Rotational Diffusion Coefficient (or Rotational Mobility) of a Nanorod in the Free-Molecular Regime

Li, Mingdong; Mulholland, George W.; Zachariah, Michael R.

doi:10.1080/02786826.2013.864752

Cited by 14 publications

(5 citation statements)

References 10 publications

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“…Theoretically, the averaged-drift-velocity approach and the averaged-drag-force approach provide two limit mobility values. One way to assess if the Brownian motion of a cylindrical particle is "slow" or "fast" by comparing to the particle translational relaxation process was shown in [30] using the rotational diffusion coefficient expression in the free molecular regime [42] and in the continuum regime [43].…”

Section: Resultsmentioning

confidence: 99%

Understanding the mobility of nonspherical particles in the free molecular regime

Mulholland

Zachariah

2014

Phys. Rev. E

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An approach to obtain the mobility of nonspherical particles is proposed by averaging the drag force orientationally, and two other widely used approaches in the literature, the averaged-collision-integral and averaged-drift-velocity methods, are summarized and extended. The concept of orientationally averaged collision integrals based on Chapman-Enskog theory for small gas-phase ions is re-examined for macromolecular ions whose surface cannot be treated as specular, but with inelastic interactions. A well accepted collision model considering inelastic collisions is Epstein's theory, which has been extended to include long-range potential forces by Li and Wang [Phys. Rev. E 68, 061206 (2003)] for spherical particles. This work extends Li and Wang's spherical particle theory to convex nonspherical particles considering long-range potential, and simplifies this collision integral to a product of the averaged projection area and an enhancement factor for short-range interactions (hard collisions), which is independent of convex particle shape and is identical to the value for a sphere that people are using. We also show that the averaged projection area of a convex particle in free molecular regime for hard collisions is equal to its mobility diameter. The second approach is the averaged-drift-velocity approach using the friction coefficient in a tensor form, which is often employed in aerosol science. We extend this approach in our previous work for axisymmetric particles to develop an expression for the mobility of nonspherical particles in a general form. Furthermore, it is pointed out that this approach is only valid when the particle Brownian rotation is slow compared with the particle translational relaxation time. If the particle Brownian rotation is fast, usually so in the case of very small ions and particles, we propose an "averaged-drag-force" approach. The three approaches are then compared for a randomly oriented rod and the protein GroEL. We show that for a cylinder rod in the free molecular regime at random orientation, the averaged-drag-force approach is identical to the averaged-collision-integral approach for short-range interactions (hard collisions). We then summarize the relationship between collision-integral based approach and tensor based approaches. For readers only interested in implementation of the theory, we provide useful expressions in Tables I and II.

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Section: Resultsmentioning

confidence: 99%

Understanding the mobility of nonspherical particles in the free molecular regime

Mulholland

Zachariah

2014

Phys. Rev. E

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“…I reduce to expressions known in the literature: the translational and rotational friction tensor of a sphere is consistent with Refs. [1,55,57], and the center-of-mass friction force on cylinders for γ s = 1 was calculated in [58], while its frictional torque was determined for γ s = 1 and for rotations orthogonal to m in [59]. The friction tensor of cuboids reduces to the one given in Ref.…”

Section: Symmetric Particlesmentioning

confidence: 99%

Gas-induced friction and diffusion of rigid rotors

2018

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We derive the Boltzmann equation for the rotranslational dynamics of an arbitrary convex rigid body in a rarefied gas. It yields as a limiting case the Fokker-Planck equation accounting for friction, diffusion, and nonconservative drift forces and torques. We provide the rotranslational friction and diffusion tensors for specular and diffuse reflection off particles with spherical, cylindrical, and cuboidal shape, and show that the theory describes thermalization, photophoresis, and the inverse Magnus effect in the free molecular regime.

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“…Boies et al have recently performed a seminal kinetic analysis of aerogel formation based on determination of collision rates of 1D nanoparticles. 79 They used simulation to determine the first collision kernel for rigid 1D nanoparticles, accounting for both particle rotation 80 and translation, for different 1D morphologies. Reduced order relations were provided to enable direct calculation of collision kernels for 1D nanoparticles from geometric parameters without the need for simulations.…”

Section: Assembly From the Gas-phase: From Aerosols To Aerogelsmentioning

confidence: 99%