Development And Applications Of Nucleation Theoretical Model With Microscopic Correction Of Surface Tension

Nucleation is a significant fundamental phenomenon in physical chemistry and plays important roles in many areas,thereby appeals extensive attention.The nucleation process involves the formation of a thermodynamic new phase accompanied by a transition from high to low free energy of the system.Based on macroscopic thermodynamic properties,classical nucleation theory（CNT）is the primary theoretical model employed to describe the free energy and nucleation rate of the nucleation process.However,since most of the critical nucleus sizes are within a few nanometers,and numerous physical and chemical properties of nanoparticles and macroscopic materials differentiate from each other largely,it is difficult for traditional CNT to accurately describe the free energy change of nucleation process from the microscopic perspective,which tremendously limits the practicability of CNT.Therefore,it is significant and challenging to develop accurate nucleation models to quantitatively describe the nucleation free energy.A key assumption of CNT is the capillary approximation,the surface tension of the droplet equals to that of the planar surface,which is one of the reasons resulting in the failure of CNT at the molecular level.Consequently,modifying CNT from the concept of surface tension at nanoscale can greatly advance the prediction accuracy of the model for nucleation free energy.In this paper,we proposed a combined approach of molecular dynamics（MD）simulation and nucleation theory models for correcting the surface tension from microscopic perspective in CNT and K（?）hler theory to obtain the modified nucleation theory models.Through modified models,we explored the free energy and nucleation rate of the nucleation process of two typical systems:atmospheric aerosols and bulk nanobubbles,which successfully explained experimental results and crucial theoretical predictions are given,involving the barrier of ion induced water molecules nucleation,the activation critical supersaturetion（）of ammonium/alkylaminium sulfates and formic/acetic acid dry particles at nucleation mode as well as the nucleation barrier of bulk nanobubbles containing different gas species.Our study provides theoretical support for the development of more accurate nanoscale nucleation models applying to droplets and nanobubbles.The main specific research contents are as follows:1.An approach combining molecular dynamics simulation and ion-induced nucleation theory（IINT）was proposed to study the barrier of ions induced water vapors nucleation.By taking the parameters obtained from MD simulation based on polarizable force field into the IINT,we predicted the free energy profiles of ion induced nucleation of water wapors at different humidities.The structure and thermodynamic properties of clusters as a function of cluster sizes and ion species were systematically studied.It is found that ions can largely improve the cluster stability,and under the same relative humidity,the ability of ions promoting nucleation follows SO₄^2->H₃O⁺>NH₄⁺>NO₃^-,consistent with the order of the solvation free energy of ions.Therefore,the solvation free energy can be used as a rough index for evaluating the IIN ability.The MD/IINT approach raised a new way to explore the ion induced nucleation process and understand the microscopic mechanisms of atmospheric-related ions,contributing to the study of mechanism of aerosol nucleation.2.Molecular dynamics simulation and K（?）hler theory were combined to explore the hygroscopicity of ammonium/alkylaminium sulfates at nucleation mode.By taking the formula of surface tension with curvature radius obtained from MD simulation into the K（?）hler equation,we derived the modified K（?）hler curves of ammonium sulfate（AS）and alkylaminium sulfates（AASs）（monomethylaminium sulfate（MMAS）,dimethylaminium sulfate（DMAS）and trimethylaminium sulfate（TMAS））at nucleation mode.The results indicate the surface tension of sulfate droplets shows a non-monotonic trend with droplet sizes.We employ the inverse of（）to characterize the hygroscopic capacity of nanoparticles.The larger the,the stronger the water-uptake ability.The modified K（?）hler curves demonstrate for dry particles with diameter over 10 nm,considering the curvature correction of surface tension can change the value of,but predicted the same activation ability as traditional K（?）hler curves（（AS）>（MMAS）>（DMAS）>（TMAS））.For dry particles with3 nm diameter,the hygroscopiity capacity is altered after considering the curvature correction of surface tension（（MMAS）≈（DMAS）>（AS）>（TMAS））,indicating that for ultrafine particles,surface tension size effect becomes essential,and even changes the hygroscopic capacity of nanoparticles.The combined MD/K（?）hler theory approach provides valuable insights into accurately assessing the hygroscopiity of nucleation mode particles,thereby advancing the understanding of aerosol-climate relationships.3.The hygroscopicity of formic/acetic acid of nucleation mode was studied through combining molecular dynamics simulation with K（?）hler theory.It is found that formic/acetic acid reduces the pressure and surface tension of droplet,both following the order of polarizable acetic acid>non-polarizable acetic acid>non-polarizable formic acid,consistent with the experimental result,indicating that polarization effect is significant for accurately descripting the interface behavior of nanoparticles.The modified K（?）hler curves demonstrate for formic/acetic acid dry particles with diameters larger than 3 nm,considering the surface tension curvature effect changes the value of,but predicted consistent hygroscopicity with the traditional K（?）hler equation（（formic acid）>（acetic acid））,indicating that for ultrafine particles,the accuracy of the K（?）hler model can be improved by considering surface tension curvature correction.4.Prediction the nucleation barrier of bulk nanobubbles by combining molecular dynamics simulation and classical nucleation theory.By introducing the parameters obtained from MD simulation into CNT,we predicted the nucleation barrier of bulk nanobubbles containing different gas molecules.The structural and thermodynamic properties of bulk nanobubbles as a function of nanobubbles sizes and gas molecular species were systematically studied.The results indicate the nucleation barrier of bulk nanobubbles can be largely reduced with increasing saturation,and under the same saturation,the nucleation barrier of different nanobubbles types follows H₂>N₂>O₂,contrary to the order of saturation concentration of gas molecules dissolved in solution.The combined MD/CNT approach provides new insights into understanding the formation and stability mechanism of bulk nanobubbles,and further prompt the development and applications of nucleation models.In conclusion,this paper combines molecular dynamics simulation with nucleation theory models to systematically study the significance of surface tension curvature correction.The systems studied include ions,ammonium/alkylaminium sulfates,formic/acetic acids and bulk nanobubbles.It is found that for both droplets and bulk nanobubbles systems,the prediction of nucleation models based on the size dependence of surface tension are in good agreement with experiments and theory results.The present study indicates the curvature dependence of surface tension,which is commonly neglected in classical nucleation models,makes significant contributions to the nucleation free energy of nanoscale particles.Based on nanoscale surface tension correction,we successfully described the free energy of nucleation process in a semi-quantitatively and qualitatively way,thereby achieving theoretical predictions of specific molecular nucleation capabilities and processes.In conclusion,our work provides theoretical guidance for better understanding the curvature effect of surface tension at nanoscale,which is beneficial for exploration of nucleation events and corresponding mechanisms,and advancing the further development and applications of more accurate nucleation theory models.