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We report here a facile method of modulating the lengthscales of self-organized dewetting of polystyrene thin films by varying the extent of silane grafting on the substrate. The self-assembled monolayers (SAM) of octadecyltrichlorosilane (OTS) were grafted on glass substrates by exposing them to different doses of OTS vapors in a controlled, low pressure environment. Measurement of water contact angles on the modified glass surfaces showed that the contact angles could be continuously increased from 40° to 70° by increasing the time of exposure to the OTS vapors from a few minutes to several hours. Polystyrene (PS) thin films were spin coated on the modified glass substrates and water-solvent mixture induced dewetting of the PS thin films was carried out, where the dewetting kinetics depended on the spreadability of water on the surface. We observed a reduction in the length scales of the dewetting, i.e. the wavelength of instability (λ) and droplet size (d), by increasing the extent of OTS exposure. The λ for a 50 nm thick PS film decreased from 12 to 4 µm while the droplet diameter (d) also decreased, from 2.5 to 1.6 µm. [ABSTRACT FROM AUTHOR]

We present a mini review of the recent progress in the fabrication of nanolenses and their use for highresolution optical imaging beyond the diffraction limit. Nanolenses break the diffraction limit by capturing near-field evanescent waves and refocusing them in the far-field image plane. The focus of this article is on our recent work on fabrication of nanolens and ordered lens arrays by a combination of the top-down and self-organization in unstable thin polymer films. Highly confined, thin (<50 nm) liquid polymer films spontaneously transform into microscale patterns of droplets by a spinodal instability leading to dewetting. The lateral length scales of these self-organized structures in air are limited by the weak van der Waals destabilizing force and a strong surface tension-induced stabilization. Limitations on slow dewetting kinetics and relatively large (>1 μm) length scales can be overcome by dewetting induced under an optimal mix of a non-solvent (water) and a good solvent, which reduces the interfacial tension without a concurrent solubilization of the polymer. This room temperature technique reduces both the time and the length scales of self-organized structures by over one order of magnitude. Further, directed dewetting combined with physico-chemically patterned substrates and films by e-beam, photolithography, laser ablation and nanoimprint lithography techniques can be used for fabrication of ordered nanostructures such as arrays of nanolenses. [ABSTRACT FROM AUTHOR]