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Manipulation of colloidal soft materials and their reconfigurable assembly show great promise as the basis for tunable optical devices. Despite the advantages of adaptability, flexibility, and scalability, the exploration of soft materials in active photonic systems faces challenges in fabrication, integration, and structural control at the nano- and microscale.
In pursuit of overcoming these challenges, I will describe two directions: simple particles dispersed in anisotropic medium and complex particles swimming in isotropic medium. First, I will describe new breeds of soft materials using anisotropic liquid crystalline(LC) materialswhere structural variation leads to tunable light propagation effects which is ideal for designing light-matter interaction at the mesoscale. We showed spontaneous emergence of microscopic LC domains serving as tunable light-scattering centers(1), whereas long-range reconfigurable self-assembly of colloids in anisotropic LC medium enables fundamental discovery of low-symmetry fluidic phases(2)as well as energy-saving applications like switchable solar gain control(3). Next, I will discuss the discovery of active nanotweezers that overcome diffraction and diffusion-limitation in optical nanomanipulation of colloidal materials(4, 5). Our approach involves utilizing plasmonic near-fields in nanogaps, combining various forcing schemes to develop efficient dynamic colloidal nanotweezersfor manipulation and assembly of nanoscale cargoes in the bulk of fluid.
Ourapproachexhibits reversibility and stimuli-responsive properties, making these strategies very interesting for designing new class of responsive materials with flexible structures and properties, created bottom-up. Such softphotonic devices may find potential applications in various areas of photonics, including smart windows, displays, biophotonics,mirorobotics and optofluidics.
References:
1. S. Ghosh, E. Abraham, I. I. Smalyukh, Low-Voltage Haze Tuning with Cellulose-Network Liquid Crystal Gels. ACS Nano17, 19767–19778 (2023).
2. J.-S. Wu, et al., Unavoidable emergent biaxiality in chiral molecular-colloidal hybrid liquid crystals. arXiv preprint arXiv:2304.07447 (2023).
3. S. Ghosh, I. Smalyukh, Electrical Switching of Nematic Plasmonic Nanocolloids for Infrared Solar Gain Control. Adv Opt Mater10, 2201513 (2022).
4. S. Ghosh, A. Ghosh, Mobile nanotweezers for active colloidal manipulation. Sci Robot3, eaaq0076 (2018).
5. S. Ghosh, A. Ghosh, All optical dynamic nanomanipulation with active colloidal tweezers. Nat Commun10, 4191 (2019).
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