Properties Of Biomimetic Selfassembled Aggregates

The asymmetric packing nature of bio-mimetic self-assembly provides a variety of unique physicochemical properties to its self- assembled aggregates. These sometimes are very comparable to those of symmetric self-assembled aggregates, and sometimes somewhat parallel. This section provides a brief description of this fact. Its implications for nanotechnology will be presented throughout Part II. 7.6.1. Directionality, Site-Specificity, and Chirality As emphasized throughout this chapter, the...

Nduced Asymmetric Packing

The primary building units described so far in this section have at least one of the intrinsic asymmetric packing factors within their molecular structural fea tures. Building units without any of the intrinsic asymmetric packing factors are usually self-assembled with the symmetric packing mode. However, when these building units interact with secondary units that have any of the intrinsic asymmetric packing factors, they can be self-assembled with the asymmetric packing mode, too. These...

Micellization Vs General Scheme Of Selfassembly

The main topic of this section is the change of micellar structure in solution. Critical factors for the evolution of micellar structures will be discussed. The concept of surfactant (or micellar) packing parameter or, simply, g-factor, will be introduced, which can be used to explain this structural change with the concept of force balance (Israelachvili et al., 1976 1992). As stated earlier, micelle formation is a process of force balance and no strong covalent bonding is involved. Any...

Emulsions

When two immiscible liquids are mixed together, the common sense of our experience is that they are not mixed up together, and soon after mechanical mixing is stopped, they will be separated into two clear phases. Mostly likely, the heavier water is on the bottom, and the lighter-density oil is on the top phase. This thermodynamic process can be dramatically altered when amphiphiles are introduced into this situation. The mixture of two immiscible liquids (usually oil and water) can be...

Self Assembled Monolayer SAM

A great deal of research has been amassed for the past several decades for SAMs, which has led to tremendous achievements in their preparations, characterizations, and applications. An excellent recent review (Love et al., 2005) is available for comprehensive detailed knowledge. This section, however, does not intend to cover these known facts again. The focus will be on the impact of the concept of force balance on the preparation, and the understanding and design of their characteristic...

Capillary Force

Whenever colloidal particles make contact with liquid-based interfaces (liquidgas interface, liquid--iquid interface, wetting liquid film, foam film, etc.), some degree of interaction is always induced between them. More specifically, a process toward a balance between the forces that act on the colloidal particles is executed. This force balance process always results in the apparent interaction between the particles. This is capillary force. Their interface with the liquid is critical for the...

Steric And Depletion Forces

Since the ancient civilizations of Egypt, Greece, and China, people have used a variety of natural polymeric materials as stabilizers for their paints, inks, and foods. Increased colloidal stability in these systems by the action of the polymers, mainly by steric and depletion forces, was one of the keys of their success. This has been an important issue for decades whenever there has been a great need to control coagulation, emulsification, and flocculation, which widely appears in traditional...

Hydrophobic Effect

Hydrophobic effect plays the central role in the understanding of molecular self-assembly phenomena in a wide-length scale. It is mainly an entropic effect, but for those who remember the thermodynamic principle, AG AH - T-AS, the hydrophobic effect is also affected by enthalpy contribution along with its entropy term. And each contribution is changing as a function of temperature and pressure. When a substance that is sparingly soluble in water, such as paraffin - chain alcohols, long-chain...

Physical Properties Of Micelles

Reverse Micelle

Again, the common aspects of the self-assembly of surfactant (and amphiphilic polymer) systems are that it is a thermodynamic, random, and nonhierarchical process with molecular-length scale. This section provides details on this issue. The definitions of three important parameters for micelles also will be given critical micelle concentration (cmc), aggregation number (n), and degree of counterion binding on the surface of micelles (a) (Tanford, 1980 Zana, 1991 Nagarajan and Ruckenstein, 2000...

Symmetric Biomimetic Selfassembled Aggregates

The bio-mimetic self-assemblies described so far were the asymmetric directional packing processes of their primary building units. However, there are some exceptional cases where the self-assembly occurs still through a directional but symmetric packing mode (or with a least degree of asymmetric packing). Even though the cooperative interaction with the structural constraint of the molecular building units is critical to guide the direction of the self- assembly, the major attractive forces...

References

Asefa, T., Yoshina-Ishii, C., MacLachlan, M. J., Ozin, G. A. New Nanocomposites Putting Organic Function 'Inside' the Channel Walls of Periodic Mesoporous Silica, J. Mater. Chem. 10, 1751 2000 . Babushkin, V. I., Matveyev, G. M., Mchedlov-Petrossyan, O. P. Thermodynamics of Silicates Springer-Verlag 1985 . Beck, J. S., Vartuli, J. C., Roth, W. J., Leonowicz, M. E., Kresge, C. T., Schmitt, K. D., Chu, C. T. W., Olson, D. H., Sheppard, E. W., McCullen, S. B., Higgins, J. B., Schlenker, J. L. A...

General Scheme For Selfassembly Process

Inter Facial Self Assembly Scheme

In the previous section, the balance between the distinctive but cooperative three classes of forces has been proposed for the formation of self-assembled aggregates. This general scheme can encompass a variety of self-assembly building units with the length scale ranging from atomic to colloidal. Since the self-assembly process can occur in such a wide range of length scale 107 difference of order from Angstr m to centimeter and the same types of forces are governing the process, the...

Asymmetric Structure of Building Units

Asymmetric packing of building units is also induced by the molecular or structural chirality that originates in the asymmetric geometry of the building units, and not from the presence of chiral carbon or centers. The packing mode is the same as for the chiral building units in Figure 7.3b. A typical class of this type of molecule is helicene Balaban, 2003 . These are mainly orthocondensed, nonplanar polycyclic aromatic molecules. The steric repulsion between the nearest bulky aromatic groups...

Multicomponent Micelles

As shown in Figure 3.9, a multicomponent or simply mixed micelle is a micelle that is formed through the self- assembly of more than two different kinds of surfactant molecules Abe and Ogino, 1992 . In most cases, the composition of monomers between the different surfactant molecules is directly related to the composition in the mixed micelles. Thus, the pseudo-phase separation model that can follow the key thermodynamics quantities is more suitable for the description of the formation of mixed...

General Scheme For The Formation Of Selfassembled Aggregates

Based on the above discussion, the general scheme for the self-assembly process that can encompass the length scale from atomic to colloidal can be drawn. Figure 1.2 shows the schematics. Self- assembly is the force balance process between three classes of forces attractive driving, repulsive opposition, and directional force. Directional force can be considered functional force in the sense that it is also responsible for the functionality. When only the first two classes of forces are in...

Selfassembly Through Force Balance

Surfactant self-assembly is often called micellization the process for the formation of micelles. With the view of the forces acting on this process, it is actually a process toward the delicate balance between the attractive and repulsive intermolecular forces. Attractive forces directly act on surfactant molecules to bring them close together, while repulsive forces act against the molecules. Hence, the former can be defined as the driving force for the micellization, and the latter as the...