Thermal Percolation in Well-Defined Nanocomposite Thin Films

Abstract

Thermal percolation in polymer nanocomposites the rapid increase in thermal transport due to the formation of networks among fillersis the subject of great interest in thermal management ranging from general utility in multifunctional nanocomposites to high-conductivity applications such as thermal interface materials. However, It remains a challenging subject encompassing both experimental and modeling hurdles. Successful reports of thermal percolation are exclusively found in high-aspectratio, conductive fillers such as graphene, albeit at filler loadings significantly higher than the electrical percolation threshold. This anomaly was attributed to the lower filler−matrix thermal conductivity contrast ratio k f /k m ∼10 4 compared to electrical conductivity ∼10 12 −10 16 . In a randomly dispersed composite, the effect of a low contrast ratio is further accentuated by uncertainties in the morphology of the percolating network and presence of other phases such as disconnected aggregates and colloidal dispersions. Thus, the general properties of percolating networks are convoluted as they lack a defined structure. In contrast, a prototypical system with controllable nanofiller placement enables the elucidation of structure−property relations such as filler size, loading, and assembly. Using self-assembled nanocomposites with a controlled 1,2,3-dimension nanoparticle (NP) arrangement, we demonstrate that thermal percolation can be achieved in spite of using spherical, nonconductive fillers (k f /k m ∼60) at a low volume fraction (9 vol %). We observe that the effects of volume fraction, interfacial thermal resistance, and filler conductivity on thermal conductivity depart from effective medium approximations. Most notably, contrast ratio plays a minor role in thermal percolation above k f /k m ∼60a common range for semiconducting nanoparticles/polymer ratios. Our findings bring new perspectives and insights to thermal percolation in nanocomposites, where the limits in contrast ratio, interfacial thermal conductance, and filler size are established.

Unexpected reduction in thermal conductivity observed in graphene/h-BN heterostructures

“…In the field of micro-nano device fabrication, 1 two-dimensional nanomaterials 2 such as graphene 3 and hexagonal boron nitride (h-BN) 4 have been gaining significant attention because of their extraordinary mechanical, [5][6][7][8] electrical, [9][10][11][12] and thermal characteristics. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Particularly, these materials show broad application prospects when they form vertically stacked van der Waals heterostructures 29 or planar heterostructures. [30][31][32] The graphene/h-BN heterostructure possesses exceptional thermal transport properties, making it a promising candidate for various applications such as thermal rectifiers, 33,34 thermal transistors, 35,36 thermal diode circuits 37 and thermal memory devices.…”

Revealing the Kinetic Phase Behavior of Block Copolymer Complexes Using Solvent Vapor Absorption–Desorption Isotherms

“…The self-assembly of block copolymers (BCPs) has been widely studied as a templating material for a plethora of nanotechnological applications such as nanomembranes, nanolithography, , and nanocomposites. , The self-assembly of BCPs occurs from the microphase separation of chemically incompatible blocks . The BCP adopts lattice structures that minimize the interfacial area between blocks and maximize the conformational entropy of the polymer chains.…”

Processive Pathways to Metastability in Block Copolymer Thin Films

“…There is no doubt that current BCP architectures are incomparable to biopolymers (i.e., proteins and DNA), however, they provide the necessary building blocks for us to comprehend (and appreciate) the complexity and hierarchical nature of the molecular machines. From inception as surfactants [ 1 ] research in BCPs have evolved into more advanced areas, including battery electrolyte membranes [ 2 , 3 ], advanced lithography [ 2 , 4 , 5 , 6 , 7 ], nanocomposites [ 8 , 9 , 10 , 11 ], ion-exchange membranes [ 12 , 13 ], nanopore templates [ 14 ], and patterned surfaces [ 15 , 16 ].…”