Highly ordered self-assembly of one-dimensional nanoparticles in amphiphilic molecular systems

Two kinds of one-dimensional (1D) nanoparticles, stable rod-like nanoparticles with highly controlled surface charge density (cROD) and non-covalently functionalized isolated single wall carbon nanotubes (p-SWNT) that were readily redispersible in water, have been developed. Using these 1D nanoparticles, various highly ordered superstructures of 1D nanoparticles by molecular self-assembling based on electrostatic interaction in amphiphilic molecular systems (two different cationic liposome systems) have been investigated. To our knowledge, this is the first demonstration of highly ordered self-assembly of 1D nanoparticles based on electrostatic interaction between 1D nanoparticles and amphiphilic molecules. The cRODs have been developed by free radical polymerization of a mixture of polymerizable cationic surfactant, cetyltrimethylammonium 4-vinylbenzoate (CTVB), and hydrotropic salt sodium 4-styrenesulfonate (NaSS) in aqueous solution. The surface charge of the cROD was controlled by varying the NaSS concentration during the polymerization process and the charge variation was interpreted in terms of the overcharging effect in colloidal systems. The small angle neutron scattering (SANS) measurements showed that the diameter of cROD is constant at 4 nm and the particle length ranges from 20 nm to 85 nm, depending on the NaSS concentration. The cRODs are longest when the NaSS concentration is 5 mol % which corresponds to the charge inversion or neutral point. The SANS and zeta potential measurements showed that the Coulomb interactions between the particles are strongly dependent on the NaSS concentration and the zeta potential of the cRODs changes from positive to negative (+ 12.8 mV ∼ - 44.2 mV) as the concentration of NaSS increases from 0 mol % to 40 mol %. As the NaSS concentration is further increased, the zeta potential is saturated at approximately - 50 mV. The p-SWNTs have been developed by 1) dispersing single wall carbon nanotubes (SWNTs) in water using cationic surfactant, CTVB which has polymerizable counterions, and 2) permanently fixing the surfactant monolayer on the SWNTs by in situ free radical polymerization of the counterions, followed by freeze drying. UV-vis-NIR spectra of p-SWNT in water and alcohol showed very sharp van Hove transition which is typical for isolated SWNT, and were essentially identical after redispersion, indicating the excellent redispersibility. The in-situ microstructures of the p-SWNTs dispersed in water and alcohols were measured with SANS, which showed the encapsulation of SWNT by the surfactant monolayer cylindrically and by a swollen polymerized surfactant layer, respectively. It should be noted that the p-SWNTs are readily redispersible in water or alcohol by only 10 minutes of mild vortex mixing after harsh processing such as freeze-drying. Two kinds of cationic liposomes (CLs) consisting of univalent cationic and zwitterionic lipids were used as the amphiphilic molecular template for the interaction with 1D nanoparticles. For highly ordered superstructure of the cRODn (n is the number of carbon in the alkyl chain) in amphiphilic molecular systems, the CLs composed of DOTAP (catioinc) and DOPC (zwitterionic) lipids with various ratios (5:5 and 3:7) were prepared. The small angle x-ray scattering (SAXS) intensities of cRODn-DOTAP/DOPC complexes showed three different highly ordered phases, intercalated lamellar, doubly intercalated lamellar and centered rectangular phases, depending on particle diameter and charge interactions between cRODn and CLs. The phase behavior of cRODn-CL complexes was explained by the dspacing/drod ratio and a new phase diagram of the complexes was established. It should be noted that the centered rectangular columnar phase of 1D nanoparticle-CL complexes has not been previously reported while the intercalated lamellar and the doubly intercalated lamellar structures were observed in rod-like biomolecule-CL complexes. For highly ordered superstructure of the SWNT in amphiphilic molecular systems, p-SWNT with negative charge (p-SWNT25) was prepared by adding 25 mol% NaSS (relative to CTVB concentration) during in-situ polymerization of surfactant and CLs were prepared by the mixture with various ratio of DOTAP and DOPE (zwitterionic) lipids. The SAXS intensity of p-SWNT25-DOTAP/DOPE complexes showed two different highly oreder phases, intercalated centered rectangular columnar structure and inverted centered rectangular columnar packing with SWNTs at their centers, depending on the spontaneous curvature of lipid monolayer. It is remarkable that this is the first demonstration of SWNT superstructures in biomolecular lipid system through molecular self-assembling based on electrostatic interaction. These observations in this thesis can be used to understand and design new highly ordered self-assemblies of 1D nanoparticles in soft matter and may provide new novel routes for scalable production of ordered 1D nanoparticle composites with new functionalities