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 as
well as with molecules forming other types of self-assembled materials.
The results also reveal several important insights into the factors
favoring the gelation of solvents by DBS. The ability of a solvent
to accept or donate a hydrogen bond is much more important than solvent
polarity in determining whether mixtures with DBS become solutions,
clear gels, or opaque gels. Thermodynamically derived parameters could
not be correlated to the physical properties of the molecular gels
unless they were dissected into their individual HSPs. The DBS solvent
phases tend to cluster in regions of Hansen space and are highly influenced
by the hydrogen-bonding HSP, δh. It is also found
that the fate of this molecular gelator, unlike that of polymers,
is influenced not only by the magnitude of the distance between the
HSPs for DBS and the HSPs of the solvent, Rij, but also by the directionality of Rij: if the solvent has a larger hydrogen-bonding
HSP (indicating stronger H-bonding) than that of the DBS, then clear
gels are formed; opaque gels form when the solvent has a lower δh than does DBS.