Another way to view the chain conformation broadening of the line-width distribution measured in dynamic light scattering

Abstract

In dynamic laser light scattering (LLS), for a given plydisperse sample, a line-width distribution G(Γ) or the translational diffusion coefficient distributionG(D) can be obtained from the measured time correlation function. For rigid colloid particles,G(Γ) can be directly related to the hydrodynamic size distribution. However, for flexible polymer chains, G (Γ) depends not only on the chain length distribution, but also on the relaxation of the chain conformation; that is, even for a monodisperse polymer sample there still exists a chain conformation distribution. If the time scale of the chain conformation relaxation is comparable to that of the translational diffusion, such as in the case of a very long polymer chain, the conformation relaxation might lead to an additional broadening in G(Γ). This ‘conformation broadening’ has been directly observed for the first time by comparing twoG(Γ)s obtained from a ply(N-iso-propyl-acrylamide) solution at ~25°C: and ~ 32°C at which the solution is thermodynamically stable, where the fact is utilized that the PNIPAM chain can change from an extended and flexible coil at ~25°C into a highly collapsed and compact globule at ~ 32°C at which pint the polymer chain conformation distribution has diminished.