Phase diagrams of the system tetrahydrofuran/γ-butyrolactone/poly(ether imide) and determination of interaction parameters

1998

Abstract The thermodynamic interactions in the ternary mixture tetrahydrofuran/γ-butyrolactone/poly(ether imide) (THF/γ-BL/PEI) are investigated from 30 to 50°C. This is a membrane-forming system with a high He-selectivity. Cloud point measurements show that the two binary polymer solutions THF/PEI and γ-BL/PEI exhibit miscibility gaps which close towards the centre of the ternary phase diagram where the mixtures become homogeneous (cosolvency). Vapour pressures were determined for the subsystem THF/γ-BL. For the theoretical calculations the Gibbs energy of mixing is formulated according to the Flory-Huggins theory and the interaction parameter χ THF γ-BL calculated from the vapour pressure…

Use of a portable device to record maximum inspiratory flow in relation to dyspnoea in patients with COPD

2011

SummaryForced inspiratory measures have been described to reflect the reduction in dyspnoea upon bronchodilation in severe COPD. Based on this we evaluated the applicability and usefulness of a portable device for the assessment of forced inspiration. In 37 patients with COPD (GOLD II/II/IV n = 16/15/6, mean ± SD FEV1 46.2 ± 15.4%pred) lung function was recorded prior to inhalation of 24 μg formoterol and 30 min later. Assessments comprised spirometry including forced inspiration, body plethysmography, maximum inspiratory flow (InCheck, Clement Clarke), and changes in dyspnoea via visual analogue scale (VAS). The sequence was repeated on a second day to assess reproducibility. Bronchodilati…

Intrinsic Viscosities of Polyelectrolytes: Determination and Modeling of the Effects of Extra Salt

2011

Based on early measurements of J. J. Hermans and co-workers (D. T. F. Pals, J. J. Hermans, Recl. Trav. Chim. Pays-Bas 1952, 71, 513-520; D. T. F. Pals, J. J. Hermans, J. Polym. Sci. 1950, 5, 733-734; D. T. F. Pals, J. J. Hermans, J. Polym. Sci. 1948, 3, 897-898), the present contribution demonstrates how primary data should be evaluated in order to obtain reliable intrinsic viscosities. This procedure yields detailed information on the changes of the intrinsic viscosities and of the corresponding viscometric interaction parameters caused by an increasing salinity of water. Both quantities decline from a maximum value in the pure solvent to a minimum value, which is approached in the limit o…

Intrinsic viscosities of polyelectrolytes in the absence and in the presence of extra salt: Consequences of the stepwise conversion of dextran into a…

2011

Abstract Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90. The dependence of the logarithm of the relative viscosity on polymer concentration c is in all cases reproduced quantitatively by three characteristic parameters: [ η ], the intrinsic viscosity; B , a viscometric interaction parameter (related to the Huggins constant); [ η ] , a parameter required only for polyelectrolytes at low concentrations of extra salt. In pure water [ η ] increases more than 80 times as the fraction f rises from zero to 0.90 and [ η ] starts from zero and goes up to ≈71 mL/g. Upon the addition of NaCl [ η …

Swelling of the buccal cheek: an unusual presentation of primary tuberculosis.

2007

On the viscosity of moderately concentrated solutions of poly(ether imide) in a mixed solvent of marginal quality

2000

Abstract Viscosities η were measured for moderately concentrated (15.5 wt%) solutions of poly(ether imide) (PEI) as a function of the composition of the cosolvent tetrahydrofuran (THF) plus γ-butyrolactone (γ-BL). The solutions are almost by a factor of four less viscous when THF predominates than when γ-BL is the major component of the solvent mixture. Furthermore, the viscosity passes a minimum as the composition of the mixed solvent is varied. Both observations can be well understood in terms of the viscosities of the mixed solvents and the hydrodynamic interaction between the polymer molecules. The pronounced dissymmetry of η as a function of the composition of the mixed solvent η resul…