Association structures amphiphilic

Friberg, S.E., Yang, C.-C., and Sjoblom, J., Amphiphilic association structures and the microemul-sion/gel method for ceramics influence on original phase regions by hydrolysis and condensation of silicon tetraethoxide, Langmuir, 8, 372, 1992. 

The formula for the dicarboxylic acid (Figure 2.9) has a hydrophilic/lipophilic balance similar to that of octanoic acid, but the influence of the two acids on amphiphilic association structures is entirely different, as shown in Figure 2.10 [93], The octanoic acid causes the formation of a liquid crystal when added to a solution of water in hexylamine. The size of the lamellar liquid crystalline region is large (Figure 2.10a). Addition of the dicarboxylic acid, in contrast, gives no liquid crystal, and it may be concluded that its action in concentrated systems is similar... 

Another approach was developed in Scandinavia following the pioneering contributions of Ekwall et al. on amphiphilic association structures [17] and in Japan by Shinoda and coworkers [18-24], who investigated the structural changes in systems of water, hydrocarbon, and nonionic surfactants of the polyethylene glycol all l ether type. 

Apart from these applications, ILs also stimulated research in classical colloid and surface chemistry. The formation of amphiphilic association structures in and with ionic liquids, such as micelles, vesicles, microemulsions and liquid crystalline phases has been reviewed three times between 2007 (Hao Zemb 2007) and 2008 (Qiu Texter 2008 Greaves Drummond 2008 a), reflecting the growing interest and progress in this field. In this review we focus on ILs in nonaqueous microemulsions, because significant new work has been reported in this field since these earher reviews have been published. 

T1he importance of association structures of amphiphilic molecules for interfacial phenomena has been realized in the last ten years with the rapid progress of knowledge concerning the structure of biomembranes and the discovery of the pronounced influence of surfactant association structures on the properties of disperse systems. 

The unterstanding of amphiphile association clearly must include detailed knowledge of the internal structure and dynamics, e.g., what is the conformation of the alkyl chains and what are their flexibility and packing conditions is the interior of micelles exclusively of hydrocarbon nature or is there any water penetration We will here consider the state of the hydrocarbon chains and defer a discussion of water penetration to the section on hydration. 

The synthesis of giant amphiphiles was recently reported by Meijer et al, who linked a linear hydrophobic poly(styrene) block to a dendritic poly(propyleneimine) as a polar head group. The association structure was found to vary with the dendrimer generation changing Irom inverse micelles for poly(styrene-JenJr-(NH2)4) through vesicles and rod-like micelles to spherical aggregates for poly-(styrene-fife fi r-(NH2)32 [210]. 

Advances in the fields of polymers and amphiphilic colloidal association structures have progressed in a most pronounced manner in the past decade. However, the interaction between these two disciplines and the beneOts of cross-fertilization have been limited. 

These are of two kinds related to each other by the difference in association structure as illustrated by the temperature variation of surfactant solubility and association. Figure 6 provides a schematic description of the interdependence. At low temperatures the solubility limit of the xmimers (s, solid line. Fig. 6) is lower than the limit for amphiphilic association (cmc, dashed line. Fig. 6), and, hence, the latter is not reached and a two-phase equilibrium, aqueous solution of monomers—hydrated surfactant, is established. At temperatures in excess of the Krafft point, Tj (Fig. 6), the association concentration (cmc, solid line, Fig. 6), is now beneath the solubility limit (s, dashed line. Fig. 6). Association takes place and the total solubility (ts. Fig. 6) is drastically increased. Hence, the water—siufactant phase diagram shows a large solubility range for the isotropic liquid solution (unimers plus micelles. Fig. 6) because the association structure, the micelle, is soluble in water. This behavior is characteristic of smfactants with Ninham R values less than 0.5. 

The criteria for thermodynamic stability is of limited use in the formulation of microemulsions for such efforts the colloidal approach to microemulsion systems (Adamson, 1969 Gillberg, 1970 Shinoda, 1973 Ahmad, 1974 Shinoda, 1975 Friberg, 1976 and Sjoblom, 1978) is advantageous with its direct relation to the association structures of the chemical components. This article will give a short description of the common association structures of amphiphilic molecules and the mutual relations with the microemulsions. 

These computational prediction results show that onchidal is not flagged to be of concern for bacterial mutagenicity, but it might be expected to induce phospholipidosis in animals despite not possessing a traditional cationic amphiphilic molecular structure (Choi et al., 2013). Predictions were also made using the QSAR approach regarding clinical cardiac adverse events related to proarrhythmia. The in silica predictions are presented in Table 30.4. The predictions show that onchidal s molecular structure is associated with QT... 

Proteins and polar lipids coexist in biological systems, mainly unassociated with each other but also as composite structures with specific actions [137]. They have a very important physical property in common an inherently amphiphilic nature, which provides the driving force for the formation of associative structures of lipids as well as for stabilizing some food colloids. 

In aqueous solutions of amphiphilic polymers, which contain both hydrophilic and hydrophobic sequences, strong interpolymer hydrophobic association often leads to bulk-phase separation or gelation. However, there are classes of amphiphilic polymers that form well-organized associated structures in aqueous solution without accompanying macroscopic phase separation. This is generally characteristic of amphiphilic AB and ABA block copolymers, where A and B represent hydrophilic and hydrophobic sequences, respectively. These types of block copolymers and low molecular weight surfactant molecules have common features in their associating behavior. 

Chapter 4 discussed the formation of relatively small, uniform, or isotropic association structures or micelles in dilute surfactant solutions. We know, however, that surfactants and related amphiphilic molecules, including the naturally occurring lipids, some proteins, and a variety of combined natural chemical species, tend to associate into structures more extensive than simple micelles in both aqueous and nonaqueous environments. In many cases, such assembUes can transform from one type to another as a result of sometimes subtle changes in solution conditions such as (1) changes in the concentration of the amphiphilic components, (2) the addition of new active components, (3) changes in solvent composition, (4) the addition of electrolytes, (5) temperature changes, (6) changes in solution pH, and (7) unspecified influences from internal and external sources—such as the phase of the moon, or so it seems at times. 

Over the years it has been confirmed that geometric factors control the packing of surfactants and lipids into association structures. The concept has already been introduced, but warrants repetition in the current context for clarity. The packing propensity of a given amphiphilic stmcmre can be conveniently given by the critical packing parameter, denoted here as and given by... 

These are molecules which contain both hydrophilic and hydrophobic units (usually one or several hydrocarbon chains), such that they love and hate water at the same time. Familiar examples are lipids and alcohols. The effect of amphiphiles on interfaces between water and nonpolar phases can be quite dramatic. For example, tiny additions of good amphiphiles reduce the interfacial tension by several orders of magnitude. Amphiphiles are thus very efficient in promoting the dispersion of organic fluids in water and vice versa. Added in larger amounts, they associate into a variety of structures, filhng the material with internal interfaces which shield the oil molecules—or in the absence of oil the hydrophobic parts of the amphiphiles—from the water [3]. Some of the possible structures are depicted in Fig. 1. A very rich phase... 

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