Flowability of Gel-Matrix and Magnetorheological Response for Carrageenan Magnetic Hydrogels

The relationship between rheological features in the absence of a magnetic field and magnetic response was investigated for κ-carrageenan magnetic hydrogels containing carbonyl iron particles. The concentration of carrageenan was varied from 1.0 to 5.0 wt%, while the concentration of carbonyl iron was kept at 70 wt%. The magnetic response revealed that the change in storage modulus ΔG' decreased inversely proportional to the carrageenan concentration. A characteristic strain γ₁ where G' equals to G″ was seen in a strain range of 10^-3. It was found that ΔG' was inversely proportional to the characteristic stress at γ₁. Another characteristic strain γ₂ where the loss tangent significantly increased was also analyzed. Similar to the behavior of γ₁, ΔG' was inversely proportional to γ₂. The characteristic stresses at γ₁ and γ₂ were distributed at 80-720 Pa and 40-310 Pa, respectively. It was revealed that a giant magnetorheology higher than 1 MPa can be observed when the characteristic stresses at γ₁ and γ₂ are below approximately 240 Pa and 110 Pa, respectively.