Concentric cylinder viscometer extremely low shear stress.

Instrumentation

Journal of Physics 35 No. 2 (1989) 274-281

Concentric Cylinder Viscometer Extremely Low Shear Stress.
R. T. Rodriguez, Raul Montiel C. and A. Romo U.
Department of Physics, University Autonomy Metropolitan - Iztapalapa, PO Box 55-534, 09340 Mexico, DF (Received August 2, 1988; accepted January 13, 1989) Summary. This paper describes the design and construction of aviscometer of ZimmCrothers type, which allows very accurate viscosity measurements at various values of shear stressesusing only an extremely small rotor. Abstract We describe the design and construction of a Zimm Crothers type viscosimeter which permits us to get very accurate neasurements of viscosity at several values of the extremely low shear stress, using only one rotor.

1. Introduction One ofthe oldest techniques and used in the characterization of materials in solution is plyometrics viscometry. This is based on the fact that the presence of large particles dissolved or suspended in a liquid produced a radical change in the flow property of the system. A very important advantage of this technique is that the amount is determined experimentally, either viscous or the torque flow timeis

directly

proportional

to

viscosity.

It may happen, however, that the viscosity of the polymer solution is dependent on the flow conditions of the instrument used: in these cases it is said that the non-Newtonian viscosity. This type of behavior is found mainly in solutions of highly asymmetric molecules rigid or flexible molecules in solutions of very high molecular weight. Thecapillary viscometer has proven to be a versatile and inexpensive,

however, due to progress in the study of biological macromolecules, has been found that many of these molecules are degraded under the action of even small shear forces found in the viscometers capillaries. Furthermore, some biological and synthetic molecules have non-Newtonian behavior when subjected to shear stressesexperienced in regular sized capillaries.

FIGURE 1. The diagram shows the position of the rotor in the stator. 2. Design and construction The viscometer of Zimm-Crothers type [1], is a concentric cylinder viscometer, which is made entirely of glass, this feature provides the facility to work with almost any solvent. The outer cylinder (called the stator) remains fixed, while the inner cylinder (calledthe rotor) is rotating (Fig.1). At the bottom of the stator was placed a tube for introducing the sample is from the bottom of the viscometer. This device also facilitate filling, very accurately adjusts the height of the rotor on the stator core to be reproducible in the viscosity measurements, in general, the relative viscosity measurements have an accuracy of no more than 0.2% . All theviscometer is introduced into a heating jacket (Fig. 2) which allows the device to operate at different temperatures. As temperature control was used brand Haake recirculating bath with platinum resistance control, which

In view of this, there is need for a viscosity comparable to convenience and availability of a capillary viscometer, but operating at high shear rates of several orders of magnitudelower than the capillary. The instrument described herein is cheap, puts the solution in contact with only glass, runs at different shear stresses and has been used in cutting forces from 0.003 to 0.0008 dynes/cm2, which are several orders of magnitude less than commonly, used capillary viscometers.

controls with ±0.05°C.

accuracy

of

The viscometer should be mounted rigidly to preservethe geometry of the system. For this is supported with a nylon ring which is mounted on a bracket that allows five movements: first, the position of the viscosity on the external magnetic field is carried out through three platforms that move in the x - y z; second, the orientation thereof with respect to the magnet takes place by three screws placed in the nylon ring which allow movement...