Mechanical Engineering Department, United States Naval Academy , Annapolis, Maryland 21402, United States.
Advanced Materials Laboratory, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States.
ACS Nano. 2017 Feb 28;11(2):1389-1396. doi: 10.1021/acsnano.6b06499. Epub 2017 Feb 1.
Control over the thermal conductance from excited molecules into an external environment is essential for the development of customized photothermal therapies and chemical processes. This control could be achieved through molecule tuning of the chemical moieties in fullerene derivatives. For example, the thermal transport properties in the fullerene derivatives indene-C monoadduct (ICMA), indene-C bisadduct (ICBA), [6,6]-phenyl C butyric acid methyl ester (PCBM), [6,6]-phenyl C butyric acid butyl ester (PCBB), and [6,6]-phenyl C butyric acid octyl ester (PCBO) could be tuned by choosing a functional group such that its intrinsic vibrational density of states bridge that of the parent molecule and a liquid. However, this effect has never been experimentally realized for molecular interfaces in liquid suspensions. Using the pump-probe technique time domain thermotransmittance, we measure the vibrational relaxation times of photoexcited fullerene derivatives in solutions and calculate an effective thermal boundary conductance from the opto-thermally excited molecule into the liquid. We relate the thermal boundary conductance to the vibrational modes of the functional groups using density of states calculations from molecular dynamics. Our findings indicate that the attachment of an ester group to a C molecule, such as in PCBM, PCBB, and PCBO, provides low-frequency modes which facilitate thermal coupling with the liquid. This offers a channel for heat flow in addition to direct coupling between the buckyball and the liquid. In contrast, the attachment of indene rings to C does not supply the same low-frequency modes and, thus, does not generate the same enhancement in thermal boundary conductance. Understanding how chemical functionalization of C affects the vibrational thermal transport in molecule/liquid systems allows the thermal boundary conductance to be manipulated and adapted for medical and chemical applications.
控制激发分子与外部环境之间的热导率对于定制光热疗法和化学过程的发展至关重要。这种控制可以通过富勒烯衍生物中化学部分的分子调节来实现。例如，可以通过选择官能团来调节富勒烯衍生物茚并-C 单加成物（ICMA）、茚并-C 双加成物（ICBA）、[6,6]-苯基 C 丁酸甲酯（PCBM）、[6,6]-苯基 C 丁酸丁酯（PCBB）和[6,6]-苯基 C 丁酸辛酯（PCBO）的热输运性质，使其本征振动态密度桥接母体分子和液体。然而，这种效应在液体悬浮液中的分子界面上从未得到过实验验证。我们使用泵浦-探测技术时域热透射率，测量了溶液中光激发富勒烯衍生物的振动弛豫时间，并从光热激发分子到液体计算了有效的热边界热导。我们使用分子动力学的态密度计算将热边界热导与官能团的振动模式联系起来。我们的发现表明，在 PCBM、PCBB 和 PCBO 等 C 分子上附加酯基可提供低频模式，有利于与液体的热耦合。这为热流提供了一个通道，除了富勒烯与液体之间的直接耦合之外。相比之下，将茚环附加到 C 上不会提供相同的低频模式，因此不会产生相同的热边界热导增强。了解化学官能化 C 如何影响分子/液体系统中的振动热输运，可以实现对热边界热导的操纵和适应，用于医疗和化学应用。
