The formation of solid solution series Cs_1-xM_xGaQ₂-mC64 (M = K, Rb; Q = S, Se; x = 0–1) was studied by X-ray diffraction and spectroscopic methods, revealing a complete miscibility of CsGaQ₂-mC64 with RbGaQ₂ and KGaSe₂, and a large miscibility gap with KGaS₂. All solid solution members exhibit similar Raman spectra, indicating the covalent Ga-Q bonding character. The similar optical band gaps likewise further contribute to this conclusion. Up to a degree of substitution, these solid solutions undergo a phase transition similar to CsGaQ₂-mC64. The influence of the substitution parameter x on phase transition process was investigated in situ using high-temperature X-ray powder diffraction experiments. Phase-pure solid solutions of the high-temperature polymorphs Cs_1-xM_xGaQ₂-mC16 were obtained up to x_max(K) = 0.1 and x_max(Rb) = 0.3. The crystal structures of these new CsGaQ₂-mC16 analogous high-temperature phases were refined from synchrotron diffraction data by Rietveld-refinement.

Low charge density nanometric ions were recently shown to bind strongly to neutral hydrated matter in aqueous solution. This phenomenon, called (super-)chaotropic effect, arises from the partial dehydration of both, the nano-ion and the solute, leading to a high gain in enthalpy. Here, we investigate the chaotropic effect of the polyoxometalate α-PW12O403- on the triblock copolymer P84: (EO)19(PO)43(EO)19 with (EO)19 the polyethoxylated and (PO)43 the polypropoxylated chains. The combination of phase diagrams, spectroscopic (nuclear magnetic resonance) and scattering (small angle neutron/X-ray scattering) techniques reveals that (i) below the micellization temperature of P84, PW12O403- exclusively binds to the propylene oxide moiety of P84 unimers and (ii) above the micellization temperature, PW12O403- mostly adsorbs on the ethylene oxide micellar corona. The preferential binding of the PW12O403- to the PPO chain over the PEO chains suggests that the binding is driven by the chaotropic effect and reinforced by the hydrophobic effect. At higher temperatures, the copolymer micellization leads to the displacement of PW12O403- from the PPO chain to the PEO chains. This study deepens the understanding of the subtle interplay between the chaotropic and hydrophobic effects in complex salt-organic matter solutions.