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Tribo-Rheology of nanosized MR-Fluids

Final Activity Report Summary - MRFLUIDS (Tribo-rheology of nanosized mr-fluids)

A class of materials called smart materials is taking more and more importance due to the growing capabilities of computer control in our surroundings. These materials are usually composite structures whose properties can be controlled by an external parameter; it can be temperature for shape memory alloys or electric fields for piezoelectric transducers. In all these cases we are interested in controlling the properties of a material by some electronic device which senses environmental changes and adapts its response accordingly.

Magneto-rheological fluids (MRF's) represent an exciting family of smart materials that possess the unique ability to undergo rapid (within milliseconds) and nearly completely reversible changes in their strength (yield stress changes from 0 to 100kPa) upon application of an external magnetic field. MRF's typically consist of fine particles of a magnetically soft material dispersed in an organic medium.

Although a wide variety of applications of MRF's have been identified (semiactive shock absorbers, dampers, computer-aided polishing of precision...) they have not yet enjoyed widespread commercialisation. A major reason for this situation is that many MRF's do not satisfy the diverse and stringent requirements demanded in their applications: i.- the stability of the fluids against sedimentation remains a central problem, and ii.- their tribo-rheological properties are not well understood.

The main objective of this project is to develop a magneto-tribo-rheometer and characterise new adaptative materials based on field-responsive nanoparticles. We synthesise inverse spinel ferrites for MR applications using a modified sol-gel coprecipitation method in the presence of a magnetic field. Both magnetic and tribo-rheological properties are studied in the presence of different shear flows in ultra-thin films using a single device.