Amorphous configuration

Generally, to make glass-clear polymers, we must prevent crystallization. This can be accomplished by placing bulky side groups on the main chains. Changing from a crystalline to an amorphous configuration... 

Although the FES is not filled completely, its main features can be recognized from the biasing potential collected (Fig. 3.10). An extensive basin associated with the amorphous configurations is readily identified, which is connected with the smaller crystalline basin over a transition region. When the MTD run was terminated, only a fraction of the walkers had crystallized, in the sense that the Qf CV had reached values higher than the selected threshold value of 0.7 (see Figs. 3.8 and 3.10). This... 

Molecular dynamics simulation methods are applied to generate amorphous configurations. A number of potential models are employed in order to highlight any... 

Another approach to help facilitate crystallisation is to bias the tr ectories of all the atoms moving in the (molten/amorphous) configuration to favour crystallisation. Specifically, order parameters (which can be bond distances, coordination numbers, nearest neighbour densities and radial distribution functions) may be used as a gauge of crystallinity and used to help drive the simulation (trajectory) to favour maximising the order parameter and, ultimately, induce crystallinity. 

Extended x-ray absorption fine stmcture measurements (EXAFS) have been performed to iavestigate the short-range stmcture of TbFe films (46). It is observed that there is an excess number of Fe—Fe and Tb—Tb pairs ia the plane of the amorphous film and an excess number of Tb—Fe pairs perpendicular to film. The iacrease of K with the substrate temperature for samples prepared by evaporation is explained by a rearrangement of local absorbed atom configurations duting the growth of the film (surface-iaduced textuting) (47). 

The optoelectronic properties of the i -Si H films depend on many deposition parameters such as the pressure of the gas, flow rate, substrate temperature, power dissipation in the plasma, excitation frequency, anode—cathode distance, gas composition, and electrode configuration. Deposition conditions that are generally employed to produce device-quahty hydrogenated amorphous Si (i -SiH) are as follows gas composition = 100% SiH flow rate is high, --- dO cm pressure is low, 26—80 Pa (200—600 mtorr) deposition temperature = 250° C radio-frequency power is low, <25 mW/cm and the anode—cathode distance is 1-4 cm. 

Thermal Properties. Before considering conventional thermal properties such as conductivity it is appropriate to consi r briefly the effect of temperature on the mechanical properties of plastics. It was stated earlier that the properties of plastics are markedly temperature dependent. This is as a result of their molecular structure. Consider first an amorphous plastic in which the molecular chains have a random configuration. Inside the material, even though it is not possible to view them, we loiow that the molecules are in a state of continual motion. As the material is heated up the molecules receive more energy and there is an increase in their relative movement. This makes the material more flexible. Conversely if the material is cooled down then molecular mobility decreases and the material becomes stiffer. 

Due to the presence of residual double bonds, the polymer could be cross inked with regular agents. TPR is a linear polymer with a high trans configuration. It is highly amorphous at normal temperatures and has a Tg of about 90°C and a density of 0.85. 

PIB exists either as a low mw (about 12,000) viscous or atactic liq or as a cryst matl of about 1.00,000 mw. In this latter form the iso tactic (chain) type configuration predominates over the atactic and amorph forms (Ref 8). Since the isotactic form is the form designated by mil spec (Ref 2), its parameters are presented below ... 

The structure of a-C H DLC consists of an essentially amorphous network with isolated clusters dominated by the sp configuration (graphite) with some sp (diamond). Hydrogen is believed to play an essential role in determining the bonding configuration by helping to form the sp bond, probably in a manner similar to the formation of CVD diamond. 

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