Suspensions Of Latex Spheres Research Articles

Determinación del tamaño de partículas pequeñas por scattering de luz

En este trabajo se describe el diseño y la construcción de un sistema para medir la distribución angular del scattering de luz de micro esferas dieléctricas suspendidas en agua, usando un láser como fuente de luz. El trabajo cubre el desarrollo de un sistema de detección óptico para mejorar la relación señal ruido. Reportamos medidas experimentales de scattering de luz de suspensiones coloidales de esferas de látex con diámetros nominales de 0,49 y 1,03 µm, y un coeficiente de variación de 3%. Se utilizaron dos láseres de diferentes longitudes de onda, 632,8 y 532,0 nm, para observar la variación de la distribución angular de scattering. Los resultados experimentales fueron comparados con distribuciones de scattering angular generadas por la teoría de Mie para determinar el tamaño de partícula. Los diámetros obtenidos fueron 0,49 y 0,95 µm con una incertidumbre relativa de 6,1 y 5,3%, respectivamente.

Polarized radiative transfer in two-dimensional scattering medium with complex geometries by natural element method

The natural element method (NEM) is extended to solve the polarized radiative transfer problem in a two-dimensional scattering medium with complex geometries, in which the angular space is discretized by the discrete-ordinates approach, and the spatial discretization is conducted by the Galerkin weighted residuals approach. The Laplace interpolation scheme is adopted to obtain the shape functions used in the Galerkin weighted residuals approach. The NEM solution to the vector radiative transfer in a square enclosure filled with a Mie scattering medium is first examined to validate our program. We then study the polarized radiative transfer in two kinds of geometries filled with scattering medium which is equivalent to a suspension of latex spheres in water. Three sizes of spheres are considered. The results for non-dimensional polarized radiative flux along the boundaries and the angular distributions of the Stokes vector at specific positions are presented and discussed. For the complex geometry bounded by the square and circular object, numerical solutions are presented for the cases both with Lambertian (diffuse) reflection and with Fresnel reflection. Some interesting phenomenon are found and analyzed.

Avoiding coffee ring structure based on hydrophobic silicon pillar arrays during single-drop evaporation

A simple and novel method for avoiding the coffee ring structure has been demonstrated based on hydrophobic silicon pillar arrays during single-drop evaporation. When a drop of a colloidal suspension of latex spheres is dropped onto hydrophobic silicon pillar arrays with high contact angle hysteresis, the latex spheres are deposited at the periphery to form a porous gel foot due to the Wenzel wetting state of the drop on the substrate, which results in an effective elimination of the coffee ring structure. The coffee ring effect is avoided by relying on radially inward mass transport: a circulatory fluid flow triggered by means of the gel foot growth. Thus, uniform and ordered macroscale colloidal photonic crystals are fabricated. In the meantime, the influences of some factors, such as concentration of latex spheres, evaporation temperature, periodicity of hydrophobic silicon pillar arrays and the distance between the top rims of adjacent silicon pillars on drop deposition are investigated. This facile approach to eliminating the coffee ring structure will be of great significance for extensive applications of drop deposition in biochemical assays and material deposition.

Four-wave mixing in a liquid suspension of dielectric microspheres

In this work a theory of the degenerate four-photon parametric scattering (FPS) is developed in a liquid suspension of transparent microspheres (heterogeneous medium), the nonlinearity of which is caused by the change in the microsphere concentration under the action of gradient forces in the electromagnetic field of interacting waves. It is shown that the water suspension of latex spheres with diameter d = 0.234 μm and concentrationN0 = 6.5·10 cm, in effect of the FPS process, corresponds to a cubic nonlinear medium with the optical Kerr coefficient n2 that is larger by a factor of 10 than in the case of CS2.

