Recent advances in anisotropic magnetic colloids: realization, assembly and applications

Tierno, Pietro

doi:10.1039/c4cp03099k

Cited by 137 publications

(140 citation statements)

References 153 publications

(154 reference statements)

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“…A reduction in the size of a measuring tool from 1 cm to 10 μm would result in a decrease in the applied torque by a factor of 10 9 . In the following, we show that reduction of the torque by several orders of magnitude is achievable by combining the use of magnetic micron‐sized wires as a shearing device and an active microrheology setup for their actuation …”

Section: Introductionmentioning

confidence: 99%

Wire‐Active Microrheology to Differentiate Viscoelastic Liquids from Soft Solids

et al. 2016

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Viscoelastic liquids are characterized by a finite static viscosity and a zero yield stress, whereas soft solids have an infinite viscosity and a non-zero yield stress. The rheological nature of viscoelastic materials has long been a challenge, and it is still a matter of debate. Here, we provide for the first time the constitutive equations of linear viscoelasticity for magnetic wires in yield stress materials, together with experimental measurements using Magnetic Rotational Spectroscopy (MRS). With MRS, the wires are submitted to a rotational magnetic field as a function of frequency and the wire motion is monitored by time-lapse microscopy. The soft solids studied are gel-forming polysaccharide aqueous dispersions (gellan gum) at concentrations above the gelification point. It is found that soft solids exhibit a clear and distinctive signature compared to viscous and viscoelastic liquids. In particular, the wire average rotation velocity equals zero over a broad frequency range. We also show the MRS technique is quantitative. From the wire oscillation amplitudes, the equilibrium elastic modulus is retrieved and agrees with polymer dynamics theory.

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Section: Introductionmentioning

confidence: 99%

Wire‐Active Microrheology to Differentiate Viscoelastic Liquids from Soft Solids

et al. 2016

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“…While our designer building blocks closely resemble recently synthesized colloidal magnetic particles, 31 our results suggest design principles, which should have general implications for programming hierarchical self-assembly of nano-and microparticles. 19 While magnetic colloidal particles are classic examples of microscale building blocks with anisotropic interactions, 32 recent years have experienced a surge in the synthesis of exotic colloidal magnetic particles. 31,33 Having drawn motivation from these research activities, a number of computational studies have focused on spherical magnetic colloids with an additional anisotropy attribute in terms of an off-centered point-dipole.…”

mentioning

confidence: 99%

Programming hierarchical self-assembly of colloids: matching stability and accessibility

Morphew

Chakrabarti

2018

Nanoscale

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Encoding hierarchical self-assembly in colloidal building blocks is a promising bottom-up route to high-level structural complexity often observed in biological materials. However, harnessing this promise faces the grand challenge of bridging hierarchies of multiple length-and time-scales, associated with structure and dynamics respectively along the self-assembly pathway. Here we report on a case study, which examines the kinetic accessibility of a series of hollow spherical structures with a two-level structural hierarchy self-assembled from charge-stabilized colloidal magnetic particles. By means of a variety of computational methods, we find that for a staged assembly pathway, the structure, which derives the strongest energetic stability from the first stage of assembly and the weakest from the second stage, is most kinetically accessible. Such a striking correspondence between energetics and kinetics for optimal design principles should have general implications for programming hierarchical self-assembly pathways for nano-and micro-particles, while matching stability and accessibility.Self-assembly of colloidal particles offers tremendous opportunities for fabricating three-dimensional structures in a bottom-up approach due to the scope for tuning the interparticle interactions.1,2 Recent advances in the synthesis of complex colloidal particles have made a wide variety of nanoand micro-scale building blocks available. Many of these colloidal building blocks involve anisotropic interparticle interactions, often due to either anisotropic shape or heterogeneous surface chemistry. 2-5 These novel colloidal particles offer rich avenues for programming colloidal self-assembly.6,7Hierarchical self-assembly of nano-and micro-particles is emerging as an attractive route to structural organization at a higher level, spanning multiple length scales. 8,9 Notably, the hierarchical self-assembly of mono-disperse colloidal octapodshaped nanocrystals resulted in a three-dimensional superlattice via the formation of linear chains of interlocked octapods. 10 The assembly of binary and ternary patchy nanoparticles produced supracolloidal ordered structures in a hierarchical scheme. 11 The 'patchiness' of colloidal triblock spherical particles was exploited to encode staged self-assembly triggered by stepwise changes of the ionic strength of the medium. 12 A computational study demonstrated an alternative scheme for patchiness without engineered surfaces en route to a variety of complex superstructures via hierarchical selfassembly. 13 A theoretical analysis was presented for programming self-assembly of octopus nanoparticles, which themselves may be self-assembled, into a target nanostructure.

