Dissertations, Theses, and Capstone Projects

Date of Degree

6-2016

Document Type

Dissertation

Degree Name

Ph.D.

Program

Physics

Advisor

Gregory S. Boutis

Committee Members

Dmitry S. Novikov

Els Fieremans

Vadim Oganesyan

Ruth E. Stark

Subject Categories

Biological and Chemical Physics | Condensed Matter Physics | Statistical, Nonlinear, and Soft Matter Physics

Keywords

Diffusion, Disordered Systems, NMR

Abstract

This thesis reports on the manifestation of structural disorder on molecular transport and it consists of two parts. Part I discusses the relations between classical transport and the underlying structural complexity of the system. Both types of molecular diffusion, namely Gaussian and non-Gaussian are presented and the relevant time regimes are discussed. In addition the concept of structural universality is introduced and connected with the diffusion metrics. One of the most robust techniques for measuring molecular mean square displacements is magnetic resonance. This method requires encoding and subsequently reading out after an experimentally controlled time, a phase ϕ to the spins using magnetic field gradients. The main limitation for probing short diffusion lengths L(t) = 1 µm with magnetic resonance is the requirement to encode and decode the phase ϕ in very short time intervals. Therefore, to probe such displacements a special probe was developed equipped with a gradient coil capable of delivering magnetic field gradients of approximately 90 G/cmA. The design of the probe is reported.

Part I also includes a discussion of experiments of transport in two qualitatively different disordered phantoms and reports on a direct observation of universality in one-dimension. The results reveal the universal power law scaling of the diffusion coefficient at the long-time regime and illustrate the essence of structural universality by experimentally determining the structure correlation function of the phantoms. In addition, the scaling of the diffusive permeability of the phantoms with respect to the pore size is investigated. Additional work presented includes a detailed study of adsorption of methane gas in Vycor disordered glass.

The techniques described in Part I of this thesis are widely used for measuring structural parameters of porous media, such as the surface-to-volume ratio or diffusive permeability. Part II of this thesis discusses the biophysical application of diffusion in disordered systems in the field of bioengineering. Elastin-based bioengineered scaffolds, which are mainly used for tissue and bone regeneration, must be able to deliver nutrients to the native tissue. It is therefore essential to quantitatively assess their structural parameters such as their surface-to-volume ratio and diffusive permeability. Part II focuses on a detailed study of structure and dynamics of elastin, the principle protein component found in tissues and one of the main components for scaffold engineering, using NMR 13C-MAS techniques. Lastly, the second half of Part II, discusses preliminary experiments of diffusion in elastin-based films.

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