Engineering of Small-Molecule Gels Based on the Thermodynamics and Kinetics of Fiber Formation - Soft Fibrillar Materials: Fabrication and Applications - page 100

size of the spherulite is significant to the engineering of the rheological properties
of a gel. When the interactions between two neighboring spherulites are very weak
(mutually exclusive), the reduction in the nucleation rate can lead to the formation
of a material with a more integrated fiber network and improved elasticity. More
details on the rheological properties of gels with spherulitic fiber networks will be
discussed later in Section 2.5.

2.4.2.2 Switching between Multi-Domain Fiber Networks and Interconnecting Fiber
Networks
As a typical multi-domain fiber network, spherulitic fiber networks are commonly
present in gels. The clear domains in such a network make it distinct from one
with a non-discernible boundary because of the good interconnectivity/integrity
between the individual fiber networks (c.f. Figure 2.2a). Such an interconnecting
fiber network behaves like a single fiber network. Compared to an interconnecting
fiber network, a network consisted of spherulites is weaker if strong interactions
between neighboring spherulites do not exist. Therefore, converting spherulitic
fiber networks into interconnecting fiber networks can be a way to improve
the elasticity of materials. This conversion has been achieved by tuning the
supersaturation of a system or by using external stimuli such as ultrasound.

Supersaturation-Controlled Topological Modification of Fiber Networks Super-
saturation-dependent crystallographic mismatch branching provides an approach
to engineering the fiber networks on a micro/nano scale. It makes it possible
to produce different fiber networks using the same gelator/solvent pair.
Interconnecting fiber networks can be produced by processing the gelation at
extremely low supersaturation [34]. The advantage of the interconnecting fiber
network is its higher integrity, contributing to the higher elasticity of a material,
which will be discussed in Section 2.5. The switching from spherulitic fiber
networks to interconnecting fiber networks at low supersaturation has also been
observed in other gel systems, such as that formed by the gelation of two n -alkanes
by 5R-cholestan-3 -yl N -(2-naphthyl)carbamate [18a]. The advantage of this

approach is its simplicity, since the conversion is induced solely by changing the
temperature of gel formation. However, the extremely low supersaturation means
that the gelation has to happen at a very high temperature (for a fixed amount
of gelator) or extremely low gelator concentration. In addition, the temperature
window for this type of network is very narrow. The pore size of the fiber network
of a gel formed under such conditions is big, which may not be desired for some
applications. In addition, forming a gel at a high temperature is limited, especially
when some temperature-sensitive biomolecules are to be incorporated into the
material. Therefore, it is desirable that interconnecting fiber networks should be
produced at low temperatures.
To address the above problem, a self-seeding method was developed [34]. It was
observed that the thermodynamic driving force at the early stage of gelation is a key
factor that determines the topology of the final fiber network [12a, 18a]. Therefore,
manipulating the thermodynamic driving force at an early stage is important in

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