Thixotropic, definition

CAS 12001-31-9 71011-27-3 EINECS/ELINCS 234-406-6 275-128-5 Synonyms Quaternary ammonium compds., bis (hydrogenated tallow alkyl) dimethyl, chlorides, reaction prods, with hectorite Definition Reaction prod, of hectorite and quaternium-18 Uses Thixotrope, gellant, thickener for solv.-based coatings vise, control agent in cosmetics, lip care, eye care suspending agent Trade Names Containing M-P-A 14... 

Brookfield viscometer The Brookfield viscometer is the most widely used instrument for measuring the viscosity of liquids, plastisols, and other materials that have a thixotropic nature. The instrument measures shearing stress on a spindle rotating at a definite, constant speed while immersed in the sample. The degree of spindle lag is indicated on a rotating dial. This reading, multiplied by a conversion factor based on spindle size and rotational speed, gives a value for viscosity in centipoise. 

Experimentally, it is sometimes difficult to detect differences between a shear-thinning liquid in which the viscosity decreases with increasing shear, and a thixotropic material in which the viscosity decreases with time, because of the combined shear and time effects that occur during a series of measurements. This is especially true if only a few data points are collected. In addition, most materials that are thixotropic are also shear thinning. In fact, one definition of a thixotropic fluid limits it to materials whose viscosity is a function of both shear rate and time (8). 

The pumps, metering, mixing and application systems must be adapted to the viscosity of both the components. The viscosities of the two components should be similar in order to get a good mixing effect a very liquid product could not be mixed efficiently with a very thick product. Rheology, of course, must be also adapted the products may be pseudoplastic, thixotropic but never dilatant (for these definitions, refer to Chapter 2 in Volume 1 Technical Characteristics of Adhesives and Sealants ). 

When subjected to shear, these thixotropic systems show a definite yield value (see chapter I, 4, p 21), but once this yield value is overcome, they flow as easily as the intermiceilar liquid ... 

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