TY - JOUR

T1 - Highly sensitive gating in pH-responsive nanochannels as a result of ionic bridging and nanoconfinement

AU - Lopez, Luis Gonzalo

AU - Nap, Rikkert J.

N1 - Funding information: Research supported as part of the Center for Bio-Inspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award # DE-SC0000989. The authors thank Prof. Igal Szleifer and Dr. Mario Tagliazucchi for useful discussions.

PY - 2018

Y1 - 2018

N2 - Sensitive switching between OFF and ON states is a desirable feature in stimuli-responsive nanopores and nanochannels. In this work, we show that nanogates modified with weak polyelectrolytes can be controlled by multivalent counterions and, more remarkably, can exhibit sensitive pH-gating due to an interplay between ionic bridging and nanoconfinement. We demonstrate these general features by systematically studying the effects of Ca 2+ binding on the molecular organization and transport properties of poly(acrylic acid)-functionalized nanochannels. To this end, we extend and apply a molecular theory that has been successfully used in the past to describe and predict the behavior of pH-responsive polymers. Two main results emerge from the present study: first, the addition of Ca 2+ to the bulk solution changes - in a concentration-dependent manner - both the ionization and structural state of the end-tethered polymers, affecting, respectively, the ionic conductivity and physical opening of the nanochannel. Second, in the presence of Ca 2+ and under specific nanoconfinement conditions, the grafted channel can exhibit a sensitive response to pH in the transition between closed and open states. We attribute this sensitivity to bistability in the system. Our results also indicate that the polymer layer can undergo a microphase separation when the brush collapses on the nanochannel walls. Taken together, these findings suggest the possibility of designing nanogates that can respond to marginal changes in pH or multivalent ion concentration. Such nanodevices may be used as logic gates or for any application that requires a sensitive control over the ions, molecules, or nanoparticles flowing through them.

AB - Sensitive switching between OFF and ON states is a desirable feature in stimuli-responsive nanopores and nanochannels. In this work, we show that nanogates modified with weak polyelectrolytes can be controlled by multivalent counterions and, more remarkably, can exhibit sensitive pH-gating due to an interplay between ionic bridging and nanoconfinement. We demonstrate these general features by systematically studying the effects of Ca 2+ binding on the molecular organization and transport properties of poly(acrylic acid)-functionalized nanochannels. To this end, we extend and apply a molecular theory that has been successfully used in the past to describe and predict the behavior of pH-responsive polymers. Two main results emerge from the present study: first, the addition of Ca 2+ to the bulk solution changes - in a concentration-dependent manner - both the ionization and structural state of the end-tethered polymers, affecting, respectively, the ionic conductivity and physical opening of the nanochannel. Second, in the presence of Ca 2+ and under specific nanoconfinement conditions, the grafted channel can exhibit a sensitive response to pH in the transition between closed and open states. We attribute this sensitivity to bistability in the system. Our results also indicate that the polymer layer can undergo a microphase separation when the brush collapses on the nanochannel walls. Taken together, these findings suggest the possibility of designing nanogates that can respond to marginal changes in pH or multivalent ion concentration. Such nanodevices may be used as logic gates or for any application that requires a sensitive control over the ions, molecules, or nanoparticles flowing through them.

UR - http://www.scopus.com/inward/record.url?scp=85048953310&partnerID=8YFLogxK

U2 - 10.1039/c8cp02028k

DO - 10.1039/c8cp02028k

M3 - Article

VL - 20

SP - 16657

EP - 16665

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 24

M1 - 16657

ER -