Microrheology

Soft materials, such as emulsions, creams and gels, are neither ideal solids nor ideal liquids. They are often viscoelastic and display time-dependent mechanical responses varying between Newtonian fluids and Hookean solids. Microrheology allows the measurement of delicate samples with complex time-dependent responses at the micron scale.

Formulaction

Microrheology has enabled the study of materials in situations wherein conventional rheometers are difficult to use, such as samples which are fragile under shear and have weak moduli that cannot be measured by conventional rheometers.
 

The advantages of using microrheology over conventional rotational viscometers include measuring in the linear viscoelastic region (LVR), no wall-slip issues, no evaporation or drying, no tool geometries required and enabling the monitoring of sample evolution through fast measurements.

 



The Rheolaser Master is a ready to use instrument to characterise the end-use properties & gel point (sol-gel transition) of any soft material.


  • Up to 6 samples can be measured simultaneously
  • Temperature control up to 90 degC
  • Tracer particles are not required for complete viscoelastic study of colloidal samples
  • One click measurement – no sample parameters required
  • Measures l* (photon transport mean free path) to monitor macroscopic evolution (l* changes when particle size or concentration changes)
  • Gel point measurement

 

 

How it works

The Rheolaser Master is based on Multi-Speckle Diffusive Wave Spectroscopy, which is an optical technique of measuring viscoelastic behaviour without introducing shear to the sample. It measures the displacement of particles in the sample due to Brownian Motion as a function of time. A Mean Square Displacement (MSD) curve is obtained which enables the characterisation of the viscoelastic behaviour of the sample in relation to the ageing time, such as the viscoelastic evolution, structure recovery and long term stability.

MSD Curve


A patented algorithm is used to translate the MSD data into 3 different graphs - Solid-Liquid Balance, Elasticity Index & Macroscopic Viscosity Index.

Solid-Liquid Balance (SLB)
  • Adhesion
  • Spreadability
  • Gel point
  • Shape stability
  • Physical Stability


Elasticity Index (EI)

  • Recovery after a shear
  • Gelation
  • Mesh or pore size
  • Hardness


Macroscopic Viscosity Index (MVI)

  • Effect of a thickening agent
  • Texture
  • Flowability
  • Physical Stability


Time Cure Superposition

  • Identify optimal parameters for gelation (pH, concentration, time, temperature etc)

Time Cure Superposition - Gel Point

The optimal temperature for gelation is identified as the tip of the "V" shape curve.




 

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