Monodisperse polystyrene latex spheres

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). 

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... 

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... 

The size distributions of colloidal suspensions of nanoparticles 74 nm to 14 nm in diameter are analyzed on-line. The sols are first diluted in water seeded with enough TFA to attain electrical conductivities in the range of 0.01 S/m. The solution is then finely dispersed into an atmosphere of CO2 via a Taylor cone-jet. The resisting electrospray of ultrafine droplets dries, transferring the solution particles virtually uncontaminated into the gas. There they are sized by means of a differential mobility analyzer and an inertial impactor of unusually high resolution. The technique is first tested successfully with previously calibrated monodisperse polystyrene latex (PSL) spheres 74 to 21 nm in diameter. It is then used to size a solution of colloidal silica with particle diameters nominally between 10 and 14 nm. 

Dried films of certain monodisperse polystyrene latexes display brilliant iridescent colors. These colors have been attributed to the diffraction of visible light by latex particle crystallites (46-48). When dried at room temperature, polystyrene latexes form opaque, white, friable, discontinuous films. Electron micrographs of surface replicas of these films show the monodisperse spheres packed in uniform hexagonal arrays without appreciable coalescence (49). If the distance between the particle centers is within a certain range, the crystallite diffracts visible light and the interference colors are observed. These color combinations are specific for the latex particle diameter (Table VII). 

The normal distribution function is rarely used to describe aerosol particle size distributions because most aerosols exhibit a skewed (long tail at large sizes) distribution function. The normal distribution is, of course, synunetrical. It can be applied to monodisperse test aerosols, to certain pollens and spores, and to specially prepared polystyrene latex spheres. The number frequency function is given by... 

An important step in tire progress of colloid science was tire development of monodisperse polymer latex suspensions in tire 1950s. These are prepared by emulsion polymerization, which is nowadays also carried out industrially on a large scale for many different polymers. Perhaps tire best-studied colloidal model system is tliat of polystyrene (PS) latex [9]. This is prepared with a hydrophilic group (such as sulphate) at tire end of each molecule. In water tliis produces well defined spheres witli a number of end groups at tire surface, which (partly) ionize to... 

Monodisperse spheres are not only uniquely easy to characterize, but also very rarely encountered. Polymerization under carefully controlled conditions allows the preparation of the polystyrene latex shown in Figure 1.8. Latexes of this sort are used as standards for the size calibration of optical and electron micrographs (also see Section 1.5a.3). However, in the majority of colloidal systems, the particles are neither spherical nor monodisperse, but it is often useful to define convenient effective linear dimensions that are representative of the sizes and shapes of the particles. There are many ways of doing this, and whether they are appropriate or not depends on the use of such dimensions in practice. There are excellent books devoted to this topic (see, for example, Allen 1990) and, therefore, we consider only a few examples here for the purpose of illustration. 

The number-size distribution of ambient particles was monitored by an optical particle counter (OPC) (RION, KC-OID). Information concerning the accuracy of the OPC s size determination was checked by the manufacmrer (RION). The four-step known size monodisperse polystyrene type latex (PSL) spheres (0.294, 0.505, 1.001, and 2.106 pm) were employed. The OPC sizing accuracy check was conducted by sampling of these PSL particles. In the field measurement, OPC was operated at intervals of every 30 min. The flow rate for the OPC was 3 X 10 m h During the sampling period, the ranges of temperature and relative humidity (RH) were 12.8-28.4 °C and 30-79%, respectively. 

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).

The mostly used methods to monitor LbL deposition on monodisperse PS-latex particles for various substances are SPLS method and microelectrophoresis. Inorganic (magnetite, silica, titania and fluorescent quantum dots) nanoparticles [32-34], lipids [35-37] and proteins (albumin, immunoglobulin and others) [29, 38, 39] were incorporated as building block for shell formation on colloidal particles. In paper [39] the construction of enzyme multilayer films on colloidal particles for biocatalysis was demonstrated. The enzyme multilayers were assembled on submicrometer-sized polystyrene spheres via the alternate adsorption of poly(ethyleneimine) and glucose oxidase. The high surface area bio-multilayer coated particles formed were subsequently utilized in enzymatic catalysis. The step-wise coating of different lipids alternated with polyelectrolytes was performed by adsorption of preformed vesicles onto... 

A polystyrene latex of monodisperse 1.0 fim diameter spheres is diluted to a volume fraction of 0.05 in water. Specific gravity of the particles is 1.05 p = 1.05p,. (a) Using the constitutive... 

The simplest photonic crystal is nature s opal. The artificial opal is composed of monodispersed spheres of a dielectric, usually silica. Considerable work has been done using latex or polystyrene spheres, but we largely will restrict ourselves here to ceramics. In producing high-quality photonic crystals, care must be taken in each of the three main steps particle synthesis, sedimentation, and sintering. 

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. 

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