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Marques Mendes Almeida da Rosa Leal, Catarina
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- Temperature dependence of the rheological properties of acetoxypropylcellulose in the thermotropic chiral nematic phasePublication . Cidade, M. T.; Leal, Catarina R.; Godinho, M. H.; Navard, P.The rheological behaviour of two different molecular weights of a thermotropic liquid crystalline cellulose derivative, acetoxypropylcellulose (APC), at T=I2OoC, has already been reported [ l]. In this work we present the temperature dependence of the rheological properties of two molecular weights of APC. The shear viscosity, q, and first normal stress difference, N,, were measured at temperatures T=120, 130 and 140°C. for Mciw = 94000 g/mole, and T=120 and 140°C for Mw = 129000 g/mole, and for shear rates, +, between 0.01 and 10 s-’. The shear viscosity q(+) decreases with increasing T, for both samples, showing a strong shear thinning behaviour at all temperatures and over the whole range of + studied, except for shear rates between about 0.2 and 1 s-’ (depending on IGiw and T), where a quasi-Newtonian plateau is observed. The first normal stress difference N1 (+) also decreases with increasing T at a given +. It increases with shear rate over the whole + range studied, and shows an inflection at + values slightly above + = 1/r, where z is the relaxation time of the polymer memory function. The temperature dependence of the shear viscosity was fitted to an Arrhenius law, giving an apparent activation energy (E,) in the order of 8-15 kcaUmole, depending on molecular weight and shear rate. The activation energy was found to increase with molecular weight (at a given + ). The variation of E, with +, , for Mw = 94000 g/mole, shows a minimum at ;i x 2 s-l. Using a continuum theory for nematic polymers, proposed by Martins [2], some fundamental parameters were obtained from the fit of the theory to the experimental data. Using these parameters it was possible to construct a “master curve” for the viscosity, q(+), in good agreement with the experimental data.
- Rheological properties of lyotropic solutions of acetoxypropylcellulose in dimethylacetamide. A comparision with the thermotropic casePublication . Cidade, M. T.; Leal, Catarina R.The rheological properties of a thermotropic acetoxypropylcellulose (APC) were already described in previous works [1,2]. In this work we present the rheo logical properties, viscosity, Z, and first normal stress difference, N1, of lyotropic solutions of APC in dimethylacetamide (DMAc). The flow curve of the lyotropic solution presents the typical behavior for this type of system (Onogi and Asada Curve) [3] however, contrary to what happens with that other lyotropic system [4–7], the APC/DMAc system presents a con tinuous increase of N1 in function of the shear rate, which we attribute to the fact that APC has higher flexibility than the other liquid crystalline polymers studied so far—namely hydroxypropylcellulose and poly-benzyl-L-glutamate— that present a negative N1 region, as well as a low molecular weight. We will also present some remarks concerning rheo-optical studies preformed with APC/DMAc, by comparison with previous studies on thermotropic APC [8,9].