Effect of poly(dimethylsiloxane) chain length on the phase behavior of A-B-type silicone copolymer in water

The phase behavior and microstructure of A-B-type silicone copolymer, Me3SiO-(Me2SiO)(m-2)-Me2SiCH2CH2CH2-O- (CH2CH2O)(51.6)H, (abbreviated as POE-PDMS or SimC3EO52) in water was investigated for a constant POE chain length (EO52) at 25 degreesC to ascertain the effect of PDMS chain length (m ranging from 5.8 to 52) on the phase behavior. Different micro structures, such as discontinuous micellar cubic (I-1), normal hexagonal (H-1), lamellar (L-alpha), and reverse hexagonal (H-2) liquid crystals, are formed depending on the volume ratio of POE to the copolymer and/ or the copolymer concentration. In the short-PDMS-chain copolymer system, the H-1-I-1-W-m phase transitions take place with the addition of water, whereas, long-PDMS-chain copolymers form the Lalpha or the H-2 phase, which coexist with excess water. The effect of the PDMS chain length on the structural parameters and hence the phase transitions was investigated by using small-angle X-ray scattering. The effective cross-sectional area per copolymer molecule is almost the same (around 0.8 nm(2)) for m = 5.8-12, whereas it increases from 0.82 to 1.13 nm(2) with an increase in m from 14 to 52. The new phase diagrams of water-Si14C3EO52 and water-Si52C3EO52 systems are also presented.