What are Shake Gels? Shake gels are mixtures of synthetic clay and polymers in water that form a gel when shaken. We use laponite-XLG and PEO with a molecular weight of 300,000 gm/mol. The mixtures have a total weight concentration of 1% or higher and the percent weight ratio of laponite to peo can range from 3:1 to approximately 25:1. Some time after being shaken (ranging from 1 minute to a few hours, depending on total weight concentration and ratio), the gels relax back into a liquid state. After about two weeks, the mixture will form a permanent gel through an ageing process that is not well understood.

What are some interesting features of the system? Besides the basic behavior of the system and the phase behavior, there are a few other interesting features. First, the system shows some gelation (without being shaken) at about 5º C above room temperature, but for higher temperatures forms only weak gels and has faster relaxation times. Also, the gel formed by shaking is a bit turbid, but the gel formed by aging is clear.

In the figure above, the vials are (right to left) water, an unshaken mixture of laponite and PEO, and finally, the shake-gel. As you can see, the turbidity increases progressively, and could be regarded as a signature of the transition.

What are we studying? First we did light scattering on the individual components of the system and on the mixture. From this we were able to show that the laponite was being partially absorbed on to the peo when they were in solution together. (put in graph showing absorption).

We are currently working on creating a phase diagram for the system. We will then move on to look more closely at the relaxation behavior and turbidity of the system. We are also interested in the rheological behavior of these shake gels.

Cute stuff The images below are of a shake gel that has been injected with dye at the top, and we watch the progress of the dye as it courses through the gel. The images are taken 0, 49, 118, 240,563 minutes after the dye injection. The shake gel showed no significant relaxation during this time period, so we are in essence measuring the porosity of the gel. The aim is to use a gel that relaxes a bit faster, and see if we can map out viscosities as a function of time.

Contact info:

Jennifer Zebrowski
jzebrows@fas.harvard.edu
Department of Physics
Harvard University
Engineering Sciences Laboratory
40 Oxford Street
Cambridge, MA 02138