Surfactant micropolarity

The polarity within a surfactant assembly will be quite different from that of the bulk solution. It is useful to know the micropolarity of these assem-bhes for such applications where different substrates are compartmentalized inside these surfactants. The micropolarity of the surfactant assembhes can be determined using any fluorescence probe whose emission characteristics change with solvent polarity. The emissions of the probe are measured in solvents of known polarities and the polarity of the surfactant assembhes is determined by comparison. 

Ultimately, the water pool and the interfacial surfactant layer can exhibit multiple catalytic effects, which result from the concentrations of reactants localized in the nano-compartmentalized region and the physicochemical properties of the micellar environment. Accordingly, the reversed micellar systems have the possibility of controlling the multiple effects on the reactions by changing the physical factors of the reversed micellar systems such as water mobility, micropolarity, and electrostatic force. 

As JVo increases, the size of the water pool increases [56] and free water appears in the center of the water pool, resulting in an increase in micropolarity [10,57-59]. It is concluded that ionization of the ionic groups of the surfactant layer of reversed micelles would be enhanced with increasing due to increase in micropolarity of the water pool... 

There are a number of studies on pyrene labelled or doped polymer materials. Dendritic size and electrostatic forces in poly(amido) dendrimers with pyrene residues have been determined through the use of a variety of quenchers. As the dendritic size increases so the Stern-Volmer quenching constant decreases, owing to blocking of the pyrene chromophore by the growing dendritic network. The photophysical properties of poly(acrylic acids) tagged with pyrene has been measured in micellar media at various pHs." The ratio of monomer to excimer gave valuable information on the micropolarity sensed by the pyrene label, as well as the influence of external stimuli. The surfactant... 

Ikushima et al. made a detailed study of the effects of pressure and molar ratio of water to surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) on the physicochemical properties such as the type of interior water molecules, micropolarity, and the structures of AOT reverse micellar aggregates in SCFs media by using high-pressure FTIR and UV spectroscopies (see Section 2.3.2 for their results) [20]. 

Using steady-state absorption studies, several other authors examined the micropolarity of confined IL in microemulsions stabilized by ionic surfactants [64,85,87], For example, Sarkar and coworkers examined [bmim][BF ]/benzene mixtures stabilized by the anionic SAIL surfactant [bmim][AOT] and observed that, within the studied range, the A for solubilized MO continued to undergo redshift with increasing R [85, 87], In another work, Falcone and coworkers compared the micropolarities of [bmim][BF4]/benzene mixtures stabilized by cationic BHDC and nonionic TX-lOO surfactants using l-methyl-8-oxyquinolinium betaine (QB), a dye that locates mainly at the surfactant interfacial layer [64]. When [bmim][BF ] was added to both BHDC/benzene and TX-lOO/benzene systems, a larger hypsochromic shift was sensed by the probe in the former. This implies that the local environments in BHDC/benzene system are more polar. The authors ascribed this phenomenon to the strong electrostatic interactions between the [BFJ anion and the BHD moiety of the cationic surfactant. 

The micropolarity and the microviscosity of the micelles of the [C H2m +1 N (CH3)2, Br ]2(CH2)j surfactants have been systematically investigated as a function of m and 5 using the fluorescent probes pyrene (micropolarity) and diphenylhexatriene or dipyrenylpropane (microviscosity) [108-110]. The results for the 12-5-12, 2Br" series have been compared to those for the series of the corresponding monomeric surfactants Ci2H25(Q/2H +i)N (CH3)2, Br". Figure 11 shows that the micropolarity is nearly the same for monomeric and gemini surfactant micelles at a given 5 value, except at 5 = 2. This result was explained on the basis of the similar compositions of the... 

Varadaraj, R., Bock, J., Valint, R, Jr., Brons, N. Micropolarity and water penetration in micellar aggregates of linear and branched hydrocarbon surfactants. Langmuir 1990, 6(8), 1376-1378. 

In addition to the effect of the head group size and the chain length of surfactants, the effect of the counterions binding with the surfactant head group on the catalytic activity of enzymes in reverse micelles was also studied by Das et al. [53]. They synthesized a series of cetyltrimethylammonium-based surfactants with different counterions, and determined their physicochemical properties in aqueous solutions (counterion binding value, critical micelle concentration (CMC), and micropolarity). It has been found that the counterions affect not only the physicochemical properties of the aggregates but also the catalytic activity of lipase... 

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