A method for the preparation of uniaxially oriented thin films of terthiophene (20–50 μm thick) is introduced. It relies on the crystal growth with a Bridgman-type process that decouples nucleation and growth phenomena. An effective thermal gradient of 6–11.6 °C/mm has been used in which the sample (terthiophene powder deposited on either glass or fluorinated glass substrates) is displaced from a hot zone to a cold zone at a constant rate of 2.5–5 μm/s. The size and orientation of crystals have been investigated by polarized optical microscopy and X-ray diffraction measurements. A coexistence of two polymorphs of terthiophene has been observed, but optimal gradient conditions enabling the selective crystallization of only the room temperature stable polymorph have been found. Terthiophene films deposited on fluorinated glass substrates and crystallized using the thermal gradient technique show a stronger tendency to polymorphism and random orientation of crystallites for all gradient conditions tested. The monoclinic unit cell (a = 15.410 Å, b = 5.709 Å, c = 26.052 Å, β = 97.77°) of the room temperature phase orients its ab plane parallel to the substrate. Pole figures demonstrate the growth of uniaxially aligned crystals with the [100] and [−100] directions along the gradient axis. Finally, a tentative explanation for this peculiar in-plane orientation is given based on crystal morphology calculations.

This article deals with the physical modeling and numerical simulation of two-phase bubbly flow in an airlift internal loop reactor. The objective is to show the ability of computational fluid dynamics (CFD) to correctly simulate hydrodynamics and axial dispersion in such a bubbly reactor. The modeling of two-phase bubbly flow is based on the so-called two-fluid model derived from Reynolds-averaged Navier-Stokes equations in two-phase flow. From the local perspective, CFD leads to the distributions of phases, interfacial area, and velocity field in the whole volume of the airlift. Numerical simulations are discussed after comparison with experimental data. Sensitivity analysis is then presented to highlight the main parameters that must be taken into account in two-fluid modeling, especially in terms of interfacial transfer of momentum and turbulence. Once local hydrodynamics has been discussed and validated, the axial dispersion is then addressed. The axial dispersion coefficient is estimated from simulation of transport equation of salt concentration. Given the time evolution of the concentration, measured by a ''numerical'' probe located in computed airlift reactor, it is possible to numerically estimate the axial dispersion in the airlift, in the same way as in the experiments. The axial dispersion coefficient determined after simulation is compared with the experimental one and the ability of CFD to simulate mixing time and axial dispersion is shown. In addition, a physical analysis of axial dispersion is proposed.

This article focuses on the physical modeling and numerical simulation of mass transfer in two-phase bubbly flow in an airlift internal loop reactor. The objective of this article is to show the ability of computational fluid dynamics (CFD) to correctly simulate mass transfer in such a bubbly reactor. The modeling of two-phase bubbly flow is based on the socalled two-fluid model derived from Reynolds-averaged Navier-Stokes equations in twophase flow. From the hydrodynamic perspective, the flow is steady state. Given the steadystate distributions of phases, interfacial area, and velocity field in the whole volume of the airlift, mass transfer is computed and the evolution of oxygen concentration in the two phases is predicted. Numerical simulations are discussed after comparison to experimental data. The simulations are validated in terms of oxygen concentration in the liquid vs. time. Then, different points are discussed, in particular, the perfectly mixed reactor assumption in the liquid phase and the spatial and temporal heterogeneity of oxygen concentration in the gas arising from oxygen impoverishment in bubbles in the downcomer. This leads to heterogeneity of the transfer driving force between the gas and the liquid. Bubble age or residence time in the airlift loop reactor has been calculated to show the weak renewal of oxygen in bubbles in the downcomer. This discussion generates questions on the estimation of a global mass transfer coefficient from experiments in such a heterogeneous airlift reactor.

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