Monodisperse latex spheres

Scattering intensity measured by the pulse height analyzer is related to particle size by calibration with monodisperse latex spheres or nearly mono-disperse NaCl particles. Calibration uncertainties have been studied and discussed (86-91). These studies show that the smallest particles that can be sensed by the ASASP probe are somewhat larger than the 0.12 xm stated by the manufacturer. Similarly, it is reported that detection of particles larger than about 2 xm is unreliable because of attenuation of the laser power. 

The experimental setup and this method have been tested on aqueous suspensions of monodisperse latex spheres with 94 and 302 nm diameters (SIGMA Chemical Co) and different concentrations from 5-10 5 to 2-10 3 gram/m3. The radii being calculated by analysis of the correlation functions were verified within a few percents. The concentrations has been calculated from the optical thickness and turned to be within 2-5% in accordance with those found by evaporating and weighting the latexes. 

Inverse opals are formed by the use of micro- or nanospheres to template a structure containing spherical cavities. One way of doing this is to use monodisperse latex spheres. These latex spheres are prepared by slow addition of an aqueous precursor solution into a reservoir of hydrophobic silicone liquid, forming emulsion droplets. The size of the droplets is controlled by the concentration of the aqueous latex, the speed at which the suspension is stirred and ratio between the silicone liquid and latex. Polymerisation results in latex spheres of well defined size of the order of a few hundred nanometers, and spherical shape. As the concentration of the latex spheres increases to its critical concentration... 

Other particles may also be used to test the membrane. Monodisperse latex spheres (produced by Dow Chemical) in concentrations of 106-109 particles per ml are sometimes used. Normally, a second membrane is used downstream of the test membrane to collect particles which pass. The number of spheres collected are Counted with the use of a scanning electron microscope. This is much more tedious and less accurate than the bacteria challenge test where bacteria collected on the second membrane may be grown into colonies visible to the naked eye. Alternatively, automatic particle counters are used before and after the membrane, but the method is not as sensitive and is limited to particles over 0.5 t in size. 

Fig. 7 compares the experimentally measured (A and C) absorption Cahs,x and (B and D) scattering Csca,x cross-sections between 400 and 700 nm of monodisperse latex spheres 2.02 and 4.5 pm diameter with Lorenz—Mie theory predictions using the complex index of refraction of latex reported by Ma et al. (2003). Flere also, the good agreement between theoretical and experimental results successfully validated the experimental setup and the data analysis. Similar vaHdation has been performed with the same polydisperse polystyrene latex microspheres and randomly oriented and infinitely long glass fibers considered for validating the scattering phase function measurements, as illustrated in Fig. 6 (Berberoglu and Pilon, 2007).

New methods of emulsion polymerization, particularly the use of swelhng agents, are needed to produce monodisperse latexes with a desired size and surface chemistiy. Samples of latex spheres with uniform diameters up to 100 pm are now commercially available. These spheres and other mono-sized particles of various shapes can be used as model colloids to study two- and three-dimensional many-body systems of very high complexity. 

Monodisperse DOP and latex spheres mixed with 220Rn... 

Calibration of these single-particle counters is usually carried out using monodisperse polystyrene latex or polyvinyl latex spheres, which are available in sizes from 0.1 to 3 /im and have a refractive index of 1.6 alternatively, aerosols with lower refractive indices may be generated from liquids such as dioctyl phthalate (m = 1.49). Whitby and Willeke (1979) discuss the... 

The method relies on the properties of monodispersed latex/silica spheres to assemble, through colloidal interactions, into a well-ordered, face-centered-cubic colloidal crystal upon centrifugation, sedimentation, electrophoresis, oscillatory shear or pressing in the form of pellets. Following pre-assembly of the colloidal crystal template, the precursor is infiltrated into the empty octahedral and tetrahedral interstitial sites that exist between the spheres. After conversion of the precursor to the desired material inside the voids, the template is removed leaving... 

Monodisperse polystyrene (latex) spheres having a radius value in the range 30-100 run with a standard deviation of 8% or less characterizing the size uniformity. Such samples can be obtained from Duke Scientific Corp. as 3000 Series Nanospheres (www. dukescientific.com), Polymer Laboratories as PL-Latex Plain White (www.polymerlabs. com), and Polysciences, Inc., as Nanobead Traceable Size Standards (www.polysciences. com). 

This form is employed in aero.sol technology to characterize panicles that are nearly monodisperse such as the polystyrene latex spheres used in laboratory. studies and in instrument calibration. The value of dp can be calculated using the moment equation (1.15). In integrating, it is necessary to set a lower limit airfj, 0 and to assume that the distribution... 

When two monodisperse colloids of CoPts nanocrystals (4.5 nm and 2.6 nm diameter) were mixed together, followed by a slow evaporation of the solvent, an ABs-type superlattice analogous to the structure of intermetallic compound CaCus [42] was obtained (Figure 4.18) [26]. A similar stmcture was observed for binary mixtures of latex spheres of two different sizes [43,44]. In the first plane of this lattice (Figure 4.18), each 4.5 nm CoPt3 nanocrystal is surrounded with a hexagon formed by 2.6 nm nanocrystals. The second plane consists only of hexagons of small particles, while the third plane repeats the first. 

Both linear and cross-linked monodisperse latexes of polystyrene in the size range 0.1 - 1.2y have been prepared by persulfate-initiated emulsion polymerization (6,7,8), and the size and size distributions of the polymer spheres detennined by electron microscopy. Free electrolyte was removed by a mixed-bed ion exchange resin, and surface charge measured by conductometric titration against standard base. Redispersion in organic media was effected by successive dialyses, first with methanol and finally against the desired solvent. 

For polydisperse samples, even in a mixture of two monodisperse spheres, the result however may still be far from satisfactory. In a round-robin study performed by eight laboratories a mixture of 400 nm and 1000 nm monodisperse latexes was measured using different PCS instruments and the data were processed using different inversion algorithms. The modality, mean diameter, and percentages of each population retrieved from the eight laboratories varied widely [81, 82]. 

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