Abstract
This article summarizes studies of the equilibrium and kinetic swelling properties of a class of hydrophobic weak polyelectrolyte copolymer gels synthesized from n-alkyl methacrylates (hydrophobic) and N,N-dimethylaminoethyl methacrylate (weak base). We present evidence for a pH-driven swelling phase transition, and consider the effect of pH buffers on equilibria. A simple model based on ideal Donnan equilibrium is able to predict qualitative trends but is unsuccessful in making quantitative predictions of buffer effects on swelling equilibria. Buffers also strongly influence swelling kinetics. It is demonstrated that suitably chosen buffers can act as proton carriers which, under the right circumstances, speed up swelling and deswelling substantially.
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Abbreviations
- n-AMA:
-
n-alkyl methacrylate
- BMA:
-
butyl methacrylate
- ClHAc:
-
chloroacetic acid
- DMA:
-
N,N-dimethylaminoethyl methacrylate
- DVB:
-
divinyl benzene
- EMA:
-
ethyl methacrylate
- HAc:
-
acetic acid
- HEMA:
-
hydroxyethyl methacrylate
- HMA:
-
hexyl methacrylate
- MA:
-
methacrylic acid
- MeOHAc:
-
methoxyacetic acid
- PMA:
-
propyl methacrylate
- h:
-
Thickness of gel
- pH:
-
pH of outer solution
- pK:
-
Log ionization constant of buffer
- pKa:
-
Log ionization constant of ionizable group on gel
- t:
-
Time
- t1/2 :
-
Half time for completion of diffusion process
- taccel :
-
Acceleration time
- w(t):
-
Fractional deswelling as function of time
- zi :
-
Valence of i-th ionic species
- {C}:
-
Set of ion concentrations in gel and outer solution
- CAH :
-
Concentration of buffer in acid form in outer solution
- CAT :
-
Total buffer concentration in outer solution
- Ci :
-
Concentration of i-th ionic species inside gel
- C′i :
-
Concentration of i-th ionic species in outer solution
- D:
-
Diffusion coefficient
- De:
-
Deborah number
- EWF:
-
Equilibrium water fraction
- I:
-
Ionic strength
- Pext :
-
Excess pressure applied to gel
- Q(t):
-
Degree of swelling as function of time
- R:
-
Gas constant
- “R”:
-
“Rate” of swelling
- T:
-
Temperature
- Tg :
-
Glass transition temperature
- V:
-
Volume of Gel
- W(t):
-
Weight of gel as function of time
- α:
-
Exponent for cumulative swelling expression
- ΔG:
-
Total free energy change due to swelling
- ΔGion :
-
Component of ΔG due to ions
- ΔGnet :
-
Component of ΔG due to polymer network and solvent
- λ:
-
Donnan ratio
- ∏ion :
-
Ion swelling pressure
- ∏net :
-
Swelling pressure due to polymer network and solvent
- ρp :
-
Specific gravity of polymer
- σ0 :
-
Molar density of amine groups in dry network
- φ:
-
Volume fraction of polymer
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Siegel, R.A. (1993). Hydrophobic weak polyelectrolyte gels: Studies of swelling equilibria and kinetics. In: Dušek, K. (eds) Responsive Gels: Volume Transitions I. Advances in Polymer Science, vol 109. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-56791-7_6
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DOI: https://doi.org/10.1007/3-540-56791-7_6
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