Water-rich system hydrotrope

Hydrotropes with their gel-prevention action are an essential part of liquid cleaners for which they provide two essential functions (a) they allow high surfactant concentrations in the formulation by preventing its gelling at the low water concentrations employed, and (b) they prevent gel formation in extremely water-rich systems under laundering conditions. 

The results are straight forward and the interpretation immediately evident. The liquid crystalline phase formed in these extremely water rich systems was destabilized by the dicarboxylic acid and transformed to an isotropic solution. The conclusion that the hydrotropic action of the dicarboxylic acid is intimately related to its capacity to destabilize a liquid crystalline phase also under the water-rich conditions during actual laundering conditions appears well justified. 

In the nonionic system (Figure 4), C21-DA K2 salt also acts as hydrotrope in the water-poor (reversed) micellar region (l.e., in the vicinity of composition d). Indeed, in this region, its efficiency appears to be greater than in the water-rich region. 

On the contrary, in the system containing the hydrotrope, ethanol, the C-OH stretching frequencies shifted only sUghtly downward by 2 cm in the y position upon addition of solely AP molecules. Unlike Transcutol, ethanol stayed in the interface and the solubilized additives were localized more in the water-rich core than in the interface. As a result, a stronger effect was detected in the water-rich core (water behavior) than in the interface that was neutralized by the presence of ethanol (3/1 or 0.5 mole ratio of ethanol/AA or AP). Additionally, based on similar effects in the P and y positions, it was assumed that the ethanol contributed to the location of the AP molecule and attracted it closer to the hydrophilic region. 

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