Magnetic Response Detects the Strength of Carrageenan Network

Abstract

The effect of carrageenan concentration on the magneto-rheological effect of magnetic gels with a magnetic particle concentration of 50 wt.% was investigated under a magnetic field of 50 mT by dynamic viscoelastic measurements. The change in the storage modulus for magnetic gels due to the magnetic field was 3.0 × 103 Pa at a carrageenan concentration of 1.0 wt.% and increased with the concentration. The modulus change showed a maximum of 2.3 × 104 Pa at ~2.0 wt.% and became lower at higher concentrations. This is an interesting phenomenon, which was first observed in this study. The critical strain, the strain where the storage modulus intersects the loss modulus in the strain dependence of the modulus, was much higher than that for carrageenan gels, indicating a strong interaction between the magnetic particles and carrageenan. At 0 mT, the critical strain for the magnetic gels increased remarkably with decreasing the concentration, indicating that magnetic gels have a structure that does not flow easily at concentrations below 1.75 wt.%. It is considered that the structure hardly flows, hindering the movement of particles. At high concentrations, the SEM photographs showed both a particle network of magnetic particles and a dense carrageenan network. It can be considered that the movement of magnetic particles was hindered due to these factors at high concentrations.

Anomalous Magnetorheological Response for Carrageenan Magnetic Hydrogels Prepared by Natural Cooling

“…Thus, an interesting result was obtained here, where the cooling rate affected the change in the storage modulus by the magnetic field; the modulus change for the naturally cooled magnetic gel was 3.6 times higher than that of the rapidly cooled one. The change in the storage modulus for the naturally cooled magnetic gel was consistent with the value we previously reported [ 17 ].…”

“…In a magnetic field of 50 mT, the magnetic force acting on magnetic particles is weak and the movement of magnetic particles is affected by the viscoelasticity of the matrix. In other words, the information relating to the viscoelasticity of the matrix can be obtained from the amplitude of elasticity changes by the magnetic field [ 17 ]. On the other hand, in a magnetic field of 500 mT, the magnetic force acting on magnetic particles is strong and the movement of magnetic particles is not influenced by the viscoelasticity of the matrix [ 16 ].…”

“…The concentration of magnetic particles was constant at Gels 2023, 9, 691 9 of 10 50 wt.%, which corresponds to a volume fraction of φ = 0.12. The volume fraction of magnetic particles was determined by the method described in our previous paper [17]. The concentration of magnetic particles in the preparation was the same as that at the final concentration.…”

“…In our previous investigations, measured at a low magnetic field and low concentration of magnetic particles, it was shown that the change in storage modulus for carrageenan magnetic hydrogels took a maximum at around 2.0 wt.% [ 17 ]. This is anomalous behavior because it is normal that the change in modulus increases with decreasing polymer concentration.…”

Voids induce wide-range modulation of elasticity for magnetic elastomers II

“…The critical strain is a yield point intersecting the G ′ and G ′′, which is the onset of a fluid-like response and has been related to the failure of the network structure. 20–23 For both elastomers of SP and LP, the critical strain was nearly constant at volume fractions ϕ < 0.35 for SP and ϕ < 0.3 for LP, then it dropped largely at high volume fractions. As discussed below, the value of the nonlinear parameter decreased near the volume fraction of 0.3, which suggests that the aggregations of magnetic particles were collapsed by the strain.…”