Single-fiber characterization

Characterization of individual nanofibers is critical to understanding their physics because invariably it is the fiber characteristics that govern the properties of their mats. But, their minute dimensions makes this a daunting task. Nanofibers of particular interest, those with dimensions smaller than the wavelength of light, are especially difficult to isolate or test. It is not practical to extract fiber-level information by manipulation of test data generated from even the best-characterized fiber mats. Several innovative techniques for the direct assessment of mechanical properties of individual nanofibers are being developed and are discussed in this section. 

Cantilever techniques that use the AFM for these types of measurements avoid some of the problems associated with handling the nanofibers that are inherent in conventional tensile test methods. The approach is particularly 

TABLE 5.5 Change in tensile properties with alignment of single nanofibers of PLLA 

Take-Up Velocity (m/min) d (nm) Modulus (GPa) Tensile Strength (MPa) Extensibility (%) 

Aldiough AFM is used mainly as a profilometric imaging method and a probe technique to study the surface chemistry of materials, it can also serve as an invaluable piece of equipment in measuring mechanical properties of fibers and even single macromolecules. Some of the sample-handling issues inherently associated with conventional tensile techniques are 

---

S. Koljenovic, T.C.B. Schut, R. Wolthuis, et al., Raman spectroscopic characterization of porcine brain tissue using a single fiber-optic probe. Anal. Chem., 79, 557-564 (2007). 

Pitkethly, M.J. and Doble, J.B. (1990). Characterizing the fiber/matrix interface of carbon fiber-reinforced composites using a single fiber pullout test. Composites 21, 389-395. 

TMA has been employed in criminalistic studies to characterize a single fiber of untextured cellulose triacetate (34). The normal thermal expansion of the material at low temperatures is followed by contraction as water is lost above 100°C. The 5% expansion associated with the Ts at 180CC is followed by contraction before melting/decomposition, properties that are diagnostic of the material. Other major classes of fibers such as Orion, Acrilon, rayon, or cotton show no distinctive features up to 300°C. 

The use of IR microscopy is still fairly new but appears to be a technique that will find increasing applications in the future. Some of its current applications include identification of polymer contaminants, imperfections in polymer films, and individual layers of laminated polymer sheets identification of tiny samples of fibers, paint, and explosives in criminalistics characterization of single fibers in the textile industry and identification of contaminants on electronic components. 

Recently, a microbeam smaU-angle scattering technique (p-SAXS) has been used for the fist time to characterize activated carbon fibers [51]. This made possible to study a single fiber rather than a bundle, and provided information on the evolution of porosity with the bum-off degree for different activating agents. 

In the following section (Sect. 5) an overview will be given over thin SiC fibers characterized by small diameters of one to few tens of a micrometer and produced via the polymer route (in most cases). This kind of fiber is applied as rovings consisting of some hundred up to more than a thousand single filaments, so-called multifilament fibers, which may be woven and is predominantly used for reinforcing brittle matrices (ceramics and glasses). 

Filament A single, thread-like fiber or a number of these fibers put together. A variety of fiber characterized by extreme length, which permits their use in yarn with little or no twist and usually without the spinning operation required for fibers. As an example, it is a form of glass that has been drawn to a small diameter and extreme length. Most filaments are less than 0.005 in. (0.013 cm) in diameter. 

Mader and Freitag (14) used the single-fiber pullout method to characterize the interfacial shear strength of chemically coupled GFRP composites having the polymer matrix also modified by acrylic acid grafted polypropylene. By using... 

---