Modified Attachment Energy Model Research Articles

Prediction of morphology of CL-20/TFAZ cocrystal crystals in binary solvents based on modified attachment energy model

Crystal morphology of CL-20/TFAZ cocrystal in vacuum was predicted using the attachment energy (AE) model. Additionally, the modified attachment energy (MAE) model and molecular dynamics (MD) method were utilized to predict the crystal morphology of CL-20/TFAZ cocrystal in four different binary solvents, namely, isopropyl alcohol (IPA)/acetone (AC), IPA/dimethyl sulfoxide (DMSO), IPA/ethyl acetate (EA), and IPA/water (H2O). The radial distribution function (RDF) between the solvent and crystal surface and the mean square displacement (MSD) of the solvent were calculated. The findings showed that the morphology of CL-20/TFAZ cocrystal in vacuum was an irregular polyhedron with eleven important growth surfaces: (001), (1−10), (110), (100), (011), (0−11), (10−1), (020), (0−20), (11−1), and (1−1−1), with the (001) surface having the highest area ratio of 31.693 %. The crystalline morphology in IPA/AC, IPA/DMSO, and IPA/EA solvents was block-shaped, while it was rod-shaped in IPA/H2O. Comparing the RDF values of the four solvents, IPA/H2O exhibited the largest g(r) value and could more easily adsorb onto the crystal surface of CL-20/TFAZ cocrystal. Interestingly, IPA/H2O solvent had the smallest MSD value, suggesting the slowest diffusion rate, while IPA/AC solvent exhibited the fastest diffusion rate. Overall, IPA/EA solvents were more suitable for the formation of CL-20/TFAZ cocrystal.

The Effect of Solvents on the Crystal Morphology of Isosorbide Mononitrate and Its Molecular Mechanisms.

In this work, the modified attachment energy model was used to predict the crystal morphology of isosorbide mononitrate (ISMN) in the dichloromethane (CH2Cl2) solvent system and dichloromethane-n-hexane (CH2Cl2-C6H14) mixed solvent system. The solvent effect can significantly affect the crystal morphology, which can profoundly impact both the drug's physicochemical properties and the subsequent technological treatment process. In addition, the interactions between solvent molecules and crystal faces were investigated using molecular dynamics simulation, and radial distribution function (RDF) analysis was performed to determine the types of interactions. The structural parameter S was introduced to characterize the roughness of each crystal surface; the change in the CH2Cl2 diffusion coefficient before and after the addition of C6H14 was analyzed using mean square displacement (MSD). The calculation results of the modified attachment energy from the two solvent systems revealed that C6H14 could accelerate crystal growth, while the crystal morphology was not greatly affected, which is of some significance as a guide for the industrial crystallization process.

Exploring the mechanism of asymmetric growth of organic polar crystals: Inherent properties, specific intermolecular interactions

Organic polar crystals (OPCs) are the foundation for photonic and non-linear optical applications in advanced materials. High-quality crystals are a key in achieving efficient performance for OPCs. This work explores the properties and mechanisms of OPC growth along the polar axis. Melt microdrop growth experiments confirm that asymmetric growth is an inherent property of OPCs and relates to the intrinsic crystal structure. Notably, the solvent also plays a non-negligible role in OPCs growth. Solvent-crystal face interactions are strongly influenced by the crystal face structure. A rough surface has a slower growth rate, and a specific recognition of the solvent molecules. Asymmetric growth correlates with the modified attachment energy model and reveals the role of the solvent in inhibiting of crystal growth. Finally, the growth pattern in different solvents is explained by the interfacial adsorption model. This work will further enrich the asymmetric growth mechanism of OPCs and provide guidance for obtaining high-quality OPCs in solution.

Prediction of Ethanol-Mediated Growth Morphology of Ammonium Dinitramide/Pyrazine-1,4-Dioxide Cocrystal at Different Temperatures.

The crystal morphology of high energetic materials plays a crucial role in aspects of their safety performance such as impact sensitivity. In order to reveal the crystal morphology of ammonium dinitramide/pyrazine-1,4-dioxide (ADN/PDO) cocrystal at different temperatures, the modified attachment energy model (MAE) was used at 298, 303, 308, and 313 K to predict the morphology of the ADN/PDO cocrystal under vacuum and ethanol. The results showed that under vacuum conditions, five growth planes of the ADN/PDO cocrystal were given, which were (1 0 0), (0 1 1), (1 1 0), (1 1 -1), and (2 0 -2). Among them, the ratios of the (1 0 0) and (0 1 1) planes were 40.744% and 26.208%, respectively. In the (0 1 1) crystal plane, the value of S was 1.513. The (0 1 1) crystal plane was more conducive to the adsorption of ethanol molecules. The order of binding energy between the ADN/PDO cocrystal and ethanol solvent was (0 1 1) > (1 1 -1) > (2 0 -2) > (1 1 0) > (1 0 0). The radial distribution function analysis revealed that there were hydrogen bonds between the ethanol and the ADN cations, van der Waals interactions with the ADN anions. As the temperature increased, the aspect ratio of the ADN/PDO cocrystal was reduced, making the crystal more spherical, which helped to further reduce the sensitivity of this explosive.

