Effect Of Selective Solvent On The Aggregate Behavior Of The Mixed Langmuir Monolayers Of PS-b-PEO And PS-b-PMMA

The mixed Langmuir monolayers and mixed Langmuir Blodgett (LB) filmsof polystyrene-block-poly(ethylene oxide)(PS-b-PEO, coded as SEO19K andSEO15K), polystyrene-block-poly(methyl methacrylate)(PS-b-PMMA, coded asSMMA34K and SMMA51K) and their two mixed systems ofSEO19K/SMMA34K and SEO15K/SMMA51K were characterized with theLangmuir film balance and atomic force microscopy (AFM), respectively. Wemainly studied the effect of selective solvent on the π A isotherms, hysteresiscurves, and the morphologies of the LB films. Furthermore, the effects of blendcomposition, block copolymer composition, transfer pressure and spreadingmethod were also considered. We firstly studied the effect of selective solvent onthe mixed Langmuir monolayers of amphipathic block copolymers, by analysisof the results, further researched the mode and mechanism of the formation ofsurface aggregates.In the mixed system of SEO19K/SMMA34K, the plateau of the PEOpancake-to-brush structure transition is observed in the isotherms when thecontent of SEO19K is above40wt%. PEO and PMMA blocks are contributed tosurface pressure in the low-pressure region of compression and expansionprocess, respectively. With the increase of the SEO19K content, the mixed LBfilms exhibit more mixed circle micelles and fewer mixed rod aggregates. Whenthe SEO19K content is20wt%, the mixed LB films prepared by the premixedspreading method exhibit the uniform structure of the mixed circular micellesand mixed rod aggregates, but the SEO19K and SMMA34K solely form surfacemicelles by the separate spreading methods.In the mixed system of SEO15K/SMMA51K, the transition plateau of the PEO blocks is observed in the isotherms when the content of SEO15K is above60wt%. PMMA blocks are mainly contributed to surface pressure in the low-pressure region of compression and expansion process. With the increase of theSEO15K content, the mixed LB films exhibit that the size and height of themixed circle micelles become smaller.Comparing with nonselective spreading solvent chloroform, the effects ofthe selective spreading solvent toluene on the the π A isotherms, hysteresiscurves, and the morphologies of the LB films are all great. It is mainly becauseof the transition from solution micelles to surface micelles. This processinfluences the stretching degree of micelle coronas, and the size and height of themicelle cores.