Abstract

A prism-cell laser light-scattering (PCLLS) spectrometer capable of measuring the angular distribution of time-averaged scattered intensity at small scattering angles (2°≲ θ ≲ 13° at λ_o = 632.8 nm and n = 1.33, corresponding to 4600 cm" ≲ K ≲ 30000 cm^-1, with K, λ_o and n being the magnitude of the scattering vector, the wavelength of light in vacuo and the refractive index of the scattering medium, respectively) by means of a linear intensified photodiode array (PDA) detector and simultaneous determination of intensity-intensity time correlation functions at two different scattering angles using two photomultiplier tube (PMT) detectors and associated digital photon correlators is described. The unique prism light-scattering cell also permits measurements of the refractive index of the scattering medium to better than one part in 10⁶. The use of high quality optical glass in the entrance window and in the exit prism of the light-scattering cell for the incident laser beam, together with an aperture after the entrance window and in the scattering medium, results in a substantial reduction of the parasitic scattering along the light path. With the PDA and one of the PMTs mounted on a rotating arm, the angular ranges of our PCLLS spectrometer are limited mainly by optical geometry. For typical dilute aqueous solutions or suspensions, self-beating light-scattering measurements down to a scattering angle of 2° have been achieved. Measurements of self-beating linewidths for a polymer solution undergoing coil-to-globule transition are reviewed and some signal-to-noise ratio considerations for particle sizing in polymer solutions are presented.

© 1988 Optical Society of America