Fluid fibers

Fibers are very important objects in our life. Examples include natural silk spim by silkworms and spiders, synthetic fabrics such as nylon, polyesfer, or optical fibers for communication networks. Fibers can be drawn only from viscous fluids that harden during the pulling process. The hardening can be achieved either by cooling, such as in glass fibers or by loosing wafer, e.g.. 

The volume under such perturbation over a wavelength A = lidk can be written as  

The volume remains constant if Rj = -RJi. In this case, the surface area, S can be expressed as  

For a Newtonian fluid cylinder, there is only a surface contribution to the potential energy, W, for which — in case of the distortion discussed by Plateau — we get  

Columnar liquid crystalline phases of disc-shaped molecules are onedimensional fluids, and they can form free-standing fibers, as it was realized in the early 1980s.  

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Estapol, a blend of polyester/polyether resins NA, not available PBA, polybutyl acrylate PUV, polyurethane varnish PVAL, polyvinylalcohol SVF, silicone vacuum fluid fiber volume fraetion. 

Figure 2.5.8 (a) Fibrous crystals of sodium myristate (light micrograph) and (b) fluid fibers made of ephedrinium myristate (cryo-electron micrograph). 

Produce eitha- solid-fiber matrix or fluid fiber matrix, low molecular weight... 

Uses Emulsifier, lubricant for formulation of sol. oils, cutting fluids, fiber finishes, agric. formulations Regulatory EPA exempt... 

Orientation studies in Newtonian fluids, fiber attains horizontal configuration where as in viscoelastic media, it rotates to attain vertical orientation in free-settling motion... 

Wee, D., Seong, D. G., and Youn, J. R., 2004. Processing of microcellular nanocomposite foams by using a supercritical fluid. Fibers and Polymers 5 160-9. 

Figure 3.1 Schematic of small-molecular-weight organogelator networks, (a) Permanent crystalline linkage giving rise to solid fiber network, (b) Transient structural network of fluid fiber matrix formed by reverse micelles which enlarge cylindrically into an entanglement of dynamic lattice that immobilizes solvent to form a gel.

Fibrillated Fibers. Instead of extmding cellulose acetate into a continuous fiber, discrete, pulp-like agglomerates of fine, individual fibrils, called fibrets or fibrids, can be produced by rapid precipitation with an attenuating coagulation fluid. The individual fibers have diameters of 0.5 to 5.0 ]lni and lengths of 20 to 200 )Jm (Fig. 10). The surface area of the fibrillated fibers are about 20 m /g, about 60—80 times that of standard textile fibers. These materials are very hydrophilic an 85% moisture content has the appearance of a dry soHd (72). One appHcation is in a paper stmcture where their fine fiber size and branched stmcture allows mechanical entrapment of small particles. The fibers can also be loaded with particles to enhance some desired performance such as enhanced opacity for papers. When filled with metal particles it was suggested they be used as a radar screen in aerial warfare (73). 

Polyester fibers have exceUent resistance to soap, detergent, bleach, and other oxidiziag agents. PET fibers are generally iasoluble ia organic solvents, including cleaning fluids, but are soluble ia some phenoHc compounds, eg, (9-chlorophenol. 

Flow processes iaside the spinneret are governed by shear viscosity and shear rate. PET is a non-Newtonian elastic fluid. Spinning filament tension and molecular orientation depend on polymer temperature and viscosity, spinneret capillary diameter and length, spin speed, rate of filament cooling, inertia, and air drag (69,70). These variables combine to attenuate the fiber and orient and sometimes crystallize the molecular chains (71). 

FLUOROTRIAZINES Riag-fluoriaated triaziaes are used ia fiber-reactive dyes. Perfluoroalkyl triaziaes are offered commercially as mass spectral markers and have been iatensively evaluated for elastomer and hydraulic fluid appHcations. Physical properties of representative fluorotriaziaes are listed ia Table 13. Toxicity data are available. For cyanuric fluoride, LD g =3.1 ppm for 4 h (iahalatioa, rat) and 160 mg/kg (skin, rabbit) (127). 

Searching a crime scene is a complex process (25), involving poHce, crime scene technicians, and forensic scientists. The procedure requires careful documentation, collection, and preservation of the evidence. Trace evidence (26) in criminal investigations typically consists of hairs (27,28) both natural and synthetic fibers (qv) (29,30), fabrics glass (qv) (31,32) plastics (33) sod plant material budding material such as cement (qv), paint (qv), stucco, wood (qv), etc (34), flammable fluid residues (35,36), eg, in arson investigations explosive residues, eg, from bombings (37,38) (see Explosives and propellents), and so on. 

Surface Tension. Interfacial surface tension between fluid and filter media is considered to play a role in the adhesion of blood cells to synthetic fibers. Interfacial tension is a result of the interaction between the surface tension of the fluid and the filter media. Direct experimental evidence has shown that varying this interfacial tension influences the adhesion of blood cells to biomaterials. The viscosity of the blood product is important in the shear forces of the fluid to the attached cells viscosity of a red cell concentrate is at least 500 times that of a platelet concentrate. This has a considerable effect on the shear and flow rates through the filter. The surface stickiness plays a role in the critical shear force for detachment of adhered blood cells. 

HoUow-fiber membranes, therefore, may be divided into two categories (/) open hoUow fibers (Eigs. 2a and 2b) where a gas or Hquid permeates across the fiber waU, while flow of the lumen medium gas or Hquid is not restricted, and (2) loaded fibers (Eig. 2c) where the lumen is flUed with an immobilized soHd, Hquid, or gas. The open hoUow fiber has two basic geometries the first is a loop of fiber or a closed bundle contained ia a pressurized vessel. Gas or Hquid passes through the smaU diameter fiber waU and exits via the open fiber ends. In the second type, fibers are open at both ends. The feed fluid can be circulated on the inside or outside of the relatively large diameter fibers. These so-caUed large capiUary (spaghetti) fibers are used in microfUtration, ultrafUtration (qv), pervaporation, and some low pressure (<1035 kPa = 10 atm) gas appHcations. 

Fiber dimensions have been studied for hemodialysis. When blood is circulated through the fiber lumen (m vivo), a significant reduction in apparent blood viscosity may occur if the flow-path diameter is below 100 p.m (11). Therefore, current dialy2ers use fibers with internal diameters of 180—250 p.m to obtain the maximum surface area within a safe range (see Dialysis). The relationship between the fiber cross section and the blood cells is shown in Figure 5. In many industrial appUcations, where the bore fluid is dialy2ed under elevated pressure (>200 kPa or 2 atm), fibers may burst at points of imperfection. Failure of this nature is especially likely for asymmetric fibers that display a large number of macro voids within the walls. 

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