Structure formation Janus particles

Fig. 58 Mean-field density profiles obtained fiom self-consistent field theory simulations. A- versus B-rich domains are displayed for a blend of A- and B-homopolymers (a) and for AB-diblock-copolymer melts (b, c). In each case, all A-, and B-blocks contain equal numbers of monomers. Here, spherical confinement is implemented by blending either A- and B-homopolymws (a), or AB-diblock-copolymers (b, c) with C-homopolymers. The C-homopolymers act as a very bad solvent, thus enforcing the formation of A-, and B-rich spherical domains. In this case, the geometry of the confined polymer phases is studied in two dimensions. Whether Janus (a), core-shell (b), or onion (c) particles form depends on the number of monomers per block, and the interactirais between different monomer species. From (a) to (c), the length of A-, and B-sequences steadily decreases the sequences in (a) are roughly four times as long as in (b), and are about 15 times as long as in (c). To form Janus particles, the A-C versus B-C inlmactions need to be equal. To form layered structures, there has to be a significant difference...

Although many techniques such as conventional TEM (sometimes on selective staining), cryo-TEM, SEM, SAXS, and 2D NOESY NMR have been employed to reveal the exact structure of anisotropic particles such as Janus, multicompartment, and patchy particles, it is still difficult to fully determine the structure of the particle. Often, TEM is used to provide direct evidence for the formation of anisotropic particles. However, for samples with poor... 

Another template-free method for the formation of self-assembled tubular structures has been shown by Jiang and co-workers. They used polymeric Janus particles prepared from mixed-shell micelles (MSMs) that self-assembled into tubular superstructures and nanosheets. The micelles were prepared by non-covalent cross-linking of poly(acrylic acid) (PAA) blocks by addition of 1,2-propanediamine (PDA) in DMF (A on Figure 5.45). The two block copolymers were composed of hydrophilic poly(ethylene... 

The use of acrylic acid not only led to a functionalization of nanoparticles, but also was important as a structure-directing monomer for the formation of nanocapsules. In this case, the hydrophilic groups of the acrylic acid [30] or methacrylic acid [31] resulted in the formation of a nanocapsule structure, instead of Janus-like or even separate nanoparticles. The copolymerization of the functional n-methylol acrylamide with vinyl acetate was found to follow (in batch miniemulsion) the Mayo-Lewis equation, despite huge differences in the solubility of the monomers in the aqueous continuous phase [32]. A functionality of fluori-nated particles could be easily introduced by copolymerizing fluoroalkylacrylates with protonated monomers, such as acrylic acid and methacryloxyethyltrimethyl ammonium chloride [33]. 

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