Nanoparticle Arrays Formed by Spatial Compartmentalization in a Complex Fluid

A mesoscopically ordered lamellar gel phase of a polymer-grafted, lipid-based complex fluid is used as a scaffolding to spatially organize inorganic nanoparticles. The complex fluid provides both a highly anisotropic environment and a segregated aqueous and organic domains in which inorganic nanoparticles can be selectively placed by tailoring their size and surface characteristics. Three types of silver nanoparticles-underivatized, surfactant-stabilized, and dodecanthiol-derivatized-were evaluated. Comparison of the surface plasmon resonance of the various silver particles dispersed in conventional solvents to those contained within the complex fluid was used to determine the region of spatial localization in the lamellar gel phase. Silver particles rendered hydrophobic by capping with an alkane thiol insert into the hydrocarbon bilayer region. Surfactant-stabilized and underivatized silver nanoparticles reside in the aqueous channels, with the latter particles preferentially interacting with the grafted PEG chains/charged membrane interface region. Interparticle interaction between encapsulated hydrophilic silver particles can be enhanced by increasing the number of PEG repeat units (i.e., the length of the lipid-appended polymer). Examination of the X-ray diffraction profiles indicates that the gel-phase structure of the complex fluid is preserved upon introduction of all three types of nanoparticles. Guinier analysis of the low-q SAXS data for the intercalated silver yields particle sizes that are in good agreement with those determined by TEM prior to introduction, indicating that they remain as nonaggregated, discrete nanoparticles. These results not only demonstrate the use of complex fluids as a matrix in which to produce periodic arrays of encapsulated nanoparticle guests, but also suggest the possibility of employing them to modulate interactions between guests and, hence, their optical and electronic properties.