document: In order for DLS based micro-rheology to be successful, there must be sufficient scattering contrast between the sample and the tracer particles. In order to achieve this, the maximum possible concentration of tracer particles was added such that single scattering events still dominated (as determined by measurements of diffusion coefficients in water at different concentrations). In order to determine whether or not the background scattering from the sample was sufficiently low compared to that of the tracer particles, we also compared the scattering intensities obtained from samples with and without tracer particles as a function of time. The results of this exercise are shown in Fig. 6. From this figure it can be seen that although initially the scattering from the sample without tracer particles is low compared to those containing tracer particles, as gelation proceeds this eventually ceases to be the case. This is presumably because of the development of supra-molecular structures, such as those seen previously (Fig. 2B). Based on the results in Fig. 6 it was decided to only use data collected in the first 240min of the experiment, after which point the scattering from the gel network became rather too large to ignore.
extractive_keyphrases: gelation sample and the tracer particles scattering tracer particles water
abstractive_keyphrases: dls based micro-rheology scattering from the gel network scattering intensities supra-molecular structures