Temperature-Dependent Transport Properties of Poly[2-(methacryloyloxy)ethyl]trimethylammonium Chloride Brushes Resulting from Ion Specific Effects

Abstract

Combined use of electrochemical techniques (electrochemical impedance spectroscopy and cyclic voltammetry) and quartz crystal microbalance with dissipation allowed to resolve separately the thermal effects on diffusion and electron-transfer steps of the electrochemical reaction of the [Fe(CN) 6 ] 3−/4− redox couple at a Au electrode modified with poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (PMETAC) brushes. Arrhenius-type dependences of the kinetic constant and the diffusion coefficient with temperature were observed in different electrolytes. Ion-paired collapsed polyelectrolyte brushes in NaClO 4 result in compact stiff structures with less amount of entrapped water and markedly different from the same brushes with a collapse driven by pure Coulombic screening in NaCl. A remarkable difference related to the type of counterion is the occurrence of a thermal transition for the polyelectrolyte brush in the presence of ClO 4 − ions at near-ambient temperature (∼17 °C). Activation energies for electron-transfer and diffusion processes become twice as large as those for temperatures above the thermal transition. These electrochemical studies demonstrate not only the critical role of ion-pairing interactions in determining the physicochemical properties of the macromolecular system but also provide experimental evidence of counterion-induced thermocontrolled transport functionality in the polyelectrolyte brush layer.

Conformational Dynamics and Responsiveness of Weak and Strong Polyelectrolyte Brushes: Atomistic Simulations of Poly(dimethyl aminoethyl methacrylate) and Poly(2-(methacryloyloxy)ethyl trimethylammonium chloride)

“…45 It was also shown that PMETAC brushes, swelling to conformations accommodating 67% water molecules, lost 17% water during collapse in 0.1 M NaCl, whereas the collapse in 0.1 M NaClO 4 led to a loss of 54% of associated water. 45 Similar observations were reported for other strong polycationic brushes such as p o l y ( v i n y l b e n z y l t r i m e t h y l a m m o n i u m c h l o r i d e ) (PVBTMAC). 46 QCM-D data gave evidence for dramatic changes in brush hydration upon exposure to chaotropic ions.…”

“…In comparison, strong polyelectrolytes do not typically respond to variations in pH but present complex conformational changes in response to variations in electrolyte type and ionic strength. For example, polycationic poly­((2-methacryloyloxy)­ethyl trimethylammonium chloride) (PMETAC) brushes display different swelling behavior in the presence of chaotropic anions, such as perchlorates, in comparison to more kosmotropic ions such as chlorides . It was also shown that PMETAC brushes, swelling to conformations accommodating 67% water molecules, lost 17% water during collapse in 0.1 M NaCl, whereas the collapse in 0.1 M NaClO 4 led to a loss of 54% of associated water .…”

“…For example, polycationic poly­((2-methacryloyloxy)­ethyl trimethylammonium chloride) (PMETAC) brushes display different swelling behavior in the presence of chaotropic anions, such as perchlorates, in comparison to more kosmotropic ions such as chlorides . It was also shown that PMETAC brushes, swelling to conformations accommodating 67% water molecules, lost 17% water during collapse in 0.1 M NaCl, whereas the collapse in 0.1 M NaClO 4 led to a loss of 54% of associated water . Similar observations were reported for other strong polycationic brushes such as poly­(vinylbenzyltrimethylammonium chloride) (PVBTMAC) .…”

Effect of Counterion Binding to Swelling of Polyelectrolyte Brushes

“…Polyelectrolyte brushes are promising approaches to the construction of highly charged interfacescharged macromolecules grafted densely onto the interfaces, including solid–liquid, liquid–liquid, and air–liquid interfaces, by physisorption and chemisorption. , Intensive research studies have been conducted continuously on polyelectrolyte brushes, the smart and responsive interfacial materials, − and believed to be perspective candidates of functional surfaces for bio-lubrication, , reactors of small scale, smart drug delivery, , controlling devices of micro-fluids, and so forth. Despite the unique and promising properties and functionalities of polyelectrolyte brushes, the physical mechanism of their structure and responsive behavior has been drawing considerable research attention, both theoretically and experimentally. − …”

Divide and Conquer: A Novel Dual‐Layered Hydrogel for Atmospheric Moisture Harvesting

“…In addition, the PNIPAM/PAEtMA‐based WAL has a ‘thicker wall’ and larger pore size in comparison with the PNIPAM/NPs‐based LHL. This result may be attributed to the lower glass transition temperature ( T g) of PAEtMA, resulting in a ‘slower’ solidification process in the freezing dry [23] . We also observed a clear boundary between the two layers (Figure 3C) and the connection is stable without sign of detachment.…”