Untersuchung von Bitumina zur Herstellung von Öl-in-Wasser-Emulsionen

This work shows the differences between O/W emulsifiable (droplets smaller than 1 micron) and not O/W emulsifiable bitumens (forming droplets much bigger than 1µm). The findings of this study were used for the production of small-scale bitumen emulsions with an initially not emulsifiable bitumen to drop sizes below 1 micron. On the way there, first the bitumen was examined itself. Bitumens, which form bitumen emulsions with big droplets, show micro-phase separations at AFM. Bitumens forming very small droplets show a homogeneous surface without microphase separation. Bitumens are divided into four solubility groups: Saturates (S), aromatics (A), resins (R) and asphaltenes; Each group consits of mixtures of different substances with different structural characteristics itself. Nevertheless, these phases are homogeneously dispersed in very good emulsifiable bitumens. On AFM images of phase-separated bitumens one can distinguish several phases. First, these are island-like domains, which are formed from the agglomeration of asphaltene flakes. These islands are surrounded by a halo, which is composed of low molecular weight paraffins (C-15 to C-17) and the resin phase. The asphalt islands are higher molecular weight paraffins (C-20 to C-23), which crystallize in the so-called wavy Catanas. The islands are located in the maltene phase, which consists of saturated, aromatic and resin phase molecules. The degree of dispersion of the asphaltenes depends on their ability to stabilize the bitumen, which in turn is determined by the molecular structure. Asphaltenes consist fundamentaly of a polyaromatic hydrocarbon (PAH) and aliphatic groups which are substituted at the aromatic nucleus. In addition to different aromaticity and molecular weight the polarity of the fractions, or molecules promotes phase separation also. The polar or polarizable groups in bitumens are the resin fraction (R) and especially the asphaltene fraction (A). The polarity of these molecules comes from their aromatic skeleton with free π-electrons on the one hand and on the other hand from heteroatoms such as nitrogen, sulfur and oxygen. In the formulation of emulsions, these two fractions are taken particularly due to their surface activity. The key role is played by the asphaltenes, as they assemble irreversible at the oil-water interface. That is contrary to the resins and external surfactants. In experiments with the drop tensiometer it turned out that the surface activity of the polar substances in the bitumen depends on their solubility in the bitumen itself more than on hydrophilic groups for example carbonylic acid groups. The asphaltenes from a very well emulsifiable bitumen are in both solvents toluene and heptane mixed with toluene (70:30), the most surface active fraction. They do not aggregate; neither in aromatic nor in aliphatic solvents. These asphaltenes are perfect phase mediator between the aromatic and saturated phase, i.e. they are able to disperse the bitumen constituents in the interfacial film and in the bitumen itself as well. The interfacial films were characterized by TEM. Will the asphaltenes be extracted from the well emulsifiable bitumen, separations occur at the interface. For the less emulsifiable bitumens the resins are more surface active than their corresponding asphaltenes. This leads to a separation of the asphaltenes at the interface and therefore to an inhomogeneous interfacial fim. The inhomogeneity of the interfacial films leads to increased coagulation of the Bitumen droplets, which finally causes droplet coalescence and large average droplet sizes. From these results it can be concluded that a bitumen that shows phase separation at the surface is not able to form a homogeneous interface also. By adding asphaltene disperson agents (e.g. dodecyl benzene sulfonic acid) to a phase separated bitumen a homogenization of the interface of its emulsion droplets occurred. Consequently small-scale bitumen emulsions from originally not emulsifiable bitumens are produced (d (50) = 0.6 microns). Bitumen preferably forms W/O emulsions. By making such a bitumen emulsion and subsequent inversion in the same emulsifying prosess with the help of two surfactants (low HLB and high HLB) very small, but less stable, mean droplet sizes (d (50) = 0.7 microns) could be achieved in this work also

