Morphology And Structure Of The Mixed LB Films Of PS-b-PEO-b-PS/PS-b-PMMA

In this paper, the aggregation behavior of Langmuir monolayers and surfacemorphology of Langmuir Blodgett (LB) films of polystyrene-block-poly(ethylene oxide)-block-polystyrene (PS-b-PEO-b-PS, coded as SEOS69K),polystyrene-block-poly(methyl methacrylate)(PS-b-PMMA, coded asSMMA34K), and their blends were characterized by the Langmuir film balancetechnology and atomic force microscopy (AFM), respectively. In addition, theeffects of subphase temperature, spreading solvent, blend composition,deposition pressure, and the spreading method of solutions on the Langmuirmonolayers and LB films were considered.With the increase of the SEOS69K content, the surface pressure area (A)isotherms of the mixed monolayers of SEOS69K/SMMA34K move to the rightside. When the SEOS69K content is above80wt%, a phase transition plateauexists in the isotherms of the blends at about10mN/m, and the surface pressureand width of the plateaus increase gradually with the increase of the SEOS69Kcontent. When the maximum pressure is10mN/m, there was no hysteresis forthe monolayers of SEOS69K, SMMA34K, and their blends spread with bothchloroform and toluene solvents in the compression expansion processes. Whenthe maximum pressure is30mN/m, obvious hysteresis is observed for the mixedmonolayers of SEOS69K/SMMA34K spread with both chloroform and toluenesolvents in the compression expansion process, and the hysteresis degreeincreases gradually with the increase of the SEOS69K content.When the SEOS69K content is10wt%, the mixed LB films ofSEOS69K/SMMA34K prepared with chloroform spreading solvent exhibit themixed structures of circular micelles and rod-like aggregates. When theSEOS69K content is above20wt%, the mixed LB films only exhibit the mixedcircular micelles. With the increase of transfer pressure, the diameters of the micelles decrease. However, the mixed LB films spread with toluene solvent onlyexhibit the mixed structures of circular micelles and rod-like aggregates. With theincrease of the SEOS69K content, more circular micelles and less rod-likeaggregates exist. Furthermore, more rod-like aggregates exist with the increase oftransfer pressure.When the SEOS69K content is20wt%, the isotherm of the mixedmonolayer prepared with a separate spreading method is on the right side of thatwith the former premixed spreading method. Furthermore, there exists largedifference in the surface morphologies of LB films prepared by these twospreading methods. The LB films prepared with chloroform by the separatespreading method exhibit the mixed structures of circular micelles and rod-likeaggregates but those with toluene exhibit the layered structures.