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. 2019;8(3):https://doi.org/10.1021/acsmacrolett.8b00952.

Lower Critical Solution Temperature in Polyelectrolyte Complex Coacervates

Samim Ali  1 , Markus Bleuel  2   3 , Vivek M Prabhu  1
Affiliations

Lower Critical Solution Temperature in Polyelectrolyte Complex Coacervates

Samim Ali et al. ACS Macro Lett. 2019.

Abstract

A model linear oppositely charged polyelectrolyte complex exhibits phase separation upon heating consistent with lower critical solution temperature (LCST) behavior. The LCST coexistence curves narrow with increasing monovalent salt concentration (C s) that reduces the polymer concentration (C p) in the polymer-rich phase. The polymer-rich phase exhibits less hydration with increasing temperature, while an increase in C s increases the hydration extent. The apparent critical temperature, taken as the minimum in the phase diagram, occurs only for a narrow range of C s. Mean field theory suggests an increasing Bjerrum length with temperature can lead to an electrostatic-driven LCST; however, the temperature dependence of the Flory-Huggins interaction parameter and solvation effects must also be considered.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1.
Figure 1.
Temperature dependence of the transmittance for (a) KPSS/PDADMAB prepared at CKBr = 2.15 mol/L and Cpi = 0.3 mol/L. The cloud point temperature Tcp is shown by the vertical dotted line and photos at (b) 15 °C and (c) 32 °C. The laser scanning confocal micrograph in (d) shows coacervate droplets in the turbid phase. (e) Shows the coexisting phases at 32 °C.
Figure 2.
Figure 2.
Cloud-point temperature vs (a) KBr concentration with fixed Cpi = 0.3 mol/L and (b) initial polymer concentration with fixed CKBr = 2.15 mol/L. Dotted lines are guide to the eye. Error bars represent one standard deviation estimated from measured uncertainty in the sampling micropipette volumes and molar extinction coefficient. While error bars are shown, they may be smaller than the symbols used.
Figure 3.
Figure 3.
Coexistence curves for KPSS/PDADMAB mixture at CKBr = 1.75, (b) 2.0, and (c) 2.05 mol/L showing the two-phase (2Φ) and one-phase (1Φ) region. The initial PSS concentration was 0.15 mol/L (circles) and 0.3 mol/L (squares) that phase separates into the supernatant (open symbols) and concentrated phases (filled symbols) at the given temperature. Measured Tcp at CPSS = 0.15 mol/L (▲) and 0.3 mol/L (▼) are indicated in (b) and (c). Error bars represent one standard deviation estimated from the uncertainty in the sampling micropipette volumes. While error bars are shown, they may be smaller than the symbols used.
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References

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