L(3) PHASE IN A BINARY BLOCK COPOLYMER WATER SYSTEM/

Block copolymers of the Poloxamer type EO(x)PO(y)EO(x) (with EO = ethy lene oxide and PO = propylene oxide) can form lyotropic liquid crystal line phases in water, as is known for small. hydrocarbon surfactants. The phase behavior of PE6200 (EO(6)-PO36-EO(6)) is investigated in mor e detail for concentrations up to 50 wt% and temperatures from 0 to 10 0 degrees C. The technical product contains about 10 wt% hydrophobic c ontaminations, which induce clouding at ambient temperatures. These '' impurities'' can be removed by filtration, but they do not affect the subsequent phase behavior. A lamellar phase (L(alpha)) and a spongelik e phase (L(3)) are found and characterized by DSC, SANS, electric bire fringence, dynamic light scattering, and specific conductivity. The te mperatures for the phase transitions decrease linearly with increasing NaCl concentration. In the L(3) phase the orientational relaxation ti me from electric birefringence decreases with the third power of the v olume fraction and the reduced diffusion coefficient derived from dyna mic light scattering increases linearly with Poloxamer concentration. The conductivity of added electrolyte clearly shows the bicontinuous s tructure of the Poloxamer L(3) phase. Comparison of the systems PE6200 /water and C(12)EO(5)/water shows analogies for the phase behavior and the properties in the different phases.