CN111783350A - Characterization method of nanoscopic aggregation state of asphalt - Google Patents
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Abstract
The invention discloses a characterization method of a nanoscopic aggregation state of asphalt, which belongs to the technical field of molecular dynamics simulation and is realized based on a molecular dynamics theory and simulation computing software MS (materials studio) software, and comprises the following steps: (1) modeling asphalt and modifier molecules: the method comprises the steps of asphalt molecule construction and modified asphalt molecule construction; (2) and (3) characterization of the nanoscopic aggregation state of the asphalt: calculation and analysis of Radial Distribution Function (RDF). The method provides a method for simulating the nano-scale aggregation state of the asphalt in Materials Studio software, solves the problem that the nano-scale aggregation state of the asphalt is difficult to evaluate in actual engineering or technical research, thereby providing a basis and foundation for judging the influence of a modifier on the nano-scale structure of the asphalt, further designing and researching a novel high-performance modified asphalt, and having good application prospect.
Description
Technical Field
The invention belongs to the technical field of molecular dynamics simulation, and particularly relates to a characterization method of a nanoscopic aggregation state of asphalt.
Background
Asphalt concrete pavements are the main form of highways in China, and asphalt is generally graded according to the physical properties of asphalt at present, but even the asphalt with the same grade shows different pavement properties due to the difference of chemical structures, and the chemical structures of the asphalt need to be researched. This is mainly because the chemical composition of the material is decisive for the properties of the material; the microstructure of the material is an important factor influencing the macroscopic properties of the material, such as strength, hardness, elastoplasticity, melting point, thermal conductivity and the like. The aggregation of asphalt molecules is the basis for generating an asphalt colloid structure, and the physicochemical property and the service performance of the asphalt are determined to a great extent. Therefore, the research on the nanoscopic aggregation state of the asphalt molecules provides important guiding significance for understanding the micro-chemical structure of the asphalt, selecting a proper modifier and the dosage of the modifier.
With the rapid development of the field of molecular mechanics, molecular simulation techniques have been widely used in a considerable number of scientific fields. The molecular simulation technology is to utilize a theoretical method and a calculation technology to simulate or simulate the movement behavior of molecules, can effectively analyze the relationship between the molecular structure and the molecular movement and arrangement rule, and can calculate the macroscopic performance index of a substance to analyze the relationship between the chemical structure and the macroscopic performance of the substance.
Asphalt molecules are complex in type, and the research on the chemical structure of the asphalt through a test means has certain difficulty. Therefore, the nanoscopic aggregation state of the asphalt molecules is researched by utilizing molecular dynamics simulation, and the tiny and detailed change of the internal aggregation state of the asphalt molecules, which is difficult to observe by the traditional laboratory experiment, is revealed and is characterized by a radial distribution function.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a characterization method of a nanoscopic aggregate state of asphalt, which establishes a three-dimensional molecular model based on a molecular dynamics theory and solves the problem that the nanoscopic aggregate state of asphalt molecules is difficult to be well characterized in a current macroscopic experiment.
The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme:
a characterization method of a nanoscopic aggregate state of asphalt comprises the following steps:
1) newly building a 3D atomic document in Materials Studio software, drawing molecules according to molecular formulas of various components of the asphalt, and obtaining a three-dimensional molecular structure of the asphalt component;
2) in a COMPASS II force field, an asphalt molecule model is constructed by using the Amorphous cell function in a Materials Studio software Modules;
3) carrying out regular ensemble balance on the asphalt molecular model constructed in the step 2), carrying out isothermal and isobaric ensemble dynamics simulation, and carrying out regular ensemble dynamics simulation to obtain a processed asphalt molecular model, so that the processed asphalt molecular model reaches a stable state for analysis;
4) respectively defining the centroids of molecules of three components including asphaltene, colloid and oil in the processed asphalt molecule model as three groups, and calculating by using Analysis of Forcite function in Modules to obtain a radial distribution function g (r) with the following formula:
wherein r is the distance from a reference atom, rho is the density of the system, and N is the number of particles in a sphere with the radius of r from the reference atom to the processed asphalt molecule model;
5) smoothing the radial distribution function g (r) obtained in the step 4), wherein the smoothing mechanism is to replace the original value by the average value of all points in the step length of the area near one point, and the function value P (i) after smoothing is as follows:
wherein P (j) is a pre-smoothing value, B is a smoothing window, and the unit is: nm, n is the number of sampling points calculated in each step, and Δ x is the sampling interval, unit: nm;
6) exporting the data after smoothing treatment in the step 5), and carrying out secondary treatment in origin by using a Savitzky-Golay method;
7) the r obtained in the step 4) is the sum of the radial distribution functions of the asphaltene and the colloid of 0.8 to 2nm ∑ g (r)A-RAnd r is the sum of 0.8-2nm of radial distribution functions of asphaltene-oil components ∑ g (r)A-SRatio of
As a basis for describing the aggregation state of the asphalt molecules.
