****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.
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.
The research funded by this grant aimed at exploring the mechanical behavior of water when it is squeezed into a space that is only a few nanometers thick. This "nanoconfined" water behaves quite differently from ordinary water: Instead of being a chaotic liquid, the confined water spontaneously forms layers of one molecular thickness each. Nanoconfined water also has a peculiar mechanical response to being gently squeezed: When squeezed at an extremely slow speed of 0.8 nanometer per second, it responds elastically (i.e. it "bounces") like a solid. This speed is so slow that it would take 12 years to move one foot of distance. We have a unique atomic force microscope (AFM) that can perform measurements as slow as 0.2 nanometer/s and allows us to measure the behavior of nanoconfined liquids (water or oil) under extremely slow compression. This AFM was developed and built in our lab at Wayne State University in Detroit, MI. With this AFM, we can probe the liquid by oscillating a small tip at amplitudes that are smaller than the size of the molecules. We have used amplitudes as small as 0.04 nm, and measured the motion of the tip with a precision of 3 picometers (this is less than the size of a single hydrogen atom). The importance of understanding nanoconfined liquids is far-reaching. Nanoconfined liquids can be found in our cells (within and between proteins, for example), in rocks, in all situations where one surface slides on another, and in nanotechnology. Understanding the mechanical response of nanoconfined liquids is important for oil recovery, friction in machines, nanofluidics, medicine and biology. Recently, we have developed a new method to measure viscosity (how "thick" a liquid is) under nanoconfinement. Measuring the viscosity of extremely small samples can have important technological uses in, for example, the pharmaceutical industry, where only small quatities of prototype drugs are available. We have also shown the strong influence if dissolved ions on the mechanics of nanoconfined water - a result that could have important implication for oil recovery out of porous rock, where water is often used to push the oil out. It has been found that dissolved ions play a large role in this process, but it is not well understood why. Our research could answer this question. We have shared our research with a broader public through outreach activities (K-12 and adult audiences), through teaching, and through the publication of a popular science book by the principal investigator ("Life's Ratchet", Basic Books, 2012). Through the grant, 3 graduate students and 2 undergraduate students were trained. While one graduate student is still completing his PhD, the others have found employment in industry or academia.
