| 학회 |
한국고분자학회 |
| 학술대회 |
2007년 봄 (04/12 ~ 04/13, 제주 ICC) |
| 권호 |
32권 1호 |
| 발표분야 |
신진연구자 특별 심포지움 |
| 제목 |
Polymer brushes on nanoparticles: their positioning in and influence on block copolymer morphology |
| 초록 |
Short thiol terminated polystyrene (PS-SH), poly(2-vinylpyridine) (P2VP-SH) and PS-r-P2VP were synthesized to allow Au nanoparticles (~ 1.5 nm radius Au core) coated with short polymer brushes to be prepared. The polymer brush coating enabled these nanoparticles to be incorporated at low volume fractions into PS-b-P2VP diblock copolymers with precise control over nanoparticle location, namely wholly within the PS or P2VP domains or segregated either strongly or weakly to the PS-b-P2VP interface. Such control is achieved with three different types of brushes on the Au nanoparticles: 1.) High areal chain density ( ＞ 1.5 chains/nm2) mixed brushes of PS-SH and P2VP-SH with fractions fPS-SH of PS-SH ranging from 0 to 1. 2.) High areal chain density brushes of PSx-r-P2VP(1-x) random copolymer with different x values. 3.) Variable areal chain density brushes of PS-SH. For mixed brushes we find that the nanoparticles are segregated to the interface over a wide range (0.90 to 0.10) in fPS-SH while for the PSx-r-P2VP(1-x) random copolymer brushes x must be close to 0.5 before these segregate to the block copolymer interface. These results strongly suggest that the PS-SH and P2VP-SH ligands are mobile on the nanoparticle surface and phase separate in the 2D brush to form “Janus” particles that bind more strongly to the interface than those coated with random copolymer brushes. For the variable areal chain density brushes of PS-SH we find that at areal chain density above a certain value that increases with decreasing molecular weight M of the brush, the nanoparticles are segregated to the center of the PS domains while below this value they are segregated to the interface. The preferential interaction between the P2VP block of the PS-b-P2VP and the imperfectly shielded Au surface is responsible for the segregation of the nanoparticles with a low areal chain density brush to the interface. The transition areal chain density is ~ 4/Rg2 where Rg is the radius of gyration of chains of M = 3.4 kg/mol but unexpectedly scales as 1/Rg as M is varied. If time permits we will discuss changes in block copolymer morphology that occur as the nanoparticle volume fraction Φ is increased for nanoparticles that segregate to the domain center as well as those that segregate to the interface, the latter behaving as nanoparticle surfactants. Small Φ of such surfactants added to lamellar diblock copolymers lead initially to a decrease in lamellar thickness, a consequence of decreasing interfacial tension, up to a critical value of Φ beyond which the block copolymer adopts a bicontinuous morphology. |
| 저자 |
Bumjoon Kim1, G. H. Fredrickson2, J. Bang1, C. J. Hawker2, E. J. Kramer1
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| 소속 |
1Univ. of California, 2Santa Barbara |
| 키워드 |
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| E-Mail |
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