SURFACE ORDERING OF BLOCK COPOLYMERS

A linear relationship between fractional surface excess of PDMS (PSI) and PDMS block length (N(A)), PSI = alpha' - beta'N(A)-1/2, is found for the PS-PDMS-PS type triblock copolymers from ESCA results over three different sampling depths, ranging from 27 to 103 angstrom. The effect of PDMS surface segregation PSI is compared within the PS-PDMS diblock, PS-PDMS-PS and PDMS-PS-PDMS triblock copolymer series as N(A) changes. At similar bulk composition, the PDMS segments in the PS-PDMS diblock copolymers are the most apt to segregate in the free surface region, while the PDMS segments of the PS-PDMS-PS triblock copolymers are the least probable to segregate in the free surface region. The surface morphologies of the PS-PDMS diblock and PS-PDMS-PS triblock copolymers are lamellar with the periods of 600 and 450 angstrom respectively, which are revealed by TEM micrographs of the cross sections of the films both near the free surface and in the bulk. A morphology of PS spheres in PDMS matrix is found for the PDMS-PS-PDMS triblock copolymer. The period of the lined PS sphere arrays separated by the PDMS domains is measured to be 130 angstrom.