Micromorphology of Asphalt Modified by Polymer and Carbon Nanotubes through Molecular Dynamics Simulation and Experiments: Role of Strengthened Interfacial Interactions

Abstract

Polymer modifiers have been used to improve the performances of asphalt binders in pavement engineering. The modifying effect of polymers on asphalt is largely dependent on the morphological characteristics of polymer-modified asphalt. The morphologies of polymer-modified asphalt are composed of a polymer-rich phase, a asphaltene-rich phase, and the interphase between the two phases. Interfacial interactions importantly contribute to the morphology but are commonly overlooked. In this study, carbon nanotubes (CNTs) were selected to improve the interfacial interactions of polymer-modified asphalt. Fluorescence microscopy (FM), scanning electron microscopy (SEM), micro-Raman spectroscopy (MRS), and molecular dynamics (MD) simulation were used to capture the characteristics of the interphase and polymer-rich phase. CNTs-polymer-modified asphalt involves stronger intermolecular forces than those in asphalt-modified by only styrene–butadiene–styrene (SBS) or CNTs. This discrepancy highlights the intensified interfacial interaction in the former material. Raman peak and MD findings reveal that the CC of CNTs interacted with the alkanes and aromatic hydrocarbons of asphalt. SBS were entwined or surrounded with CNTs through the π–π conjugation of the benzene rings of the two components. Consequently, a synergistic effect enhanced the intermolecular force between SBS and CNTs in the interphase. SEM results indicated that CNTs were enriched in the interphase, enhancing mechanical anchorage between the polymer and asphalt. As a result, CNTs increased the roughness of the interphase and produced a prominent cage construction of polymer-rich phase. Moreover, the observed pullout behaviors of CNTs alleviated interfacial failure. FM images displayed that CNTs enhanced the swelling degree of the polymer-rich phase. This effect was realized because CNTs served as a tunnel for transporting saturates, aromatics, and small resin molecules, as shown by molecular dynamics MD analysis. This work revealed the importance of the interfacial interactions on the micromorphologies of polymer-modified asphalt.

Effect of Nanoclay Particles on the Performance of High-Density Polyethylene-Modified Asphalt Concrete Mixture

“…FTIR is a reliable, widely-used technique that is able to analyse modification mechanisms and recognize chemical changes in the functional groups within asphalt materials [ 12 , 50 ]. Characterization of chemical change and molecular-level interactions plays a critical role in the storage stability and mechanical properties of the asphalt cement [ 51 ]. In this study, the Thermo-Scientific Nicolet-iS10 FTIR Spectrometer, with a spectra (band) range of 4000–400 cm −1 , was utilized.…”

Role of Aliphatic Chain Characteristics on the Anti-Cracking Properties of Polymer-Modified Asphalt at Low Temperatures

“…In the fingerprint area, SBS showed characteristic peaks at wavenumbers of 699, 760, 910, and 966 cm −1 , which belonged to benzene or aromatics. The peaks at 699 and 966 cm −1 belonged to the polystyrene phase of SBS [19][20][21][22]. The main functional group in POE was an aliphatic long-chain.…”

The Effect of Direct-to-Plant Styrene-Butadiene-Styrene Block Copolymer Components on Bitumen Modification

“…Therefore, it is of importance to investigate the proportion of each component in a direct-to-plant SBS modifier from both micro and macro perspectives. In recent years, the development of microimaging has provided support for microresearch, especially the invention of the fluorescence microscope [24,25]. When the short wavelength light of fluorescence microscope is used to irradiate SBS modified bitumen film, the SBS emits yellow light, while bitumen and other substances are basically black [26,27,28].…”