Tuning the wall thickness of templated polystyrene nanotubes produced from melt infiltration

In this work, we demonstrate methods of varying the wall thickness of polystyrene nanotubes produced from template synthesis by utilizing classical theories of liquids spreading on flat and curved substrates. We find that factors which affect the surface energy of the polymer and substrate such as the annealing temperature, annealing atmosphere and polymer molecular weight influence the thickness of the nanotubes which are achieved. Results from this study are in qualitative agreement with what is predicted from classical theories. Nanotubes with wall thicknesses ranging from 18 to 40 nm were achieved by infiltrating different molecular weight polystyrene. Higher molecular weight samples possessed larger wall thicknesses compared to lower molecular weight samples. Thermal characterization with differential scanning calorimetry measurements revealed significant Tg-confinement behavior as a function of wall thickness. Post infiltration processing such as annealing was also found to affect the thickness. Supported tubes annealed at high temperatures possessed thinner wall diameters compared to those annealed at lower temperatures. Additional results suggest that atmosphere can have an effect on the wall thickness. Alteration of the surface energy through changes to factors such as the temperature, polymer molecular weight and atmosphere affects the equilibrium tube thickness and may allow for dimensional control over the nanostructures produced from template synthesis. The ability to tune the dimensions of nanomaterials is critical for applications which rely upon the unique properties which arise due to the greater effect of free surfaces, interfacial interactions and small diffusion lengths at the nanoscale. Confinement in one or more dimensions can lead to enhancements in the mechanical strength, electrical, optical, thermal properties of materials and benefit areas involving drug delivery, medical devices, interconnects, sensing, catalysis, filtration and nanocomposites. The ability to adjust material properties using the length scale of these structures imparts additional requirements e.g. the ability to achieve uniform size and shapes and the means by which one can tune their dimensions.