Simulation of the Influence Mechanism of Hydrothermal Modification on Magnesium Hydroxide

AbstractTo overcome the drawbacks of strong polarity and easy agglomeration of ordinary magnesium hydroxide (MH), hydrothermal modification is customary applied to achieve its excellent dispersion as well as controllable morphology and particle size. In this paper, the influence mechanism of hydrothermal modification is elaborated from microstructure of MH. Structures and surface energy of crystal planes, affinity of water molecules for crystal planes, and crystal growth process are calculated by Materials Studio software. Furthermore, molecular dynamics simulations about solid–liquid interface model of MH and 1 mol L−1 NaOH solution at different temperatures are performed based on the theory of modified attachment energy model. The results indicate that (0 0 1) plane with the smallest surface energy has the strongest thermodynamic stability, equipping modified crystals with lamellar morphology and excellent dispersion. (0 0 1) plane cannot be dissolved easily because of the smallest affinity of water molecules. The magnesium atoms and hydroxyl groups on (1 0 1) plane dissolved are absorbed on (0 0 1) plane, resulting in the large value of I001/I101 in the X‐ray diffraction pattern. The relative growth rate of (1 0 1) plane R101 decreases with the increasing temperature, explaining why crystals become thicker with raising temperature.

Morphology prediction of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) crystal in different solvent systems using modified attachment energy model

Effects of solvent, temperature, mixed solvent and its volume ratio on the morphology of TKX-50 crystal. (DMF: N , N -dimethylformamide; H 2 O: water; FA: formic acid; AcOH: acetic acid; EG: ethylene glycol). In order to theoretically study the growth morphology of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) crystal in different solvent systems, crystal–solvent models were established, and then molecular dynamics (MD) methods were adopted as a means to simulate particle motion. Modified attachment energy (MAE) model was employed to calculate the growth morphology of TKX-50. The simulation results demonstrate that COMPASS force field and RESP charge are suitable for molecular dynamics simulation of TKX-50. The morphologically dominant growth surfaces of TKX-50 in vacuum are (0 2 0), (0 1 1), (1 1 –1), (1 0 0) and (1 2 0), respectively. In water (H 2 O) and N , N -dimethylformamide (DMF) solvents, the (1 1 –1) face is the largest in the habit face, the growth rate of (0 2 0) face becomes faster. With the increase of temperature, the aspect ratios of TKX-50 crystal in DMF solvent increase, and the areas of the (1 2 0) faces decrease. In ethylene glycol / H 2 O mixed solvent system with volume ratio of 1 / 1, aspect ratio of TKX-50 is relatively small. In formic acid / H 2 O mixed solvents with different volume ratios (1 / 4, 1 / 3, 1 / 2, 1 / 1 and 2 / 1), aspect ratio of TKX-50 is relatively small when volume ratio is 1 / 2.

A theoretical investigation into the effect of solvent on crystal morphology of 1-methyl-3,4,5-trinitro-1H-pyrazole (MTNP)

The solvent has a significant effect on the crystal morphology of 1-methyl-3,4,5-trinitro-1H-pyrazole (MTNP). The attachment energy model was employed to predict the crystal morphology of MTNP in vacuum, and the main habit facets were obtained. On this basis, the interface models between the ethanol solvent and the crystal surface were constructed and simulated by molecular dynamics method, their interactions were analyzed in detail by radial distribution function and mean square displacement. The final crystal morphology of MTNP in ethanol solvent was obtained using the modified attachment energy model. The results show that MTNP crystals simulated in vacuum have up to 10 habit faces, of which the (1 1 0) and (2 0 0) faces are morphologically more important, accounting for 43.67% and 10.59% of the total surface area, respectively. There is significant hydrogen bonding interaction between the crystal surfaces and the ethanol solvent, which alters the relative growth rates of the different faces and leads to changes in the crystal morphology. The diffusing ability of the ethanol solvent on the crystal face also has a non-negligible effect on the interaction, and the stronger the diffusing ability, the more favorable the interaction. In the presence of ethanol solvent, the (2 0 0) surface disappears and the crystal morphology of MTNP shows a fusiform.

