Critical packing parameters

In developing controlled-release matrices, the solubilization capacity of miaoanulsions should be optimized, which depends on various factors, such as the oitical micelle concentration, the surfactant s HLB value, the critical packing parameter and molecular compatibility between the oil, surfactant and co-surfactant (Friberg et al., 1994 Aboofazeli et al., 1995 von Corswant and Soderman, 1998). 

The critical packing parameter (CPP) is a measure of the preferred geometry adopted by a surfactant in solution  

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The molecular descriptors refer to the molecular size and shape, to the size and shape of hydrophilic and hydrophobic regions, and to the balance between them. Hydrogen bonding, amphiphilic moments, critical packing parameters are other useful descriptors. The VolSurf descriptors have been presented and explained in detail elsewhere [8]. The VolSurf descriptors encode physico-chemical properties and, therefore, allow both for a design in the physico-chemical property space in order to rationally modulate pharmacokinetic properties, and for establishing quantitative structure-property relationships (QSPR). 

Introduction to the variety of types of surfactants, effect of surfactants on aqueous solution properties. Law of mass action applied to the self-assembly of surfactant molecules in water. Spontaneous self-assembly of surfactants in aqueous media. Formation of micelles, vesicles and lamellar structures. Critical packing parameter. Detergency. Laboratory project on determining the charge of a micelle. 

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 ... 

Figure 4.6 Use of the critical packing parameter to predict aggregate structures.

Describe how the critical packing parameter for surfactant self-assembly can be used to describe the structure of typical biological lipid membranes. 

Explain the link between the critical packing parameter and the interaction forces between surfactant molecules in water. 

Chapter 8 has been revised to include a discussion of the critical packing parameter of surfactants and its relation to the structure of resulting surfactant aggregates. This simple geometric basis for the formation of micelles, bilayers, and other structures is intuitively easier to understand for a beginning student. 

Critical packing parameter defined as the volume of the hydrophobic part divided by the product of the surface of the hydrophilic part times the length of the hydrophobic part... 

Critical packing parameter (CP) is the ratio between the hydrophobic and lipophilic parts of a molecule. In contrast to HL balance, CP refers just to the molecular shape. 

The shape of the micelle formed by a particular surfactant is influenced to a large extent by the geometry of the surfactant molecule, as can be seen if we consider the packing of space-filling models of the surfactants. The dimensionless parameter of use in these considerations is called the critical packing parameter (CPP) and is defined as... 

Figure 6.25 Influence of the critical packing parameter, CPP = vl(l a], on the type of aggregate formed by surfactants in solution.

Fig. 4 Critical packing parameters and characteristic structure typical to mesoporous silica films. The top shows a cross-section of a micelle, displaying the parameters used to calculate the CPP. The spherical head group for the surfactant represents the effective cross-sectional area that the head group occupies. (View this art in color at www.dekker.com.)...

A useful concept for characterizing micelle geometry is the critical packing parameter (CPP) [2]. The aggregation number N is the ratio between the micellar core volume, V and the volume of one chain, v. 

Critical packing parameter, defined as the ratio of surface of the hydrophobic regions at —0.6 kcal/mol to the surface of the hydrophilic regions at —3 kcal/mol... 

The thermodynamic modeling of microemulsions has taken various lines and gave conflicting results in the period before the thermodynamic stability and microstructure were established. It was early realized that a maximal solubilization of oil and water simultaneously could be discussed in terms of a balance between hydrophilic and lipophilic interactions the surfactant (surfactant mixture) must be balanced. This can be expressed in terms of the HLB balance of Shinoda,Winsor s R value, and a critical packing parameter (or surfactant number), as introduced to microemulsions by Israelachvili et al. [37], Mitchell and Ninham [38], and others. The last has become very popular and useful for an understanding of surfactant aggregate structures in general. 

Molecular dynamics simulations are consistent with calculations based on the critical packing parameter p, which indicate that the structure of the surfactant controls the shape of the micelle at the cmc. Esselink et al. [16] show that the surfactants / 2/5, hihts, and h thts form bilayers, cylindrical micelles, and spherical micelles, respectively, as expected. However, /14/4, expected to form micelles of low curvature based on p, instead forms sphere-like structures due to the coiling of the headgroup. If this increased effective headgroup area is accounted for in the calculation of the packing parameter, then a spherical shape is predicted, in agreement with the result of the simulations. 

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