Micro-stereolithography (MSL) employing a polymer/magnetite nanocomposite for digital manufacturing of functional flow sensors

Leigh, Simon; Purssell, Christopher; Bowen, James; Covington, James; Billson, Duncan and Hutchins, David (2011). Micro-stereolithography (MSL) employing a polymer/magnetite nanocomposite for digital manufacturing of functional flow sensors. In: Tenth International Conference on Materials Chemistry (MC10), 4-7 Jul 2011, Manchester, UK.

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Micro-stereolithography (MSL) is an advanced manufacturing technology capable of producing highly detailed, real-world components directly from 3D digital designs. When combined with functional polymer composites, the low volume and low cost manufacture of functional sensing devices becomes a reality
MSL technology builds-up components in an additive, layer-by-layer fashion, through the spatially controlled polymerisation of polymer resin. The resin normally consists of a diacrylate functionalised monomer and an acrylate cross-linker (tetra-/penta-/hexa- acrylates). The polymerisation reaction is initiated photochemically using photoinitiator which is activated by the light output from a digital projector.
The required component is drafted up in Computer Aided Design (CAD) software and digitally sectioned into a number of horizontal image slices. Each image slice is then in turn sent to the digital projector, which solidifies a layer of the polymer resin. A motion stage then steps upwards by a precisely defined amount (25 μm) and another image is sent to the projector, solidifying a further polymer resin layer to the previous layer. This process is repeated until the final required component is achieved. The process significantly differs from more conventional subtractive manufacturing methods (e.g milling) and allows almost complete design flexibility while rapidly manufacturing (hours as opposed to days) complex components.
Traditionally, components manufactured with MSL have been confined to purely structural elements. Polymer resin composites have been investigated for manufacturing of components with increased strength. However, the drive is now to incorporate functional materials within the composites to yet further enhance the capabilities of this advanced manufacturing technology. The medical and electronic industries are the most active in this area. In both cases the incentives are the same: making smaller components with more capabilities.
Here we show how the incorporation of magnetite (Fe3O4) nanoparticles (approx 50 nm diameter) into a composite matrix can be used for the fabrication of a physical flow sensor for microfluidic and micropneumatic applications. The devices are composed of polymer housing and a magnetite/acrylic composite impeller, all manufactured using MSL. The magnetic field of the fabricated impeller structures can then be used to sense their orientation. Any rotation of the magnetite composite impeller is detected by an externally placed magnetic field sensor and used to determine the flow rate of interest.

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