Structures and Morphologies

Polycarbonates exhibit no crystalline structure when used in common manufacturing processes. At the molecular level, there is some evidence of localized ordering along a chain. It is believed that the polycarbonate repeat units can fold back onto the chain in a structure that resembles the letter Z. These individual units do not associate on a large enough scale to create a regular crystalline material. Under specific conditions, such as forcing the polymer to cool very slowly, we can create small crystalline domains. Since these conditions are not met in commercial processes, it is safe to say that the polycarbonates that we encounter are universally amorphous. 

The knowledge of the structure and the morphology of the metal clusters is necessary if we want to understand the reaction kinetics at the atomic level. The more versatile technique to study the structure and the morphology of supported metal cluster is TEM. It can provide directly the structure and the epitaxial relationships on a collection of clusters in the diffraction mode. By High Resolution TEM it is possible to get this information at the level of one cluster [83]. By using high-resolution profile imaging it is possible to measure the lattice distortion at the interface [84], These capabilities are very unique for TEM. Such structural information can be obtained in situ by diffraction techniques but only on a collection of clusters [14, 29]. To illustrate the structural characterization by TEM we present the case of Pd clusters on MgO(l 0 0), which will be discussed in the next sections. 

We have seen that electron microscopy and scanning probe microscopies are very complementary techniques to characterize the structure and the morphology of supported clusters. The internal structure can only be resolved by HRTEM while the surface atomic structure can be only revealed by STM or AFM. TEM gives accurate diameter measurements and height can only be measured in profile view that needs special sample preparation. STM or AFM give accurate height measurements but diameters can be obtained only after correction from the tip-sample convolution effect. 

In addition to the size of the molecules and their distribution, the shapes or structures of individual polymer molecules also play an important role in determining the properties and processability of plastics. There are those that are formed by aligning themselves into long chains of molecules and others with branches or lateral connections to form complex structures. All these forms exist in either two or three dimensions. 

Because of the geometry, or morphology, of these molecules some can come closer together and more orderly than others. These are identified as crystalline and all others that behave like spagetti as amorphous. Morphology influences such properties as mechanical and thermal, swelling and solubility, specific gravity, and other properties (mechanical, physical, chemical, electric, etc.). 

This behavior of morphology basically occurs with TP, not TS plastics. When TSs are processed, their individual chain segments are strongly bonded together during a chemical reaction that is irreversible. 

Thermal Expansion Phenoxy glass Epoxy-glass fiber 

Moisture Absorption Chlorotrifluorethylene Alkyd-glass fiber 

So far in this book, we have focused on aspects of polymer synthetic chemistry and what can be considered local structure, the arrangements of units in a chain and how these can be characterized spectroscopically. In the next few chapters our focus shifts to a more global scale and involves the physics and physical chemistry of polymer materials. We will start with the shapes or conformations available to chains in solution and the solid state, how these chains interact with one another and other molecules (e.g., solvents), and the- conditions under which chains can organize and aggregate into larger scale structures, as in crystallization (or, more briefly, some of the fascinating morphologies formed by block copolymers). 

FIGURE 8-1 Nylon spherulites observed under a polarized optical microscope. 

FIGURE 8-2 Schematic diagram of the volume of matter as a function of temperature 

However, certain materials, like window glass, have difficulty in crystallizing, sometimes because of their irregular structure and sometimes because it takes a while for the initially formed very small crystals, called 

Moreover, the polymer liquid state has certain characteristics that we normally associate with solids. This is because of chain 

There are a few polymers, such as polyfbutylene terephthalate) [178], poly-(trimethylene terephthelate) [179], poly(pivalolactone) [180,181], poly(methylene oxide) [182], linear polyethylene over an extended temperature range [183-185], and isotactic poly(propylene) [186-190], that crystallize in a temperature interval well removed from T, for which III-II regime transitions have been reported but without a maximum in the rate. There are many problems associated with the proper assignment of this transition. A major problem is the correct selection of the equilibrium melting temperature. This turns out to be a cmcial matter. 

