Fiber surfaces, electron

The following brief account is concerned with factors that affect the acces-sibihty of the OH groups of cellulose, since this is the determining factor for its dissolution, hence subsequent derivatization. Electron microscopy. X-ray scattering and porosimetry of cellulose fibers have clearly shown the presence of non-uniform pores, capillaries, voids and interstices in the fiber surface [25]. Consequently, the total surface area of cellulose fibers exceeds by far the geometrical outer surface. Pore structure determines the internal... 

The essential step is the efficient grinding and blending of raw materials. The final properties of cement strongly depend on its mineral composition so that raw composition and firing conditions are adjusted, depending on the type of cement to be produced. The microstructure of the steel fiber-cement paste interface was studied by scanning electron microscopy (SEM). The interfacial zone surrounding the fiber was found to be substantially different from the bulk paste further away from the fiber surface. The interfacial zone consisted of... 

Polymers of MMA, AAc, and MAA were grafted onto an ultrahigh molecular weight polyethylene (UHMWPE) fiber surface after pretreatment with electron beam irradiation [31]. Sundell et al. [32] pretreated a PE film with electron beams to facilitate the graft polymerization of vinyl benzylchloride onto the substrate. The inner surface of porous PE hollow fiber had also been modified by grafting of glycidyl methacrylate (GMA) polymer after electron beam irradiation [33]. 

Fig. 20.8. Neuromuscular junctions analyzed by transmission electron microscopy. (A) In wild-type mice, the motor nerve terminal (MN) is depressed into the muscle fiber surface. The terminal is polarized, with small clear vesicles near the presynaptic membrane and mitochondria in the more proximal portion of the terminal. The postsynaptic membrane has deep convolutions (junctional folds, JF) and the membrane near the tops of these folds is very electron dense because of the high density of acetylcholine receptors (arrowheads). (B) In some myasthenias where the nerve sprouts but remains in contact with the muscle, terminals with mitochondria and vesicles are observed in the absence of any postsynaptic specialization. Presumably these are sprouting terminals that have not established a functional connection. (C) Partial innervation of postsynaptic sites is evident as elaborate junctional folds in the muscle membrane with no overlying nerve terminal. In these examples, the interpretations were aided by light microscopy examination of other samples as described in Fig. 20.8 in parallel with electron microscopy. The mutation shown in (B, C) is an unpublished ENU-induced allele of agrin.

Figure 8.9 (a) Scanning electron micrograph of AS4 carbon fibers. The fiber diameter is Tixm (b) atom-force microscope picture showing the fiber surface roughness at an extremely fine scale (courtesy of R.K. Eby). 

The organic molecules or "probes used to investigate the dispersive surface energies of the fiber surfaces were a series of n-alkanes. The probes used to study the non dispersive forces were chosen based on their acidic or basic character as determined by Gutmann (8). Gutmann has practically defined basicity as the donor number, DN, or electron-donor capability in the Lewis sense. The donor scale is based on the value of the molar enthalpy for the reaction of the electron donor with a reference acceptor, SbCl. ... 

On the other hand, the acceptor number, AN, characterizes the acidity or electron acceptor jpability of a material. It is based on the NMR chemical shift of XP contained in (C H 3P0 when reacting with the acceptor. Each probe selected had a known AN and DN in order to quantitatively "sample" the respective surfaces involved in the composite. Three probes were used to study the fiber surfaces. Chloroform (CHC1,) was used as the acidic probe and had an AN equal to 23.1 and DN equal to 0. Tetrahydrofuran (THF) was used as the basic probe with AN equal to 8.0 and DN equal to 20.0. Ethyl acetate (EA) is considered to be amphoteric with an AN equal to 9.3 and DN equal to 17.1. For the fiber investigations CHCl, THF and EA proved to be satisfactory from a chromatographic standpoint. 

Scanning Electron Microscopy. The surface of an untreated nylon sample appeared smooth and uniform (Figure 10(A)). Similar results were observed for the control nylon samples exposed to 640 AFU of darkness conditions (Figure 10(B)). However, following 640 AFU of light exposure, the fiber surface of the control fabric showed some pitting and cavities (Figure 10(C)). 

Fig. 6. Scanning electron micrographs of the different stages of the interaction between Trichoderma harzianum and nylon fibers coated with purified ScleroUum rolfsii lectin. (A) A typical branching of the Trichoderma towards the fibers and contact of the branch tip with the fiber surface (bar=10pm) (B) subsequent elongation of the firmly attached tip along the fiber surface (bar= I pm) (C) Trichoderma hyphae coiled fibre, producing additional branches. The hyphal coils and branches adhere tightly to the fiber surface (bar = 10 pm). (From ref. [132], by permission from publisher.)...

Robbins and Bahl [6] have examined the effects of sunlight and ultraviolet radiation on disulfide sulfur in hair via electron spectroscopy for chemical analysis [6]. Both UV-A (320-400 nm) and UV-B (290-320 nm) radiation were shown to oxidize sulfur in hair. The primary oxidation occurs closer to the hair fiber surface, producing a steep gradient of oxidized to less oxidized hair from the outer circumference of the hair to the fiber core. 

Figure 5-2. Scanning electron micrographs of hair fiber surfaces illustrating sebaceous soil versus a fiber cleaned with sodium lauryl sulfate solution.

---