Colloidal magnetic brushes: influence of the magnetic content and presence of short-range attractive forces in the micro-structure and field response

Cerda, James J.; Bona-Casas, Carles; Cerrato, Antonio; Sintes, Tomàs; Massó, Joan

doi:10.1039/d0sm02006k

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“…These magnetic polymers or filaments are equivalent at the supramolecular scale of the chemical magnetic polymers: they are formed by sequentially linking magnetic colloidal particles to form a chain of colloids (see Ref. [ 117 ] and cites therein). The depletion interactions induced by these magnetic colloidal polymers have never been addressed before and, as we will show in this work, they exhibit very interesting properties.…”

Section: Introductionmentioning

confidence: 99%

Depletion Interactions at Interfaces Induced by Ferromagnetic Colloidal Polymers

Cerdà,

Batle,

Bona-Casas

et al. 2024

Polymers

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The pair-interaction force profiles for two non-magnetic colloids immersed in a suspension of ferromagnetic colloidal polymers are investigated via Langevin simulations. A quasi-two-dimensional approach is taken to study the interface case and a range of colloidal size ratios (non-magnetic:magnetic) from 6:1 up to 20:1 have been considered in this work. Simulations show that when compared with non-magnetic suspensions, the magnetic polymers strongly modify the depletion force profiles leading to strongly oscillatory behavior. Larger polymer densities and size ratios increase the range of the depletion forces, and in general, also their strength; the force barrier peaks at short distances show more complex behavior. As the length of the ferromagnetic polymers increases, the force profiles become more regular, and stable points with their corresponding attraction basins develop. The number of stable points and the distance at which they occur can be tuned through the modification of the field strength H and the angle θ formed by the field and the imaginary axis joining the centers of the two non-magnetic colloids. When not constrained, the net forces acting on the two colloids tend to align them with the field till θ=0∘. At this angle, the force profiles turn out to be purely attractive, and therefore, these systems could be used as a funneling tool to form long linear arrays of non-magnetic particles. Torsional forces peak at θ=45∘ and have minimums at θ=0∘ as well as θ=90∘ which is an unstable orientation as slight deviations will evolve towards θ→0∘. Nonetheless, results suggest that the θ=90∘ orientation could be easily stabilized in several ways. In such a case, the stable points that the radial force profiles exhibit for this orthogonal orientation to the field could be used to control the distance between the two large colloids: their position and number can be controlled via H. Therefore, suspensions made of ferromagnetic colloidal polymers can be also useful in the creation of magnetic colloidal tweezers or ratchets. A qualitative explanation of all the observed phenomena can be provided in terms of how the geometrical constraints and the external field modify the conformations of the ferromagnetic polymers near the two large particles, and in turn, how both factors combine to create unbalanced Kelvin forces that oscillate in strength with the distance between the two non-magnetic colloids.

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Section: Introductionmentioning

confidence: 99%

Depletion Interactions at Interfaces Induced by Ferromagnetic Colloidal Polymers

Cerdà,

Batle,

Bona-Casas

et al. 2024

Polymers

Self Cite

View full text Add to dashboard Cite

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Colloidal magnetic brushes: influence of the magnetic content and presence of short-range attractive forces in the micro-structure and field response

Abstract: The behaviour of supramolecular brushes, whose filaments are composed by sequences of mag- netic and non-magnetic colloidal particles, has been studied using Langevin dynamics simula- tions. Two types of brushes...

Cited by 1 publication

References 74 publications

Depletion Interactions at Interfaces Induced by Ferromagnetic Colloidal Polymers

Depletion Interactions at Interfaces Induced by Ferromagnetic Colloidal Polymers

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