It is well-known that the collapse of cavitation bubbles under ultrasonic treatment can release and transfer a good deal of energy into the nanofluid, which greatly decrease the agglomeration of nanoparticles.
Oil-soluble type functionalization employed in order to prevent or decrease the agglomeration of iron oxide NPs and increase the stability give rise to the monodispersity, for instance, iron oxide NPs frequently dispersed in long-chain substance of hexadecane, the classic example being oleic acid (CH3(CH2)7CH=CH(CH2)7CO2H), which has a C18 tail with a cis-double-bond in the middle, forming a kink.
Results showed that the GO and RGO significantly decreased the agglomeration of MnO2.
In fact, upon adding the surfactant, some ALES molecules are adsorbed on the surface of the particles creating a negatively supercharged system (Table 2), through increasing the effective charge on silica surface, which creates high repulsion forces among the silica particles, hence decreasing the agglomeration of the particles.
In order to decrease these agglomerations of particles, the surface of the silica shell modifies with the coupling agents.
This fact may be due to the role of surfactants in the decrease of the agglomeration of particles [31].
In this regard, the utilization of appropriate substrate material in the synthesis procedure of metal oxide nanoparticles can prevent agglomeration, decrease the diameter of nanoparticles, and change the cluster-like morphology of nanoparticles to a powdered morphology.
Although surfactants might increase the internal stress of the coating and lead to cracks in the composite structure, they are notable positively as they tend to change the surface charge (zeta potential) of the particles and decrease the tendency of particle agglomeration [23, 24], promoting the co-deposition and uniformity of the particles throughout composite layers [14, 23, 24].
These test results demonstrate that for the functionalized TiO2 nanoparticles, the shear force at a high agitation speed can decrease the tendency of particle agglomeration and the nanofluid with a good dispersion stability can be observed by stirring for 180 min.
Nevertheless, as shown in Fig. 10e, f, the disordered aggregation of MWCNTs is observed, and micropores or microcracks are formed in the agglomeration region, which decrease the strength of the nanocomposites.
