| 1. |
- Forsman, Jan, et al.
(författare)
-
Density Functional Study of Surface Forces in Athermal Polymer Solutions with Addititve Hard Sphere Interactions. Solvent Effects, Capillary Condensation and Capillary-Induced Surface Transitions.
- 2002
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 117:4, s. 1915-1926
-
Tidskriftsartikel (refereegranskat)abstract
- A density functional theory for polymer solutions is generalized to cases where the monomers have a different diameter to the solvent. An appropriate free energy functional is obtained by integration of the generalized Flory equation of state for such systems. This functional predicts that entropic demixing may occur in polymer solutions in which the solvent particles are smaller than the monomers. Demixing is promoted not only by a large size disparity, but also by a high pressure as well as by polymer length. The existence of two separate phases in the bulk solution suggests the possibility of capillary-induced phase transitions, even when the confining surfaces are hard, but otherwise inert. We examine such phase transitions and their relation to surface forces and colloidal stability. The density functional theory also predicts that under certain conditions, layering transitions will occur at hard and flat surfaces. A transition from a thin to a thick polymer-rich surface layer may take place as the separation between two surfaces is decreased, and we study the concomitant change on the surface force. Stable thick phases are predicted even at very large undersaturations, and they give rise to a profound increase of the range and strength of the surface force.We furthermore include comparisons with predictions from a model in which the solvent only enters the description implicitly. Responses of the surface forces to changes in monomer diameter, solvent diameter, polymer density, and chain length are investigated.
|
|
| 2. |
- Ullner, Magnus, et al.
(författare)
-
Orientational correlation function and persistence lengths of flexible polyelectrolytes
- 2002
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:4, s. 1437-1445
-
Tidskriftsartikel (refereegranskat)abstract
- Orientational correlation functions have been obtained from Monte Carlo simulations of long, freely jointed chains (1000 monomers and more) with screened Coulomb interactions truncated after a certain number of bonds. This makes it possible to study chain-length dependence without "end effects" and to display excluded-volume effects. These correlation functions form the basis for a discussion of the conformational response to electrostatic interactions. In particular, they are related to the concept of electrostatic persistence length and the correlation functions illustrate the differences between different definitions of persistence length. To facilitate future discussions, we have identified four types of definitions and given them separate names: (1.) projection length, which involves: integration of the orientational correlation function; (2) orientational correlation length, which is the decay length of an exponential function; (3) bending coefficient, which is a length representing a bending force constant; and (4) crossover distance, which is the monomer-monomer distance at the boundary between a rodlike and a swollen behavior. Previous conclusions that the projection length obeys a power law at high salt concentrations, while the orientational correlation length does not, are confirmed. Furthermore, a power law is also found in the salt-free limit for the projection length corresponding to an infinite chain with a finite range of interactions. The two power laws make it possible to construct a universal curve that gives an almost quantitative description of the chain behavior.
|
|
