Nanoscale Self-Assembly of Well-Defined Binary Mixed Homopolymer Brushes Grafted on Inorganic Particles

Lei Zhu, Case Western Reserve University, DMR 1007918

The focus of this Materials World Network project is the phase morphology of binary mixed polymer brushes composed of two distinct homopolymers randomly or alternately immobilized via covalent bonds on inorganic particles and their applications in polymer nanocomposites. We seek to achieve fundamental understanding of the effects of molecular weight, surface free energy, grafting density, substrate geometry, and environmental conditions on the phase behavior of two surface-tethered polymers in a nanoscale confined geometry. The gained knowledge from this work will be crucial for technological applications of binary mixed polymer brushes in many other areas. In this year, we studied the self-assembly of mixed polystyrene (PS)/poly(tert-butylacrylate) (PtBA) brushes in selective polymer matrices. When PtBA homopolymers with different molecular weights are used as the matrix, both wet-brush [matrix molecular weight (MW) is lower than the brush MW] and dry-brush (matrix MW is higher than the brush MW) states can be obtained. Fig. 1 shows that the self-assembly of mixed PS/PtBA brushes on 150-nm SiO2 particles changed from isolated PS domains to bicontinueous PS/PtBA morphology with increasing the PtBA matrix MW.

Fig. 1. (top panel) : TEM micrographs of mixed brush-grafted silica particles in the matrix of (A) PtBA, Mn=7k Da, (B) PtBA, Mn=23k Da, (C) PtBA, Mn=65k Da, and (D) without PtBA matrix. (bottom panel) Schematic representation of mixed brush-grafted SiO2 particles in the (left) wet-brush and (right) dry-brush states.

Nanoscale Self-Assembly of Well-Defined Binary Mixed Homopolymer Brushes Grafted on Inorganic Particles

Lei Zhu,Case Western Reserve University, DMR 1007918

Education in 2010-2011Graduate Research Ph.D. student: Saide Tang (1st yr.) Visiting graduate students from China: Ganji Zhong and Run Su

Undergraduate Research Mr. Maosheng Lu (Chem. Eng.)

International Collaborations1. 2011 US-China MWN Grantee Workshop held in San Francisco, CA2. Prof. Ping Tang visited CWRU after the 2011 US-China MWN Workshop3. Prof. Zhao and Zhu visited Fudan University: i) presented research on mixed polymer brushes, ii) exchanged experience with Prof. Tang and Qiu and their students, iii) planned future research directions.

Fig. 2. (top) Prof. Qiu, Tang, and Zhu attended 2011 US-China MWN Grantee Meeting in San Francisco.

Prof. Tang visited Case Western Reserve University in May and discussed research and education on mixed polymer brushes on nanoparticles.

In July 5-12, Prof. Zhao and Zhu visited Fudan University, giving lectures and discussing future research directions with Prof. Qiu and Tang. Publications in 2010-2011:

1. Jiang, X., et al. Macromolecules 2010, 43, 5387–5395.2. Jiang, X., et al. Macromolecules 2010, 43, 8209–8217.3. Wang, Y., et al. J. Chem. Phys. 2011, 134, 134903.