Optical investigation of shear- and time-dependent microstructural changes to stabilized and depletion-flocculated concentrated latex sphere suspensions

An original experimental set up was designed combining a Couette flow system and an optical sensor measuring the light flux multiple scattered from a flowing suspension. The method was used to study shear- or time-dependent microstructural changes to a concentrated suspension of monodispersed latex spheres (diameter 170 nm) for particle volume fraction ranging from 1% up to 48%. Microstructural changes were caused either by shear forces acting upon stabilized latex particles or by the addition of carboxymethylcellulose polymer chains inducing reversible depletion flocculation of latex spheres.

Mueller matrix of dense polystyrene latex sphere suspensions: measurements and Monte Carlo simulation

Mueller matrices of dense aqueous suspensions of different concentrations are measured with a phase-modulated Mueller ellipsometer as a function of the scattering angle. Different concentrations of a solution containing 404-nm-diameter polystyrene latex spheres dispersed in water were prepared. Experimental results are compared with a three-dimensional Monte Carlo simulation of the propagation of photons with the cell geometry accounted for. The Fresnel laws and the Mie theory determine the changes in direction and polarization during the propagation of the photon. Excellent agreement over the whole angular range is found between experimental and simulated Mueller matrices.

Particle size determination: An undergraduate lab in Mie scattering

A technique for determining the size of microscopic spherical particles using light scattering is presented as an undergraduate physics lab. Scatterer size is determined from angular scattering distribution measurements of laser light scattered from a dilute suspension of latex spheres with diameters of 4.99±0.05 and 6.038±0.045 μm. Previous experiments of this type used approximate theoretical corrections and required the construction of specialized sample cells to minimize complicating effects. As a significant improvement to these, we generate angular scattering distributions from Mie theory and, using an accurate numerical procedure, correct these distributions for Snell’s law and foreshortening effects. Scatterer size is then determined using a fast, robust fitting algorithm to compare these corrected angular scattering distributions to measured angular scattering distributions. We fit the scatter from a solution of 6.04-μm-diam spheres to spheres of 5.95±0.11 μm diameter, and that from a solution of 4.99-μm spheres to 4.85±0.15 μm. Additionally, scattering data for a 2:1 mixture of spheres of diameters 4.99 and 6.04 μm are taken, and after numerical adjustment for Snell’s law and foreshortening effects, good agreement with theory is obtained.

Phase-modulated Mueller ellipsometry characterization of scattering by latex sphere suspensions

Phase-modulated Mueller ellipsometry (PMME) is used to probe scattering by suspensions of polystyrene latex spheres, with particle diameters ranging from 400 nm to 3 microm. PMME allows simultaneous measurement of the 16 coefficients of the Mueller matrix. Furthermore PMME measurements can easily be carried out owing to a calibration procedure implemented in a scattering configuration. The measurements performed on low concentrations show good agreement with Mie theory. Moreover size distribution could be obtained with a least-squares method based on a genetic fit algorithm. Experimental evidence of multiple scattering on PMME measurements is also presented.

受精卵活性評価のためのファイバー化散乱光計測システム(II)

We evaluated the newly designed fiber-optic measurement system to measure human embryo viability. We measured angular distribution of the light scattering intensity to measure the embryonic mitodchondrial density in which localization may relate to the developmental ability. The size selectivity of the system was investigated with the latex sphere suspensions. The measured light scattering of these suspensions showed good agreement with the calculated results of which scattering distribution were differerent according to the latex diameter. We measured the light scattering of live mouse embryo. Since the measured scattering patterns of the embryo were similar to the pattern abtained from mitochondria equivalent particle, we think the measured light scattering manly originated from mitochondria in the live embryo. Our measurement method might become the practical selecting method of embryo to suppress the multiple pregnancy on current in vitro fertilization-embryo transfer.

