| As an emerging technology,microfluidic technology has broad application prospects in the preparation of drug-loaded particles.As a natural phenomenon that occurs all the time in the marine environment,the bursting of bubbles has attracted attention in the generation and transportation of marine aerogels.In this study,a reasonable combination of microfluidic technology and bubble bursting behavior was proposed,and a new method for preparing nanoparticles was proposed.This method used nano-scale droplets formed by the bursting of microbubbles to prepare nanoparticles,which provided a scalable energy-saving approach for the application of nano-drug delivery.The microfluidic technology was applied to prepare monodisperse microbubbles with controllable size and generation frequency at first.We investigated the two-phase and multi-phase flows in the microchannels,and obtained the effective methods to control the characteristics of microbubbles.Next,the investigation focused on the bursting behavior of single-layered and double-layered drug-loaded microbubbles prepared by the microchannels on the free liquid surface,and established the control method of nano-scale droplet generation and the regulation mechanism of nanoparticle generation.Finally,the correlation theory and control method of microbubble formation mechanism,droplet formation mechanism and nanoparticle performance were constructed,which provided new quantitative theories and technical means for the preparation of nanoparticles.The main research contents and conclusions of this article are as follows:(1)The high-speed microscopy and digital imaging technology were applied to observe and record the gas-liquid two-phase flow process in the T-shaped and Y-shaped microchannels under different gas and liquid input conditions to obtain the bubble flow generation range and realize the controllable generation of microbubbles.The effects of gas pressure,liquid flow rate,liquid viscosity and surface tension on the generation frequency and size of the microbubbles prepared by T-shaped and Y-shaped microchannels were studied,and the following conclusions were obtained:The size of microbubbles increased with the increase of air pressure,and decreased with the increase of liquid phase flow rate;The generation frequency of microbubble increased with the increase of air pressure,and as the liquid phase flow rate increased,it first increased and then decreased.The transition point corresponded to the transition point from shearing-to-squeezing mechanism;The generation frequency and size of microbubbles decreased with the increase of viscosity,and slightly changed with the increase of surface tension.(2)The new structure of the combination of Y-junction and flow focusing junction successfully prepared double-layered microbubbles and multiple micro-products.Similarly,the high-speed microscopy and digital imaging technology were used to observe and record the three-phase flow in the microchannel of the new structure and the generation characteristics of double-layered microbubbles under different three-phase input conditions,and the following conclusions were drawn:The flow formed upstream of the microchannel of the new structure was mainly affected by air pressure and oil phase flow rate.Once an unstable annular flow or stratified flow occurred upstream,none micro-products could be generated downstream.The flow rate of the aqueous phase mainly controlled the pinching-off process of the gas slug and oil phase.Adjusting the air pressure,oil phase and aqueous phase flow rates within a specific range could prepare specific targeted micro-products.(3)The high-speed microscopy and digital imaging technology were also used to observe and record the evolution of microbubble before and after it bursting on the free liquid surface.The analysis of the influences of microbubble size,liquid physical properties and other factors on the microbubble bursting process were conducted then.The microbubble bursting conditions,the fluid mechanics phenomena involved in the process of bubble film drainage,puncture and fragmentation during the bursting process were analyzed theoretically,and the applicability of the formulas were verified by the experimental results.Finally,the conclusions were summarized as follows:The Ostwald ripening effect hindered the bursting of microbubbles on the free liquid surface,so it is necessary to ensure the monodispersity of the microbubbles to reduce the influence of Ostwald ripening;Adjusting the concentration of surfactant in the microbubble liquid film below the critical level could avoid the formation of black film and increased the microbubble bursting rate;The theoretical formulas of the thinning rate of microbubble liquid film,the critical bursting thickness and the microbubble instability time could be derived from the DLVO theory combined with the thermal fluctuation theory.(4)Through multi-method analysis of the morphology and size of the nanoparticles prepared by the microbubble bursting,the following conclusions were obtained:The average particle size of the nanoparticles increased with the increase of microbubble size;The particle size conformed to the Gamma distribution.The calculated formula of the average particle size derived based on the Rayleigh-Taylor and Plateau-Rayleigh instability could effectively predicted the average size of the nanoparticles;The bursting of A/O/W double-layered microbubbles could produce drug-loaded nanocapsules,and the size of the nanocapsules increased with the increase in the size of double-layered microbubbles,and decreased with the increase of the viscosity of aqueous phase;The preparation process parameters of the A/O/W double-layered microbubbles were related to the nanocapsule size.The size of the nanocapsules increased with the increase of air pressure and oil phase flow rate,while the aqueous phase flow rate had little effect on the size of the nanocapsules. |
