Colloids electron microscopy

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

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

FIGURE 5.4 Stages in sol-gel processing are captured by a new electron microscopy technique. (1) Spherical particles tens of nanometers across can be seen in a colloidal silica sol. (2) Addition of a concentrated salt solution initiates gelation. (3) The gelled sample, after drying under the electron beam of the microscope, shows a highly porous structure. Courtesy, J. R. Bellare, J. K. Bailey, and M. L. Mecartney, University of Minnesota. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

Hinton, DP Johnson, CS, Diffusion Coefficients, Electrophoretic Mobilities, and Morphologies of Charged Phospholipid Vesicles by Pulsed Field Gradient NMR and Electron Microscopy, Journal of Colloid and Interface Science 173, 364, 1995. 

Herein we briefly mention historical aspects on preparation of monometallic or bimetallic nanoparticles as science. In 1857, Faraday prepared dispersion solution of Au colloids by chemical reduction of aqueous solution of Au(III) ions with phosphorous [6]. One hundred and thirty-one years later, in 1988, Thomas confirmed that the colloids were composed of Au nanoparticles with 3-30 nm in particle size by means of electron microscope [7]. In 1941, Rampino and Nord prepared colloidal dispersion of Pd by reduction with hydrogen, protected the colloids by addition of synthetic pol5mer like polyvinylalcohol, applied to the catalysts for the first time [8-10]. In 1951, Turkevich et al. [11] reported an important paper on preparation method of Au nanoparticles. They prepared aqueous dispersions of Au nanoparticles by reducing Au(III) with phosphorous or carbon monoxide (CO), and characterized the nanoparticles by electron microscopy. They also prepared Au nanoparticles with quite narrow... 

In order to obtain Pt nanoparticles, aqueous solution of 10 M K2PtCl4, which contained 10 M (as monomer unit) of poly-NIPA or poly-NEA, was bubbled with Ar gas and then H2 gas. Then the reaction vessel was sealed tightly and kept in a water bath at a suitable temperature. At given reaction times, the vessels were opened and the samples for transmission electron microscopy (TEM) were prepared by soaking a grid (carbon substrate, Oken) in the colloidal solution and then drying it in the air. The TEM (Hitachi H-8100) was operated at 200 kV. 

Figure 6 Detail of the interface space (IN) between the fungal wall (U) of Glomuf versiforvte and the host membrane of leek (PL), as seen by electron microscopy. Xylo-glucan molecules are revealed by using a specific antibody and colloidal gold granules. P, host cell F, fungus, X 30,000.

Colloidal dispersion 1.0 nm-1.0 pm Particles not resolved by ordinary microscope but visible by electron microscopy pass through filter paper but not semipermeable membranes generally slow diffusion Colloidal silver sols, surfactant micelles in an aqueous phase, aqueous latices and pseudolatices... 

Heard SM, Grieser F, Barraclough CG, Sanders JV (1983) The characterization of Ag sols by electron microscopy, optical absorption and electrophoresis. J Colloid Interface Sci 93(2) 545-555... 

A review of preparative methods for metal sols (colloidal metal particles) suspended in solution is given. The problems involved with the preparation and stabilization of non-aqueous metal colloidal particles are noted. A new method is described for preparing non-aqueous metal sols based on the clustering of solvated metal atoms (from metal vaporization) in cold organic solvents. Gold-acetone colloidal solutions are discussed in detail, especially their preparation, control of particle size (2-9 nm), electrophoresis measurements, electron microscopy, GC-MS, resistivity, and related studies. Particle stabilization involves both electrostatic and steric mechanisms and these are discussed in comparison with aqueous systems. 

Honisbenger, M., and Rosset, J. (1977) Colloidal gold, a useful marker for transmission and scanning electron microscopy./. Histochem. Cytochem. 25, 295. 

An electron microscopy study by Mullen et al. (1989) showed that Cd2+, Cu2+ and La3+ accumulated on the cell surface of Bacillus cereus, B. subtilis, E. coli and Pseudomonas aeruginosa as needle-like, crystalline precipitates, while Ag+ precipitated as discrete colloidal aggregates at the cell surface and occasionally in the cytoplasm. The needle-like and hexagonal precipitates were also found for the biosorption of Ni2+ on the cell surface of P. fluorescens 4F39 at pH 9 and it was suggested as a microprecipitation process that followed on ion exchange (Lopez et al. 2000). 

Core-shell colloidal crystal films were prepared in three steps as outlined in Table 4.2. First, spherical submicron polystyrene particles were prepared by known methods38 39. The size of isolated polystyrene beads was 326 5 nm as determined by analysis of scanning electron microscopy (SEM) images using standard techniques. 

Akashi and coworkers prepared small platinum nanoparticles by ethanol reduction of PtCl in the presence of various vinyl polymers with amide side chains [49]. These authors studied the effects of molecular weight and molar ratio [monomeric unit]/[Pt] on the particle sizes and size distributions by electron microscopy, and in some cases by the dispersion stability of the Pt colloids. The hydrogenation in aqueous phase of allyl alcohol was used as a model reaction to examine the change in catalytic activity of polymer-stabilized Pt colloids upon addition of Na2S04 to the reaction solution. The catalytic tests were performed in water or in Na2S04 aqueous solution at 25 °C under atmospheric pressure of... 

Labeling antibodies with colloidal gold was developed for electron microscopy, but the procedure can be used for light microscopy as well. 

Romano EL, Stolinski C, Hughes-Jones NC. An antiglobulin reagent labeled with colloidal gold for use in electron microscopy. Immunochemistry 1974 11 521-522. 

Romano EL, Romano M. Staphyloccal protein A bound to colloidal gold a useful reagent to label antigen-antibody sites for electron microscopy. Immunochemistry 1977 14 711-715. 

Tanaka K, Mitsushima A, Yamagata N, Kashima Y, Takayama H. Direct visualization of colloidal gold-bound molecules and a cell surface receptor by ultrahigh resolution scanning electron microscopy. J Microsc 1990 161 455—461. 

Duff, D.G. et al., Structural characterization of colloidal platinum by high resolution electron microscopy and EXAFS analysis, Angew. Chem. 101, 610, 1989 Angew. Chem. Int. Ed. Engl., 28, 590,1989. 

Goldraich M, Talmon Y (2000) Direct-imaging cryo-transmission electron microscopy in the study of colloids and polymer solutions. In Alexandridis P, Lindman B (eds) Amphiphilic block copolymers self assembly and applications. Elsevier, Amsterdam... 

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