Physical and chemical effects of red cells in the shear-induced aggregation of human platelets

Both chemical and physical effects of red cells have been implicated in the spontaneous aggregation of platelets in sheared whole blood (WB). To determine whether the chemical effect is due to ADP leaking from the red cells, a previously described technique for measuring the concentration and size of single platelets and aggregates was used to study the shear-induced aggregation of platelets in WB flowing through 1.19-mm-diameter polyethylene tubing in the presence and absence of the ADP scavenger enzyme system phosphocreatine-creatine phosphokinase (CP-CPK). Significant spontaneous aggregation was observed at mean tube shear rates, (G) = 41.9 and 335 s-1 (42% and 13% decrease in single platelets after a mean transit time (t) = 43 s, compared to 89 and 95% decrease with 0.2 microM ADP). The addition of CP-CPK, either at the time of, or 30 min before each run, completely abolished aggregation. In the presence of 0.2 microM ADP, CP-CPK caused a reversal of aggregation at (t) = 17 s after 30% of single cells had aggregated. To determine whether red cells exert a physical effect by increasing the time of interaction of two colliding platelets (thereby increasing the proportion of collisions resulting in the formation of aggregates), an optically transparent suspension of 40% reconstituted red cell ghosts in serum containing 2.5-micron-diameter latex spheres (3 x 10(5)/microliters) flowing through 100-microns-diameter tubes was used as a model of platelets in blood, and the results were compared with those obtained in a control suspension of latex spheres in serum alone. Two-body collisions between microspheres in the interior of the flowing ghost cell or serum suspensions at shear rates from 5 to 90 s-1 were recorded on cine film. The films were subsequently analyzed, and the measured doublet lifetime, tau meas, was compared with that predicted by theory in the absence of interactions with other particles, tau theor. The mean (tau meas/tau theor) for doublets in ghost cell suspensions was 1.614 +/- 1.795 (SD; n = 320), compared to a value of 1.001 +/- 0.312 (n = 90) for doublets in serum. Whereas 11% of doublets in ghost cell suspensions had lifetimes from 2.5 to 5 times greater than predicted, in serum, no doublets had lifetimes greater than 1.91 times that predicted. There was no statistically significant correlation between tau meas/tau theor and shear rate, but the values of tau meas/tau theor for low-angle collisions in ghost cell suspensions were significantly greater than for high-angle collisions.

Comments on ultrasonic propagation in suspensions

In determining the velocity and attenuation of suspensions of spherical particles, results obtained from the computationally simpler multiple scattering approach of Waterman and Truell (WTF) and from a multiple scattering formalism (MSF), which considers the pair correlation function, have been compared in order to justify the range and applicability of the former method. Although the difference between the results increases as the concentration of suspensions increases, the frequency-dependent attenuation computed from the two approaches can be quite different particularly in the low-frequency range even at lower concentrations. Due to the unavailability of experimental data for ultrasonic propagation, data from analogous optical experiments on suspensions of latex spheres are compared. The MSF shows excellent agreement, whereas the WTF shows large discrepancies from the experimental data.

Method of measuring the phase function of a turbid medium in the small scattering angle range

A method is described for measuring the phase scattering function of a turbid medium in the near forward direction. The method is based on the use of a transmissometer with a variable field of view and is suitable for measurements on natural media, such as water or turbid atmospheres. Some precautions to be taken to avoid the effects of multiple scattering are indicated. Results of laboratory tests on suspensions of latex spheres in water are presented. An example of the use of the instrument in natural fog is also shown.

Comparison between measured and calculated contributions of multiply scattered radiation to the transmittance of a light beam through a turbid medium

Results are presented of measurements pertaining to multiple scattering effects on the propagation of a HeNe laser beam through suspensions of latex spheres in water. Both spheres with a large radius in comparison with the radiation wavelength and spheres with a small radius were used. The data are compared with numerical results obtained by means of a Monte Carlo method employing scaling relations. The effect of varying the distance between the diffusing medium and the receiver was examined.

Cytochemical localisation of acid phosphatase in the phagocytising conjunctival epithelium of the guinea pig.

