Glassy dynamics of model colloidal polymers: Effect of controlled chain stiffness

Colloidal polymers with tunable chain stiffness have been successfully assembled in experiments recently.Similar to molecular polymers,chain stiffness is an important feature which can distinctly affect the dynamical behaviors of colloidal polymers.Hence,we model colloidal polymers with controlled chain stiffness and study the effect of chain stiffness on glassy behaviors.For stiff chains,there are long-ranged periodic intrachain correlations besides two incompatible local length scales,i.e.,monomer size and bond length.The mean square displacement of monomers exhibits sub-diffusion at intermediate time/length scale and the sub-diffusive exponent increases with chain stiffness.The data of localization length of stiff polymers versus rescaled volume fraction for different monomer sizes can gather close to an exponential curve and decay slower than those of flexible polymers.The increase of chain stiffness linearly increases the activation energy of the colloidal-polymer system and thus makes the colloidal polymers vitrify at lower volume fraction.Static and dynamic equivalences between stiff colloidal polymers of different monomer sizes have been checked.

Vibrational Properties of Vacancy in Na and K Using MEAM Potential

The modified embedded atom method(MEAM)with the universal form of embedding function and a modified energy term along with the pair potential has been employed to determine the potentials for alkali metals:Na,K,by fitting to the Cauchy pressure(C_(12)−C_(44))/2,shear constants Gv=(C_(11)−C_(12)+3C_(44))/5 and C_(44),the cohesive energy and the vacancy formation energy.The obtained potentials are used to calculate the phonon dispersions of these metals.Using these calculated phonons we evaluate the local density of states of neighbours of vacancy using Green’s function method.The local density of states of neighbours of vacancy has been used to calculate mean square displacements of these atoms and formation entropy of vacancy.The calculated mean square displacements of both 1st and 2nd neighbours of vacancy are found to be lower than that of host atom.The calculated phonon dispersions agree well with the experimental phonon dispersion curves and the calculated results of vacancy formation entropy compare well with the other available results.