Integrated microfluidic viscometer for edible oil analysis

Viscosity is a key parameter to discriminate origin, industrial/thermal treatments, and contamination of edible oils. For a number of applications, miniaturized, portable, and single-use tools to monitor oil quality on-field are advisable. Here we propose an easy-to-use, disposable microfluidic device to measure rheology and material properties of oils in extensional capillary flows. The integrated viscometer proposed is able to discriminate between pure oils of different origin and oils mixture. The device consists of a polydimethylsiloxane (PDMS) linear microchannel with an oleophobic functionalization, interfaced to an optical microscope, and a custom made software able to detect the capillary dynamics of the injected fluids. The microfluidic viscometer has been tested with commercial and home-made extravirgin olive oils, with sunflowers oil, with commercial frying oil and home-made mixture. The oleophobic coating, consisting of a fluoropolymer bonded to the PDMS through a protein adhesion layer, is needed to decrease oil adsorption during the flow and to reconstruct the capillary dynamics along the entire length of the microchannel. Beyond calculating absolute values of dynamic viscosity, the chip allows to separate and identify components in oils mixtures thanks to an accurate method of data analysis in the constant pressure region and a correlation with microfluidic viscosities of known oils.