Self-Assembly of Amphiphilic Nanoparticles and Tubules

Open Access
Lewis, Sean A
Area of Honors:
Chemical Engineering
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Kyle Jeffrey Magnuson Bishop, Thesis Supervisor
  • Wayne Roger Curtis, Honors Advisor
  • self-assembly
  • amphiphilic
  • nanoparticles
Molecular amphiphiles organize spontaneously to form diverse molecular assemblies – micelles, vesicles, and bilayers – through the competition of attractive and repulsive forces between their hydrophilic and hydrophobic components and the surrounding environment. By analogy, nanostructures functionalized with hydrophilic and hydrophobic domains should allow for the programmable assembly of nano-scale components into various higher order structures depending on the shape of the formative units and their surface chemistry. In this thesis, I describe two such colloidal amphiphiles: 1) spherical nanoparticles functionalized with hydrophilic and hydrophobic ligands capable of dynamic redistribution and 2) cylindrical tubules with hydrophobic interiors and hydrophobic exteriors (or vice versa). In the first set of experiments, gold nanoparticles functionalized with mixed hydrophilic and hydrophobic ligands were successfully incorporated into the membrane bilayers of surfactant vesicles. Because the ligands will redistribute in response to environmental stimuli, the hydrophobic ligands can rearrange to interact with the hydrophobic membrane core and tether the nanoparticle to the vesicle. In contrast to previous reports, the size of these nanoparticles may be larger than the bilayer thickness, and the spontaneous integration upon simple mixing eliminates any membrane denaturing requirements. In the second set of experiments, tubules of nanometer, micrometer, and millimeter diameters with differing internal and external functionalization were examined in the presence of aqueous and organic fluids to determine their potential to assemble end-on-end into chains. Desired solvents or materials could then be transported through the channels formed by these tubules. Solvent contained within each tubule by hydrophobic or hydrophilic interactions should guide the association of the open ends of each tube with one another by minimizing their interfacial surface tension when submerged in solution. While macro-scale tests demonstrate some favorable interactions by forcep-assisted manual manipulation – tubules can drag one another when connected by exposed toluene and moved through water – further experiments are required to test of the validity of their usage and self-assembly. Supramolecular structures created from these amphiphiles are useful most notably for controlled particle transport. By modifying the specific ligands, desired substances can be loaded into vesicles or tubules and then directed or released via external forces (such as ultraviolet or infrared light for nanoparticles and solvent flow or local variations in surface energy in the case of tubules). Future experiments will focus on integrating magnetic materials into these systems for targeted delivery applications.