6 Cocoon Silk: From Mesoscopic Materials Design …
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RSF solution and found that quickly several white fibrous flocs were generated after
shearing the RSF solution, suggesting that shear flow has an impact on the formation
of SF nanofibrils [46].
6.4.2.4 Atomic Force Microscopic (AFM) Imaging
AFM can provide a nanoscale 3D profile of a sample surface by measuring the forces
between a sharp probe (with a radius of less than 10 nm) and the sample surface.
Different surface topographies and properties of samples can lead to different interaction values, which can be reflected and detected by the AFM instruments. To date,
AFM height imaging techniques have been widely applied to study the morphology
of silk materials. An advantage of AFM is that it can provide height information for
the samples at a very high resolution. It is determined that the thickness of nanofibrils
is much smaller than the diameters, suggesting that the SF nanofibrils are flat and
ribbon-like rather than symmetrical cylinder-like aggregates.
Recently, AFM has also been applied to distinguish the locations of different
constituents within composite RSF films. For instance, Xing et al. [61] have
incorporated wool keratin molecules @ gold nanoclusters (WK@AuNCs) into the
mesoscopic network structures of SF films and synthesized novel bio-degradable
WK@AuNCs-SF memristors and then successfully identified the location of such
clusters via AFM. As the WK@AuNCs accumulate electrons on their surfaces,
interactions with the conductive AFM tip can significantly differ from those of the
SF molecules. In this regard, Kelvin probe force microscopy (KPFM) is capable
ofimaging potential differences by measuring the surface charge distribution [61].
6.5 Self-assembly Kinetic Pathways of Silk Materials
6.5.1 Key Mesoscopic Structural Elements: Crystallites,
Crystal Networks, and Nanofibril Networks
From the introduction, it is clear that the mesoscopic hierarchical structure, to a
large extent, determines the macroscopic mechanical properties of SF materials. In
addition, the crystalline binding force turned out to be the most important factor
in stabilizing SF materials, while the nano-fishnet topology crystal networks and
nanofibril networks are another two of the other most essential structural elements at
the mesoscopic scale (Fig. 6.23). Specifically, after the formation of large amounts
of β-crystallites, a crystal network (also known as a nano-helical fibril) is spontaneously produced. Nevertheless, individual nano-helical fibrils are insufficient for
maintaining the structural integrity of SF materials. Several nearby nano-helical
fibrils can associate with each other and consequently form a nanofibril that displays
a nanorope structure. Finally, the gathering of the aforementioned nanofibers together
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RSF solution and found that quickly several white fibrous flocs were generated after
shearing the RSF solution, suggesting that shear flow has an impact on the formation
of SF nanofibrils [46].
6.4.2.4 Atomic Force Microscopic (AFM) Imaging
AFM can provide a nanoscale 3D profile of a sample surface by measuring the forces
between a sharp probe (with a radius of less than 10 nm) and the sample surface.
Different surface topographies and properties of samples can lead to different interaction values, which can be reflected and detected by the AFM instruments. To date,
AFM height imaging techniques have been widely applied to study the morphology
of silk materials. An advantage of AFM is that it can provide height information for
the samples at a very high resolution. It is determined that the thickness of nanofibrils
is much smaller than the diameters, suggesting that the SF nanofibrils are flat and
ribbon-like rather than symmetrical cylinder-like aggregates.
Recently, AFM has also been applied to distinguish the locations of different
constituents within composite RSF films. For instance, Xing et al. [61] have
incorporated wool keratin molecules @ gold nanoclusters (WK@AuNCs) into the
mesoscopic network structures of SF films and synthesized novel bio-degradable
WK@AuNCs-SF memristors and then successfully identified the location of such
clusters via AFM. As the WK@AuNCs accumulate electrons on their surfaces,
interactions with the conductive AFM tip can significantly differ from those of the
SF molecules. In this regard, Kelvin probe force microscopy (KPFM) is capable
ofimaging potential differences by measuring the surface charge distribution [61].
6.5 Self-assembly Kinetic Pathways of Silk Materials
6.5.1 Key Mesoscopic Structural Elements: Crystallites,
Crystal Networks, and Nanofibril Networks
From the introduction, it is clear that the mesoscopic hierarchical structure, to a
large extent, determines the macroscopic mechanical properties of SF materials. In
addition, the crystalline binding force turned out to be the most important factor
in stabilizing SF materials, while the nano-fishnet topology crystal networks and
nanofibril networks are another two of the other most essential structural elements at
the mesoscopic scale (Fig. 6.23). Specifically, after the formation of large amounts
of β-crystallites, a crystal network (also known as a nano-helical fibril) is spontaneously produced. Nevertheless, individual nano-helical fibrils are insufficient for
maintaining the structural integrity of SF materials. Several nearby nano-helical
fibrils can associate with each other and consequently form a nanofibril that displays
a nanorope structure. Finally, the gathering of the aforementioned nanofibers together