Rheology of Concentrated Dendrimer Solutions

Compared to dilute solution viscometry and to some extent to bulk rheology, the flow properties of dendrimers in concentrated solutions have been the least investigated area of dendrimer rheology. In fact, with the notable exception of some recent data on generation 4 PPI in water [22] the only [32] reported 

Ra/RH ratio. Unfortunately, in this respect the available data are not conclusive enough (compare with Table 14.1) [45]. 

Within the temperature range from 10 to 40°C, both PAMAM dendrimers in EDA [5] and PPI dendrimers in water [22] showed a linear relationship between In r and /T, in good agreement with the kinetic rate theory of flow [46]. The apparent activation energies of flow (En) were constant and independent of temperature, and it was shown for PAMAM/EDA systems that the dependence of En on solution concentration was linear for all generations examined [5]. This was considerably different from the typical relationships for the solutions of linear and/or randomly branched chain polymers, where a break in the slope of 

En vs c [47] is usually associated with the establishment of entanglement couplings [48], Thus, the observed linearity of En vs c dependencies of dendrimer solutions seems to be another manifestation of dendrimer reluctance to interpenetrate, either with other dendrimers or with their parts. 

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