Adhesives, collection surfaces

Some concentrating units use chemical solvents some use mechanical methods, sometimes coating a surface with a material for which the quarry molecules have a distinct affinity. One of the most convenient characteristics of explosive molecules is the way temperature affects their adhesion to surfaces. They adhere readily to cool surfaces but are easily released by a modest rise in temperature. Concentrating units often exploit this characteristic by alternately chilling and warming a collection surface. The surface is chilled while sampling and warmed for sensing. 

The charged particles migrate toward the collecting electrodes in the applied electric field by the Coulomb force. Upon contact with the collecting electrodes, the particles lose their charges and thus can be removed either by adhesion to the collecting surface or by... 

Overload. The tendency to overload the collection surface in the small-particle stages in an attempt to collect measurable sample masses has been observed [67]. Attempts to avoid this problem by the use of adhesive layers or fibrous filters on the impaction plates create other, unanticipated complications [51,57,70-73],... 

Particle bounce can be effectively controlled by coating an adhesives layer on the collection surface to keep collected particles from bouncing off the plates. Typical coating materials include Antifoam A, Hi-Vac silicone grease, Apiezon L, viscous oils, Vaseline, and glycerin. The typical thickness of the adhesive... 

If an elastomer is bonded to a substrate such as steel, it is usual for the bond to have small areas of imperfection where the adhesive or the chemical preparation of the surface is defective. Such areas are known as holidays. In high-pressure gas environments, these holidays form nucleation sites for the growth of half-bubbles or domes, under conditions where gas has been dissolved in the elastomer and the pressure has subsequently been reduced. Gas collecting at the imperfection at the interface will inflate the mbber layer, and domes will show as bumps on the surface of the mbber-coating layer—just as a paint layer bubbles up in domes when the wood underneath gives off moisrnre or solvents in particular areas. 

Wet adhesion phenomena represent a potentially fruitful area of research since so little is known. Some of the important questions are (1) How does one measure quantitatively the magnitude of the adhesion when the coating is wet (2) What is the governing principle that determines whether or not water collects at an organic coating/metal interface (3) What is the thickness of the water layer at the interface and what determines the thickness A recent paper (1.) correlates the wet adhesion properties of a phosphated surface with the crystalline nature of the zinc phosphate at the metal surface. 

Micromechanical experiments made so far can be roughly divided into two parts (i) design of special techniques to measure and evaluate separately different contributions in the net force, such as adhesion, friction, deformation, and (ii) imaging of various heterogeneous surfaces such as blends, composites and microphase separated structures by conventional SFM s to collect statistical information and understand the origin of the mechanical contrast. Many of the micromechanical experiments were discussed elsewhere [58, 67, 68, 381, 412-414]. Here we will focus on recent advances in analytical applications of the active probe SFM. 

A successful coating process requires that the encapsulation substance adheres sufficiently to the surface of the fluidized-bed material. Of course, the adhesion also affects the collection efficiency. In literature [4,8,9], the impact of adhesion to the coating process is taken into consideration by introduction of the adhesion coefficient X. Thus effective single particle collection efficiency cp may be formulated ... 

Fig. 3 Relationship between cell adhesion and water-air contact angle for a variety of polymer surfaces. The data have been collected and plotted by Saltzman, and are summarized in a book by Lanza et al. (Figure reproduced, with permission, from [33])...

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