Polyaromatic Assembly Mechanisms and Structure Selection in Carbon Materials

Abstract

This article reports on the interfacial behavior of large liquid-phase polycyclic aromatic hydrocarbons in pitches that are common precursors to carbon materials. Experiments were conducted to identify preferred angles of molecular orientation ("surface anchoring" states) and to measure contact angles on a variety of well-characterized substrates. The results show that the large disklike polyaromatic molecules exhibit anomalously weak noncovalent interactions with a variety of surfaces, a fact that we attribute to inhibition of dispersion forces due to geometric mismatch at the interface. It is further found that large polyaromatics prefer edge-on molecular orientation at most interfaces, a configuration that preserves internal aromatic π-π bonds at the expense of inhibited π-surface bonds. A theory of π-π bond preservation is proposed to explain many aspects of wetting, adsorption, anchoring, and supramolecular assembly in this important class of compounds, including the formation mechanism for the classic bipolar Brooks-Taylor mesocarbon spheres. The results are used to discuss the mechanisms of structure selection in carbon materials prepared at high and low temperatures. The results are also used to demonstrate a new approach for molecular engineering of carbon that employs anchoring templates to synthesize new materials with preprogrammed patterns of graphene layer orientation.

Novel Mesoporous Carbon Supports for PEMFC Catalysts

“…This synthesis was based on the unique physical properties of a naphthalene-based mesophase pitch precursor, which is a polycyclic aromatic hydrocarbon (PAH) and a common by-product of the petroleum industry. These PAHs interact through long range London dispersion forces and arrange in an ordered, liquid crystalline structure [33]. A synthetic naphthalene-based mesophase pitch (Mitsubishi AR pitch) was chosen by Li et al [30], as petroleum-based pitches often contain sulphur impurities.…”

Structure of the carbon nanofilaments formed by liquid phase carbonization in porous anodic alumina template

“…In the pitch-like liquid formed during carbonization of PVC, it is believed that poly-aromatic compounds are developed [26]. Hurt et al have examined interaction of liquid phase poly-aromatic compounds in pitch with various substrates at 325°C, reporting that large poly-aromatic compounds prefer edge-on molecular orientation at the interface with many substrates including aluminum oxide [27]. Thus, it is likely that the development of platelet structure of carbon nanofilaments originates the edge-on interaction of poly-aromatic compounds in a liquid phase formed from PVC with pore wall of anodic alumina.…”

Linear viscoelasticity of textured carbonaceous mesophases

“…32,33 The edge-on anchoring (see Figure 5) is the more frequently found, and is the result of strong non-covalent interactions involving aromatic π clouds. 32,33 In the analytical equations derived in our previous studies to describe the orientation field in capillary flow the average molecular orientation at the boundaries are assumed to be planar, and this also will be the case in this study.…”

“…32,33 The edge-on anchoring (see Figure 5) is the more frequently found, and is the result of strong non-covalent interactions involving aromatic π clouds. 32,33 In the analytical equations derived in our previous studies to describe the orientation field in capillary flow the average molecular orientation at the boundaries are assumed to be planar, and this also will be the case in this study. 20,31,[34][35][36] A detailed discussion about the viscoelastic properties involved in the small amplitude oscillatory shear of discotic nematics can be found in our previous papers, 20,31,[34][35][36] here we briefly present the essential features of the material properties.…”