Self-assembled aggregates in the gravitational field: Growth and nematic order

Abstract

The influence of the gravitational field on the reversible process of assembly and disassembly of linear aggregates is focus of this paper. Even the earth gravitational field can affect the equilibrium properties of heavy biological aggregates such as microtubules or actin filaments. The gravity gives rise to the concentration gradient which results in the distribution of aggregates of different lengths with height. Strong enough gravitational field induces the overall growth of the aggregates. The gravitational field facilitates the isotropic to nematic phase transition reflecting in a broader transition region. Coexisting phases have notedly different length distributions and the phase transition represent the interplay between the growth in the isotropic phase and the precipitation into nematic phase. The fields in an ultracentrifuge can only reinforce the effect of gravity, so the present description can be applied to a wider range of systems.

RETRACTED ARTICLE: Nematic Ordering Pattern Formation in the Process of Self-Organization of Microtubules in a Gravitational Field

“…Although the gravitational field is often neglected in the description of physicochemical processes, its influence on biological heavy objects such as MTs is noticeable and important because this influence on biological living polymers is much stronger than that for nonaggregating particles [25]. Moreover, this always occurs even under normal earth gravity conditions.…”

Settled and unsettled issues in particle settling

“…Being so long, microtubules organize into a nematic phase at very low concentration: yet, even natural gravity seems to play a role in their phase behavior, for in microgravity conditions no sign of the nematic order displayed in ground experiments is apparently observed [83]. Prompted by this puzzling result, Baulin has tried to develop a general analysis of self-assembled aggregates in the gravitational field [84], which moves along a line similar to the approach in [82], but also takes into account the finite flexibility of the aggregates, which are then described similarly to those reversible worm-like surfactant aggregates known as 'living polymers' [85]. The analysis generates several surprises.…”

Nematic order of model goethite nanorods in a magnetic field

“…The curve is virtually independent of the packing fraction since the ODF in the dilute regime is mainly determined by the Boltzmann factor in Eq. (7).…”

“…The presence of an interface or wall breaks the translational and orientational symmetry and leads to local structures drastically different from those found in the bulk [2,3,4,5]. Macroscopically different behavior may be brought about for instance by a gravitational field [6,7]. If the buoyant mass of the colloids is sufficiently high, inhomogeneous density profiles are built up along the vertical dimension of the system.…”