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To interpret the diffusion behavior of oxygen in epoxy asphalt with different cross‐linking degrees, epoxy asphalt‐oxygen diffusion layer models were constructed. The effect of temperature on oxygen diffusion and the number of oxygen molecules penetrating the epoxy asphalt was quantitatively analyzed. Fick's second law was used to determine the oxygen diffusion coefficient. The Mean square displacement (MSD) was extracted to analyze the effect of cross‐linking degree on the molecular motion of the base asphalt. The results show that as the cross‐linking degree increases, the number of oxygen in the epoxy asphalt decreases, accompanied by a reduction in the oxygen diffusion coefficient. Temperature significantly affects the rate of oxygen diffusion, with higher temperatures leading to greater diffusion depths over the same simulation time. The oxygen diffusion coefficient of epoxy asphalt ranges from 4.60 × 10−11 to 2.20 × 10−10 m2/s at temperatures of 298–373 K. The epoxy system markedly restricts the movement of base asphalt molecules, with saturate being most affected by cross‐linking degree and asphaltene the least. A high cross‐linking network impedes the asphalt‐oxygen contact oxidation, enhancing epoxy asphalt's anti‐aging capacity. These findings provide support for optimizing epoxy asphalt formulations and guiding the development of anti‐oxidant epoxy asphalt. [ABSTRACT FROM AUTHOR]

This paper investigated the cross‐linking network structure of epoxy asphalt (EA) with the different ratio of composite curing agents, and further determined the effect of photooxidation aging on the tensile and interfacial adhesion behavior of EA with different cross‐linking network structures through molecular simulation. Based on the molecular models of EA and the interface model between EA and aggregate, the crosslinking network structural characteristics and tensile mechanical behavior were determined. The interfacial adhesion behavior and the mechanization were further studied. The results indicate that 20‐EA and 6‐EA have an epoxy resin cross‐linked network with uniform pore structure and phase distribution. 2‐EA showed a denser cross‐linking network and uneven aggregation phenomenon. Photooxidative aging alleviated the aggregation phenomenon. A dense cross‐linking network improved the tensile strength and the ability of tensile performance to resist photooxidation aging. The interface of EA‐quartz exhibited higher adhesion strength than EA‐calcite due to the closer distance and stronger nonbonding interactions between EA and quartz. The low anhydride content and photooxidation aging made EA approach to the aggregate interface, increasing nonbonding interaction and interfacial adhesion strength. In addition, quartz aggregates were more suitable for application in EA mixtures due to the higher interfacial adhesion strength and lower water sensitivity. [ABSTRACT FROM AUTHOR]

To study the effects of curing agent ratio, asphalt content, and crosslinking degree on the properties and distribution of epoxy asphalt with a compound system of dicarboxylic acid and acid anhydride, epoxy asphalt molecular models with two asphalt contents of 25% and 65% and three curing agent ratios of 10:1, 5:1 and 1:1 were constructed by Materials Studio. Various epoxy resin crosslinking degrees were further realised by Perl language crosslinking script. Glass transition temperatures were calculated to characterise low temperature flexibility. Energy systems and interaction energy were simulated to characterise the compatibility of epoxy asphalt. The radial distribution function (RDF) was calculated to observe the composition distribution of epoxy asphalt. The results show that the raise of the crosslinking degree and the proportion of anhydride curing agent increased the Tg of epoxy asphalt, impairing the low temperature performance. The increase in asphalt content was beneficial to the stability of the epoxy asphalt. Resin-based epoxy asphalt had stronger interaction between epoxy resin phase and asphalt phase, and the interaction energies both reached the maximum values at crosslinking degree of around 25%. Resin-based and asphalt-based epoxy asphalt had the most notable composition difference in the distribution of asphaltenes and acid anhydrides. [ABSTRACT FROM AUTHOR]

