Investigating the effect of pH on the swelling process, mechanical and thermal attributes of polyacrylamide hydrogel structure: A molecular dynamics study

Stimuli-responsive hydrogels are a class of hydrogels that undergo reversible changes in their physical or chemical properties in response to specific external stimuli. The pH is a critical environmental stimulus for stimuli-responsive hydrogels. When the pH of the surrounding environment changes, it can lead to significant alterations in the properties of the hydrogel, such as swelling behavior, mechanical strength, etc. So, understanding how pH affects the swelling behavior and mechanical properties of these hydrogels is crucial to optimize their performance in biomedical applications. Therefore, in the present study, the effect of pH on the swelling process, mechanical and thermal attributes of polyacrylamide hydrogel structure were studied using molecular dynamics simulation and LAMMPS software. The results reveal that as the pH increased from 2 to 11, the structural volume increased from 342,583 to Å3. The increase in the volume of the structure was in terms of the increase in atomic fluctuations by increasing the pH, and consequently, it led to more swelling. The mechanical properties show that the ultimate strength and Young's modulus of the sample increase from 0.0298 to 0.0007 to 0.0359 and 0.0012 MPa, respectively. The reason for the increase in these parameters was that by increasing the pH, the attraction force among different components of the PAM hydrogel structure increased. This issue led to an increase in the stability of the nanostructure. Finally, the thermal properties showed that thermal conductivity increased from 0.51 to 0.62 W/m K by increasing pH to 11. The findings may lead to the development of pH-responsive hydrogels with enhanced properties, offering more effective and tailored solutions for biomedical applications.