Disorder of the second kind

This discussion has shown that the diffraction pattern can reveal three types of disorder, as discussed fully by several authors (Wiener and White, 1991a Blaurock, 1982 Hosemann and Bagchi, 1962). Thermal disorder is generally referred to as disorder of the first kind and lattice disorder as disorder of the second kind. The disorder due to the mosaic nature of the sample is referred to as orientational disorder. Thermal disorder and small amounts of orientational disorder are not particularly troublesome in the diffraction experiment. Lattice disorder, on the other hand, can be extremely problematic because one can never achieve a fully resolved image of the stmcture since there are too few stmcture factors available to obtain a faithful model. Thermal disorder simply means that the position of the atoms are .smeared in some fashion, determined by the equation of state of the molecules. If the lattice is excellent so that all of the stmcture factors observable within the limits of the... 

Disorder of the second kind, originally characterized by Zemike and Prins and by Kratky in the discussion of the structure of liquids, refers to a situation. 

Fig. 5a-c. Diffraction patterns of lamellar stacks with perfect stacking order (a), with disorder of the first kind (b), and disorder of the second kind (c). For details of the model parameters, see Ref. 4. (From Ref. 4, with permission)... 

Fig. 10a and b. Small-angle diffraction pattern from an oriented, stacked sample of sarcoplasmic reticulum vesicles, obtained in 1 s with synchrotron radiation at Stanford Synchrotron Radiation Laboratory. The peaks correspond to the first seven orders of a lamellar diffraction pattern with a lattice periodicity of 200 A and exhibit the significant effects of lattice disorder of the second kind. The intensity distribution in (b) was obtained by integration of the two-dimensional pattern (a) between the limits indicated in (a). (From Ref. 85, with permission)... 

The order-disorder transformation is not unique to two-layer fluids, which is readily concluded from the second maximum of n in the vicinity of s 3.55 where the fluid consists of three strata. However, it turns out that only the innermost, middle stratum undergoes the same kind of structural reorganization just explained for the two-layer fluid the two contact strata (i.e., the strata closest to the substrate) do not participate in the transformation. The intensity of the second maximum in n is therefore reduced by roughly 2/3 compared with the first one, as one would expect. 

In the second section a classification of the different kinds of polymorphism in polymers is made on the basis of idealized structural models and upon consideration of limiting models of the order-disorder phenomena which may occur at the molecular level. The determination of structural models and degree of order can be made appropriately through diffraction experiments. Polymorphism in polymers is, here, discussed only with reference to cases and models, for which long-range positional order is preserved at least in one dimension. 

Er2MnS -type. This structure, previously described by way of Y2MnS4 (Chevalier, 1968), was solved later with better accuracy from a crystal of Er2MnS4. The cell is orthorhombic, space group Cmc2. The metal atoms have two kinds of positions, one is a 7-coordinated site (7-prismatic) which contains one of the two Er atoms of the formula. The second type consists of two 6-coordinated sites (octahedral) containing a mixture in equal proportions of the second Er atom and the Mn atom in a disordered arrangement... 

The extensive disorder in any DNA structure leads to a myriad of mechanisms for electron transfer in rate constant measurements, and for electron or hole transport in conduction measurements. The major difficulties of understanding electron motion mechanisms in DNA are then of two sorts. First, the different kinds of disorder make reproducible measurements difficult to obtain. Second, the different sorts of interactions (Coulombic, vi-bronic, polarization, dynamical relaxation) make well-defined models difficult to formulate and deceptive in their predictions. 

---