Rheomicroscopy – simultaneous determination of rheology and structure

Crystallisation of polymers and fat is complex and difficult to explain, as is process effects during incipient structure formation. The explanation is considerably easier when you can measure material properties while simultaneously observing the microstructure – this is Rheomicroscopy.

When a liquid fat is cooled it will crystallise. The video shows the difference between crystallisation under shear and at rest.

By combining rheometry and microscopy it is possible to determine the underlying mechanisms responsible for deformation-induced structure breakdown (thixotropy) and formation (rheopexi), droplet break-up in emulsions, particle aggregation and breakup in dispersions, melting of fat and polymers and more. Such mechanisms drive texture formation and breakdown in food applications (oral processing and industrial processing), limit shelf-life and determine tactile perception of cosmetics as well as regulating structure formation in cementitious and other construction materials (additives, coatings, fibre alignment in 3D-printing formulations).

A laser equipped microscope is mounted under a glass plate in an advanced rheometer. The sample is enclosed between the glass plate and an upper heat-controlled plate, and observed from below while shearing, compressing or oscillating the sample. The two plates can be counter-rotated to form a stagnant layer for fixed observation during shearing. The microscope is equipped with polarisers for polarization microscopy and a filter for fluorescence microscopy. The rheomicroscope setup is a Modular Microscope Acessory from TA Instruments.

Below you can see some examples of rheomicroscopy in different applications.

When starch is heated in water the starch granules swell. On further heating and shear they lose their crystallinity and form a homogeneous gel.

When we apply shaving foam on the skin it is heated and sheared when we smear it out. The video shows the microstructure of the foam during a measurement of viscosity from 20-40°C.

Cement pastes need to exceed a certain yield stress to start flowing. As cement particles hydrate and the paste structure forms, the viscosity decreases, allowing the material to flow more easily.