The ultrastructural localisation of acid phosphatase activity was investigated on the guinea pig conjunctival epithelium incubated in vivo with a suspension of latex spheres. Deposits of acid phosphatase reaction product were concentrated on the elements of GERL, the phagocytic vacuoles, and the cell membrane. Acid phosphatase activity in GERL was intense in basal and suprabasal cells and decreased towards the superficial cells. Phagosomes containing latex spheres and reaction product of acid phosphatase were observed mainly in the centrospheral region of the superficial and intermediate epithelial cells. Acid phosphatase activity in phagocytising cells was not increased as compared to that in non-phagocytising cells. The observations indicate that existing acid phosphatase in unstimulated conjunctival epithelial cells is released into heterophagosomes brought within the lysosomal compartment. The number of secondary phagosomes seems to be increased by intercellular transport of latex spheres to the acid phosphatase rich cells in the deep layers of the epithelium.

Two-dimensional aggregation and crystallization of a colloidal suspension of latex spheres

Etude experimentale de cristallisation bidimensionnelle de spheres de latex calibrees, Browniennes en suspension dans l'eau. L'interaction, controlee par un champ electrique alternatif, s'avere attractive dans une large gamme de frequence. Elle conduit a un phenomene d'agregation de cristallites fractals. La dimension fractale mesuree D=1,74±0,05 est en bon accord avec la theorie d'agregation dynamique des amas. La fusion continue des cristallites intervient lorsque la frequence augmente. La diffusion de la lumiere montre alors l'existence d'une phase intermediaire de symetrie hexatique

Laser heterodyne apparatus for measuring small angle scattering from particles

A laser heterodyne apparatus for measuring small angle scattering from streaming particles in gases and liquids has been developed. A diffraction grating is used to create the local oscillator light beam, which makes the apparatus simple and practical to handle. A quantitative theory of the complete apparatus is presented together with experimental confirmation by measurements on water suspensions of latex spheres with known diameters and concentrations. The apparatus could be used to measure continuously mass contents and mass flows in streaming media.

Ordering in colloidal systems

The role played by statistical mechanics in the ordering of colloidal systems is examined. This role is made explicit through a study of phase (order-disorder) transitions in 1, 2 and 3 dimensions which exist in the examples provided by clay plate, tobacco mossaic virus and latex sphere suspensions. Essentially the statement is that the extrapolation of DLVO theory which attributes stability to a balance between attractive and repulsive two-body forces is not always a panacea. The ideas of Langmuir and Onsager who dealt with statistical mechanics and repulsive forces and considered that attractive long-range forces are not always important are paramount for some systems and must be built into existing theories.

Laser spectrophotometer for measuring differential cross sections of biological particles

A tunable laser spectrophotometer is described that can accurately measure the differential scattering cross sections of small particle suspensions in the visible spectral range. The instrument was calibrated using a suspension of latex spheres of known size and index of refraction. By increasing the intensity of the illuminating laser, it should be possible to study differential scattering processes of individual particles on a microsecond time scale.

Two-channel laboratory scattering meter

An instrument was designed and built that measures the light scattered at 2° and at 90° simultaneously. The instrument employs a laser source, solid-state detectors, and a flow-through scattering cell for laboratory use. A Mie theory computer program was used to calculate the theoretical volume-scattering function for suspensions of latex spheres. The ratios of the theoretical to measured scattering functions for these suspensions are not greatly different from unity, thereby providing acceptable verification of the calibration technique employed.

Light transmission measurements on suspensions

Measurements of the efficiency factor K under rigorously controlled experimental conditions are reported for nine monodisperse suspensions of latex spheres in water for the wavelength range in air from 0?38 to 0?63 ?m. These show good agreement in the range x = 0-30 with Irvine's computations from Mie's theory for m = 1?2, but the effect of optical dispersion on the (K, x) curve is significant. Secondary oscillation (ripple) has been detected in the K value for x values in the range 25-28.