Dynamics of Semiflexible Polymer Solutions in the Highly Entangled Regime

Abstract

We present experimental evidence that the effective medium approximation (EMA), [D. C. Morse, Phys. Rev. E 63, 031502 (2001)], provides the correct scaling law of the plateau modulus G0 proportional variantrho4/3Lp(-1/3) (with rho the contour length per unit volume and Lp the persistence length) of semiflexible polymer solutions, in the highly entangled regime. Competing theories, including a binary collision approximation (BCA), instead predict G0 proportional, variantrho7/5Lp(-1/5). We have tested both predictions using F-actin solutions which permit experimental control of Lp independently of other parameters. A combination of video particle tracking microrheology and dynamic light scattering yields independent measurements of G0 and Lp, respectively. Thus we can distinguish between the two proposed laws, in contrast to previous experimental studies focused on the (less discriminating) concentration dependence.

Confining Potential when a Biopolymer Filament Reptates

“…This concentration dependence of the tube radius has been recently revisited [21,22] but we show below that this simple relation is consistent with our experimental data. The BCA allows us to employ this relation locally, on a mesh-by-mesh basis, in order to relate local spatial variation of actin density to local spatial variation of the tube radius.…”

i-Rheo: Measuring the materials' linear viscoelastic properties “in a step”!

“…Moreover, it offers the opportunity to revise the outcomes of previous rheological studies where original measurements were either interpreted by means of theoretical models or "partially discarded" because of the absence of an effective tool for data analysis. This new tool allows the investigation of frequency regions previously "difficult" or "impossible" to access by conventional methods; thus, the opportunity to gather new insights on relaxation phenomena for a variety of materials, with particular attention to those for which the TTS method is not applicable (e.g., polymer solutions [63,64] and biological samples [65][66][67]). Indeed, we envisage the impact that this new analytical tool will have on all those biological systems (e.g., actin-fascin network [68]) for which the knowledge of their LVE properties, over a wide range of frequencies, can provide a better understanding of both the molecular structure and interactions at different length scales.…”

Fluctuations of Stiff Polymers and Cell Mechanics

“…This characteristic dependence on concentration has indeed been observed experimentally (Hinner et al, 1998;Tassieri et al, 2008;Vincent et al, 2007). The tube model predicts a high-frequency limiting form of the complex, frequencydependent shear modulus, resulting from the dynamic response of longitudinal fluctuations (see Sec.…”

“…Both theories give rise to conflicting predictions for the concentrationdependence of R and L e , opening a debate on the appropriate theoretical description of semiflexible polymer solutions, and they have therefore been challenged by experiments and simulations, which have either been in favor of the BCA (Romanowska et al, 2009;Wang et al, 2010;Ramanathan & Morse, 2007) or of the EMA (Tassieri et al, 2008). This controversy results in part from the close match of the scaling exponents in the BCA (R ∝ c −3/5 ) and the EMA (R ∝ c −1/2 ), suggesting that an unambiguous distinction between the two power-laws is extremely difficult to establish experimentally (Tassieri et al, 2008). In addition, respective conclusions must be drawn with care, since experiments typically yield skewed distributions of the tube radius, rendering an interpretation in terms of mere average values problematic (Wang et al, 2010;Glaser et al, 2010).…”