Laser light scattering Latex

Seed Latex The seed latex was prepared as described before (10). It had a solids content of 17.0% and its number average diameter was about 0.045 y as measured by quasielastic laser light scattering (15). 

Chang, K., Litt, M., and Jamieson, A. M., "The Measurement of Latex Particle Size by Quasielastic Laser Light Scatter-ing", J. Poly. Sci.-Phys., to be published. 

The physical significance attached to the a1 and a2 dimensions in this study is identical to that which we obtained for a series of MBAS impact plastics (2) containing butadiene rubber where rubber latex particle size was determined independently. We found that both laser light scattering and electron microscopy results agreed. 

Homogeneous assays can be performed without the need for separation. This can be advantageous with respect to convenience, time and cost of the assay and also facilitates automation. The detection method must be able to differentiate between bound and free antibodies without physically separating them from each other. An example of such a detection method is the turbidity measurement of the reaction mixture by laser light scattering or absorption. The more immuno-complexes are present in the reaction mixture, the higher its turbidity. Often, latex or gold particles are attached to the antibodies to enhance this turbidity effect. 

An example of an application of homodyne spectroscopy is the measurement of the size distribution of small particles in the nanometer range that are dispersed in liquids or gases and fly through a laser beam. The intensity 4 of the scattered light depends in a nonlinear way on the size and the refractive index of the particles. For small homogeneous spheres with diameters d, which are small compared to the wavelength (d A), the relation oc d holds. In Fig. 12.25 the measured intensity distribution of laser light scattered by a mixture of latex spheres with d = 22.8 nm and d = 5.7 nm (small squares) is compared with the size distribution obtained from electron microscopy, which can be used for calibration [12.91]. 

The theoretical analysis of the scattered spectrum was first presented by Komarov and Fisher (3) and Pecora (4) independently in 1963. In 1964 the spectrum of laser light scattered by dilute solutions of polystyrene latex spheres was observed (5) and was foimd to exhibit a lineshape in good agreement with theory. In a typical scattering experiment (6) a monochromatic beam of radiation is incident on the material the wave vector is denoted as ko and the frequency by coo- The scattered radiation is recorded as a function of the scattering angle and frequency shift co, where... 

Pig. 9. Particle size distribution of rubber particles purified from guayule stem bark and Hevea latex. Measurements were made on rubber particles in aqueous suspension using a Horiba LA-900 Laser Light Scattering Particle Size Distribution Analyzer. —O—, Hevea — —, Guasnile. Data from Ref 12. 

Our experiments are typically carried out at DNA concentrations of 20-50 /ig/ml with 1 ethidium per 300 bp, so that depolarization by excitation transfer is negligible.(18) The sample is excited with 575-nm light, and the fluorescence is detected at 630, 640, or 645 nm. Less than one fluorescent photon is detected for every 100 laser shots. The instrument response function e(t) is determined using 575-nm incident light scattered from a suspension of polystyrene latex spheres. 

There are special problems that occur when the particle diameter Is large relative to the wavelength of Incident light. This Is of Interest since many latex systems have particles with diameters of 300 to 1000 nm and a large ratio of particle to fluid refractive Index (1.2 for polystyrene latex). The most common wavelengths for lasers used In light scattering are on the order of 500 nm. 

Figure 5.S Variation of ligjji scattering over the angle from 35 to 120 from the forward direction for a He-Ne laser light source (A = 0.633 m). Particles were latex On = 1.588) and nigrosin dye Oti = 1.67 — 0.26/). The lower branch shows the approach to the Rayleigh seattering range (response tmd the upper branch shows the approach to geometric optics (response (Garvey and Pin nick. 1983).

Fig. 11. Light scattering profiles for Hevea and guaynle latex rubber gathered from 18 different angles of Wyatt Technology Corporation DAWN DSP Laser Photometer, analyzing rubber passed through an Agilent Technolc ies HP 1100 HPLC, with 2 P-gel columns in series.

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