Measuring The Nanomechanics Of Nanoconfined Water Layers

<p>Nanoconfined water has been the subject of special interest due to its applications in various fields such as biology, geology, medicine, and engineering tribology. While there is a general agreement on the layering of water molecules along atomically smooth surfaces, the behavior and properties of nanoconfined water is still poorly understood. A significant controversy exists whether there is a phase transformation imposed by confinement. We have measured the stiffness and damping coefficient of nanoconfined water using a small amplitude (0.5-1 Å) atomic force microscope. The results were analyzed with the help of two viscoelastic models, the Kelvin model and the Maxwell model. The stiffness and damping coefficient oscillate with period 2.7 ± 0.8 Å below 1 nm thickness of the water film. The retardation time and the relaxation time were measured as a function of both the strain rate and the film thickness. Above a critical strain rate, the retardation time shows valleys, and the relaxation time shows peaks commensurate with the stiffness peaks in the oscillatory profile. We call this phenomenon the Dynamic Solidification.</p> <p>The relaxation time was also measured as a function of the concentration of sodium chloride. It was found that the critical strain rate for the dynamic solidification is a function of the strength of the molarity of the solution. We found that above a critical sodium chloride concentration, water shows the dynamic solidification, even at significantly lower strain rates.</p> <p>To standardize the AFM measurements, we measured the effects of the tip size on the stiffness and damping of a nanoconfined model liquid tetrakis-2-ethyhexoxysilane (TEHOS) by using a number of tips of different sizes. We found that the stiffness and damping coefficient of the liquid increase linearly with the tip-size. We also measured an effective elastic modulus of the nanoconfined liquid and found it to be independent on the tip-size.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Open Access Dissertation

Discipline thesis:degree_discipline

Physics and Astronomy

Year dc:date.available

2010

Author dc:creator

• Khan, Shah Haidar

Contributors dc:contributor

• Peter M. Hoffmann

• AFM
• Nanoconfined Water
• Condensed Matter Physics

Repository record dc:identifier

https://digitalcommons.wayne.edu/oa_dissertations/171

OAI identifier oai:identifier

oai:digitalcommons.wayne.edu:oa_dissertations-1170