Diffusion of a rodlike virus in complex solutions
Entanglement phenomena in concentrated polymer solutions remain an interesting and challenging problem. It is still unclear how entanglement onset affects polymer chain motion at small distance scales. One way to study such motion is to follow the diffusion of a probe particle while increasing the concentration of the polymer. Many such studies have been done using probes ranging from linear and star polymers to various colloidal particles; however, relatively few studies have used rodlike probes. Rodlike probes are potentially more interesting due to the added information that may be gained by following rotational as well as translational diffusion. The anisotropic diffusion may allow the probe to sense something different as chains begin to entangle. The situation is unclear even for the simpler polymeric structures such as rigid rods. Due to lack of experimental data, the nature of interactions of rigid rods in concentrated solutions remains uncertain. Given the vast theoretical descriptions available, the current challenge is to find suitable rigid model particles. To date, self diffusion data for truly rigid rods is limited to only one system, colloidal boehmite, which was quite polydisperse. Described here is the use of depolarized dynamic light scattering to measure the rotational and translational diffusion of the rodlike virus, Tobacco Mosaic Virus (TMV), through solutions of random coil and globular polysaccharides, taken separately. The polymers are effectively invisible in the depolarized scattering experiment allowing only the TMV probe to be seen. Also described is the use of fluorescence photobleaching recovery to measure the self-diffusion of TMV as a function of concentration in the isotropic regime.
depolarized dynamic light scattering, tobacco mosaic virus, tmv
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