Page 496 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Testing and Spectrometric Characterization of Polymers 459

dislocation mechanism. In all cases, the thickness of the lamellar sheets is about 12 nm indicating
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multiple folding of the PEO chains. The lamellar sheets disappear at about 60 C though the melting
o
o
point is listed to be 70 C. On cooling, the lamellar structures reappear about 50 C.

The morphology of spin-cast film, thickness of 180 nm, from polycaprolactone shows many

spherulitic structures with fibrillar nanostructures formed of lamellae lying edge on (about 10 nm
thick) and areas with lamellar sheets lying flat on. Different crystalline structures are found when

the sample is melted and crystallized as a function of temperature. These two studies reinforce the
complex inner relationship between physical treatment and nanostructure.
While some structures show seemingly independent spherulitic structures on the surface we
know from other studies that these structures are connected to one another and to the more amor-
phous regions overall giving a material with a characteristic flexibility and strength. In general,

chains are shared with adjacent areas allowing a sharing of stress–strain factors.
Atomic force microscopy is important for biological as well as synthetic macromolecules. Several
examples are given to illustrate applications. Collagen is an important natural protein that is pre-
sent in many tissues, including bones, skin, tendons, and the cornea. It is also employed in medical
devices such as artificial skin, tendons, cardiac valves, ligaments, hemostatic sponges, and blood

vessels. There are at least 13 different types of collagen. ATF can image collagen molecules and
fibers and their organization allowing identification of the different kinds of collagen and at least

surface interactions.
Atomic force microscopy allows the study of cell membranes. The precise organization of such
cell membranes is important since they play a role in cell communication, replication, and regula-
tion. It is possible to study real-time interactions of such biologically important surfaces. Further,
bilayers modeled or containing naturally produced bilayers are used as biosensors. Again, inter-
actions of these biomembranes can be studied employing AFM. For instance, the degradation of
bilayers by phospholipases, attachment of DNA, and so on can be studied on a molecular level.
In another application, antibody–antigen interactions have been studied employing AFM. One
application of this is the creation of biosensors to detect specific interactions between antigens and

antibodies.

13.2.5 SECONDARY ION MASS SPECTROSCOPY
Secondary ion mass spectroscopy (SIMS) is a sensitive surface analysis tool. Here, the mass analy-
sis of negative and positive ions sputtered from the polymer surface through ion bombardment is
analyzed. The sputtering ion beam is called the primary ion beam. This beam causes erosion of the
polymer surface removing atomic and molecular ions. Then these newly created ions, composing
what is called the secondary ion beam, are analyzed as a function of mass and intensity. Depth of
detection for SIMS is of the order of 20–50 Å. Because it is the ions in the secondary ion beam that
are detected, the mass spectra obtained from SIMS is different from those obtained using simple
electron impact methods. The extent of particular ion fragments observed is dependent on a number
of factors, including the ionization efficiency of the particular atoms and molecules composing the

polymer surface.
Secondary ion mass spectroscopy can detect species that are present on surfaces of the order of
parts-per-million to parts-per-billion.

13.3 AMORPHOUS REGION DETERMINATIONS
Experimental tools that have been employed in an attempt to characterize amorphous regions are
given in Table 13.1. Techniques such as birefringence and Raman scattering give information related
to the short-range (< 20 Å) nature of the amorphous domains while techniques such as neutron scat-
tering, electron diffraction, and electron microscopy gives information concerning the longer-range
nature of these regions.

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