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New developments in surface analysis technologies allow surface characterizations of the order of microns to be achieved. More recently, with the improvement of vacuum techniques and photoelectricity electrons emitted from matter after the absorption of energy from electromagnetic radiation , more sensitive surface characterization at the angstrom and nanometer levels has become possible by using techniques such as SPM, XPS, etc. As it is believed that fiber surface behavior is determined by a surface layer of less than 10 nm thickness, it is clearly important to differentiate the properties of this thin layer from the bulk properties.
In addition, techniques such as SEM, SPM and wettability analysis provide information about a range of surface properties of fibers important to their specific applications. SEM makes use of a primary beam of electrons that interact with the specimen of interest, in a vacuum environment, resulting in the emission of secondary electrons, backscattered electrons, photons, X-rays, excitation of phonons and diffraction under specific conditions.
The secondary electrons ejected from the specimen surface are collected and displayed to provide a high-resolution micrograph. The resolution and depth of field of the image are determined by a number of factors, such as beam current, beam energy, interaction volume and the final spot size, which can be adjusted as illustrated in Fig. SEM scans a surface in the X—Y plane with a suitable detector and records the topography of the surface under observation with a resolution of the order of 1—2 nm and a magnification range from to Information on structures, 28 Surface modification of textiles Electron gun Condenser lenses Scan coils Objective lens Specimen stub X-ray detector Secondary electron detector 2.
The utilization of SEM involves sample preparation, imaging and image analysis. SEM sample preparation requires fixation hardening the specimen with a chemical or chemicals followed by drying, attachment to a metallic stub as sample holder and then coating with a metal prior to imaging. The thin metallic coating, usually deposited by sputter coating, is typically 10—30 nm in thickness.
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Common conductive metals used include gold, platinum and gold—palladium alloy. It should be noted that the drying and metal coating processes used in the preparation of textiles might alter surface morphology, particularly fine surface features Wei et al. Structural characterization of textiles by scanning electron microscopy Textile materials are usually designed and manufactured into various forms with different types of fibers to meet special requirements for a wide range of Textile surface characterization methods 29 a b c 2. The structures of textiles are affected not only by fibers but also by the processing techniques involved.
An understanding of the effects of fibers and processes on the properties of the finished materials is of importance in manufacturing textiles with the desired properties. The use of SEM techniques gives researchers and engineers insights into the fundamental understanding of the phenomena that have occurred. An example of the use of SEM in the structural characterization of textiles is presented in Fig. The aligned nanofibers were formed by controlling the electrospinning conditions and collecting set-up, as shown in Fig.
Aligned or oriented nanofibers have great potential in such applications as tissue engineering, high-strength nanocomposites, electronic and sensing applications. Porous nanofibers were also produced by using different solvents, controlling electrospinning conditions or environmental conditions. The porous nanofibers produced had much higher surface areas than conventional 30 Surface modification of textiles a b c d 2. The combination of porosity with flexibility in the porous nanofibers provides great potential for applications in many industries. Nanofibers containing a pore size gradient, as displayed in Fig.
SEM observations on the structural characteristics of the electrospun nanofibers demonstrate the applications of SEM in textile imaging. Surface characterization of textiles by scanning electron microscopy Textile surfaces have various properties, derived from the origin of the fibers and the way in which they are assembled. The surface characteristics of textiles are closely related to the phenomena of friction, wetting, dyeing, biocompatibility and other performance properties. Based on the understanding of surface properties, novel textiles and their applications may be created or engineered.
SEM has been increasingly applied to examine textile surfaces at different levels. Figure 2. The series of SEM images in Fig. The SEM image in Fig. In addition, the coarser nanofibers caused decreases in the pore sizes.
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Carbonization significantly altered the surface characteristics of the nanofibers, as displayed in Fig. The ZnO coating formed larger clusters on the surface of the carbon nanofibers after carbonization.
The SEM observation clearly reveals the evolution of the surface morphology of the nanofibers. Interface characterization of textiles by scanning electron microscopy Textile materials are always designed and manufactured to meet the demands of various applications. In these applications of textiles, interfaces are usually formed between two phases of either the same or different materials.
The goal of textile interface studies is to understand the interfacial behaviors of textile materials and their resulting influence on material processes in order to facilitate the manufacture of technological textiles with optimized properties. The interfacial behaviors of textile materials are always associated with phenomena, such as friction, adhesion and adsorption. The SEM images in Fig. As shown in Fig. The ZnO coating was performed by magnetron sputter coating and cracks in the coating layer on the fiber surface reveal the poor bonding between the coating layer and the fiber.
SEM provides a useful tool for observing the interfaces formed between textiles and other materials. Other characterization of textiles by scanning electron microscopy SEM has been consistently improved to meet the new demands for obtaining high resolution images of various structures of textile materials. The new generation of scanning electron microscopes provides compositional contrast observation using backscattered electrons.
A clear contrast was obtained for blend polymers by employing the secondary electron image under a low accelerating voltage, but this also provided increased detail such as the lamellar structure Goizueta et al. Through the use of backscattered electrons BSEs and a relatively low accelerating voltage on the scanning electron microscopy, the surface finish that is required to enable characterization has been found to be less demanding than that needed for secondary electrons. The identification of crystallographic phases in the scanning electron microscope has been limited by the lack of a simple way to obtain electron diffraction data of an unknown subject while examining the microstructures of a sample.
