Phase separation in gels

Such a shape of the curves Ap (and Ap ) points to the possibility of existence of two phases of a network polymer with different conformations of network chains. In equilibrium, the condition 

Little is known on the morphological realization of this separation kind. Most likely, the separation proceeds in small volumes of the system and leads to a great heterogeneity in the gel structure. Such a separation is called microsyneresis. 

While X (temperature) continuously changes, conditions 94 give rise to a phase transition, which sharply changes the network chain conformation, which, in turn, leads to a significant decrea.se (or increase) in the gel volume — a so-called collapse (or overswelling, superswelling) of gels. 

Of special interest is the case of P 0 (when polymer is placed into a fixed volume accessible to LMWL molecules). Then, the equality between the chemical potentials of LMWL in the network and outside it is due to the LMWL transport into the network, which cau.ses a pressure increase in the gel by 

In this case, the situation is similar to a solvent and a solution separated with a semiper-meable membrane (see subsection 1.2.2). 

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The dominant influence t/ (in compzirison with x) niay lead lo the fact that phase separation in gel takes place in the pre.scnce of LMWL being a good. solvent in sointion.s of the linear modification of a polymer. 

Moseley PT, Norris JOW, Williams DE (1991) Techniques and mechanisms in gas sensing. Adam Hilger, Bristol Nakaso K, Han B, Ahn KH, Choi M, Okuyama K (2003) Synthesis of non-agglomerated nanoparticles by an electrospray assisted chemical vapor deposition (ES-CVD) method. J Aerosol Sci 34 869-881 Narendar Y, Messing GL (1997) Mechanisms of phase separation in gel-based synthesis of multicomponent metal oxides. Catal Today 35 247-268... 

We have purposely narrowed the scope of all multidimensional chromatography to those techniques that incorporate separations in the liquid phase and to those in which the use of the comprehensive mode prevails but is not exclusive. This text neither incorporates elements of multidimensional thin-layer chromatography, multidimensional separations in gel media such as those commonly employed for the separation of complex mixtures of proteins, nor the techniques that utilize multidimensional gas chromatography. Some of the same principles apply, particularly in the theory section, but our emphasis is strictly on separations carried out in the liquid phase and by columns, rather than in the gas phase or in planar configurations. 

Nakanishi, K. and Soga, N., Phase-separation in silica sol-gel system containing polyacryhc-acid. 1. Gel formation behavior and effect of solvent composition, Journal of Non-Crystalline Solids 139(1), 1-13, 1992. 

Loren, N., Hermansson, A.-M. (2000). Phase separation and gel formation in kinetically trapped gelatin/maltodextrin gels. International Journal of Biological Macromolecules, 27, 249-262. 

The laser output intensity of the C153 and R6G ORMOSIL gels was studied as a function of the number of laser pump pulses. Both materials could be pulsed for more than 3000 shots with a reduction of the emission amplitude of about a factor of four. Specifically, the C153 gel laser intensity decreased by a factor of 6 after more than 6000 pulses of 500 MW/cmA The plot of the intensity versus number of shots has a double exponential decay. This phenomenon is not yet completely understood, but it could be associated with microscopic phase separation in the medium. The R6G decay plot shows that the intensity undergoes a 90% reduction after 5300 laser pulses. 

Bian, J. and Roberts, M. F. (1990). Phase separation in short-chain lecithin/gel state long-chain lecithin aggregated3iochemistry, 29, 7928-7935. 

Rubber Phase Domain Size and Shape. Phase domain size seems to be controlled in part by the time of phase separation in relationship to the gel time of the reaction. Smaller phases are generally produced when phase separation is delayed until near or after the gel point of the total reaction. It is possible to tell if phase separation has occurred near the gel point by the clarity of the mix. If phase separation has occurred, the mix is cloudy or milky. In addition the bimodal distribution of phase domain sizes found in some samples is evidence that the reactions are truly simultaneous because the larger domains are probably formed before gelation and smaller domains by continued phase separation after gelation. 

The temperature of the binodal and onset of phase separation is dependent on the composition. In a quench experiment, the time evolution of the phase separation is dependent on the end temperature and the composition. This means that the depth into the incompatibility region at a given position has an impact on the time evolution. Phase separation will then be trapped by gel formation, and it is the relative kinetics between phase separation and gel formation that determines the final morphology. Figure 13.12 gives an example of how the morphology of a discontinuous system depends on the composition and the relative kinetics of phase separation and gel formation (Loren and Hermansson 2000). 

Kasapis, S., Morris, E. R., Norton, I. X, and Brown, C. R. X 1993a. Phase-equilibria and gelation in gelatin maltodextrin systems. 3. Phase-separation in mixed gels. Carbohydr. Polym. 21 261-268. 

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