Nano-channel Creation in a Polymer Thin Film Studied by GISAXS

Xuefa Li, Christopher K. OberSol M. Gruner, Detlef-M Smilgies

Lewis Fetters  

Dept. of Materials Science & EngineeringDept. of Physics

CHESS

The Idea

CC H 2

C H 2

C H 2C H 2

C H 2

C H 3

C H 3

C H 3

C H

C HC

Cx

yn m

b

1 2

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

AFM Results

2 m

Before UV exposure After UV exposure

2 m

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

CCD

CCD

side view

top view

beamstop

α: incident angleβ: exit angleψ: scattering angle

S1S2S3

GISAXS Scattering Geometry-II

qz

q

thin filmSurface plane

Scattering plane

diffuse XR:normal density profile

SAXS:lateral surfacestructure

Nano-channel Creation-I

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.

Before UV exposure After 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 exposeto UV. After UV decomposes poly(-methylstyrene) block, the nano-channelscollapse 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-coatedthin film forms standing-up cylinders. After annealing, the cylinders tend to lie parallel to the substrate.

Application of GISAXS

Micelleson substrate

Cylindersparallel to substrate

Mixed lamellar domainsparallel and normalto substrate

Summary

Poly(isoprene-b--methylstyrene) diblock copolymer forms standing-upcylinders 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.

AcknowledgementCCMR and NSF for financial support

CHESS, CNF and CCMR for facility uses.Prof. Gruner group