Responsive polymer conformation and resulting permeability of clay–polymer nanocomposites

Abstract

Changes in conformation are inherently critical to the behaviour of tunable clay–polymer nanocomposites (CPNs), including swelling potential and permeability. We investigated the conformational behaviour of a pH-responsive polymer and an expandable clay through dissipative particle dynamics (DPD) and pressurised permeability tests. Three different conditions were studied by DPD: (1) polymer in an aqueous solution, (2) polymer adsorbed on a clay surface and (3) polymer sandwiched between two clay surfaces. Pressurised permeability tests were conducted to investigate the pH-dependency of the CPN material. DPD simulations showed extended conformation of the polymer at high pH resulting in large interlayer spacing. Contracted coil conformation of the polymer led to small interlayer spacing at low pH. Intermediate conformation (expanded coil) and interlayer spacing were observed at pH near the pK _a value of the polymer. Swelling of the CPN increased with increasing pH resulting in permeability reduction. The combined results of the experimental permeability tests and DPD simulations indicate that as the interlayer spacing increased with increasing pH, the permeability of CPN decreased. Thus, conformational changes of polymer molecules can be related to swelling potential of CPN and its tunability predicted as a function of pH for a desirable minimal permeability.

Keywords:

• tunable clay–polymer nanocomposite (CPN)
• pH-responsive polymer
• permeability
• dissipative particle dynamics (DPD)

Acknowledgements

This material was based upon work supported by the National Science Foundation under CMMI Grant No. 1041995. Computational resources were provided by the Materials Simulation Center and the RCC unit at Penn State.