Monodispersed latexes

Kose A and Hachisu S 1974 Kirkwood-Alder transition in monodisperse latexes. I. Nonaqueous systems J. Coiioid interface Sc/. 46 460-9... 

Flachisu S and Kobayashi Y 1974 Kirkwood-Alder transition in monodisperse latexes. II. Aqueous latexes of high electrolyte concentration J. Colloid Interface Sol. 46 470-6... 

Kose A and Flachisu S 1976 Ordered structure in weakly flocculated monodisperse latex J. Colloid Interface Sol. 55 487-98... 

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. 

Figure 3 shows calibration plots of log (particle diameter) vs. elution voliame difference (AV) between marker and particle using three different monodisperse latexes at a low eluant ionic strength of 1.29 mM SLS. These results illustrate the featiire of universal calibration behavior predicted by the capillary bed model as mentioned earlier. Of note also is the fact that the curve deviates from linearity for the 38 nm particle and begins to approach the origin as also indicated by the model calculations. 

SLS) or sodiiim dihexylsulfosuccinate (AMA) with no added salt. Monodisperse latex (the Dow polystyrene standards and PVC standards) samples were used. 

Binks BP, Lumsdon SO. Pickering emulsions stabilized by monodisperse latex particles effects of particle size. Langmuir 2001 17 4540-4547. 

High molecular weight monodisperse polystyrene latexes have been prepared by this method [158]. A number of factors were found to influence the size and dispersity of the particles. The size decreased with increasing surfactant concentration and decreasing internal phase volume, and a more monodisperse latex... 

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. 

Spherical particles of known diameter (e.g., 5% to 20% of the diameter of the aperture in the glass tube) are used to calibrate the electrical pulse counting instrument. The particles are suspended to an appropriate concentration in electrolyte solution (see recipe). Monodisperse latex particles are commercially available, which can be used for this purpose. Particle size calibration standards can be obtained from a number of chemical suppliers or from the National Institute of Standards and Technology (e.g., NBS 1003b). Lines (1996) lists a number of standards that are appropriate for this purpose. 

Most technological suspensions consist of very polydisperse particles. In order to simplify his experimental system Stotz employed monodispersed latex suspensions (particle diameter = 6 or 30y). In an interesting comparative experiment, he also measured the particle mobilities using the simple... 

Seven polystyrene latexes prepared with persulfate initiator and bicarbonate buffer were characterized to demonstrate the efficacy of this method (6). Three were monodisperse latexes prepared using conventional emulsifiers four were prepared using sodium styrene sulfonate or sodium vinyltoluene sulfonate as canan-omeric emulsifiers. Each latex was subjected to serum replacement with... 

The Effect of NaCl on the Electrophoretic Mobility of PS Latex Particle. The em of the Dow 357 nm latex in the H-form and Na-form, along with two other Dow monodisperse latexes in the H-form with diameters of 795 and 1100 nm, was measured as a function of NaCl concentration. The results in Figure 1 show that the em for all three latexes increased with increasing concentration of NaCl to a maximum at about 1 x 10 "2 M NaCl followed by a rapid decrease. Converting the electrophoretic mobility to zeta potential, using tables derived by Ottewill and Shaw (6) from the results of Wiersma et al. in order to account for relaxation and retardation effects, led to the same dependency as shown in Figure 2. 

Dispersion polymerization is defined as a type of precipitation polymerization by which polymeric microspheres are formed in the presence of a suitable steric stabilizer from an initially homogeneous reaction mixture. Under favorable circumstances, this polymerization can yield, in a batch process, monodisperse, or nearly monodisperse, latex particles with a relatively large diameter (up to 15 pm) [103]. The solvent selected as the reaction medium is a good solvent for both the monomer and the steric stabilizer, but a non-solvent for the polymer being formed and therefore a selective solvent for the graft copolymer. This restriction on the choice of solvent means that these reactions can be carried out... 

In order to make a better evaluation of the relative and absolute performance of various instruments, it was necessary to obtain well characterized, monodisperse latexes having a density greater than that of polystyrene. Polymethylmethacrylate PMMA) latex with a polymer density of approximately 1.21 gm/cm was selected for this purpose. 

The particle-sizes and particle-size distribution of the two monodisperse carboxylated S/B latexes are shown in the hydrodynamic chromatograms of Figure 1. The average diameters of the large, Df, and the small, Dg, relatively monodisperse latexes were 2100A and 720Arespectively. 

The computerized HDC technique was used to quantify the relative amounts of the large 2100A and small 700A monodisperse latexes in different binary mixtures. The HDC measurements for the relative amounts of the two components were within 1% of the actual amounts. 

Polymerizable surfactants capable of working as transfer agents include thiosulfonates, thioalkoxylates and methyl methacrylate dimer/trimer surfactants. Thioalkoxylates with 17-90 ethylene oxide units were produced from ethoxylated 11 bromo-undecanol by replacing the bromine with a thiol group via the thiazonium salt route [8]. In the presence of water-soluble azo initiator the thio ended Transurfs (used at a concentration above the CMC) gave monodispersed latex particles in emulsion polymerization of styrene. However, the incorporation of the Transurf remained low, irrespective of the process used for the polymerization (batch, semibatch, seeded). The stability of the lattices when the surfactant and the transfer function were incorporated in the same molecule was better than when they were decoupled. 

In the seeded emulsion polymerization of some monomers —e.g., styrene—it is possible to obtain final latexes with uniform, large particles by adjusting, during polymerization, the quantity of added emulsifier the formation of new particles is prevented by the limited amount of emulsifier. For vinyl chloride, limited emulsifier is not sufficient to prevent the formation of new particles in fact, to obtain a monodispersed latex, the surface of the particles seeded in a given water volume must be controlled. It is assumed that the growth of new nuclei is related either to the rate of formation of primary useful radicals or to the rate that these are taken by the surface of sized particles. 

The main results are reported in Table X. In the last two series of experiments, poly- or monodispersed latexes were obtained according to the adopted formulation. 

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... 

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. 

Table VI. Preparation of Rubber Graft Polymer Using 360-A Monodisperse Latex...

We have used a suspension made of commercial monodisperse latex particles (ref. Rhone Poulenc Estapor L. 300) dispersed in water with a radius a = 1.5 /tm and a density p = 1.045. The volume fraction (0 = 10-4) is low in order to reduce particle interactions and collisions. The diffusion coefficient is determined by analyzing the trajectory of a Brownian particle in a plane perpendicular to the optical axis. A typical trajectory consisting of 22,000 different positions with a time interval of 0.1 s projected on the x-y plane is represented in Fig. 4. The diffusion coefficients along the x and y axes can be calculated independently from the records of the x(t) and y(t) positions ... 

---