Micelles behavior

The micellization behavior of copolymers containing two hydrophobic blocks, or double-hydrophobic block copolymers, has been shown to be mainly controlled by the solvent and its interaction with the copolymer blocks. It is thus possible to tune the micellization of these copolymers by changing the organic solvent. In this respect, large differences in Z, i h, Rc, etc. are expected whenever the interaction parameter between the polymer and the solvent is varied. This is illustrated by, e.g., the work of Pit-sikalis et al. [87] for PS-PSMA diblock copolymers dissolved in either ethyl-or methylacetate. The effect of temperature has been studied by Quintana et al. [88,89], who have clearly shown that CMC decreases with increasing temperature for PS-PEB copolymers in alkanes. 

Recent studies on PEO-PPO, PEO-PBO di- and triblock copolymers include the works of Bahadur et al. [121], who examined the role of various additives on the micellization behavior, of Guo et al. [122], who used FT-Raman spectroscopy to study the hydration and conformation as a function of temperature, of Booth and coworkers [ 123], who were mainly interested in PEO-PBO block copolymers with long PEO sequences, and of Hamley et al., who used in situ AFM measurements in water to characterize the morphology of PEO-PPO micelles [56,57]. 

Block copolymer micelles with a polyelectrolyte corona are a very important class of colloidal particles in aqueous medium and are often referred to as polyelectrolyte block copolymer micelles. The micellization behavior of these charged micelles has been very recently reviewed by Riess [14] and FOrster et al. [15]. A brief overview of the topic will therefore be presented in what follows. Amphiphilic block copolymers consisting of one hydrophobic block linked to one ionic block will only be discussed in this section. Blocks copolymers containing one hydrophilic block and one ionic block will be discussed in Sect. 4.3. 

Previous sections discussed the micellization behavior of AB or ABA linear block copolymers. With the recent progress achieved in the field of controlled polymerization techniques, more sophisticated block copolymer architectures are now available. Investigation of the micellization behavior of such... 

In this section, we would like to briefly describe the micellization behavior of hybrid AB copolymers, leading to remarkable structures with new potential applications. By hybrid AB block copolymers we mean copolymers in which at least one of the constituent blocks is not a classical poly-... 

Up to now, we have considered the micellization behavior of isolated block copolymer chains. It has been, however, demonstrated that micellization... 

Although many amphiphilic block copolymer architectures including starshaped, H-shaped, graft, and ABC block copolymers can now be succesfully synthesized, their micellization behavior remains poorly investigated. 

Zhou, Z. and B. Chu. 1988. Anomalous micellization behavior and composition heterogeneity of a triblock ABA copolymer of (a) ethylene oxide and (b) propylene oxide in aqueous solUM laaromolecules 21 2548-2554. 

Tsitsilianis and coworkers [41] presented results on the micellization behavior of anionically synthesized amphiphilic miktoarm star copolymers with PS... 

The first theories on the micellization of polyelectrolyte block copolymers were published by Marko and Rabin [26], Dan and Tirrell [27] and Shusha-rina et al. [28]. They predict a strong influence of the polyelectrolyte blocks on the micellization behavior. Thus not unexpectedly, a qualitatively differ-... 

The experiments and the necessary theory were developed by Mohammad Abu-Hamdiyyah, Pasupati Mukerjee, and myself in connection with a related but different problem—an attempt to determine unambiguously the rate of transport of simple non-micellized detergent ions through a membrane (I, 18). We needed information about the ability of the micelles to cross the membrane, and the insoluble material was used mainly to indicate micelle behavior. The paper reporting that work (I) gives experimental details and further interpretation of the results. Since then I found that Dean and Vinograd (4) developed the qualitative aspects of this argument 25 years ago. 

Figure 2 compares the variation of a with solvent composition for related surfactants as obtained from emf (12) and conductivity data. The emf results (at 308.15 K) have made use of the Botre Equation (39), the validity of which has been questioned (40,41). However, the main characteristics of these results are that they qualitatively present the same micelle behavior, i.e. an increase of a with the addition of acetone or propanol to water. The increase is much faster with propanol using the emf method than with the conductivity method and as Miyagishi apparently could not determine an a value above mole fraction 0.02 we suspect some electrode problems in this particular case. In the water -f-acetone mixtures the two methods yield similar results. Nevertheless, we believe that the conductivity method is more reliable than the emf method. Finally, Mathews et al. (13) found no change of a with addition of organic molecules in apparent contradistinction with the present results. However, these authors used scarcely soluble additives (e.g., CCL ) and Figure 2 shows that a changes slowly with the addition of acetone or propanol. 

Figure 10. The soluhility-micellization behavior of surfactants in solution, showing the Krafft point.

We have studied the phase and micellization behavior of a series of model surfactant systems using Monte Carlo simulations on cubic lattices of coordination number z = 26. The phase behavior and thermodynamic properties were studied through the use of histogram reweighting methods, and the nanostructure formation was studied through examination ofthe behavior ofthe osmotic pressure as a function of composition and through analysis of configurations. 

Comparing micellization behavior in the cosolvents formamide, ethanol, and glycerol, some interesting trends were observed [64], With formamide or ethanol as cosolvent the micelle formation of Pluronic P105 occurs at higher concentrations and temperatures compared to water without cosolvent. However, for glycerol the results show an opposite trend. The addition of glycerol promotes the formation of... 

No theoretical treatment exists so far, to our knowledge, which deals explicitly with the very interesting subject of the influence of chain architecture of nonlinear block copolymers on their micellization behavior in selective solvents. 

The behavior of nonlinear block copolymers with different macromolecular architectures has been studied extensively in different solvent environments. Most studies are concerned with the conformation of these complex molecules in good solvents and their micellization behavior in selective, for one part of the copolymer, solvents. 

Tuzar and coworkers [294] investigated the micellization behavior of styrene-butadiene star-block copolymers with four arms and polybutadiene inner blocks in the mixed solvent tetrahydrofuran/ethanol, selective for polystyrene blocks. 

The second example involves a mixture of two different types of commercial foam-forming surfactants anionic and amphoteric (7). Unlike the mixture of the previous example, an anionic—amphoteric surfactant mixture probably does not follow ideal mixed micelle behavior (138). The results of three core-floods, performed separately with each surfactant and with a mixture of the two surfactants, are summarized as follows. The anionic surfactant adsorbs negligibly when used either by itself or when mixed with the betaine (at least at the low salinity used in these particular core-floods). Betaine adsorption is lowered by about an order of magnitude by mixing it with the anionic surfactant, from 1.7 down to 0.2 mg/g. 

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