non-stick properties also prevent accumulation of resin particles at the exit of the die, so eliminating the major cause of die build-up. The coating is continuously renewed by the additive through the extrusion process. 

The findings described in this chapter focus on fluorous copolyoxetane soft block surface modifiers. These copolyoxetane polyurethane modifiers bring about new surface properties due to surface concentration and/or phase separation of the soft block. An important theme concerns the effectiveness of a fluorous chaperone in conferring a surface function to a commodity or base polyurethane at 2 wt% or less. Thus, from one perspective, this chapter describes literally and figuratively the interface between specialty fluoropolymers and commodity polyurethanes. A significant applications niche would result if only a small fraction of the 55 billion polyurethane market (2016) [1] employed specialty fluorous modifiers. 

The objective of this work was the utilization of some recently developed techniques that may be of value in the characterization of the adhesive process between a titanium alloy and a variety of polylmide resin systems. The techniques utilized were electron spectroscopy for chemical analysis (ESCA), specular reflectance infrared spectroscopy, and scanning electron microscopy. Contact angles of various liquids on the titanium alloy were also measured. Specifically, the question arises to what extent are any of these techniques of value in the characterization of the interface and in the determination of interactions for the titanium 6-4/polyimide resin systems. Dwight and Riggs (5) successfully used ESCA, soft X-ray spectroscopy, contact angle hysteresis and electron microscopy to examine fluoropolymer surfaces. 

To determine the cause of GDL hydrophobicity loss and associated degradation mechanism(s), changes in the exposed carbon phases (graphite fibers and carbon particles), the fluoropolymer coating (PTFE, EEP, etc.) overlaying the carbon surfaces, and the bonding interface between the sintered fluoropolymer particles and carbon surfaces must be studied. All three of these aspects play at least some role in GDL and MPL hydrophobicity losses, and delineation of the relative importance of each surface or interface is a central theme of this work. The relative... 

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