Polymer lamellar systems

Additional neutron scattering studies on different polymer systems could prove very important. Strobl [31,32,47,103] provides evidence that, for some polymers, lamellar crystallization is preceded by pre-ordering of the melt followed by formation of planar arrays of blocks. Investigating crystallization from the melt, Kaji and coworkers [25] find pre-ordering phenomena relating to orientational fluctuations of stiff polymer segments which, under appropriate conditions, determine phase separation prior to crystallization. 

A second important aspect is the structure of the l.c. phases. At low concentrations the polymer/water system exhibits in analogy to the monomer/water system a hexagonal phase, showing the typical fan like texture (Fig. 48). Additionally at higher concentrations a lamellar phase exists, which is separated from the hexagonal phase by a cubic phase of small extent (black area in Fig. 47). With this finding, the... 

Equation 19.11 means that the observed intensity must be multiplied by a factor q to obtain a better estimation of the periodicity in lamellar systems of semicrystalline polymers. The factor q is related to the change from the scatterers oriented at random to dispersers perfectly aligned (Fig. 19.8). This correction is implied, for instance, in the use of models of one-dimensional stacking [19]. As li iq) has been obtained from a one-dimensional model, it can be written as / (g) [19]. 

In both theories, the concentration of surfactant influences the morphology. In fact, a particular morphology (spherical micelles, cylinders, or lamellas) occurs at a certain concentration range. Ruokolainen et al. estimated that the lamellar morphology is highly preferable for polymer/surfactant systems in the wide concentration range [38]. 

Lamellar structures of polymer/surfactant systems were studied for polyelectrolyte/surfactant systems [37] as well as for coordination complexes [38]. 

Disregarding any detailed morphological models proposed for the lamellar crystals in semicrystalline polymers in the past half centiny, crystal imit cells in semicrys-talUne poisoners exactly obey the rules of classical crystallography, which consist of 7 crystal systems and 14 Bravais lattices (more precisely, there are only 6 crystal systems in polymer crystals, and the cubic system does not exist). Most of the unit cell determinations of the semicrystalline polymers rely on the wide-angle x-ray diffraction (waxd) experiments on oriented poisoner fibers and films. This is be-canse of small crystal sizes in polymers, which lead to a difficult experimental task to obtain single-crystal waxd results on semicrystalfine polymers. It is also possible to nse electron diffraction (ed) method in transmission electron microscopy (tern) to determine polymer lamellar crystal unit cell structures, dimensions, and symmetries. 

Crystallization of cis—1,4-polyisoprene from solution at -65 C has been carried out it is therefore possible that block copolymer preparation by epoxidation, bromination or some other reaction could be accomplished with lamellas of this polymer. Lamellar crystallization of cellulose, of amylose and of polyacrylic acid have been reported substitution reactions such as acetylation or ether formation with the hydroxyl groups and esterfication of the acid groups are possible reactions to carry out with lamellas of those polymers. The use of nonaqueous systems may be better suited to prevent swelling, and therefore, attack of the crystalline regions. It should also be possible to react poly(vinylalcohol) lamellas in suspension with acids or anhydrides to form vinyl-alcohol-vinyl ester block copolymers or with phosgene to obtain chloroformate groups which can undergo further reactions. 

The problem of small-angle X-ray scattering of lamellar systems will be treated in the following chapters mainfy by means of biomembiane assets. Nevertheless, the concepts should generalfy ap fy to other lamellar systems, such as polymer systems. 

Another natural polymer that needs a fresh look into its structure and properties is bitumen [123], also called asphaltines, that are used in highway construction. Although a petroleum by-product, it is a naturally existing polymer. It primarily consists of polynuclear aromatic and cyclocaliphatic ring systems and possesses a lamellar-type structure. It is a potential material that requires more study, and high-performance materials such as liquid crystalline polymer (LCP) could be made from it. 

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