Dispersion of polymer-grafted magnetic nanoparticles in homopolymers and block copolymers

Abstract

The dispersion of magnetic nanoparticles (NPs) in homopolymer poly(methyl methacrylate) (PMMA) and block copolymer poly(styrene-b-methyl methacrylate) (PS-b-PMMA) films is investigated by TEM and AFM. The magnetite (Fe 3 O 4 ) NPs are grafted with PMMA brushes with molecular weights from M = 2.7 to 35.7 kg/mol. Whereas a uniform dispersion of NPs with the longest brush is obtained in a PMMA matrix (P = 37 and 77 kg/mol), NPs with shorter brushes are found to aggregate. This behavior is attributed to wet and dry brush theory, respectively. Upon mixing NPs with the shortest brush in PS-b-PMMA, as-cast and annealed films show a uniform dispersion at 1 wt%. However, at 10 wt%, PS-b-PMMA remains disordered upon annealing and the NPs aggregate into 22 nm domains, which is greater than the domain size of the PMMA lamellae, 18 nm. For the longest brush length, the NPs aggregate into domains that are much larger than the lamellae and are encapsulated by PS-b-PMMA which form an onion-ring morphology. Using a multicomponent Flory-Huggins theory, the concentrations at which the NPs are expected to phase separate in solution are calculated and found to be in good agreement with experimental observations of aggregation. The dispersion of magnetic nanoparticles (NPs) in homopolymer poly(methyl methacrylate) (PMMA) and block copolymer poly(styrene-b-methyl methacrylate) (PS-b-PMMA) films is investigated by TEM and AFM. The magnetite (Fe 3 O 4 ) NPs are grafted with PMMA brushes with molecular weights from M ¼ 2.7 to 35.7 kg/mol. Whereas a uniform dispersion of NPs with the longest brush is obtained in a PMMA matrix (P ¼ 37 and 77 kg/mol), NPs with shorter brushes are found to aggregate. This behavior is attributed to wet and dry brush theory, respectively. Upon mixing NPs with the shortest brush in PS-b-PMMA, as-cast and annealed films show a uniform dispersion at 1 wt%. However, at 10 wt%, PS-b-PMMA remains disordered upon annealing and the NPs aggregate into 22 nm domains, which is greater than the domain size of the PMMA lamellae, 18 nm. For the longest brush length, the NPs aggregate into domains that are much larger than the lamellae and are encapsulated by PS-b-PMMA which form an onion-ring morphology. Using a multi-component Flory-Huggins theory, the concentrations at which the NPs are expected to phase separate in solution are calculated and found to be in good agreement with experimental observations of aggregation.

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

“…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].…”

Ferroferric oxide/polystyrene (Fe3O4/PS) superparamagnetic nanocomposite via facile in situ bulk radical polymerization

“…By far, there are two main approaches for the preparation of the polymer-based magnetic nanocomposites: physical mixing and in situ polymerization. In the first approach, the magnetic nanoparticles were physically mixed into polymeric matrices after being surface-modified with polymers [2][3][4][5][6][7]. The strategy is suitable for the largescale industrial manufacturing, however, the uniform dispersion of the magnetic nanoparticles in the polymeric matrices could not be guaranteed [2].…”

“…In the first approach, the magnetic nanoparticles were physically mixed into polymeric matrices after being surface-modified with polymers [2][3][4][5][6][7]. The strategy is suitable for the largescale industrial manufacturing, however, the uniform dispersion of the magnetic nanoparticles in the polymeric matrices could not be guaranteed [2]. As for the in situ polymerization approach via the solution polymerization [8,9], dispersion polymerization [10,11], and emulsion polymerization techniques [12][13][14][15][16][17][18], the magnetic nanoparticles are dispersed well in the polymeric matrices.…”

Dispersion of organophilic Ag nanoparticles in PS-PMMA blends

“…Apart from blends, this phenomenon of selective loading has also been reported for block copolymers. As example, various types of SiO 2 [16], Au [17], BaTiO 3 [18], TiO 2 [19], Fe 3 O 4 [20], and CdSe [21] nanoparticles were employed in a PS-b-PMMA matrix.…”