Here we present a review of x-ray absorption spectroscopy and x-ray Raman scattering with the perspective to understand the spectra of water including changes with temperature, mass of the water molecule and presence of monovalent ions. The different detection schemes are discussed and it is concluded that transmission x-ray absorption measurements, using a small area where the thickness is uniform, and x-ray Raman scattering give the most reliable spectra. Different model systems are discussed such as the surface and bulk of ice and various adsorbed monolayer structures on metal surfaces.

Extension-induced crystallization under nearequilibrium condition has been studied in a series of lightly cross-linked high density polyethylene (XL-HDPE) with a combination of extensional rheology and in situ synchrotron radiation small-angle X-ray scattering (SAXS) and wide-angle Xray diffraction (WAXD) measurements. According to crystal morphology and structure, four regions were defined in straintemperature space, namely "orthorhombic lamellar crystal" (OLC), "orthorhombic shish crystal" (OSC), "hexagonal shish crystal" (HSC) and "oriented shish precursor" (OSP), respectively. This indicates that flow not only induces entropic reduction of initial melt, but also modifies the free energies of the final states, which is overlooked in the classical stretched network model (SNM) for flow induced crystallization (FIC). Incorporating the free energies of various final states, a modified SNM is developed and employed to analyze strain-temperature equivalence on nucleation in FIC, which reveals that the critical nucleus thickness l* at different regions leads to a natural transition from lamellar to shish nuclei. The results suggest that classical nucleation theory is still valid for FIC under near-equilibrium condition provided that the free energy changes of initial melt and final states induced by flow are taken into account.

Based on classical nucleation theory, the current entropic reduction model (ERM) of flow-induced crystallization (FIC) treats external work as perturbation on the framework of equilibrium thermodynamics, which, however, obscures the nonequilibrium nature of FIC. In this work, in situ investigation on FIC under strong flow by combining a unique homemade extensional rheometer and ultrafast X-ray scattering reveals a constant critical strain or time for nucleation in isotactic polypropylene melt in a wide temperature range from 130 to 170 °C. Our discovery contradicts the strain–temperature equivalence predicted by ERM but unveils the nonequilibrium nature of FIC. To account for the temperature independence of flow-induced nucleation, a tentative kinetic pathway of nucleation describing stretch-induced hierarchical structural transitions is proposed through which the capability of flow as driving force is justified.