Increasing Number Of Arms Research Articles

Intramolecular Janus Segregation of a Heteroarm Star Copolymer

Conformations of heteroarm star copolymers AnBn are investigated by off-lattice Monte Carlo simulations. Intramolecular segregation is always observed in selective solvents. It can also be found in a common good solvent, which however gives block incompatibility. The degree of Janus segregation is characterized by the mean-square separation between A and B blocks, 〈(xA - xB) 2 〉, or by the orientation correlation between the two blocks, 〈xA‚xB〉, where xi denotes the relative position of the center of mass associated with the block arms i from the star core. The degree of segregation grows with increasing arm numbers while the effect of arm lengths is insignificant. The influence of the intramolecular segregation on the aggregation behavior in solution can be revealed through interactions between two star copolymers. The potential of mean force and second virial coefficient are calculated for various solvent qualities. In a selective solvent, the blockarm star copolymer can form a unimolecular micelle structure and always shows intermolecular repulsions. In contrast, the heteroarm star copolymer may display the Janus segregation, which leads to intermolecular attractions. This consequence facilitates the formation of multimolecular micelles.

Partial structure factors in star polymer/colloid mixtures

Addition of polymer to colloidal suspensions in- duces an attractive part to the colloid pair potential, which is of purely entropic origin ("depletion interaction"). We in- vestigated the influence of polymer branching on depletion forces by studying mixtures of hard sphere colloids and star polymers with increasing arm number f = 2-32, but con- stant Rg ≈ 500 A. We found a pronounced effect of branching on the position of the gas/liquid demixing transition. Using small angle neutron scattering (SANS) we were able to meas- ure partial structure factors in star polymer/colloid mixtures. The relative distance to the demixing transition is reflected in our scattering data.