Further, the oil content in the asphalt in the step 1) adopts a straight chain model C22H46The colloid is 1, 7-dimethylnaphthalene model, and the asphaltene is Artok model C63H50S2。
Further, in the step 2), the constructed model is specifically subjected to regular ensemble balance of 200-500 ps, isothermal and isobaric ensemble dynamics simulation of 200-500 ps, and then regular ensemble dynamics simulation of 300-500 ps, so that the system reaches a stable state for analysis.
Further, the construction process in the step 3) adopts a COMPASS II force field; the kinetic simulation used a Nose-Hoover thermostat and Andersen barostat to control temperature and pressure.
Further, the radial distribution function in step 4) includes centroid radial distribution functions of asphaltene, oil, colloid, asphaltene-oil and asphaltene-colloid.
Further, the smoothing process in step 5) is implemented by Matlab software, and the size of the smoothing process window B is 10, i.e. 0.2 nm.
Further, the window sizes of the secondary processing in origin by the Savitzky-Golay method in step 6) are respectively: asphaltene 40, oil 20, gum 20.
Has the advantages that: compared with the prior art, the method solves the problem that the nano-scale chemical structure of the asphalt is difficult to be well characterized through macroscopic test and physical performance, intuitively characterizes the nano-scale aggregation state of the asphalt through molecular dynamics simulation, and can be combined with other methods based on radial distribution functions in actual engineering or technical research, such as normalization treatment and coordination number solution, so as to judge the influence of different modifiers on the aggregation state of the asphalt molecules, thereby providing great help for the selection of the modifiers in actual construction.
Drawings
FIG. 1 is a generic bitumen molecule model;
FIG. 2 is a radial distribution function of three components (asphaltene, oil, aromatic) of general asphalt;
FIG. 3 is radial distribution function of three components (asphaltene, oil, aromatic) of SBS modified asphalt;
FIG. 4 is a radial distribution function ratio of asphaltenes-colloid to asphaltenes-oil components for regular asphalt and SBS modified asphalt;
FIG. 5 is radial distribution function of three components (asphaltene, oil, aromatic) of SBR modified asphalt;
FIG. 6 is a layered structure of SBR modified asphalt;
FIG. 7 is a radial distribution function ratio of asphaltenes-colloid to asphaltenes-oil components for regular and SBR modified asphalts;
FIG. 8 is radial distribution function of three components (asphaltene, oil, aromatic) of SBS-MAH modified asphalt;
FIG. 9 is the ratio of the radial distribution function of the asphaltene-gum to the asphaltene-oil components of regular asphalt and SBS-MAH modified asphalt.
Detailed Description
The structure and performance of the present invention will be further explained with reference to the accompanying drawings.
