Assembly of Polymer-Grafted Magnetic Nanoparticles in Polymer Melts

Abstract

Hydrophobic iron oxide nanoparticles grafted with hydrophobic polymer chains of varying molecular weights and graft densities are synthesized to underpin the role of brush entanglement and dipolar forces on creating nanostructures. Grafting density on magnetic nanoparticles is controlled in graftingto method by changing the concentration of functionalized polymer in solution. The grafting density and brush length have varied systemically to observe the changes in nanostructures. Bridging between grafted chains and dipolar forces become effective only at low grafting density and result in long chains of particles. We demonstrate experimentally that structural transition of magnetic nanoparticles is controlled with the balance between grafted chain entanglements and dipolar forces.

Wetting–Dewetting and Dispersion–Aggregation Transitions Are Distinct for Polymer Grafted Nanoparticles in Chemically Dissimilar Polymer Matrix

“…40 In the above studies, the wetting-dewetting transition and dispersion-aggregation transition have been assumed to occur simultaneously, and are treated synonymously. 10,12,20,22,[24][25][26][41][42][43][44] . In contrast, in this paper, using simulations and experiments, we show that in chemically dissimilar graft-matrix polymer nanocomposites, the wetting-dewetting transition occurs gradually with increasing temperature and is distinct from the sharp dispersion-aggregation (phase separation) transition.…”

Assessing magnetic nanoparticle aggregation in polymer melts by dynamic magnetic susceptibility measurements

“…Unfortunately, controlling the dispersion of NPs in polymers remains a challenge [1]. In order to prevent particle agglomeration and accomplish homogeneous dispersion, NPs are often coated with surfactants [8][9][10] or polymers [4,[11][12][13][14][15]. These molecules stabilize the NP by adding steric repulsion that prevents aggregation [16].…”

“…Even so, if there is incompatibility between the NP surface and the polymer, dewetting may occur, leading to phase segregation and NP agglomeration. Significant efforts are dedicated to understanding and predicting miscibility of NPs in polymers, both theoretically [17][18][19][20][21][22][23] and experimentally [4,11,12,15,[24][25][26][27].…”

Polymer grafted nanoparticles: Effect of chemical and physical heterogeneity in polymer grafts on particle assembly and dispersion

“…In this regard, we direct readers to recent studies on polymer grafted magnetic nanoparticles where the dipolar nature of particle-particles interactions can compete with the homopolymer-homopolymer interactions, as shown by Jiao and Akcora. 4 In summary, chemical heterogeneity in polymer grafts can be a valuable design parameter to tune the effective interparticle interactions and in turn assembly in a small molecule solvent and polymer matrix. The complex interplay of the copolymer sequence and chemistry, particle size relative to the grafted chain molecular weight, and grafting density along with the medium chemistry dictate the monomer arrangement around the grafted nanoparticle surface and as a result the effective interparticle interactions and assembly.…”

“…Computational 6,7,9,12,16,[18][19][20][21][24][25][26][27]33 and experimental 3,4,10,13,14,22,[28][29][30][31]35,40 studies on nanocomposites, consisting of homopolymer-functionalized nanoparticles in a polymer matrix, have demonstrated that the chemistry and relative molecular weights of the graft and matrix polymers, grafting density, and nanoparticle size are parameters that play a critical role in dictating the spatial organization of the nanoparticles. For example, experimental studies 30,42,43 have achieved the migration of the polymer-grafted nanoparticles from one domain to another domain in the matrix by thermally changing the chemistry of the grafted homopolymers on the nanoparticle, and thus the compatibility of the grafted polymer and matrix.…”