Monodisperse latices functionalities

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. 

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. 

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. 

Since monodisperse latex particles are frequently coupled to proteins, it may be desirable to produce particles with functional groups on their surfaces that... 

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).

Quantitative studies of Bragg reflection from monodisperse latexes have been conducted in this laboratory as functions of concentration, particle diameter and ionic content (3). In addition, iridescent redispersions of the polymer particles in organic media have been prepared and studied (, 5). This paper discusses the results of these studies, conclusions arrived at with respect to the type and extent of order in monodisperse latexes, and the suitability of these systems as models for the investigation of order-disorder transitions. 

In continuous operation mode, both feed and effluent streams flow continuously. The main characteristic of a continuous stirred tank reactor (CSTR) is the broad residence time distribution (RTD), which is characterized by a decreasing exponential function. The same behavior describes the age of the particles in the reactor and hence the particle size distribution (PSD) at the exit. Therefore, it is not possible to obtain narrow monodisperse latexes using a single CSTR. In addition, CSTRs are hable to suffer intermittent nucleations [89, 90) that lead to multimodal PSDs. This may be alleviated by using a tubular reactor before the CSTR, in which polymer particles are formed in a smooth way [91]. On the other hand, the copolymer composition is quite constant, even though it is different from that of the feed. 

Intensity autocorrelation functions sampled at 2m =128 equidistant time delays were recorded at a scattering angle of 90° for several monodisperse latex dispersions. For a monodisperse sample the information content can be modelled by a sum of two exponentials so that in this case eq. (10) can be written as... 

Figure 1 Singular values of the Hankel matrix of the intensity autocorrelation function of a 220 nm diameter monodisperse latex, sampled at 128 equidistant time windows at a single angle of 90° (semi-logarithmic scale).

FIGURE 5.15 An example of a correlation function g(t) collected in a dynamic light-scattering experiment on 100-nm monodisperse latex beads. 

Figure 5.15 shows an example of a correlation function measured for a sample consisting of monodisperse latex beads. For a polydisperse sample (i.e., particles with a size distribution), the analysis of scattering data is more complicated, but the molecular weight distribution can be determined by modeling the correlation function as the sum of the contributions from different discrete molecular weights. 

Fig. 12.22 Particle sizes of suspensions of monodisperse latex particles in water with a particle size of Xspec = 214pm determined with different SE-Sensors as function of the mean value of the transmission T...

Even this equivalent size distribution may be biased due to sampling efficiency as a function of particle size. Let us assume a calibration curve obtained using five monodisperse latex samples. In the measurement of a real sample of polydisperse latex particles, even though each pulse will correspond to the right size, the number of pulses in each size segment will be distorted due to non-constant sampling efficiency therefore the particle size distribution will... 

Investigations of the electrophoretic behaviour of monodispersed carboxylated polystyrene latex dispersions as a function of particle size and electrolyte concentration by Shaw and Ottewill191 have confirmed, at least qualitatively, the existence of tea and relaxation effects. 

The foregoing methods developed for the preparation and characterization of monodisperse polystyrene latexes to be used as model colloids can also be applied to the characterization of industrial latexes. The recipes used for the preparation of these industrial latexes are complex, and most contain a small amount of a functional monomer, e.g., acrylic acid, 2-sulfoethyl methacrylate, or N-methylolacrylamide. These functional monomers are often predominantly water-soluble, so that their use may have several results (i) the monomer may polymerize in the aqueous phase to form a water-soluble polymer that remains in the serum ... 

The latexes investigated were the 357 nm Dow monodisperse polystyrene (LS-1010) and two polydisperse polystyrene latexes prepared in our laboratory (2) where the concentration of functional monomer, Cops II (Alcolac-ammonium salt of a short chain vinyl sulfonate), added to the recipe was 10 3 and 10 -M for and C, respectively. 

The various latexes were characterized with respect to particle size and size distribution, surface charge and functional group density, and electrophoretic mobility behavior. As observed by transmission electron microscopy all latexes were found highly monodisperse with a uniformity ratio between 1.001 and 1.010, a property due to the short duration of the nucleation period involved in the various radical-initiated heterogeneous polymerization processes. The surface charge density was determined by a colorimetric titration method reported elsewhere [13]. 

Figure 10 shows the variation of the relative viscosity with the counterion molarity at different reduced shear stress values for monodisperse polystyrene latex having a diameter of 0.192 xm at dispersed-phase volume fraction = 0.509. Clearly, is a function of the electrolyte concentration in addition to the reduced shear stress. 

A priori, latices formed by the polymerization of dispersions of a water-insoluble monomer in aqueous media are expected to exhibit a wide distribution of particle sizes. In the 1950 s, chemists at the Dow Chemical Company discovered that a batch of polystyrene latex consisted of spherical particles that were uniform in diameter. At the time, this was considered a laboratory curiosity. Nowadays, monodisperse latices have found a wide variety of applications [74]. An early application was in pregnancy testing kits. Other uses are in diagnostic tests for various ailments and for the presence of illegal drugs. These microparticles are available in a variety of colors and with various functionalities along the polymer chains. They may be prepared as porous particles and as... 

---