Another matter of interest is the relationship between the temperature maximum, T nax. in the rate of crystallization and the equihbrium melting temperature. The analysis of extensive experimental data for the rates of growth of spherulites and overall crystallization shows that 

The determination of the unit-cell stmcture can be treated in a classical manner. The problem was initially thought to be a very complicated one. However, it became simplified when it was recognized that the whole of a long-chain molecule need not be in the unit cell. The deduction of the unit cell has not presented any major interpretative problems. In most cases the chains are parallel to one another in the 

Although we will not dwell in any detail on the properties of solution crystals in this chapter, it is important to recognize that electron-microscope observations of this kind do not lend themselves to a description of the interfacial structure on a molecular level. The gross morphological form and the orientation features are, however, well established. The molecular interfacial stmcture is consistent with several extremes, as is schematically indicated in Fig. 4.31 [196]. 

In one extreme, termed the regularly folded-adjacent-re-entry stmcture, the molecular chains appear to be accordion-like, making precise hairpin turns in order to yield the optimum level of possible crystallinity. However, equally consistent with the gross morphological features is the other model illustrated. Here, there is a distinct, disordered, amorphous overlayer. This schematic representation has popularly been termed the switchboard model. Both of these interfacial stmctures, and those in between, are consistent with the electron micrographs. The reason for introducing these concepts here is that a lamellar-type crystallite is also the universal mode of crystallization of a homopolymer from the pure melt. 

The liquid crystalline polymeric fibers exhibit high degree of order and orientation (greater than 0.9) compare to commodity polymeric fibers such as polyester, nylon, and polypropylene. The structure of commodity fibers is highly defective and contains chain folds and low amorphous orientation and typically crystallinity 30-65%, while the crystalline orientation is in the range of 0.9-0.98. 

The SEM images of PBO fibers show fibrillar structure. A hierarchical structure model [81] was proposed for oriented liquid crystalline polymers, in which a fiber is made up of macrofibrils. 

PBO molecuies are highly oriented in the microfibrii. (orientation factor 0.95) 

Static lattice simulation methods predict the tendency of polymers to avoid the strict regularity of a crystal by finding several lattice structures with similar energies but that vary in their chain-setting angle and cell vectors. The readiness with which the polymer sublattice in doped systems lowers its symmetry is echoed in both the defective static lattice simulations and the molecular dynamics treatment of lattice motions. In the former we observed the wide ranging response of the chains to even a small displacement of a dopant ion as described in Sections 5.3.2, 5.3.4, 5.4.2. and 5.6.3 while the dopant s power spectrum calculated in the course of the MD lattice simulations in Section 6.1 testifies to the important host-dopant interactions in potassium-doped polyacetylene. 

Some polymers (e.g., polyacetylene and polythiophene ) exhibit an additional morphological heterogeneity consisting of fibrils of dense material dispersed in a void, such that the polymer material and dopants occupy only about 50% of the volume. Although the sample is formally heterogeneous within the solid material, constituent phases are in such close proximity that not only may it be difficult to distinguish a boundary between them, but the constituents of the microdomains themselves are uncertain. Even single crystals which have been 

Most aromatic polyesters are semi-crystalline materials they exhibit crystalline and amorphous regions within one article. The processing of the polyester will have a profound effect on the relative ratios of the two morphologies. There is also the possibility, especially in highly oriented specimens such as biaxially oriented films and fibres, that a third morphology may emerge oriented amorphous . 

Polymer morphology will have a direct effect on the degradation and on the potential for stabilisation of the substrate. In most cases. 

Though it is outside the scope of this review to fully discuss the morphological complexities of aromatic polyesters, data are provided on the differences in crystallinity and structure of several important aromatic polyesters. 

Early work on morphological changes on tensile testing of PET 

Two studies [45, 46] on PTT structure were published almost simultaneously. Both determined that the unit cell was triclinic, with the parameters shown in Table 1.1. 

7 Wide-angle XRD patterns of injection-moulded nanocomposites. 

2 Wide-angle X-ray patterns of nanocomposites in feedstock compound form. 

3XRD patterns of melt-spun nanocomposite fibres. 

