Date of Award
Doctor of Philosophy (PhD)
Materials Science and Engineering
Konstantin G. Kornev
Michael S. Ellison
This Dissertation is focused on the development of new methods for characterization and control of fluid rheology using magnetic nanorods. This Dissertation consists of five chapters. In the first chapter, we review current microrheologial methods and develop a Magnetic Rotational Spectroscopy (MRS) model describing nanorod response to a rotating magnetic field. Using numerical modeling, we analyze the effects of materials parameters of nanorods and fluids on the MRS characteristic features. The model is designed for a specific experimental protocol. We introduce and examine physical parameters which can be measured experimentally. The model allows identification of MRS features enabling the calculation of fluid viscosity. The MRS of Non-Newtonian fluids with exponentially increasing viscosity is discussed for the first time. In the second chapter, we review the techniques for magnetic nanorods synthesis. We describe a setup and experimental protocol to synthesize nickel nanorods with the desired geometrical properties, in particular, with the controlled length to diameter ratio. We review magnetic systems used for manipulation of magnetic nanoparticles. A multifunctional magnetic rotator is introduced and described in detail in this chapter. We believe that this multifunctional magnetic system will be useful not only for micro and nanorheological studies, but will find much broader applications requiring remotely controlled manipulation of micro and nanoobjects. In the third chapter, we describe the MRS experiments and use the model developed in the first chapter for characterization of magnetic properties of synthesized nickel nanorods. The same setup is used to measure viscosity of microdroplets. We show that the diffraction pattern from the suspension of nickel nanorods aligned in a magnetic field can be rotated by a spinning magnetic field. This effect opens up an opportunity for the MRS using much smaller nanorods. Another practical application of the controlled diffraction patterns is discussed: the use of this pattern in medical optofluidic devices producing stationary illuminating spots, for example, in endoscopes. In the fourth chapter, we report on a new MRS method which can be used for the in-situ (or in-vivo) rheological measurements of fluids and polymer systems when the fluid viscosity increases exponentially with time. We use this method to measure the exponential change of the viscosity of HEMA (2-hydroxyethyl-methacrylate) undergoing photopolymerization. Remarkably, an exponential increase of viscosity can be traced beyond the point when the polymer system undergoes transition to a gel and the gel domains start to appear. We expect that this method will open up new horizons in the quantitative rheological analysis of fluids inside living cells, microorganisms, and aerosol droplets with thickeners. In the fifth chapter, we describe a physical principle of self-assembly of magnetic nanorods into droplets of different sizes. These droplets can be formed on demand using magneto-static interactions between magnetic nanorods and a magnetic field gradient. We theoretically and experimentally confirmed that the cluster of nanorods at the top of the droplet is acting as a cone-shape solid body deforming the top part of the droplet when moving towards the magnet. The developed model allows one to selectively concentrate a finite amount of magnetic nanorods at the free surface and print multiple microdroplets on demand.
Tokarev, Alexander, "PROBING AND CONTROLLING FLUID RHEOLOGY AT MICROSCALE WITH MAGNETIC NANORODS" (2012). All Dissertations. 1519.