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 f...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.展开更多
基金Supported by the Climbing Project of the Chinese National Basic Project--Macromolecule Condensed State, the Research Grants Council (RGC) of Hong Kong Government Earmarked Grants 1997/98 (CUHK4181/97P, 2160082, RGC/96-97/03)the National Distinguish
文摘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.
