Latex wide-angle light scattering

Wide angle light scattering is used as the principal probe to examine the core-shell structure proposed for certain acrylic acid acrylate ester copolymer latexes. Additional techniques were sedimentation and photon correlation spectroscopy. 

Since the accuracy of the light scattering apparatus and the reliability of the inversion procedure had been proven by comparison of four methods on Dow polystyrene latex LS-1028-E (6), it was decided to examine a larger latex in more detail as a further study of the method of determining the internal structure of a latex by wide-angle light scattering. 

The typical results of the wide-angle light-scattering (WALS) analysis on the latex particles that were presumed to be cores are given in Table I where the theoretical model to be fitted was either S = sphere or CS = core-shell, the variance measured the goodness of fit, the modal size parameter is given by aM = 27rr/A, aQ is the log normal breadth parameter, DM is the core diameter in ym, mi the relative refractive index of the core and m2 the relative refractive index of the shell of indicated thickness. 

Table I. Wide-Angle Light Scattering Results on Latex 41BRD30 (No-acid cores with turbidimetric diameter of 0.41 ym)...

Table II. Wide-Angle Light Scattering Results on Latex 42BRD47...

Independent of the model used, it is quite clear that the core diameter is 0.44 to 0.45 ym and the relative refractive index of the core is 1.22+0.02. The evidence for a shell structure is again very tenuous. The "shell" thickness is unrealistically large, constant in extent, and little different from the results for the no-acid latex. If a shell structure was present it was at best marginally observable in the wide-angle light scattering. 

Wide angle light scattering experiments have been carried out with sufficient accuracy to separately identify dust or extraordinary particles, latex particles and small-molecule scattering. 

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