Untersuchung von Bitumina zur Herstellung von Öl-in-Wasser-Emulsionen

This work shows the differences between O/W emulsifiable (droplets smaller than 1 micron) and not O/W emulsifiable bitumens (forming droplets much bigger than 1µm). The findings of this study were used for the production of small-scale bitumen emulsions with an initially not emulsifiable bitumen to drop sizes below 1 micron. On the way there, first the bitumen was examined itself. Bitumens, which form bitumen emulsions with big droplets, show micro-phase separations at AFM. Bitumens forming very small droplets show a homogeneous surface without microphase separation. Bitumens are divided into four solubility groups: Saturates (S), aromatics (A), resins (R) and asphaltenes; Each group consits of mixtures of different substances with different structural characteristics itself. Nevertheless, these phases are homogeneously dispersed in very good emulsifiable bitumens. On AFM images of phase-separated bitumens one can distinguish several phases. First, these are island-like domains, which are formed from the agglomeration of asphaltene flakes. These islands are surrounded by a halo, which is composed of low molecular weight paraffins (C-15 to C-17) and the resin phase. The asphalt islands are higher molecular weight paraffins (C-20 to C-23), which crystallize in the so-called wavy Catanas. The islands are located in the maltene phase, which consists of saturated, aromatic and resin phase molecules. The degree of dispersion of the asphaltenes depends on their ability to stabilize the bitumen, which in turn is determined by the molecular structure. Asphaltenes consist fundamentaly of a polyaromatic hydrocarbon (PAH) and aliphatic groups which are substituted at the aromatic nucleus. In addition to different aromaticity and molecular weight the polarity of the fractions, or molecules promotes phase separation also. The polar or polarizable groups in bitumens are the resin fraction (R) and especially the asphaltene fraction (A). The polarity of these molecules comes from their aromatic skeleton with free π-electrons on the one hand and on the other hand from heteroatoms such as nitrogen, sulfur and oxygen. In the formulation of emulsions, these two fractions are taken particularly due to their surface activity. The key role is played by the asphaltenes, as they assemble irreversible at the oil-water interface. That is contrary to the resins and external surfactants. In experiments with the drop tensiometer it turned out that the surface activity of the polar substances in the bitumen depends on their solubility in the bitumen itself more than on hydrophilic groups for example carbonylic acid groups. The asphaltenes from a very well emulsifiable bitumen are in both solvents toluene and heptane mixed with toluene (70:30), the most surface active fraction. They do not aggregate; neither in aromatic nor in aliphatic solvents. These asphaltenes are perfect phase mediator between the aromatic and saturated phase, i.e. they are able to disperse the bitumen constituents in the interfacial film and in the bitumen itself as well. The interfacial films were characterized by TEM. Will the asphaltenes be extracted from the well emulsifiable bitumen, separations occur at the interface. For the less emulsifiable bitumens the resins are more surface active than their corresponding asphaltenes. This leads to a separation of the asphaltenes at the interface and therefore to an inhomogeneous interfacial fim. The inhomogeneity of the interfacial films leads to increased coagulation of the Bitumen droplets, which finally causes droplet coalescence and large average droplet sizes. From these results it can be concluded that a bitumen that shows phase separation at the surface is not able to form a homogeneous interface also. By adding asphaltene disperson agents (e.g. dodecyl benzene sulfonic acid) to a phase separated bitumen a homogenization of the interface of its emulsion droplets occurred. Consequently small-scale bitumen emulsions from originally not emulsifiable bitumens are produced (d (50) = 0.6 microns). Bitumen preferably forms W/O emulsions. By making such a bitumen emulsion and subsequent inversion in the same emulsifying prosess with the help of two surfactants (low HLB and high HLB) very small, but less stable, mean droplet sizes (d (50) = 0.7 microns) could be achieved in this work also

Depression, Antidepressants, and Neurogenesis: A Critical Reappraisal

The neurogenesis hypothesis of depression posits (1) that neurogenesis in the subgranular zone of the dentate gyrus is regulated negatively by stressful experiences and positively by treatment with antidepressant drugs and (2) that alterations in the rate of neurogenesis play a fundamental role in the pathology and treatment of major depression. This hypothesis is supported by important experimental observations, but is challenged by equally compelling contradictory reports. This review summarizes the phenomenon of adult hippocampal neurogenesis, the initial and continued evidence leading to the development of the neurogenesis hypothesis of depression, and the recent studies that have disputed and/or qualified those findings, to conclude that it can be affected by stress and antidepressants under certain conditions, but that these effects do not appear in all cases of psychological stress, depression, and antidepressant treatment