SANS investigation of polyether block copolymer micelle structure in mixedsolvents of water and formamide, ethanol, or glycerol

The solution structure of a representative polyether block copolymer (Pluro nic P105: EO37-PO58EO37, where EO and PO denote ethylene oxide and propylen e oxide segments, respectively) has been investigated in mixed solvents (se lective for the PEO block) consisting of water and one of the following pol ar cosolvents: formamide, ethanol, and glycerol. EO37PO58EO37 self-assemble s to form micelles in all the cosolvent-water mixed solvents examined, abov e a certain concentration (cmc) and temperature (cmt) which depend on the c osolvent type and content. Micelle structural parameters were obtained as a function of the cosolvent-water ratio, solution temperature, and block cop olymer concentration by fitting a core-corona form factor and a hard-sphere interaction structure factor to small-angle neutron scattering (SANS) data . The micelle radii, micelle core radii, micelle association numbers, and p olymer volume fractions in the micelle core and corona decreased with incre asing cosolvent-water ratio in the mixed solvents containing formamide or e thanol. Addition of glycerol led to higher micelle association number and h igher polymer volume fraction in the micelle corona. The above findings are discussed in terms of the solvent quality in the mixed solvents. An increa se in temperature resulted in higher micelle association number and a lower degree of solvation in the micelle core and corona in all the cosolvent-wa ter mixed solvents examined.