Surfactant diblock

FI. Kamitakahara, F. Nakatsubo, and D. Klemm, New class of carbohydrate-based non-ionic surfactants Diblock co-oligosaccharides of tri-O-methylated and unmodified celloohgosaccharides. Cellulose, 14 (2007) 513-528. 

Bibi, I., A. Khan, N. Rehman, S. Pervaiz, K. Mahmood, and M. Siddiq (2012). Characterization of surfactant-diblock copolymer interactions and its thermodynamic studies. Journal of Dispersion Science and Technology 33(6) 792-798. 

Block copolymers are closer to blends of homopolymers in properties, but without the latter s tendency to undergo phase separation. As a matter of fact, diblock copolymers can be used as surfactants to bind immiscible homopolymer blends together and thus improve their mechanical properties. Block copolymers are generally prepared by sequential addition of monomers to living polymers, rather than by depending on the improbable rjr2 > 1 criterion in monomers. 

W. Gozdz, R. Holyst. From the plateau problem to minimal surfaces in lipids, surfactants and diblock copolymer systems. Macromol Theory Simul 5 321-332, 1996. 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

In what follows we will discuss systems with internal surfaces, ordered surfaces, topological transformations, and dynamical scaling. In Section II we shall show specific examples of mesoscopic systems with special attention devoted to the surfaces in the system—that is, periodic surfaces in surfactant systems, periodic surfaces in diblock copolymers, bicontinuous disordered interfaces in spinodally decomposing blends, ordered charge density wave patterns in electron liquids, and dissipative structures in reaction-diffusion systems. In Section III we will present the detailed theory of morphological measures the Euler characteristic, the Gaussian and mean curvatures, and so on. In fact, Sections II and III can be read independently because Section II shows specific models while Section III is devoted to the numerical and analytical computations of the surface characteristics. In a sense, Section III is robust that is, the methods presented in Section III apply to a variety of systems, not only the systems shown as examples in Section II. Brief conclusions are presented in Section IV. 

Fig. 10 Aggregation numbers 2 as function of degree of polymerization of insoluble block for uncharged block copolymers. Open symbols different diblock-, triblock-, graft-, and star polymers. Filled symbols low-MW surfactants. Reprinted with permission from [211]. Copyright (2002) Wiley...

D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chmelka, and G. D. Smcky, Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures, J. Am. Chem. Soc. 120(24), 6024-6036 (1998). 

Exploiting ATRP as an enabling technology, we have recently synthesised a wide range of new, controlled-structure copolymers. These include (1) branched analogues of Pluronic non-ionic surfactants (2) schizophrenic polymeric surfactants which can form two types of micelles in aqueous solution (3) novel sulfate-based copolymers for use as crystal habit modifiers (4) zwitterionic diblock copolymers, which may prove to be interesting pigment dispersants. Each of these systems is discussed in turn below. 

Poly(alkylene oxide)-based (PEO-PPO-PEO) triblock and diblock copolymers are commercially successful, linear non-ionic surfactants which are manufactured by BASF and ICI. Over the last four decades, these block copolymers have been used as stabilisers, emulsifiers and dispersants in a wide range of applications. With the development of ATRP, it is now possible to synthesise semi-branched analogues of these polymeric surfactants. In this approach, the hydro-phobic PPO block remains linear and the terminal hydroxyl group(s) are esteri-fied using an excess of 2-bromoisobutyryl bromide to produce either a monofunctional or a bifunctional macro-initiator. These macro-initiators are then used to polymerise OEGMA, which acts as the branched analogue of the PEO block (see Figures 2 and 3). 

The addition of large linear blocks to dendrons with opposite polarity creates a desymmetrized structure predisposed to sequester insoluble components by aggregation rather than intramolecular hydrogen-bonding. Amphiphilic, linear-dendritic diblock (AB) and triblock (ABA) copolymers self-assemble into multimolecular micelles with CMC values that are well below those of low molecular weight surfactants. Typically, a hydrophilic linear block such as PEG is attached to the focal point... 

The dispersion polymerization of styrene in supercritical CO2 using amphiphilic diblock copolymers to impart steric stabilization has been investigated. Lipophilic, C02-insoluble materials can be effectively emulsified in carbon dioxide using amphiphilic diblock copolymer surfactants. The resulting high yield (> 90%) of polystyrene is obtained in the form of a stable polymer colloid comprised of submicron-sized particles (Canelas et al., 1996). 

Riess demonstrated recently that poly(styrene-b-oxirane) copolymers could act as non-ionic surfactants and lead to water/ toluene microemulsions (29, 30). Using isopropanol as cosurfactant, both 0/W and W/0 microemulsions are obtained (3l). This is a very important conclusion, since PO based diblock copolymers give rise only to 0/W microemulsions under the same experimental conditions (8, 31,). In this respect the "branched structure" of the PO hydrophilic component could favor a decrease in the packing density of the inverse micelle forming molecular and explain the different behavior of the linear and star-shaped PS/PO block copolymers in the W/0 microemulsification process. 

Figure 7 compares the water/toluene interfacial tensions measured in the presence of various commercial surfactants and P0/PS based diblock (8) and star-shaped copolymers the higher activity of the star-shaped block copolymers over a broad range of concentrations is clearly put in evidence. 

In fact, even in pure block copolymer (say, diblock copolymer) solutions the self-association behavior of blocks of each type leads to very useful microstructures (see Fig. 1.7), analogous to association colloids formed by short-chain surfactants. The optical, electrical, and mechanical properties of such composites can be significantly different from those of conventional polymer blends (usually simple spherical dispersions). Conventional blends are formed by quenching processes and result in coarse composites in contrast, the above materials result from equilibrium structures and reversible phase transitions and therefore could lead to smart materials capable of responding to suitable external stimuli. 

More than two surfactants can be put together to form tri,- tetra- or polymeric surfactants. Trimeric or even tetrameric surfactants show properties often superior to monomeric surfactants. Besides, they are intermediate between conventional surfactants and polymeric surfactants. In a normal polymeric surfactant each monomer unit is amphiphilic. Another type of polymeric surfactant, called block copolymer [522], consists of at least two parts. One part is made of monomer type A, the other part is made of monomer B. If A is polar and B nonpolar, the blockcopolymer will be strongly surface active and show many properties of a conventional surfactant. If there are two different blocks we talk about a diblock copolymer. In the following part of this chapter we concentrate on conventional surfactants. 

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