Transport of Probe Particles in Semidilute Polymer Solutions

Abstract

Dynamic light scattering and sedimentation measurements are carried out to study the motion of probe particles in neutral and adsorbing polymer solutions. By varying the microscopic interaction between the colloidal particle and the polymer molecule, we observe three different behaviors to the Stokes−Einstein (SE) equation in the same colloid−polymer system. The measurements clearly delineate the sample conditions under which the three different behaviors are observed, respectively. It is shown that the three different behaviors can be explained consistently in terms of the microstructures formed in the colloid−polymer mixture. The experiment demonstrates the importance of restraining the particle−medium interaction in the measurement of the microrheological properties of complex fluids.

Gel trapping of dense colloids

“…Using a conservative estimate for correlation length, ξ , which gives an idea of the size of gaps in a gel network, it was found that the gels in this study had a mesh size no larger than 0.1 µm, while the solids studied here were two orders of magnitude larger than that [10]. This ruled out the possibility of solids falling through the network.…”

Influence of polymer architectures on diffusion in unentangled polymer melts

“…Recent simulations 48,49 and experiments 50 have shown that the tracer D of nanoparticles having a size R similar or smaller than the R g of the polymers in the melt scales with a power law relation, D ∝ R −3 rather than to D ∝ R −1 relation expected from Stokes law with a fixed solution viscosity. This scaling was rationalized by Wyart and DeGennes, 51 and others following them, 52–55 as arising from the particles “sensing” a local viscosity distinct from the macroscopic viscosity. These observations suggest that we might think of the polymers in the melt as being similar in a coarse-grained sense to tracer particles having dimensions comparable to the surrounding polymers.…”

Charge and Size Dependence of Liposome Diffusion in Semidilute Biopolymer Solutions

“…Our analysis of particle diffusion in polymer networks is based on the theory of colloids in macromolecules described by Brochard‐Wyart and de Gennes 14, 38, 39. According to this description, the viscosity experienced by the colloid‐like probe is expressed in terms of the local viscosity η c .…”

“…For this reason, diffusion measurements of colloids in macromolecular networks,6, 7 biological gels8 or living cells9 have attracted growing interest in recent years 1, 10–12. Transport of spherical particles through macromolecular solutions can be measured using various experimental techniques such as static and dynamic light scattering,11, 13, 14 particle tracing within fluorescence microscopy data,15, 16 or fluorescence correlation spectroscopy (FCS) 17, 18. FCS is selective for the fluorescently labeled probe, a feature which distinguishes this method from light scattering, and which allows selective probing of liposome diffusion in dense, as well as possibly turbid medium 19.…”