AFM and transmission electron microscopy

To characterize dendrimers, analytical methods used in synthetic organic chemistry as well as in macromolecular chemistry can be applied. Mass spectrometry and NMR spectroscopy are especially useful tools to estimate purity and structural perfection. To get an idea of the size of dendrimers, direct visualization methods such as atomic force microscopy (AFM) and transmission electron microscopy (TEM), or indirect methods such as size exclusion chromatography (SEC) or viscosimetry, are valuable. Computer aided simulation also became a very useful tool not only for the simulation of the geometry of a distinct molecule, but also for the estimation of the dynamics in a dendritic system, especially concerning mobility, shape-persistence, and end-group disposition. 

It is difficult to evaluate the shape of such dendritic particles experimentally. However, some insight can be gained by atomic force microscopy (AFM) and transmission electron microscopy experiments (TEM). AFM experiments can give information about the overall size of the dendrimers, as shown by De Schryver [43], by spincoating very dilute solutions of dendrimers like 30 on mica, then visualizing single dendrimers. Their height measured in this manner corresponds very well to the diameters calculated by molecular mechanics simulations. First results from TEM measurements also confirm the expected dimensions [44]. Unfortunately, due to resolution limits, up to now direct visual information could not be obtained about the shape of the dendrimers. 

Interesting information about the organization of fibrils has been obtained from atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both methods give high resolution images of fibrils and show that fibrils are unbranched, twisted, and several ttm long. These techniques are usually used to support data obtained from Thiofiavin T assays, as this method gives no information about the presence of fibrils (it only confirms presence of 3-sheets). 

The basical theories, equipments, measurement practices, analysis procedures and many results obtained by gas adsorption have been reviewed in different publications. For macropores, mercury porosimetry has been frequently applied. Identification of intrinsic pores, the interlayer space between hexagonal carbon layers in the case of carbon materials, can be carried out by X-ray dififaction (XRD). Recently, direct observation of extrinsic pores on the surface of carbon materials has been reported using microscopy techniques coupled with image processing techniques, namely scarming tunneling microscopy (STM) and atomic force microscopy (AFM) and transmission electron microscopy (TEM) for micropores and mesopores, and scanning electron microscopy (SEM) and optical microscopy for macropores [1-3],... 

Start and Mauritz [396] used environmental SEM-EDAX, and also AFM and transmission electron microscopy, to study the formation of organic-inorganic nanocomposites within surlyn(PE-co-methacrylate-cation forms) random copolymers. SEM-EDAX has also been used to study of thin films of Prussian blue and N-substituted polypyrroles [397], epoxy resins [399], and the cause of failure in acetal plumbing fittings caused by exposure to chlorine [400]. 

Recently, a few heterogeneous Rh catalysts have been reported. Kopaczynska et demonstrated that rhodium nanoparticles stabilized by polyvinylpyrrolidone exhibit catalytic activity in the polymerization of PA. The stereochemistry of the polymer produced with this catalyst is purely cis-transoidal. The progress in polymerization can be monitored by atomic force miaoscopy (AFM) and transmission electron microscopy (TEM). This report includes the first detection of a spectacular helical poly(PA) using AFM imaging. Son and co-workers reported that the nanopartides composed of the (benzoquinone)Rh(cod) complex and aluminum compounds catalyze the polymerization of PA. The catalyst nanopartides can he recovered hy centrifugation, and the recovered nanopartides show almost the same artivity. 

The most popular tools for the visualization of engineered nanoparticles are electron and scanning probe microscopes. The visualization, the state of aggregation, dispersion sorption, size, structure, and shape can be observed by means of atomic force microscopy (AFM), scanning electron (SEM), and transmission electron microscopy (TEM). Analytical tools (mostly spectroscopic) can be coupled to... 

The oldest microscopy technique for materials analysis was optical microscopy. Even to this day, for feature sizes above 1 pm, this is one of the most popular tools. For smaller features, electron microscopy techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are the tools of choice. A third family of microscopy includes scanning probe tools such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). In these relatively recent techniques, sample preparation concerns are of minor importance compared to other problems, such as vibration isolation and processing of atomically sharp probes. Therefore, the latter techniques are not discussed here. This chapter is aimed at introducing the user to general specimen preparation steps involved in optical and electron microscopy [3 7], which to date are the most common... 

We have roughly described three main microscopy techniques, namely local probe microscopy (STM, AFM, etc.), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). 

In this context, the SPM techniques (and especially STM and AFM) appear, a priori, ideally suited for the direct visualization of the porous structure of materials at scales which are not so readily accessible by other means (e.g., scaiming and transmission electron microscopies). However, the performance of such a task is confronted with two major limitations. The first one arises from the fact that detection with SPM is exclusively restricted to the outermost surface of the sample. Accordingly, this implies that only the most external porosity of the material can be probed, whereas no information on the bulk (inner) porosity, which might not be identical to the former, is revealed. The second drawback is related to the finite dimensions of the probing tip, which limits the size of the voids (pores) physically accessible (and thus detectable) by the tip on the sample surface. Obviously, pores significantly smaller than the tip diameter will pass uimoticed to the instrument when the surface is scanned. As a specific example, the tips normally employed in AFM are not sharp enough to provide access to the whole mesopore range (between 2 and 50 nm). 

X-ray diffraction technique is a non-destructive analytical technique that reveals information about crystallographic structure, chemical composition and physical properties of nanostructured materials. UV/Vis spectroscopy is routinely used in the quantitative determination of films of nanostructured metal oxides. The size, shape (nanocomb and nanorods etc,) and arrangement of the nanoparticles can be observed through transmission electron microscope (TEM) studies. Surface morphology of nanostructured metal oxides can be observed in atomic force microscopy (AFM) and scanning electron microscopy (SEM) studies. 

Gum Arabica and its complexes used in the present study contain fine structures which affect their properties. The microscopy may be informative in investigating the molecular domain and block structure in it. The different types of microscopy used in the characterization of gum specimen are (i) Optical microscopy, where only structures separated about Ipm across can be investigated. (ii) Electron microscopy in the form of transmission electron microscopy (TEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mentioned techniques and tools are able to provide a magnification up to 10 and at very high resolution. 

Although nanochemical control was proposed decades ago, it was only recently that many of the tools necessary for studying the nanoworld were developed. These include the scanning tunneling microscope (STM), atomic force microscope (AFM), high resolution scanning and transmission electron microscopies, x rays, ion and electron beam probes, and new methods for nanofabrication and Uthography. 

At both routes, the determination of the size and shape of the nanoparticles is a prerequisite for description of the optical properties. Besides atomic force microscopy (AFM) and scanning electron microscopy (SEM), transmission electron microscopy (TEM) is the most powerful method to determine size and shape distributions of the nanoparticle assemblies. However, extensive sample preparation that is often required can cause preparation effects, and the TEM micrographs sometimes are not representative of the whole nanoparticle-containing insulating material. Therefore, an experimental material is required which can be investigated very easily without extensive TEM preparation. 

Fig. 7.20 Atomic force microscopy (AFM) (top) and transmission electron microscopy (TEM) (bottom) images of BPSH-6FK multi-block copolymer membranes (a) BPSH5-6FK5, (b) BPSH10-6FK10, and (c) BPSHIO for AFM or BPSH15 for TEM-6FK15. Numbers represent molecular weight of each block component in kDa (Reprinted from [47] with permission from Wiley Interscience)...

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