Star-like morphology

Figure 9.3 Morphology control in the preparation of arborescent copolymers (a) core-shell morphology from short side chains, and (b) star-like morphology from long side chains...

Triblock copolymers of ABA-type have basically the same behavior in giving a star-like morphology (Fig. 6a) when dissolving into a selective solvent for the outer A blocks. However, the micellization of ABA-type triblock copolymers in selective solvent for the middle B blocks deals with a much more complex situation [42], A relatively low concentration of the copolymer in the selective solvent and/or a low molecular weight of the A blocks can lead to isolated flower-like micelles (Fig. 6b) with the middle B block being looped - referred to as petals - and with the two outer A blocks taking part of the same micellar core. However, if the copolymer concentration or the A block molecular weight is increased, a micelle association... 

Figure 1.55. The relationships between the concentration product, (Ba " )i(S04 )i, at the initiation of barite precipitation, and morphologies of barite crystals (Shikazono, 1994). The dashed line represents the boundary between dendritic barite crystals and well-formed rhombohedral, rectangular, and polyhedral barite crystals. The 150°C data are from Shikazono (1994) the others from other investigations. D dendritic (spindle-like, rodlike, star-like, cross-like) barite Dp feather-like dendritic barite W well-formed rectangular, rhombohedral, and polyhedral barite. The boundary between the diffusion-controlled mechanism (Di) and the surface reaction mechanism (S) for barite precipitation at 25°C estimated by Nielsen (1958) The solubility product for barite in 1 molal NaCl solution at 150°C based on data by Helgeson (1969) and Blount (1977). A-B The solubility product for barite in 1 molal NaCl solution from 25 to 150°C based on data by Helgeson (1969).

Several morphologies of dendritic barite, such as feather-like, rod-like, spindlelike, star-like, and cross-like crystals have been recognized when the (niQ. 2+)i(msoj )i values were considerably higher than the equilibrium values, although no detailed studies have been made on the relationship between the various morphologies of dendritic barites and the degree of supersaturation. 

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... 

Morphological observation by SEM showed interlocking of the adhesive in the adherend surface due to microstructures (star-like or spheres) formed by the hyperbranches or dendrimer clusters on the interface. 

A very large number of morphologies can be found in the world of polymers and copolymers. Polymers can be linear, branched, comb-type, star-like, micelles, macrocyclic or cross-linked, when chains are linked together for copolymers the order can be random, alternating, in block or graft as illustrated in Figure 10.1. The order of the repeating units has to be specified, as different orders result in different properties. 

The Vilgis and Halperin theory [46] does help shed light on the possible different morphological behaviors of micelles of coU-coU and crystalline-coil diblock copolymers. It can not be used to predict quantitatively the copolymer compositions at which the different micellar morphological transitions take place, because only scaling relations and not quantitative relations were derived for the free energies of three types of micelles. Aside from the semi-quantitative nature of the free energy expressions, the theory did not discuss tubular micelles at alL It examined only hairy disks, star-like micelles with a cubic core, and cylindrical micelles with a cubic-prism-shaped core. 

Figure 1.4 Polymer backbone morphology is varied linear (a), branched (b), star-like (c), cross-linked (d).

Ionic amphiphilic diblock copolymers are well known to self-assemble into core-corona aggregates (micelles) in aqueous media. The micelle comprises a hydrophobic core formed by nonpolar blocks and a hydrophilic corona built up from polyelectrolyte blocks. The properties of such macromolecular self-assemblies are reviewed in detail elsewhere [57, 58]. In many cases, the micelles are characterized by a spherical morphology. When the radius of the hydrophobic core is considerably smaller than the thickness of the polyelectrolyte corona, such macromolecular self-assemblies are regarded as star-like micelles (Eig. 6b). 

The morphologies of star copolymers AB2, A2B, and (AB)3 and linear block copolymer AB, which were annealed under vacuum at 150°C for 2 days, were observed by means of transmission electron microscopy (TEM) (Fig. 4). In the case of a sample of AB-type diblock copolymer, lamellar morphology consisting of alternating dark polystyrene and bright aromatic polyether regions was observed (Fig. 4a). On the other hand, samples of AB2, A2B, and (AB)3 star copolymers showed spherical or plate-like morphology (Fig. 4b-d). Such unexpected and novel... 

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