How Rheology Touches Our Lives

摘要

Measurement and control of rheological properties touches our lives each day in morernways than might be imagined. This is an overview of several industrial applications ofrninteresting and unique rheological measurements. These are: salad dressings, ink jet printing, gelrntexture / flavor and syrup stringiness. The variety of rheological measurements needed for eachrnone of these is described. Some of these techniques are unique and not often discussed.rnThe intent of this paper is to make users to be more aware of the need for multiplernrheological measurements to fully understand the properties of a material. For salad dressings,rnthe industrial measurement often performed for quality control uses the Brookfieldò RVTrnviscometer at 20 rpm. This simple test does not relate to two important properties of therndressing. The emulsion stability of the dressing is determined by the viscosity at shear rates ofrn10-2 s-1 and below while the mouthfeel and creaminess are related to shear rate of 102 s-1. Arnsingle measurement cannot predict both of these since the relevant shear rates are different byrnroughly four orders of magnitude.rnInkjet printing of carpet and fabric is another example of balancing diverse rheologicalrnrequirements. Shear viscosity controls penetration of the dye into the fabric matrix. Extensionalrnviscosity controls droplet breakup and tailing of the fluid jet. Elastic modulus (G') at higherrntemperatures controls definition and color yield in the dye setting process. Finally, elasticrnmodulus also plays a role in edge definition and color mixing.rnGel texture is closely related to rheological measurements. Relating instrumentalrnmeasurements to human perception is done with a technique called "Texture Profile "Analysis."rnThis instrumental data can be related to sensory properties such as firmness, brittleness and evenrnthe flavor release of the gel.rnTable syrups used for pancakes and waffles are sometimes thickened when less sugar isrnused to reduce the calorie content of the product. These thickened syrups can exhibit long flow,rntailing or stringiness if their extensional viscosity is too high. In this case, the extensionalrnviscosity can be related to consumer perception of the syrup.