The data show shadowgraph signals vs. scattering wave vector for a mixture of glycerol and water undergoing free diffusion in the presence of a concentration gradient. The gradient was formed by layering one liquid on another. The presence of a gradient enhances greatly the scattering of light by the sample, and it is this scattering that is measured. The instrument has an oscillatory transfer function, and that is why the data oscillates as it does. As diffusion proceeds the initially sharp interface becomes more and more diffuse. Strangely enough, this has little effect on the signal as demonstrated by the two upper data sets, one of which (squares) was taken 10 minutes after forming the interface, and the other of which (circles) was taken 5.6 hours later. However, as soon as the diffusing zone reaches the cell boundaries, the signal begins to fall as demonstrated by the data sets with triangles, taken 20 hours after forming the interface, and the one with diamonds taken 43.5 hours after forming the interface. The solid lines show least-mean-square fits of a simple theory to the data.
The graph is an example of the type of data that the authors hope to obtain while running an experiment called Gradflex during a mission known as Foton M3.
Acknowledgements
David S. Cannell is a physics professor at UC Santa Barbara. He is collaborating with Marzio Giglio (another physics professor at the University of Milan) and his group to develop an experiment to be flown in a satellite by the European Space Agency. Marzio's group includes: Fabrizio Croccolo, Doriano Brogioli, and Alberto Vailati.
Foton M3 is scheduled to be flown for about 12 days during September, 2007. Gradflex stands for GRAdient Driven FLuctuations EXperiment. All of David's work in the US has been supported by NASA, and the European Space Agency is supporting the major costs of hardware development and flight.
The graph was created collaboratively by Fabrizio Croccolo and David Cannell. Both the raw data and fit curves (generated using another program) were imported from ASCII files and then plotted.
The data was taken by Fabrizio Croccolo in Professor Marzio Giglio's group at the University of Milan.