The project investigated the structural dynamics of interfacial water adjacent to solid surfaces and polymeric materials using vibrational spectroscopy, with a central focus on testing the hypothesis of long-range ordering in exclusion zone (EZ) water. Three interconnected work packages were designed to explore how surface chemistry, nanoscale topology, and polymer self-assembly influence water structure and behavior. The work involved the development and refinement of experimental setups, extensive spectroscopic analysis, and synthetic chemistry, yielding both novel findings and important methodological insights.
Work Package 1 focused on spectroscopic characterization of water near hydrophilic surfaces, with Nafion selected as the primary model system. A custom-built setup was developed to enable spatially resolved Raman and ATR-IR spectroscopy up to 800 µm from the surface. Optical microscopy confirmed the formation of an exclusion zone approximately 200 µm thick adjacent to the Nafion membrane. Raman spectra, however, revealed no significant changes in the OH-stretching region of water outside the membrane, even within the visually confirmed EZ. These results challenge the assumption that exclusion zones are associated with long-range structural reorganization in water that is detectable by vibrational spectroscopy.
In contrast, Raman and ATR-IR measurements taken from within the membrane showed reduced hydrogen bonding, suggesting altered water dynamics within the confined polymer matrix itself. To ensure robustness of the Raman results, multiple excitation wavelengths were employed to probe potential differences in scattering efficiency and to minimize fluorescence. Specifically, we tested 325 nm (UV), 488 nm, and 514 nm laser lines across different setups. Despite these efforts, no consistent or reproducible spectral differences were observed in water adjacent to the membrane compared to bulk, across the full spectral range. While the 325 nm excitation provided improved spectral contrast in some cases, it also increased baseline instability and sample degradation. Ultimately, the Raman measurements consistently indicated a lack of vibrational spectral signatures corresponding to ordered water structures outside the membrane, even under carefully optimized conditions.
Complementary ATR-IR spectroscopy supported these findings by confirming changes in water structure only inside the Nafion, not in adjacent interfacial layers. THz spectroscopy was also initially planned to extend the investigation of collective water modes but was eventually excluded due to irreproducibility and sensitivity to ambient humidity and signal drift. Investigations on silicon oxide surfaces were halted early, as optical microscopy revealed no observable exclusion zone, deprioritizing further spectroscopic analysis of this system.
The outcomes of this work package were significant: they provided strong experimental evidence that, while EZ water can be detected optically, it does not exhibit measurable long-range vibrational ordering in Raman or ATR-IR spectra. These results have been compiled into a manuscript currently under peer review. All planned milestones related to setup development, data acquisition on Nafion, and manuscript submission were achieved, while tasks involving silicon oxide and THz spectroscopy were only partially completed. To address the limited success of the THz and silicon oxide studies, the project scope was adaptively expanded to include a new line of investigation: the effect of cryoprotectants (PEG and trehalose) on EZ formation and water dynamics under cooling conditions. This exploratory work yielded promising preliminary results that are currently being prepared for publication.
Work Package 2 aimed to explore the molecular behavior of water near graphene layers, hypothesizing that graphene’s unique electronic and structural properties might influence interfacial water ordering. Despite securing high-quality graphene samples through collaboration with a specialized group, spectroscopic investigations proved technically infeasible. Raman spectroscopy was strongly compromised by persistent background fluorescence from both the graphene substrate and residual surface contamination. Several experimental strategies were implemented to overcome this challenge, including the use of 488 nm, 514 nm, and 325 nm excitation wavelengths, as well as variations in sample geometry and laser power. Nonetheless, fluorescence consistently overwhelmed the water vibrational signal, making it impossible to extract meaningful information about water dynamics. As a result, no scientific deliverables or milestones were achieved in this work package. However, the technical challenges encountered provided critical insight into the limitations of Raman spectroscopy for graphene–water interface studies, which may guide future work employing fluorescence suppression strategies or alternative measurement techniques.
Work Package 3 focused on the synthesis, characterization, and self-assembly of amphiphilic triblock copolymers with systematically varied aromatic functional groups, including methoxy, nitro, fluoro, ethyl, and hexyl substituents. These polymers were synthesized via RAFT polymerization during a secondment at ETH Zurich and fully characterized using NMR, GPC, and ATR-IR spectroscopy. Their self-assembly in aqueous media was successfully examined via electron microscopy, revealing that the nature of the aromatic substituent significantly influenced the resulting morphology and aggregate structure.
Spectroscopic investigation of water–polymer interactions was carried out using ATR-IR and Raman spectroscopy. While ATR-IR measurements were completed for all polymer types, they revealed only subtle and non-systematic differences in the OH-stretching band, providing limited information about solvent dynamics. Raman spectroscopy, once again, was severely limited by fluorescence, which originated from both the polymer backbone and aromatic substituents. Despite extensive testing with different excitation wavelengths—including 514 nm and 488 nm—fluorescence could not be sufficiently suppressed, and reliable spectral information on water vibrations was not obtained. Consequently, the spectroscopic subtask within this work package remained inconclusive.
Nonetheless, the successful synthesis and self-assembly of a family of amphiphilic polymers represented a major scientific output of the project. The results shed light on the influence of electronic effects on polymer morphology and provide a foundation for future studies aimed at disentangling polymer–solvent interactions using refined spectroscopic approaches.
In summary, the project successfully delivered on its core scientific objectives, producing valuable data on the structural behavior of water near hydrophilic membranes, advancing polymer design strategies, and highlighting the methodological boundaries of vibrational spectroscopy in soft materials. Although spectroscopic analysis of some systems was hampered by fluorescence or instrumental limitations, the project yielded critical insights into the limitations of current techniques and set the stage for methodological innovation. Several results are being prepared for publication, and the project’s outcomes contribute meaningfully to the understanding of interfacial hydration in material and polymer science.
