Comparing and Correlating Solubility Parameters Governingthe Self-Assembly of Molecular Gels Using 13:24-Dibenzylidene Sorbitolas the Gelator

摘要

Solvent properties play a central role in mediating the aggregation and self-assembly of molecular gelators and their growth into fibers. Numerous attempts have been made to correlate the solubility parameters of solvents and gelation abilities of molecular gelators, but a comprehensive comparison of the most important parameters has yet to appear. Here, the degree to which partition coefficients (log P), Henry’s law constants (HLC), dipole moments, static relative permittivities (εr), solvatochromic ET(30) parameters, Kamlet–Taft parameters (β, α, and π), Catalan’s solvatochromic parameters (SPP, SB, and SA), Hildebrand solubility parameters (δi), and Hansen solubility parameters (δp, δd, δh) and the associated Hansen distance (Rij) of 62 solvents (covering a wide range of properties) can be correlated with the self-assembly and gelation of 1,3:2,4-dibenzylidene sorbitol (DBS) gelation, a classic molecular gelator, is assessed systematically. The approach presented describes the basis for each of the parameters and how it can be applied. As such, it is an instructional blueprint for how to assess the appropriate type of solvent parameter for use with other molecular gelators aswell as with molecules forming other types of self-assembled materials.The results also reveal several important insights into the factorsfavoring the gelation of solvents by DBS. The ability of a solventto accept or donate a hydrogen bond is much more important than solventpolarity in determining whether mixtures with DBS become solutions,clear gels, or opaque gels. Thermodynamically derived parameters couldnot be correlated to the physical properties of the molecular gelsunless they were dissected into their individual HSPs. The DBS solventphases tend to cluster in regions of Hansen space and are highly influencedby the hydrogen-bonding HSP, δh. It is also foundthat the fate of this molecular gelator, unlike that of polymers,is influenced not only by the magnitude of the distance between theHSPs for DBS and the HSPs of the solvent, Rij, but also by the directionality of Rij: if the solvent has a larger hydrogen-bondingHSP (indicating stronger H-bonding) than that of the DBS, then cleargels are formed; opaque gels form when the solvent has a lower δh than does DBS.