# Relation in Alginate-Based Magnetic Suspensions
## 4 Discussion  
From the basic physical point of view, any measurable property of the physicochemical system takes its origin in the balance of all molecular interactions of the interior. If there are no chemical reactions in the system as in the case of alginate-based MRSs then all the features of the macroscopic properties are governed by the following types of interaction: hydration of alginate, hydration of solid magnetic particle, interfacial adhesion of alginate to the surface of particles, and magnetic forces among particles. The study was focused on the influence of interfacial adhesion on the rheological properties of alginate MRSs. Presented experimental results revealed the correlation between the viscoelastic properties of alginate-based suspensions and the enthalpy of adhesion of alginate polymer to the  
Figure 8: Concentration dependences of the enthalpy of adhesion of Na-alginate polymer to the surface of MNPs. Temperature 25 \({}^{\circ}\)C. Lines are drawn for the eye-guide only. surface of magnetic particles in composites. If the values of the enthalpy of adhesion of Na-alginate to the solid surface of MPs were negative, which meant the energetically favorable interaction, then it led to a fluidic type of deformation of magneto-rheological suspensions at the same time. In other words, good interfacial adhesion at the interface depressed the elevation of the dynamic moduli and the descent of the shift angle with the increase in MPs content. Thus, the enhancement of polymer-solid interaction might be favorable to preserve the fluidity of the suspension. Oppositely, if the interaction of the polymer and the solid at the interface was poor, it provided the boost of the dynamical moduli and the dropdown of the shift angle at a relatively low volume fraction of MPs. Thus, based on the obtained results we may conclude that to shift the properties of MRS to elasticity rather than fluidity and to transform the fluid to a gel phase one needs to block polymer-solid interaction somehow. At the molecular level, we may suppose the following explanation of the observed dependence of the DMA behavior of MRS on the interaction at the interfaces. If the interaction of Na-alginate with the surface of MPs is energetically favorable, then polymer chains adsorb at the surface and form a steric protective layer which prevents a close contact between magnetic particles. Based on the extended Derjaguin-Landau-Verwey-Overbeek theory it was shown earlier [26], that magnetic interactions between Fe MPs in colloids dominated over van der Waals and electrostatic forces. Therefore, thick steric protective polymeric layers on the surface of MPs are needed to prevent aggregation of MPs due to the magnetic forces and to provide colloidal stability of the suspension. In the present study, no special alignment of particles in the preparation of MRSs was provided. Therefore, the distribution of magnetic particles in MRS was macroscopically random. Meanwhile, the possibility of aggregation at the microscopic scale could not be completely excluded. The analysis of particle aggregation in condensed phases is very complicated and to a large extent an unresolved problem. In the present study, we could not evaluate the aggregation as the content of magnetic particles in suspensions was too large for optical microscopy. In this respect, the following model consideration might refer not only to individual MPs but too small aggregates of MPs as well. The caliper diameter of MPs in the present study (see Table 1) was above the threshold to a single domain state which is about 128 nm for Fe\({}_{3}\)O\({}_{4}\), 14-30 nm for Fe, and 55 nm for Ni [29]. Thus, the MPs under study consisted of several domains each.