16 



VISCOMETRY 



IN BIOCHEMICAL 



INVESTIGATIONS 



MAX A. LAUFFER, associate research professor of physics, 



UNIVERSITY OF PITTSBURGH; THE LILLY AWARD IN BIOCHEMISTRY 



r. 



ISCOSITY has been recognized for many years as an im- 

 portant characteristic of colloidal and biological materials. 

 In spite of this fact, however, in terms of the properties of molecules 

 and macromolecules, the meaning of viscosity remained almost com- 

 pletely obscure until recently. The cause of the sustained popu- 

 larity of this technique during the past years should probably be at- 

 tributed to the extreme ease of viscosity measurements, as contrasted 

 with other physical approaches to the study of biological and bio- 

 chemical systems, rather than to the theoretical significance of the 

 results obtained. The outlook for the future, however, is brighter, 

 for reasonably satisfactory theories have recently become available 

 which describe quantitatively the viscosity of liquids and of macro- 

 molecular solutions in terms of molecular size, shape, and thermo- 

 dynamic properties (22,24). Much progress has also been made in 

 late years from a purely empirical point of view in the correlation of 

 viscosity with the size and structure of molecules, particularly in the 

 field of high-polymer chemistiy (11). 



In its most general sense, viscosity is a measure of the amount 

 of work which must be expended in order to maintain a certain rate 

 of flow. In the case of some liquids, the rate of flow at a fixed tem- 



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