Dynamic Anion-Adaptive Poly(ionic liquid) Films via Surface-Initiated Ring-Opening Metathesis Polymerization

Abstract

We report the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of ionic liquid-tethered monomers to grow poly(ionic liquid) (PIL) films on gold and silicon substrates. The kinetics of film growth are rapid, with profilometric thicknesses approaching 600 nm within 15 min of polymerization in a 0.1 M monomer solution and substantial film growth observed at monomer concentrations as low as 0.02 M. The ionic liquid (IL) monomer consists of the cation 3- [(bicyclo[2.2.1]film whose PF 6 − anion can be easily interchanged to tune the film properties. The p[N 1 -dMIm][PF 6 ] films were shown to be adaptive to their anionic environment with the extent of anion exchange characterized by reflectance-absorption infrared spectroscopy and utlraviolet-visible spectroscopy. Anionic dyes incorporated into the p[N 1 -dMIm] films via anion exchange resulted in a reversible color change in the films. The surface and bulk interaction of the p[N 1 -dMIm] films with water was analyzed by contact angle goniometry and quartz crystal microbalance with dissipation (QCM-D). The p[N 1 -dMIm] film with the perchlorate (ClO 4 − ) ion exhibited the lowest advancing contact angle with water of 35 ± 3°compared to the p[N 1 -dMIm] film with the bistriflate ( − NTf 2 ) ion which exhibited the highest water contact advancing angle of 65 ± 3°. The p[N 1 -dMIm][ClO 4 ] film demonstrated an 8% increase in bulk water content, as determined by QCM-D, compared to the p[N 1 -dMIm][PF 6 ] film. The rate of ion transfer through the film was highly dependent on the anion as characterized by electrochemical impedance spectroscopy (EIS) in different electrolytes. In particular, resistances to ion transfer ranged from 7.90 ± 0.11 KΩ•cm 2 for films containing the PF 6 − anion to ≤ (4.34 ± 0.04) × 10 −3 KΩ•cm 2 for films containing the perchlorate ClO 4 − anion.

Co-Poly(ionic liquid) Films via Anion Exchange for the Continuous Tunability of Ion Transport and Wettability

“…2 The ion transport resistance of the p[N 1 -dMIm] films was shown to follow the order ClO 4 – ≪ FSI – ≪ − NTf 2 < PF 6 – . 2 p[N 1 -dMIm][PF 6 ][ClO 4 ] ion transport was investigated by utilizing electrochemical impedance spectroscopy (EIS). In EIS, a low amplitude sinusoidal potential ( E ac ) perturbation of varying frequency is applied around the equilibrium potential of the working electrode.…”

“…The IR spectrum for the p[N 1 -dMIm][PF 6 ][ClO 4 ] film displays both the P–F stretching peak at 855 cm –1 and the Cl–O stretching peak at 1106 cm –1 and retains the absorbance bands due to the polymer carbon backbone. 2 The binary anion mole fractions of PF 6 – ( y PF 6 – ) and ClO 4 – ( y ClO 4 – ) in the coPIL film were determined as described in the Supporting Information.…”

“…Grubbs third generation catalyst ([(H 2 IMes) (3-Br-py) 2 (Cl) 2 Ru = CHPh]) was synthesized as described by Love et al 30 3-[(bicyclo[2.2.1]hept-5-en-2-yl)methyl]-1,2-dimethylimidazol-3-ium hexafluorophosphate ([N 1 -dMIm][PF 6 ]) was synthesized as described by Njoroge et al 2…”

“…In particular, p[N 1 -dMIm][PF6] films exhibit an advancing water contact angle of 61 ± 2° and a film conductivity of 0.008 ± 0.001 μS/cm, whereas p[N 1 -dMIm][ClO 4 ] films exhibit an advancing water contact angle of 35 ± 3° and a film conductivity of ≥13.6 ± 0.8 μS/cm. 2 Therefore, a p[N 1 -dMIm][PF 6 ][ClO 4 ] film can provide a versatile test bed to elucidate the effects of anion composition on both wettability and ion conduction. Our recent work enabled us to discretely vary film properties based on the selection of anion.…”

pH-Responsive Copolymer Films Prepared by Surface-Initiated Polymerization and Simple Modification

“…Grubbs third generation catalyst was synthesized as shown in our previous work . The gold-coated wafers were typically cut into 1 cm × 4 cm samples after gold evaporation and placed into a 1 mM ethanolic solution of 4-mercapto-1-butanol for at least 1 h to yield a hydroxyl-terminated self-assembled monolayer (SAM) on the gold surface.…”