Order-disorder processes

While in neither system the total film thickness exceeded several nanometers, swelling and contact angle measurements displayed dynamic behavior of the amphiphilic surface, and reversibility of the ordering-disordering process. 

The interaction of NF-kB with IkB provides a wealth of examples of several different kinds of order-disorder processes. This work was started in our lab as a collaboration with Dr. E.A. Komives at the University of California, San Diego. Nuclear factor-kappaB (NF-kB) is a dimeric transcription factor widely employed for the transcription of stress-response genes, as it binds to kB upstream enhancer DNA sequences, where it recruits the transcriptional activator CBP. In an unstressed cell, the majority of the NF-kB resides in the cytoplasm, in complex with the inhibitor of NF-kB (IkB). Response to stress involves phosphorylation and ubiquitination of IkB and its subsequent degradation by the proteasome. The free NF-kB is transported to the nucleus, where it binds to the kB enhancer sequences and mediates the transcription of genes that include that of IkB, which acts subsequently to remove NF-kB from the DNA and return it to the cytoplasm as the NF-kB-IkB complex. 

This shows that the Bragg-Williams model predicts that the transition temperature is a direct function of the exchange energy for the order-disorder process. Furthermore, the equilibrium condition dddQ = 0 gives the solution... 

Carpenter, M.A., Salje, E.K.H. (1989) Time-dependent Landau theory for order/disorder processes in minerals. Mineral Mag 53 483-504... 

Figure 6-6. Schematic view of the electrochemically controlled order-disorder process disclosed by the in situ STM images in Fig. 6-5. Reprinted from ref 5 with permission.

At ambient temperature, ferrocene/thiourea has the conventional rhoinbohedral thiourea host structure.The Fe atoms of the fessocene guest molecules occupy the sites of 32 symmetry within the host tunnel, and the cyclopenta-dienyl rings are disordered. Heat capacity measure-ments have suggested that there are five phase transitions (at ca. 147, 160, 171, 186, and 220 K) between 13-280 K, which led to the proposal that the transitions at 147 K and 160 K are associated with reorientational order-disorder processes involving the molecular axis of ferrocene. 

Mossbauer spectroscopy in solid state chemistry under in situ conditions at high temperatures and at defined oxygen partial pressures have been made by Becker (2001) for order-disorder processes and their kinetics in nickel alu-minate spinel and magnetite. The study has also been carried out for heterogeneous solid olid and solid-gas reactions which relate to the formation of cobalt aluminate spinel and to redox processes in fayalite, Fe2Si04, respectively. The diffusion of the iron cations in Fc2Si04 has also been observed by means of Mossbauer spectroscopy. 

The kinetics of ordering in solid solutions and even more so rate processes during phase transformations are both expermentally and theoretically very difficult subjects. Furthermore, in light of the previous discussion it is highly questionable whether order-disorder processes as they occur in simple glass forming (i.e., metal alloys) substances also take place in polymers. Nevertheless, attempts are being made to improve... 

The important question remains is this second critical point the key to understanding the anomalies of water, or does the cooperation of the configurational excitations at some parameter or some thermodynamic field choice produce a critical point The cooperation of the configurational excitation is implied by the form of the heat capacity extracted by confined water, in particular, that of water confined in silica gel materials [128] at < = 1.1 nm. In this case, water remains in the liquid state at very low T and shows a Cp peak at approximately 227K (see, e.g.. Fig. 21). The hump at 227K supports the order disorder process hypothesis of water molecules in the liquid state. This silica gel sample —dH/dt does not give a water GT at this temperature, the 227K peak can be attributed to an order-disorder process, and the Tg is located at lower temperatures. 

R.B. Scorzelli, J. Danon, Mossbauer spectroscopy and X-ray diffraction studies of Fe-Ni order-disorder processes in a 35 % Ni meteorite (Santa Catharina). Phys. Scr. 32, 143-148... 

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