Columns aggregations, chromonics

The tendency for the molecnles of chromonic phases to aggregate into colnmns is present even in dilute solution where colnmn formation occnrs before a phase is formed. Althongh there may be a threshold concentration before aggregation begins to occur, there is no optimum column length and hence no critical concentration, with a further distinction being the absence of a Krafft temperature. Since the process of mesophase formation does not depend on the presence of flexible alkyl chains, there is no threshold temperature below which mesophases cannot form because the vital flexibility of the molecules has been frozen out. 

The tendency of chromonic molecules (Fig. 1) to aggregate into columns is present even in dilute solution (just as for amphiphile systems, where micelle formation occurs before a mesophase is formed). How-... 

A simple view of the state of a chromonic system is that the molecules are effectively insoluble in one dimension. The energy involved in their aggregation is more or less comparable to kT for each aromatic ring and only at extremely low dilution are there individual, unaggregated molecules. For ionic systems, the columns attract counterions, forming electrical double layers. This results in column-column repulsion, which causes the columns to behave as if they were separated by compressed springs. This effect presumably stabilizes the hexagonal structure of the M phase and causes the columns to move apart equally when the mesophase is diluted. 

Figure 3. The contrast between the pattern of aggregation of amphiphiles and chromonic molecules For amphiphiles, the energetically unfavorable contact between the hydrophobic alkyl chains and water molecules is reduced to more or less zero when a closed micelle is formed. In contrast, for chromonic systems, the fraction of the total molecular surface exposed to the solvent decreases as the columns lengthen, but there is no optimum aggregate size directly comparable to a micelle.

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