LIPID MEMBRANES MEDIATED INTERACTIONS AND SELF-ASSEMBLY OF JANUS NANOPARTICLES

Since many advanced applications require specific assemblies of nanoparticles (NPs), considerable efforts have been made to fabricate nanoassemblies with specific geometries. In this dissertation, we demonstrate the potential of lipid membranes as a medium for the self-assembly of NPs. To control their degree of adhesion to lipid membranes, the NPs are surface modified into hydrophilic Janus NPs such as one moiety interacts more attractively with the lipid head groups than water while the other moiety interacts more attractively with water than the lipid head groups. First, using extensive molecular dynamics simulations of a coarse-grained implicit-solvent model, in conjunction with the weighted histogram analysis method, we show that the modes of adhesion of two spherical Janus NPs on a lipid vesicle depend on whether they adhere to the outer or inner side of the vesicle. Second, three or more Janus NPs, adhering to the outer side of a lipid vesicle, self-assemble into an array of ordered nanoassemblies. The specific geometries of these assemblies are the result of an effective curvature-mediated repulsion between the NPs and their total number on the vesicle. Interestingly, the NPs arrange on the vesicle into polyhedra which satisfies the upper limit of Euler’s polyhedral formula. These include several deltahedra and three Platonic solids, corresponding to the tetrahedron, octahedron, and icosahedron. Third, we show that many Janus NPs adhering to a tensionless planar membrane exhibit multiple phases depending on their number density and adhesion strength. These include a monomeric phase, in which the NPs are apart, a chains phase, a tube phase, and an endocytosis phase. The monomeric phase is subdivided into a disordered phase, and an ordered hexagonal phase. Investigation of both translational and bond-orientational orders demonstrates that the transition from disordered phase to the hexagonal phase proceeds via an intermediate hexatic phase, in accord with the Kosterlitz-Thouless-Halperin-Nelson-Young theory. Fourth, we also investigated the arrangement of many spherical NPs adhering to the inner side of a vesicle and found that they self-assemble into interesting quasi-two-dimensional star-like structures that do not occur when the NPs adhere to the outer side of the vesicle