A vapor barrier Couette shear cell for small angle neutron scattering measurements

Abstract

We describe the design and operation of a temperature controlled Couette shear cell for small angle neutron scattering ͑SANS͒ studies of complex fluids under flow. This design incorporates a vapor barrier, which prevents sample evaporation to relatively high shear rates. This cell enables the investigation of systems which are highly sensitive to evaporation. Over the duration of a Couette SANS measurement composition phase transitions due to evaporation can be misinterpreted as true shear-induced transformations. We give a brief report of recent experiments performed on one such system: bicontinuous L 3 sponge phases for which the surfactant membrane constituents are Cetylpyridinium chloride and hexanol. These clearly demonstrate the limitations of previous designs and the utility of the vapor barrier in measurements of a predicted shear induced sponge to lamellar phase transition. Using this cell we also describe and test a simple and effective way to put SANS data taken in the tangential Couette configuration on an absolute scale.

A new parallel plate shear cell for in situ real-space measurements of complex fluids under shear flow

“…Therefore, shear cells have been designed such that it can examine the sample's microstructure under shear. At first, they were mostly combined with scattering techniques such as smallangle x-ray scattering ͑SAXS͒, [15][16][17][18][19] small-angle neutron scattering ͑SANS͒, [20][21][22] and small-angle light scattering ͑SALS͒, [23][24][25][26][27] which yield information over a large sample volume. In many cases, structural data are needed on a more local level than scattering can provide, or the flow itself becomes nonuniform.…”

Topological Relaxation of a Shear-Induced Lamellar Phase to Sponge Equilibrium and the Energetics of Membrane Fusion

“…Even with the slowed dynamics of this system L to L 3 relaxation takes only a few seconds. To track this (for SANS) rapidly changing structural signal we employed the National Institute of Standards and Technology (NIST) SANS instrument NG7 in ''time-slicing'' mode: synchronizing time-binned SANS data acquisition with the ORNL Couette SANS shear cell [12] to cycle through the process of shearing to a steady L state, stopping, and relaxing to L 3 equilibrium repeatedly to accumulate statistically significant measurements on much shorter time scales than is possible for individual runs [13]. Each cycle was begun with 20 s of Couette shear at a rescaled shear rate for that sample of _ s = 3 3 10 8 cP s ÿ1 , the center of the saturated L SANS signal range.…”

Rheo–small-angle neutron scattering at the National Institute of Standards and Technology Center for Neutron Research

“…A theodolite is used to align the vertical edge of the bob with the vertical edge of the slit. Once the vertical axes are matched, the slit is carefully aligned so that the beam impinges on the gap by a procedure described elsewhere 9 where the transmission is plotted as a function of slit position as the slit is translated across the gap. For scattering in the radial geometry, the raw data sets are then corrected for detector background, sensitivity and empty cell scattering and placed in an absolute scale using the direct beam measurement as done for conventional SANS data 10,11 while in the tangential geometry, a procedure as described in Ref.…”