Engineering of Small-Molecule Gels Based on the Thermodynamics and Kinetics of Fiber Formation - Soft Fibrillar Materials: Fabrication and Applications - page 97

More and smaller
spherulites

Nucleation
center

Δμ 2 (< Δμ 1 )

Fewer and
Bigger spherulites

Additive

Δμ 3 (= Δμ 1 )

Deactivated
nucleation center

Figure 2.9 Illustration of engineering of the multi-domain fiber networks of supramolecular
materials by controlling the primary nucleation.

be reduced by converting the small single fiber networks into bigger ones, which
can be achieved by reducing the primary nucleation rate (Figure 2.9). Another
way to strengthen such a material is to convert its multi-domain network into a
three-dimensionally interconnecting fibrillar network. In the following sections, the
different approaches that have been used to engineer the microstructures of multi-
domain networks will be presented. These include reducing the nucleation rate by
lowering the thermodynamic driving force and using suitable additives to reduce
the number of active nucleation centers, as well as by converting multi-domain net-
works into interconnecting fiber networks through thermodynamic control, seed-
ing, and ultrasound treatment. The volume confinement effects on the formation
of multi-domain fiber networks and the properties of the gels will also be presented.

2.4.2.1 Manipulating Fiber Network by Controlling Primary Nucleation
As mentioned earlier, the number of individual fiber networks in a unit volume
of a gel is determined by the primary nucleation rate of the gelator. From each
active nucleation center, an individual/single fiber network forms. According to
Equations 2.15, 2.16, and 2.22, the nucleation rate J can be reduced by producing
the gel at a higher temperature (a lower supersaturation μ / kT ), which reduces the
thermodynamic driving force or the degree of supercooling T . Equation 2.22 also

indicates that the nucleation kinetics can be controlled by manipulating the kink
kinetics coefficient and the correlation between the substrates and the nucleation
phase. It follows that suitable additives can shield the active nucleation centers (i.e.,
dust particles, bubbles, metaphases, etc.) and reduce the number of active nucle-
ating centers [27]. As illustrated by Figure 2.9, the number of spherulites will also