Control of the liquid-liquid transition in a molecular liquid by spatial confinement

Generally, phase transitions are seriously affected by spatial confinement. This effect is important for its own sake, but also for applications to nanotechnology. Here we report the first systematic experimental study on confinement effects on a liquid-liquid transition of a molecular liquid. We found that one liquid can be transformed into another purely by spatial confinement. This indicates that the liquid state cannot be specified by the temperature and pressure alone, but it is also affected by its size in a discontinuous manner: the phase of a liquid in a narrow space can, in principle, be different from that in the bulk. This finding would deepen our basic understanding of the liquid state.