Preliminary Findings from the SHERE ISS Experiment

The Shear History Extensional Rheology Experiment (SHERE) is an International Space Station (ISS) glovebox experiment designed to study the effect of preshear on the transient evolution of the microstructure and viscoelastic tensile stresses for monodisperse dilute polymer solutions. The SHERE experiment hardware was launched on Shuttle Mission STS-120 (ISS Flight 10A) on October 22, 2007, and 20 fluid samples were launched on Shuttle Mission STS-123 (ISS Flight 10/A) on March 11, 2008. Astronaut Gregory Chamitoff performed experiments during Increment 17 on the ISS between June and September 2008. A summary of the ten year history of the hardware development, the experiment's science objectives, and Increment 17's flight operations are discussed in the paper. A brief summary of the preliminary science results is also discussed

Microfluidic extensional rheometry using a hyperbolic contraction geometry

Microfluidic devices are ideally suited for the study of complex fluids undergoing large deformation rates in the absence of inertial complications. In particular, a microfluidic contraction geometry can be utilized to characterize the material response of complex fluids in an extensionally-dominated flow, but the mixed nature of the flow kinematics makes quantitative measurements of material functions such as the true extensional viscosity challenging. In this paper, we introduce the ‘extensional viscometer-rheometer-on-a-chip’ (EVROC), which is a hyperbolically-shaped contraction-expansion geometry fabricated using microfluidic technology for characterizing the importance of viscoelastic effects in an extensionally-dominated flow at large extension rates (λ[. over ε][subscript a] ≫ 1, where λ is the characteristic relaxation time, or for many industrial processes . over ε][subscript a] ≫ 1 s[superscript −1]). We combine measurements of the flow kinematics, the mechanical pressure drop across the contraction and spatially-resolved flow-induced birefringence to study a number of model rheological fluids, as well as several representative liquid consumer products, in order to assess the utility of EVROC as an extensional viscosity indexer.National Science Foundation (U.S.). Graduate Research FellowshipUnited States. National Aeronautics and Space Administration (Microgravity Fluid Sciences Grant NNX09AV99G)European Commission. Marie Curie Actions (FP7-PEOPLE-2011-IIF Grant 298220

Spatially resolved quantitative rheo-optics of complex fluids in a microfluidic device

In this study, we use microparticle image velocimetry (μ-PIV) and adapt a commercial birefringence microscopy system for making full-field, quantitative measurements of flow-induced birefringence (FIB) for the purpose of microfluidic, optical rheometry of two wormlike micellar solutions. In combination with conventional rheometric techniques, we use our microfluidic rheometer to study the properties of a shear-banding solution of cetylpyridinium chloride (CPyCl) with sodium salicylate (NaSal) and a nominally shear-thinning system of cetyltrimethylammonium bromide (CTAB) with NaSal across many orders of magnitude of deformation rates (10-2 ≤ math ≤ 104s-1). We use μ-PIV to quantify the local kinematics and use the birefringence microscopy system in order to obtain high-resolution measurements of the changes in molecular orientation in the wormlike fluids under strong deformations in a microchannel. The FIB measurements reveal that the CPyCl system exhibits regions of localized, high optical anisotropy indicative of shear bands near the channel walls, whereas the birefringence in the shear-thinning CTAB system varies more smoothly across the width of the channel as the volumetric flow rate is increased. We compare the experimental results to the predictions of a simple constitutive model, and we document the breakdown in the stress-optical rule as the characteristic rate of deformation is increased.National Science Foundation (U.S.) (Graduate Research Fellowship

Controlled Synthesis, Characterization, and Flow Properties of Ethylene–Diene Copolymers

The flow response of branched entangled resins is dominated by the branching topology of the constituent molecules, a property that is not directly accessible using experimental analytical tools for industrially relevant complex resins. In this paper, the controlled terpolymerization of ethylene, 1,9-decadiene, and either hexene or octene in a continuous stirred tank reactor with a metallocene catalyst, is reported. The synthesized samples are characterized extensively with various analytical tools and their rheological properties are measured with small amplitude oscillatory shear and start-up uniaxial extension experiments. A model is developed for the polymerization process with the mass balance during synthesis providing strong constraints on the rate constants. In silico ensembles of molecules, generated via Monte Carlo sampling, are used to reproduce the experimental results. The computer model allows us to infer the detailed branching structure of the molecules and to predict the optimum range of reactor conditions for this synthesis

Modeling of synthesis and flow properties of propylene-diene copolymers

Copolymerization with nonconjugated dienes offers an attractive route for introducing long-chain branching in polypropylene. From a simplified set of rate equations for such copolymerization with a metallocene catalyst, we derive the probabilities of branch formation at different stages of the reaction in a semibatch reactor. Using these probabilities, we generate an ensemble of molecules via a Monte Carlo sampling. The knowledge of the branching topology and segment lengths allows us to compute the flow properties of the resins from computational rheology. We compare our model predictions with existing experimental data, namely the molar mass distribution and small amplitude oscillatory shear response, for a set of resins with varying diene content. The rheology data suggest that the entanglement time Ï.,e depends sensitively and in a well-defined fashion on the diene content