Probing the Surface Hydration of Nonfouling Zwitterionic and Poly(ethylene glycol) Materials with Isotopic Dilution Spectroscopy

Abstract

Understanding the surface hydration of nonfouling materials such as zwitterionic polymers and poly(ethylene glycol) (PEG) aids in the design of new and effective nonfouling materials. Sum frequency generation (SFG) vibrational spectroscopy is a powerful technique used to probe water structures at solid/liquid interfaces. However, SFG signals of H 2 O consisting of symmetric and asymmetric stretches and Fermi resonance overlap heavily, which complicates the interpretation of the spectra and leads to controversy. In this work, isotopically diluted water was used instead of H 2 O to study the surface hydration of three zwitterionic polymers and a PEG coating. Because the water signal contains only an O−H stretch, strongly and weakly hydrogen-bonded water structures were easily distinguished. SFG results showed a majority of strongly hydrogen-bonded water molecules at the nonfouling polymer surfaces. For comparison, the water spectra at the surfaces of poly(methyl methacrylate) and poly(ethylene terephthalate) suggested significant amounts of weakly hydrogen-bonded water. The effects of pH on the surface hydration of the nonfouling polymers were also investigated. The materials respond to pH differently because of their different structural formulas. The flip of the water molecules at a carboxybetaine polymer surface in response to pH was also observed.

Cleaning of Oil Fouling with Water Enabled by Zwitterionic Polyelectrolyte Coatings: Overcoming the Imperative Challenge of Oil–Water Separation Membranes

“…It has been reported that zwitterions can superiorly bind water molecules through ion-dipole interactions between the two charged-units and water compared to other hydrophilic species, such as single-charged groups and the oligo-(ethylene glycol). [12][13][14] Applying sum frequency generation vibrational spectroscopy (SFG), an ordered and tightly immobilized interfacial water layer was detected at the zwitterionic polymer/water interfaces, 35,36 which can well explain the excellent underwater oil repellency of the PMPC surface observed in our work.…”

Role of Interfacial Water in Protein Adsorption onto Polymer Brushes as Studied by SFG Spectroscopy and QCM

“…The peak center position of the OH stretching vibration measured by SFG is interpreted as the strength of hydrogen bonding between water molecules and water molecules or water molecules and materials. 27,28 This time, we focused on the interface between polymer brushes and water molecules. Therefore, we interpreted the peak center position of the OH stretching vibration as the interaction between interfacial water molecules and polymer brushes.…”

“…The SFG spectrum of the OH stretching region is influenced by intermolecular and/or intramolecular coupling of H 2 O. [24][25][26][27][28]43 The isotopically diluted water (HOD) can simplify the SFG spectrum by eliminating the effect. 24,25,28 Therefore, in our case we used isotopically diluted water (…”

Effect of pH and content of reduction‐sensitive copolymer on the guest exchange kinetics of micelles

“…As shown in Figure (a), the normalized FRET ratios increase slightly over time at various pH values in the absence of DTT, which indicates that the guest molecules escapes from the original micelles into different micelles due to the exchange of copolymer chains . It is apparent that the increase of the normalized FRET ratio is the fastest at pH 4.5 in the absence of DTT, presumably due to the reason that the interaction between H + and the oxygen atom on POEGA chains at pH 4.5 enhances the hydrogen‐bonded interaction between the polymer and water and increases the solubility of POEGA chains and facilitate the exchange of the copolymer chains . Moreover, the solubility of the dyes molecules might be slightly improved at lower pH to accelerate the exchange rate of dye molecules …”