No abstract

When acrylonitrile is added to the Belousov−Zhabotinsky reaction, periodic polymerization is observed. (Pojman, J. A.; Leard, D. C.; West, W. W. J. Am. Chem. Soc. 1992, 114, 8298). The polymer's structure and the amount of bromine in the polymer sample were determined by 13C NMR and elemental analysis, respectively. Carbon-13-labeled malonic acid indicates that polymerization of acrylonitrile is initiated by malonyl radical. The bromous radicals are believed to terminate the polymer leaving an alcohol group on the polymer end. Further analysis of the polymer sample confirms that the sample is partially brominated. Numerical simulations based on a modified FKN mechanism are found to be in good agreement with experimental findings. Simulations indicate that periodic termination of the polymer chain by bromine dioxide, not the periodic initiation by malonyl radical, is the dominant cause of the periodic polymerization. Similar results were found in the malonyl-controlled variant of the BZ reaction.

New experimental results on the oscillatory dynamics of the radical-controlled Belousov-Zhabotinsky reaction (the Ra ´cz system) in a batch reactor are reported. The system exhibits oscillations with no induction period, a typical feature of the radical-controlled mechanism. However, in the presence of acetylacetone (CH 2 -(COCH 3 ) 2 ), an induction period is observed before oscillations start, which increases with increasing acetylacetone concentration. There is a critical concentration of acetylacetone at which no oscillations occur. Quenching of radical-controlled oscillations is also observed at low and high malonic acid concentrations as well as at low and high sulfuric acid concentrations. An induction period is observed before the onset of radical-controlled oscillations at sulfuric acid concentrations g5.5 M. The duration of radical-controlled oscillations reaches a maximum at an intermediate sulfuric acid concentration. Numerical simulations based on the Radicalator model predict limits of malonic acid and sulfuric acid concentration within which oscillations are observed. The Radicalator model with additional reactions involving (i) CH 2 (COCH 3 ) 2 + Ce 4+ f • CH-(COCH 3 ) 2 , (ii) • CH(COCH 3 ) 2 + BrO 2 • f products, and (iii) • CH(COCH 3 ) 2 + • CH(COCH 3 ) 2 f products also predicts lengthening of induction period with the increase of acetylacetone concentration and suppression of oscillations at high acetylacetone concentration. Inclusion of the reaction between acetylacetone and HOBr had no effect.

The fabrication of ordered inorganic arrays of varying length scales and with multimodal porosities is of practical importance owing to their potential application in many areas of materials chemistry, including catalysis and separations science. [1,2] A common approach to the controlled synthesis of this class of materials, first exploited in the synthesis of the MCM-41 family of molecular sieves, is to polymerize the inorganic phase around an organic template by using a sol-gel process.[3] The organic phase is then removed by calcination leaving a void space that is a replica of the size, orientation, and arrangement in space of the template. By using multiple templates of different length scales, hierarchically porous inorganic structures containing various combinations of micro-, meso-, and macropores have been realized. [4][5][6][7][8][9] We report herein the creation of a mesoporous silica monolith that contains oriented macroporous channels, which is achieved by the application of an electric field to a hydrogel template during polymerization and cross-linking. [8,9] To the best of our knowledge, this is first time an external electric field has been used to create ordered, hierarchical meso-/ macroporous silicate materials.The template matrix is created through the electrical alignment of a polyacrylamide hydrogel, which is accomplished by copolymerizing a mixture of acrylamide functionalized with immobiline and bisacrylamide in the presence of an electric field (60 V cm À1 ). The presence of this field creates interstitial voids of approximately 10 mm in diameter. The channel structure, which can be imaged through confocal microscopy, is present in the field-oriented hydrogel (Figure 1 a), but is replaced by a disordered structure (Figure 1 b) when no field is applied.The silicate phase is introduced through the immersion of a freestanding hydrogel monolith in neat tetramethylorthosilicate (TMOS). Hydrolysis and condensation occurs as the TMOS infuses the hydrogel and reacts with water trapped in the voids. After a period of 24 h a hard solid white monolith, close in size to the hydrogel template, is formed. Calcination under O 2 at 500 8C removes the organic phase leaving a porous silica monolith.Scanning electron micrographs of this material, imaged parallel to the electric field direction (Figure 2 a), show striations oriented in the field direction. No such features are observed when the disordered template is used, which suggests that the channel/hydrogel interface is replicated

The fabrication of ordered inorganic arrays of varying length scales and with multimodal porosities is of practical importance owing to their potential application in many areas of materials chemistry, including catalysis and separations science. [1,2] A common approach to the controlled synthesis of this class of materials, first exploited in the synthesis of the MCM-41 family of molecular sieves, is to polymerize the inorganic phase around an organic template by using a sol-gel process.[3] The organic phase is then removed by calcination leaving a void space that is a replica of the size, orientation, and arrangement in space of the template. By using multiple templates of different length scales, hierarchically porous inorganic structures containing various combinations of micro-, meso-, and macropores have been realized. [4][5][6][7][8][9] We report herein the creation of a mesoporous silica monolith that contains oriented macroporous channels, which is achieved by the application of an electric field to a hydrogel template during polymerization and cross-linking. [8,9] To the best of our knowledge, this is first time an external electric field has been used to create ordered, hierarchical meso-/ macroporous silicate materials.The template matrix is created through the electrical alignment of a polyacrylamide hydrogel, which is accomplished by copolymerizing a mixture of acrylamide functionalized with immobiline and bisacrylamide in the presence of an electric field (60 V cm À1 ). The presence of this field creates interstitial voids of approximately 10 mm in diameter. The channel structure, which can be imaged through confocal microscopy, is present in the field-oriented hydrogel (Figure 1 a), but is replaced by a disordered structure (Figure 1 b) when no field is applied.The silicate phase is introduced through the immersion of a freestanding hydrogel monolith in neat tetramethylorthosilicate (TMOS). Hydrolysis and condensation occurs as the TMOS infuses the hydrogel and reacts with water trapped in the voids. After a period of 24 h a hard solid white monolith, close in size to the hydrogel template, is formed. Calcination under O 2 at 500 8C removes the organic phase leaving a porous silica monolith.Scanning electron micrographs of this material, imaged parallel to the electric field direction (Figure 2 a), show striations oriented in the field direction. No such features are observed when the disordered template is used, which suggests that the channel/hydrogel interface is replicated