Networks crystal

Figure 9.15 Temperature profile within a crystallizer network Sheikh and Jones, 1997)...

Sheikh, A.Y. and Jones, A.G., 1998. Optimal synthesis of stage wise continuous crystallization networks. American Institution of Chemical Engineers Journal, 44, 1637-1645. 

Marangoni, A.G. and Hartel, R.W. 1998. Visualization and structural analysis of fat crystal networks. FoodTechnol. 52 46-51. 

At temperatures above 25°C, the presence of emulsifier results in only a slight reduction in interfacial tension compared to a pure oii-water interface (7 25 mN/m). When the temperature is decreased further, a significant drop in interfacial tension (7) is registered due to interfacial crystallization followed by crystallization of emulsifier in the bulk oil phase below 15°C. The increase in 7 observed at temperatures below 10°C is artificial being caused by a viscosity increase due to the crystal network which has formed. 

Tetrathiafulvalene (TTF) derivatives containing fused 1,2,5-thiadiazole rings have been prepared in the interest of synthetic organic conductors. The extended -conjugation and unique two-dimensional crystal network of the derivative (13) may be expected to confer useful conducting... 

Electron delocalization is most extreme in solid and liquid metals. Here valence electrons are spread over not two, four, or six atoms, but over the entire crystal network. The extreme mobility of electrons accounts for their typically high electrical and thermal conductivity. Non-loealized electrons carry an electric current more effectively than any other species, and, because of their slight weight, are particularly quick to respond to thermal disturbance. 

Modeling Fat Crystal Networks and Relating Structure to Rheology... 

Based on this description of a fat crystal network, it makes sense that its macroscopic properties should depend significantly on the nature of the microstructures since this level of structure is closest to the macroscopic world. 

Figure 7.13. Schematic model of a fat crystal network showing particles of diameter a (i.e., small circles, <10 p,m) arranged into clusters of diameter f (i.e., large circles, > 100 p,m) with liquid oil interspersed.

Figure 7.14. Schematic of fat crystal network under extension when the weak-link theory is applicable ( is the diameter of crystal clusters, La is the size of the microscopic system, AL is the extension due to elongational stress, a is the size of a primary particle within a cluster and da is the interfloc distance).

The fractal dimension of a crystal network is an important parameter in terms of its relation to mechanical strength. However, the values of the pre-exponential term, A, (and the solid fat content) are equally important. For spherical microstructures (Narine and Marangoni, 1999c Marangoni, 2000 Marangoni and Rogers, 2003),... 

The fractal dimension of the fat crystal network in milk fat decreased from 2.5 to 2.0 when the cooling rate was increased. Concomitantly, the particle-related constant, A, increases. These results demonstrate how a faster cooling rate leads to a less ordered spatial distribution of mass within the microstructural network, which would result in a lower value of D, and a decrease in the average particle diameter, which would result in a higher value of A, as predicted by our model. These microstructural changes were correlated with a much higher yield force value for the rapidly cooled milk fat (64.1 3.3N versus 33.0 3.9N for the samples cooled at 5.0°C/min and 0.1°C/min, respectively). 

Narine, S.S., Marangoni, A.G. 1999a. Relating structure of fat crystal networks to mechanical properties a review. Food Res. Int. 31, 227-248. 

Narine, S.S., Maranongi, A.G. 2001. Elastic modulus as an indicator of macroscopic hardness of fat crystal networks. Lebensm. Wiss. Techonl. 34, 33—40. 

Rye, G., Litwinenko, J., Marangoni, A.G., 2005. Fat crystal networks - structure and rheology. In, Bailey s Industrial Oil Fat Products (F. Shaihidi, ed.), John Wiley, New York (In press). 

Other methods of imaging fat crystals and fat crystal networks (not all of them optical) include confocal laser scanning fluorescence microscopy, multiple photon microscopy, atomic force microscopy and electron microscopy (Narine and Marangoni, 1999). 

P-31P POST-C7 correlation spectra (Figure 20A-C) of Na2ATP hydrates were employed by Potrzebowski and co-workers for the analysis of the distances between phosphorus centres in crystal lattices.52 The structural constraints were further used for the prediction of crystal network of the monohydrate for which the X-ray structure is unknown. 

Many interrelated factors influence the texture of plastic fats. Fatty acid and glyceride composition are basic factors in establishing the properties of a fat. These factors, in turn, are related to solid fat content, crystal size and shape, and polymorphic behavior. Once the crystal network is formed, mechanical treatment and temperature history may influence the texture. 

The network systems in plastic fats differ from those in protein or carbohydrate systems. Fat crystals are embedded in liquid oil and the crystals have no ionized groups. Therefore, the interactive forces in fat crystal networks are low. The minimum concentration of solid particles in a fat to provide a yield value is in the range of 10 to 15 percent. 

DeMan and Beers (1987) have reviewed the factors that influence the formation of three-dimensional fat crystal networks. The fat crystal networks in plastic fats (Figure 8-44) are highly thixotropic, and mechanical action on these products will result in a drastic reduction of hardness. 

A variety of rheological tests can be used to evaluate the nature and properties of different network structures in foods. The strength of bonds in a fat crystal network can be evaluated by stress relaxation and by the decrease in elastic recovery in creep tests as a function of loading time (deMan et al. 1985). Van Kleef et al. (1978) have reported on the determination of the number of crosslinks in a protein gel from its mechanical and swelling properties. Oakenfull (1984) used shear modulus measurements to estimate the size and thermodynamic stability of junction zones in noncovalently cross-linked gels. 

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