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“…In rotational method, commonly called magnetic rotational spectroscopy (MRS), a rotating magnetic field is applied to a magnetic wire, rod, filament, or platelet, the corresponding trajectory and orientation as a function of time are monitored by optical microscopy . In a viscous liquid, the torque exerted on a magnetic nanowire under a constant magnetic excitation H and the torque from the viscous liquid with static viscosity η 0 is balanced, giving a differential equation with respect to the angle β between the wire and H

\frac{d β}{d t} = ω - ω_{normalc} \sin (2 β)

ω_{normalc} = \frac{3}{8} \frac{μ_{0} Δ χ}{η_{0}} g (\frac{L}{D}) \frac{D^{2}}{L^{2}} H_{0}^{2}

where μ 0 is the permeability in vacuum, Δχ = χ 2 /(2 + χ) with χ is the susceptibility, η 0 is the static viscosity of the fluid, and g is a dimensionless function of wire's length L and diameter D .…”

Section: Active Microrheologymentioning

confidence: 99%

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Liu

2017

Macro Chemistry & Physics

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To overcome these shortcomings of macrorheology, a number of novel microrheological methods have emerged during the last few decades, [2] often involving a small tracking or probing particle (micrometer size) dispersed in a softmatter medium. By tracking the fluctuation due to thermal energy or applying an external force, usually in the form of magnetic force or optical trap, one can measure local mechanical responses. The local disturbance in a micrometer scale avoids reconstruction of local viscoelastic response, an inevitable problem in bulk rheology, especially when the probe particle size is smaller than the characteristic length of a soft matter. Depending on whether the probe is manipulated by an external force instead of a random walk due to thermal fluctuation, microrheometers can be generally characterized as active or passive ones. For an equilibrium system, the fluctuationdissipation theorem (FDT) guarantees that these two methods are equivalent. [3] In this review, we will detail these two classes of microrheometers, including their basic principles and typical setups as well as some recently developed hybrid microrheometers, [4][5][6] often used in characterizing polymer solutions and biological materials. Passive MicrorheologyIn a passive microrheometry method, the fluctuation of probes dispersed in a soft-matter medium is detected and analyzed by calculating the mean-square displacement (MSD) often from their video-based trajectories or scattered light intensities. Since the fluctuation of probes in space is driven by an extremely small thermal energy (k B T), the results from a passive method are always fallen inside the linear range of viscoelasticity. Generally, the elastic modulus is estimated within an upper limit of hundreds of Pa, which means that passive microrheometers are more suitable for measuring "soft" materials with a low viscosity and elasticity. Otherwise, the probes would be trapped without a measurable movement. Even newly developed super-resolution microscopes can provide a sub-nanometer resolution, [7] they are still not widely available methods and have a limited frequency range (up to 100 Hz). Mechanical properties of a soft matter can be obtained from MSD by using the generalized Stokes-Einstein relation (GSER). [8,9] In two extreme cases, (1) the probe is dispersed in a Newtonian viscous fluid and undergoes a Brownian motion with an MSD of 〈Δr 2 (t)〉. The viscosity η is related to the translational diffusion coefficient D as Microrheological TechniquesRheological properties of soft matter like polymer solutions/gels, colloidal dispersions, and biological materials have been extensively studied by macroscopic methods. Recently, a set of microrheometers has emerged as powerful tools to investigate the dynamics and structures of homogeneous or heterogeneous soft matter at the micro-or nanoscale. In this review, these microrheometers, including some novel hybrid microrheometers are summarized and compared.

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Recent advances in anisotropic magnetic colloids: realization, assembly and applications

Cited by 137 publications

References 153 publications

Wire‐Active Microrheology to Differentiate Viscoelastic Liquids from Soft Solids

Wire‐Active Microrheology to Differentiate Viscoelastic Liquids from Soft Solids

Programming hierarchical self-assembly of colloids: matching stability and accessibility

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

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