Ionic surfactants, effect structure

Physical properties of the protein structure should be considered in designing strategies to achieve stable formulations because they can often yield clues about which solution environment would be appropriate for stabilization. For example, the insulin molecule is known to self-associate via a nonspecific hydrophobic mechanism66 Stabilizers tested include phenol derivatives, nonionic and ionic surfactants, polypropylene glycol, glycerol, and carbohydrates. The choice of using stabilizers that are amphiphilic in nature to minimize interactions where protein hydrophobic surfaces instigate the instability is founded upon the hydro-phobic effect.19 It has already been mentioned that hydrophobic surfaces prefer... 

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. 

Counterion Binding. Counterion binding on mixed micelles is of crucial importance toward understanding the structure and electrostatic forces involved in micelle formiation involving ionic surfactants. Specific ion electrodes are effective at measuring counterion bindings... 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary structures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover all of a solid interface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally follows the order cationic > anionic > nonionic. Surfaces to which this rule applies include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inoiganic salts in surfactant solutions (14). 

Attwood, D., P. H. Elworthy, and M. J. Lawrence. 1994. Effect of structural variations of non-ionic surfactants on surface properties Surfactants with semi-polar hydrophdb Siarm. Pharmacol. 42 581-583. 

Most of the experimental and theoretical work on the aggregation of ionic surfactants in water has been devoted to understanding how this phenomenon is affected by such factors as concentration, temperature or chemical nature of the surfactants. Much less is known as to how surfactant aggregation is affected by an increase in hydrostatic pressure. Advances in the technique of high pressure vibrational spectroscopy (FT-IR and Raman) of aqueous systems have allowed us now to examine the effect of hydrostatic pressure on the structural and dynamic properties of a large number of surfactants in solution. 

Non-ionic surfactants either decrease or have insignificant effects on the rate constants for hydrolysis of carboxylic esters (Lach and Pauh, 1959 Riegelman, 1960 Nogami et al., 1960, 1962 Kakemi et al., 1962 Mitchell, 1963 Behme et al., 1965 Mitchell and Broadhead, 1967 Saheki et al., 1968 Ullmann et al., 1968). The available data do not warrant conclusions on the relationship between substrate or surfactant structure on the magnitude or nature of catalysis by non-ionic micelles, but it should be noted that synthetic and naturally occurring amphiphiles cause very similar retardations of the rate of alkaline hydrolysis of ethyl p-aminobenzoate (Lach and Pauli, 1969). 

Therefore, it is conceivable that the micropore and macropore are interparticle pores, while the mesopore presumably is the intra-particle pore. During the course of calcination, the connection of interparticle was destroyed and this finally resulted in the vanishing of macropore. Because the mesopore was the intraparticle pores, it had relative fine thermal stability though the pore size was enlarged in the calcination. The reasons may be attributed to the steric dispersant effect of non-ionic surfactant PEG [12]. In the synthesis course, PEG gave steric hindrance to the assembling of mesophase and improved the pore structure. 

In this study, it is foimd that the effects of (CH3CH2)3N on the formation of mesopore structures and the effects of the PEG on the thermal stability of the precipitated powders are very interesting. The results show that the Ce02 powders prepared by the precipitation method are mesoporous with crystalline walls. The mesoporous structure can be maintained upon calcination up to 873K. The mesoporous Ce02 synthesized from the system in the presence of non-ionic surfactant PEG exhibits better thermal stability than that prepared using one template of (CH3CH2)3N only. 

Most non-polymeric antistatic finishes are also surfactants that can orient themselves in specific ways at fibre surfaces. The hydrophobic structure parts of the molecule act as lubricants to reduce charge buildup. This is particularly true with cationic antistatic surfactants that align with the hydrophobic group away from the fibre surface, similar to cationic softeners (see Chapter 3, Fig. 3.1). The main antistatic effect from anionic and non-ionic surfactants is increased conductivity from mobile ions and the hydration layer that surrounds the hydrophilic portion of the molecule since the surface orientation for these materials places the hydrated layer at the air interface. 

It should be noted that high concentrations of ionic species can alter the phase stability of microemulsions based upon ionic surfactant systems. Nonionic surfactant systems are much less susceptible to this effect. The curvature of the interfacial film of the microemulsion droplet is determined by a balance between the electrostatic interactions of the head groups and repulsive interactions of the surfactant tail group. Addition of ionic solutes can upset this delicate balance and induce phase separation. By changing the structure of the surfactant or through the addition of cosurfactants one can restore this balance and thus allow the dissolution of high concentrations of ionic species. 

There are only a limited number of studies comparing the systematic changes in the structure of enhancers and their influence on the oral mucosal membranes. For example, for insulin absorption in rats, it was shown that sodium glycocholate, laureth-9, sodium laurate, and sodium lauryl sulphate were approximately equipotent. Several non-ionic surfactants having a Ci2 hydrophobic tail were much less effective.P 24]... 

Oils. SANS has been used to establish the effect of the addition of a hydrophobic guest (dodecane) on the behavior of liquid crystalline phases, in particular the lamellar and columnar phases of mixtures of the non-ionic surfactant C16E7 with D2O, as well as to determine the distribution of the hydrophobic guest in the microstructure. SANS showed that the presence of the hydrophobic guest molecule, in some cases, stabilized a particular phase structure, (for example lamellar phases formed at lower temperatures in the presence of dodecane) while in other cases it destabilized it, eventually (depending upon the concentration of dodecane added) causing the phase to disappear. In the lamellar phase, dodecane was found to be totally segregated in the center of the bilayer. 

Dekker et al. (50) reported that the addition of a non-ionic surfactant to a micellar solution of TOMAC enhanced the capacity of solubilization of a-amylase and broadened the pH range of solubilization as well. Although this effect should be studied in more detail, it can be supposed that the nonionic surfactant was involved in a reorganization of the structure of the organic phase and allowed the formation of larger micelles. 

This paper reports on the structural and porosity effects of different platinum salts included in the synthetic gel used to synthesize various types of mesoporous silica solids in the presence of a polyglycol ether (non-ionic) surfactant as template. 

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