Optical Microrheology of Gelling Biopolymer Solutions Based on Diffusing Wave Spectroscopy - Food Colloids: Self-Assembly and Material Science - page 325

Figure 4 Frequency dependence of the ratio of the storage and loss moduli, G 0 ( o )/
G 00 ( o ), for different waiting times. The ratio is found to be constant over the
full range of accessible frequencies at time 24 min ( K ), thereby defining the gel
point
gives the best fit the Winter-Chambon criterion. At this waiting time the slope
is n ¼ 0.8 over the full range of accessible frequencies.
21.6 Conclusions
The use of DWS as an optical probe of local tracer particle motion provides
noninvasive access to the linear viscoelastic properties of a gelling sample at any
time during the gelation process. The detailed information about G 0 (o) and
G 00 (o), in particular the high-frequency part, provides a new basis to describe
local relaxation processes. Thereby a better understanding of the molecular and
supramolecular changes underlying the sol-gel transition can be obtained.
Our experimental setup allows simultaneous capture of the fast and slow
dynamics of the system, and it thus provides access to the viscoelastic moduli
covering a frequency range of up to six decades or more. The superior time
resolution and simplicity of the measurement offers important advantages in
the study of gelling systems.
Acknowledgements
We thank Pedro Diaz-Leyva for help preparing the manuscript. Financial
support from the Swiss National Science foundation is gratefully acknowledged.
References
1. T.G. Mason and D.A. Weitz, Phys. Rev. Lett., 1995, 74, 1250.
2. J.L. Harden and V. Viasnoff, Curr. Opin. Colloid Interface Sci., 2001, 6, 438.