On the heterogeneous character of water's amorphous polymorphism
Abstract
In this letter we report in situ small--angle neutron scattering results on the high--density (HDA) and low-density amorphous (LDA) ice structures and on intermediate structures as found during the temperature induced transformation of HDA into LDA. We show that the small--angle signal is characterised by two Q regimes featuring different properties (Q is the modulus of the scattering vector defined as Q = 4π()/λ i with being half the scattering angle and λ i the incident neutron wavelength). The very low--Q regime (< 5× 10-2 -1) is dominated by a Porod--limit scattering. Its intensity reduces in the course of the HDA to LDA transformation following a kinetics reminiscent of that observed in wide--angle diffraction experiments. The small--angle neutron scattering formfactor in the intermediate regime of 5 × 10-2 < Q < 0.5 -1 HDA and LDA features a rather flat plateau. However, the HDA signal shows an ascending intensity towards smaller Q marking this amorphous structure as heterogeneous. When following the HDA to LDA transition the formfactor shows a pronounced transient excess in intensity marking all intermediate structures as strongly heterogeneous on a length scale of some nano--meters.