Ballman method

Two techniques for measuring uniaxial extensional viscosity of polymer melts are shown in Figure 3.24. In the first technique (Ballman method) poiymer melt is either glued or clamped at both ends, and then one end is moved in such a manner as to generate either a uniform extension rate, e, or a constant tensile stress. In the Meissner method, both ends of the melt are pulled at a constant velocity either to achieve a uniform extension rate or to provide a constant stress. 

In the Ballman method, to generate a uniform s throughout the sample, one end of the sample must be deformed such that the length of the sample is increased exponentially with time that is, L = Lo e. An apparatus based on the Ballman method is shown in Figure 3.25. The sample must be supported in an oil of similar density as shown in Figure 3.25. The limitations of the technique include (1) the availability of a suitable adhesive for gluing the sample to metal clips ... 

FIGURE 3.25 Extensional rheometer for polymer melts based on the Ballman method. The length of the sample is increased exponentially with time to generate a constant extension rate. 

Thus, we felt it particularly worthwhile to try to improve the preparation of KTP since we were willing to make the bet that drastically improved new materials were not just around the comer. Two KTP preparation methods are in general use, anhydrous flux growth as described by Loiacono and his co-workers 40) and by Ballman 41) and relatively high temperature hydrothermal growth as perfected by Belt and his colleagues. 42) We will not attempt a historical review of the development of these methods. Instead we will outline some features and preparative improvements 43,45) which we discovered as a result of a preliminary study of the process physical chemistry of hydrothermal KTP growth. 

A. E. Everage and R. L. Ballman, The extensional flow capillary as a new method for extensional viscosity measurement. Nature 273, 213-215 (1978). 

The most common method for measurement of extensional viscosity is to stretch the filament of material shown in Figure 3.7 vertically as done by Ballman [82] or horizontally as done by Meissner [83]. The polymer must have a higji enough melt viscosity of 10 Pa.sec or greater in order to be amenable for such extensional experiments. 

In the method of Ballman [82], which has been used by others [84,85], a vertical thermostated filament is clamped at both ends and stretched at the rate dl/dt such as to maintain a constant deformation rate. Thus,... 

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