Hi to all polymer physicists,
is it possible, that E modulus of Jello (or it's German version "Göttersspeisse" - the protein content may differ) is, according to the concentrations of the Jello ("GS") powder for preparation of series of "gels", about 1900 to 28 000 Pa?
Thanks & Cheers,
Jan
Hello Jan,
this is an interesting question. Lets assume, we press a jello with a spoon of 1cm² and need 1N to press the jello down for 1mm. The thickness of the jello we assume 1dm. Then the stress is sigma = 1N/1cm²=1E4 Pa. The strain is epsilon = 1mm/1dm=1E-2. this gives an module =sigma/epsilon = 1E6 Pa= 1GPa. This is one order of magnitude higher than your upper limit. For more accurate estimations you must experimentally determine the parameter.
Yours
R. Mitdank
Thanks!
Yes, we have done it, however through the indentation of an iron ball, similarly to Henderson & Sperling et al. (Article Gelatin as a physically crosslinked elastomer
), who used a steel bearing and a mixture of gelatin and Jello, obtaining moduli from ca (0.5–4) x10^-4 Pa.We have used iron ball and "Götterspeisse" and obtained moduli 1900–28 000 Pa, however we have come to similr crosslinking densities (3.5x10^-7 to 2.6x10^-6 mol/cm^3 in the paper vs. 1.4x10^-7 to 2.0x10^-6 mol/cm^3 by us).
So, maybe the difference is caused by the different protein concentration (Jello + gelatin vs. "Götterspeisse"), slightly different deformation (steel bearing vs. iron ball), or they have a mistake in the paper and there should be stated (0.5–4) x10^+4 Pa.
Well, things have moved on a bit since Sperling in 1985 :-). The shear modulus of gelatin gels depends on its molecular weight (which is closely related to the commercial gel grade (in Bloom units)), its concentration, the temperature and the gel maturation time. All of these parameters fall onto a master curve that is described in Normand et al. Gelation Kinetics of Gelatin: A Master Curve and Network Modeling, Macromolecules 2000, 33, 3, 1063-1071. I was involved too. So ask if you'd like a copy.
By the way, gelatin gels are not elastomeric, so the modelling in the paper is not right. They are rod gels. The elasticity is due to interactions between the stiff helices, not the entropy of the coiled parts. See Langmuir 2005, 21, 9792-9794 .
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