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Microstructure thermal analysis

 monitoring of Microstructure evolution under thermal stress

Formulation of materials containing oils, fats or waxes is a complex task. These products may undergo phase transitions, under thermal stress. Thus, they are likely to be the source of heterogeneities appearing during manufacturing, blending, storing... An unpredicted melting, crystallization or polymorphic transition, when products are thermally stressed, directly affects product quality and can be a source of visible deterioration of the product. Some common examples are exudation of lipsticks, crystal formation inside ointment, blooming of chocolate.

Reproducing temperature conditions, that products are exposed during their life cycle, and thus performing accelerated thermal aging, is achievable with Rheolaser CRYSTAL. This unique instrument allows detecting any microstructure changes, at the nanometer scale, during thermal stress (temperature ramps and cycles) by an optical method (MultiSpeckle Diffusing Wave Spectroscopy).

Key benefits

  • Non-contact analysis on a macroscopic sample
  • Monitoring of any structure evolution
  • Temperature cycles for accelerated aging

How does it work?

Rheolaser CRYSTAL measures micro-Dynamics (Hz) over temperature or time. Since the structure dynamics change when a transition occurs, when the sample shows a microstructure evolution such as phase transition, structure rearrangement…a characteristic peak appears.

Micro-Dynamics is measured by MultiSpeckle Diffusing Wave Spectroscopy (MS-DWS). Incoming light scattered by the particles creates a specific interfering pattern that is captured by a camera. The variation of the images (speckles) relates to particle mobility or network structure and by mathematical calculations allows to determine structure dynamics. Micro-Dynamics Evolution is the integration of the Micro-Dynamics signal, providing characteristic temperatures of the structure evolution.

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Data and key features

> Phase Transitions

Micro-Dynamics corresponds to the speed of change at the microstructure scale in the sample. Characteristic peaks are observed when the microstructure changes due to applied temperature (or time). Phenomena such as phase transition, structure rearrangement or other physical events can be detected. Depending on the energy of the transition and sample structure, the peak shape varies providing useful insight about the occurring structure evolution.

> accelerated thermal aging

The structure can be monitored as the sample undergoes multiple temperature cycles. This enables the study thermal stability in an accelerated period of time while reproducing temperature conditions that products go through during their life cycle.

The global decrease of micro-Dynamics over the temperature cycles is a sign that the samples are loosing their stability. The changes that occur with time and temperature won't allow to return to the initial state of the matter.

> Representative sample size

Thanks to the innovative design and measurement principle, it is possible to measure "macroscopic" samples (up to 5g). Reduced sample handling and preparation minimize the risk of damaging the sample structure. Working on a bigger sample volume provides more representative analysis of the microscopic structure evolution despite any heterogeneities.

> Characteristic transition temperatures

  • 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.

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