On the friction coefficient of straight-chain aggregates

A methodology to calculate the friction coefficient of an aggregate in the continuum regime is proposed. The friction coefficient and the monomer shielding factors, aggregate-average or individual, are related to the molecule-aggregate collision rate that is obtained from the molecular diffusion equation with an absorbing boundary condition on the aggregate surface. Calculated friction coefficients of straight chains are in very good agreement with previous results, suggesting that the friction coefficients may be accurately calculated from the product of the collision rate and an average momentum transfer, the latter being independent of aggregate morphology. Langevin-dynamics simulations show that the diffusive motion of straight-chain aggregates may be described either by a monomer-dependent or an aggregate-average random force, if the shielding factors are appropriately chosen.

Calculated friction coefficients of straight chains composed of k = 2–64 spherical monomers for motion parallel (a) and perpendicular (b) to the chain symmetry axis plotted against the number of monomers. Comparison with previous results.Figure optionsDownload high-quality image (100 K)Download as PowerPoint slideResearch highlights
► A methodology is proposed to calculate the friction coefficient of aggregates in the continuum regime from the fluid diffusion equation.
► The friction coefficient is related to the ratio of two molecular collision rates.
► The calculated friction coefficients and mobility radius of straight chains are in good agreement with previous results.
► The monomer shielding factors determine the chain friction and diffusion coefficients.