Particle radius, change

Each of the resonances appearing in the spectra are identified and characterized by the type (TE or TM), mode number n, and mode order 5 (i.e., TE J. Allowances were made in the fit for a small amount of scattered light polarized perpendicular to the scattering plane (due to imperfect alignment of the polarizer) and a small change in the particle radius due to evaporation during the experiment. Once the resonances are identified there are no adjustable parameters in the simulation of an excitation spectrum of a... 

An increase of the particle radius is observed at 25 C (the smaller one in the case of a two exponentials fit) as the starting concentration is increased. Furthermore, for Cq = 1.2 and 1.6 a second species of particles appears with a radius about twice larger. These two kinds of particles seem to coexist with no change of size distribution as the temperature is increased from 25to for a starting concentration of 1.6 %, Yet, at 60°C, only the smaller particle species remain in solution. 

Colloidal CdS particles 2-7 nm in diameter exhibit a blue shift in their absorption and luminescence characteristics due to quantum confinement effects [45,46]. It is known that particle size has a pronounced effect on semiconductor spectral properties when their size becomes comparable with that of an exciton. This so called quantum size effect occurs when R < as (R = particle radius, ub = Bohr radius see Chapter 4, coinciding with a gradual change in the energy bands of a semiconductor into a set of discrete electronic levels. The observation of a discrete excitonic transition in the absorption and luminescence spectra of such particles, so called Q-particles, requires samples of very narrow size distribution and well-defined crystal structure [47,48]. Semiconductor nanocrystals, or... 

EXAMPLE 13.4 Change of Stability Ratio with Ionic Concentration. Colloidal gold stabilized by citrate ions and having a mean particle radius of 103 A was coagulated by the addition of NaCI04. The kinetics of coagulation were studied colorimetrically and the stability ratio W for different NaCI04 concentrations was determined (Enustun and Turkevich 1963) ... 

The experimental diffusion parameters, D /r., at 30°C. are presented in Table II for all the coals. Clearly, no correlation exists between diffusion parameter and rank. If r<> is taken as the average particle radius for the 200 X 325 mesh samples, an upper limit to the values of diffusion coefficient, D, is obtained. The diffusion coefficient ranges from 1.92 X 10 9 sq. cm./sec. for Kelley coal to 1.41 X 10"8 sk. cm./sec. for the Dorrance anthracite. Our previous studies on the change of D /n with particle size suggested that n is not necessarily the particle radius (7) but is a smaller distance related to the average length of the micropores in the particles. That is, the calculated... 

The applicability of Maxwell s equation is limited in describing particle growth or depletion by mass transfer. Strictly speaking, mass transfer to a small droplet cannot be a steady process because the radius changes, causing a change in the transfer rate. However, when the difference between vapor concentration far from the droplet and at the droplet surface is small, the transport rate given by Maxwell s equation holds at any instant. That is, the diffusional transport process proceeds as a quasi-stationary process. 

The above set of equations may be simplified by some assumptions not changing the equilibrium qualitatively. Indeed, let us assume that the whole complexing process is described by the addition of a single ligand and [L°], [S°] [Cd°]. In this case, the set of equations (2) reduces to a single equation interrelating the particles radius R and the stability constant Ki of the complex ... 

It is estimated that to maintain a temperature differential between particle and gas of no greater than 100°C, the particle radius should be less than lp. This result is based on rate of change of gas temperature in the nozzle of 107°C/sec. 

Fig. 6. A plot of the characteristic peak positions (dashed line) in a solution X-ray scattering experiment (Q = 4w sin d/l, where d is half the X-ray scattering angle and 1 is 1.38 A, the wavelength of the X-rays) used to monitor the change in Na V particle size as a function of pH. The spherically averaged particle radius is shown by the solid line. The plot illustrates the highly cooperative pH dependence of the transition (Canady et al, 2001).

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