Molecular Gels and their Fibrillar Networks - Soft Fibrillar Materials: Fabrication and Applications - page 5

greater than about the amorphous (non-crystalline) ones. Yet, the ability of gels
made with the amorphous (non-crystalline) 1D objects to recover their viscoelastic
properties after cessation of severe shearing [24b] is much greater because many
of them are in dynamic equilibria which allows self-annealing with time.
The study of 1D objects, especially those composed of s, and their

gels requires multidisciplinary approaches among chemists, physicists, chemi-
cal engineers, biologists, and theoreticians. Research in this area, a branch of
supramolecular chemistry, is important because systems based upon 1D objects
and their assemblies, especially if the keys to designing them de novo can be
discovered, can yield fundamental understanding of complex and highly selective
catalytic processes, useful devices, and new ways to exploit systems available in
nature. It can also shed light on the evolution and function (or malfunction) of
systems of important biomolecular fibers that are involved with blood clotting
and neurodegenerative diseases such as Alzheimer's, mad cow disease, and sickle
cell anemia [29]. Also, fiber aggregates of small molecules are used to modify
the mechanical properties of polymers [30] and food-related oils [31]. Ingenious
manipulation of gelators in sols can lead to monodomains of 1D viscoelastic objects
which are centimeters long [32] and may be useful in biological applications.
The questions of ''How'' and ''Why'' molecules with such diverse structures
organize into 1D objects - fibers, tapes, nanotubes, and so on, with very high
aspect ratios - remain largely unanswered. Although there are several theoretical
[33-36] and experimental approaches [9, 15-17b, 19c,d,e, 37-40] to explain such
aggregation and growth and even some predictive models for molecules with
specific structures [19a,b, 35, 41-43], a generally applicable set of rules for when
1D objects will form is not available. It is likely that more than one basic
mechanism controls the aggregation of molecules into the 1D objects, and the
specific mechanism depends on the structure of the molecules, the nature of the
solvent in which aggregation occurs [44], and the mode by which the sol phase
is transformed into a gel [45]. Besides the need for strong attractive interactions
along the long axis of the objects [46], there seem to be no real unifying principles.
Although this chapter cannot present solutions to the parts of this science that
remain unresolved, it can, is intended to, and hopefully will present a current
picture of the state of the art in ways that allow the reader to discern where fruitful
approaches to solutions may lie.

LMOG

1.2
Advances and Perspectives for Design of Gelators

1.2.1
Analyses of Structure Packing via X-Ray, Synchrotron, and Other Techniques,
Including Spectroscopic Tools

Elucidation of the molecular packing within the fibers formed during organogela-
tion remains a challenging task. However, this information can provide key