Molecular mobihty

Andronis, V. Zografi, G. The molecular mobihty of supercooled amorphous indomethacin as a function of temperature and relative humidity. Pharm. Res. 1998, 15 (6), 835-842. 

Many plasma components can exist either free in solution or in a more organized physicochemical domain such as a micelle or hpoprotein complex. On changing from one environment to another, the motional properties of the compound under study are altered with a concomitant change in the T2 relaxation times of their protons. Consequently, it is possible to monitor some of these transitions by observing line width changes, or by use of spin-echo techniques to edit the spectra according to molecular mobihty. 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammabiHty ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). For an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, 7 at which the molecular mobihty is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabHshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Formation of weak boundary layers is confirmed by a study of the molecular mobility of filled epoxy polymers. The availabihty of the solid surface results in a decrease of the molecular mobihty in the boundary layer [21] as a result of limiting the conformation set and adsorption interactions of the polymer molecules with a solid body at the boundary. The nature of the filler surface has little effect on the molecular mobility of the epoxy polymer and on the change of mobility of its side-groups and segments. It has been concluded [21] that the primary role in the change of mobility is played by geometric limitation of the number of possible conformations of macromolecules close to the surface of the particles, i.e., by the entropy factor rather than by energetic interactions of the surfaces. 

To establish the dependence of the filled polymer coating—metal substrate adhesive bond strength on the modified filler concentration, let us consider experimental data for adhesion strength in comparison with the results of molecular mobihty investigations. 

However, crosslinked pol5Utrethanes are not considered a good model for investigation of molecular mobihty and its dependence on the amoimt of filler because at high temperatures there is no clear tan maximum for dipole-segmental relaxation processes. For hnear polyurethanes, the clearly expressed dipole-group relaxation process at 168-179 K and dielectric losses connected with macromolecule segments relaxation at 238-248 K are typical (Fig. 6.5). As seen from the... 

As shown above, introduction of filler into pol5Uirethane results in the growth of adhesion strength, most intensively for small amounts of filler. This change in adhesion is certainly caused by reconstruction of polyurethane structure under the influence of the introduced filler surface (demonstrated by the data on molecular mobihty variation), and in particular of the polymer adhesive layer structure. In this con-... 

Lipatov (22) investigated the effects of interphase thickness on the calorimetric response of particulate-filled polymer composites. Based on experimental evidence, his analysis led to the conclusion that the interphase region surrounding filler particles had sufficient thickness to give rise to measurable calorimetric response. The proposed existence of a thick interphase region correlates with limitations of molecular mobihty for supermolecular structures extending beyond the two-dimensional filler boundary surface. 

BordaUo HN, Zakharov BA, Boldyreva EV, Johnson MR, Koza MM, Seydel T, Fischer J (2012) Application of incoherent inelastic neutron scattering in pharmaceutical analysis relaxation dynamics in phenacetin. Mol Pharm 9 2434-2441 Bptker JP, Karmwar P, Strachan CJ, Cornett C, Tian F, Zujovic Z, Rantanen J, Rades T (2011) Assessment of crystalline disorder in cryo-milled samples of indomethacin using atomic pairwise distribution functions. Int J Pharm 417 112-119 Boutonnet-Fagegaltier N, Menegotto J, Lamure A, Duplaa H, Caron A, Lacabanne C, Bauer M (2002) Molecular mobihty study of amorphous and crystalline phases of a pharmaceutical product by thermally stimulated current spectrometry. J Pharm Sci 91 1548-1560 Bras AR, Noronha JP, Antunes AMM, Cardoso MM, Schdnhals A, Affouard Fdr, Dionfsio M, Correia NIT (2008) Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy. J Phys Chem B 112 11087-11099... 

The rates of biochemical reactions are dependent on the proximity and mobility of the reactants. Mobility is determined by the mutual interactions of the solvent with the solutes. The state of water (the solvent) determines the mobility of the solutes and in return, the solutes change the structural organization of nearby water molecules through hydrophihc and hydrophobic interactions. In the cytoplasm, the thermodynamic state of the medium (and therefore the molecular mobihty) determines the rate of metabolic activity. 

Maeda, 2010). They showed that time-temperature superposition in creep behavior and crystallinity-time superposition are equivalent for HDPE samples having a wide range of crystallinities. The increase in amorphous phase fraction enhances the overall molecular mobihty or extends the experimental timescale, corresponding to the enhancement of molecular mobihty due to a rise in temperature. 

The thicknesses of the surface layers of some elastomers are 100 A and depend on the surface nature. For elastomers the formation of more dense and less dense layers was also observed. The loose layer has the greatest thickness. The values determined by the ellipsometry method depend on temperature, because with growing temperature the molecular mobihty of chains increases, and because of the increase in the surface of the molecular contact, the density of the layer increases. Much less data are available on packing density in filled crosshnked polymers. For cured epoxy resin it was formd that the properties of the surface layer at the interface with a sohd depend on the curing conditions. The ordered surface layer has a thickness of 0.5-0.6x10 m, which is by one order higher when compared with hnear polymers. 

DMA is a very powerful method capable of providing information on the thermal mechanical behavior of polymer composites as well as viscoelastic polymer materials and the blends due to the temperature dependence of the storage modulus, loss modulus, and tan S. The glass transition behavior, which is sensitive to molecular mobihty, material stiffness, and damping behavior of a polymeric material, can be studied using DMA. 

By considering these data, we take into account the influence of morphological features on the dynamic mechanical properties of the two-phase system. This effect may also determine the relaxation characteristics and the activation energies. Since any relaxation process is coimected with molecular mobihty and interchain physical interactions, the morphology definitely affects the relaxation properties. 

Figure 14.16 illustrates a possible proton exchange mechanism of the neutral histidine 64 in the active site of HCA II. As indicated by Aj, the local environment resembles a wet polar aprotic solution exhibiting a high molecular mobihty, which enables the tautomerism by simple reorganization of some water molecules. 

Burnside S D, Giannelis E P, Nanostructure and properties of polysiloxane-layered silicate nanocomposites , J. Polym. Sci. Part B Polymer Physics, 2000 38 1595-604. Bohning M, Goering H, Hao N, Mach R, Oleszak F, Schonhals A, Molecular mobihty and gas transport properties of polycarbonate-based nanocomposites . Rev. Adv. Mater. Sci., 2003 5 155-9. 

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