Nano-channel Creation in a Polymer Thin Film Studied

Nano-channel Creation in a Polymer Thin Film Studied by GISAXS Xuefa Li, Christopher K. Ober Sol M. Gruner, Detlef-M Smilgies Lewis Fetters Dept. of Materials Science & Engineering Dept. of Physics CHESS The Idea CH CH 2 C

CH 3 b x CH 2 CH C CH 1

CH n CH 2 3 2 C 3 m y

CH CH 2 2 A two-step strategy was developed to create nano-channels: In step 1 a low-dose UV was used to crosslink the matrix. In step 2 a high-dose UV was used to decompose the cylinder phase. AFM Results 2 m 2 m

Before UV exposure After UV exposure Poly(isoprene-b--methylstyrene) diblock copolymer: Cylinders stand up in the thin film (left). After poly(-methylstyrene) blocks were selectively decomposed by UV exposure, hydrophobic nano-channels were created (right). GISAXS Scattering Geometry-I C C D side view S3

beam stop S2 S1 top view C C D : incident angle : exit angle : scattering angle GISAXS Scattering Geometry-II

qz diffuse XR: normal density profile q SAXS: lateral surface structure Scattering plane Surface plane thin film

Nano-channel Creation-I Before UV exposure After UV exposure Poly(isoprene-b--methylstyrene) diblock copolymer: Hydrophobic nano-channels form in the thin film and still stand up after poly(-methylstyrene) blocks were selectively decomposed by UV exposure. Nano-channel Creation-II Before UV exposure After UV exposure Poly(hydroxy-styrene-b--methylstyrene) diblock copolymer:

Hydrophilic nano-channels form in the thin film and stand up after poly(-methylstyrene) blocks were selectively decomposed by UV exposure. Effect of Photo-crosslinker Before UV after UV A thin film without photo-crosslinker shows standing-up cylinders before expose to UV. After UV decomposes poly(-methylstyrene) block, the nano-channels collapse due to the soft matrix. Therefore, a photo-crosslinker is essential. Annealing Effect Fresh film

2 hr annealing 24 hr annealing Poly(isoprene-b--methylstyrene) block copolymer in freshly spin-coated thin film forms standing-up cylinders. After annealing, the cylinders tend to lie parallel to the substrate. Application of GISAXS Micelles on substrate Cylinders parallel to substrate Mixed lamellar domains

parallel and normal to substrate Summary Poly(isoprene-b--methylstyrene) diblock copolymer forms standing-up cylinders in the thin films. With added photo-crosslinker, the poly(isoprene) matrix can be selectively crosslinked and poly(-methylstyrene) block can be decomposed by using a two-step UV exposure strategy. The nano-channels were created as proved by both AFM and GISAXS. Acknowledgement CCMR and NSF for financial support CHESS, CNF and CCMR for facility uses. Prof. Gruner group