Scattering and Microscopy

One of the manifestations of depletion effects in a colloidal dispersion is that its fluid structure is affected by the presence of non-adsorbing depletants (for instance polymer chains). This is reflected in the radial distribution function g r) the local concentration of particle centers from a distance r to a fixed particle center. Statistical mechanics links g(r) to the potential of mean force W f [90], 

For a dilute colloidal dispersion, g(r) = exp[—lT(r)/kr], where W r) is the pair interaction. The quantity g r) can be measured using confocal laser scanning microscopy. This method allows to perform quantitative three-dimensional real space measmements of the positions of the (fluorescently labeled) colloidal particles. Analysis of the positions of the particles yields g(r). This means that confocal microscopy enables to indirectly measure both the potential of mean force and (using a dilute dispersion) the pair interaction in a mixture of colloids and depletants. Royall et al. [91] have performed such a study in a colloid-polymer mixture with free polymers as depletants. 

Scattering techniques allow to measure the structure factor S(Q) as a function of the wave vector Q of colloidal dispersions defined as 

Here is the wavelength of radiation through the medium and Og the scattering angle. Statistical mechanics relates the structure factor S(Q) to the radial distribution function g r) [92]  

via (2.122), (2.124) reveals S(Q) contains the potential of mean force in the long wavelength limit (Q 0). 

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Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

Descriptions of the experimental scattering and microscopy conditions have been published elsewhere and are referenced in each section. Throughout this report certain conventions will be used when describing uncertainties in measurements. Plots of small angle scattering data have been calculated from circular averaging of two-dimensional files. The uncertainties are calculated as the estimated standard deviation of the mean. The total combined uncertainty is not specified in each case since comparisons are made with data obtained under... 

Three different sieved size fractions (20-45, 74-105 and 105-450 pm) of a SDDP batch have been characterized for their in vitro dissolution profiles and the textural properties of the three fractions and the original unsieved batch have been investigated by gas adsorption (B.E.T. method). Mercury Intrusion Porosimetry (MIP), light scattering and microscopy (optical and electron) techniques. 

CRJ Cristiano, C.M.Z., Soldi, V., Li, C., Aimes, S.P., Rochas, C., Pignot-Paintrand, I., and Borsali, R., Thermo-responsive copolymers based on poly(A-isopropyl acrylamide) and poly[2-(methacryloyloxy)ethyl phosphotylcholine] Light scattering and microscopy experiments, Macromol. Chem. Pltys., 210, 1726, 2009. 

Ho, D. L., Briber, R. M., and Glinka, C. J., Characterization of organically modified clays using scattering and microscopy techniques, Chem. Mater., 13, 1923-1931 (2001). 

Hong, K. Strobl, G. (2006). Network stretching during tensile drawing of pwlyethylene A study using X-ray scattering and microscopy. Macromolecules Vol.39 (2006), p>p.268-273... 

MatSjfCek, P., Cfgler, P, Prochazka, K. et al. 2006. Molecular assembly of metallacarboranes in water Light scattering and microscopy study. Langmuir 22 575-581. 

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