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 γ(1) 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 γ(1). Another characteristic strain γ(2) where the loss tangent significantly increased was also analyzed. Similar to the behavior of γ(1), ΔG′ was inversely proportional to γ(2). The characteristic stresses at γ(1) and γ(2) 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 γ(1) and γ(2) are below approximately 240 Pa and 110 Pa, respectively.