Particle microscopy

Particle composition is far more difficult to evaluate. Bulk elemental analysis [atomic absorption spectroscopy (AA) or inductively coupled plasma mass spectrometry (ICP-MS) are most common for metals] is useful in confirming the overall bimetallic composition of the sample, but provides no information regarding individual particles. Microscopy techniques, particularly Energy Dispersive Spectroscopy (EDS), has supported the assertion that bimetallic DENs are bimetallic nanoparticles, rather than a physical mixture of monometallics [16]. Provided the particle density is low... 

Sonnichsen,C.andAlivisatos, A.R (2005) Gold nanorods as novel nonbleaching plasm on-based orientation sensors for polarized single-particle microscopy. Nano Lett., 5, 301-304. 

For non-spherical particles, microscopies and light scattering can provide shape information, as discussed in Section 2.3. Shape information can also be obtained from the influence of particle shape on, for example, sedimentation. One such me asure is the dynamic shape factor (j), which is given by the square of the equivalent diameter divided by the aerodynamic diameter x = X 1-00 for a... 

Rubber toughening was discovered nearly sixty years ago, and the original theories to explain the phenomenon were proposed 25 years ago and have been reviewed [224]. Since that time, however, numerous deformation studies in the TEM have been conducted and reported by Kramer and his colleagues [218, 225, 226] and others [41] (Section 4.8.3). Control of the toughening process has depended on characterization of the structures resulting from the dispersion of the rubber particles, their grafting, crosslinking and copolymerization. Optical and electron microscopy allow measurement of the size and shape of the dispersed phase particles. Microscopy also permits observation of their internal... 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

The specific surface area of a solid is one of the first things that must be determined if any detailed physical chemical interpretation of its behavior as an adsorbent is to be possible. Such a determination can be made through adsorption studies themselves, and this aspect is taken up in the next chapter there are a number of other methods, however, that are summarized in the following material. Space does not permit a full discussion, and, in particular, the methods that really amount to a particle or pore size determination, such as optical and electron microscopy, x-ray or neutron diffraction, and permeability studies are largely omitted. 

With the exception of the scanning probe microscopies, most surface analysis teclmiques involve scattering of one type or another, as illustrated in figure A1.7.11. A particle is incident onto a surface, and its interaction with the surface either causes a change to the particles energy and/or trajectory, or the interaction induces the emission of a secondary particle(s). The particles that interact with the surface can be electrons, ions, photons or even heat. An analysis of the mass, energy and/or trajectory of the emitted particles, or the dependence of the emitted particle yield on a property of the incident particles, is used to infer infomiation about the surface. Although these probes are indirect, they do provide reliable infomiation about the surface composition and structure. 

A wide variety of measurements can now be made on single molecules, including electrical (e.g. scanning tunnelling microscopy), magnetic (e.g. spin resonance), force (e.g. atomic force microscopy), optical (e.g. near-field and far-field fluorescence microscopies) and hybrid teclmiques. This contribution addresses only Arose teclmiques tliat are at least partially optical. Single-particle electrical and force measurements are discussed in tire sections on scanning probe microscopies (B1.19) and surface forces apparatus (B1.20). 

Electron microscopy (see section B1.18) is very valuable in characterizing particles (see, for instance, figure C2.6.1). The suspension stmcture is, of course, not represented well because of tire vacuum conditions in tire microscope. This can be overcome using environmental SEM [241. 

Particles can be manipulated in suspension using strongly focused laser beams ( optical tweezers ) [25] or magnetic fields [26] and by collecting statistics on tire particle movements using video microscopy, infonnation on the particle interactions can be obtained. 

Surfaces can be characterized using scaiming probe microscopies (see section B1.19). In addition, by attaching a colloidal particle to tire tip of an atomic force microscope, colloidal interactions can be probed as well [27]. Interactions between surfaces can be studied using tire surface force apparatus (see section B1.20). This also helps one to understand tire interactions between colloidal particles. 

Figure C2.17.4. Transmission electron micrograph of a field of Zr02 (tetragonal) nanocrystals. Lower-resolution electron microscopy is useful for characterizing tire size distribution of a collection of nanocrystals. This image is an example of a typical particle field used for sizing puriDoses. Here, tire nanocrystalline zirconia has an average diameter of 3.6 nm witli a polydispersity of only 5% 1801.

Flueli M, Buffat P A and Borel J P 1988 Real time observation by high resolution electron microscopy (HREM) of the coalescence of small gold particles in the electron beam Surf. Sc/. 202 343... 

Pocza J F, Barna A and Barna P B 1969 Formation processes of vacuum deposited indium films and thermodynamical properties of submicroscopic particles observed by in situ electron microscopy J. Vac. Sc/. Techno . 6 472... 

Comparison of particle diameter of colloidal silica by electron microscopy (cf,). by nitrogen adsorption (d ) and by light scattering (d,)... 

The slit-shaped model has come into prominence in recent years, as electron microscopy has revealed the prevalence of solids composed of platelike particles the technique, indeed, has now developed to the point where it is possible to identify the presence of slit-shaped pores, and even to measure their width. In the ideal case where the sides of the slit are truly planar and parallel, the hysteresis takes an extreme form since the mean radius of curva-... 

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