Self-Assembly of Mesoscopic Materials To Form Controlled and Continuous Patterns by Thermo-Optically Manipulated Laser Induced Microbubbles

Abstract

The formation of continuous patterns of nanostructured materials using directed self-assembly under external fields has generated considerable current research interest. We demonstrate for the first time such continuous patterning by inducing irreversible self-assembly leading to nucleation in mesocopic materials (inorganic, organic, and nanoparticles) using a tightly focused laser beam in an optical tweezers apparatus. A dense aqueous dispersion or solution of the material which has high absorption at the laser wavelength is taken in a sample holder so that some material is adsorbed on the top surface. A hot spot is created on the top surface when the adsorbed material absorbs the high intensity at the focus of the laser beam (a submicrometer sized spot), due to which a water vapor bubble is formed. This causes self-assembly of material around the bubble due to Gibbs-Marangoni convection and capillary flow after which the material eventually nucleates into a crystalline state. The bubble is "trapped" at the hot spot due to the temperature gradient around it and can be manipulated by thermal forces generated optically, so that the system may be described as a "thermo-optical" tweezers. We translate the trapped bubble using the microscope sample holder stage of the apparatus so that the nucleation site of the material is simultaneously translated generating continuous patterns. We have demonstrated the technique using exotic inorganic materials such as soft oxometalates, an organic material such as glycine, and a fluorescent dye such as perylene as well as with carbon nanotubes. We have written patterns over lengths of nearly 1 mm at the rate of 1 Hz, with best resolution of about 4 μm. The technique has potential for a wide range of applications ranging from solution processed printable electronics to controlled catalysis.

Competitive Self-Assembly Manifests Supramolecular Darwinism in Soft-Oxometalates

“…It has been shown by us and others that each of the components of the above host-guest species [PMo 12 @Mo 72 Fe 30 ] i.e., PMo 12 and Mo 72 Fe 30 independently shows superstructured soft-oxometalate (SOM) formation by spontaneous assembly in colloidal lengthscales. 1,2,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] We have previously shown that a dilute sonicated dispersion of PMo 12 leads to the formation of peapod 37 like SOM structures. Initially, the peapods have nanosphere-type morphology and with time these spheres get converted to nanorods with nanospheres embedded inside this rod.…”

Photochemical Water Oxidation Using {PMo12O40@Mo72Fe30}n Based Soft Oxometalate

“…[61][62][63][64][65][66] 68 Now we ask, is it possible to synthesize a polyoxometalate in turn a soft oxometalate (SOM). [69][70][71][72][73] which can generate oxygen from water photo-chemically?…”

“…Polyoxometalate units self-assemble in dispersion to form super structures which are known as soft oxometalates (SOMs). 70,74,75 We have explored di®erent properties of soft oxometalates over the last few year. [76][77][78] Soft oxometalates can under-go topological transformation in the presence of light.…”

Laser-induced wavelength-controlled self-assembly of colloidal quasi-resonant quantum dots

“…Formation of QDs' structures under optical irradiation due to various non-electrodynamical mechanisms were studied, e.g. in [11][12][13]. Surprisingly, no experimental attempts were done up to date to perform electrodynamically-driven laser-induced self-assembly of semiconductor nanoparticles, that may be of interest for quantum information, spintronics, single-electron transport, and sensoric devices.…”