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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Physics

Year Degree Awarded

2017

Month Degree Awarded

September

First Advisor

Anthony Dinsmore

Second Advisor

Christian Santangelo

Third Advisor

Jennifer Ross

Fourth Advisor

Vincent Rotello

Subject Categories

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

Abstract

In this thesis we explore two specific topics within the broad field of particle adhesion. First, we examine the effect of substrate shape and geometry on the self assembly of adsorbed particles, by performing molecular dynamics simulations of interacting particles constrained to the surface of cylinders of varying diameters. We find the diameter of the cylinder imposes a constraint on the shape and crystallographic orientation of the self-assembled lattice, essentially determining the optimal arrangement of particles a priori. We propose a simple one-dimensional model to explain the optimal arrangement of particles as a function of the particle interaction potential and the physical size of the constraining cylinder. We next investigate the stiffness of these cylindrical lattices, and find that thin cylindrical crystals are anomalously softer than large ones. We then propose this effect is a consequence of the geometric arrangement of particles in a tight cylindrical shape, and quantify how the stiffness depends on the circumference of the cylinder and on the strength of interaction between the particles.

Second, we explore how adhesion of particles can reshape the substrate, for the purpose of designing novel functional materials. We perform experiments exposing cationic nanoparticles to lipid bilayer vesicles, where we vary the adhesion energy between the two by adjusting the fraction of anionic lipid (DOPS) in the otherwise zwitterionic lipid (DOPC) bilayer membrane. We find two distinct types of behavior: when the DOPS content of the membrane is 5% or higher, the high adhesion energy causes the nanoparticles to disrupt the vesicles upon adsorption. When the DOPS content is 4% or less, the adhesion of nanoparticles caused the vesicles to adhere to one another and form a rigid liposome gel. We propose that these two behaviors are explained by a transition from a partial wrapping of the nanoparticles to their complete envelopment by the membrane when the DOPS content exceeds 4.5%. We also detail methods for producing large quantities of the vesicle gel using cationic polymers in place of the nanoparticles. These findings could be used to to engineer new solid, semi-permeable materials that can encapsulate cargo, or to create cargo-carrying liposomes with the ability to rupture on trigger.

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