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Molecular Tensile Machines: a New To...

Li, Yuanchao.

Molecular Tensile Machines: a New Tool for Quantitative Mechanochemistry.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Molecular Tensile Machines: a New Tool for Quantitative Mechanochemistry.
Author:	Li, Yuanchao.
Description:	123 p.
Notes:	Source: Dissertation Abstracts International, Volume: 74-09(E), Section: B.
Notes:	Adviser: Sergei Sheiko.
Contained By:	Dissertation Abstracts International74-09B(E).
Subject:	Chemistry, General.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3562760
ISBN:	9781303105685

Molecular Tensile Machines: a New Tool for Quantitative Mechanochemistry.
Li, Yuanchao.

Molecular Tensile Machines: a New Tool for Quantitative Mechanochemistry. - 123 p.

Source: Dissertation Abstracts International, Volume: 74-09(E), Section: B.

Thesis (Ph.D.)--The University of North Carolina at Chapel Hill, 2013.

Controlling force at molecular length scales is a challenge in mechanochemistry. Well-defined macromolecules and tools that allow accurate control of both magnitude and direction of bond tension have been developed during the past two decades. Our contribution to this endeavor has been the design of molecular tensile machines that are highly branched macromolecular architectures (e.g. bottlebrushes, pom-poms, and dendrimers), which are able to generate bond tensions up to nanoNewton range due to steric repulsion between densely grafted branches. Furthermore, these macromolecular devices allow accurate variation of the bond tension through changes in the surrounding environment such as temperature, solvent quality, and salinity, making them ideal systems for the study of quantitative mechanochemistry.

ISBN: 9781303105685Subjects--Topical Terms:

226910
Chemistry, General.

Molecular Tensile Machines: a New Tool for Quantitative Mechanochemistry.
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100 1 $a Li, Yuanchao. $3 660290
245 1 0 $a Molecular Tensile Machines: a New Tool for Quantitative Mechanochemistry.
300 $a 123 p.
500 $a Source: Dissertation Abstracts International, Volume: 74-09(E), Section: B.
500 $a Adviser: Sergei Sheiko.
502 $a Thesis (Ph.D.)--The University of North Carolina at Chapel Hill, 2013.
520 $a Controlling force at molecular length scales is a challenge in mechanochemistry. Well-defined macromolecules and tools that allow accurate control of both magnitude and direction of bond tension have been developed during the past two decades. Our contribution to this endeavor has been the design of molecular tensile machines that are highly branched macromolecular architectures (e.g. bottlebrushes, pom-poms, and dendrimers), which are able to generate bond tensions up to nanoNewton range due to steric repulsion between densely grafted branches. Furthermore, these macromolecular devices allow accurate variation of the bond tension through changes in the surrounding environment such as temperature, solvent quality, and salinity, making them ideal systems for the study of quantitative mechanochemistry.
520 $a In this dissertation, we focus on bottlebrushes that can generate bond tension along the backbone and also amplify & focus this tension to a chemical group of interest. We have explored two complementary effects of the self-generated tension: activation of chemical reactions and electronic properties. Specifically, we have studied homolytic cleavage and reduction of disulfides under controlled force and analyze the bond activation parameters quantitatively. We have shown that the scission rate of disulfide increases exponentially with tension as reported by others but decreases with temperature. This anti-Arrhenius behavior is ascribed to the decrease of backbone tension with temperature, which can overpower thermal effect. Moreover, the reduction rate constant at zero force was found significantly lower than that in bulk solution, which suggests an acidic composition of the water surface with pH=3.7. To investigate the effect of tension on electronic structures, we have synthesized bottlebrushes with a polythiophene backbone and constructed a unique experimental set-up enabling measurements of fluorescence spectra of sub-monolayer films as a function of backbone tension. The energy band gap was found decreasing with tension due to the increase of conjugation length and then increasing due to the deformation of bond lengths and angles, which agrees with our prediction by DFT calculations.
520 $a In addition to bottlebrushes, we have explored other types of strained molecular architectures including spoked-wheel macromolecules and block-copolymer brushes. Molecular dimensions and emission spectra of these unique molecular architectures have been characterized.
590 $a School code: 0153.
650 4 $a Chemistry, General. $3 226910
650 4 $a Chemistry, Physical. $3 226924
690 $a 0485
690 $a 0494
710 2 $a The University of North Carolina at Chapel Hill. $b Chemistry. $3 660291
773 0 $t Dissertation Abstracts International $g 74-09B(E).
790 $a 0153
791 $a Ph.D.
792 $a 2013
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3562760

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