Polymers orientation effects

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. 

The stretching properties of polymers are investigated by examining the effect of polymer orientation, polymer chain length, stretching rate, and temperature. Homogeneity of polymer films and consistency between lots of polymer films also are investigated. Statistical analysis of data includes Q-tests and f-tests. 

Anisotropic behaviour is also exhibited in optical properties and orientation effects can be observed and to some extent measured by birefringence methods. In such oriented materials the molecules are in effect frozen in an unstable state and they will normally endeavour to take up a more coiled conformation due to rotation about the single bonds. If an oriented sample is heated up the molecules will start to coil as soon as they possess sufficient energy and the mass will often distort. Because of this oriented materials usually have a lower heat distortion temperature than non-oriented polymers. 

In Chapter 3 it was pointed out that certain rod-like polymers showed many of the attributes of liquid crystals in the melt. In particular, these molecules were oriented in shear to such an extent that interchain entanglement was small and the melts had a low viscosity. On cooling of the melt these rod-like molecules remained oriented, effectively self-reinforcing the polymer in the direction of flow. The essential differences in the properties of liquid crystal polymers... 

In [332] it was noted that the strength of samples cut out at different locations of an article made from filled thermoplastics by pressure molding may differ widely — which is due to the non uniform orientation of the polymer at different locations of the mold. The very high strength parameters of composites with PMF in molded specimens are obviously also due to orientation effects, while for standard mixed samples of similar composition (that is, a matrix which, apart from the filler, contains some superhigh molecular polyethylene imitating the PMF coats) the... 

The introduction of large gas phase volumes into the polymer alters the physical characteristics of the material volume weight, permeability to fluids and gases, and physico-mechanical properties. Moreover, the properties of the polymer matrix itself are changed (owing to orientation effects, supermolecular structure of the polymer in the walls, ribs and tension bars of cells), which drives up the value of specific strength on impact, and results in anisotropy of elasticity. 

For a biaxially drawn polymer with orthorhombic symmetry, the chain axis is preferentially oriented with respect to the XtX2 plane of the sample, and the direction normal to the chain axis is also preferentially oriented. Infra-red measurements enable the determination of the quantities Pf20 and PL202 and P222, which define these orientation effects as discussed in case (iv) above. 

Sugawara, A., Nishimura, T., Yamamoto, Y., Inoue, H., Nagasawa, H. and Kato, T. (2006) Self-organization of oriented calcium carbonate/polymer composites effects of a matrix peptide isolated from the exoskeleton of a crayfish. Angewandte Chemie International Edition, 45, 2876-2879. 

Orientation effects are strongly coupled to nonlinear behavior, discussed in Section V, and the stress-strain response discussed in Chapter 5, Orientation makes an initially isotropic polymer anisotropic so that five or nine modulus/compliance values arc required to describe the linear response instead of two, as discussed in Chapter 2. For an initially anisotropic polymer the various modulus/compliance components can be altered by the orientation. It may not be necessary to know all components for an... 

There has been much interest in flow and flow orientation effects with polymer melts containing anisometric particles which may be plate-like or fibrous. Flow-induced orientation of short reinforcing fibres is an area of considerable commercial importance, which is beyond the scope of the review [30]. 

In NMR experiments, molecular mobility leads to narrowing of the resonance lines. Conversely, restricted molecular motion, as occurs in crystalline phases, causes line-broadening. Until the advent of magic angle spinning and related techniques, tliis was a hindrance to NMR studies of solid polymers. We have used it to advantage in following the orientation effects in solid PTFE. 

The conductivity of poly(acrylic acid) and polyfmethacrylic acid) has been measured as a function of orientation (65). Little effect is seen. It is suggested that orientation effects depend upon the nature of the polymer chain-like molecules show a slight decrease in conductivity on orientation, whereas that of globular molecules increases. 

So far, the experiments were concerned with static experiments. Looking at the dynamics of the field effects, valuable information can be obtained concerning the viscous properties of the polymers. For the orientation effect of the l.c. discussed before, the deformation of the l.c. requires time from the former to the new equilibrium state, if the voltage V > is applied. This response time ton depends in a first... 

All electrooptical effects known to the present time for polymeric liquid crystals may be divided into two groups. First of all there are so called orientational effects, which are due solely to the effect of the electric field (field effect) on LC polymers, but are not a result of a current flowing. The second group of electrooptical effects is attributed to the phenomena ascribed to the anisotropy of electrical conductivity (Act) of liquid crystals. These are called electrohydrodynamic effects. 

Preceding the discussion of orientational effects in LC polymers, it is worth mentioning that for a nematic and a smectic phase A of LC polymers only the S-effect was discovered and investigated. This started with works U9,124, 137 138), that demonstrated the ability of LC polymers to orient in permanent and alternating electric fields. The structural formulas of some of the polymers and copolymers investigated are given below ... 

One of the manifestations of orientational effect in LC polymers is presented by a so called guest-host effect, which is well-known for low-molecular liquid crystals. 

Electrochemical synthesis of various cyclic alkylsilanes has been performed similarly113. It should be noted that 5-silaspiro[4,4]nonane is formed despite the high probability of polymer formation due to the high functionality of the silicon. Such high selectivity in the electrochemical ring closure seems to be due to the orientating effect of an electrode in the course of an irreversible reduction of a carbon-halogen bond in the monosilylated intermediate (equations 87 and 88). 

Fig. 11.24 The effects of the fiber aspect ratio, at constant 30% wt loading, on glass-filled polyamide-6. [Reprinted by permission from H. M. Latin, Orientation Effects and Rheology of Short Glass Fiber-reinforced Thermoplastics, Colloid Polym. Sci., 267, 257 (1984).]...

H. M. Laun, Orientation Effects and Rheology of Short Glass Fiber-reinforced Thermoplastics, Colloid Polym. Sci., 262, 257-269 (1984). 

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