Elastic behaviour of magnetic gels and elastomers

In the absence of an external magnetic field a ferrogel presents a mechanical behaviour very close to that of a swollen filler-loaded network. Since a typical magnetic gel can be considered a dilute magnetic system, we may neglect the influence of magnetic interactions on the modulus. Thus the stress-strain 

In order to test the applicability of Equations [5.1] and [5.5] for gels filled with magnetic particles, a Mooney-Rivlin representation of experimental data obtained in the absence of external magnetic field is shown in Fig. 5.11. 

77 Stress-strain measurements for PDMS samples filled with randomly distributed carbonyl iron particles, (a) On the basis of statistical theory of rubber elasticity and (b) Mooney-Rivlin representation of experimental data. Symbols represent different amounts of iron particles as indicated in the figure. 

It may be seen that the nominal stress divided by A-seems to be slightly dependent on the strain. 

In order to determine the nature of the force generated by a polymer gel, one must consider all the relevant interactions that contribute to the force or displacement. We learned from the thermodynamics of rubber elasticity that the molecular mechanism of force generation in the network chains is made up of two different contributions. In general, energetic and entropic effects must be taken into account  

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