Solution properties of star polyelectrolytes having a moderate number of arms

Abstract

We investigate polyelectrolyte stars having a moderate number of arms by molecular dynamics simulations of a coarse-grained model over a range of polyelectrolyte concentrations, where both the counter-ions and solvent are treated explicitly. This class of polymeric materials is found to exhibit rather distinct static and dynamic properties from linear and highly branched star polyelectrolyte solutions emphasized in past studies. Moderately branched polymers are particle-like in many of their properties, while at the same time they exhibit large fluctuations in size and shape as in the case of linear chain polymers. Correspondingly, these fluctuations suppress crystallization at high polymer concentrations, leading apparently to an amorphous rather than crystalline solid state at high polyelectrolyte concentrations. We quantify the onset of this transition by measuring the polymer size and shape fluctuations of our model star polyelectrolytes and the static and dynamic structure factor of these solutions over a wide range of polyelectrolyte concentration. Our findings for star polyelectrolytes are similar to those of polymer-grafted nanoparticles having a moderate grafting density, which is natural given the soft and highly deformable nature of both of these ‘particles’.

50th Anniversary Perspective: A Perspective on Polyelectrolyte Solutions

“…The literature on polyelectrolyte solutions is vast, 1−159 encompassing a large body of publications over the past seven decades, based on experiments, 1−61 theory, 62−132 and simulations. 133−159 Because of the difficult nature of the subject, where every molecule essentially knows every other one in the system, the particular aspects of the various publications have been quite diverse.…”

“…133−159 Because of the difficult nature of the subject, where every molecule essentially knows every other one in the system, the particular aspects of the various publications have been quite diverse. In terms of experiments, the most notable issues are charge and size of isolated molecules, titration curves, colligative properties, structural organization in solutions, complexation, phase diagrams, and dynamical properties such as diffusion, viscosity, and ionic conductivity.…”

“…While the Manning argument is exact for the particular model of an infinitely thin and infinitely long perfectly one-dimensional line charge, it cannot be applied to experimental systems involving flexible and semiflexible polyelectrolyte chains and even for rods with finite diameter. 30,63,64 Considerable effort has been made to understand counterion condensation by using computer simulations 133−159 in terms of the valency of counterions, salt concentration, chain length, and polymer concentration. The Manning transition as given by eq 13 is not observed in the simulations.…”

Free Surface Relaxations of Star-Shaped Polymer Films

“…This is an additional effect associated with the emergence of particle-like behavior and molecular packing with increasing f in the bulk as discussed in a previous study. 29 …”

“…Recent oscillatory shear experiments reveal that for bulk systems, the molecules with f ≥ 8 and M arm < M e undergo flow via a cooperative mechanism, unlike the conventional arm retraction mechanism characteristic of the long-range dynamics of long armed ( M arm >> M e ) star shaped macromolecules. 29 This new phenomenon –slow surface dynamics– should be general and exhibited by branched molecules whose motions become “caged” due to a tendency toward aggregation or localization at the free surface. These findings have important implications with the regard to the use of polymers for applications that include lubrication, tribology, and adhesion.…”