A relatively new approach
Using the diamagnetic anisotropy of polymers for the characterization of polymers and their aggregates is a relatively new approach in the field of soft-matter and polymer research. For crystals and individual molecules the diamagnetic anistropy is often relavily easily obtained, either through experiment or through calculations. However, a good and thorough quantitative description of the diamagnetic properties of polymer aggregates has been lacking due to their random nature. Using a simple equation that links the magnetic properties of an average polymer repeating unit to that of the polymer vesicle of any shape (disc, tube, rod, stomatocyte), we measured, using magnetic birefringence, the average diamagnetic anisotropy of a polystyrene (PS) repeating unit, , inside a poly(ethylene glycol)-polystyrene polymersome membrane as a function of the PS-length and as function of the preparation method. All obtained values of have a negative sign which results into polymers tending to align perpendicularly to an applied magnetic field. A very similar value for (10‑12 m3/mol) was found for all polymersome shapes, which shows that the individual polymers are organized very similarly in each case. Moreover, the value found is only a fraction (~1 %) of what it could maximally be if the polymers were fully organized. Yet, it is enough to be useful in aligning and deforming various shapes of polymersomes, albeit at rather high fields. We, therefore, predict that further ordering of the polymers within the membrane will lead to similar responses at much lower magnetic fields, possibly obtainable with permanent magnets, which would be highly advantageous for practical applications.
