Abstract
The association between a randomly pyrene labeled PAA polymer (PAAMePy55) and a PEO-PPO-PEO
triblock copolymer (P123) in aqueous solutions of different NaCl concentrations and pHs has been studied
by means of dynamic light scattering (DLS) and steady-state fluorescence spectroscopy at 40 °C. At acidic
pH values, in the low P123/PAAMePy55 molar ratio regime (i.e., at low P123 concentrations), the relaxation
time distributions retrieved from the DLS data analysis were monomodal and very similar to those obtained
for the pure PAAMePy55 solution. The apparent hydrodynamic radius of PAAMePy55 at low pH is 18 nm.
At higher molar ratios (i.e., at high P123 concentrations), still in the acidic pH regime, bimodal relaxation
time distributions were obtained, where the fast relaxation mode is connected to the translational diffusion of
free P123 micelles with a hydrodynamic radius obtained at infinite P123 dilution (RH,P123)0) of 10-11 nm.
This value coincides perfectly with the hydrodynamic radius of the pure P123 micelles at 40 °C, which was
found to be ca. 10 nm at all pH values. The second mode corresponds to a complex consisting of one
PAAMePy55 polymer chain and about 42 P123 micelles and with a RH,P123)0 between 35 and 36 nm depending
on pH. At pH 9, the mixed system also presented bimodal relaxation time distributions. At this high pH, the
intermolecular association between PAAMePy55 and P123 is less strong than at acidic pH according to the
steady-state fluorescence measurements. The fast mode is also in this case attributed to free P123 micelles
whereas the second mode is related to the so-called “slow mode” commonly observed for polyelectrolyte
solutions. In this system, it is related to the formation of multichain domains, that is, large domains formed
by several PAAMePy55 chains that move in a common electrostatic field (i.e., a structure factor effect). The
presence of P123 micelles does not lead to the total disruption of these domains. They may either contain
entrapped P123 micelles or hydrophilic diblock impurities (originating from the P123 sample) that associate
with the PAAMePy55 chains.
triblock copolymer (P123) in aqueous solutions of different NaCl concentrations and pHs has been studied
by means of dynamic light scattering (DLS) and steady-state fluorescence spectroscopy at 40 °C. At acidic
pH values, in the low P123/PAAMePy55 molar ratio regime (i.e., at low P123 concentrations), the relaxation
time distributions retrieved from the DLS data analysis were monomodal and very similar to those obtained
for the pure PAAMePy55 solution. The apparent hydrodynamic radius of PAAMePy55 at low pH is 18 nm.
At higher molar ratios (i.e., at high P123 concentrations), still in the acidic pH regime, bimodal relaxation
time distributions were obtained, where the fast relaxation mode is connected to the translational diffusion of
free P123 micelles with a hydrodynamic radius obtained at infinite P123 dilution (RH,P123)0) of 10-11 nm.
This value coincides perfectly with the hydrodynamic radius of the pure P123 micelles at 40 °C, which was
found to be ca. 10 nm at all pH values. The second mode corresponds to a complex consisting of one
PAAMePy55 polymer chain and about 42 P123 micelles and with a RH,P123)0 between 35 and 36 nm depending
on pH. At pH 9, the mixed system also presented bimodal relaxation time distributions. At this high pH, the
intermolecular association between PAAMePy55 and P123 is less strong than at acidic pH according to the
steady-state fluorescence measurements. The fast mode is also in this case attributed to free P123 micelles
whereas the second mode is related to the so-called “slow mode” commonly observed for polyelectrolyte
solutions. In this system, it is related to the formation of multichain domains, that is, large domains formed
by several PAAMePy55 chains that move in a common electrostatic field (i.e., a structure factor effect). The
presence of P123 micelles does not lead to the total disruption of these domains. They may either contain
entrapped P123 micelles or hydrophilic diblock impurities (originating from the P123 sample) that associate
with the PAAMePy55 chains.
| Original language | English |
|---|---|
| Pages (from-to) | 6205-6214 |
| Journal | The Journal of Physical Chemistry Part B |
| Volume | 113 |
| Issue number | 18 |
| DOIs | |
| Publication status | Published - 2009 |
Subject classification (UKÄ)
- Physical Chemistry