Correlation between sagging and shear elasticity in pectin, gelatin and polyacrylamide gels

The relationship between the height of gels determined by a sag test and th eir elastic shear modulus (G ') has been both investigated experimentally a nd simulated using a finite element analysis for the inhomogeneous deformat ion of gels due to gravity. It was assumed in the simulations that gels can be modeled as incompressible linear elastic materials. General relationshi ps between the sag of gels and their elastic modulus were obtained from the simulations for slip and no-slip conditions. The relationships were tested experimentally on pectin, gelatin and polyacrylamide gels with a range of concentrations and rigidities. The good agreement between the predictions a nd the results shows that these gels can be modeled accurately as incompres sible elastic materials. A standard 150 degrees SAG pectin gel, which sags 23.5% in the SAG test, has G ' moduli of 429 and 379 Pa under slip and no-s lip conditions, respectively. (C) 2001 Elsevier Science Ltd. All rights res erved.