The structural properties of PEO-PPO-PEO block copolymers dissolved in water have been studied by small-angle neutron scattering. Three different phases appear. At low temperature (T≤15°C) the block copolymers are dissolved as individual Gaussian chains (unimers). At intermediate temperatures, the hydrophobic nature of PPO causes aggregation into a liquid of micelles. At even higher temperature (T≥36.5 °C for the 28% polymer solution) the micellar liquid “freezes” into a cubic crystalline powder, which can be aligned by shear into a single crystal.