Dendrimer Bulk Rheology

it seems that bulk dendrimers change their rheological behavior from Maxwell-like at lower generations to Rousean at higher ones. For PAMAMs for 

In attempts to better understand dendrimer intramolecular morphology, considerable attention was devoted to the fractional free volume near the glass temperature [40, 49, 50], Because all of the studies were performed within the WLF temperature range, the data were analyzed using the equation 

It was also noted by Farrington and co-workers that the chemical nature of the end-groups may have a substantial effect on the viscosity of bulk dendrimers, even under iso-free volume conditions [49]. This seems consistent with the establishment of interdendrimer interactions and supramolecular organization at rest in the bulk state. However, as in most other areas of dendrimer rheology, more data are desirable before definite conclusions can be drawn. 

Although a body of data on dendrimer rheological behavior has been accumulated, and new reports are appearing at an increasing pace, the field is still in its infancy and will remain an intriguing and important subject of research for some 

Nevertheless, the existence of the famed maximum in the dendrimer [ 7] vs G relationship, and whether this behavior could be a characteristic fingerprint property of this type of macromolecular architecture, was questioned recently [19, 23], In fact, so was the linearity of the dependence of dendrimer molecular radii on M1/3 [19], so that whether this may be the beginning of yet another controversy, remains to be seen. Perhaps the future may bring an interesting debate on these subjects, but until new data become available, one should refrain from drawing premature conclusions because the exciting architectural beauty of idealized dendrimer structures has already proven itself to easily tempt the most astonishing hypotheses that may not be readily substantiated by reality. 

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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... 

Research on the bulk rheological properties of dendrimers is still hampered due to the restrictive quantities necessary for these investigations since dendrimer synthesis is conducted mainly on the milligram scale, and the few commerdal products are very costly to obtain for these studies. In addition, the dendrimers must possess suffident thermal stability and care must be taken to avoid thermal oxidation as well as moisture absorption for more polar dendrimers. 

Uppuluri, S. Morrison, E.A. Dvornic, P.R. Rheology of dendrimers. 2. Bulk polyamidoamine dendrimers under steady shear, creep, and dynamic oscillatory shear. Macromolecules 2000, 33, 2551-2560. 

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