Small-Amplitude AFM Studies of Nanoconfined Water

Wayne State University, Detroit MI

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** Although water is the most ubiquitous liquid in the environment, its properties are still not well understood. In the context of nanotechnology, the behavior of nanoscale water is a subject of great controversy and great importance. Nanoscale water plays an important role in biology, where it determines the shape of the macromolecules in our cells, and in nanotechnology, where engineers are developing new devices that can analyze ever smaller water samples for medical diagnoses. This award supports a project to study the mechanical properties of water confined between two surfaces that are only 1-20 water molecules apart. When water is confined to such tight places, it behaves quite differently from bulk water. So far, experiments by different research groups have yielded contradictory results. A novel Atomic Force Microscopy (AFM), developed at Wayne State University, will be used to conduct careful measurements under varied conditions, such as changes in ion concentration or different confining surfaces in an attempt to elucidate the properties of water confined to nanoscale spaces. This project is integrated with training opportunities through a new graduate interdisciplinary Materials Science program and undergraduate Biomedical Physics program. Students who will be involved in this research will be trained in instrument development and state-of-the-art nanoscience research. The results of this research will be communicated through ongoing outreach efforts, which have so far reached hundreds of middle and high school students, teachers and parents. ****TECHNICAL ABSTRACT**** The properties of water, as the primary solvent of biological systems, are not fully understood, especially in situations where water is confined to nanoscale spaces. When water is confined to only a few molecular layers, continuum models break down, and oscillatory force profiles are observed. However, experiments to measure the mechanical properties of nanoconfined water have yielded contradictory results. This project will use novel Atomic Force Microscopy (AFM) Techniques, developed at Wayne State University, to study the mechanics and dynamics of nanoconfined water layers. The home-built AFM systems use ultra-small amplitudes of order 0.03 nm to perform linear measurements of the viscoelastic properties of confined water layers. This project will study how the dynamics of water change under various conditions, including changes in dissolved ion concentrations, applied shear, compression speeds, chemistry of confining surfaces, and external DC and RF electromagnetic fields. The latter is intended to elucidate the role of polarity and hydrogen bonding in nanoconfined water on its viscoelastic characteristics. This research is integrated with new educational programs at Wayne State, including a new interdisciplinary Materials Science graduate program and a new undergraduate Biomedical Physics program. Through these programs and this research projects graduate and undergraduate students will be trained in state-of-the-art instrumentation and nanoscience research.