Sánchez PA, Pyanzina ES, Novak EV, Cerdà JJ, Sintes T, Kantorovich SS. Supramolecular Magnetic Brushes: The Impact of Dipolar Interactions on the Equilibrium Structure.
Macromolecules 2015;
48:7658-7669. [PMID:
26538768 PMCID:
PMC4625168 DOI:
10.1021/acs.macromol.5b01086]
[Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 09/08/2015] [Indexed: 11/30/2022]
Abstract
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The
equilibrium structure of supramolecular magnetic filament brushes
is analyzed at two different scales. First, we study the density and
height distributions for brushes with various grafting densities and
chain lengths. We use Langevin dynamics simulations with a bead–spring
model that takes into account the cross-links between the surface
of the ferromagnetic particles, whose magnetization is characterized
by a point dipole. Magnetic filament brushes are shown to be more
compact near the substrate than nonmagnetic ones, with a bimodal height
distribution for large grafting densities. This latter feature makes
them also different from brushes with electric dipoles. Next, in order
to explain the observed behavior at the filament scale, we introduce
a graph theory analysis to elucidate for the first time the structure
of the brush at the scale of individual beads. It turns out that,
in contrast to nonmagnetic brushes, in which the internal structure
is determined by random density fluctuations, magnetic forces introduce
a certain order in the system. Because of their highly directional
nature, magnetic dipolar interactions prevent some of the random connections
to be formed. On the other hand, they favor a higher connectivity
of the chains’ free and grafted ends. We show that this complex
dipolar brush microstructure has a strong impact on the magnetic response
of the brush, as any weak applied field has to compete with the dipole–dipole
interactions within the crowded environment.
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