Engineering of Small-Molecule Gels Based on the Thermodynamics and Kinetics of Fiber Formation - Soft Fibrillar Materials: Fabrication and Applications - page 104

(a)

T

T1 > Tg

(a) uncontrolled
nucleation

(b) Inhibited
nucleation

(b)

T2 < Tg

(c)

T3 < T2

Mixed fiber network Pure fiber network

Figure 2.12 (A) A schematic description of
the homogenization of fiber network formed
during a non-isothermal crystallization pro-
cess by kinetically controlling the nucleation
of fibers. (a) a heterogeneous fiber network
formed due to the nucleation and growth
of fibers at different temperatures ( T 2 and
T 3 ) during the cooling period and (b) by ki-
netically inhibiting the nucleation of fibers
to suppress the fiber formation during the
early stage of a cooling process ( T 2 ), a

homogeneous fiber network can be formed
(at T 3 ). (B) Fiber networks of GP-1 (2 wt%)
formed in the absence (a) and presence of
0.005 wt% (b) and 0.01 wt% EVACP (c). Clear
boundary between individual spherulites are
discernible when the polymer is present.
With increase in polymer concentration, the
spherulites becomes larger, indicating inhib-
ited nucleation of GP-1 at a higher polymer
concentration. Reprinted with permission
from Ref. [24].

On the basis of the nucleation-growth mechanism, it is feasible that by kinetically
inhibiting the primary nucleation of the gelator molecules to prevent the occurrence
of fibers formed at the early stage of cooling, a system consisting of a homogeneous
fiber network can be created (Figure 2.12A). As has been mentioned, primary
nucleation is activated by nucleation centers, that is, dusts, bubbles, and so on, under
normal circumstances [10]. It has been demonstrated that the presence of certain
additives, particularly large polymer molecules with a rigid molecular structure, can
inactivate the nucleation centers by enhancing the structural mismatch between the
nucleating phase and the substrate [4c, 6c, 36]. This can retard the fiber nucleation
in the systems. On the basis of this, success has been gained in changing a
heterogeneous fiber network into a homogeneous network. A copolymer EVACP,
which has been demonstrated to be able to adsorb on fiber surface and enhance