A characterization method of a nanoscopic aggregate state of asphalt comprises the following steps:
as shown in FIGS. 1 to 8, the invention provides a method for characterizing the nanoscopic aggregation state of asphalt molecules and the influence of a modifier on the nanoscopic aggregation state of asphalt molecules, which is implemented by the following steps:
1) newly building a 3D atomic document in Materials Studio software, drawing molecules according to molecular formulas of various components of asphalt, and obtaining a three-dimensional molecular structure;
2) in a COMPASS II force field, an asphalt model is constructed by using the Amorphous cell function in an MS software Modules; asphaltThe middle oil adopts a straight-chain model C22H46The colloid is 1, 7-dimethylnaphthalene model, and the asphaltene is Artok model C63H50S2；
3) Carrying out regular ensemble (NVT) balance of 200-500 ps on the asphalt molecule model constructed in the step 2), then carrying out isothermal and isobaric ensemble (NPT) kinetic simulation of 200-500 ps, and then carrying out regular ensemble (NVT) kinetic simulation of 300-500 ps to obtain a processed asphalt molecule model, so that the processed asphalt molecule model reaches a stable state for analysis; the construction process adopts a COMPASS II force field; the dynamics simulation adopts a Nose-Hoover thermostat and an Andersen constant pressure device to control the temperature and the pressure;
4) the centroids of the molecules of the three components of the asphaltene, the colloid and the oil in the processed asphalt molecule model are respectively defined as three groups (sets), and Radial Distribution Functions (RDF) including the centroids of the asphaltene, the oil, the colloid, the asphaltene-oil and the asphaltene-colloid are calculated by using Analysis of Forcite functions in Modules. The radial distribution function is formulated as follows:
wherein r is the distance from a reference atom, rho is the density of the system, and N is the number of particles in a sphere with the radius of r from the reference atom to the processed asphalt molecule model;
5) smoothing the radial distribution function g (r) obtained in the step 4), wherein the smoothing mechanism is to replace the original value by the average value of all points in the step length of the area near one point, and the function value P (i) after smoothing is as follows:
wherein P (i) is a function value after smoothing, P (j) is a numerical value before smoothing, B is a smoothing window (unit: nm), n is the number of sampling points calculated in each step, and deltax is a sampling interval (unit: nm); realized by Matlab, the size of the smoothing window is 10, namely 0.2 nm;
6) exporting the smoothed data obtained in the step 5), and carrying out secondary processing windows in origin software by a Savitzky-Golay method, wherein the secondary processing windows respectively comprise: asphaltene 40, oil 20, gum 20;
7) r obtained in the step 4) is the sum of 0.8-2nm of asphaltene-colloid radial distribution functions ∑ g (r)A-RAnd r is the sum of 0.8-2nm of radial distribution functions of asphaltene-oil components ∑ g (r)A-SRatio of
As a basis for describing the aggregation state of the asphalt molecules.
The first embodiment is as follows:
the effect of SBS modifiers on the nanoscopic aggregate state of asphalt was evaluated at T298K. The centroid radial distribution functions of the asphaltenes, oil content and colloid of the smoothed ordinary asphalt and SBS modified asphalt are respectively shown in figures 1 and 2.
The asphaltene molecule aggregation is characterized by the ratio of the sum of the 0.8-2nm asphaltene-colloid radial distribution functions to the sum of the 0.8-2nm asphaltene-oil radial distribution functions, as shown in figure 3.
As can be seen from the figure, the SBS modifier has a certain influence on the aggregation state of asphalt molecules when T298K, which is specifically shown as follows: compared with common asphalt molecules, the aggregation phenomenon of colloid molecules in SBS asphalt molecules is not obviously changed, and the distribution of molecules of asphaltene and oil is more uniform; the colloid structure formed between the asphaltene and the colloid is more uniformly distributed.
Example two:
the nanoscopic aggregate state of the SBR-modified asphalt was characterized at T358K. The centroid radial distribution function of the asphaltenes, oil and colloid of the smoothed SBR-modified asphalt is shown in fig. 4.
As shown in FIG. 5, the nano-scale aggregation state of the asphaltenes of the SBR modified asphalt shows a distinct layered structure.
The asphaltene molecule aggregation is characterized by the ratio of the sum of the 0.8-2nm asphaltene-colloid radial distribution functions to the sum of the 0.8-2nm asphaltene-oil radial distribution functions, as shown in figure 6.
Example three:
the effect of SBS-MAH modifier on the nanoscopic aggregate state of asphalt was evaluated at T418K. The centroid radial distribution function of the smoothed SBS-MAH modified asphaltenes, oil, and gum is shown in fig. 7.
The asphaltene molecule aggregation is characterized by the ratio of the sum of the 0.8-2nm asphaltene-colloid radial distribution functions to the sum of the 0.8-2nm asphaltene-oil radial distribution functions, as shown in FIG. 8.
As can be seen from the figure, the SBS-MAH modifier has a certain influence on the aggregation state of asphalt molecules when T ═ 418K, and the specific expression is as follows: compared with common asphalt molecules, the oil molecule aggregation phenomenon in the SBS-MAH asphalt molecules is more obvious, and the distribution of asphaltene and colloid molecules is not obviously changed; the colloid structure formed between the asphaltene and the colloid has no significant change.
