PEI or PAC component. This is not the case for the major-to-minor scenario, where
immediately after exceeding the critical 1:1 stoichiometry the excess oppositely
charged PAC or PEI component can “crosslink” the secondary particles to form
colloidal networks with lower structural density. We emphasize that for both scenarios
the suggested PEC structures are not in equilibrium and that local and kinetic factors
play a substantial role. The minor-to-major scenario might result in more “equilibrated”
PEC structures because the charge sign is never reversed, whereas the major-to-minor
scenario might result in “unequilibrated” and looser PEC structures.
2.2.4 Refinement
Another influence on PEC parameters can be achieved by post treatment of the PEC
dispersion. Among other treatments, freshly prepared raw dispersions can be refined
by consecutive centrifugation steps [16]. Thereby, the initial raw dispersion was
centrifuged, the supernatant discarded and the formed coacervate phase of the serum
dissolved again to the original volume. Figure 8 shows the effect of consecutive
centrifugation on PEC dispersions prepared by mixing 0.002 M PMA-MS into
0.002 M PDADMAC at a mixing ratio n
À /n
+
¼ 0.66. The black curve represents
the initial raw dispersion (PEC-0x), while dark gray and light gray curves represent the
dispersion after one (PEC-1x) or two (PEC-2x) centrifugations (11,000 revolutions/
min for 20 min), discarding the supernatant and redispersion of the coacervate phase
with an equal volume. While the polydispersity index (PDI) could be significantly
lowered from PEC-0x to PEC-1x to PEC-2x, the intensity maximum of the size
Fig. 8 Size (hydrodynamic radius R H ) distributions of PEC dispersions of PDADMAC/PMA-MS
(300 kg/mol/23 kg/mol, n
À
/n
+ ¼ 0.66) with different numbers of centrifugation steps: PEC-0x no
centrifugation, PEC-1x one centrifugation, and PEC-2x two centrifugations. (From [16] with kind
permission of ACS)
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
207
immediately after exceeding the critical 1:1 stoichiometry the excess oppositely
charged PAC or PEI component can “crosslink” the secondary particles to form
colloidal networks with lower structural density. We emphasize that for both scenarios
the suggested PEC structures are not in equilibrium and that local and kinetic factors
play a substantial role. The minor-to-major scenario might result in more “equilibrated”
PEC structures because the charge sign is never reversed, whereas the major-to-minor
scenario might result in “unequilibrated” and looser PEC structures.
2.2.4 Refinement
Another influence on PEC parameters can be achieved by post treatment of the PEC
dispersion. Among other treatments, freshly prepared raw dispersions can be refined
by consecutive centrifugation steps [16]. Thereby, the initial raw dispersion was
centrifuged, the supernatant discarded and the formed coacervate phase of the serum
dissolved again to the original volume. Figure 8 shows the effect of consecutive
centrifugation on PEC dispersions prepared by mixing 0.002 M PMA-MS into
0.002 M PDADMAC at a mixing ratio n
À /n
+
¼ 0.66. The black curve represents
the initial raw dispersion (PEC-0x), while dark gray and light gray curves represent the
dispersion after one (PEC-1x) or two (PEC-2x) centrifugations (11,000 revolutions/
min for 20 min), discarding the supernatant and redispersion of the coacervate phase
with an equal volume. While the polydispersity index (PDI) could be significantly
lowered from PEC-0x to PEC-1x to PEC-2x, the intensity maximum of the size
Fig. 8 Size (hydrodynamic radius R H ) distributions of PEC dispersions of PDADMAC/PMA-MS
(300 kg/mol/23 kg/mol, n
À
/n
+ ¼ 0.66) with different numbers of centrifugation steps: PEC-0x no
centrifugation, PEC-1x one centrifugation, and PEC-2x two centrifugations. (From [16] with kind
permission of ACS)
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
207