To study the influence of the cross‐linking network on the thermal oxygen aging performance of the epoxy asphalt, the laser copolymerization microscopy, Fourier transform infrared spectroscopy and element analysis tests were used to characterize the changes in chemical components of epoxy asphalt with composite curing system during thermal oxygen aging. According to the changes in chemical components, the epoxy asphalt molecular models were constructed. The diffusion behavior of oxygen atoms was analyzed, the aging degree was determined. Moreover, the Tg and radial distribution function were calculated to determine the effect of aging on the low‐temperature performance and component distribution of epoxy asphalt. The results show that a proper proportion of curing agent helped to uniform distribution of the asphalt phase. The rise in anhydride curing agent content increased the density of crosslinking network, limited the diffusion of oxygen atoms, and contributed to the resistance of epoxy asphalt chemical components to thermal oxygen aging. However, the high proportion of anhydride aggravated the oxidation reaction of the asphalt phase due to the uneven coating of the asphalt phase. After thermal oxygen aging, the distribution of asphaltene and epoxy resin phase showed a concomitant phenomenon due to polarity adsorption. [ABSTRACT FROM AUTHOR]

In order to explore the effect of composite curing agent ratio on the photooxidative aging behavior of epoxy asphalt with an acidic composite curing system, three curing agent ratios of epoxy asphalt were prepared to obtain different cross-linking network densities. The prepared epoxy asphalt was subjected to photooxidation aging for 240 h at 60 ℃. Fourier transform infrared (FTIR) and elemental analysis tests were conducted to determine the evolution of chemical components during photooxidative aging. Based on the chemical components before and after aging, molecular models of photooxidation aged epoxy asphalt with different curing agent ratios were constructed. The mean square displacement (MSD) of oxygen atoms and the oxygen uptake of each component were calculated to study the diffusion behavior of oxygen atoms and the oxidation degree of each component under various cross-linking networks. Glass transition temperature (Tg) and interaction energy were determined to characterize the thermodynamic properties and interaction between asphalt phase and epoxy resin phase of epoxy asphalt before and after aging. The radial distribution function (RDF) was determined to simulate the distribution of asphaltene and epoxy resin crosslinked networks in different cross-linking networks. The results show that the formation of carbonyl groups, alcohol hydroxyl groups, and the fracture of methylene groups was observed during the photooxidative aging process of epoxy asphalt. The rise in the proportion of anhydride curing agents improved the stability of the chemical components in epoxy asphalt under photooxidation aging. High cross-linking density and methylene fracture weakened the diffusion ability of oxygen atoms in epoxy asphalt due to a reduction in free volume. In addition, photooxidation aging had a negative impact on the low-temperature performance and interaction between asphalt phase and epoxy resin phase of epoxy asphalt. However, a high content of acid anhydride alleviated the damage of photooxidation aging to low-temperature performance. Photooxidation aging developed the polar functional groups of epoxy asphalt, promoting the stacking of asphaltene under a high content of dicarboxylic acid curing agent, while breaking the stacking of asphaltene under a high content of acid anhydride curing agent. • High content of anhydride improved the stability of chemical components during aging. • The photooxidative aging process of epoxy asphalt was successfully simulated. • A dense cross-linked network resisted the diffusion of oxygen atoms effectively. • A dense cross-linking network benefited aging resistance of epoxy asphalt. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation technology was introduced into the characterization of epoxy asphalt performance, to display the reaction process between the epoxy resin and curing agent in epoxy asphalt clearly and explore the influence of epoxy resin content and conversion rate on the epoxy asphalt performance containing thermodynamic, compatibility, component distribution and diffusion. The reaction between the epoxy resin and curing agent was realized through Perl script, and epoxy asphalt molecular dynamics models with different resin content (25%, 45%, and 65%), and various conversion rates were prepared. Results demonstrated that the addition of epoxy resin enhanced the low-temperature performance of epoxy asphalt, but the increase in conversion rate played a negative impact on low-temperature performance. The CED and solubility parameter were synergistically affected by the epoxy resin content and conversion rate. Furthermore, the raise in the content of epoxy resin was the main reason for enhancing the compatibility between epoxy resin and asphalt. Therefore, the reasonable control of the resin content and conversion rate was beneficial to enhance the stability of the epoxy asphalt system and improve the compatibility between the resin phase and the asphalt phase. 25%-EA and 45%-EA were considered as asphalt phase materials. Aggregation behaviors exhibited between asphaltenes, and adsorption behaviors presented between epoxy resin and asphaltene. With the increase of conversion rate, the adsorption behavior gradually disappeared. 65%-EA belonged to the resin phase material, and the aggregation between asphaltenes was diminished. In addition, the epoxy resin without conversion reaction had the smooth diffusion behavior in epoxy asphalt. [ABSTRACT FROM AUTHOR]

