Study On Mass Transfer Behavior Of Emulsifier/Aggregate Chemical Composition System

The demulsification conditions of emulsified asphalt are uncontrollable,which makes it extremely limited in the application of road engineering.There are two main reasons for this problem:the emulsified asphalt itself is a thermodynamically unstable system,and the mechanism of interaction with the aggregate is not thorough enough.Studies by scholars have focused on the research of emulsified asphalt itself,ignoring the role of aggregates.Therefore,this paper starts with the interaction mechanism between emulsified asphalt and aggregate,simplifies the test materials,and take the main components of the aggregate and emulsifier as research objects.Through the methods of conductivity test and molecular dynamics simulation,studied the mechanism of adsorption and mass transfer of the two types of ionic emulsifiers on the surface of aggregate components,which provided preliminary experimental verification and theoretical support for the controllability of emulsified asphalt demulsification conditions.The experiment selected the five most important components of limestone and basalt?calcium oxide,magnesium oxide,ferric oxide,silica,alumina?and two commonly used ionic emulsifiers?anionic emulsifier:Sodium Dodecyl Benzene Sulfonate,SDBS;cationic emulsifier:Stearyl Trimethyl Ammonium Chloride,STAC?as the test materials.By testing the conductivity of the material under different conditions,analyzing the relationship of the conductivity with the material itself,temperature,concentration and other factors.Based on the conductivity loss of the mixed solution,calculated the adsorption amount of the emulsifier in the chemical composition/emulsifier mixed solution system.The result shows that the chemical composition of the aggregate has different degrees of adsorption on the two ionic emulsifiers.Different aggregate components have the same adsorption tendency for the two emulsifiers,which are:CaCO₃>Al₂O₃>SiO₂>Fe₂O₃>MgO;the adsorption characteristics of the same aggregate components on the two emulsifiers are different,and the results indicate that the adsorption of STAC emulsifier is greater than that of SDBS emulsifier.By the test data,calculated the adsorption isotherms of the emulsifier on the surface of the aggregate chemical composition.After fitting the curve,it was found that the Langmuir type adsorption isotherm was obtained,and the adsorption amount of the emulsifier was quantitatively calculated.The molecular dynamics method was used to simulate the aggregate components/emulsifier interface model.To simulate the microscopic behavior of the emulsifier molecules under the action of aggregate components and water,the calculation used the COMPASS force field,the NVT ensemble,and the simulation duration is 1200 ps.The molecular dynamics calculation results were analyzed from the aspects of structural characteristics and dynamic properties.The following conclusions were obtained:?1?By analyzing the adsorption configuration and relative concentration,the results show that there are differences in the adsorption configuration and spatial distribution of the emulsifier between different material interface models.The hydrophilic group of emulsifier tends to be in water,the hydrophilic group is adsorbed on the surface of aggregate chemical composition,and the molecular structure of emulsifier has a certain torsional deformation.In addition,the free emulsifier molecule in water accumulates spontaneously,forming the micelle structure with hydrophilic group as the core and hydrophilic group facing the outer layer.?2?According to the radial distribution function,interface energy,diffusion coefficient and other indicators,the adsorption effect is quantitatively analyzed,the results show that different aggregate chemical composition/emulsifier interface model,the adsorption effect of emulsifier is inconsistent,according to the adsorption strength is:CaCO₃>Al₂O₃>Fe₂O₃>SiO₂>MgO.At the same time,the adsorption effect of aggregate chemical composition on two emulsifiers was different,and the adsorption effect on STAC molecule was significantly stronger than that of SDBS molecule.