Translational and Rotational Diffusions of Nanorods within Semidilute and Entangled Polymer Solutions

Alam, Sharmine; Mukhopadhyay, Ashis

doi:10.1021/ma5014995

Cited by 33 publications

(59 citation statements)

References 30 publications

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“…While the use of anisotropic nanoparticle tracers would greatly facilitate the application of this approach to stiffer materials and much smaller length and time scales than possible with larger tracers, microrheology places stringent requirements on the accuracy of the tracer's inferred meansquared displacement. Indeed, despite several reports of gold nanorod (GNR) rotational tracking using imaging [19][20][21][22][23][24][25][26][27][28][29][30][31] and depolarized scattering [32][33][34][35][36], no one has demonstrated the use of GNRs to accurately measure the rheology of a viscoelastic material. Moreover, no models of the complex anisotropic translational diffusion [32,33,37] that these particles would execute in a viscoelastic material, or its coupling to the rotational diffusion, have been reported or validated.…”

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confidence: 99%

“…Indeed, despite several reports of gold nanorod (GNR) rotational tracking using imaging [19][20][21][22][23][24][25][26][27][28][29][30][31] and depolarized scattering [32][33][34][35][36], no one has demonstrated the use of GNRs to accurately measure the rheology of a viscoelastic material. Moreover, no models of the complex anisotropic translational diffusion [32,33,37] that these particles would execute in a viscoelastic material, or its coupling to the rotational diffusion, have been reported or validated.…”

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confidence: 99%

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Nanoscale Rheology and Anisotropic Diffusion Using Single Gold Nanorod Probes

2018

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The complex rotational and translational Brownian motion of anisotropic particles depends on their shape and the viscoelasticity of their surroundings. Because of their strong optical scattering and chemical versatility, gold nanorods would seem to provide the ultimate probes of rheology at the nanoscale, but the suitably accurate orientational tracking required to compute rheology has not been demonstrated. Here we image single gold nanorods with a laser-illuminated dark-field microscope and use optical polarization to determine their three-dimensional orientation to better than one degree. We convert the rotational diffusion of single nanorods in viscoelastic polyethylene glycol solutions to rheology and obtain excellent agreement with bulk measurements. Extensions of earlier models of anisotropic translational diffusion to three dimensions and viscoelastic fluids give excellent agreement with the observed motion of single nanorods. We find that nanorod tracking provides a uniquely capable approach to microrheology and provides a powerful tool for probing nanoscale dynamics and structure in a range of soft materials.

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Nanoscale Rheology and Anisotropic Diffusion Using Single Gold Nanorod Probes

2018

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“…In neat solvent an isotropic diffusion is expected, i.e., D T∥ /D T⊥ = 1, but diffusion anisotropy can be extremely large within a semidilute or concentrated solution. 29 DE theory assumed an extreme situation, where diffusion along the hard direction is completely quenched (D T⊥ ≈ 0). Along the easy direction, D T∥ is unaffected by the presence of the other particles.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Translational Anisotropy and Rotational Diffusion of Gold Nanorods in Colloidal Sphere Solutions

Alam

Mukhopadhyay

2015

Langmuir

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We studied the translational and rotational diffusion of gold nanorods within a rod/sphere composite liquid using fluctuation correlation spectroscopy (FCS). The nanorods of length L ∼ 60 nm and diameter d ∼ 17 nm were used at a fixed concentration of ∼1 pM. The concentration of colloidal Ludox spheres (size ∼ 26 nm) was varied up to a volume fraction of ϕ = 0.3 or approximately 7 spheres/L(3). Our experiments showed significant translational anisotropy as the sphere concentration was increased. The translational diffusion parallel to the rod axis (D(T∥)) followed very close to the bulk viscosity of the solution. However, the diffusion normal to the rod axis (D(T⊥)) experienced a significantly higher frictional force. For volume fraction ϕ > 0.1 a slightly modified caging theory by Pecora and Deutch could explain the rotational diffusion of the rods very well. At low volume fraction the agreement is poor, which we interpreted as modification of the local ordering of the spheres, which can affect the rod rotation.

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“…However, in many industrial and biological processes, colloidal rods flow in crowded environments of polymers in solution where the characteristic length scale of suspended rods is similar to those of the surrounding macromolecules, e.g., the polymer radius of gyration, Rg p , or the polymer mesh size, ξ p (also referred to as the correlation length). 20,[22][23][24][25][26][27] In this scenario, the continuum assumption breaks down and the rods experience a local viscosity (η local ) that lies between the solvent viscosity and the bulk viscosity of the polymeric solution. [22][23][24]27 In principle, by knowing η local it is possible to predict the shear rate for the onset of colloidal alignment based on the criterion of P e 0 = 1 using η local in place of η s in eqn.1.…”

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confidence: 99%

Alignment of colloidal rods in crowded environments

Calabrese,

Varchanis,

Haward

et al. 2022

Preprint

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Understanding the hydrodynamic alignment of colloidal rods in polymer solutions is pivotal for manufacturing structurally ordered materials. How polymer crowding influences the flow-induced alignment of suspended colloidal rods remains unclear when rods and polymers share similar length-scales. We tackle this problem by analyzing the alignment of colloidal rods suspended in crowded polymer solutions, and comparing against the case where crowding is provided by additional colloidal rods in a pure solvent. We find that the polymer dynamics govern the onset of shear-induced alignment of colloidal rods suspended in polymer solutions, and the control parameter for the alignment of rods is the Weissenberg number, quantifying the elastic response of the polymer to an imposed flow. Moreover, we show that the increasing colloidal alignment with the shear rate follows a universal trend that is independent of the surrounding crowding environment. Our results indicate that colloidal rod alignment in polymer solutions can be predicted based on the critical shear rate at which polymer coils are deformed by the flow, aiding the synthesis and design of anisotropic materials.

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Translational and Rotational Diffusions of Nanorods within Semidilute and Entangled Polymer Solutions

Cited by 33 publications

References 30 publications

Nanoscale Rheology and Anisotropic Diffusion Using Single Gold Nanorod Probes

Nanoscale Rheology and Anisotropic Diffusion Using Single Gold Nanorod Probes

Translational Anisotropy and Rotational Diffusion of Gold Nanorods in Colloidal Sphere Solutions

Alignment of colloidal rods in crowded environments

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