The development of synthetic routes to porous materials containing multiple, discrete sets of pores having disparate length scales is of high interest for a wide range of applications.

An understanding of water’s anomalies is closely linked to an understanding of the phase diagram of water’s metastable noncrystalline states. Despite the considerable effort, such an understanding has remained elusive and many puzzles regarding phase transitions in supercooled liquid water and their possible amorphous proxies at low temperatures remain. Here, decompression of very high density amorphous ice (VHDA) from 1.1to0.02GPa at 140K is studied by means of dilatometry and powder x-ray diffraction of quench-recovered states. It is shown that the three amorphous states of ice are reversibly connected to each other, i.e., LDA↔e-HDA↔VHDA. However, while the downstroke VHDA→e-HDA transition takes place in the pressure range of 0.06GPa<p<0.40GPa, the e-HDA→LDA transition takes place quasi-discontinuously at p∼0.06GPa. That is, two amorphous-amorphous transitions of a distinct nature are observed for the first time in a one-component system–a first-order-like transition (e-HDA→LDA) and a transition which is not first-order like but possibly of higher order (VHDA→e-HDA). VHDA and e-HDA are established as the most stable and limiting states in the course of the transition. We interpret this as evidence disfavoring the hypothesis of multiple first-order liquid-liquid transitions (and the option of a third critical point), but favoring a single first-order liquid-liquid transition (and the option of a second critical point).

In this tutorial review the preparation of monolithic silica materials with hierarchical porosity by the competing processes of sol–gel transition and chemical phase separation is summarized. Four principally different routes will be discussed in detail, including multiple micellar as well as high internal phase emulsion templating routes. Special emphasis is given to polymer-induced phase separation strategies either based on the deliberate choice of the polymer that is mixed into the gelling system or by the application of specifically designed hydrophilic silane precursors.

We here report differential scanning calorimetry (DSC) scans recorded by repeatedly heating the H₂O (D₂O) low density amorph (LDA) which was made by isothermal decompression of very high-density amorphous ice (VHDA) at 140 K from 1.1 to 0.006 GPa. These DSC scans show a glass → liquid transition endotherm with an onset temperature (T_g) of ≈137 (140) K at a heating rate of 30 K min⁻¹ accompanied by an increase in heat capacity of ≈1.7 (1.5) J K⁻¹ mol⁻¹. We establish the reversibility of this effect by thermally cycling between its glassy state below 137 K and its highly viscous liquid state at 149 K. All calorimetric signatures, including H/D isotope effect, are highly similar to the signatures in hyperquenched glassy water (HGW). We argue that the observation of almost identical calorimetric traces for HGW and LDA implies that there is no need to reassign HGWs T_g to higher temperatures provided that the viscous liquid state connected to both LDA and HGW behaves as an ideally “strong” liquid in the Angell classification. We furthermore show that LDA prepared by isothermal decompression of VHDA is more crystallization-resistant than LDA made from high-density amorphous ice (HDA) by isobaric warming. We suggest that the former route via VHDA removes “nanocrystalline remnants” in LDA which are still present in the latter after pressure-amorphization of hexagonal ice to HDA at 77 K.

Dilatometry experiments on low- and high-density amorphous ices up to 0.30 GPa are presented together with powder x-ray diffraction data. Repeated isobaric heating and cooling cycles reveal three competing processes: irreversible (micro)structural relaxation, reversible relaxation, and (irreversible) crystallization. The third and subsequent heating runs produce identical curves, i.e., irreversible relaxation is absent. We interpret the deviation from linear expansivity in these curves as the onset temperature of the volumetric glass-to-liquid transition (Tg,$\hskip0.3em${}onset) and report its dependence on pressure.