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1.
Soft Matter ; 13(12): 2322-2329, 2017 Mar 22.
Article in English | MEDLINE | ID: mdl-28261727

ABSTRACT

Film forming properties of semiconducting organic molecules comprising alkyl-chains combined with an aromatic unit have a decisive impact on possible applications in organic electronics. In particular, knowledge on the film formation process in terms of wetting or dewetting, and the precise control of these processes, is of high importance. In the present work, the subtle effect of temperature on the morphology and structure of dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) films deposited on silica surfaces by spin coating is investigated in situ via X-ray diffraction techniques and atomic force microscopy. Depending on temperature, bulk C8-BTBT exhibits a crystalline, a smectic A and an isotropic phase. Heating of thin C8-BTBT layers at temperatures below the smectic phase transition temperature leads to a strong dewetting of the films. Upon approaching the smectic phase transition, the molecules start to rewet the surface in the form of discrete monolayers with a defined number of monolayers being present at a given temperature. The wetting process and layer formation is well defined and thermally stable at a given temperature. On cooling the reverse effect is observed and dewetting occurs. This demonstrates the full reversibility of the film formation behavior and reveals that the layering process is defined by an equilibrium thermodynamic state, rather than by kinetic effects.

2.
J Colloid Interface Sci ; 430: 56-60, 2014 Sep 15.
Article in English | MEDLINE | ID: mdl-24998054

ABSTRACT

Steady shear viscosity measurements have been performed on 100 kDa poly(ethylene oxide) (PEO) dissolved in the protic ionic liquids ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) and in water. The zero shear viscosity in all three solvents increases with polymer concentration, falling into three concentration regimes corresponding to dilute, semi-dilute and network solutions. Huggins plots reveal three distinct solvent conditions: good (water), good-theta (EAN) and theta (PAN). However, differences in the transition concentrations, power law behaviour of the viscosities, and relaxation times arising from shear thinning in the two ILs can be directly related to the effects of solvent nanostructure.


Subject(s)
Ionic Liquids/chemistry , Polyethylene Glycols/chemistry , Quaternary Ammonium Compounds/chemistry , Viscosity
3.
Mol Pharm ; 11(2): 599-609, 2014 Feb 03.
Article in English | MEDLINE | ID: mdl-24400735

ABSTRACT

Drying is a common pharmaceutical process, whose potential to alter the final drug properties-even at relatively low temperatures-is often neglected. The present study addresses the impact of drying at 20 and 50 °C on wet-extruded calcium stearate (CaSt) pellets. Drying at 20 °C caused the majority of ibuprofen to accumulate at the pellet surface due to a strong convective flow from the pellet's center to the surface. In contrast, pellets dried at 50 °C still contained ibuprofen in the pellet's interior due to the higher drying rate and the associated film breakage during drying. Moreover, the higher drying temperature caused CaSt to form a second lamellar phase and ibuprofen to convert (partly) into its amorphous state. Overall, the drying process affected the solid state and the spatial ibuprofen distribution within the pellet. Knowledge of these effects can aid in tailoring advanced multipellet formulations.


Subject(s)
Calcium/chemistry , Chemistry, Pharmaceutical , Cold Temperature , Desiccation , Ibuprofen/chemistry , Ibuprofen/metabolism , Stearates/chemistry , Calorimetry, Differential Scanning , Spectrum Analysis, Raman
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