Structure And Morphology Of The Mixed LB Films Of Stearic Acid And PS-b-PMMA

The Langmuir film balance technology and atomic force microscopy (AFM)were respectively used to study the aggregation behavior of the mixed monolayerof small molecule stearic acid (SA) and two kinds of polystyrene-b-poly(methylmethacrylate)(PS-b-PMMA, SMMA) at the air/water interface and the surfacemorphology of the LB films. Effects of blend composition, copolymercomposition, concentration, spreading volume, and spreading method on the π-Aisotherms and hysteresis curves of the mixed Langmuir monolayers of SA andSMMA and the surface morphology of the LB films were studied in detail.When the concentration and volume of the spreading solution were constant,and with the increase of SA content, π-A isotherms of the mixed Langmuirmonolayers moved to the right, and the phase transition points were basicallyunchanged, but the collapse pressures decreased. When the content of SA wasconstant, and with the increase of of PMMA block length, π-A isotherms of theblends moved to the right. According to the AFM height images, when thedeposition pressure was constant, and with the increase of SA content, themorphology of the LB films of SA/SMMA with short PMMA block lengthexhibited from mixed structure of circular and rodlike micelles to circularmicelles to local network structure; while the morphology of the LB films ofSA/SMMA with long PMMA block length exhibited circular micelles and thediameter of cores decreased gradually. When the content of SA was constant,with the increase of deposition pressure, the packing degree of the mixed LBfilms increased.As for the mixed LB films of SA/SMMA with long PMMA block length,when the spreading volume was constant, and with the increase of concentration,π-A isotherms of the blends move to the left and the collapse pressure increased.The density and diameter of the circular micelles in the mixed LB films of SA and SMMA increased gradually. When the spreading concentration was constant,and with the increase of volume, π-A isotherms of the blends move to the rightand the collapse pressure increased. The diameter and height of the circularmicelles in the mixed LB films of SA and SMMA increased gradually.Furthermore, there existed a large influence of spreading method on themorphology of LB films. When the solutions were premixed, the LB filmsexhibited circular micelles with uniform dimension. When SA was first spread,the LB films exhibited circular micelles with asymmetry dimension. WhenSMMA was first spread, the LB films exhibited wormlike structure.