PubMed · 5701320
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N G Toremalm. 1968. A tracheotomy speech valve.. https://doi.org/10.1288/00005537-196812000-00011
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A series of polyurethanes with novel copolymer soft blocks display a new surface phenomenon, contraphilic wetting, in which the dry surface is hydrophilic and the wetted surface is hydrophobic. A precursor polymer was prepared with copolymer soft blocks containing semifluorinated (trifluoroethoxy, 3FOx, or pentafluoropropoxy, 5FOx) and bromomethyl functional pendant groups with 2:1, 1:1, and 1:2 semifluorinated/bromomethyl ratios. The hard block consists of isophorone diisocyanate (IPDI) and 1,4-butanediol (BD). 5,5-Dimethylhydantoin was introduced by the substitution of Br via reaction-on-polymer. The composition, structure, and percent of 5,5-dimethylhydantoin substitution for both the precursor and the 5,5-dimethylhydantoin-substituted polyurethanes were analyzed by 1H NMR. The difference between the advancing contact angle on the wetted surface and that on the dry surface (deltaC) is highest (38 degrees ) for the polyurethane with the highest ratio of semifluorinated/hydantoin soft block side chains. A model is proposed according to which contraphilic wetting is driven enthalpically by hydrogen bonding. For the dry surface, hydrogen bonding of 5,5-dimethylhydantoin amide carbonyl groups to methylene hydrogens of semifluorinated groups disrupts the normal surface concentration of semifluorinated groups, whereas the geometric arrangement of hydantoin N-H results in availability for hydrogen bonding with water. Upon exposure to water, amide groups switch from hydrogen bonding to -CH2CF2CF3 to stronger hydrogen bonding with water. As a result, semifluorinated groups are "released", and the surface becomes hydrophobic. Drying the coating (50 degrees C) reversibly restores hydrophilic character. Coatings stored at ambient temperature and humidity have deltaC values intermediate between dry and wet states.
Transmission infrared spectroscopy was applied to investigate properties of the perfluorosulfonated polymer Nafion. Measurements were made on thin films formed by casting the polymer from solution onto ZnSe windows. Effects of water vapor permeation were studied. A complex band structure between 1350 and 1100 cm(-1) was analyzed qualitatively by fitting the region to Gaussian functions. Features associated with vibrational modes of -CF(2) and -SO(3)(-) groups were identified and observed to be sensitive to film hydration. The intensities of bands for the -SO(3)(-) modes increased with film hydration, while bands assignable to -CF(2) modes decreased. The results were applied to interpret infrared difference spectra of Nafion and shed light on the complicated features that appear. Vibrational bands for water were also examined. In partially hydrated films, the stretching mode of the free -OH group for interfacial water present in pores and channels of the polymer and bands for hydrated proton clusters were detected.
Solvation properties of the hydrated excess proton are studied in a hydrophilic pocket of Nafion 117 through a series of molecular dynamics simulations. The multistate empirical valence bond (MS-EVB) methodology, which enables the delocalization of the excess proton through the Grotthuss hopping mechanism, was employed for one of the excess protons in the simulation cell. Simulations were performed such that "classical" nondissociable hydronium cations and a single excess proton treated with the MS-EVB methodology were at a concentration ratio of 39:1. Two degrees of hydration of the Nafion polymer electrolyte membrane were simulated, each displaying the same marked difference between the solvation structures of the classical versus MS-EVB treated (Grotthuss shuttling) excess proton species. These differences are attributed to the solvent dynamics needed to transfer the cation between the solvent separated and contact pair positions about the sulfonic acid counterion. The results demonstrate that it is generally impossible to describe the low pH conditions in the hydrophilic domains of Nafion without the explicit treatment of Grotthuss delocalization in the underlying molecular dynamics model for the excess protons.