# Relation in Alginate-Based Magnetic Suspensions
## 5 Conclusions  
Rheological properties were characterized for the Na-alginate based magnetic suspensions with four different types of embedded magnetic particles (MPs): magnetite (Fe\({}_{3}\)O\({}_{4}\)), metallic iron (Fe), metallic nickel (Ni), and metallic nickel with a deposited carbon layer (Ni@C). These batches of MPs differed in the enthalpy of the interaction of Na-alginate polymer with the surface, as determined by the calorimetry using a thermodynamic cycle. The viscoelastic properties of Na-alginate suspensions showed two definite regimes depending on the concentration of MPs and their chemical nature. At low content of MPs in suspension the regime of deformation was \"fluid-type\", which meant that the value of the loss modulus was substantially higher than the value of the storage modulus and the shift angle between stress and strain was close to 90\({}^{\circ}\). At low content of MPs, no noticeable influence of the intensity of molecular interaction at the surface on the rheological properties was revealed. The situation changed if the content of MPs in Na-alginate suspensions increased. While the deformation of suspensions with Fe\({}_{3}\)O\({}_{4}\) particles remained  
Figure 9: Schematic presentation of the two types of structuring in Na-alginate MRS with MPs depended on the interfacial adhesion among the particles and the polymer. (**a**)—strong adhesion between Na-alginate and MPs leads to the polymeric layers at the surface which favor fluid-type behavior. It is the case of Fe\({}_{3}\)O\({}_{4}\) and Ni@C MNPs. (**b**)—weak interaction at the interface leads to the networking of MPs due to the magnetic forces which promote elastic deformation and the gelation of MRS. It is the case of Fe and Ni MPs.  
\"fluid-type\", the deformation of suspensions with Fe and Ni metal particles switched to the \"solid-type\" regime which meant that storage modulus became substantially larger than the loss modulus and the shift angle diminished to low values around 10\({}^{\circ}\), which is typical for the elasticity of gels. A distinct correlation was found between these two types of deformation to the intensity of interaction between Na-alginate and the surface of MPs. In suspensions with negative enthalpy of interaction at the surface, in other words, strong interaction, viscoelastic behavior was \"fluid-type\". On the contrary, the pronounced elastic deformation was observed in suspensions with positive enthalpy of interaction (poor interaction). Thus, it may be concluded that the elasticity of magnetic suspensions based on Na-alginate is inversely related to the intensity of molecular interactions at the surface of the embedded magnetic particles. Most likely it stems from the formation of the microscopic network of associated magnetic particles which is favored by the poor interaction with alginate.  
Conceptualization, A.P.S. and T.V.T.; methodology, E.V.R. and T.V.T.; software, E.V.R.; validation, A.P.S., E.V.R. and T.V.T.; formal analysis, Y.S.Z. and N.M.K.; investigation, Y.S.Z. and N.M.K. resources, I.V.B.; data curation, A.P.S., E.V.R., Y.S.Z. and N.M.K.; writing--original draft preparation, A.P.S.; writing--review and editing, A.P.S., E.V.R., T.V.T. and A.Y.Z.; visualization, A.P.S. and T.V.T.; supervision, A.P.S.; project administration, I.V.B. and A.Y.Z.; funding acquisition, A.Y.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Russian Science Foundation, grant number 20-12-00031.  
Not applicable.  
Valuable technical assistance of [PERSON] in XRD studies, [PERSON] in TEM, and [PERSON] in magnetic characterization are highly appreciated.  
The authors declare no conflict of interest.