Trains, tails and loops of partially adsorbed semi-flexible filaments

Polymer adsorption is a fundamental problem in statistical mechanics that has direct relevance to diverse disciplines ranging from biological lubrication to stability of colloidal suspensions. We combine experiments with computer simulations to investigate depletion induced adsorption of semi-flexible polymers onto a hard-wall. Three dimensional filament configurations of partially adsorbed F-actin polymers are visualized with total internal reflection fluorescence microscopy. This information is used to determine the location of the adsorption/desorption transition and extract the statistics of trains, tails and loops of partially adsorbed filament configurations. In contrast to long flexible filaments which primarily desorb by the formation of loops, the desorption of stiff, finite-sized filaments is largely driven by fluctuating filament tails. Simulations quantitatively reproduce our experimental data and allow us to extract universal laws that explain scaling of the adsorption-desorption transition with relevant microscopic parameters. Our results demonstrate how the adhesion strength, filament stiffness, length, as well as the configurational space accessible to the desorbed filament can be used to design the characteristics of filament adsorption and thus engineer properties of composite biopolymeric materials

Kinetic pathways of the Nematic-Isotropic phase transition as studied by confocal microscopy on rod-like viruses

We investigate the kinetics of phase separation for a mixture of rodlike viruses (fd) and polymer (dextran), which effectively constitutes a system of attractive rods. This dispersion is quenched from a flow-induced fully nematic state into the region where the nematic and the isotropic phase coexist. We show experimental evidence that the kinetic pathway depends on the overall concentration. When the quench is made at high concentrations, the system is meta-stable and we observe typical nucleation-and-growth. For quenches at low concentration the system is unstable and the system undergoes a spinodal decomposition. At intermediate concentrations we see the transition between both demixing processes, where we locate the spinodal point.Comment: 11 pages, 6 figures, accepted in J. Phys.: Condens. Matter as symposium paper for the 6th Liquid Matter Conference in Utrech

Multiple shear-banding transitions in a supramolecular polymer solution

We report on the nonlinear rheology of a reversible supramolecular polymer based on hydrogen bonding. The coupling between the flow-induced chain alignment and breakage and recombination of bonds between monomers leads to a very unusual flow behavior. Measured velocity profiles indicate three different shear-banding regimes upon increasing shear rate, each with different characteristics. While the first of these regimes has features of a mechanical instability, the second shear-banding regime is related to a shear-induced phase separation and the appearance of birefringent textures. The shear-induced phase itself becomes unstable at very high shear rates, giving rise to a third banding regime

Collective diffusion in charge-stabilized suspensions: Concentration and salt effects

The authors present a joint experimental-theoretical study of collective diffusion properties in aqueous suspensions of charge-stabilized fluorinated latex spheres. Small-angle x-ray scattering and x-ray photon correlation spectroscopy have been used to explore the concentration and ionic-strength dependence of the static and short-time dynamic properties including the hydrodynamic function H (q), the wave-number-dependent collective diffusion coefficient D (q), and the intermediate scattering function over the entire accessible range. They show that all experimental data can be quantitatively described and explained by means of a recently developed accelerated Stokesian dynamics simulation method, in combination with a modified hydrodynamic many-body theory. In particular, the behavior of H (q) for de-ionized and dense suspensions can be attributed to the influence of many-body hydrodynamics, without any need for postulating hydrodynamic screening to be present, as it was done in earlier work. Upper and lower boundaries are provided for the peak height of the hydrodynamic function and for the short-time self-diffusion coefficient over the entire range of added salt concentrations.Fil: Gapinski, J.. A. Mickiewicz University; PoloniaFil: Patkowski, A.. A. Mickiewicz University; PoloniaFil: Banchio, Adolfo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Holmqvist, P.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Meier, Guillermo Enrique. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Lettinga, M.P.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Nägele, G.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; Alemani

Influence of the phase separator design on the performance of the UASB reactor and on excess sludge production

Abstract The efficiency of the phase separator in UASB reactors can be increased by placing additional parallel plates above the conventional device, thus forming a high rate settler. From settling theory it can be deducted the performance of the plates improves when the height of the zone with parallel plates increases or the distance between plates and the angle of the plates decreases. In practice the height is limited by the construction cost of the reactor. The distance between the plates must be sufficient for maintenance and the angle to allow the retained sludge to slide readily back into the digestion zone. The experimental data show that indeed the digested COD fraction is greatly increased by adding parallel plates to a UASB reactor. As a consequence, the improved separator opens the possibility of a considerable increase of the applied load to the UASB reactor: Parallel plates used in a pilot scale (1500 l) UASB reactor led to an increase of the treatment capacity by a factor 2. The experimental data also showed that the fundamental operational variable to describe the behaviour of the UASB reactor is in fact the sludge age: at any particular temperature the effluent quality and the quality and quantity of excess sludge will be equal in two UASB reactors, if the sludge age in these is the same

The operating cost of an anaerobic membrane bioreactor (AnMBR) treating sulphate-rich urban wastewater

The objective of this study was to evaluate the operating cost of an anaerobic membrane bioreactor (AnMBR) treating sulphate-rich urban wastewater (UWW) at ambient temperature (ranging from 17 to 33 degrees C). To this aim, energy consumption, methane production, and sludge handling and recycling to land were evaluated. The results revealed that optimising specific gas demand with respect to permeate volume (SGDp) and sludge retention time (for given ambient temperature conditions) is essential to maximise energy savings (minimum energy demand: 0.07 kW h m(-3)). Moreover, low/moderate sludge productions were obtained (minimum value: 0.16 kg TSS kg(-1) CODRemoved), which further enhanced the overall operating cost of the plant (minimum value: is an element of 0.011 per m(3) of treated water). The sulphate content in the influent UWW significantly affected the final production of methane and thereby the overall operating cost. Indeed, the evaluated AnMBR system presented energy surplus potential when treating low-sulphate UWWThis research work was possible thanks to projects CTM2011-28595-C0-01/02 (funded by the Spanish Ministry of Economy and Competitiveness jointly with the European Regional Development Fund) and aqualia INNPRONTA IISIS IPT-20111023 (partially funded by the Centre for Industrial Technological Development (CDTI) and supported by the Spanish Ministry of Economy and Competitiveness).Pretel Jolis, R.; Robles Martínez, Á.; Ruano García, MV.; Seco Torrecillas, A.; Ferrer, J. (2014). The operating cost of an anaerobic membrane bioreactor (AnMBR) treating sulphate-rich urban wastewater. Separation and Purification Technology. 126(15):30-38. doi:10.1016/j.seppur.2014.02.013S30381261