Star copolymers particles

Tire morphology of a micelle is primarily determined by the composition of the copolymer and the incompatibility between the blocks and the solvent.. Symmetric block copolymers produce micelles in which the core and the corona have comparable volume, leading to colloidal particles akin to the sterically stabilized particles described above. By contrast, very asymmetric copolymers form star-like particles... 

Zhang, C., Wang, X., Min, K., Lee, D., Wei, C., Schulhauser, H., et al. Developing porous honeycomb films using miktoarm star copolymers and exploring their application in particle separation. Macromol. Rapid Comm 35, 221-227 (2014)... 

A special case of a miktoarm star copolymer with many arms are so-called Janus Micelles, which are formed by cross-linking the short middle block of a triblock terpolymer in the microphase separated bulk state, in which the center block self-assembles in spherical [ 189,190] or cylindrical domains [191]. By this procedure the two different outer blocks are oriented to the two opposite hemicoronas around the center block domain and subsequent dissolution leads to amphiphilic particles (Figure 14). While spherical Janus Micelles form superstructures in solution, the cylindrically shaped Janus Micelles seem to have a lower tendency of self-aggregation to higher superstructures. 

Well-characterized systems. This depends on the appropriate chemistry and subsequent characterization (typical issues here are the polydispersity, control of grafting density, reproducibility of procedure to obtain identical particles). One frequent problem here is that the price one pays for such systems is tlie availability of small amounts (sometimes only fractions of 1 g) of material. For example, multiarm star polymers are in many ways unique, clean, soft colloids [ 19,23], but their nontrivial synthesis makes them not readily available. On the other hand, recent developments witli block copolymer micelles from anionically synthesized polymers [54-58] and arborescent graft copolymer synthesis [40] appear to have adequately addressed this issue for making available different alternative star-like systems. 

We argue that the above features of star dynamics are generic for soft systems of the core-shell type for which stars serve as prototype. Support for this comes from the dynamic light scattering (DLS) investigation of large block copolymer micelles, where all three relaxation modes, i.e., cooperative, structural and selfdiffusion are observed [188]. In particular, the star model discussed above applies to core-shell particles with a small spherical core relative to the chain (shell) dimensions. For a surface number density a = f / (47i r ) the polymer layer thickness under good solvent conditions is L ... 

When soft colloids (such as stars, block copolymer micelles, or particles sterically stabilized with grafted chains) are suspended in solvents of intermediate quality at high concentrations, an increase of temperature leads to an increase of their effective volume fraction, which in turn can yield vitrification [26,190,199]. A representative example is depicted in Fig. 23a for a star with nominal / = 128 and... 

Polymer-colloids refer to particles consisting of a solid core surrounded by a polymeric corona. Tills broad class of materials encompasses systems as different as star polymers, block copolymer micelles, and grafted particles. 

Multiarm star polymers have recently emerged as ideal model polymer-colloids, with properties interpolating between those of polymers and hard spheres [62-64]. They are representatives of a large class of soft colloids encompassing grafted particles and block copolymer micelles. Star polymers consist of f polymer chains attached to a solid core, which plays the role of a topological constraint (Fig. Ic). When fire functionality f is large, stars are virtually spherical objects, and for f = oo the hard sphere limit is recovered. A considerable literature describes the synthesis, structure, and dynamics of star polymers both in melt and in solution (for a review see [2]). 

Pistel KF, Bittner B, Koll H, Winter G, Kissel T. Biodegradable recombinant human erythropoietin loaded microspheres prepared from linear and star-branched block copolymers Influence of encapsulation technique and polymer composition on particle characteristics. J Control Release 1999 59 309-325. 

Iron-centered six-arm star block copolymers 7.37 (Fig. 7.6) have been investigated in detail by small-angle X-ray scattering, TEM, and AFM [64]. When heated for ca. 2 days at 160°C, thin films of the polymers form iron nanodusters with diameters of ca. 20-40 nm (see TEM image. Fig. 7.7). This type of approach offers considerable potential for the single-step fabrication of nanoscale-pattemed inorganic particles in polymer films. 

This tunable potential also describes a variety of similar haiiy-partide-like sj tems, such as star-like micelles, that is, block copolymer micelles with a very small core compared to the corona layer. On the other hand, for typical colloidal spheres grafted with small stabiB2ang layers or for micelles with a core occupying a significant fiacdon of the overall particle, this potential is inappropriate. V(r) of eqn [18] is one of the very few anal Uic forms of pair interaction potential, tuned with a single parameter, further justifying the choice of star polymers as model soft colloids. 

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