Molecular Gels for Controlled Formation of Micro-/Nano-Structures - Soft Fibrillar Materials: Fabrication and Applications - page 160

5
Molecular Gels for Controlled Formation of
Micro-/Nano-Structures
Jing-Liang Li and Xiang Yang Liu

5.1
Introduction

The preparation of nanostructured materials such as nanoparticles, nanofibers,
and nanowires have been a focus of research in the last two decades. Due to their
large surface-to-volume ratio and superior properties compared to the conventional
macroscopic materials, these materials promise to revolutionize many fields such
as electronics, catalysis, and biomedicine. Hence, controlling the growth of these
nanostructures has been a global interest. Although controlling the formation of
macroscopically sized inorganic materials can be easily achieved, it is a challenge
if the size of a material is reduced to a micrometer or nanometer scale. Synthesis
of structures using organic templates has been demonstrated to be a simple and
convenient approach, since the organic matter can be easily removed by calcination
or suitable solvents. Theses organic templates include colloidal particles [1] and
fibers of polymers [2], aggregates of surfactants [3], carbon materials such as
carbon nanotubes [4], organic crystals and fibers in small-molecule gels ( SMGs ),

and polymer gels [5].
An SMG (also known as a molecular gel) is a two-phase system, in which
the molecules of a gelator self-assemble into a three-dimensional (3D) network
through non-covalent forces [6]. The 3D network traps the liquid/solvent and serves
as a backbone to make the gel a semi-solid self-supporting material. Although
nanostructures have been synthesized with polymer gels as templates [7], the
advantage of SMGs is that they are physically reversible due to the non-covalent
assembly of the gelator molecules. That is, the fiber network can be dissolved by
suitable stimuli such as elevated temperature or the addition of certain additives
[8]. The reversible assembly can thus allow convenient recovery of the materials
synthesized [8a]. Depending on the properties of the inorganic materials formed,
the gel composites can be readily used for various purposes such as antimicrobial
applications (with silver nanoparticles) [9].
The supramolecular architectures formed in SMGs are diverse, and include
fibers, helical, thin sheets, and lamellar structures, and so on [6, 10]. This solid part
is generally less than 5% of the total mass of a gel. Therefore, a gel is essentially