| In recent years,with the global energy shortage and increasing environmental problems as well as the urgent need for high heat flux density for high-performance electronic device applications,the design and development of super-wetting interfaces with eficient condensation heat transfer performance has attracted widespread interest.Up to now,although a lot of work has been reported that the superhydrophobic surfaces with condensate microdrop self-removal function can improve the efficiency of condensation heat and mass transfer performance,the pure superhydrophobic surfaces have some inherent disadvantages that are not good for further enhancing the condensation heat transfer performance,such as low surface energy and high nucleation energy barrier are not easy for nucleation,nucleation of condensate microdrops is randomly distributed and the microdrop departure diameter is uncontrollable,the superhydrophobic nanostructures can be pierced by vapor molecules and followed by the superhydrophobicity completely fails under the high supersaturation or supercooling.Therefore,how to further couple the surface energy difference or the three-dimensional morphology difference on the pure superhydrophobic surface for high-efficiency nucleation and self-removal of condensate microdrops is still a great challenge.In this paper,combined with experimental research and physical model establishment,we systematically studied the effects of introduction of randomly distributed hydrophilic microdomians,heterogeneously-patterned superhydrophilic microdots and heterogeneously-patterned hydrophobic microcavities on the low-adhesion superhydrophobic surface for enhancing condensation mass and heat transfer performances.The details are as follows:1.Superhydrophobic-hydrophilic hybrid surfaces have attracted intensive interest because of their significant academic and commercial values.However,almost all reported microdomain hydrophilicization methods rely on costly micropatteming techniques that need special instruments.Here,we report a microdrop-assisted method for microdomain hydrophilicization of a low-adhesive superhydrophobic surface and demonstrate its utility in highefficiency nucleation and self-removal of condensate microdrops.Micrometersized fogdrops containing polyvinyl alcohol molecules can be selectively captured by breath figures of superhydrophobic surfaces with specific sizes and spatial distributions and can be converted into desired hydrophilic microdomains after thermal evaporation.After exploring the influence of hydrophilic microdomains’distributions and sizes to surface wettability,adhesion,and condensation dynamics,we achieved an optimal hybrid surface,which possesses 240%average microdrop density,387%microdrop selfremoval rate,and 75%average microdrop diameter as compared to the contrast superhydrophobic surface with uniform chemistry nature.This method is dispensed with special equipment,easy to implement,very cheap,and eco-friendly,which would help develop other superhydrophobic-hydrophilic hybrid surfaces with different functions such as water harvesting,dehumidification,and heat exchange.2.Manipulating condensate nucleation,growth,coalescence,and self-removal via bionic super-wettability surfaces has attracted intensive interest because of their significance in fundamental researches and technological innovations,e.g.,water harvesting,power generation,air conditioning and thermal management.However,it is still a challenge to simultaneously realize confined growth,coalescence,and self-ejection of condensate microdrops,which has not been reported up to now.Here,we propose and demonstrate a type of new and more efficient coalescence/self-removal way based on spatially-confined growth/coalescence/self-ej ection of condensate microdrops,which can be realized by rationally-designed superhydrophobic surface with spatially heterogeneously-patterned superhydrophilic microdots(SMDs).Exemplified by superhydrophobic closely-packed zinc oxide nanoneedles with SMD patterns,we investigate how the geometric parameters of SMD patterns design to simultaneously realize the spatially confined growth/coalescence/self-ejection of patterned microdrops,which are rationalized via theoretical analyses.3.We propose and demonstrate that the confined growth and controlled coalescence/self-ej ection of condensate microdrops can be realized by the discrete microcavity pattern of superhydrophobic surface.Patterned microdrops can be realized by utilizing the high-thermal-conductivity nature of microcavity bottom to generate higher subcooling as compared to the top surface and sidewalls of surrounding nanoneedles and simultaneously controlling proper microcavity interspaces to ensure that only microcavities can reach the supersaturation threshold required for nucleation.To ensure the self-ejection of merged microdrops,the interspace of microcavities cannot be too small,which is a prerequisite condition to ensure that the coalescence-released surface energy can overcome the energy dissipation caused by droplet adhesion.However,to realize the controlled coalescence/self-ejection,the discrete microcavity pattern with a proper interspace between unit cells is vital,which can eliminate the random coalescence of patterned microdrops.Such novel surface engineering strategy helps develop high-efficiency condensers and other functional materials.4.Based on the above work,we then investigated the comparison of the mass transfer performance of the heterogeneously-patterned hybrid surfaces with superhydrophilic microdots or hydrophobic microcavities and the cotntrast superhydrophobic surface.Taking the tetragonal heterogeneous pattern as an example,comparing the contrast superhydrophobic surface,quantitative statistics can show that the tetragonal heterogeneously-patterned superhydrophobic-superhydrophilic hybird surface has the best mass transfer efficiency,on which the density,the self-ejected frequency and the volumn drainage of the condensate droplets increased by 61.54%,546.25%and 1020.34%,respectively.Then,comparing the condensation mass transfer performance of different heterogeneously-patterned hybrid surfaces,it is confirmed that the design of the tetragonal heterogeneous pattern is the most ideal.The introduction of heterogeneously-patterned superhydrophilic microdrots not only increases the density of condensate droplets,but also enhances the condensation mass transfer efficiency.Finally,by comparing the condensation heat transfer performance of heterogeneously-patterned hybrid surface,homogeneously-patterned hybrid surface and the contrast superhydrophobic surface under the same vapor condition,the effect of introducing heterogeneous hydrophilic microdomains on condensation heat transfer was studied.It provides important value and guiding significance for the subsequent optimization and design of a reasonable patterned hybrid surface to enhance the condensation heat transfer performance. |
