Force-Extension Relation and Plateau Modulus for Wormlike Chains

We derive the linear force-extension relation for a wormlike chain of arbitrary stiffness including entropy elasticity, bending and thermodynamic buckling. From this we infer the plateau modulus $G^0$ of an isotropic entangled solution of wormlike chains. The entanglement length $L_e$ is expressed in terms of the characteristic network parameters for three different scaling regimes in the entangled phase. The entanglement transition and the concentration dependence of $G^0$ are analyzed. Finally we compare our findings with experimental data.Comment: 5 pages, 1 eps-figure, to appear in PR

Linear and nonlinear rheology of wormlike micelles

Several surfactant molecules self-assemble in solution to form long, cylindrical, flexible wormlike micelles. These micelles can be entangled with each other leading to viscoelastic phases. The rheological properties of such phases are very interesting and have been the subject of a large number of experimental and theoretical studies in recent years. We shall report on our recent work on the macrorheology, microrheology and nonlinear flow behaviour of dilute aqueous solutions of a surfactant CTAT (Cetyltrimethylammonium Tosilate). This system forms elongated micelles and exhibits strong viscoelasticity at low concentrations ($\sim$ 0.9 wt%) without the addition of electrolytes. Microrheology measurements of $G(\omega)$ have been done using diffusing wave spectroscopy which will be compared with the conventional frequency sweep measurements done using a cone and plate rheometer. The second part of the paper deals with the nonlinear rheology where the measured shear stress $\sigma$ is a nonmonotonic function of the shear rate $\dot{\gamma}$. In stress-controlled experiments, the shear stress shows a plateau for $\dot{\gamma}$ larger than some critical strain rate, similar to the earlier reports on CPyCl/NaSal system. Cates et al have proposed that the plateau is a signature of mechanical instability in the form of shear bands. We have carried out extensive experiments under controlled strain rate conditions, to study the time-dependence of shear stress. The measured time series of shear stress has been analysed in terms of correlation integrals and Lyapunov exponents to show unambiguously that the behaviour is typical of low dimensional dynamical systems.Comment: 15 pages, 10 eps figure

Anatomy of life and well-being: A framework for the contributions of phenomenology and complexity theory

This paper proposes an anatomy of the phenomena of life and of correlate qualitative modes of empirical research, theory, and professional practice concerned with health and well-being. I explicate the qualitative dynamic operative at every level of order, from the biological realm of cells and organisms, through distinctively human lifeworld experiences and practices, to communities of organisms in ecosystems and bio-cultural regions. This paper clarifies the unity of the dimensions of life and aligns these with demonstrated and emerging contributions of hermeneutical phenomenology and current complexity–autopoietic theory (including disciplinary and professional interpretations of empirical findings). The intent is begin to delineate a common framework upon which we could build—facilitating better understanding of the distinctive contributions of each specialization as well as the integration of diverse qualitative approaches with each other (and with quantitative complements)

Biological Ion Exchanger Resins: II. QUERP Water and Ion Exchange Selectivity

Biological selectivity is shown to vary with medium osmotic strength and temperature. Selectivity reversals occur at 4°C and at an external osmolality of 0.800 indicating that intracellular hydration and endosolvent (intracellular water) structure are important determinants in selectivity. Magnetic resonance measurements of line width by steady-state nuclear magnetic resonance (NMR) indicate a difference in the intracellular water signal of 16 Hz between the K form and Na form of Escherichia coli, providing additional evidence that changes in the ionic composition of cells are accompanied by changes in endosolvent structure. The changes were found to be consistent with the thermodynamic and magnetic resonance properties of aqueous electrolyte solutions. Calculation of the dependence of ion-pairing forces on medium dielectric reinforces the role of endosolvent structure in determining ion exchange selectivity

Nonideality of volume flows and phase transitions of F-actin solutions in response to osmotic stress.

Ovalbumin and G-actin solutions decreased their volume in a concentration-dependent manner in response to an osmotic stress, arising from an osmotic pressure gradient of 5-20 cm H2O at 25 degrees C, at protein concentrations as high as 20 mg/ml. In contrast, solutions of F-actin exhibited a concentration-dependent decrease in their rate of volume change in response to the osmotic stress. Shortening of F-actin by gelsolin did not affect this decrease, suggesting that the elastic response of the filaments underlies the osmotically nonideal behavior. However, above a critical actin concentration of approximately 7 mg/ml, no volume change occurred in response to osmotic gradients as high as 20 cm H2O. The concentration at which this critical phenomenon occurred and its abolition by shortening of F-actin by gelsolin suggest that a transition of diffusible rods to a glassy state is the cause of this critical phenomenon. Above the critical concentration, an increase in the osmotic pressure applied to an F-actin solution to greater than 20 cm H2O produced a transient increase in flow rate to that expected for a solution containing no polymer. This finding may represent a transition from an isotropic glassy state to an anisotropic and heterogeneous one wherein regions of pure solvent coexist with domains of pure polymer