High-Shear Viscometric properties of Poly[2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] in o-Dioctyl phthalate

• Main Authors: Hsu Pi Yen, 薛弼彥
• Other Authors: Hua c. c.
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/31150028486592883849

碩士 === 國立中正大學 === 化學工程研究所 === 93 === The viscometric properties of dilute poly[2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)/dioctyl phthalate (DOP) solutions were systematically investigated in view of the interrelation with the associated aggregation properties. The utility of a high-viscosity solvent—DOP—makes it possible to probe the non-Newtonian solution properties within the accessible range of shear rates in a Couette rheometry. Firstly, low-shear viscosity measurements revealed similar aggregation properties of MEH-PPV in DOP as observed earlier in two low-viscosity solvents, chloroform and toluene. Specifically, similar low-shear viscometric features in response to the effect of constant-temperature aging or short-term thermal annealing have been observed in the aforementioned MEH-PPV solutions. On the other hand, a two-stage viscosity thinning in the polymer contribution to the solution viscosity with increasing shear rate was, for the first time, revealed for a conjugated polymer solution. In addition, the onset of a viscosity thinning occurs at surprisingly low shear rates compared with the estimated relaxation time for individual MEH-PPV chains. The experimental phenomena were subsequently analyzed in view of the effect of aggregate formation using polymer kinetic theories, which led us to the following essential implications: The first viscosity thinning might be due to the effect of excluded volume associated with the suspended polymer aggregates, in analogy to colloidal suspension systems. The second is likely to arise from a flow-induced variation in the average chain environment within individual aggregates. Overall, the experiments revealed, once again, a close correspondence between the viscometric and aggregation properties for conjugated polymer solutions, in which relatively unstable aggregation properties had been linked to weak interchain attractions.