Uncovering the Morphological Regulation Mechanism of Low Sensitivity and Highly Energetic Materials in Solvents: Changing Crystal Morphology Induced by Hydrogen Bonding

Low sensitivity and highly energetic materials (LSHEMs) are currently the most promising high-energy materials due to their structural stability. However, many problems exist due to their abundant hydrogen bonding (HB) in the structure, such as low solubility and difficulty controlling the crystallization process. In this paper, aiming at regulating the crystal morphology of LSHEMs, 4,4′,5,5′-tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine is used as a model substance to explore the mechanism of controlling the crystal morphology in solvents. The molecular structure, crystal structure, and HB sites on crystal faces were investigated by molecular electrostatic potential surface, Hirshfeld surface, and HB analyses, and it was found that the HB density [δ(HB)] of faces is of the order (011) > (11–1) > (110) > (100) in crystal or solution, determining the tendency of interaction with polar solvents. Then, using molecular dynamics simulation and the modified attachment energy model, we found that the attachment energy of crystal faces and the predicted crystal morphologies in different solvents were determined by HB sites on faces and strongly correlated with the solvent polarity. The experimental morphologies were consistent with the trend predicted including the aspect ratio trend, which confirmed our theoretical speculation. This work provides an effective method of choosing solvents for morphology customization of LSHEMs, which will help guide the morphology control and realize the industry application of LSHEMs.

Molecular dynamics study of H4TTP crystal morphology

AbstractTo understand the role of dimethyl sulfoxide (DMSO) on the crystal growth morphology of 2,3,5,6‐tetra(1H‐tetrazol‐5‐yl)pyrazine (H4TTP), the vacuum morphology of H4TTP crystal was predicted by the Bravais–Friedel–Donnay–Harker (BFDH) and the attachment energy (AE) models. The growth morphology of H4TTP in DMSO solvent was predicted using a modified AE model. The results show that the main growth surfaces of H4TTP in vacuum are (1 0 0), (0 0 2), (0 1 1), and (1 1 0) surfaces. Among them, (1 0 0) surface is the most important growth surface. (0 0 2) surface is the roughest crystal surface, while (1 1 0) surface is the flattest. (1 1 0) surface grows rapidly, and (1 0 0) surface has the greatest morphological importance. The analysis of radial distribution function shows that (1 0 0) surface has the strongest hydrogen bonding interactions in the interface between H4TTP and DMSO solvent.

Crystal morphology regulation of pronamide through solvent selection: Prediction and implementation

Molecular dynamics simulation was performed for the solvent selection to regulate the growth morphology of pronamide crystals using the attachment energy model. Five dominant crystal planes were revealed during morphology prediction of pronamide in vacuum, on basis of which the modified attachment energy model was employed to regulate the crystal morphology with three typical solvents (toluene, acetone and methanol) according to their electrostatic potential. Variable morphology of pronamide from needle-like, plate-like to bulk was predicted in the three solvents under the frame of this thermodynamic model. The pronamide crystals obtained from slow evaporation crystallization process were in good agreement with theoretical prediction, showing that molecular dynamics simulation could aid the solvent selection for the crystal morphology regulation effectively.

Molecular Dynamics Simulation of β-HMX Crystal Morphology Induced by Polymer Additives

To simulate the crystal morphology of β-HMX crystallized in the presence of different polymer additives in the solution, a modified attachment energy model was used to simulate the crystal morphology of β-HMX recrystallized in PVA-DMSO solution when the mass fractions of PVA were 0.5%, 1%, 3%, 5%, and 10%, respectively. When the mass fraction of additive was 10%, the simulation results were in good agreement with the experiment. Molecular dynamics simulations were performed on the solution systems of different types of polymer additives to predict the morphology of β-HMX crystals. In addition, the effect of water on the crystal morphology of β-HMX was studied, and the effect of additive PVA on the solute and solvent diffusion ability during crystal crystallization was studied. The simulation results have certain reference significance in the crystallization process of β-HMX under additive conditions.

