Ultramicroscope

Ultramicroscope, Shaker Verlag, Aachen (b) Turkevich, J. (1985) Colloidal gold. Part I. Flistorical and preparative aspects, morphology and structure. 

The velocity of particle migration, v, across the field is a function of the surface charge or zeta potential and is observed visually by means of an ultramicroscope equipped with a calibrated eyepiece and a scale. The movement is measured by timing the individual particles over a certain distance, and the results of approximately 10-15 timing measurements are then averaged. From the measured particle velocity, the electrophoretic mobility (defined as v/E, where E is the potential gradient) can be calculated. 

If a beam of light is passed through a colloidal solution, the colloidal particles will reflect or scatter the light so that the beam becomes visible when the solution is viewed from the side against a dark background. This Tyndall effect is used in the ultramicroscope. 

An instrument used to observe particles too small to be seen by the ordinary light microscope. The ultramicroscope makes use of the Tyndall effect. Ultrasonics... 

Greater durability of the colloidal Pd/C catalysts was also observed in this case. The catalytic activity was found to have declined much less than a conventionally manufactured Pd/C catalyst after recycling both catalysts 25 times under similar conditions. Obviously, the lipophilic (Oct)4NCl surfactant layer prevents the colloid particles from coagulating and being poisoned in the alkaline aqueous reaction medium. Shape-selective hydrocarbon oxidation catalysts have been described, where active Pt colloid particles are present exclusively in the pores of ultramicroscopic tungsten heteropoly compounds [162], Phosphine-free Suzuki and Heck reactions involving iodo-, bromo-or activated chloroatoms were performed catalytically with ammonium salt- or poly(vinylpyrroli-done)-stabilized palladium or palladium nickel colloids (Equation 3.9) [162, 163],... 

A forthcoming era of photonics circuitry embodying laser generators and various photo detectors and storage systems, will provide similar ultramicroscopic circuits for communications, logic and memory. 

Klosterkotter W Effects of ultramicroscopic y-aluminum oxide on rats and mice. AMA Arch Lnd ILealth 21 458, 1960. 

Coalescence does not immediatelyfollow after contact. Zsigmondy has noted, in the case of gold sols, under the ultramicroscope, that the small primary particles coalesce on contact to form secondary particles, that a primary will coalesce with a secondary, but two secondary particles do not coalesce. 

The ultramicroscopic examination of a gelatinising sol reveals the presence of very small particles termed ultramicrons, it is assumed on the fibrillar theory that the ultramicrons aggregate to invisible threads or fibrils. As the gelatinisation proceeds the fibrils thicken and lengthen and in many cases may actually be rendered visible by powerful magnification under the microscope. The fibrils are diffused at random in the form of a felt through the material and may, as we have noted, be markedly crystalline in the filamentous, somewhat flexible in the fibrillary and distinctly mobile and flexible in the streptrococcic forms visible under the microscope. 

The tiny particles in colloidal gold were not seen directly until the early twentieth century, when the Austrian chemist Richard Adolf Zsigmondy invented the ultramicroscope, a device capable of resolving such small objects. For elucidating the nature of colloids Zsigmondy was awarded the Nobel Prize in chemistry in 1925. 

According to J. Amann,7 brown soln. of iodine contain ultra-microscopic particles, while the violet soln. contain none. The violet-red soln. in benzene, toluene, and xylene are photosensitive in that clouds of ultramicroscopic particles are formed in white light, and the soln. rapidly turn brown. The soln. return to their original state in darkness. In some cases, iodine soln. are true soln. either of free iodine or of an addition compound and in other cases they contain free colloidal iodine or of a polymerized addition compound. In some cases ultra-microscopic suspended particles of iodine are present. 

Ultramicroscopic Too small to be seen with an ordinary microscope. 

Grimley (G10, Gil) used an ultramicroscope technique to determine the velocities of colloidal particles suspended in a falling film of tap water. It was assumed that the particles moved with the local liquid velocity, so that, by observing the velocities of particles at different distances from the wall, a complete velocity profile could be obtained. These results indicated that the velocity did not follow the semiparabolic pattern predicted by Eq. (11) instead, the maximum velocity occurred a short distance below the free surface, while nearer the wall the experimental results were lower than those given by Eq. (11). It was found, however, that the velocity profile approached the theoretical shape when surface-active material was added and the waves were damped out, and, in the light of later results, it seems probable that the discrepancies in the presence of wavy flow are due to the inclusion of the fluctuating wavy velocities near the free surface. 

Colloidal Dispersions or Solutions (Sols) and Colloids. Colloidal solutions (or rather "pseudo solutions ), also called sols (or in case of liquids hydrosols) are heterogeneous systems consisting of a "dispersion medium (mostly a liquid) and a "dispersed or "suspended medium known as a "colloid . Colloidal particles are invisible under ordinary microscope but detectable by the ultramicroscope. Their size ranges from ca 1 x 10 7 to 1 x 5 smm. If the dispersion is a viscous, sticky, transparent liquid, it is what is generally known as a "colloidal solution . As examples of this may be cited a soln of gum-arabic in water and sol ns of NC in acetone, ethyl acetate or ether alcohol. When "solns are dialized, most of the colloidal particles do not pass thru the membrane. This is their principal distinction from "crystalloids , which are substances like Na chloride, etc. If part of the volatile liquid (dispersing medium), is evaporated the resulting tacky, jellylike substance is known as a gel. 

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