|Reducer Size||Gear Size||γmax(s-1)||γmin(s-1)|
The NCNR has two shear cells available to probe the microstructure of viscoelastic materials under shear flow in the 1-2 (velocity-gradient) plane. Cells are available in either aluminum or stainless steel, while the bob is composed of titanium. The sample is enclosed in a Couette geometry with a gap of 1 mm that requires a minimum sample volume of 5 mL. Temperatures ranging from -25 °C to 130 °C can be used when combined with a circulating bath.
Several types of shear flows can be imposed using the 1-2 cell including steady shear, small and large amplitude oscillatory shear (SAOS and LAOS, respectively), and start-up measurements. All shear settings are synchronized with the SANS measurements by a series of TTL on/off signals. Time-resolution is available for time dependent measurements such as LAOS or start-up by additional synchronization of the neutron detector time stamp and the start point of each repeat of the shear event. Each neutron is then correlated with a given time within a period of repeated shear motion using post-processing software available at the NCNR.
Limitations of the servo motor rotational velocity restrict the shear rates that can be used during steady shear measurements. The range of accessible shear rates can be shifted with an appropriate combination of the three available gear reducers (3x, 10x, 70x) and gear sizes (15, 32, 48) relative to the shaft gear size (15).
Similarly, the conditions available for oscillatory shear using the 1-2 cell are limited by the rate of acceleration the servo motor can execute. A wide range of frequencies are available for SAOS, but careful consideration must be made for the reducer and gear size used during LAOS.