Soft Microfluidic Reactors for the Deposition/Synthesis of Morphologically Controlled Inorganic Crystals

Hybrid or hierarchical nanomaterials with precisely controlled size, shape, and composition have potential applications in, for example, energy storage and conversion, photo-catalysis, and bio-sensing. While several strategies exist for the synthesis of hybrid or hierarchical structures, they are limited to the control of parameters such as, time, temperature, chemistry, and concentration. Strategies that take advantage of flow effects are relatively less explored, and present the opportunity to tune additional parameters (e.g., flow velocity and direction), providing higher levels of control in the bottom-up synthesis of nanomaterials. In the present work, the fabrication of soft, stretchable microfluidic systems via 3D printing and soft-lithography using elastomeric polymers, and their application to the controlled synthesis or deposition of inorganic materials is reported. The micro-reactors are reversibly sealed via compression or tension to various planar and non-planar substrates, and enable: (i) sequential synthesis or depositions, (ii) easy reuse of the reactors or substrates, and (iii) characterization of the device or substrate. Additionally, by tuning the compressive stress applied, the channel morphology and dimensions can be controlled. This phenomenon was further investigated using finite elemental analysis method (FEM) and experimental observations, and led to the fabrication of soft robotic systems with “programmable” transport properties that have integrated touch and actuation sensing. The soft micro-reactors were applied to: (i) synthesis of graded arrays of ZnO nanorods with spatial and compositional control through the rational control of the mass-transport phenomena, and (ii) the deposition of conductive copper traces on arbitrary substrates through a process referred to as microfluidic-directed electroless copper deposition (micro-DECD). The methods and insights emerging through these studies can be applied to the controlled synthesis and deposition of materials with diverse functional properties (e.g., optical, magnetic, electronic) with applications in the fields of micro-electronics, energy conversion, point-of-care diagnostics, etc. In addition to their synthetic applications, the bi-layered channel networks were also used in fabrication of a microfluidic system for infield sampling and analysis. Furthermore, the fabrication skills gained through this research were helpful in developing an educational and outreach activity that introduces soft robotics and general fabrication strategies such as 3D printing, soft lithography, replica molding, etc., to students as they build their own soft robot