Handbook of Solvents - George Wypych - ChemTech - Ventech!

12.1 Rheological properties, aggregation, permeability 691
Figure 12.1.15. TEM micrograph of assemblies of
cylindrical aggregates. [Adapted, by permission, from
G Liu, Macromol. Symp., 113, 233 (1997).]
Figure 12.1.17. TEM micrograph of knots and strands
formed in carbohydrate amphiphile. [Adapted, by
permission, from U Beginn, S Keinath, M Moller,
Macromol. Chem. Phys., 199, No.11, 2379-84
(1998).]
R g ,nm
Figure 12.1.16. TEM micrograph of nanofibers.
[Adapted, by permission, from G Liu, Macromol.
Symp., 113, 233 (1997).]
50
20 30 40 50 60 70
mation as Figure 12.1.13 shows. As polymer concentration increases, spherical micelles are
replaced by a mixture of rod-like structures and vesicles. With a further increase in concentration,
the rod-like shapes disappear and only vesicles remain.
Figures 12.1.14-12.1.16 show a variety of shapes which have been observed. These
include nanospheres, assemblies of cylindrical aggregates, and nanofibers. 11 Nanospheres
were obtained by the gradual removal of solvent by dialysis, fibers were produced by a series
of processes involving dissolution, crosslinking, and annealing. Figure 12.1.17 sheds
some light on the mechanism of aggregate formation. Two elements are clearly visible from
micrographs: knots and strands. Based on studies of carbohydrate amphiphiles, it is concluded
that knots are formed early in the process by spinodal decomposition. Formation of
350
300
250
200
150
100
PVC/BrBz
PVC/DOA
Temperature, o C
Figure 12.1.18. Radius of gyration vs. temperature for
PVC solutions in bromobenzene, BrBz, and dioxane,
DOA. [Adapted, by permission, from Hong Po-Da,
Chen Jean-Hong Chen, Polymer, 40, 4077-4085,
(1999).]