1. Design and Development of Intelligent Catalytic Nanobots - DST NANO MISSION (2013-2016)
We plan to design, develop, and study the behavior of programmed gen-next artificial micro/nanobot, which can be employed as futuristic drug transporter, defect healer, swarm robot, and distributed sensor. Previously, the sub-micron scale first generation ‘Janus’ micro/nanobots achieved auto-propulsion chemically by the catalytic decomposition of peroxide fuel. These motors achieved some success in picking up and delivering cargos under simple artificial environments. Further, they showed self-propulsion under varied chemical, magnetic and photo gradients. However, the functionalities of the first generation are still in the infancy as compared to their biological counterparts. The major challenge is to achieve the motion in realistic environments, infuse multi-dimensional targeted functionality, and then to gain control over them. Further, the physics associated with these active systems is complex and not well understood because it is in the transition domain of macro/microscopic hydrodynamics and Brownian dynamics originating from the non-equilibrium nature of these systems.
2. A computational study on the phase separation induced pattern formation employing ultrathin films – CSIR (2013-2016)
Instability and dynamics of ultrathin (< 100 nm) films engendered by the intermolecular forces or by substrate wettability gradient have been extensively studied in recent times owing to their potential in the nanostructure formation. Functional coatings of ultrathin films for protection, heat and mass transfer, or adhesives are found to be spontaneously unstable under the influence of van der Waals forces. Further, the functional surfaces are very often decorated with physic-chemical patterns for the technological needs. Consequently, the thin protective coatings can also be unstable owing the presence of these spatial wettability gradients on the surface. Interestingly, the instabilities of ultrathin films generates exotic mesoscale structures, which also have technological importance in fabricating super-hydrophobic surfaces, micro/nano fluidic devices, MEMS, NEMS, and drug delivery modules. In addition, the stability/ instability of ultrathin films also uncover a host of interesting features of a number of scientific issues such as intermolecular force, wetting/dewetting, adhesion/debonding, friction/slippage, phase transition, adsorption, and finite-size effects. Thus, extensive research efforts have been invested in the recent past to uncover the key features of the stability or instability of the ultrathin (< 100 nm) films. The previous studies indicate that ultrathin bilayers show richer varieties of interfacial morphologies important for fabricating embedded and encapsulated structures, which is otherwise impossible involving thin single layers. In this proposal, we plan to explore computationally various scientifically interesting and technologically important interfacial morphologies employing ultrathin bilayers.
3. External Field Driven Flow Induced micro/nanoscale Patterning, Mixing, Heat and Mass transfer in micro/nano Fluidic Devices, SERC project in Engineering Sciences, DST (2011-2014)
The micro/nano-scale interfacial instabilities of thin-micro/nano films engendered by the externally applied Electric (electro-hydrodynamics: EHD) and Electro-Magnetic (electro-magneto-hydrodynamics: EMHD) fields will be investigated. Previous studies suggest that external field induced (EHD or EMHD) flows and related instabilities can be of importance for transporting, patterning, mixing and pumping liquids inside the micro/nano scale devices. We plan to investigate the dynamics and morphology of thin films composed of a pair of liquid electrolytes/ polymer films/ liquid crystals/ polymer gels or composites of any two of these materials. The major aims of this study to explore the conditions at which the control of instability can lead to ordered micro/nano patterns, guide micro-channel flows for transport, enhance the heat and mass transfer, mixing, emulsification, etc. The scientific understanding and the related applications can be of importance especially in the context of micro/nano fluidics in lab-on-a-chip, microelectronic, and drug-delivery devices among others.
4. A combined experimental and theoretical study on the instability and patterning of thin liquid crystal films, FAST TRACK Project, DST, (2010-2013)
We propose to study the dynamic behavior of thin films and drops of nematic LCs. The specific objectives of this proposal are three fold: (1) Experimental study on the deformation, pattern formation and phase transition of thin LC films on smooth and patterned surfaces; (2) Development of long-wave models from the nematohydrodynamic transport equations and compare them with the experiments that involves deformations/pattern formation at the free surfaces and moving contact lines; (3) Develop long-wave models from the bulk equations, which describe films in the nematic and/or isotropic phase and transitions between them. These studies will allow us to answer the set of intriguing open questions in this area of research.
5. Influence of Porous Substrates on the Instabilities and Patterning of Thin Polymer films, SEED grant, Indian Institute of Technology Guwahati (2009-2012)
In the proposed research work, we plan to study the dynamics and morphology of thin (< 100 nm) polymer films on a porous substrates. Thus far, the studies involving the instabilities in macroscopic films (~ mm) on porous-media uncover that instead of placing the film on a rigid substrate, coating the film on a porous-media can significantly alter the length and time scales of the instability.24,25 We extend this analysis to the thin film (<100-nm) domain and study the influence of porous medium on the length and time scales of instability. We intend to carry out a detailed linear stability analysis based on the stokes equation for the film and Darcy–Brinkman equation for the porous media to uncover the dependence of time and length scales of the instabilities on the permeability, slippage, tortuocity, surface roughness of the porous medium. In addition, we plan to carry out nonlinear simulations to demonstrate the pathway of the morphological evolution and the respective interfacial morphologies.