Packing, chain

In order to characterize the neighboring chain-chain correlation quantitatively, a measure of the order of the chain packing has been introduced [53]. We define the following function  

We can surmise a slowing down of the DPhPC Upid motion from the enhanced entanglements among the neighboring lipid chains. In this section, we will see how and which motion is actually decreased or not. One of the bluest advantages of the MD simulation is that the dynamical properties are straightforwardly evaluated from the MD trajectories using a variety of correlation frmctions [54]. 

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Snetivy D and Vancso G J 1994 Atomic force microscopy of polymer crystals 7. Chain packing, disorder and imaging of methyl groups in oriented isotactic polypropylene Po/yme/ 35 461... 

SY Chung, S Subbiah. The use of side-chain packing methods m modeling bacteriophage repressor and cro proteins. Pi-otem Sci 4 2300-2309, 1995. 

Figure 3.8 Schematic diagram of the dimeric Rop molecule. Each subunit comprises two a helices arranged in a coiled-coil structure with side chains packed into the hydrophobic core according to the "knobs in holes" model. The two subunits are arranged in such a way that a bundle of four a helices is formed.

The homopolymers of p-hydroxybenzoic acid have such a high value for the that they are somewhat intractable. Useful materials may, however, be made by copolymerising with a view to introducing some molecular flexibility or reducing chain packing or introducing some non-linear links. Commercially important liquid crystal polyesters are discussed in Chapter 25. 

Frustrated chain packing in this approach aromatic substituents are pendantly attached to the main chain rings. 

The amorphous polyesters are becoming increasingly important for one-component 100% solid moisture-curing adhesives. These materials are usually viscous, amorphous liquids. Poly(2-methylpropane adipate), an example of an amorphous polyester, is a liquid even at a molecular weight of 2000. The amorphous polyesters are usually asymmetrical in structure. In the poly(2-methylpropane adipate) example, the pendant methyl group would be expected to interfere with chain packing, thereby preventing crystallization [27]. 

The two structures appear very similar. Poly( 1,2-propylene adipate) has the same basic structure as poly(ethylene adipate), except for a pendant methyl group. This pendant methyl group on the poly( 1,2-propylene adipate) makes a large difference, however. Poly( 1,2-propylene adipate) has no crystalline melting point. Trappe theorizes that the pendant methyl prevents chain packing and therefore, prevents crystallization [42]. 

The effect of the substituents on chain mobility and chain packing has been related to the gas transport properties [209]. Role of symmetry of methyl group placement on bisphenol rings in PES shows the permeability coefficients in the following order ... 

The most important feature of polymers obtained by these methods is their high mechanical strength, primarily their elastic moduli and tenacities that, in some cases, approach the theoretical values. It has been recognized that these mechanical properties are uniquely related to the existence of ECC with very perfect chain packing in fibrillar crystals. 

Differently from the cases of ETFE, PTFE, 1,4-trans-polybutadiene, and PE, in the mesomorphic form of i-PP it is believed that there is a nearly complete conformational order, in the chains packed with parallel axes, (intrachain long range 3-D order) and only short-range lateral order in the positioning of the chain axes [60, 61]. 

Although the diffraction techniques are unique in providing detailed information on the structural organization at the molecular level in the different crystalline forms, there are other characterization techniques which are sensitive to the chain conformation and in some cases to the chain packing, which can be used advantageously (and in some case more efficiently than diffraction techniques) in the recognition and quantification of the different polymorphs in polymeric materials. 

The strength of the London forces between alkane molecules increases as the molar mass of the molecules increases hydrocarbons with unbranched chains pack together more closely than their branched isomers. Alkanes are not very reactive. but they do undergo oxidation (combustion) and substitution reactions. 

It appears that the main determinant in polyolefin miscibility is the way the chains pack together, a feature that controls the intermolecular interaction between molecules. The solubihty parameter approach is predictive in most cases and can be useful in designing polyolefin blends. 

Electrochemical redox studies of electroactive species solubilized in the water core of reverse microemulsions of water, toluene, cosurfactant, and AOT [28,29] have illustrated a percolation phenomenon in faradaic electron transfer. This phenomenon was observed when the cosurfactant used was acrylamide or other primary amide [28,30]. The oxidation or reduction chemistry appeared to switch on when cosurfactant chemical potential was raised above a certain threshold value. This switching phenomenon was later confirmed to coincide with percolation in electrical conductivity [31], as suggested by earlier work from the group of Francoise Candau [32]. The explanations for this amide-cosurfactant-induced percolation center around increases in interfacial flexibility [32] and increased disorder in surfactant chain packing [33]. These increases in flexibility and disorder appear to lead to increased interdroplet attraction, coalescence, and cluster formation. 

The Size of the Solute and the Degree of Lipid Chain Packing in Membranes... 

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