Molecular Gels and their Fibrillar Networks - Soft Fibrillar Materials: Fabrication and Applications - page 6

insights into the design of better gelators. Typically, fibers are characterized in
the gel state (native gel, henceforth) or the dried gel state (xerogel). Microscopic
characterization techniques such as polarized optical microscopy (POM), scanning
electron microscopy (SEM), transmission electron microscopy (TEM), and atomic
force microscopy (AFM) have provided pictures of fiber morphologies in xerogels.
Various characterization methods, as described in this section, can yield detailed
information on the structures of s of gels at different length scales. How-

ever, information from a single characterization method is usually insufficient to
reveal all aspects of a gel structure. Complementary tools should be employed and
data from them used to build a cohesive picture of gel structure, including fiber
morphology, molecular packing, intermolecular interactions, and so on.
A caveat noted by many others is reiterated here: the morphology of a xerogel does
not represent necessarily that of the native gel because fiber damage or secondary
assembly may occur during the drying process [47]. To minimize the possibility of
such complications, freeze-fracture/etching SEM, and cryo-TEM techniques have
been employed to visualize

SAFIN

SAFIN structures of native gels. For example, the 3D

network of 1D fibers of a steroid LMOG ( 2 ) in cyclohexane gel was revealed by

O

N

17

HO

2 3

B

A

100 μ m

(b)

(a)

Figure 1.2 (a) Electron micrograph of a
gel ( 2 ) replica with a carbon film overlay
showing the filament gel network protected
(Scale bars are 100 nm for the main im-
age and 10 nm for the inset); each filament
is imaged as three layers and consists of
a core (region A) sandwiched between a
more electron-transparent coating, the outer

edges of which are marked with arrows at
B. Reprinted with permission from Ref. [48].
Copyright 1986 Elsevier.) (b) Optical micro-
graphs of a 0.01 M 3 /silicone oil gel at room
temperature viewed through crossed polars;
sample thickness = 0.8 mm. (Reprinted with
permission from Ref. [49]. Copyright 2000
American Chemical Society.