Capillary Nematization of Semiflexible Polymers

Abstract

Semiflexible polymers under good solvent conditions confined by two planar parallel repulsive walls are investigated for a wide range of monomer concentrations and distances between the walls, for a case where persistence length and contour length of the macromolecules are almost equal. Chain conformations and local nematic ordering near the walls are studied by both molecular dynamics methods and density functional theory, putting it in perspective with the recent work where the isotropic phase of semiflexible polymer solutions in the vicinity of a single repulsive wall in semi‐infinite geometry is considered. Profiles of the total density of monomers as well as densities of end‐ and middle‐monomers and also the local orientational order parameter across the slit are computed. For small distances between the walls, the increase of monomer density causes a gradual onset of nematic order without a sharp transition while for large distances between the walls a first‐order “capillary nematization” transition is found at a monomer concentration somewhat smaller than needed for the onset of nematic order in the bulk. A brief comparison with related treatments for other models is made.

Conformations and orientational ordering of semiflexible polymers in spherical confinement

“…Specifically, in accord with our previous DFT work, [42][43][44]55,56 polymer molecules are described as necklaces of tangent hard spheres of diameter σ, while the bending potential still is given by Eq. (3).…”

“…A clear advantage of our model is that in the limit R → ∞ it reduces to the choice made in our previous work on solutions of semiflexible polymers confined by planar repulsive walls. 55,56 This model is studied by standard MD methods, 58,59 using graphics processing units (GPUs) employing the HOOMDblue software package. 60,61 The standard velocity Verlet algorithm 58,59 is used to integrate Newton's equations of motion, employing a time step ∆t = 10 −2 τ MD with an intrinsic MD time unit of τ MD = (mσ 2 / ) 1/2 .…”

“…Also, the repulsive surface is simply modeled by a hard wall potential, U(r) = ∞ at the sphere surface and U(r) = 0 inside of the sphere. The technical aspects of the DFT calculations closely follow the procedure used for planar surfaces 55,56 but suitably modified to account for the spherical cavity geometry. 63,64 However, unlike the latter work, the "no-end" approximation, whereby all the monomers in the chains are treated as equivalent, is avoided.…”

“…Our model, however, has the distinct advantage that extensive results for confinement effects due to hard repulsive walls are already available. 55,56 We expect the boundary effects for confinement by a sphere of radius R and for a planar wall to become equivalent for R → ∞.…”

Conformation of Tunable Nanocylinders: Up to Sixth-Generation Dendronized Polymers via Graft-Through Approach by ROMP

“…According to Borisov and co-workers, 14 the ratio l p / R cs is an important structural quantity also for nondilute denpols solutions, since it can control the anisotropic excluded volume interactions between denpols, 61 thereby forming liquid crystalline phase. 63 Since l p / R cs was found to increase with generation for both PTD and PNB backbones, as displayed in Figure 5c, the persistence length should increase faster than R cs . However, their values remain below 10, which renders the formation of a liquid crystalline phase…”