Structural evolution of low-molecular-weight poly(ethylene oxide)-block-polystyrene diblock copolymer thin film.

Hui Wu,Xiaohua Huang

doi:10.1155/2013/539457

Abstract

The structural evolution of low-molecular-weight poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer thin film with various initial film thicknesses on silicon substrate under thermal annealing was investigated by atomic force microscopy, optical microscopy, and contact angle measurement. At film thickness below half of the interlamellar spacing of the diblock copolymer (6.2 nm), the entire silicon is covered by a polymer brush with PEO blocks anchored on the Si substrate due to the substrate-induced effect. When the film is thicker than 6.2 nm, a dense polymer brush which is equal to half of an interlamellar layer was formed on the silicon, while the excess material dewet this layer to form droplets. The droplet surface was rich with PS block and the PEO block crystallized inside the bigger droplet to form spherulite.

Highlights

The formation of diverse patterns in polymer thin films is of considerable technological and scientific importance in coatings, adhesives, photoresists, electronics, biomaterials, and optical devices [1,2,3,4,5]
The initial thickness of Poly(ethylene oxide) (PEO)-b-PS film is controlled by varying the diblock copolymer solution concentration
We studied the structural evolution of low-molecular-weight PS-b-PEO diblock copolymer thin film with various initial film thicknesses on SiOx substrate

Summary

Introduction

The formation of diverse patterns in polymer thin films is of considerable technological and scientific importance in coatings, adhesives, photoresists, electronics, biomaterials, and optical devices [1,2,3,4,5]. Due to a combination of block/interfacial interactions and entropy, the morphologies and properties of thin films with different thicknesses differ appreciably from bulk materials. The ultrathin films of a polystyreneblock-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer on mica formed a chemically heterogeneous surface pattern [16]. Thin diblock copolymer films under thermal annealing exhibited a hierarchy of morphologies because of the interfacial interactions between the copolymers and substrate and the complex coupling and competition between dewetting and microphase separation [2, 17,18,19,20]. The bulk order-disorder transition temperature (TODT) of symmetric polystyrene-block-poly(methyl methacrylate) (PS-bPMMA), the mismatching of film thickness and bulk periodicity result in the hierarchical formation, ranging from spinodal morphology to islands/holes [2, 17]. To achieve the minimization tendency of surface tension, superimposed lamellae are formed in poly(styrene)-block-poly(εcaprolactone) (PS-b-PCL) thin films when annealed lower than TODT [18]

Results

Discussion

Conclusion