ABSTRACT: We present a numerical self-consistent field (SCF) method which describes freely jointed chains of spherical monomers applied to densely grafted polymer brushes. We discuss both the Flory-Huggins model and the Carnahan-Starling equation of state and show the latter being preferable within our model at polymer volume fractions above 10%. We compare the results of our numerical method with data from molecular dynamics (MD) simulations [G.-L. He, H. Merlitz, J.-U. Sommer, and C.-X. Wu, Macromolecules 40, 6721 (2007)] and analytical SCF calculations [P. M. Biesheuvel, W. M. de Vos, and V. M. Amoskov, Macromolecules 41, 6254 (2008)] and obtain close agreement between the density profiles up to high grafting densities. In contrast to prior numerical and analytical studies of densely grafted polymer brushes our method provides detailed information about chain configurations including fluctuation, depletion, and packing effects. Using our model we could study the recently discovered instability of densely grafted polymer brushes with respect to slight variations of individual chain lengths, driven by fluctuation effects [H. Merlitz, G.-L. He, C.-X. Wu, and J.-U. Sommer, Macromolecules 41, 5070 (2008)]. The obtained results are in very close agreement with corresponding MD simulations.
The Journal of chemical physics 01/2012; 136(4):044903. · 3.09 Impact Factor
ABSTRACT: In this paper, polymer brushes are studied via molecular-dynamics simulations at very high grafting densities, where the crossover between the brush regime and the polymer-crystal regime is taking place. This crossover is directly observed with the structure factor and pair-correlation function. With increasing grafting density, this crystallization is progressing from the core layer of the brush towards the surface layer. The same process is analyzed using the lateral fluctuations of the monomers as a signature of their diminishing mobility. Additionally, bond forces and the chain excess free energy indicate a transition from the brush regime to the overstretched regime, which is in agreement with predictions of a modified self-consistent field theory.
The European Physical Journal E 01/2008; 24(4):325-30. · 1.94 Impact Factor
ABSTRACT: A discrete shell model is proposed to describe the radial
deformation of carbon nanotubes under a hydrostatic pressure and the
radial Young's modulus of (single- or multi-walled) nanotubes is
obtained. It is found that the radial modulus decreases with
increasing tube diameter while increases with increasing number of
layers. The computational results agree well with the previous
results of SWNTs and indicate that the radial modulus of carbon
nanotubes is independent of the Poisson's ratio.
Physics of Condensed Matter 10/2006; 54(1):109-112. · 1.53 Impact Factor