Layers rotational viscosity

In Equation (8.5), yi is the rotational viscosity, K22 is the twist elastic constant, Ae is the dielectric anisotropy, E is the electric field strength, and (p is the LC rotation angle. The homogeneous LC layers having cell gap d are along the z axis. 

The relaxation time constant T is proportional to the rotational viscosity coefficient. Furthermore, it depends on the layer thickness a and the elastic coefficient 22 ot the anisotropy of the magnetic susceptibility and the critical field strength Hf. for this geometry. Two of these quantities have to be determined in a separate experiment. 

A divergence of the rotational viscosity is observed in the neighbourhood of transitions to smectic phases as the molecular rotation will be hindered by the pretransition-al formation of the smectic layer structure. Figure 10 shows this effect for 80CBP [9]. The divergence can be described by an equation similar to Eq. (35) [52-54] ... 

Illustration of the motion around the cone with rotational viscosity. The variable. the motion of the c director around the layer normal. 

The optimal transmission occurs at 6=22.5° and 5=ti. In order to achieve a uniform rotation, the SSFLC layer thickness is often limited to about 2pm. As mentioned before, FLC cells, in general, switch faster than nematic cells the response time ranges from Ips to several tens of microseconds, owed largely to the lower rotational viscosity, larger spontaneous polarization, and higher switching fields. 

The viscosity coefficient A4 is related to the rotation of the local smectic layer normal a and is the only rotational viscosity to appear in the SmA classification on page 297. The key rotational viscosity in SmC is A5, with the coefficients Ae and re being ac-coupling rotational viscosities. 

Rheology. Flow properties of latices are important during processing and in many latex appHcations such as dipped goods, paint, inks (qv), and fabric coatings. For dilute, nonionic latices, the relative latex viscosity is a power—law expansion of the particle volume fraction. The terms in the expansion account for flow around the particles and particle—particle interactions. For ionic latices, electrostatic contributions to the flow around the diffuse double layer and enhanced particle—particle interactions must be considered (92). A relative viscosity relationship for concentrated latices was first presented in 1972 (93). A review of empirical relative viscosity models is available (92). In practice, latex viscosity measurements are carried out with rotational viscometers (see Rpleologicalmeasurement). 

Effect of Fluid Viscosity and Inertia The dynamic effect of viscosity on a rotating liquid slurry as found in a sedimenting centrifuge is confined in veiy thin fluid layers, known as Ekman layers. These layers are adjacent to rotating surfaces which are perpendicular to the axis of rotation, such as bowl heads, flanges, and conveyor blades, etc. The thickness of the Ekman layer 6 is of the order... 

By the total internal reflection condition at the liquid-liquid interface, one can observe interfacial reaction in the evanescent layer, a very thin layer of a ca. 100 nm thickness. Fluorometry is an effective method for a sensitive detection of interfacial species and their dynamics [10]. Time-resolved laser spectrofluorometry is a powerful tool for the elucidation of rapid dynamic phenomena at the interface [11]. Time-resolved total reflection fluorometry can be used for the evaluation of rotational relaxation time and the viscosity of the interface [12]. Laser excitation can produce excited states of adsorbed compound. Thus, the triplet-triplet absorption of interfacial species was observed at the interface [13]. 

In consideration of the hydrodynamic problem alone, it is usually attempted to characterize the studied system by three quantities, the characteristic length / (e.g. the length of the plate in the direction of the flowing liquid or the radius of a rotating disk), the velocity of the flowing liquid outside the Prandtl layer V0 and the kinematic viscosity v. 

A reciprocal proportionality exists between the square root of the characteristic flow rate, t/A, and the thickness of the effective hydrodynamic boundary layer, <5Hl- Moreover, f)HL depends on the diffusion coefficient D, characteristic length L, and kinematic viscosity v of the fluid. Based on Levich s convective diffusion theory the combination model ( Kombi-nations-Modell ) was derived to describe the dissolution of particles and solid formulations exposed to agitated systems [(10), Chapter 5.2]. In contrast to the rotating disc method, the combination model is intended to serve as an approximation describing the dissolution in hydrodynamic systems where the solid solvendum is not necessarily fixed but is likely to move within the dissolution medium. Introducing the term... 

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