Monolayer crystallized

Fig. 5.39 Atomic force microscopy profiles of a crystal of PEO41PBO22PEO41 on silicon (Hamley et al. 1998). (a) Surface plot showing the edge of a monolayer crystal, (b) Topography of steps, showing typical heights.

Figure 5.16 A) Solid state CPMAS- C-NMR spectra of crystalline and microcrystalline N-octyl-D-gluconamide (= d-GIu-8) materials are well-resolved. The signals have been assigned by considering gauche effects and by comparisons with solution state NMR spectra. The chemical shifts in the first spectrum correspond to an all-anti conformation, shifts in the second spectrum to a gauche bend (b). The methyl carbon C-8 signal indicates a polar environment oriented for the monolayer crystal a), and an unpolar environment for the bilayer crystal b) and micellar fibre c). The signals for the lyophilizedfibre in the third spectrum are somewhat broadened, but the shift of the C-2 signals can be clearly detected. This points to a G conformation (b).

Monodisperse diblock oligo (ethylene oxide) mono-n-alkyl ethers have also been prepared and studied.143 Oligomers with hydroxy-ended E-blocks formed bilayer crystals (cf. Section II.G and Figure 22), and the methoxy-ended oligomers formed monolayer crystals. The helical oxyethylene blocks were perpendicular to the layer plane, while the alkyl blocks were generally tilted at 30° to the layer normal. Monodisperse triblock oligomers with a central methylene block and outer oxyethylene blocks were also studied subsequently144 and both fully crystalline and partly crystalline structures were found, with chains in wholly trans-planar and mixed trans-planar/helical conformations. 

The racemic material spontaneously resolves into monolayer crystals of pure R and 5 material forming a 2D conglomerate. 

The crystals formed through these two mechanisms must be diastereomeric, but it is not possible to distinguish between these two possibilities by measuring physical properties such as optical activity. If resolution occurs, and the monolayer crystal domains are enantiomerically pure, the chiral images observed from the racemic material must be identical to those obtained from one or the other of the pure enantiomers. Over 100 images were analyzed for each material [enantiomerically pure (R)-... 

Stevens F. Dyer. D.J. Walba, D.M. Direct observation of enantiomorphous monolayer crystals from enantiomers by scanning tunneling microscopy. Angew. Chem., Int. Ed. Engl. 1996, 35, 900-901. 

D nano-stmctured arrays, wettability, superhydrophobicity, colloidal monolayer crystal... 

Studies of the crystal structure of the polymerized monolayers were undertaken using electron diffraction data.( ) The kinematic approximation could bemade, since a monolayer crystal contained only 1/2 the a-axis repeat of the normal structure of both the monomer and the polymer. The monomer structure is monoclinic with a 33° tilt of the hydrocarbon side chains (a-axis) from the be plane towards the b-axis. Thus c is the unique axis and the monolayer is 31A thick (a-axis 62A). A complete structure of the polymqr has been performed. Jhe unit ce l was orthorhqmbic with a = 70A (monolayer thickness 35A) b = 8.11A and c = 4.89A (chain axis). The monolayer contains 2 monomer repeats in 2 chains (unit cell contains 4 monomer repeats in 4 chains) related by a glide along the b-axis. The final residual was 9% indicating an excellent fit between calculated and observed intensities. 

An exception to this concerns the formation of monomolecular crystalline layers on the surfaces of molten alkane waxes at temperatures close to the melting point as reported by, for example, Gang et al. [32], This layer causes increases in the lifetimes of the transient froths formed by such materials. Presumably, the stress at the surface due to such a layer will result in the formation of velocity gradients and therefore shear stress to resist drainage. Gang et al. [32] state, however, that the stabilization of a foam by surface crystallization or surface-induced crystallization of the interior, by a nonsurfactant component, is clearly not common but may be an additional mechanism at work in complex systems where a monolayer crystallizes at a higher temperature than the bulk. ... 

Facetted Monolayer Crystals from Dilute Solution, 75... 

Figure 3.1 Monolayer crystals of polyethylene grown from 0.1% tetrachloroethylene solution by free cooling from about 120°C. The pleats were formed when the hollow pyramid shape crystals collapsed. A small spiral growth is evident on the largest crystal. Transmission electron micrograph from Reneker and Geil [2] with permission from the American Institute of Physics.

Figure 3.7 Dark-field electron micrograph of a monolayer crystal of poly(4-methylpentene-l) grown from a 0.1% solution in equivolume xylene and amyl acetate solution at 90°C. Each of the four sectors has a 100 growth face contrast is described in the text. From Khoury and Barnes [7] contribution of the National Institute of Standards and Technology.

Figure 3.12 (a) TEM of monolayer crystals of polyethylene, M = 10 kDa, grown at 80°C from 0.01 % xylene solution. There are no pleats or creases that indicate a nonplanar shape, (b) Exactly as in (a), except that the polyethylene has M = 120 kDa. The pleat along the b-axis (small diagonal) indicates that the crystal was a hollow pyramid in solution. Note also the spiral growths. From Holland and Lindenmeyer [16] with permission from John Wiley Sons, Inc. 

A different sort of three-dimensional structure may arise from chain folding, however. Should the folds on one side of a monolayer crystal be bulkier than those on the other side, the resultant strain can cause the lamella to curve to the point where it is best described as a scroll. Nylon 6.6 crystallized under conditions that give amine folds on one basal surface and acid folds on the other surface is shown in Figure 3.14 [22]. The... 

Figure 3.40 Phase contrast optical image of a monolayer crystal of poly(ethylene oxide) grown at 55°C in a 10 pm molten film. Edges of the 22 nm thick lamella are revealed by self-decoration after quenching. The 6-axis is vertical and the a -axis is horizontal this shape may be compared with that in Figure 3.9. Width of the micrograph is 150 pm. From Kovacs and Gonthier [57] with kind permission from Springer Science-tBusiness Media B.V.

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