Abstract
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.
Highlights
Magnetic soft material consisting of polymeric matrix and magnetic particles demonstrates drastic changes in physical properties in response to magnetic fields, and it has great potential in various applications [1,2,3]
The change in storage modulus decreased inversely proportional to the carrageenan concentration, suggesting that magnetic particles are difficult to move in the gel-matrix
As a parameter indicating the flowability of magnetic particles, we proposed two kinds of characteristic stresses σ1 and σ2
Summary
Magnetic soft material consisting of polymeric matrix and magnetic particles demonstrates drastic changes in physical properties in response to magnetic fields, and it has great potential in various applications [1,2,3]. Under a gradient magnetic field, magnetic soft material undergoes elongation behavior proportionally to the field gradient [10]. Under a uniform magnetic field, the magnetorheological effect (MR effect) is observed, where the viscoelastic properties vary in response to the magnetic field. The MR effect is basically caused by an anisotropic structure of magnetic particles formed in a matrix of a cross-linked polymer, which is called a chain structure. The structure can be observed by an optical microscopy when the concentration of magnetic particles is low [11]
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