Monte Carlo, small angle light scattering, and dynamic light scattering studies of dilute polymer solutions.

摘要

The adsorption of negatively charged polymer, negative/neutral block copolymer and a polyampholyte to patterned surfaces is investigated using off-lattice Monte Carlo simulations. The surface is decorated by stripe and checkerboard patterns of mixed charges. The polymer has periodic charge segments, which potentially match the periodicity of the surface pattern. Results show that the chain entropy of a flexible polymer disrupts and prevents full pattern recognition. Quantities such as average adsorption energy and the radii of gyration of the adsorbed polymer are calculated and found to be dictated by the size of the surface pattern and its correlation to the polymer charge density. We performed small angle light scattering on dilute-solution-grown polyethylene crystals grown from quenches in para-xylene. The quench depths ranged from 60 to 85°C for 0.05 wt.% and 0.1 wt.% linear-low-polydispersity polyethylenes. We found asymmetric scattering patterns for the lower temperature quenches to 65°C, and symmetric scattering patterns for the higher temperature quenches to 80°C. There is a smooth transition from asymmetric to symmetric scattering as we change the quench depth. The correlation lengths d=2pi/qmax corresponding to the peaks of intensity versus q ranged from 15 to 30 mum. We find evidence that these length scales correspond to assemblies of single polyethylene crystals. Also, we have performed dynamic light scattering on solutions of sodium-poly(styrene-sulfonate) (NaPSS) and poly(ethylene-oxide) (PEO) in water with BaCl2. The fast mode ( Dfast) and slow mode (Dslow) diffusion coefficients were measured as a function of polymer concentration for both polymers in dilute solution. We found that the diffusion coefficients remained relatively constant in the concentration regimes investigated and Dfast and Dslow for both polymers differed by about 1½ orders of magnitude: 1.1 x 10-6 cm2/s versus 7.8 x 10-8 cm2/s for NaPSS and 6.7 x 10-7 cm2/s versus 4.2 x 10-8 cm2/s for PEO. Also, we studied more concentrated solutions of PEO without salt and used Dfast and Dslow to calculate hydrodynamic radii of single and aggregated PEO chains. Using a concentration-dependent viscosity for PEO in water, we found single chain radii from 1 to 5 nm and aggregate radii from 45 to 60 nm.