Aggregates architecture

The critical packing parameter can be used as a guide to the aggregate architecture for a given surfactant (as shown in Figure 4.6). Typical values and their corresponding aggregate structures are ... 

These are repulsive interactions of short range (0.2-0.3 nm) arising from the highly unfavourable overlap of full electron clouds. They are sometimes called steric interactions because they restrict the relative spatial arrangement of pairs of segments on the same or different macromolecules. The excluded volume expression arises from the fact that the volume occupied by one biopolymer molecule in solution is not available to other biopolymer molecules. Thus the size and shape of the biopolymer molecule/particle (as determined by the macromolecular conformation/ flexibility or aggregate architecture) is of prime importance in relation to steric5 interactions. 

Orchard, 1995). Such a modification of aggregate architecture results in a complex and discontinuous pattern in pore spaces of various sizes and shapes (Haider and Guggenberger, 2005) and would thus greatly influence the physical, chemical, and biological properties of soils. The dimension of pore sizes ranges from <2 nm (micropores) to 2 to 50 nm (mesopores) to >50 nm (macropores). The pore neck... 

A multitude of different variants of this model has been investigated using Monte Carlo simulations (see, for example [M])- The studies aim at correlating the phase behaviour with the molecular architecture and revealing the local structure of the aggregates. This type of model has also proven useful for studying rather complex structures (e.g., vesicles or pores in bilayers). 

Figure 6-25. Fluorescence spectra at 4.2 K of T,. thin lilms with morphology characterized by a) grains b) layers c) islands d) sub-monolayer. The lower density ol aggregate states in the sub-monolayer architecture decreases the energy transfer efficiency to low energy stales and the fluorescence acquires dominant excitonie character (sec Section 6.6.2.2J.

Overall, the alkali metal alkoxide and aryloxide systems are excellent examples in demonstrating the effects of steric influences on both molecular aggregation and also on the nature of any extended network architecture adopted. The large database of O-M complexes that have now been identified has led to a good deal of predictability regarding the coordination chemistry of these species. 

Bauer, H. H., Aebi, U., Haner, M., Hermann, R., Muller, M., and Merkle, H. P. (1995). Architecture and polymorphism of fibrillar supramolecular assemblies produced by in vitro aggregation of human calcitonin./. Struct. Biol. 115, 1-15. 

---