Surface-attached polydicyclopentadiene (pDCPD) films were prepared on gold and silicon substrates via surface-initiated ring-opening metathesis polymerization (SI-ROMP) of dicyclopentadiene (DCPD). The films were grown utilizing monomer in both the vapor phase and the solution phase with the former process exhibiting rapid kinetics, producing ∼400-nm-thick pDCPD films in less than 1 min of polymerization. No significant differences in thickness were observed for films grown from monomer in the vapor phase with the different isomers (exo and endo) of DCPD. Decane was used as an inert additive to control the concentration of DCPD monomer in the vapor phase enabling the preparation of pDCPD films with thickness ranging from tens of nanometers to hundreds of nanometers. The thickness of pDCPD films polymerized using monomer in the vapor phase was enhanced by the presence of a rinse solvent on the surface of the ROMP-active gold substrates. The choice of ROMP catalyst was found to be an important consideration when SI-ROMP was conducted on different substrates. Electrochemical impedance spectroscopy was used to reveal that the films provide effective barriers to the diffusion of aqueous ions in excess of 1 × 10 Ω·cm. The mechanical properties of the surface-tethered pDCPD films were quantified with AFM PeakForce quantitative nanomechanical mapping (QNM) with a measured reduced Young's modulus (E) of 15 GPa. The measured E was greater than that of a non-cross-linked surface-tethered polymer, pNB, indicating that the pDCPD films are stiffer.
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.
We report the preparation of polymer/ionic liquid (IL) gels by incorporating ILs into surface-initiated poly(dicyclopentadiene) (pDCPD) films using a simple immersion method. In the method, a surface-initiated pDCPD film was exposed to a solution of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) in dichloromethane, which led to incorporation of the IL within the film. The volume ratio of the incorporated [bmim][PF6] to the original pDCPD film was adjusted as high as 0.5, and it is strongly dependent on the solvent, IL solution concentration, and the sample immersion time. The maximum IL loading is affected by the swellability of pDCPD films in the solvent, the solubility of the IL in the solvent, and interactions between the IL and the polymer. The method is also proven to be feasible in preparing pDCPD-IL gels with different IL species. The incorporated ILs dramatically change the properties of the pDCPD films. The pDCPD-IL gel film has a higher shear loss modulus than that of the pure pDCPD film based on quartz crystal microbalance with dissipation. The resistance of the film against ion transfer is at least 4 orders of magnitude lower at high levels of IL incorporation than the resistance of pure pDCPD.
This manuscript details a novel and simple approach to achieve surface-tethered co-poly(ionic liquid) (coPIL) films through the exchange of the resident anion of a poly(ionic liquid) (PIL) film with two or more anions. Initially, surface-tethered PIL films were prepared by the surface-initiated ring-opening metathesis polymerization of the ionic liquid monomer 3-[(bicyclo[2.2.1]hept-5-en-2-yl)methyl]-1,2-dimethylimidazol-3-ium hexafluorophosphate ([N 1 -dMIm][PF 6 ]) whose PF 6 – anion was easily interchanged with aqueous solutions containing a binary mixture of the PF 6 − anion, along with perchlorate (ClO 4 − ) or bis(fluorosulfonyl)imide (FSI − ) anions. The binary mole fraction of each anion in the film was determined from the infrared spectra of the coPIL films. The thermodynamically driven anion selectivity for exchange from the liquid phase into the coPIL films was determined to follow the order ClO 4 – < PF 6 – < FSI – . The aqueous wettability of p[N 1 -dMIm] coPIL films containing both the PF 6 – and ClO 4 – anions (p[N 1 -dMIm][PF 6 ][ClO 4 ]) was quantified by contact angle goniometry with the observation that the surface showed an enrichment in the ClO 4 – anion compared to the average binary anion mole fraction of ClO 4 – in the film ( y ClO 4 – ). The rate of ion transport through the p[N 1 -dMIm][PF 6 ][ClO 4 ] coPIL films, quantified by electrochemical impedance spectroscopy, linearly depends on the binary anion mole fraction of ClO 4 – in solution ( x ClO 4 – ), enabling continuous tunability by over three orders of magnitude for ion conductivity in the coPIL films.
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