Size distribution measurement

Quasi-elastic hght scattering (QELS), also called photon correlation spectroscopy (PCS), was used to determine the mean diameter of nanospheres and to follow their aggregation and deaggregation behavior (Gref et al, 1994). It was thus established that the emulsion/evaporation procedure leads to the formation of nanospheres with a very narrow size distribution. The influence of different parameters involved in the nano- 

It appeared that the lower the PVA molecular weight, the smaller was the nanosphere size. A similar observation was drawn from size-optimization studies of nanospheres prepared from PLGA (Scholes et al, 1993). The lower the polymer concentration was, the lower the viscosity of the organic phase and thus the smaller the resulting nanospheres. However, reducing the polymer concentration leads to lower particle recovery. 

PLGA nanospheres were prepared by the precipitation-solvent evaporation method in the presence of PEG PLA polymers (Stolnik et al, 1995). The resulting PEG-coated particles had an average particle size between 120 and 140nm and a polydispersity index between 0.08 and 0.13, indicative of a relatively narrow size distribution. 

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Moisio, Mikko. Real Time Size Distribution Measurement of Combustion Aerosols. Docror of technology thesis, Tampere University of Technology (1999). 

It is evident that most studies reported to date have used number density, average size or weight per eent as eontrol variables. Often these variables are inferred from other measurements, ineluding density, solution supersaturation, refraetive index ete. Inferential teehniques have been shown to be partieularly suitable for industrial seale applieations where laser seattering deviees for on-line size distribution measurement are not yet praetieal for industrial eontrol purposes, although substantial progress is being made to that end. Even when usable, however, these measurement deviees are often eharaeterized by noise and require operation at very low solids eoneentration. 

Figure 6. Pt particle size distributions measured from TEM images.

For a monodisperse system this result is in good agreement with the values obtained from pore size distribution measurements, but it can be significantly in error if one is dealing with a bimodal pore size distribution (see Section 6.4.2). 

Aerosol size distribution measurements were not made. 

Figure 2. Size distributions measured with separated single screen method (EML), stacked single screen method (USBM), and mobility analyzer (UI).

Figure 4. Size distributions measured with stacked single screen method.

The pore structure of a solid can contribute to the disintegration, dissolution, adsorption, and diffusion of a drug material [26,27]. Because of this, porosity and pore size distribution measurements have been used extensively to study tablets [28-30], granules [31,32], and excipients [33]. The following classification system of pore sizes has been developed based on the average pore radii [6] ... 

The surface area of PSs can be measured by means of quantitative electron microscopy (EM) [49-51], knowing the sizes of particles and pores [51,52], wetting heat [7,53] measurements, etc. But, the most universal methods are based on adsorption measurements [51,53-55], corresponding to the traditional methods of pore size distribution measurements in the range 0.3 to 100 nm. 

Parameters of Particle Size Distributions Measured by Light Scattering... 

Laboratory data collected over honeycomb catalyst samples of various lengths and under a variety of experimental conditions were described satisfactorily by the model on a purely predictive basis. Indeed, the effective diffusivities of NO and NH3 were estimated from the pore size distribution measurements and the intrinsic rate parameters were obtained from independent kinetic data collected over the same catalyst ground to very fine particles [27], so that the model did not include any adaptive parameters. 

It was found that the requirements were satisfied for application of the linear regression technique to species mass concentrations in a multicomponent aerosol. The results of 254 particle size distributions measured at China Lake in 1979 indicate that the normalized fine aerosol volume distribution remained approximately constant. The agreement between the calculated and measrued fine particle scattering coefficients was excellent. The measured aerosol sulfur mass distribution usually followed the total distribution for particles less than 1 ym. It was assumed that organic aerosol also followed the total submicron distribution. 

