Aggregate formation in poly(ethylene oxide) solutions

Abstract

Static light scattering and viscosity measurements were performed on different molecular weight poly (ethylene oxide) to see the formation of aggregates in its dilute solutions. Viscosity measurements were carried out for PEO samples in water and methanol at 20-458C and in chloroform at 20-308C. Using Huggin's equation, the viscosity plots showed distinct upward curvature indicating the presence of aggregates in both PEO/H 2 O and PEO/CH 3 OH solutions The [Z] values for PEO/H 2 O and PEO/CH 3 OH system were 2-4 times as large as observed for other linear flexible polymers in good solvents thus showing extensive coil swelling/aggregation. This is also apparent from the exponent a values of the Mark-Houwink-Sakurada equation. Light Scattering results using Zimm method showed that aggregation occurred in low molecular weight samples; however, in higher molecular weight samples there was a little evidence for aggregation both in water and methanol.

Reduced colloidal repulsion imparted by adsorbed polymer of particle dimensions

“…As can be seen from Table 2, for PEO concentrations above 1 mg/ml, there is an abrupt increase in the hydrodynamic radius of the slow mode, R h,2 , suggestive of the formation of large aggregate species. These aggregate species likely were formed by non-adsorbed PEO chains, as PEO aggregates of similar size have been detected for pure PEO solutions in early studies [67,68] as well as in the present experiment (not shown). On the other hand, the values of R h,2 for sample dispersions with PEO concentrations equal to or below 1 mg/ml are almost identical, suggesting that it basically reflects the polydispersity of the core (silica) particle itself.…”

Substituent effects on the stabilities of polymeric and small molecule bis-terpyridine complexes

“…the PEO chains slowed decomposition as compared to complexes (2) 2 CoCl 2 and (3) 2 CoCl 2 either by coordinating to cobalt, thereby enhancing the stability of the bis complexes, or by increasing the viscosity locally in the vicinity of the complexes. However, when complex (2) 2 CoCl 2 was decomposed in the presence of an equimolar amount of 5k PEO, no change in k À2 was observed, and even a 5k-PEO concentration of 66 mg mL À1 ($80% of the overlap concentration 61,62 ) yielded a minor increase in decay rate to 6.4 Â 10 À3 s À1 . We note that excluded volume effects could be important as well, but these are expected to lead to faster decay of polymer-functionalized ligands, i.e., due to the tension applied to the chain, whereas in this case we find that the higher molecular weight ligand leads to significantly slower decay.…”

Poly(oxyethylene) and ramie whiskers based nanocomposites: influence of processing: extrusion and casting/evaporation

“…For PEO, HMS constants at 25°C are equal to K = 6.103 9 10 -3 cm 3 g -1 and a = 0.83 (Khan 2006). The intrinsic viscosity of PEO solutions obtained from the cast/evaporated film is about [g] cast-evap = 900 ± 150 cm -3 g -1 while the one measured for the extruded film is [g] cast-evap = 520 ± 80 cm -3 g -1 , corresponding to an average molecular weight M cast-evap = (1.69 ± 0.2) 9 10 6 g/mol and M extr.…”