Emulsions Characterization

 

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Conclusion

 

We applied DWS microrheology to an oil-in-water emulsion and compared the results to mechanical rheology. In the overlapping frequency range, very good agreement between the two techniques was found. Moreover, the continuous phase (xanthan solution) has been characterized separately by DWS microrheology and mechanical rheology and found in excellent agreement with each other and also with literature. This demonstrates that the droplets, i.e. the dispersed phase, can act as tracer particles to probe the rheological properties of the emulsion. Moreover, provided the droplet size is known, we showed that DWS microrheology is well suited for the quantitative characterization of emulsions.

 

However, care must be taken when the continuous phase of an emulsion is inhomogeneous on the length scale of the droplets. In this case, a quantitative characterization of emulsions is more difficult because the droplets probe a variety of different local environments [6]. In the investigated model system this was not the case since the mesh size of the xanthan network at the chosen concentration is on the order of 40 nm [4], thus well below the droplet size.

 

Finally, the values obtained by DWS microrheology are highly reproducible and might thus allow the study of time dependent properties of emulsions such as aging or stability.

 

References

 

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[2]   D. Lopez-Diaz, and R. Castillo, Microrheology of solutions embedded with thread-like supramolecular structures,

       Soft Matter 7, 5926–5937 (2011).

[3]   E. Choppe, F. Puaud, T. Nicolai, and L. Benyahia, Rheology of xanthan solutions as a function of temperature,

       concentration and ionic strength, Carbohydrate Polymers 82 (2010).

[4]   K.v Gruijthuijsen, H. Vishweshwara, R. Tuinier, P. Schurtenberger, and A. Stradner, Origin of suppressed demixing

       in casein/xanthan-mixtures, Soft Matter 8 (2011).

[5]   S.R. Derkach, Rheology on the way from dilute to concentrated emulsions, Inter. Rev. Chem. Eng. 2 (2009).

[6]   F.K. Oppong, L. Rubatat, B.J. Frisken, A.E. Bailey and J.R. de Bruyn, Microrheology and structure of a yield-stress

       polymer gel, Physical Review E 73 (2006).