Order tendency

The dispersive tendency dominates in a high-temperature system containing only a few particles, while the order tendency is important in a system in which the particles are themselves ordered, as in a crystal or the DNA helix. The real states of systems of matter lie somewhere between these two extremes. 

In the further discussion, we must distinguish whether X is positive or negative. In the latter case, the ordering tendency of the thin film is enhanced as compared to the bulk, i.e. the critical temperature TC(D) in the thin film exceeds the critical temperature Tcb of the bulk, b being still finite at TC(D). The transition simply results from the vanishing of the denominator, [x=D/(2 b) ... 

Are the C.C. the expression of an ordering tendency, related to the movement towards minimum potential energy of complex low temperature systems, which can account both for the genesis... 

Fig.3. Schematics of the evolution of equilibrium segregation with temperature in alloys with order-segregation competition (a) dominant surface segregation tendency (Langmuir-McLean behaviour), (b) dominant ordering tendency. Signs of enthalpy and entropy of segregation are indicated.

The role of bulk off-stoichiometry is exemplified in Fig.7. Even slight negative deviations diminish considerably segregation levels, while positive deviations lead to strong enhancement relative to the levels calculated for the exactly equiatomic bulk. These somewhat surprising findings can be understood in terms of the dominant bulk ordering tendency, by which excess atoms (>50%) are effectively pushed out from the bulk (due to its reduced coordination,... 

This shows us that the ordering tendency decreases in the sequence PtFe, PtNi and PtCo. 

Turning to other ordered phases of the Cu-Au system, we again find that the (100) surface terminations are compatible with both Au segregation and ordering. The Llg and LI2 structures of CuAu and AU3CU, respectively, allow a pure Au termination, and thus segregation of Au (cf. Fig. 8). Thus, in spite of the moderate to weak ordering tendencies (Tj ans m resp.),... 

Other secondary factors that could influence the enthalpy-relaxation process are substantial subsidiary modes of motion and structure-forming capability. Enthalpy-relaxation rates for blsphenol-A polycarbonate (PC), which has substantial mcdn-chcdn motion in the glassy states (8.10-17), and for poly(ethylene terephthalate) (PET), which in addition to having subsidiary modes of motion has significant crystal-ordering tendency (8,9)> were studied in detail, and the results are reported here. 

These data concerning the molecular-structure dependency of the enthalpy-relaxation process suggest that the f u tors that influence the onset of segmental mobility influence enthalpy relaxation, but that the presence of mobile groups in the main chain or the ciystal-ordering tendency of polymers does not seem to have a significant effect on the rate of enthalpy relaxation. 

The only reasonably plausible interpretation which reconciles this evidence in a self-consistent fashion appears to be that summarized in Fig. 6. This model argues that chain expansion at low ionic strength and the attendant increase in congestion in the solution lead to cooperative intermolecular interactions, viz. an ordering tendency between near neighbors. As described above, it appears based on the known structural features of PGS that a reasonably accurate determination of the particle scattering function P(K) can be obtained by extrapolation at each angle to c = 0. This permits a determination of S(K) via eq. (4). These S(K) data permit a rationalization of... 

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