title: Adjusting Local Molecular Environment for Giant Ambient Thermal Contraction.
abstract: A low-energy triggered switch that can generate mechanoresponse has great technological potential. A submolecular moiety, S-dibenzocyclooctadiene (DBCOD) that is composed of a flexible eight-membered ring connecting to a phenyl ring at each end, undergoes a conformational change from twist-boat to chair under a low-energy stimulus such as near infrared irradiation, resulting in thermal contraction of DBCOD-based polymer. Experimental evidence corroborated by theoretical calculations indicates that introducing molecular asymmetry can reduce crystallinity significantly and consequently facilitate the kinetics of the conformational change. It has been demonstrated that the negative thermal expansion (NTE) coefficient of a DBCOD-based polymer system can be adjusted in a range from -1140 to -2350 ppm K-1. -2350 ppm K-1is ≈10 times better than the value reported by the second best NTE system.
authors.affiliation: State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science and Laboratory of Advanced Materials, Fudan University, Shanghai, 200438, China.|Materials Science and Engineering, School of Engineering, University of California at Merced, Merced, CA, 95343, USA.
authors.forename: Xingyuan
authors.initials: X
authors.lastname: Shen
authors.affiliation: Chemistry, School of Natural Science, University of California at Merced, Merced, CA, 95343, USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Connolly
authors.affiliation: State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science and Laboratory of Advanced Materials, Fudan University, Shanghai, 200438, China.
authors.forename: Yuhui
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Chemistry, School of Natural Science, University of California at Merced, Merced, CA, 95343, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Colvin
authors.affiliation: State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science and Laboratory of Advanced Materials, Fudan University, Shanghai, 200438, China.
authors.forename: Changchun
authors.initials: C
authors.lastname: Wang
authors.affiliation: Materials Science and Engineering, School of Engineering, University of California at Merced, Merced, CA, 95343, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lu
mesh_terms: D034242:Cyclooctanes / Q000737:chemistry*; D015394:Molecular Structure; D010316:Particle Size; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
chemical_list: D034242:Cyclooctanes; D011108:Polymers; C511097:dibenzocyclooctadiene
keywords: molecular dynamics; negative thermal expansion; polymers; stimuli responses; submolecular switches