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Thermodynamics, electrostatics, and ionic current in nanochannels grafted with pH-responsive end-charged
1Department of Mechanical Engineering, University of Maryland, College Park, MD, USA.
Electrophoresis
|November 30, 2016
Summary
This study reveals how pH and salt concentration influence polyelectrolyte brush height and ionic current in nanochannels. Higher pH increases brush height deviation, while lower pH drives larger ionic currents due to abundant, mobile H+ ions.
Area of Science:
- Physical Chemistry
- Nanotechnology
- Materials Science
Background:
- Polyelectrolyte (PE) brushes in nanochannels are crucial for tunable surface properties.
- Understanding the interplay of pH, salt concentration, and electrostatics is key to controlling PE brush behavior.
- Nanochannel ionic current is sensitive to surface charge and ion concentration.
Purpose of the Study:
- To investigate the thermodynamics, electrostatics, and electric field-driven ionic current in pH-responsive PE brush grafted nanochannels.
- To elucidate the nonintuitive relationship between pH, salt concentration, and PE brush height.
- To establish a framework for computing ionic current based on PE brush configuration and electrostatics.
Main Methods:
- Mean field theory was employed to model the PE brush behavior.
- Thermodynamic and electrostatic interactions were analyzed.
- Ionic current was computed using a combined PE-brush-configuration-EDL-electrostatics framework.
Main Results:
- pH and salt concentration exhibit a complex interplay affecting PE brush height, causing deviations from the uncharged state.
- Brush height changes depend on ionization, EDL energy, and PE end location relative to the channel half-height.
- Lower pH results in significantly higher ionic current despite lower electrostatic potential, attributed to high H+ ion concentration and mobility.
Conclusions:
- The study provides a comprehensive understanding of pH-responsive PE brushes in nanochannels.
- The findings highlight a tunable mechanism for controlling ionic current via pH, with potential applications in sensing and characterization.
- The steep pH dependence of ionic current offers opportunities for novel nanochannel device designs.
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