The above examples analyze the effect of the modifier on the aggregation state of asphalt molecules by simulating the computational software and using the processed radial distribution function to characterize the nanoscopic structure of the asphalt. For researching the influence of different modifiers on the molecular structure of the asphalt under different conditions, different modifiers and modified asphalt molecular models can be constructed, and simulation calculation and analysis can be carried out at different temperatures and pressures.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.
Claims (7)
1. A characterization method of a nanoscopic aggregate state of asphalt is characterized by comprising the following steps:
1) newly building a 3D atomic document in Materials Studio software, drawing molecules according to molecular formulas of various components of the asphalt, and obtaining a three-dimensional molecular structure of the asphalt component;
2) in a COMPASS II force field, an asphalt molecule model is constructed by using the Amorphous cell function in a Materials Studio software Modules;
3) carrying out regular ensemble balance on the asphalt molecular model constructed in the step 2), carrying out isothermal and isobaric ensemble dynamics simulation, and carrying out regular ensemble dynamics simulation to obtain a processed asphalt molecular model, so that the processed asphalt molecular model reaches a stable state for analysis;
4) respectively defining the centroids of molecules of three components including asphaltene, colloid and oil in the processed asphalt molecule model as three groups, and calculating by using Analysis of Forcite function in Modules to obtain a radial distribution function g (r) with the following formula:
wherein r is the distance from a reference atom, rho is the density of the system, and N is the number of particles in a sphere with the radius of r from the reference atom to the processed asphalt molecule model;
5) smoothing the radial distribution function g (r) obtained in the step 4), wherein the smoothing mechanism is to replace the original value by the average value of all points in the step length of the area near one point, and the function value P (i) after smoothing is as follows:
wherein P (j) is a pre-smoothing value, B is a smoothing window, and the unit is: nm, n is the number of sampling points calculated in each step, and Δ x is the sampling interval, unit: nm;
6) exporting the data after smoothing treatment in the step 5), and carrying out secondary treatment in origin by using a Savitzky-Golay method;
7) the r obtained in the step 4) is the sum of the radial distribution functions of the asphaltene and the colloid of 0.8 to 2nm ∑ g (r)A-RAnd r is 0.8-2nm, the asphaltene-oil component is radialSum of distribution function ∑ g (r)A-SRatio of
As a basis for describing the aggregation state of the asphalt molecules.
2. The method for characterizing the nanoscopic aggregate state of asphalt of claim 1, wherein: the oil content in the asphalt in the step 1) adopts a straight chain model C22H46The colloid is 1, 7-dimethylnaphthalene model, and the asphaltene is Artok model C63H50S2。
3. The method for characterizing the nanoscopic aggregate state of asphalt of claim 1, wherein: in the step 2), the constructed model is specifically subjected to regular ensemble balance of 200-500 ps, isothermal and isobaric ensemble dynamics simulation of 200-500 ps, and then regular ensemble dynamics simulation of 300-500 ps, so that the system reaches a stable state for analysis.
4. The method for characterizing the nanoscopic aggregate state of asphalt of claim 1, wherein: step 3), adopting a COMPASS II force field in the construction process; the kinetic simulation used a Nose-Hoover thermostat and Andersen barostat to control temperature and pressure.
5. The method for characterizing the nanoscopic aggregate state of asphalt of claim 1, wherein: the radial distribution function in the step 4) comprises a centroid radial distribution function of asphaltene, oil content, colloid, asphaltene-oil content and asphaltene-colloid.
6. The method for characterizing the nanoscopic aggregate state of asphalt of claim 1, wherein: the smoothing in step 5) is realized by Matlab software, and the size of the smoothing window B is 10, namely 0.2 nm.
7. The method for characterizing the nanoscopic aggregate state of asphalt of claim 1, wherein: the window sizes of the secondary treatment in origin by the Savitzky-Golay method in step 6) are respectively as follows: asphaltene 40, oil 20, gum 20.
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| CN109872778A (en) * | 2019-01-30 | 2019-06-11 | 东南大学 | A kind of evaluation method of regenerative agent diffusion in waste asphalt mixture |
| CN110491452A (en) * | 2019-08-13 | 2019-11-22 | 南京林业大学 | Performance of modified bitumen prediction technique based on molecular dynamics simulation |
| CN110489858A (en) * | 2019-08-14 | 2019-11-22 | 南京林业大学 | Pitch and SBS Compatibility Evaluation method based on molecular dynamics simulation |
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