Poly lamellar structure

With diblock copolymers, similar behavior is also observed. One component is enriched at the surface and depending on miscibility and composition a surface-induced ordered lamellar structure normal to the surface may be formed. Recent investigations include poly (urethanes) [111], poly(methoxy poly (ethyleneglycol) methacrylate)/PS [112] and PS/PMMA [113, 114]. In particular the last case has been extensively studied by various techniques including XPS, SIMS, NR and optical interferometry. PS is enriched at the surface depending on blockcopolymer composition and temperature. A well ordered lamellar structure normal to the surface is found under favourable conditions. Another example is shown in Fig. 6 where the enrichment of poly(paramethylstyrene), PMS(H), in a thin film of a di-... 

Recent developments have allowed atomic force microscopic (AFM) studies to follow the course of spherulite development and the internal lamellar structures as the spherulite evolves [206-209]. The major steps in spherulite formation were followed by AFM for poly(bisphenol) A octane ether [210,211] and more recently, as seen in the example of Figure 12 for a propylene 1-hexene copolymer [212] with 20 mol% comonomer. Accommodation of significant content of 1-hexene in the lattice allows formation and propagation of sheaf-like lamellar structure in this copolymer. The onset of sheave formation is clearly discerned in the micrographs of Figure 12 after crystallization for 10 h. Branching and development of the sheave are shown at later times. The direct observation of sheave and spherulitic formation by AFM supports the major features that have been deduced from transmission electron and optical microscopy. The fibrous internal spherulite structure could be directly observed by AFM. 

As an example of blends with attractive interactions, Fig. 65 shows a superstructure in which interactions between methacrylic acid groups and pyridine side groups of a polystyrene-fc-polybutadiene-fo-poly(f-butyl methacry-late-staf-methacrylic acid) (PS-b-PB-b-P(MAA-sfaf-fBMA)) triblock quater-polymer and a PS- -P2VP diblock copolymer lead to a wavy lamellar structure with cylinders from mixed P2VP and P(MAA-sfaf-fBMA) blocks [194],... 

Crystallization from the melt often leads to a distinct (usually lamellar) structure, with a different periodicity from the melt. Crystallization from solution can lead to non-lamellar crystalline structures, although these may often be trapped non-equilibrium morphologies. In addition to the formation of extended or folded chains, crystallization may also lead to gross orientational changes of chains. For example, chain folding with stems parallel to the lamellar interface has been observed for block copolymers containing poly(ethylene), whilst tilted structures may be formed by other crystalline block copolymers. The kinetics of crystallization have been studied in some detail, and appear to be largely similar to the crystallization dynamics of homopolymers. 

Crystallization in asymmetric diblocks with compositions = 0.35 and 0.46 was also investigated by Hamley et al. (19966). It was found that a lamellar structure melted epitaxially (i.e. the domain spacing and orientation were maintained across the transition) to a hexagonal-packed cylinder structure in the /PE = 0.35 sample. This is illustrated in Fig. 5.15, which shows SAXS patterns in the solid and melt states, with a schematic of the epitaxial melting process (Hamley et al. 1996a.b). The same epitaxial transition has been observed for a polyethylene oxide)-poly(buty)ene oxide) diblock (Ryan et at. 1997) vide infra). 

Teyssie and coworkers [86] studied the effect of macromolecular architecture on the lamellar structure of the poly(ethylene oxide) crystallizable arms in (poly tert-butyl styrene)(poly(ethylene oxide))2 [PtBuS(PEO)2] miktoarm stars by using SAXS and differential scanning calorimetry (DSC). The results were compared with the ones obtained on poly(tBuS-fe-EO) materials. At the same total molecular weight and composition the melting temperature, the degree of crystallinity and the number of folds of PEO chains were found to be lower for the branched samples. 

Table 1. Examples of structural parameters (in A) of organized copolymers with a lamellar structure. Low Ange X-ray diffraction values (XR), electron microscopy values (EM) d Total thickness of a sheet, d/v Thickness of the non-polydiene layer, dg Thickness of the poly diene layer...

Fig. 1. Example of electron micrograph of the lamellar structure. Copolymer polyisoprene-poly(vinyl-2-pyridine) (IVP.42) containing 60,5% of polyisoprene, swollen with 25% MMA and post-polymerized.

Fig. 9. Example of phase diagram concentration/temperature. Copolymer polystyrene-poly bu tadiene SB. 11 containing 39% polybutadiene and exhibiting a lamellar structure.

Fig. 53 Formation of lamellar-within-lamellar structures by pentadecylphenol (PDP) of nonadecylphenol (NDP) bound to poly(4-vinylpyridine). Reprinted with permission from [200]...

Complexes of sodium poly(a,L-glutamate) with salts of various fatty acids form a lamellar structure, consisting of alternating layers of polymer-chain and double-... 

Mesophases prepared by dissolution of the copolymer in a preferential solvent for the poly(vinylpyridine) block (acrylic acid, nitromethane, dfoxane, octanol, methylethyl ketone, ethyl acetate, vinyl acetate, styrene and methyl methaaylate) and dry copolymers obtained by slow evaporation of the solvent from the mesophases have been studied by low-angle X-r diffraction electron microscopy Copolymers of isoprene and vinylpyridine exhibit cylindrical hexagonal or lamellar structures dependii upon their comi siton.The influence of the nature, concentration, and polymerization of the solvent, molecular weight and composition of the copolymer, microstructure of the polyisoprene block, and position of the nitrogen atom in the vinylpyridine block on the values of the geometrical parameters of the periodic structures have been establidied ... 

Another motivation for measurement of the microhardness of materials is the correlation of microhardness with other mechanical properties. For example, the microhardness value for a pyramid indenter producing plastic flow is approximately three times the yield stress, i.e. // 3T (Tabor, 1951). This is the basic relation between indentation microhardness and bulk properties. It is, however, only applicable to an ideally plastic solid showing no elastic strains. The correlation between H and Y is given in Fig. 1.1 for linear polyethylene (PE) and poly(ethylene terephthalate) (PET) samples with different morphologies. The lower hardness values of 30-45 MPa obtained for melt-crystallized PE materials fall below the /// T cu 3 value, which may be related to a lower stiff-compliant ratio for these lamellar structures (BaM Calleja, 1985b). PE annealed at ca 130 °C... 

Crystallization-induced phase separation can occur for concentrated solutions (gels) of diblocks [58,59]. SAXS/WAXS experiments on short PM-PEO [PM=poly(methylene) i.e. alkyl chain] diblocks revealed that crystallization of PEO occurs at low temperature in sufficiently concentrated gels (>ca. 50% copolymer). This led to a semicrystalline lamellar structure coexisting with the cubic micellar phase which can be supercooled from high temperatures where PEO is molten. These experiments on oligomeric amphiphilic diblocks establish a connection to the crystallization behaviour of related nonionic surfactants. 

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