Nonionic surfactants chemical structure

A list of the CMC values of selected surfactants at 25°C is given in Table 19.2, while in Table 19.3 a list for nonionic surfactants is given. From these and other data, several general remarks about the variation of the CMC with the surfactant chemical structure can be made, as follows ... 

The EO/PO nonionics are also mild surfactants. Chemical structure... 

Biodegradable oil spill dispersants with high efficiency and low toxicity have been prepared and tested. They consist of nonionic and low-toxicity surfactants with different molecular weights [2]. The relationship between interfacial tension and the efficiency and chemical structure of the prepared oil spill dispersants was also studied. 

Since levelling agents are invariably surfactants, they may be anionic, cationic, nonionic or amphoteric in nature. Sometimes combinations of these are used. The chemical structure of commercial products is seldom revealed, however hence only general principles can be covered here. The main mechanisms by which levelling agents operate [337-341] are as follows ... 

The correct understanding of the relationships between chemical structure and properties in surfactants is most important to both their effective use in many applications and to molecular designing of new surfactants. Some reliable information is available on various structural effects in ionic surfactants. On the other hand, only a limited amount of reliable information is a-vailable for nonionics with much of the data in the literature being insufficient both in reliability and in the variety of structures dealt with, mainly because of the difficulty in obtaining well-characterized compounds. 

In tile application of surfactants, physical and use properties, precisely specified, are of primary concern. Chemical homogeneity is of little significance in practice. In fact, surfactants are generally polydisperse mixtures, such as the natural fats as precursors of fatty acid-derived surfactant structures e.g., coconut oil contains glycerol esters of Cc-Qa fatly acids. Nonionic surfactants of die alcohol edioxylate type are polydisperse not only with respect to the hydrophobe but also in the number of edivlene oxide units attached. 

Microemulsions are thermodynamically stable, clear fluids, composed of oil, water, surfactant, and sometimes co-surfactant that have been widely investigated during recent years because of their numerous practical applications. The chemical structure of surfactants may have a low molecular weight as well as being polymeric, with nonionic or ionic components [138-141]. For a water/oil-continuous (W/O) microemulsion, at low concentration of the dispersed phase, the structure consists of spherical water droplets surrounded by a monomolecular layer of surfactant molecules whose hydrophobic tails are oriented toward the continuous oil phase (see Fig. 6). When the volume fractions of oil and water are high and comparable, random bicontinuous structures are expected to form. 

Niosomes In order to circumvent some of the limitations encountered with liposomes, such as their chemical instability, the cost and purity of the natural phospholipids, and oxidative degradation of the phospholipids, niosomes have been developed. Niosomes are nonionic surfactant vesicles which exhibit the same bilay-ered structures as liposomes. Their advantages over liposomes include improved chemical stability and low production costs. Moreover, niosomes are biocompatible, biodegradable, and nonimmunogenic [215], They were also shown to increase the ocular bioavailability of hydrophilic drugs significantly more than liposomes. This is due to the fact that the surfactants in the niosomes act as penetrations enhancers and remove the mucous layer from the ocular surface [209]. 

Using the DDT and nonionic exan jles cited above, we can evaluate the proposed mathematical model. This example also lias the benefit of comparing two surfactants that are very similar in chemical structure and physical characteristics. 

In aqueous solutions the micellar assembly structure allows sparingly soluble or water-insoluble chemical species to be solubilized, because they can associate and bind to the micelles. The interaction between surfactant and analyte can be electrostatic, hydrophobic, or a combination of both [76]. The solubilization site varies with the nature of the solubilized species and surfactant [77]. Micelles of nonionic surfactants demonstrate the greatest ability for solubilization of a wide group of various compounds for example, it is possible to solubilize hydrocarbons or metal complexes in aqueous solutions or polar compounds in nonpolar organic solutions. As the temperature of an aqueous nonionic surfactant solution is increased, the solution turns cloudy and phase separation occurs to give a surfactant-rich phase (SRP) of small volume containing the analyte trapped in micelle structures and a bulk diluted aqueous phase. The temperature at which phase separation occurs is known as the cloud point. Both CMC and cloud point depend on the structure of the surfactant and the presence of additives. Table 6.10 gives the values of CMC and cloud point for the surfactants most frequently applied in the CPE process. 

Materiala. Nonionic surfactants Brij 52 (B52) and Brij 30 (B30) were obtained from the Sigma Chemical Company and used as received. These surfactants are ethoxylated alcohols with the nominal structures Cie a and C12E4, respectively, where E represents the number of ethylene oxide units. Acrylamide was obtained from the Aldrich Chemical Company (Gold Label 99-1-%) and recrystallized twice from chloroform. Azo bis(isobutyrnitrile) (AIBN), obtained from the Alfa Products Division of Morton Thiokol, was recrystallized from methanol. Water was doubly deionized. Propane obtained from Union Carbide Linde Division (CP Grade) and ethane from Air Products (CP Grade) were used without further purification. 

It can be seen from the structure of the glycol ethers (Figure 13.4) that if the alkyl chain is extended sufficiently then it begins to approximate the structure of simple nonionic surfactants, those of the ethoxylated alcohol family. This has led some chemical producers in recent times to introduce compounds meant to be hybrid chemicals with the properties of both solvent and surfactant. They are not at present used to any great extent in household cleaners, but remain a possibility for future formulations. 

The present study makes an attempt to increase mesoporosity within the pillared structure of montmorillonite and to study the catalytic property of the resulting material. Enhancement of mesoporous areas has been observed in a smectite seunple pillared by aluminium polyoxy cations by chemical modification in presence of varied amounts of a nonionic surfactant. The effeet of the enhaneement in mesoporous areas on the pillar density and the deaetivation of the pillared materials in a typical alkylation reaction has been studied. 

Based on their chemical nature, organic surfactants with diphilic structures are classified as anionic, cationic, amphyphilic, and nonionic. Anionic surfactants are reasonably inexpensive and fairly universal, so they occupy a predominant place of about 60% in the world surfactant market. The contribution of nonionic surfactants to world production is about 30% and is growing cationics constitute about 10%, while synthetic amphyphilic surfactants account for only fractions of a percent. 

Surfactants have been used for over 1000 years in everyday applications, for example as emulsifiers in cleaning and in foods. They occur widely in nature, where as a bilayer they constitute a vital structural unit of biological membranes. Their functionality derives from the molecular structure, with a polar (hydrophilic) head-group, which conveys water-solubility, being attached to a non-polar (hydrophobic) tail, which drives the formation of self-assembled aggregates (micelles). Other chapters in this volume detail the wide variety of chemical structures that can form the polar groups (ionic, nonionic, zwitterionic, etc.) and tail structures. 

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