Dautzenberg and Kriz [77] for a copolymer of PDADMAC and acrylamide
complexed by polymethacrylate. A constant mixing ratio of X ¼ 0.6 was used
and LiCl, NaCl, and KCl were used as the salts. As shown in Fig. 19, using this
salt addition mode, there was an increase from around 70 nm at c NaCl ¼ 0 up to a
sharp peak of 370 nm at around c NaC l % 0.5 M and a decrease to again around
80 nm at c NaCl > 0.5 M.
The other salts showed a similar trend, which was interpreted in terms of saltinduced aggregation of small soluble complexes to larger aggregates at salt
concentrations of 0–0.5 M, which was also supported by the decrease in PDI to a
value suggesting monodisperse, large aggregate particles. To explain the sharp
particle size drop for c S > 0.5 M, dissolution of PEC aggregates to small soluble
complexes or partly to the PEL components was proposed. The change in structural
density r with c S is in line with this finding because at low c S PEC particles have a
typical value of r % 0.4 g/mL, which drops down to 0.001 g/mL due to formation
of loose larger aggregates (370 nm for NaCl) at c S % 0.5 M. It is surprising that r
stays approximately constant for c S > 0.5 M, since the radii were again about the
same as the initial r values at low c S .
3.2.4 pH
In Fig. 20, the influence of pH combination on PEC particle size is shown for
the PEC system consisting of the weak PELs PEI (M w 750,000 g/mol) and PAC
(M w 50,000 g/mol) at the molar mixing ratio n
À /n
+
¼ 1.50. Significantly, a
decrease in particle size from D H % 400 to % 160 nm was obtained with decreasing values of pH (10, 8.5, 7, and 4) of the PEI solution at a constant pH ¼ 4 of the PAC
solution. This trend can be explained at the intramolecular level by the graded charging
up of the PEI, resulting in a rather stretched conformation. Moreover, for pH ¼ 4/10 a
400
350
300
250
200
150
100
0
0.0
0.2
0.4
0.6
1
0.1
0.01
0.001
[CI
– ] (mol/L)
[CI
–
] (mol/L)
0.0001
0.2
0.4
0.6
50
radius a
m (nm)
density
ρ (g/mL)
Fig. 19 Salt dependence of radius (a m ), and structural density (r) of PEC Cop47/NaPMA at
X ¼ 0.6 for different monovalent salts: black circles NaCl, black triangles LiCl, and open
triangles KCl. (From [77] with kind permission of ACS)
222
M. M€ uller
complexed by polymethacrylate. A constant mixing ratio of X ¼ 0.6 was used
and LiCl, NaCl, and KCl were used as the salts. As shown in Fig. 19, using this
salt addition mode, there was an increase from around 70 nm at c NaCl ¼ 0 up to a
sharp peak of 370 nm at around c NaC l % 0.5 M and a decrease to again around
80 nm at c NaCl > 0.5 M.
The other salts showed a similar trend, which was interpreted in terms of saltinduced aggregation of small soluble complexes to larger aggregates at salt
concentrations of 0–0.5 M, which was also supported by the decrease in PDI to a
value suggesting monodisperse, large aggregate particles. To explain the sharp
particle size drop for c S > 0.5 M, dissolution of PEC aggregates to small soluble
complexes or partly to the PEL components was proposed. The change in structural
density r with c S is in line with this finding because at low c S PEC particles have a
typical value of r % 0.4 g/mL, which drops down to 0.001 g/mL due to formation
of loose larger aggregates (370 nm for NaCl) at c S % 0.5 M. It is surprising that r
stays approximately constant for c S > 0.5 M, since the radii were again about the
same as the initial r values at low c S .
3.2.4 pH
In Fig. 20, the influence of pH combination on PEC particle size is shown for
the PEC system consisting of the weak PELs PEI (M w 750,000 g/mol) and PAC
(M w 50,000 g/mol) at the molar mixing ratio n
À /n
+
¼ 1.50. Significantly, a
decrease in particle size from D H % 400 to % 160 nm was obtained with decreasing values of pH (10, 8.5, 7, and 4) of the PEI solution at a constant pH ¼ 4 of the PAC
solution. This trend can be explained at the intramolecular level by the graded charging
up of the PEI, resulting in a rather stretched conformation. Moreover, for pH ¼ 4/10 a
400
350
300
250
200
150
100
0
0.0
0.2
0.4
0.6
1
0.1
0.01
0.001
[CI
– ] (mol/L)
[CI
–
] (mol/L)
0.0001
0.2
0.4
0.6
50
radius a
m (nm)
density
ρ (g/mL)
Fig. 19 Salt dependence of radius (a m ), and structural density (r) of PEC Cop47/NaPMA at
X ¼ 0.6 for different monovalent salts: black circles NaCl, black triangles LiCl, and open
triangles KCl. (From [77] with kind permission of ACS)
222
M. M€ uller