In contrast, the XRD spectra for the nanocomposite fibres recorded only two peaks at 20 position of 2.2 and 4.4°. The disappearance of the third and fourth order peaks (at 6 to 9° region) further suggest exfoliation of layered-silicate during the melt-spinning process. This may be associated with the elongational deformation of the the PP matrix during melt-spuming, which 

The appearance of tactoid layered-silicate in the PPEZ matrix may be attributed to high-concentration (12.5%) incorporation of low (9100) 

---

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

Structure and morphology. Most of the rare-earth elements were encapsulated in multilayered graphitic cages, being in the form of single-domain carbides. The carbides encapsulated were in the phase of RC2 (R stands for rare-earth elements) except for Sc, for which Sc3C4(20] was encapsulated[21]. 

Hartman, P. and Perdok, W.G., 1955. On the relations between structure and morphology of crystals. Acta Crystallogr., 8, 49. 

Mechanical properties of crystalline plastics are much more complex than those of amorphous plastics (Chapter 6, STRUCTURE AND MORPHOLOGY). For... 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

In order to get a quantitative idea of the magnitude of the effects of these temperature variations on molecular structure and morphology an experimental study was undertaken. Two types of polymerizations were conducted. One type was isothermal polymerization at fixed reaction time at a series of temperatures. The other type was a nonisothermal polymerization in the geometry of a RIM mold. Intrinsic viscosities, size exclusion chromotograms (gpc) and differential scanning calorimetry traces (dsc) were obtained for the various isothermal products and from spatially different sections of the nonisothermal products. Complete experimental details are given below. 

R. Borghi 1985, On the structure and morphology of turbulent premixed flames, in C. Bruno and S. Casci (Eds.), Recent Advances in the Aerospace Sciences, Plenum Press, New York, pp. 117-138. 

This review of PCL and its copolymers is largely drawn from the nonpatent literature and focuses primarily on aspects relevant to drug delivery. Methods of polymerization are considered at some length because of the impact on polymer structure and morphology, which in turn determine the permeability and biodegradability of the product. 

Lu CY, Adams JA, Yu Q, Ohta T, Olmstead MA, Ohuchi FS (2008) Heteroepitaxial growth of the intrinsic vacancy semiconductor AQSes on Si(l 11) Initial structure and morphology. Phys Rev B 78 075321-075326... 

Since 1976 until present time Toshima-t5q)e nanocolloids always had a major impact on catalysis and electrocatalysis at nanoparticle surfaces [47,210-213,398-407]. The main advantages of these products lie in the efficient control of the inner structure and morphology especially of bimetallic and even multimetallic catalyst systems. 

Structure and morphology of supported metal nanoparticles may differ drastically, depending on (i) their size, (ii) their interaction with support, (iii) the (electro)chemical environment, and, (iv) since very often particles do not attain equUibrium shapes, also on the preparation conditions and sample prehistory. 

Full evaluation of functionalized ceramics requires the ability to characterize the spatial variations in structure and morphology. Using NMRI, it is possible to map the underlying structure on a spatial scale of hundreds of microns. 

Usually polymeric substances of appropriate chemical structure and morphology which promote the miscibility of incompatible materials. Block copolymers are especially useful surfactants at the polymer/polymer interface because the two blocks can be made up from molecules of the individual polymers to be mixed. Typical compatibilisers in polymer blends are LDPE-g-PS in PE/PS CPE in PE/PVC acrylic- -PE, -PP, -EPDM in polyolefin/PA and maleic-g-PE, -PP, -EPDM, -SEBS in polyolefin/polyesters. 

The importance of hydrophobic binding interactions in facilitating catalysis in enzyme reactions is well known. The impact of this phenomenon in the action of synthetic polymer catalysts for reactions such as described above is significant. A full investigation of a variety of monomeric and polymeric catalysts with nucleophilic sites is currently underway. They are being used to study the effect of polymer structure and morphology on catalytic activity in transacylation and other reactions. 

---