Microstructure lamellar

The alignment of a lamellar microstructure by electric fields has been reported [64], The electric fields were applied across a melt of a PS-PMMA block copolymer and were maintained throughout cooling down to below the glass transition point. SAXS studies show persuasive evidence that the microstructure was aligned by an electric field. 

Fig. Z6 (a) The lamellar microstructure of a PS-PI diblock with /PS = 0.64 and M — 39 kgmor1 shown by TEM where the PI is stained dark (Khandpur et al. 1995) (b) SAXS powder pattern from the same material.

Transdermal patches are marketed worldwide with the drug substances glycerole trinitrate, estradiol, testosterone, clonidine, scopolamine, fentanyl and nicotine, respectively. The patch has to remain for up to one week at the appropiate body site. In this case the drug amount in the reservoir is rather high. As liquid crystalline vehicles with lamellar microstructure have... 

The orientation of PE stems with respect to the lamellar microstructure has been determined for an asymmetric PE-PEP-PE triblock using SAXS and WAXS... 

Lamellar Microstructures. The precipitate microstructures described above have a geometric distribution such that a description in terms of a background matrix that is riddled with second-phase particles is appropriate. A second class of multiphase microstructure is lamellar microstructure like that shown in fig. 10.7. To better... 

The stated considerations are correct for titanium. In titanium alloys evolution of lamellar microstructure (typical for titanium alloys) takes place due to development of globularization [8], The process develops by means of substructure formation in the lamellas of phases, division of lamellas and transformation of lamellas parts into globular particles. Keep the process its main features in the case of SMC structure formation There are no such investigations in the scientific literature. The relative simplicity of the method and its commercial application bring up a question to investigate the features of microstructure evolution and mechanical behavior of titanium and its alloys during successive deformation/rotation of samples as well as scale up process capability for production of SMC structure in large-scale billets and sheets. 

Li, C.J. and Wang, W.Z. (2004) Quantitative characterization of lamellar microstructure of plasma-sprayed ceramic coatings through visualization of void distribution. Mater. Sci. Eng., A, 386, 10-19. 

In recent years a new type of 7-alloy, containing a dispersion of TiB2 (the XD process) [4], has been the subject of much interest. The addition of 0.8 v/o T1B2 leads to grain refinement of cast 7-alloy microstructures. The 7-alloy used in this study is a Ti-45Al-2Nb-2Mn alloy, with a 0.8v/oTiB2 addition. This alloy is a 7 + a2 alloy with a lamellar microstructure. 

A transformation product resulting from slow cooling from austenite, comprising a lamellar microstructure of ferrite and iron carbide. 

Liquid crystallinity and block microphase separation both compete during the minimization of free energy of the system. As we will show later in this review, in the case of a rod-coil diblock copolymer, liquid crystallinity plays a very important role in the microphase separation process and leads to morphologies distinctly different from the conventional spheres, cylinders and lamellar microstructures and include the arrow head, zig-zag, and wavy lamellae phases [40, 41], In the case of SGLC-coil... 

At an industrial applications, the TBC coverings can be produced by thermal spraying method in the air plasma spray (APS) atmosphere, at lowered pressure low pressure plasma spray (EPPS) from APS or by the electron beam physical vapor deposition method (EB-PVD), these are all dry-route processes. By these processes, coatings have different microstructures lamellar microstructure consisting... 

Table lc.29 Influence of the surface treatment on the rotating bending fatigue (fine lamellar microstructure, produced by annealing in 15 min/1050°C/H20 + 1 h/800°C/H20) (Ref. 35)... 

During a eutectic solidification L a + / , if the interfacial energy between the a and / phases is low compared to the liquid-a and liquid-/ interfacial energies, then the a and p phases will prefer to wet each rather than the liquid. Under rapid, directional solidification, this can lead to the coordinated growth of long alternating lamellar or plateletlike formations of the a and / phases. Such lamellar microstructures are common feature of eutectic phase transformations... 

Let us halt for a moment and consider the relationship between block copolymer materials and liquid crystals. A block copolymer exhibiting a lamellar microstructure can be classified as a smectic A liquid crystal because it has positional disorder in two dimensions and a periodic pattern in the third. Here, the periodic pattern can be identified with the variation in the local monomer compo,sition. In small-molecule smectics, the analogous periodicity arises from the molecular center-of-mass distribution. A block copolymer exhibiting a cylindrical microstructure is analogous to a columnar liquid crystal. The OBDD and spherical microstructures have three-dimensional order and have no liquid cry.stal analogs. 

For a lamellar microstructure, the wave vectors of the Fourier components are antiparallel, and the electrostatic contribution to the free energy density is... 

FIGURE 21 The dielectric tensor represented as an ellipse. A general ellipse is shown in (a) with the three eigenvalues e, e, and e, in (b) an oblate ellipsoid for a block copolymer with a lamellar microstructure, in (c) a prolate ellipsoid for a block copolymer with a cylindrical microstructure, and in (d) a sphere for a spherical or OBDD microstructure. 

In 1971, LeMeur et al. [62] reported that dilute (6-9 wt%) solutions of a symmetric poly sty rene-polyisoprene diblock copolymer (molecular weight 1,400,000) in toluene and styrene exhibited anisotropic diffraction of (ultraviolet) light after application of either mechanical shear or a 15 kV/cm electric field. The diffracting element had a repeat distance of about 360 nm. Light diffraction from this solution shows that even this dilute solution exhibits a periodic structure. It is reasonable that this periodic element is the lamellar microstructure with a large period resulting from swelling by the solvent. 

Alignment of Lamellar Microstructure in a Polystyrene-Polylmethyl methacrylate) Block Copolymer... 

In 1991, we reported on the alignment of a lamellar microstructure in a block copolymer melt [63]. The material of this study was a symmetric polystyrene-poly(methyl methacrylate) diblock copolymer (PS-PMMA) of molecular weight 37,000. This copolymer was chosen because of the relatively strong dielectric contrast between the two blocks (cp = 2.55, = 3.78) and the relatively small... 

We also noted that the alignment persisted through thermal cycles even 14°C above ODT and in the absence of an electric field. This suggests that ordered structure persists well above the rheologically determined ODT, presumably in a metastable state. This surprising result could be explained by the possibility that the rheological experiments used to measure the order-disorder transition temperature destroy metastable structure that persists in our quiescent experiments. A theory by Fredrickson and Binder [74] predicts that lamellar microstructure will persist as metastable up to 9°C above ODT-... 

FIGURE 24 (a) Evolution of the orientational order parameter, S, of the lamellar microstructure in a PS-PMMA diblock (MW = 31,000) in a 15 kV/cm electric field and at three temperatures. In (b) the time axis is multiplied by the rheological temperature shift factor, a-r- (Adapted from Ref. 64.)... 

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