Phase behaviors of polymer solution confined between two concentric cylinders

Helical insertion of polyphenylene chains into confined cylindrical slits composed of two carbon nanotubes

The helical insertion behavior of poly(para-phenylene) (PP) chains into confined cylindrical slits constructed by two carbon nanotubes (CNTs) with different diameters is studied by molecular dynamics simulations. The contribution of system energy and each energy component to helical self-assembly is discussed to further explain the conditions, driving force and mechanism. The width and length of the slit, the diameter of the outer tube and the temperature have a great impact on the helical insertion of PP chains. Two equations are proposed to confirm the diameter and the distances between the PP helix and the inner and outer walls of the given CNTs. The helical self-assembly of PP with different numbers of chains inserted into the slits is further studied. This study has a great benefit in understanding the conformational behavior of polymers, even biological macromolecules in confinements.

Critical polyelectrolyte adsorption under confinement: planar slit, cylindrical pore, and spherical cavity

We explore the properties of adsorption of flexible polyelectrolyte chains in confined spaces between the oppositely charged surfaces in three basic geometries. A method of approximate uniformly valid solutions for the Green function equation for the eigenfunctions of polymer density distributions is developed to rationalize the critical adsorption conditions. The same approach was implemented in our recent study for the "inverse" problem of polyelectrolyte adsorption onto a planar surface, and on the outer surface of rod-like and spherical obstacles. For the three adsorption geometries investigated, the theory yields simple scaling relations for the minimal surface charge density that triggers the chain adsorption, as a function of the Debye screening length and surface curvature. The encapsulation of polyelectrolytes is governed by interplay of the electrostatic attraction energy toward the adsorbing surface and entropic repulsion of the chain squeezed into a thin slit or small cavities. Under the conditions of surface-mediated confinement, substantially larger polymer linear charge densities are required to adsorb a polyelectrolyte inside a charged spherical cavity, relative to a cylindrical pore and to a planar slit (at the same interfacial surface charge density). Possible biological implications are discussed briefly in the end.