Molecular Tuning of the Vibrational Thermal Transport Mechanisms in Fullerene Derivative Solutions

Abstract

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.

Ultrafast and Nanoscale Energy Transduction Mechanisms and Coupled Thermal Transport across Interfaces

“…In this limit, the thermal boundary conductance at the nanoparticle/liquid interface is given by TBC = italicr italicC v 3 τ , where r is the particle radius, C v is the particle’s volumetric heat capacity, and τ is the thermal decay time constant. This method has been widely applied to a number of colloidal particle systems, providing, arguably, the largest breadth of experiments associated with nanoscale solid–liquid interfacial thermal transport; these studies include metal nanoparticles composed of various elements, nanorods and nanotubes, and suspended molecules . The primary limitation of this approach is the viability of suspending such particles in the fluid of interest.…”

“…This method has been widely applied to a number of colloidal particle systems, providing, arguably, the largest breadth of experiments associated with nanoscale solid−liquid interfacial thermal transport; these studies include metal nanoparticles composed of various elements, 249 nanorods and nanotubes, 250 and suspended molecules. 251 The primary limitation of this approach is the viability of suspending such particles in the fluid of interest. For example, it is difficult to manufacture colloidal metal nanoparticles lacking an adhesion layer in an arbitrary liquid of choice, thus making this approach inapplicable for the study of a "bare" metal/liquid interface.…”

Graphullerite: A Thermally Conductive and Remarkably Ductile Allotrope of Polymerized Carbon

“…For instance, graphene is endowed with metal-like electronic conductivity, , an extremely high Young’s modulus (∼1 TPa), and one of the highest thermal conductivities ever measured (in excess of ∼5000 W m –1 K –1 ) . Likewise, in the case of fullerite, which is a 3D bulk structure of C 60 molecules, even though the molecules are held together by weaker van der Waals interactions, they are accompanied by several remarkable physical properties. − For example, the fullerite structure has been theorized as being among the least compressible materials, as well as possessing a wide band gap with an electrical resistance that can be tuned via mechanical strain and pressure. , Their thermal conductivity, however, has been shown to be on the opposite end of the spectrum (in comparison to graphene) with values <0.4 W m –1 K –1 . ,,,, This has been mainly attributed to the vibrational localization resulting from the weak nonbonded interactions. ,,,, Therefore, combining some of the exceptional physical properties of the different carbon allotropes in one material system could open the doors for engineering the next generation of fully organic, multifunctional materials potentially with large tunability in their physical properties. In this regard, incorporating C 60 molecules in graphene-like sheets (with strong carbon–carbon bonds along the 2D sheets) that are stacked together to form a 3D structure (with nonbonded and relatively weaker interactions in the out-of-plane direction), such as in the case of graphullerite, could potentially offer the prospect of achieving highly anisotropic and potentially unrivaled physical properties in one material system.…”

“… 7 , 9 , 10 , 15 , 16 This has been mainly attributed to the vibrational localization resulting from the weak nonbonded interactions. 6 , 8 , 15 , 17 , 18 Therefore, combining some of the exceptional physical properties of the different carbon allotropes in one material system could open the doors for engineering the next generation of fully organic, multifunctional materials potentially with large tunability in their physical properties. In this regard, incorporating C 60 molecules in graphene-like sheets (with strong carbon–carbon bonds along the 2D sheets) that are stacked together to form a 3D structure (with nonbonded and relatively weaker interactions in the out-of-plane direction), such as in the case of graphullerite, could potentially offer the prospect of achieving highly anisotropic and potentially unrivaled physical properties in one material system.…”

Elimination of Extreme Boundary Scattering via Polymer Thermal Bridging in Silica Nanoparticle Packings: Implications for Thermal Management

“…A widely accepted means to account for this additional phonon scattering mechanism comes from the introduction of an additional mean free path limitation that is proportional to the diameter of the grain or nanoparticle, which itself is directly related to the thermal conductance across the individual nanoparticle boundary (or boundaries) [16]. Significant work has also been done to achieve thermal bridging and promote heat flow across boundaries by matching materials and vibrational properties [17][18][19]. In this work, we show that the voids between nanoparticles lead to an extremely large boundary scattering mechanism and that by the infiltration of polystyrene into the interstitial voids, we are able to eliminate the effects of that boundary scattering and bridge between the nanoparticles and polymer as one effective composite film.…”