Polyelectrolyte gels exhibit complex swelling behavior in response to environmental stimuli such as pH and ionic strength, making them valuable for biomedical applications including drug delivery and biosensing. This study presents a comprehensive thermomechanical model to describe the equilibrium swelling of anionic copolymer gels in aqueous solutions with variable pH and monovalent salt concentration. The model integrates electrostatic interactions, osmotic pressure balance, and the kinetics of physical bond formation above the volume phase transition temperature (VPTT). Unlike conventional approaches that neglect secondary chain interactions, this framework explicitly accounts for hydrogen bonding between thermo-responsive and ionic monomers, which critically influences the nature of the phase transition.

The gel is modeled as a three-phase medium consisting of a polymer network, water molecules, and mobile ions: H⁺, OH⁻, Na⁺, and Cl⁻. The degree of ionization of carboxylic groups is governed by a generalized Henderson-Hasselbalch equation that incorporates ion-pair formation between Na⁺ and COO⁻. The Flory-Huggins parameter is treated as a function of both temperature and ionization level, capturing the shift in VPTT due to electrostatic repulsion. Above VPTT, hydrophobic segments aggregate into clusters, forming physical cross-links. The rate of aggregation is described by a kinetic equation dependent on the concentration of ionized functional groups and ion pairs, reflecting the competition between hydrophilic repulsion and hydrophobic attraction.

Material parameters were determined by fitting experimental data from poly(-isopropylacrylamide-co-sodium acrylate) gels under varying pH and NaCl concentrations. The model successfully reproduces key observations: abrupt swelling transitions at low pH, smooth transitions at high pH, and sharp reductions in swelling with increasing salt content.NR1I3 Antibody manufacturer Numerical simulations reveal that increasing ionic strength suppresses swelling below VPTT and lowers VPTT significantly. At physiological salt levels, the distinction between swollen and collapsed states becomes blurred, especially for gels with higher ionic monomer content. The effect of pH is most pronounced near pKa, where small changes induce large shifts in swelling behavior. Ion-pair formation reduces hydrogen bonding capacity, delaying aggregation and weakening the phase transition sharpness.HSPA1A Antibody site

The model provides a robust framework for predicting the swelling response of multi-stimuli-responsive gels across diverse conditions.PMID:34128136 It highlights the critical role of secondary interactions in determining macroscopic behavior and explains why random copolymerization may fail in biological environments. By quantifying the interplay between electrostatics, hydrophobicity, and kinetics, the model enables rational design of responsive materials with tailored switching characteristics. Future extensions could incorporate dynamic cross-linkers or hierarchical structures to enhance responsiveness and stability under complex physiological conditions.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com