Phase Transitions

Phase transition / Crystallisation

Crystalline phase transitions of heterogeneous products can be detected with a new and innovative optical method based on Diffusing Wave Spectroscopy (DWS). This technique combines a non-destructive, non-invasive measurement with sufficiently large volumes to overcome problems of heterogeneities. This enables to measure finished products with high level of heterogeneity, such as food (chocolate, butter…) or cosmetics, and determine the transition temperatures of polymers, waxes or other fats.


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Measurement principle

Crystal_Messprinzip_Abbildung 1
RHEOLASER Crystal uses the DWS principle. Light is scattered by the particles, creating an interference pattern (Speckle Image). The variation of this image is related to the motion of the particles. By a mathematical analysis of this variation, decorrelation functions can be computed and then processed, to obtain a characteristic time τ as a function of time or temperature.

How it works – Diffusing Wave Spectroscopy (DWS)


Values of 1/τ or Micro-Dynamics (Hz), are then plotted against time or temperature, resulting in characteristic peaks when the product shows a microstructural evolution, such as a phase transition or any other physical event. The signal can then be integrated for an easier visualisation, obtaining the so-called Micro-Dynamics Evolution (%).

Crystal_Messprinzip_Abbildung 2

Benefits and key features

  • Monitor any physical phenomenon
    Micro-Dynamics corresponds to the speed of change at the microstructure scale in the sample.
    When there is a transition (phase transition, such as melting or crystallization, or polymorphic transition, from a crystal form to another), microstructure will move very quickly because of restructuring. This is observed by the apparition of characteristic peaks.
  • T50 & ∆T, T10 & T90
    T50 is the average transition temperature (temperature for which half the change happened). ∆T is the transition range, it represents the “polydispersity” of the microstructure. T10 & T90 are used to define the beginning and ending of the transition phenomena. They correspond to the temperatures for which 10 and 90% of the transition happened.
  • Macroscopic samples
    Thanks to the innovative measurement principle, it is possible to measure “macroscopic” samples (up to 5g), enabling to measure directly finished products, without any sample preparation or denaturation.

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References and norms

/1/ PARTICLE WORLD 19; p. 12 – 13, “Heat resistance of lipid based ointments”



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