Poly(butylene succinate-co-furandicarboxylate) (PBSF) and poly(butylene adipate-co-furandicarboxylate) (PBAF) are novel furandicarboxylic acid-based biodegradable copolyesters with great potential to replace fossil-derived terephthalic acid-based copolyesters such as poly(butylene succinate-co-terephthalate) (PBST) and poly(butylene adipate-co-terephthalate) (PBAT). In this study, quantum chemistry techniques after molecular dynamics simulations are employed to investigate the degradation mechanism of PBSF and PBAF catalyzed by Candida antarctica lipase B (CALB). Computational analysis indicates that the catalytic reaction follows a four-step mechanism resembling the ping-pong bibi mechanism, with the initial two steps being acylation reactions and the subsequent two being hydrolysis reactions. Notably, the first step of the hydrolysis is identified as the rate-determining step. Moreover, by introducing single-point mutations to expand the substrate entrance tunnel, the catalytic distance of the first acylation step decreases. Additionally, energy barrier of the rate-determining step is decreased in the PBSF system by site-directed mutations on key residues increasing hydrophobicity of the enzyme's active site. This study unprecedently show the substrate binding pocket and hydrophobicity of the enzyme's active site have the potential to be engineered to enhance the degradation of copolyesters catalyzed by CALB. [ABSTRACT FROM AUTHOR]

Poly(butylene digly co late-co-furandicarboxylate) (PBDF) is a newly developed biodegradable copolyester. Candida antarctica lipase B (CALB) has been identified as an effective catalyst for PBDF degradation. The mechanism is elucidated using a combination of molecular dynamics simulations and quantum chemistry approaches. The findings unveil a four-step catalytic reaction pathway. Furthermore, bond analysis, charge and interaction analysis are conducted to gain a more comprehensive understanding of the PBDF degradation process. Additionally, through the introduction of single-point mutations to crucial residues in CALB's active sites, two mutants, T138I and D134I, are discovered to exhibit improved catalytic efficiency. These significant findings contribute to the advancement of our comprehension concerning the molecular mechanism of underlying copolyesters degradation, while also presenting a novel approach for expediting the degradation rate by the CALB enzyme modification. [ABSTRACT FROM AUTHOR]

[Display omitted] • The combined 3D-QSAR biodegradability model was established. • Using molecular docking to obtain the biodegradability scoring function of FQs. • Binding energy analysis based on molecular dynamics (MD). • Use MD to simulate the actual operating conditions of sewage treatment plants. • Molecular parameters analysis based on 2D-QSAR model and sensitivity analysis. Molecular docking was used to calculate the docking scores of fluoroquinolones (FQs) and manganese peroxidase isolated from Phanerochaete chrysosporium , cytochrome oxidase isolated from Paracoccus denitrificans, and oxidoreductase isolated from Candidatus Kuenenia stuttgartiensis , which represented the aerobic, facultative, and anaerobic biodegradability of FQs, respectively. The comprehensive index (CI) of the above three sets of docking scores was calculated using the averaging method to characterize the aerobic, facultative, and anaerobic biodegradation of FQs. Using CI as a dependent variable, a comprehensive aerobic, aerobic, and anaerobic biodegradation CoMSIA model of FQs was constructed. Taking gatifloxacin (GAT) as the target molecule and using molecular modification information, 25 FQ derivatives suitable for aerobic, facultative, and anaerobic biodegradation were designed. After evaluating the environmental friendliness (bioconcentration and photodegradability) and the functional characteristics (genotoxicity) of FQs, six derivatives were finally screened. The combined biodegradation of 1-butylbenzene-3-fluorine-GAT in six derivatives was increased by 14.06 %, and its performance under aerobic, facultative, and anaerobic biodegradation conditions was increased by 31.33 %, 36.54 %, and 35.50 %, respectively. This improvement in the performance was in line with the equal weighting set by averaging. Molecular dynamic calculations showed that the binding energy (Δ G b) of 1-butylbenzene-3-fluorine-GAT was lower than that of GAT (the lower the value of Δ G b , the stronger the binding ability), indicating that it had a stronger affinity for degrading enzymes. [ABSTRACT FROM AUTHOR]