Portable extensional rheometer for the characterisation of complex fluids

PI: Alfonso Castrejon-Pita

Department: Engineering Science

Inks, paints, medicines, detergents, creams and emulsions are common examples of complex liquids widely used in commercial products. In industry, the properties of these liquids are paramount, as they determine the quality, speed or reliability of their dispensing processes. Moreover, most printers, dispensers, sprays and injectors are restricted to operate within a very narrow range of fluid properties under very extreme conditions. Consequently, fluid characterisation represents an important part of these industries’ R&D activities.

As a liquid surface approaches breakup (e.g. when a drop of water forms and detaches from the tap), the properties of the fluid such as viscosity, elasticity, surface tension, density, and particle contents, uniquely determine its temporal and spatial dynamics. Research carried out by Prof Castrejon-Pita’s group over the past five years has resulted in a series of ‘rules’ (i.e. scaling laws) that can be used to extract these properties by studying the shape of the fluid surface during the breakup/pinch-off process.

This project aims to develop a fully portable system to characterise the dynamical properties (viscosity, viscoelasticity, etc.) of liquids by means of tracking and characterising the breakup dynamics of small volumes of liquid between two rods moving at a controlled speed.

By designing and manufacturing a self-contained proof-of-concept device and corresponding appropriate protocols to assess the breakup behaviour of liquids, Prof Castrejon-Pita proposes to develop the next-generation filament stretching rheometer for measurement of the flow of viscoelastic, colloidal and polymer-based fluids. Optical techniques such as high-speed imaging and holography will be incorporated to produce a system that is faster, more accurate and more reliable than current devices.