Scales of Structure in Polymers

Figure 12.4. Hierarchy of length scales of structure and time scales of motion in polymers. Tg denotes the glass transition temperature. After Uhlherr and Theodorou (1998) (courtesy Elsevier...

The nano-scale structures in polymer layered-silicate nano-composites can be thoroughly characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD is used to identify intercalated structures. XRD allows quantification of changes in layer spacing and the most commonly used to probe the nano-composite structure and... 

Thus, there are three possible pathways for the radiation degradation of polymer molecules neutral radical, cation-radical and/or anion-radical intermediates. Interest in the formation of these three types of reaction intermediates has fluctuated over the years with the utilization of different techniques and with the particular interests of different investigators. It is likely that all three species will be produced, but their relative importance in the degradation mechanism will depend on the chemical structure of the polymer. Evidence for their involvement will depend on the experimental methods used and the temperature and time scale of observation. In this paper we illustrate our investigations of many of the fundamental aspects of the radiation degradation of polymers through studies of series of polymers and copolymers. 

Contemporary polymer theory considers segments of the primary structure to be the statistical unit comparable in size to that of solvent molecules. The large number of segments in polymers and the small scale of AGmix, A Hmix, and A.Smix allow their thermodynamics to be preferably described statistically (Smith, 1982), thereby permitting the following equations ... 

The structure of polymer surfaces and thin polymeric films at the mesoscopic scale is of interest, both for application and basic research [1] As the size of many technological devices decreases, the natural length scales of many typical polymers such as the radius of gyration, the persistence length, or the domain size in block copolymers, match the feature size and thus the materials are expected to display a new behaviour [2-5], On the other hand, the tendency towards spontaneous structure forma-... 

As our understanding of polymer processibility increases there is greater scope to produce increasingly complex and subtle structures. The trend has been towards a progressively finer scale of structure which in some cases, has moved well below the sub micron barrier. 

As the molecular size of most gases is much smaller than any scale of structure expected in polymer blend morphology, diffusion and permeability of gases can be employed to determine the phase behavior of a polymer blend. Therefore, the study of transport phenomena in blends would be motivated not only by the requirements of producing improved barrier materials but also by the continuous interest in the nature and characterization of polymer blend morphology. 

Growth processes as they emerge from crystallization have an enormous potential for pattern formation at multiple length scales. Again, the example of polymer crystallization can be applied to demonstrate this feature in the bulk, banded, spheruUtic patterns are formed which display order at scales up to the cm-scale. A deeper imderstanding of non-equilibrium growth mechanisms will be an essential key for creating ordered structures in polymer systems. 

There is yet a larger scale of organization in many crystalline polymers, known as spherulites. These spherical structures are composed of many crystalline lamellae, which have grown radially in three dimensions and which are connected by amorphous molecular segments (Keith, 1969). Spherulites are easily seen with an optical microscope between crossed polarizers, and under these conditions they exhibit a characteristic pattern with circular birefringent areas possessing a Maltese cross pattern, as shown in Figure 1.11. 

In conclusion, a simple and practical method of scraping was proposed to construct large-scale rough structures on polymer surfaces so as to control their surface wettability effectively. This method can be readily extended to most of the engineering plastics and to enhance the hydrophilicity of hydrophilic polymers as well as the hydrophobicity of hydrophobic ones. Importantly, this study sheds some light on the new boundary between hydrophilicity and hydrophobicity from the physicochemical viewpoint, which may offer a promising future for practical applications. 

Tertiary structure (1) The folding of a protein molecule into globular shapes. (2) Large-scale folding structure in a linear polymer that is at a higher order than secondary structure. For proteins and RNA molecules, the tertiary structure is the specific three-dimensional shape into which the entire chain is folded. Compare primary structure, quaternary structure, and secondary structure. 

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