Semiflexible Polymers in the Bulk and Confined by Planar Walls

Abstract

Semiflexible polymers in solution under good solvent conditions can undergo an isotropic-nematic transition. This transition is reminiscent of the well-known entropically-driven transition of hard rods described by Onsager's theory, but the flexibility of the macromolecules causes specific differences in behavior, such as anomalous long wavelength fluctuations in the ordered phase, which can be understood by the concept of the deflection length. A brief review of the recent progress in the understanding of these problems is given, summarizing results obtained by large-scale molecular dynamics simulations and density functional theory. These results include also the interaction of semiflexible polymers with hard walls and the wall-induced nematic order, which can give rise to capillary nematization in thin film geometry. Various earlier theoretical approaches to these problems are briefly mentioned, and an outlook on the status of experiments is given. It is argued that in many cases of interest, it is not possible to describe the scaled densities at the isotropic-nematic transition as functions of the ratio of the contour length and the persistence length alone, but the dependence on the ratio of chain diameter and persistence length also needs to be considered.

The interplay of interfaces, supramolecular assembly, and electronics in organic semiconductors

“…The model was parameterized to represent chains of the conjugated polymer P3HT. Consistent with previous findings for semiflexible polymers [50], the surface was found to induce alignment of the chains parallel to the surface, with the thickness of the aligned layer on the order of the persistence length. Nevertheless, since the model did not account for monomer orientation, it was not able to distinguish edge-on versus face-on alignment of interest in electronic applications.…”

Semiflexible Polymers Interacting with Planar Surfaces: Weak versus Strong Adsorption

“…When one deals with the liquid-crystalline order of semiflexible polymers in lyotropic solution [6,7], it is clear that a description in terms of two lengths only, the contour length L of the WLC and its persistence length, p , does not suffice: the effective chain diameter D controls the interchain repulsion and hence the possible onset of nematic order (see, e.g., [8][9][10][11]). However, for single semiflexible chains in d = 3 dimensions (as they matter in dilute solutions), the excluded volume interactions due to nonzero D do not matter for large p /D, provided L is much smaller than L * = D( p /D) 3 [12,13].…”

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).…”

“…This rounding is particularly pronounced since the spherical confinement causes a strong "frustration" effect, uniform nematic orientation of the chain molecules obviously is impossible, and the maximal nematic order parameters that can be reached here are much smaller than those for comparable parameter choices in the bulk. [42][43][44]. Variation of the eigenvalues λ + and λ − of the orientation tensor for semiflexible polymer chains with the rigidity parameter κ, for a sphere with radius R = 70, average density ρ av = 0.2, and several chain lengths N, as indicated.…”

“…Such large linear dimensions require the use of coarse-grained models. 39 Thus, we describe the semiflexible polymers in terms of the standard bead-spring model 40,41 amended by a bond-angle potential [42][43][44] which allows controlling the persistence length over a wide range. We use the same bond-angle potential also in the framework of our density functional theory (DFT), but for these calculations it is more convenient to model the polymers in terms of tangent hard spheres.…”