MORPHOLOGICAL CARACTERIZATION OF BLOCK COPOLYMERS BY TRANSMISSION ELECTRON MICROSCOPY (TEM)

MARÍA J. YÁÑEZ; MARIO D. NINAGO; LEOPOLDO R. GÓMEZ; ANDRÉS E. CIOLINO; ENRIQUE M. VALLÉS; DANIEL A. VEGA; MARCELO A. VILLAR

ACTA MICROSCOPICA

Committee of Societies for Electron Microscopy (CIASEM)

Año: 2009 vol. 18 p. 311 - 312

0798-4545

Block copolymers are macromolecules composed of at least two blocks of different monomers. They often exhibit unique and useful properties in solution and in the solid state as a consequence of a microphase separation produced by thermodynamic incompatibility of the blocks. Domains obtained show different morphology (spheric, cylindric or lamellar, among others) as a function of the volume fraction and the relative length of each block as well as the nature of the blocks involved. On the other hand, defects associated to some morphologies can be modified by thermal treatments. In this work we present the morphological characterization of siloxane-based di-block copolymers by Transmission Electron Microscopy (TEM). Two kind of block copolymers based on siloxane were studied: poly(styrene)-bpoly(dimethylsiloxane), and poly(butadiene)-b-poly(dimethylsilxoane) (PS-b-PDMS and PB-b-PDMS, respectively). Block copolymers samples were dissolved in selective solvents (toluene and cyclohexane) in order to obtain different solutions (1 and 5 wt%). From these solutions, films were prepared by casting one-drop using water as substrate. The films obtainedwere transferred to a copper grid, and observed in a JEOL 100 CXII, at 100 kV. Staining techniques were unnecessary due to the difference in electron absorption and scattering of the PDMS block relative to the others (PS and PB). The ultrastructure of the films obtained depend on the solvent and reflects, to some extent, the nature of the molecular associations in solution. For the studied copolymers, cast films from toluene solutions showed better results. For PB-b-PDMS copolymers, the total molar mass of the block copolymer strongly affects the morphology and then the quality of TEM microphotographs as it is shown in Figures 1 and 2. The darker regions represent phases containing PDMS. Although both samples showed morphological arrangements, a better microphase separation was observed for the PB-b-PDMS copolymer with a higher molar mass. Films cast from 1 wt% toluene solution of lower molar mass PB-b-PDMS copolymer shown different morphological arrangements. On the other hand, the PS-b-PDMS copolymer sample studied in this work showed morphological arrangements similar to those reported in the literature. In this case, a rodlike microphase separation is observed. Thin film morphology obtained by solvent casting is strongly affected by the nature of the solvent as well as the molar mass of block copolymer.