Measuring The Nanomechanics Of Nanoconfined Water Layers

MEASURING THE NANOMECHANICS OF NANOCONFINED WATERLAYERS bySHAH HAIDAR KHANDecember 2010Advisor: Dr. Peter M. HoffmannMajor: PhysicsDegree: Doctor of Philosophy Nanoconfined water has been the subject of special interest due to its applications invarious fields such as biology, geology, medicine, and engineering tribology. While there is ageneral agreement on the layering of water molecules along atomically smooth surfaces, thebehavior and properties of nanoconfined water is still poorly understood. A significantcontroversy exists whether there is a phase transformation imposed by confinement. We havemeasured the stiffness and damping coefficient of nanoconfined water using a smallamplitude (0.5-1 Å) atomic force microscope. The results were analyzed with the help of twoviscoelastic models, the Kelvin model and the Maxwell model. The stiffness and dampingcoefficient oscillate with period 2.7 ± 0.8 Å below 1 nm thickness of the water film. Theretardation time and the relaxation time were measured as a function of both the strain rateand the film thickness. Above a critical strain rate, the retardation time shows valleys, and therelaxation time shows peaks commensurate with the stiffness peaks in the oscillatory profile.We call this phenomenon the Dynamic Solidification.