Network phases

Fig. 18 Phase space of PI-fc-PS-fc-PEO in vicinity of ODT. Filled and open circles-. ordered and disordered states, respectively, within experimental temperature range 100 < T/° C< 225. Outlined areas compositions with two- and three-domain lamellae (identified by sketches) shaded regions three network phases, core-shell double gyroid (Q230), orthorhombic (O70), and alternating gyroid (Q214). Overlap of latter two phase boundaries indicates high- and low-temperature occurrence, respectively, of each phase. Dashed line condition tfin = 0peo associated with symmetric PI-fc-PS-fc-PEO molecules. From [75]. Copyright 2004 American Chemical Society...

Depending on the conditions of synthesis, copolymerization of divinyl/vinyl-monomers in the presence of an inert solvent leads to the formation of expanded (preswollen) or heterogeneous (porous) structures [54,99,100]. If the solvent remains in the network (gel) phase throughout the copolymerization, expanded networks are formed. If the solvent separates from the network phase the network becomes heterogeneous. According to Dusek et al., heterogeneities may appear in poor solvents due to the polymer-solvent incompatibility (x-induced syneresis), while in good solvents due to an increase in crosslink density (v-induced syneresis) [99]. 

Figure 10 O-H radial distribution function as a function of density at 2000 K. At 34 GPa, we find a fluid state. At 75 GPa, we show a covalent solid phase. At 115 GPa, we find a network phase with symmetric hydrogen bonding. Graphs are offset by 0.5 for clarity.

In recent years few topics have generated a more spirited discussion among coal scientists than the issue of the putative binary (mobile + network) phase nature of coals (y. Initially based on NMR observations (, the concept of a "mobile phase" in coal soon came to encompass a broad range of more or less readily extractable and/or distillable lower molecular weight (MW) components, variously referred to as "guest molecules" (3), "clathrates" (1,4) or simply, and perhaps most succinctly, "bitumen"... 

In the context of the present discussion the term "mobile phase will be used to describe those components which can be thermally extracted ("distilled", "desorbed ) under vacuum at temperatures below the thermal degradation range of the coal. The residue, designated as the nonmobile ("network ) phase, is thermally degraded in the pyrolysis temperature range. Of course, the onset of pyrolysis may vary considerably, depending on heating rate, rank and coal type (10). 

The above observations point to the importance of rank and depositional environment in defining the molecular characteristics of the mobile phase as well as the network phase of coals. 

Meluch AA, Hainsworth JD, Gray JR, et al. Preoperative combined modality therapy with paclitaxel, carboplatin, prolonged infusion 5-fluorouracil, and radiation therapy in localized esophageal cancer preliminary results of a Minnie Pearl Cancer Research Network phase II trial. Cancer J Sci Am 1999 5 (2) 84-91. 

The degree of swelling at equilibrium will be determined by the equality of the chemical potential inside and outside the swollen network phase. If the outside diluent is at activity a1 we will have... 

Passing this point, excess diluent is separated outside the network phase 49). The development of two phases is called (macro)syneresis. 

To predict macrosyneresis in the case of dissolved polymer chains being crosslinked it is necessary to know the change in the number of elastically effective network chains as a result of changing the number of chemical crosslinks and the effect of v on (r2),. and possibly on y. Moreover, if the molecular weight of primary chains is finite and the sol fraction is important, a complete description of the phase separation requires treating the system as a multicomponent one, containing a network phase and a multicomponent diluent with branched polymer species. If additional crosslinking is carried on in an extracted network the latter complication can be eliminated. 

Fig. 17. Equilibrium swelling and relative volume of the network phase after phase separation in crosslinking of existing chains. Initial volume fraction of the polymer 0.2, x = 0.45, P -> oo [DuSbk (49)]...

Pearl Cancer Research Network phase II trial. J Clin Oncol 2001 19 ... 

Fig. 6 FuUy reticulated nanoporous Fe-carboxylate networks comprising diiron centers as coordination motif. a,b STM topographs of isomeric FeTPA network phases a identical and b alternating Fe dimer arrangement, c High-resolution STM image of the FeBDA network. d STM image of the FeTDA network phase. Tentative models are superimposed on the STM images. Adapted from [207]...

In this equation, (l — f ) is the volume fraction of the diluent in the network phase at the moment of phase separation (or, which is the same, in the solution prior to phase separation), Uj the volume fraction of the network phase, i/ (mol/cm ) the concentration of the network active chains in unit dry volume of the gel (which is proportional to the concentration of crosshnks), Xi3 the Flory—Huggins parameter, Fj the partial molar volume of the diluent, and subscripts 1 and 3 relate to the diluent and polymer, respectively. Notably, Eq. [3.6] incorporates four independent parameters the thermodynamic quahty of the diluent Xi3> its partial molar volume Fj, the dilution of the system 1 — Vj, and the varying crosslinking density zz. ... 

Figure 1.7 Interconversion of the highly porous, homochiral 3D MOF [Ni3(btc)2(py)6(l,2-pd)3]- (guest) upon guest desorption and exposure to ethanol vapour (a), involving transformation from a doubly interpenetrated, distorted (10,3)-a network phase to one in which four regular (10,3)-a nets interpenetrate (b). Reprinted with permission from C.J. Kepert, T.J. Prior and M.J. Rosseinsky, /. Am. Chem. Soc., 122, 5158. Copyright (2000) American Chemical Society...

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