Study On The Interaction Between Carbon Nanomaterials And SBS Modified Asphalt And The Regulation Method

The objectives of this study were to explore the microscopic mechanism of two-phase structure formation and separation of styrene-butadiene-styrene(SBS)modified asphalt,so as to select suitable carbon nanomaterials to suppress the phase separation phenomenon,and to investigate the mechanism of carbon nanomaterials on the performance enhancement of SBS modified asphalt from a multiscale perspective.To achieve the above objectives,the following work was carried out in this study: 1)Density functional theory(DFT)simulations were used to explore the interaction mechanism between SBS polymer and asphalt matrix at the atomic scale to explain the molecular mechanism of the formation and separation of the two-phase structure;2)Carbon nanotubes(CNT)were selected as additives,and molecular dynamics simulations,scanning electron microscopy(SEM),fluorescence microscopy,and dynamic mechanical analysis(DMA)were used to investigate the enhancement mechanism of CNT on SBS modified asphalt from multiple scales;3)For the self-aggregation phenomenon of CNT in the modified asphalt matrix,graphene oxide(GO)was additionally selected as an additive,and molecular dynamics simulation,Fourier transform infrared spectroscopy(FTIR),atomic force microscopy(AFM),fluorescence microscopy,and DMA were combined to investigate the interaction mechanism of GO with SBS modified asphalt and its performance response pathway.This study has the following main components.First,the nature of the interaction between SBS polymer and various molecules of asphalt was explored.The optimal molecular models of SBS polymer and CNT were selected,and the interaction models between SBS polymer and various molecules of asphalt were constructed using DFT simulations,and the strength,stability and types of intermolecular interactions were investigated;the results showed that the optimal polymerization degree of SBS polymer was 15-10-15(15 for styrene and 10 for butadiene)and The results show that the optimal model of CNT has a helix angle of 5,a radius of 5 and a repetition unit of 1.The results of binding energy indicate that SBS has different interaction stability with different components of asphalt,in the following order: aromatics > saturates > resins > asphaltenes;the results of charge transfer number indicate that there is no chemical reaction between SBS and various fractions of asphalt;the results of intermolecular interaction morphology indicate that there is no chemical reaction between SBS and aromatics and some resin molecules.The simulation results of DFT can well explain the formation of two-phase structure of SBS modified asphalt and obtain the molecular mechanism of phase separation,which can provide theoretical reference for the performance design of SBS modified asphalt.Second,CNT was used to enhance the interface between SBS and asphalt matrix and explore the multi-scale enhancement mechanism.The molecular models of three systems,namely,virgin asphalt,CNT/SBS modified asphalt and SBS modified asphalt,were constructed,and the rationality of the models was verified by using the four-component content,RDF and glass transition temperature,and molecular dynamics simulations were performed.The results of binding energy showed that CNT could enhance the binding energy of SBS with lighter components of asphalt(aromatics and saturates),which helped to enhance the weak interface between polymer-rich and asphaltene-rich phases of modified asphalt;the results of mean square displacement(MSD)and diffusion coefficient showed that the addition of CNT reduced the diffusion coefficient of asphalt molecules,but the molecular diffusion coefficient was not significantly correlated with molecular weight,surface area and volume.The main factor affecting the molecular motion is the interaction between molecules;the results of relative concentration distribution show that the addition of CNT does not change the colloidal structure of asphalt,but will play a re-equilibrium effect,and this effect is beneficial to the absorption of lighter components by SBS.The modified asphalt samples were prepared,and microscopic characterization and performance tests were performed.The SEM results showed that the SBS appeared aggregated and flocculated in the SBS modified asphalt system,and the interface with the asphalt matrix was weak and prone to phase separation;while the addition of CNT promoted the distribution of SBS and obviously improved the interface state between SBS and the asphalt matrix;the uniformly distributed SBS polymer would interact with the non-polar The well-distributed SBS polymer will fully interact with the non-polar components of the asphalt,making the development of the polymer-rich phase network in the CNT/SBS modified asphalt system significantly better than that of the SBS modified asphalt,which was confirmed by fluorescence microscopy;a good polymer-rich phase predicts better road performance,and DSR experiments showed that the CNT/SBS modified asphalt has better rutting resistance than the SBS modified asphalt.However,the self-aggregation effect of CNT was observed by SEM,and this phenomenon hindered the maximum enhancement effect of CNT.Third,to address the self-aggregation phenomenon of CNT,GO was selected instead of CNT,and the multi-scale interaction mechanism between GO and SBS modified asphalt was explored.Molecular dynamics simulations,fluorescence microscopy,FTIR,AFM and DMA were used to analyze the interaction mechanism of GO,SBS and asphalt from a multiscale perspective.The results showed that the rutting resistance,shear resistance and deformation resistance of GO/SBS modified asphalt were significantly improved compared with that of virgin SBS modified asphalt,and the optimum content of GO was 0.3 Wt.%.The microscopic characterization and FTIR results showed that the improved high-temperature performance of GO/SBS modified asphalt was not only due to the good adhesion of GO itself with non-polar components,but it also promoted the adsorption of SBS polymer with light components,resulting in a more developed polymer-rich phase in the GO/SBS modified asphalt system.The well-developed polymer-rich phase forms a three-dimensional network and confines the asphalt to a small phase transition range,which results in a significant decrease in the area of bee-like structures in the asphalt matrix and a significant increase in their number.The above process was verified by molecular dynamics simulations,in which the binding energy of SBS with lighter components in GO/SBS modified asphalt system was larger than that of the native SBS modified asphalt system,while the diffusion coefficient of asphalt molecules was significantly smaller than that of the SBS modified asphalt system.