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

Lei Zhu, Case Western Reserve University, DMR 1007918 BA

C D

The focus of this Materials World Network project is the phase morphology of binary mixed polymer brushes composed of two distinct homopolymers 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. In this year, we studied the self-assembly behavior of 67 nm-silica particles grafted with mixed polystyrene (PS)/poly(tert-butylacrylate) (PtBA) brushes in selective polymer matrices. When particles are embedded in low molecular weight (MW) PtBA matrix, isolated PS (dark) domains can be seen, because PtBA brushes are miscible with the matrix and force PS brushes to aggregate into isolated microdomains. When MW of the matrix increases, the miscibility between PtBA brushes and the matrix decreases. The morphology of the mixed brushes changes to bicontinuous, which is similar to the situation without polymer matrix (top panel of Fig. 1). If the matrix is poly(cyclohexyl methacrylate)

Fig. 1. (top panel): TEM micrographs of paricle-1: (A) without any matrix and with the PtBA matrix at molecular weights of (B) 7 kDa, (C) 23 kDa, and (D) 65 kDa. (bottom panel) TEM micrographs of paricle-2: (A) without any matrix and with the PCHMA matrix at molecular weights of (B) 3 kDa, (C) 19 kDa, and (D) 70 kDa. The scale bars show 100 nm.

A

C

B

DSample PtBA, PSMn (kDa)

σPtBA , σPS(chains/nm2)

Particle-1 22.2, 23.4 0.54, 0.31

Particle-2 24.0, 24.4 0.50, 0.49

Table 1. Molecular Characteristics of Particles(PCHMA), which is miscible with PS brushes, the inverted phase behavior can be observed (bottom panel of Fig. 1).

Education in 2011-2012Graduate Research Ph.D. student: Saide Tang (2nd yr.) Visiting graduate students from China: Run Su

Undergraduate Research Anise Grant

International Collaborations1. Jonathan Horton and Chunhui Bao, the students in Prof. Bin Zhao’s group, synthesized mixed brush-grafted silica particles and came to CWRU a couple of times to collaborate on TEM study.

2. Prof. Zhu and Saide Tang visited Fudan University:i) exchanged experience with Prof. Tang, Qiu and Li and their students, ii) planned future research on simulation of mixed brush self-assembly.

3. Saide Tang won a Third Tier Award for student posters in the Polymer Physics 2012 Conference in Chengdu, China .

Publication:1. Horton, J. M.; Tang, S.; Bao, C.; Tang, P.; Qiu, F.; Zhu, L.*; Zhao, B.* ACS Macro Lett. 2012, 45, doi: 10.1021/mz3003193.

Fig. 2. Graduate students Saide Tang (right) from CWRU, and Chunhui Bao and Jonathan Horton (left two) from University of Tennessee at Knoxville in TEM lab.

In June 2012, Prof. Zhu and Saide Tang visited Fudan University and discussed future research on simulations of mixed brush self-assembly with Prof. Feng Qiu, Ping Tang and Weihua Li.

Graduate student Saide Tang (left) with undergraduate student Anise Grant (right).

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

Lei Zhu, Case Western Reserve University, DMR 1007918

Tang Zhu Qiu Li