With the development of charge-coupled device CCD -based detectors, electron backscattered diffraction EBSD patterns can be easily collected. SEM is a high-resolution imaging technique providing topographical and structural information in plan view or in cross-section. In the past, when functionally independent SEM and EDX techniques were used for analysis, equipment operation was complicated. A schematic presentation of the transmission electron microscope is shown in Fig. Using an electron gun, an electron beam is formed, which is accelerated by an electric field formed by a voltage difference of, typically, kV.
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Electrons are scattered by the sample, situated in the object plane of the objective lens. Electrons scattered in the same direction are focused in the back focal plane, and, as a result, a diffraction pattern is formed there. Electrons coming from the same point on the object are focused in Textile surface characterization methods 33 Electron gun Condenser lens Specimen grid Objective lens Projective lens Phosphor screen 2. The image of a thin sample is formed by the electrons that pass the film without diffraction.
Materials for TEM observations must be specifically prepared to thicknesses that allow electrons to be transmitted through the specimen. Samples for TEM in the form of films mounted on fine-meshed grids are required to be very thin. Moreover, the sample has to withstand the vacuum condition inside the transmission electron microscope.
TEM sample preparation involves fixation, processing, embedding and sectioning Radnoczi and Pecz, Embedding media used include methacrylates, polyester and acrylic resins, although epoxy resins are now commonly used.
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Specimens are typically sectioned using a microtome and need to be very thin since electrons with an accelerating voltage of kV will not penetrate specimens more than nm thick. It should however be noted that the embedding and sectioning processes used in the preparation of some polymeric materials may alter the materials themselves.
The sample must also be able to withstand the electron beam. Surface and interface characterization of textiles by transmission electron microscopy The main use of the TEM technique is to examine fiber surface morphology, crosssections and interfacial phenomena in submicroscopic detail. Fine morphology with high resolution can be viewed after specimen preparation. The images in Fig. A PVAc nanofiber and a barrel-shaped bead were observed, indicating the formation mechanism of jet stretching in the electropsinning.
In another example, TEM observation also confirms the formation of composite nanofibers and the distribution of the organically modified montmorillonite O-MMT nanoparticles in a polyamide 6 PA6 nanofiber matrix, as presented in Fig. It can be clearly observed that the O-MMT formed a dark line in the nanofiber.
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The TEM images also clearly reveal that the nanoclays were almost aligned along the nanofiber axis Li et al. TEM has been increasingly used in the observation of nanostructured textiles. Crystallographic characterization of textiles by transmission electron microscopy In high-resolution transmission electron microscopy HRTEM , it is also possible to produce an image from electrons deflected by a particular crystal plane. By either moving the aperture to the position of the deflected electrons, or tilting the electron beam so that the deflected electrons pass through the centered aperture, an image can be formed of only deflected electrons, known as a dark field DF image.
Textile surface characterization methods 35 In DF images, the direct beam is blocked by the aperture while one or more diffracted beams are allowed to pass the objective aperture. Information about planar defects, stacking faults or particle size can be obtained from DF images Dobb et al. The TEM technique has been used to observe the texture, structure and chemistry of a boron nitride BN fiber Chassagneux et al.
soilstones.com/wp-content/2020-03-19/1424.php The TEM analysis revealed that the general structure of the fiber consisted of two concentric parts: the finely nanocrystallized region near surface and the bulk with larger crystallites. It was also found that all grains appeared to be randomly oriented with respect to the fiber axis, resulting in the modest mechanical properties of the fiber.
Li et al. The TEM observation revealed that crystallization taking place in the smectic phase could form both flat-elongated and double-twist helical single lamellar crystals. Justice et al.
Other characterization of textiles by transmission electron microscopy The capabilities of TEM have been increasingly extended by additional stages and detectors. A transmission electron microscope equipped with a cryo-stage is capable of maintaining the specimen at liquid nitrogen temperature. This allows the observation of frozen-hydrated samples. TEM can also be integrated with an EDX analyzer for detecting the elemental composition of the specimen. However, the entire column of the scanning electron microscope is normally under a high vacuum to minimize beamscattering effects. The high vacuum and the imaging process in SEM impose special requirements for specimen preparation.
Coating specimens with a thin layer of a conductive material is often required for non-conductive specimens. One of the major disadvantages of SEM is that it is normally not possible to examine hydrated specimens or dynamic processes involving specimens in a wet state. Many technical applications of textiles in connection with liquids like grease, adhesives, water, oil, dyes and others cannot be examined.
The ESEM technique is able to image uncoated and hydrated samples by means of a differential pumping system, and a gaseous secondary electron detector Danilatos, The differential pumping system shown in Fig. Pressure limiting apertures PLAs allow the electron beam to pass through, but minimize the leakage of gases between zones pumped at different rates.
Within the specimen chamber, pressures of up to 20 Torr can be maintained. ESEM can also be used to observe and record dynamic processes directly as they Textile surface characterization methods a 37 b 2.