K2SO4-PAA

The face-selective PAA adsorption onto orthorhombic K2SO4 crystals led to the formation of tilted unit crystals, which were assembled in a diffusion-Hmited condition resulting in various complex morphologies like hehces or zig-zag assembly of twinned crystals [250]. A conclusive explanation of the various possibilities of particle growth in an anisotropic diffusion field was given. It is remarkable that the K2SO4-PAA system has six hierarchical levels from the nanometer scale to that of several himdreds of micrometers, which is a typical featme of biominerals and has so far only ben rarely reported for a synthetic system (Fig. 16) [252]. 

Potassium sulfate and potassium hydrogen phthalate both formed a nacrelike structure when the PAA concentration was adjusted to a suitable value [235-237] (Fig. 17). Just like the nacre in Nature (Japanese pearl oyster Pinctada fucata) [235], the nacre-Uke structure of potassium sulfate-PAA and potassiiun hydrogen phthalate-PAA can absorb and store dyes [235-237] (Fig. 17). With a different concentration of PAA, the K2SO4 crystal exhibited a different hierarchical architecture by iso-oriented assembly or oriented attachment mechanisms [236]. 

Fig. 17 Typical FESEM images, a K2SO4 in PAA gel, Cpaa = 8gdm. (Reproduced with permission from [236], 2005, Wiley), b Potassium hydrogen phthalate in PAA gel, CpAA = 10-15gdm . (Reproduced from [237], 2005, RSC)...

Fig. 9 Hierarchical architectures based on K2SO4 (a-d) and CaCOs (e,f) mesocrystals formed in the presence of PAA. Reprinted with permission from Wiley-VCH and Nature Publishing... 

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