Chelladurai Devadoss

Functional hydrogel structures for autonomous flow control inside microfluidic channels

Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.

Dendrimer photoantenna supermolecules: energetic funnels, exciton hopping and correlated excimer formation

Abstract A novel set of purely hydrocarbon dendrimer supermolecules has been studied, providing direct evidence of unusual photophysical and photochemical characteristics. The molecular structure gives rise to discrete exciton localization, allowing the formation of a highly photoactive antenna with a discrete energetic funnel. Steady state and fluorescence lifetime measurements have shown rapid and efficient exciton trapping at the molecular locus. Unique geometric and energetic attributes are observed which provide a means of protection from photobleaching, enhancing the longevity of these molecules. In addition, unexpected wavelength-dependent excimer formations are seen, suggesting unusual excitation-induced intermolecular interactions and dimer formations in more than one single excited state.

Molecular Nano-Lenses: Directed Energy Migration and Back-Transfer in Dendrimeric Antenna Supermolecules

Abstract Experimental and theoretical evidence is presented for the process of directed, multistep energy transport in a unique class of fractal-like dendrimeric supermolecules. Due to the meta-position branching arrangement of these Cayley trees, tight excitation localization is observed at the branching nodes. Particular forms of these dendrimers have been synthesized with localized states of decreasing energy toward the molecular locus, creating a rapid and efficient exciton funnel. Spectroscppic data is presented illustrating nearly unit transfer efficiency from the dendrimer periphery to a specialized trap at the molecular center. In addition, the energetics and spatial arrangement of these molecules allow for the destruction of multiphoton excitations at the trap, providing protection from permanent photochemical bleaching.