PMMA, oriented

Crazing in anisotropic polymers has seldom been studied by means of optical interferometry. A block copolymer (Isoprene-Styrene) with a highly oriented fibrillar structure, and a PMMA oriented by means of drawing above Tg, have been studied so far. These results are reported in and The same subject has often been studied, however, using other experimental techniques... 

Orientation of polymers has been increasingly studied by Raman. PMMA orientation (148). oriented PP and PE (149). quantitative data on chain orientation of PP (150). and vibrational spectroscopic studies of polymer chain order have been reviewed (151). 

The results of the present investigation have shown that independently determined parameters of cluster entanglement network enable rather accurate description of the experimental data on molecular PMMA orientation. The cluster model of structure is postulated in [1, 2] and this is the one that is used in this chapter. 

Figure 20 Schematic diagram of a nanoporous BCP template prepared from athickfilm of PS-A-PMMA oriented with an electric field. The PMMA was removed leaving a template. Subsequent electrochemical deposition generated nanowires in a cross-linked PS matrix. On the right is a scanning electron microscopy image of cobalt nanowires electrochemically deposited in the cross-linked PS template.

A thin layer of crosslinked block copolymer can also act as a pattern upon which a thicker lamellar morphology can assemble perpendicularly. For the crosslinked underlayer, Park et al. used a monolayer of lamellar PS-b-PMMA oriented perpendicularly via a neutral substrate underlayer, while Ruiz et al. used parallel cylinders, which form larger grains than perpendicular lamellae, to direct a block copolymer with perpendicular lamellae deposited on top to form with large grain size. °°... 

Mixtures of polymers at surfaces provide the interesting possibility of exploring polymer miscibility in two dimensions. Baglioni and co-workers [17] have shown that polymers having the same orientation at the interface are compatible while those having different orientations are not. Some polymers have their hydrophobic portions parallel to the surface, while others have a perpendicular disposition. The surface orientation effect is also present in mixtures of poly(methyl methacrylate), PMMA, and fatty acids. 

Figure Bl.22.11. Near-field scanning optical microscopy fluorescence image of oxazine molecules dispersed on a PMMA film surface. Each protuberance in this three-dimensional plot corresponds to the detection of a single molecule, the different intensities of those features being due to different orientations of the molecules. Sub-diffraction resolution, in this case on the order of a fraction of a micron, can be achieved by the near-field scaiming arrangement. Spectroscopic characterization of each molecule is also possible. (Reprinted with pennission from [82]. Copyright 1996 American Chemical Society.)...

Figure Cl.5.3. Near-field fluorescence image 4.5 p.m square) of single oxazine 720 molecules dispersed on die surface of a PMMA film. Each peak (fwhm 100 nm) is due to a single molecule. The different intensities are due to different molecular orientations and spectra. Reprinted widi pennission from Xie 11221. Copyright 1996 American Chemical Society.

Such considerations appear to be very relevant to the deformation of polymethylmethacrylate (PMMA) in the glassy state. At first sight, the development of P200 with draw ratio appears to follow the pseudo-affine deformation scheme rather than the rubber network model. It is, however, not possible to reconcile this conclusion with the temperature dependence of the behaviour where the development of orientation reduces in absolute magnitude with increasing temperature of deformation. It was proposed by Raha and Bowden 25) that an alternative deformation scheme, which fits the data well, is to assume that the deformation is akin to a rubber network, where the number of cross-links systematically reduces as the draw ratio is increased. It is assumed that the reduction in the number of cross-links per unit volume N i.e. molecular entanglements is proportional to the degree of deformation. 

Fig. 1.18 A film of silicone oil of 1 mm thickness is flowing along a vertically oriented planer sheet of PMMA. In a tagging experiment, a horizontal slice of 2 mm thickness is marked and its deformation is recorded as a function of the separation time A between the...

Ito, A. and Kashiwagi, T., Characterization of flame spread over PMMA using holographic interferometry, sample orientation effects, Combustion and Flame, 1988, 71, 189. 

Fig. 3 Schematic representation of control over block copolymer thin film orientation by applying an electric field to orient PS-6-PMMA cylinders perpendicular to the substrate (taken from [43])...

Nealey and coworkers [75,76,146] took a similar approach and applied lithographically defined self-assembled monolayers as substrates to direct the orientation of block copolymer thin films. After EUV interferometic lithography on octadecyltrichlorosilane (OTS) or phenylethyltrichlorosilane (PETS) monolayers, PS-fr-PMMA block copolymers were deposited and annealed on the substrates. Due to the selective wetting of PS and PMMA on the unexposed and exposed regions, respectively, they were able to obtain large areas of perpendicular lamella when the commensurate condition was fulfilled. 

Tubular membranes of 8 long were prepared from blend composition consisting of CA and PMMA and performance data for one month operation was collected. These datas show high product water flux (18-20 gfd.) with low flux decline slope. However, it was observed that these membranes initially showed fountains" which disappeared in about 30 minutes time. This was attributed to the peculiar membrane rheology and orientation of PMMA molecule with respect to CA molecule. This needed further study for confirmation. 

Fig. 7 2D thickness-surface energy gradient library for mapping the effects of these parameters on the self-assembly of PS-b-PMMA block copolymer thin films. See text for a fuU description. Lq is the equilibrium self-assembly period and h is the film thickness. Dashed white lines delineate the neutral surface energy region, which exhibits nanostructures oriented perpendicular to the substrate plane. (Derived from [18] with permission)... 

Atactic PMMA is a brittle amorphous polymer with low elongation at break. Without molecular orientation, PVDF has also a low elongation under tensile stress as shown in Figine 7.9. However, the elongation of PVDF/PMMA blends... 

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