Anchoring shear viscosity

Under steady shearing, these trapped disclinations should play the role of an anchoring condition, much like the role solid walls play in the flow properties of small-molecule nematics. A scaling analysis of this problem in Section 10.2.5 gives an equation, (10-28), for the steady-state shear viscosity for flow between surfaces with strong, homeotropic anchoring ... 

As is well known, at 21 °C and 30mN/m film pressure a pure DPPC monolayer is solid and stiff, having high shear viscosity [18], but a relatively low surface dilational viscosity and elasticity [3]. The drop impact pattern on pure DPPC monolayers has a long tail and no anchor form (Fig. 10). The target monolayer is so stiff that the impacting drop caimot induce any surface movement in it as schematically drawn in Fig. 3. 

DPPC monolayers with 60 mol % cholesterol are in a fluid/lluid phase. Microscopically, they show domains of condensed complexes surrounded by a cholesterol rich phase [3,19], but this pm-sized structures are at least two orders of magnitude smaller than the bright spots which we show in Fig. 11. As already shown in the hterature [13,18], cholesterol greatly reduces the shear viscosity of DPPC monolayers. The fluidifying effect of cholesterol in a saturated monolayer can be seen very well in our results by comparing the drop impact patterns of pure DPPC mono-layer with the ones of DPlt with 60 mol % cholesterol. The last one present an anchor forming pattern similar to the drop impact pattern on the liquid DOPC and DOPC-cholesterol monolayers. 

Anchor Mixers Anchor mixers are the simplest and one of the more common types of high-viscosity mixers (Fig. 18-42). The diameter of the anchor D is typically 90 to 95 percent of the tank diameter T. The result is a small clearance C between the rotating impeller and the tank wall. Within this gap the fluid is sheared by the relative motion between the rotating blade and the stationary tank wall. The shear near the wall typically reduces the buildup of stagnant material and promotes heat transfer. To reduce buildups further, flexible or spring-loaded scrapers, typically made of polymeric material, can be mounted on the rotating blades to move material physically away from the wall. 

Many types of multishaft mixers do not require planetary motion. Instead the mixers rely on an anchor-style impeller to move and shear material near the tank wall, while another mixer provides a different type of mixing. The second or third mixer shafts may have a pitched-blade turbine, hydrofoil impeller, high-shear blade, rotor-stator mixer, or other type of mixer. The combination of multiple impeller types adds to the flexibility of the total mixer. Many batch processes involve different types of mixing over a range of viscosities. Some mixer types provide the top-to-bottom motion that is missing from the anchor impeller alone. 

In nematic liquid crystals, the viscosity depends on the relative orientation between the shear gradient and the orientation of the nematic phase. Close to a surface, the orientation is usually governed by surface orientational anchoring [77]. Anchoring transitions, for instance induced by the adsorption of an analyte molecule to the surface [78], can therefore be easily detected with the QCM [79,80]. This reorientation induced by adsorption amounts to an amplification scheme the expected shift in the resonance frequency and bandwidth... 

Figure 16 shows the steady shear relative viscosity variation with the effective Peclet number, Peeg, based on the effective particle diameter at each temperature level, and the temperature for a PMMA suspension. The particles of 0.8 pm are sterically stabilized by a thick layer of terminally anchored poly(dimethylsiloxane) and suspended in n-hexadecane at the volume fraction of 0 = 0.282. The data points are... 

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