Dramatically Tuning Friction Using Responsive Polyelectrolyte Brushes
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- 作者：Qiangbing Wei ; Meirong Cai ; Feng Zhou ; Weimin Liu
- 刊名：Macromolecules
- 出版年：2013
- 出版时间：December 10, 2013
- 年：2013
- 卷：46
- 期：23
- 页码：9368-9379
- 全文大小：661K
- 年卷期：v.46,no.23(December 10, 2013)
- ISSN：1520-5835
文摘
We present a paradigm that dramatically tunes friction from superior lubrication (渭 10鈥?) to ultrahigh friction (渭 > 1) using responsive polyelectrolyte brushes. The tunable friction is based on counterion-driven interactions in polyelectrolyte brushes that can be simply achieved by exchanging the counterions. We systematically investigated the effects of opposite counterions of different types on the friction properties of polyanionic, polycationic, and polyzwitterionic brushes. For cationic brushes with quaternary ammonium groups, the friction coefficient was progressively tuned from 10鈥? to 100 according to the counterions series Cl鈥?/sup> < ClO4鈥?/sup> < PF6鈥?/sup> < TFSI鈥?/sup>. The friction of anionic brushes can be tuned by oppositely charged surfactants (tetraalkylammonium) with different length of hydrophobic tails, multivalent metal ions, and protons. The friction increase of cationic brushes is due to the dehydration and the collapse of polyelectrolyte chains induced by ion-pairing interactions. For anionic brushes, the friction increased with the length of hydrophobic tails of surfactants, which resulted from hydrophobicity induced electrostatic interaction among surfactants and polymer chains. The anionic brushes with the carboxylate and the sulfonate side groups revealed different friction responses, which is owing to the carboxylate groups getting stronger specific interaction with the quaternary ammonium and thus with the multivalent metal ions as well. The mechanism of tuning friction was finally concluded; that is, highly hydrated and swelling polymer brushes show superior lubrication, partially collapsed polymer chains have moderate lubrication, and completely dehydrated and collapsed conformation loses lubricating capability.