Effect of external growth environment on cocrystal habits of HNIW/DNB: a molecular dynamics simulation

The modified attachment energy model was applied to predict the crystal morphology of hexanitrohexaazaisowurtzitane/1,3-dinitrobenzene (HNIW/DNB) cocrystal in ethanol. A double-layer interface structure was established based on experiments. Molecular dynamics simulation was employed to investigate the interaction of flat faces and ethanol solvents. We used periodic bond chains and roughness calculations to analyze the characteristics of the HNIW/DNB cocrystal. The crystal morphology of the HNIW/DNB cocrystal is mainly composed of the (001), (010), (102), and (111) faces in vacuum. The (001) face occupies the largest area (49.54%). In ethanol, the area of the (001) face increases to 68.58%. Ethanol molecules are adsorbed on the polar face through hydrogen bonding. In the slowest growth direction, two HNIW layers and one DNB layer alternately appear. The higher molecular recognition of the (001) face of HNIW/DNB resulted in this face becoming the most important growth face. Meanwhile, we also predicted the crystal morphologies of ε-HNIW and DNB in ethanol. The prediction morphologies are in excellent agreement with the experimental shapes. These simulation results can provide guidance for the recrystallization of HNIW/DNB.

Solvent Effects on Catechol Crystal Habits and Aspect Ratios: A Combination of Experiments and Molecular Dynamics Simulation Study

This work could help to better understand the solvent effects on crystal habits and aspect ratio changes at the molecular level, which provide some guidance for solvent selection in industrial crystallization processes. With the catechol crystal habits acquired using both experimental and simulation methods in isopropanol, methyl acetate and ethyl acetate, solvent effects on crystal morphology were explored based on the modified attachment energy model. Firstly, morphologically dominant crystal faces were obtained with the predicted crystal habit in vacuum. Then, modified attachment energies were calculated by the molecular dynamics simulation to modify the crystal shapes in a real solvent environment, and the simulation results were in agreement with the experimental ones. Meanwhile, the surface properties such as roughness and the diffusion coefficient were introduced to analyze the solvent adsorption behaviors and the radial distribution function curves were generated to distinguish diverse types of interactions like hydrogen bonds and van der Waals forces. Results show that the catechol crystal habits were affected by the combination of the attachment energy, surface structures and molecular interaction types. Moreover, the changing aspect ratios of catechol crystals are closely related to the existence of hydrogen bonds which contribute to growth inhibition on specific faces.

A study of Solvent and Antisolvent Influence on the Crystal Morphology of ϵ‐CL‐20 by a Modified Attachment Energy Model

AbstractIn this work the dominant crystal faces of ϵ‐CL‐20 in vacuum was firstly obtained as (011), (10‐1), (110), (11‐1), (002), (101), (021) by the attachment energy (AE) model. Then the modified AE (MAE) model was used to predict the crystal morphologies of ϵ‐CL‐20 in five pure solvents including ethyl acetate (EA), acetone, acetonitrile, cyclohexane and methanol, and five solvent mixtures of EA/chloroform, EA/dichloromethane, EA/n‐heptane, EA/cyclohexane and EA/1‐propyl alcohol. Results demonstrate that different types of solvent and antisolvent can produce different dominant faces and the corresponding face area, consequently, affecting the crystal morphology. The effect of the volume ratio of the antisolvent to the solvent on the crystal morphologies was further investigated. Finally, the radial distribution function (RDF) of the interfacial model was used to analyze the adsorption behaviors of the solvent molecules on the CL‐20 surfaces.

Molecular dynamics simulations of solvent effects on the crystal morphology of lithium carbonate.

The attachment energy (AE) model was employed to investigate the growth morphology of Li2CO3 under vacuum and water solvent conditions by molecular dynamics simulations. The attachment energy calculation predicted the growth morphology in vacuum dominated by the (1 1 −1), (0 0 2) and (1 1 0) crystal faces. A modified attachment energy model, accounting for the surface chemistry and the corresponding topography of the habit crystal plane, was established to predict the morphological importance of crystal faces in a water solvent. Moreover, radial distribution function (RDF) and diffusion coefficient analyses were performed to explore the adsorption and diffusion behaviors of solvent molecules on the Li2CO3 crystal faces. The calculated results showed that with the solvent effects, the (0 0 2) and (1 1 0) faces were of great morphological importance, while the (1 1 −1) face disappeared gradually. These finally resulted in a cuboid-like Li2CO3 crystal. The growth morphology and the corresponding X-ray powder diffraction pattern derived from the modified AE model were in accordance with the results observed in experiments. The related model provides an important basis for the further investigation of the effects of impurities.

Molecular Modeling on Morphology of 3,4-Bis(3-nitrofurazan-4-yl)furoxan Crystals in Dichloroethane or Benzene Mixture Solvents.

