Temperature dependent cubic and hexagonal close packing in micellar structures

The interfacial structure and phase diagram of a micellar solution formed by the three block copolymer (EO 20 -PO 70 -EO 20 ) also known as P123 solved in deuterated water close to a solid boundary is investigated with respect to temperature. We find a hysteretic behavior of the d -spacing of the micellar crystal and a spontaneous change in the lateral correlation length going hand in hand with a structural reorganization between cubic and hexagonal. The phase transitions may be initiated by a change in the shape of the micelles from spherical to elongated together with a minimization of the polymer water interface. The delicate correlation of temperature, micellar properties and type of structure is investigated for a micellar crystal at a solid boundary. The cubic and hexagonal close packing is analyzed in detail by grazing incidence neutron scattering.