Study On The Stability Of Bulk Nanobubbles Based On Dissipative Particle Dynamic

Nanobubbles play an important role in fields such as biological growth acceleration,mineral flotation,and drug delivery.The bulk nanobubbles in nanobubbles are special,and their stability does not match the predictions of classical theory.Experimentally observed nanobubbles can stably exist for tens of hours or even days.This unexpected result has caused scientists to delve into the mechanism of nanobubble stability.Dissipative particle dynamics emerged as a bottom-up coarse-grained mesoscopic simulation method.By splitting the inter-particle forces into conservative forces,dissipative forces,and random forces,the interaction forces between more microscopic molecules and atoms are simplified,reducing the consumption of computational resources and expanding the research system.It meets the time and space scales of nanobubble experimental observations and has good advantages for the study of nanobubble stability.This study mainly includes three parts.Firstly,two bulk nanobubble models are constructed through dissipative particle dynamics.Based on the insoluble bulk nanobubble model,a soluble bulk nanobubble is constructed by modifying the attraction amplitude between gas and liquid.The constructed soluble bulk nanobubble system is verified by calculation,and the results show that the pressure difference characteristics of the bubble inside and outside conform to the prediction of the Y-L equation.The internal pressure,density and root mean square displacement of the soluble bulk nanobubble are then calculated,and the results show that the high-density layer on the surface of the soluble bulk nanobubble will maintain the stability of the bubble itself.Secondly,according to the pressure control advantage of dissipative particle dynamics itself,a new pressure control method is proposed by combining the pressure control method of dissipative particle dynamics with that of molecular dynamics.The effectiveness and rationality of the new pressure control method are verified by taking the temperature and pressure of the system as indicators.The periodic pressure change process is split and simplified,and the process of generating stable nanobubbles by pressure fluctuation is simulated by theoretical calculation.The research results show that decompression in a closed space will lead to a large number of nanobubbles,while pressurization will lead to the dissolution of unstable nanobubbles,while stable nanobubbles will continue to exist.Finally,based on the constructed soluble nanobubble model and the proposed new pressure control method,an organic skin nanobubble model is built and its stability is studied.By calculating the tension and viscosity of solution and organic skin to distinguish their properties,when the thickness of organic skin on nanobubble surface is thin,organic skin will shrink into organic droplets;on the contrary,when organic skin is thick,organic skin will stably cover on nanobubble surface.Two different organic skin models have different effects on the stability of nanobubbles.When gas is insoluble in organic skin,the thicker organic skin is,the more stable nanobubbles are;when gas solubility is consistent in organic skin and solution,thinner organic skin leads to less dissolution of nanobubbles in organic skin and more stable nanobubbles.This study has important theoretical significance for building bulk nanobubble systems and stabilizing bulk nanobubbles.