According to the experiments, DNTF crystallizes in benzene/methylbenzene (1:1), benzene/methylbenzene/ethanol (2:3:5), and sym-dichloroethane solvents into two similar crystal shapes, namely strip and tetrahedral. There is a possibility that solvent changes the crystal morphology. In order to explain this phenomenon, the DNTF growth interface model was constructed according to the actual solution environment. The interaction energy between the solvent phase and the DNTF crystal face was studied by means of molecular dynamics simulation. The crystal morphology of DNTF was predicted using the classical modified attachment energy model (MAE) in benzene, methylbenzene, benzene/methylbenzene (1:1), benzene/methylbenzene/ethanol (2:3:5), and sym-dichloroethane. The results show that the DNTF growths are mainly dominated by the (011), (001), (101), (110), (111), and (11[Formula: see text]) faces in vacuum. However, only a few faces will remain in the solvents, of which the (011) and (101) faces are exposed in benzene, methylbenzene, and benzene/methylbenzene (1:1), and only the (111) faces constitute the crystal shape of the DNTF in benzene/methylbenzene/ethanol (2:3:5) and sym-dichloroethane. The predicted results successfully explained the observed phenomena in the experiment. The simulation results can provide some guidance for the crystallization process of DNTF.

The effect of solvents on crystal morphology of sucralose: Experiments and molecular dynamics simulation studies

• The crystal morphology of sucralose was precisely simulated via the MAE model. • Roughness and solvent-crystal contacting angle are vital for solvent adsorption. • The solvent-crystal interactions are dominated by strong hydrogen bonds. • Different inhibitory degree of solvents on two faces arouses varied aspect ratios. The effect of solvents on sucralose crystal morphology was studied both experimentally and theoretically in water, methanol and ethanol. Hirshfeld surfaces and 2-D fingerprint plots were used to investigate the solute-solute interactions which were involved in the calculation of crystal morphology in vacuum. Moreover, solvent-crystal interactions were considered by using the modified attachment energy model and molecular dynamics simulation, leading to a precise simulation of sucralose crystal morphology in all the three solvents. In order to have a better understanding of the solvent effect, surface structure as well as the strength and the type of the solvent-crystal interactions on the morphologically important faces including the (0 1 1) and (1 0 1) faces were discussed. Both surface roughness and solvent-crystal contacting angle were found to be important to the effective solvent adsorption. Based on the diffusion coefficient of solvent molecules on the crystal faces, the crystal morphology of sucralose was also affected by the solvent diffusion. Radial distribution function analysis showed strong hydrogen bonds between the hydrogen atoms in the solutes and the oxygen atoms in the solvents on the (0 1 1) and (1 0 1) faces. Furthermore, different inhibitory degrees of the solvents on the two faces can cause varied aspect ratios of crystals in the tested three solvents.

Crystalline behaviors of HMX-Al composites in solvents: A molecular dynamics and experimental study

Abstract

Theoretical study on crystal morphologies of 1,1-diamino-2,2-dinitroethene in solvents: Modified attachment energy model and occupancy model

In this study, the growth morphologies of 1,1-diamino-2,2-dinitroethene (FOX-7) in vacuum and solvent conditions were investigated by molecular dynamics simulation. The modified attachment energy (MAE) model and occupancy model were used separately to predict the crystal morphology by calculating relative growth rate of different crystal faces in H2O/NMP and DMSO/AC solvent system. The calculated results show that the (0 1 1) face and (1 0 1) face are the most important crystal face in both two solvents towards the MAE model and the occupancy model, respectively. Compared with that from the MAE model, the predicted morphologies from the occupancy model are in better agreement with the experimental results. Radial distribution function (RDF) analyses were employed to demonstrate that the hydrogen bonds and vdW interactions play the dominant role between solvent molecules and FOX-7 surfaces. The above results allow us to understand the role played by solvents and solute molecules on growth morphologies of FOX-7 crystals.

Morphology and Growth Mechanism Study of Lithium Carbonate Synthesized by Reactive Crystallization

AbstractIn the reactive crystallization of lithium carbonate, molecular dynamics simulations are performed for crystal faces of lithium carbonate in contact with sodium chloride‐water molecules. A modified attachment energy model, accounting for the Connolly surface, spacing between crystal faces and solvent molecules, is applied to predict the morphological importance of crystal surface in solvent. From the solvent‐effected attachment energy calculations it is found that the (2 0 ‐2) and (1 1 ‐1) faces become more morphologically important compared with those in vacuum, while the growth rates of (0 0 2) and (1 1 0) faces become quicker, and their area of crystal faces decreases gradually. The observed growth morphology and X‐ray powder diffraction patterns are in accordance with the predicted morphology derived from the modified AE model.