A smart functional gelator containing salen and sorbitol moieties has been synthesized, and it shows excellent gelation behavior in organic-water mixtures. The gel exhibits an efficient 'naked eye' response to copper (II) through a reversible gel-sol transition, which is associated with a color 10 80
The gelation behaviour of a low molecular weight gelator 2,4-(3,4-dichlorobenzylidene)-D-sorbitol (DCBS) in a binary solvent system has been studied. DCBS was soluble in pure ethanol and insoluble in pure methylcyclohexane. However, DCBS formed opaque gels in ethanol-methylcyclohexane mixtures when the methylcyclohexane content varied from 50% to 80%. Within this range, an increase in the amount of methylcyclohexane reduced the gelation time and also caused the minimum gelation concentration to decrease. Scanning electron microscopy showed that the three-dimensional network structures of the xerogels became denser (from tape-like structures to uniform fibres) when the methylcyclohexane content increased from 40% to 80%. The precipitates that formed in 90% and 100% methylcyclohexane had rod-like structures. X-ray diffraction of the xerogels showed that in the gel state, the DCBS gelator had lamellar packing, which was different from the structure of the precipitate. Fourier transform infrared spectroscopy of the xerogels showed that H-bonding was a driving force for the self-aggregation of the DCBS and it was enhanced as the methylcyclohexane content increased. To estimate the gelator-solvent interactions, the Flory-Huggins parameter was calculated for the DCBS gelator in the binary mixed solvent systems. Based on the values of the Flory-Huggins parameter, the gelation behaviours could be grouped into four domains (solution, partial gel, gel and precipitation). This is a simple method to predict the gelation behaviour of DCBS in some mixed solvents.
The gelation behavior of 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) in binary solvents has been systematically investigated. DMDBS is soluble in DMSO and insoluble in toluene (apolar) or 1-propanol (polar). When DMSO is added to a poor solvent at a certain volume fraction, DMDBS forms an organogel in the mixed solvent. With increasing DMSO content, the minimum gelation concentration increases and the gel-to-sol transition temperature decreases in both systems. However, compared with those in toluene-DMSO mixtures, the gelation ability and thermal stability are better in 1-propanol-DMSO mixtures. Scanning electron microscopy images reveal that the gelators aggregate to form three-dimensional networks. X-ray diffraction shows that the gel has a lamellar structure, which is different from the structure of the precipitate. Fourier transform infrared results reveal H-bonding is the main driving force for self-aggregation and indicate that stronger H-bonding interactions exist between gelators in 1-propanol-DMSO mixtures in contrast with toluene-DMSO mixtures. Attempts have been taken to correlate solvent parameters to gelation behavior in binary solvents. A Teas plot exhibits distinctly different solvent zones in the studied mixed solvents. The polar parameter (δp) indicates a narrow favorable domain for gel formation in the range of 1.64-7.99 MPa(1/2) for some apolar solvent-DMSO mixtures. The hydrogen-bonding parameter (δh) predicts that gelation occurs for values of 14.00-16.50 MPa(1/2) for some polar solvent-DMSO mixtures. The result may have potential applications in predicting the gelation behavior of 1,3:2,4-di-O-benzylidene-d-sorbitol derivatives in mixed solvents.
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