Electrophoretic transport of highly charged polyelectrolytes in the presence or absence of a gel matrix has been studied, with the objective of an improved understanding at a molecular level of the transport mechanisms responsible for molecular weight discrimination. In the presence of a gel and low applied fields, based on the ratio of the probe size to gel mesh spacing, three transport mechanisms are identified as confinement level increases: sieving, entropic barriers, and reptation. For sieving models the widely accepted notion that nonspherical and flexible molecules can be represented as effective spheres during motion through highly porous gels is shown to be a poor approximation. At intermediate confinement, probe mobility trends are explained by the entropic barriers theory, where spatial variations in chain entropy control the motion. In the most confined state, transport is governed by reptation. Capillary electrophoresis is established as the method of choice for measurements of the free-solution mobility as a function of ionic strength and chain length. A traditionally assumed chain-length independent free-solution mobility is monitored by the method, but a transition to molecular weight dependence is noted for flexible short chains of degree of polymerization less than 50. Increasing ionic strength decreases mobility because the cylindrically symmetric counter-ion cloud is shifted towards smaller radial distances from the chain backbone; this shift increases the hydrodynamic forces propagated to the chain by these ions. The trends with ionic strength, however, do not follow previous theories.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8750 |
| Date | 01 January 1993 |
| Creators | Arvanitidou, Evangelia Stelios |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
Page generated in 0.001 seconds