The binary phase behavior of short-chain PDMS-b-PEO diblock copolymers in aqueous solutions in dependence of the PDMS chain length—a combined polarized optical microscopy, 2H NMR and SAXS study

The binary phase behavior of three short-chain polydimethylsiloxane-b-poly(ethylene oxide) (PDMS-b-PEO) diblock copolymers with the compositions DMS4-b-EO12, DMS6-b-EO12 and DMS10-b-EO12 (DMS = dimethylsiloxane unit, EO = ethylene oxide unit) was investigated in aqueous solutions using polarizing light microscopy, deuterium NMR spectroscopy, and SAXS measurements. At low surfactant concentrations all three diblock copolymers show a mixed water/lamellar phase (W + Lα), which switches to a lamellar phase depending on the DMS length and temperature in the region of 40 wt.% for DMS4 to over 50 wt.% for DMS10. The surfactants consisting of DMS4 and DMS6 show further on in the concentration range between 40 and 85 wt.% predominately lamellar phases. While at very high concentration a surfactant rich phase L2 developed. If the DMS segment was increased to 10 units the region between 55 wt.% and approximately 75% was dominated by a mixed “inverse hexagonal” and lamellar phase at higher concentration a pure “inverse hexagonal” and afterwards a surfactant rich lamellar phase developed, respectively.