SANS and SAXS study of packing behavior of 1d nanoparticles in hexagonal micellar phase of non-ionic surfactant system depending on diameter ratio and concentration

Abstract

The self-assembly of binary mixtures of nanoparticles into superlattices has attained growing interest due to its new emerging properties through synergetic collective coupling between different types of nanoparticles. However, most research interests have been concentrated on shpere-like nanoparticles as building blocks for binary superlattices and binary superlattices of 1D nanoparticles are rarely reported. For fabrication of binary 1D nanoparticle superlattices, synthesis of 1D nanoparticle with well controlled shape and size is required. Ahthough recent progress in synthesizing method gives an opportunity to fabricate controllable 1D nanoparticle, self-assembly of 1D nanoparticles into highly ordered structure still remains challenging. Here, we systematically investigated self-assembled binary mixture of polymerized cylindrical micelle (p-CTVB) and non-ionic surfactant (C_{12}E_5) in water using small-angle neutron and x-ray scattering measurements. Different amounts of p-CTVBs with various diameters were mixed with 45wt% $C_{12}E_5$ in aqueous solution (which shows isotropic cylindrical micellar and hexagonal phases as temperature decreases from 30℃ to 4℃). When adding p-CTVBs(1D nanoparticle) into the hexagonal phase formed by cylindrical micelles of (C_{12}E_5), p-CTVBs are hexagonally packed in the hexagonal structure of (C_{12}E_5) cylinders by substituting some of the (C_{12}E_5) cylinders, resulting hierarchical structure in which two hexagonal structures are intercalated each other. The hierarchical structure was investigated systematically by changing diameter and number ratio of two nanoparticles. It was found that p-CTVBs took a different position in such a way that lattice parameter ratio of two hexagonal structures is √3 or 2 depending on the diameter and number ratio. This study can give a useful methodology to fabricate binary 1D nanoparticle superlattices and further understanding about what determines the formation of binary 1D nanopar...