Mesophase precipitation

EFFECT ON FOAMABILITY OF MESOPHASE PRECIPITATION IN AQUEOUS SURFACTANT SOLUTIONS... 

The heHcoidal stmcture of such Hquid crystals can be carried to the soHd state by cross-linking (119,120) or by careful evaporation of solvent (121,122). Underivatized ceUulose can also form ordered mesophases (123,124), and gel films precipitated from lithium chloride—dimethyl acetamide retain some mesophase stmcture (122). 

Precipitation of Mesophase. If the modified, cropped feedstock is suitable then it is possible -... 

Ga203-based dodecyl sulfate mesophase[184] with a hexagonal structure was synthesized by the homogeneous precipitation method using urea. On removal of the incorporated surfactants by chemical or thermal treatment the mesophase structure collapsed. 

In the case of (Al,Ca)-MCM-41 type samples, because Ca nitrate was initially added into a basic solution (pH around 11), it was speculated that Ca(OH)j probably precipitated during the formation of the mesophase as a separate phase [4]. Upon the first calcination aiming at removing the surfactant molecules, Ca(OH)2, species present within the mesoporous volume, will undergo dehydration, yielding ultimately isolated CaO. The calcination temperature is... 

Precipitation from toluene at room temperature yields samples with only one transition at 285-286 K upon heating (type A). These samples are sticky solids at room temperature, in agreement with their low phase-transition temperatures. Type A is probably the type of material that most authors have obtained and investigated. Its Si MAS spectra below the transition temperature show one major peak at 8 = -28.5 ppm together with a much smaller peak at 5 = -20.8 ppm. These peaks disappear simultaneously at the transition to the mesophase whether or not they belong to one structure is not clear. The chemical shift value of the smaller peak indicates a transoid structure similar to that of PD6S. 

Solubility is governed not only by the solubility limits of the individual pitch species, but will also be affected by associations known to occur in pitch solutions. These may enhance or reduce the solubility of a particular pitch component. Precipitation of associated clusters or micelles broaden the MWD of the extract pitch and may provide the mechanism for direct mesophase conversion upon melting. The lower molecular weight species reduce viscosity to permit low temperature realignment of the larger, more aromatic species(10. From the MWD s, a larger fraction of pitch may be capable of mesophase formation if an optimized separation technique could be developed. 

---