early formation of (loose) larger PEC particles, which are stabilized by the further
addition of excess PEL so that no secondary aggregates are formed (low PDI). By
contrast, when the minority component is added to the majority component an early
formation of small compact particles takes place, which can readily aggregate to
different aggregate sizes (high PDI).
Schatz and coworkers [49] reported similar trends for CHT/DS particles, where
CHT had a low charge density. Under these conditions, PEC size also dropped from
about 1,000 nm at values of X ¼ 20 down to about 400 nm at X ¼ 1; however, PDI
values were 0.2 and higher, with no significant X dependence.
Also related to mixing ratio variations van der Burgh [33] at first reported and
discussed DLS titration experiments on complexes between homopolyelectrolytes
(HP, e.g. PDMAEMA) and oppositely charged diblock copolymers (CP, e.g. poly
(acrylic acid-block-acrylamide)) under variation of the cationic fraction F
+ = HP/
(HP + CP) related to the chargeable monomer units, which were later reviewed and
extended by Lindhoud [32]. Based on plots of light scattering intensity as function
of the composition I(F
+ ) these authors claimed a symmetrical pattern consisting of
four regions (I–IV). Starting at F
+
=0, I(F
+
) increases slightly upon titrant (HP)
addition, which has been argued to be due to the formation of small soluble
complexes having a negative charge (I). Thereupon at a certain F
+ value the slope
(dI/dF
+
) becomes steeper and PEC micelles start to form (II) until at F
+
% 0.5 the
system is neutral and maximum intensity (micelle number) is found. Further
increase of F
+ results in the disintegration of PEC micelles, leading to a decrease
of I(F
+
) similar to the formation of micelles (III) but with negative slope. Finally,
the slope becomes less pronounced, and the solution contains again soluble
complexes (disintegrated micelles) but with positive charge (IV).
3.2.2 PEL Concentration
At first glance, PEL concentration seems to be an easily and frequently applied
parameter that can influence PEC particle size. However, only a few related reports
are available in the open literature.
Among them, Dautzenberg et al. reported early work on the influence of PEL
concentration on the mass (M w , not to be confused with the molecular weight of the
PEL components) and size (herein: R G ¼ a m ) of PEC particles, based on SLS
measurements of the PDADMAC/PSS system [27] (see Fig. 15). The plot of
R G versus c PEL could be fitted by a simple power law of the type R G ~ c PEL
0.58
and that of M W versus c PEL by M W ~ c PEL
1.70 . Moreover, the direct dependence
between R G and M W reads R G ~ M W
0.58/1.70 ¼ M W
0.34 , from which an exponent
close to 1/3 could be obtained, which is in line with the expected classical relation
for homogeneous spheres or polymer globules (R G ~ M W
0.33
). In this work, the
structural density of PEC particles was found to be invariant of concentration and
was r ¼ 0.43 g/mL.
Furthermore, Schatz et al. [49] reported the influence of c PEL on the size of
biopolyelectrolyte complex particles of CHT/DS. Increasing particle sizes were
obtained with increasing DS concentration, but only at high mixing ratios n
+
/n
À .
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
217
addition of excess PEL so that no secondary aggregates are formed (low PDI). By
contrast, when the minority component is added to the majority component an early
formation of small compact particles takes place, which can readily aggregate to
different aggregate sizes (high PDI).
Schatz and coworkers [49] reported similar trends for CHT/DS particles, where
CHT had a low charge density. Under these conditions, PEC size also dropped from
about 1,000 nm at values of X ¼ 20 down to about 400 nm at X ¼ 1; however, PDI
values were 0.2 and higher, with no significant X dependence.
Also related to mixing ratio variations van der Burgh [33] at first reported and
discussed DLS titration experiments on complexes between homopolyelectrolytes
(HP, e.g. PDMAEMA) and oppositely charged diblock copolymers (CP, e.g. poly
(acrylic acid-block-acrylamide)) under variation of the cationic fraction F
+ = HP/
(HP + CP) related to the chargeable monomer units, which were later reviewed and
extended by Lindhoud [32]. Based on plots of light scattering intensity as function
of the composition I(F
+ ) these authors claimed a symmetrical pattern consisting of
four regions (I–IV). Starting at F
+
=0, I(F
+
) increases slightly upon titrant (HP)
addition, which has been argued to be due to the formation of small soluble
complexes having a negative charge (I). Thereupon at a certain F
+ value the slope
(dI/dF
+
) becomes steeper and PEC micelles start to form (II) until at F
+
% 0.5 the
system is neutral and maximum intensity (micelle number) is found. Further
increase of F
+ results in the disintegration of PEC micelles, leading to a decrease
of I(F
+
) similar to the formation of micelles (III) but with negative slope. Finally,
the slope becomes less pronounced, and the solution contains again soluble
complexes (disintegrated micelles) but with positive charge (IV).
3.2.2 PEL Concentration
At first glance, PEL concentration seems to be an easily and frequently applied
parameter that can influence PEC particle size. However, only a few related reports
are available in the open literature.
Among them, Dautzenberg et al. reported early work on the influence of PEL
concentration on the mass (M w , not to be confused with the molecular weight of the
PEL components) and size (herein: R G ¼ a m ) of PEC particles, based on SLS
measurements of the PDADMAC/PSS system [27] (see Fig. 15). The plot of
R G versus c PEL could be fitted by a simple power law of the type R G ~ c PEL
0.58
and that of M W versus c PEL by M W ~ c PEL
1.70 . Moreover, the direct dependence
between R G and M W reads R G ~ M W
0.58/1.70 ¼ M W
0.34 , from which an exponent
close to 1/3 could be obtained, which is in line with the expected classical relation
for homogeneous spheres or polymer globules (R G ~ M W
0.33
). In this work, the
structural density of PEC particles was found to be invariant of concentration and
was r ¼ 0.43 g/mL.
Furthermore, Schatz et al. [49] reported the influence of c PEL on the size of
biopolyelectrolyte complex particles of CHT/DS. Increasing particle sizes were
obtained with increasing DS concentration, but only at high mixing ratios n
+
/n
À .
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
217