Figure 2 indicates Mn/Fe to be somewhat above the crustal ratio through 19 March, and thereafter a marked Increase is seen. The aerosol ratio Zn/Fe averages about 20 times greater than in the earth crust (somewhat greater on 20-21 March), showing "anomalous" atmospheric enrichment of Zn first recognized by Rahn (7). Since particle size distribution measurements, discussed below, show substantial fine particle concentrations of both Zn and Mn, the processes for their transfer to the atmosphere must be different from those for the other six elements of Figure 2. However, their concentration variations in time still resemble those of Fe shown in Figure 1 and therefore these elements may also be relatively large scale characteristics of air masses, in contrast to S where regional pollution sources and aerosol formation processes must be Important.

FIGURE 9.9 Particle number size distributions measured at Cheeka Peak, Washington, in 1991 (adapted from Quinn et at., 1993). 

Based on numerous size distributions measured in air, various categories of tropospheric aerosols have been proposed. Table 9.2, for example, shows a typical set of categories and some of their associated characteristics. However, these should be taken merely as examples rather than as fixed categories since many aerosols will display characteristics of more than one category. 

FIGURE 9.23 (a) Aerosol particle size distribution measured at Pomona during the 1972 State of California Air Resources Board ACHEX program, (b) Calculated optical scattering by particles, bsp, for measured size distribution (adapted from Waggoner and Charl-son, 1976). 

Sverdrup, G. M., and K. T. Whitby, The Effect of Changing Relative Humidity on Aerosol Size Distribution Measurements, Adr. Environ. Sci, Technoi, 10, 527-538 (1980a). 

Eldering, A., and R. M. Glasgow, Short-Term Particulate Matter Mass and Aerosol-Size Distribution Measurements Transient Pollution Episodes and Bimodal Aerosol-Mass Distributions, Atmos. Environ., 32, 2017-2024 (1998). 

Hoppel, W. A., and G. M. Frick, Submicron Aerosol Size Distributions Measured over the Tropical and South Pacific, Atmos. Environ., 24A, 645-659 (1990). 

Stein SW. Size distribution measurements of metered dose inhalers using Andersen Mark II cascade impactors. Int J Pharma 1999 186(1) 43—52. 

Chu 1991 Schmitz 1990). For example, the dynamic version of the diffusing wave spectroscopy described in Vignette V is a form of DLS, although in diffusing wave spectroscopy the method of analysis is different in view of multiple scattering. Most of the advanced developments are beyond the scope of this book. However, DLS is currently a routine laboratory technique for measuring diffusion coefficients, particle size, and particle size distributions in colloidal dispersions, and our objective in this section is to present the most essential ideas behind the method and show how they are used for particle size and size distribution measurements. 

How is the particle size measured in DLS experiments How is the size distribution measured in such experiments in the case of polydispersed colloids Comment on the method(s) critically. How do interparticle interactions affect the above measurements ... 

Figure 1. Core processing (scale in cm). Samples taken for area and pore-size distribution measurements (A), petrographic thin sections (Bj, B2, and B3), sorption experiments (Ci and C2), and permeability measurements (D).

In this paper we report on the results of size distribution measurements of cloud samples from three coral surface bursts and one silicate surface burst and present the results of the calculations of the sedimentation correction. 

Size Measurement. After the fractions were filtered, the millipore filters were sectioned to provide separate portions for chemical analysis and for size distribution measurements. One-eighth or one-fourth was set aside in reserve. The section designated for optical microscopy was transferred to a microscope slide and placed in a covered petri dish with a few drops of acetone. The acetone vapor is absorbed by the millipore and renders the filter transparent. 

Gravitational sedimentation causes a change in the particle size distribution anywhere in and below the cloud compared with the size distribution at stabilization time. Thus, to reconstruct the size distribution at stabilization time, corrections must be applied to the size distributions measured in the samples. These corrections were calculated by assuming Stokesian settling modified by a drag slip correction. It was assumed further that at stabilization time the cloud was axially symmetric and consisted of spherical particles. Wind and diffusion effects were neglected. 

To reconstruct an initial particle size distribution from observations at a later time, one must either have particle size distribution measurements at many different space-time points or make some assumption about the initial spatial distribution. The simplest assumption is that the initial spatial and particle size distributions are independent. 

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