Abstract. The diffraction results for the formation of ice in 86Å diameter pores of a SBA-15 silica sample are analysed to provide information on the characteristics of the ice created in the pores. The asymmetric triplet at ∼1.7Å −1 , which involves several overlapping peaks, is particularly relevant to the different ice phases and contains a number of components that can be individually identified. The use of a set of three peaks with an asymmetric profile to represent the possibility of facetted growth in the pores was found to give an unsatisfactory fit to the data. The alternative method involving the introduction of additional peaks with a normal symmetric profile was found to give excellent fits with five components and was the preferred analytic procedure. Three peaks could be directly linked to the positions for the triplet of hexagonal ice, I h , and one of the other two broad peaks could be associated with a form of amorphous ice. The variation of the peak intensity [and position] was systematic with temperature for both cooling and heating runs. The results indicate that a disordered state of ice is formed as a component with the defective crystalline ices. The position of a broad diffraction peak is intermediate between that of high density [hda] and low-density [lda] amorphous ice. The remaining component peak is less broad but does not relate directly to any of the known ice phases and cannot be assigned to any specific structural feature at the present time.

Small aqueous droplets on homogeneous surfaces surrounded by a reservoir of vapor are inherently unstable. Depending on the humidity, they keep evaporating and ultimately disappear or grow until they fully wet the surface under supersaturation. We are considering a system departing from this common picture. For nanoscale droplets sitting above hydrophilic patches on a heterogeneous surface, there can exist a range of supersaturated pressures at which the droplets maintain a stable volume, determined by the pertinent contact angle and the size of the patches. The region under the droplet perimeter controls the drop's curvature. Vapor pressure rises along with increased curvature as soon as the drop extends into the hydrophobic area. The drop size may therefore remain stable when its base just covers the hydrophilic patch. The finite range of water−substrate interactions, however, blurs the boundaries between surface regions with different hydrophilicities; hence, the nanodrop contact angle varies with the patch size in a gradual manner. We use molecular simulations to examine this dependence on model surfaces with either chemical or topological heterogeneities. For both types of heterogeneities, our results show the contact angle of a nanodroplet can be predicted by the local Cassie−Baxter mixing relation applied to the area within the interaction range from the drop's perimeter, which, in turn, enables predictions for drop condensation and saturated vapor pressure above partially wetted nanopatterned hydrophilic/hydrophobic surfaces.

Abstract. Neutron diffraction measurements for D 2 O in SBA-15 silica of pore diameter 86Å have been made in a temperature range from 300 K to 100 K. The pore-filling factor for the liquid phase is 0.95, resulting in an 'almost-filled' sample. The nucleation and transformation of the ice phase was determined for cooling and warming cycles at two different rates. The primary nucleation event at 258 K leads to a defective form of ice-I with predominantly cubic ice features. For temperatures below the main nucleation event, the data indicate the formation of an interfacial layer of disordered water/ice that varies with temperature and is reversible. The main diffraction peak for the water phase shows similar features to those observed in earlier studies, indicating enhanced hydrogen-bonding and network correlations for the confined phase as the temperature is decreased. A detailed profile analysis of the triplet-peak is presented in the accompanying Paper 3.