Calibrated latex

Figure 5 Comparison of Modified HIAC and Coulter Calibration Latex Size Distribution...

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. 

Adsorption Isotherms. The adsorption isotherms were determined using the serum-replacement adsorption or desorption methods (7). For the adsorption method, the latex samples (50 or 100 cm 2% solids) containing varying amounts of PVA were equilibrated for 36 hours at 25°C, placed in the serum replacement cell equipped with a Nuclepore membrane of the appropriate pore size, and pressurized to separate a small sample of the serum from the latex. For the desorption method, the latex samples (250 cm 2.5% solids) were equilibrated for 36 hours at 25°C and subjected to serum replacement with DDI water at a constant 9-10 cm /hour. The exit stream was monitored using a differential refractometer. The mean residence time of the feed stream was ca. 25 hours. It was assumed that equilibrium between the adsorbed and solute PVA was maintained throughout the serum replacement. For both methods, the PVA concentration was determined using a An-C calibration curve. 

The amounts oi adsorption of the polymer on latex and silica particles were measured as follows. Three milliliters of the polymer solution containing a known concentration was introduced into an adsorption tube(lO ml volume) which contained 2 ml of latex (C = l+.O wt %) and silica(C = 2.0 wt %) suspensions. After being rotated(l0 rpm) end-over-end for 1 hr in a water bath at a constant temperature, the colloid particles were separated from the solution by centrifugation(25000 G, 30 min.) under a controlled temperature. The polymer concentration that remained in the supernatant was measured colorimetrically, using sulfuric acid and phenol for the cellulose derivatives(12), and potassium iodide, iodine and boric acid for PVA(13). From these measurements, the number of milligrams of adsorbed polymer per square meter of the adsorbent surface was calculated using a calibration curve. 

M=2879, is recommended as a primary calibration standard in preference to pure liquids (too sensitive to impurities) or uniform-particle-size latexes (too sensitive to residual polydispersity). 

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

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... 

FIG. 1.8 Electron micrograph of cross-linked monodisperse polystyrene latex particles. The latex is a commercial product (d = 0.500 jun) sold as a calibration standard. (Photograph courtesy of R. S. Daniel and L. X. Oakford, California State Polytechnic University, Pomona, CA.)... 

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. 

In the optical microscope, measurements were made with a Crookes image-splitting eyepiece that was calibrated with a measuring slide. The electron microscope (Hitachi HU-11) was calibrated with latex spheres of known size. 

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. 

Bauer, C. Amram, B. Agnely, M. etal On-Line Monitoring of a Latex Emulsion Polymerization by Fiber-Optic FT-Raman Spectroscopy. Part I Calibration Appl. Spectrosc. 2000, 54, 528-535. 

The useful range of the transmission electron microscope for particle size measurement is c. 1 nm-5 p,m diameter. Owing to the complexity of calculating the degree of magnification directly, this is usually determined by calibration using characterised polystyrene latex particles or a diffraction grating. 

For this description of PCS, it is evident that, for mono-disperse systems, the technique can provide an absolute measurement of hydrodynamic size knowledge of the density or refractive index of the particles is not required, and no calibration or correction is needed. With the advent of digital correlators and microprocessors, PCS has also become a very fast and precise technique. Recent studies of latex using PCS include adsorbed layers (8), particle sizes (16), surface characterization (17) and aggregation (181- ... 

Practical difficulties in obtaining IQ led to the use of a reference intensity IR so that Igo/ljjc was plotted versus c and extrapolated to zero concentration. The method required a calibration constant which was obtained by the use of polyvinyl-toluene latex spheres of known size from electron microscopy. 

Controls, Ltd.) The apparatus was calibrated using certified viscosity standards No. S60 and S600 (Cannon Instrument Co.). The solid contents of latex samples were 2.0 wt. %. The pH adjustment was carried out using NaOH solution 24 hours prior to viscosity measurement. The viscosity measurements were carried out over a range of shear rate of 102-1()4 sec l. 

Ha et al. [93,94] prepared monodisperse polymer microspheres from 1 to 40 pm in diameter for medical diagnostic tests, as chromatography column packing and as calibration standards. The work deals with the synthesis of large and uniform poly (butadiene-styrene) latex. The ceramic SPG membrane, with a pore diameter of 1.6 pm, was employed. The uniform particle sizes were in the diameter range of 4-6 pm. 

Single-particle optical analyzers are especially useful for continuous measurement of particles of uniform physical properties. However, as discussed earlier, uncertainties develop in the measurement of particle clouds that are heterogeneous in composition because the refractive index may vary from particle to particle. Thus, in making atmospheric aerosol measurements, workers have assumed an average refractive index characteristic of the mixture to estimate a calibration curve or have reported data in terms of the equivalent particle diameter for a standard aerosol, such as suspended polystyrene latex spheres. 

A dry packed column with porous material was used for the characterization according to size of the PVAc latex samples. The packing employed was CPG (Controlled Pore Glass), 2000 A, 200-400 mesh size. Deionized water with 0.8 gr/lit Aerosol O.T. (dioctyl sodium sulphosuccinate), 0.8 gr/lit sodium nitrate and 0.4 gr/lit sodium azide served as the carrier fluid under a constant flowrate. The sample loop volume was 10 pC A Beckman UV detector operating at 254 nm was connected at the column outlet to monitor particle size. A particle size-mean retention volume calibration curve was constructed from commercially available polystyrene standards. For reasons of comparison, the samples previously characterized by turbidity spectra were also characterized by SEC. A number of injections were repeated to check for the reproducibility of the method. 

As a preliminary indication of the capability of SEC to qualitatively follow particle growth, the diameters corresponding to the peak retention volume were calculated directly from the calibration curve (without any correction for axial dispersion). "Peak average particle diameters are plotted vs. conversion for the batch runs in Figure 7, where it is clearly shown that runs B10 and Bll are replications, with latex particles smaller than those produced from run B7, as expected. In the continuous run, shown in Figure 8,... 

Prior to the measurements of the different reactor latex samples the computerized HDC was calibrated for particle-size using the standard procedure (3) and also for particle-size distribution quantification. For the particle-size distribution calibration two different particle-size monodisperse carboxylated S/B latexes were polymerized. Various mixtures of these latexes were prepared by blending the large 2100A and the small 700A latexes in different ratios by weight 60/40, 70/30, 80/20 and 90/100 respectively. 

The relative amount of each latex (Vj, Vg) in the different blends, as determined by HDC are shown in Figures 2 and 3. There was excellent correlation between the actual and the measured quantities of each component in the different binary mixtures. This calibration for particle-size distribution demonstrated that the computerized HDC could be used to determine the relative amount of each latex in the various binary mixtures within IX. 

The AeroSizer, manufactured by Amherst Process Instmments Inc. (Hadley, Massachusetts), is equipped with a special device called the AeroDisperser for ensuring efficient dispersal of the powders to be inspected. The disperser and the measurement instmment are shown schematically in Figure 13. The aerosol particles to be characterized are sucked into the inspection zone which operates at a partial vacuum. As the air leaves the nozzle at near sonic velocities, the particles in the stream are accelerated across an inspection zone where they cross two laser beams. The time of flight between the two laser beams is used to deduce the size of the particles. The instmment is calibrated with latex particles of known size. A stream of clean air confines the aerosol stream to the measurement zone. This technique is known as hydrodynamic focusing. A computer correlation establishes which peak in the second laser inspection matches the initiation of action from the first laser beam. The equipment can measure particles at a rate of 10,000/s. The output from the AeroSizer can either be displayed as a number count or a volume percentage count. 

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