Effect of the molecular weight of hte homopolymers on the morphology in ternary blends of polystyrene,polyisoprene,polystyrene-block-polyisoprene copolymer

摘要

Three nearly symmetrical ternary systems made of ternary blends of polystyrene,polyisoprene,polystyrene-block-polyisoprne copolymer have been investigated by small angle X-ray scattering (SAXS).The molecular weights of the homopolymers were varied,keeping the diblock length constant,to obtain ratios of homopolymer ot diblock length,alpha,of 0.19,0.38 and 0.74.For all experimental phase diagrams setermined,a phase transition from lamellar to bicontinuous microemulsion,and then macroscopic phase separation have been observed with increasing homopolymer content.In addition,for alpha=0.38 and 0.74,a region of coexistence of bicontinuous microemulsions and lamellae.between the periodicaly ordred phase (lamellar)and the channel of microemulsion is reported at low temperature,which transform into a pure bicontinuous microemulsions at a higher one.For alpha=0.74,the concentration at which the macroscopic phase separation occurs is lower than the one obtained with alpha=0.19 and 0.34,suggesting that,as the molecular weight of hte two homopolymers is increased,the micromulsion morphology becomes less stable.the thrmal flucturations begin to destroy the micromulsion morphology in favour of macroscopic phase separated system.This observation is further confirmed by the study of hte variation of the d-spacing for the lamellar phase,where no wetting of the diblock monolyers was noticed for alpha=0.74 as compared to alpha=0.19 and 0.38.