Noncrystalline phase

Two types of reactions producing a new phase can be distinguished (1) those producing a noncrystalline phase (gas bubbles liquid drops as, e.g., in the electrolytic deposition of mercury on substrates not forming amalgams), and (2) those producing a crystalline phase (cathodic metal deposition, anodic deposition of oxides or salts having low solubility). 

Chowdhury, M.A.J., Boysen, R.I., lhara, H., and Hearn, M.T.W., Binding behavior of crystalline and noncrystalline phases evaluation of the enthalpic and entropic contributions to the separation selectivity of nonpolar solutes with a novel chromatographic sorbent, J. Phys. Chem. B, 106, 11936, 2002. 

Polytetrafluoroethylene (PTFE) is an attractive model substance for understanding the relationships between structure and properties among crystalline polymers. The crystallinity of PTFE (based on X-ray data) can be controlled by solidification and heat treatments. The crystals are large and one is relieved of the complexity of a spherulitic superstructure because, with rare exceptions, spherulites are absent from PTFE. What is present are lamellar crystals (XL) and a noncrystalline phase (NXL) both of which have important effects on mechanical behavior. 

Measurements by many researchers have shown that PTFE s equilibrium melting temperature is 327°C. ° Once it is heated above its melting temperature, its initial properties are irrecoverable. Compaction of PTFE powder and heating above 327°C results in a partially crystalline solid polymer composed of large crystals with a coexisting noncrystalline phase. Crystal size and perfection depend on die crystallization conditions slow cooling results in larger, more perfect crystals. On this point, we present detailed information from electron microscopy, corroborated by measurements of X-ray line breadth. 

The half-width of the crystalline component line was estimated to be 18 Hz. This value reflects the very stable orthorhombic crystalline phase of this sample. The component line shape centered at 31.0 ppm represents the contribution from the amorphous phase in which the molecular conformations are changed rapidly over all permitted conformations. The relatively narrow line width estimated as 38 Hz is caused by the rapid molecular motion. The line centered at 31.3 ppm represents the noncrystalline phase in which the local molecular motion can occur in the same manner as in the amorphous phase (in Tic time frame), but a long-range molecular motion accompanying a conformational change related to a 10-20 methylene sequence is severely restricted. The wide line width as 85 Hz... 

Recently, various techniques that produce highly oriented linear polyethylene with a ultra high modulus (hereafter, referred to as UHMPE) have been developed. In this section, we will examine the structure of the UHMPE that was prepared by highly drawing a dried gel [69]. Even if bulk polyethylene is uniaxially highly drawn by a normal method at a temperature between the Tg and Tm, the phase structure is essentially similar to the undrawn sample. That is, it involves three phases of the crystalline and two noncrystalline phases, although the mass fraction and detailed content of each phase are somewhat different. However, UHMPE samples may have a particular phase structure. 

As can be seen from the Table 15, 70 and 30% of the solvent are respectively in the bound and free state. The mass fractions of the bound and free solvents are in rough accordance with those of the crystalline-amorphous interphase and the amorphous phase in the two noncrystalline phases of the polymer. This result suggests that the solvent exists in the two noncrystalline phases of the polymer, as the bound solvent in the crystalline-amorphous interphase and as the free solvent in the amorphous phase, leaving the crystalline phase pure. It is concluded that the sPP/o-dichlorobenzene gel involves three phases, (1) the pure crystalline... 

In this discussion, we have considered a molecular motion that includes two independent motions in order to explain qualitatively the fact that two noncrystalline phase involve the same Tic and different T2c s. To analyze these phenomena more quantitatively, we have to evaluate Tic and T2C theoretically, assuming an adequate motional model. Refer to our article Murayama K, Horii F, Kitamaru R (1983) Bull Inst Chem Res, Kyoto Univ, 61 299... 

In addition, one hypothesis for the secondary structure in spidroin suggests that there are amorphous phases, highly oriented crystals, and oriented noncrystalline phases coexisting (Grubb et al., 1997). This structure model has been used to explain the super-contraction of dragline (Liu et al., 2005b). 

The problem of whether an amorphous material may or may not be considered a form of a solid substance has been discussed [18a]. Many compounds yield stable noncrystalline phases either as the exclusive product of a crystallization process, or in a mixture with crystals or as a consequence of the treatment of otherwise crystalline phases [18]. The fundamental drawback when dealing with amorphous phases is the dearth of techniques for the thorough characterization of an amorphous phase or for the discrimination between different amorphous phases. In general, diffraction techniques are of little help when dealing with amorphous materials and one has to rely mainly on spectroscopic means (see below). Clearly, if one takes the fulfilment of Bragg s law as the pre-condition for the existence of a crystalline phase, and hence for the existence of a molecular crystal polymorph, amorphous materials are not to be considered. 

The CBPC structure is a mixture of both crystalline and noncrystalline material. The crystalline phases are detectable by X-ray diffraction, but noncrystalline phases are difficult to identify, even though their presence is indicated by a broad hump in the X-ray diffraction pattern. We shall see such complex structures in almost all CBPC formations in the subsequent chapters. 

Structure and Dynamics of Crystalline and Noncrystalline Phases in Polymers... 

---