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 their elastic shear modulus (Gʹ) has been both investigated experimentally and simulated using a finite element analysis for the inhomogeneous deformation of gels due to gravity. It was assumed in the simulations that gels can be modeled as incompressible linear elastic materials. General relationships 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 and the results shows that these gels can be modeled accurately as incompressible elastic materials. A standard 150° SAG pectin gel, which sags 23.5% in the SAG test, has Gʹ moduli of 429 and 379 Pa under slip and no-slip conditions, respectively.