沥青质分子结构与沥青材料性能关系的分子模拟

Molecular Dynamics Study on the Relationship Between Asphaltene Molecular Structures and Asphalt Material Properties

沥青是一种分子组成多样且介观相态构成复杂的黏弹性材料,其骨架结构为沥青质组成的高贮能模量相,常温环境在外力作用下以弹性响应为主。为了研究分子结构对沥青材料性能的影响,利用分子动力学模拟方法研究不同结构的沥青质在沥青工作温度(250~353 K)区间内的相态,并近似地用剪切模量和杨氏模量分别对各相的切向与正向应力-应变关系进行描述。通过测量不同结构沥青质堆积相模型的密度和模量随温度变化的关系,确定玻璃化转变温度和黏流温度,并描述模量随温度的变化趋势。不同结构要素均不同程度影响沥青质聚集体的相态变化和力学性能。迫位缩合沥青质分子聚集体的玻璃化转变温度高于渺位缩合沥青质,模量随温度变化更小。饱和侧链会显著降低沥青质的相转变温度和较高温度下的强度,同时使沥青质聚集体模量对温度更加敏感。含硫沥青质的玻璃化转变温度小于烃类和含氮沥青质,模量随温度的变化也远小于其他两者。通过以上结论,可以评价不同沥青质对沥青整体材料性能的贡献,从理论层面指导沥青材料的开发。

Asphalt is a kind of viscoelastic material with extremely diverse ingredients,and molecules distribute as polydisperse mesoscopic phases.The high storage modulus phase as the skeleton of the asphalt are mainly composed of asphaltenes,and the elastic responding dominates under stress loading at the normal temperature.To obtain the effects of molecular structures on asphalt material properties,the phase states of different structure asphaltenes were studied by molecular dynamics simulations in the range of asphalt working temperature(250—353 K),and the tangential and forward stress-strain relations of each phase were described approximately by shear modulus and Young′s modulus,respectively.The glass transition temperatures and viscous flow temperatures of different asphaltene layered phase models were obtained by measuring the density and modulus.The variation tendencies of Young′s modulus and shear modulus for each phase model at different temperatures were also explored.The phase state and mechanical properties of asphaltene aggregates were affected by various structural elements.The glass transition temperature of peri-condensed asphaltene aggregate is higher than that of cata-condensed asphaltene aggregate,and the modulus variation with temperature is also smaller.Alkyl side chains significantly reduce the phase transition temperatures and higher temperature strength of asphaltenes,which make the asphaltene aggregate modulus more sensitive to temperature.The glass transition temperature of sulphuric asphaltene is lower than that of hydrocarbon and nitrogenous asphaltenes,and the modulus change with temperature is also much lower than the other two.Based on the above conclusions,the contributions of asphaltenes to the asphalt material performance were estimated,which can guide the improvement and upgrading of asphalt materials theoretically.