单液滴介观润湿行为理论模型与动态特征

Theoretical model and dynamic characteristics of mesoscopic wetting behavior of single droplet

为从介观尺度考察液滴在固体基面的铺展特性,基于格子玻尔兹曼方法(LBM),在D2Q9物理模型中,通过离散速度和作用力,建立单个液滴动态润湿二维模型;利用上述理论模型,结合解析解,验证模型准确性,进一步引入无量纲参数Bond数,表征重力与表面张力相对大小对液滴润湿轮廓的影响,定量分析气-液界面参数和壁面属性对接触角和铺展系数的影响特征。研究结果表明:终态接触角和铺展系数由固体基面固有润湿属性和表面力决定;势能和表面能的相互转化是液滴实现动态润湿的关键,介观尺度下液滴特征半径不大于25时,液滴越大,终态接触角越小,铺展系数越大,一旦超出区间临界值,终态接触角和铺展系数将趋于定值;固体基面属性越大,则亲水性越强,终态接触角越小,液滴越容易铺展;气-液界面属性的绝对值越大,则表面张力越小,铺展系数越大,润湿效果越好。

In order to investigate the spreading characteristics of droplets on the solid substrate from the mesoscopic scale,based on the lattice Boltzmann method(LBM),a two-dimensional dynamic wetting model of a single droplet was established in the D2Q9 physical model by discrete velocity and force.Using the above theoretical model,combined with the analytical solution,the accuracy of the model was verified.The dimensionless parameter Bond number was further introduced to characterize the influence of the relative size of gravity and surface tension on the wetting profile of droplets,and the influence of gas-liquid interface parameters and wall properties on contact angle and spreading coefficient was quantitatively analyzed.The results show that the final contact angle and spreading coefficient are determined by the inherent wetting properties and surface force of the solid substrate.The mutual conversion of potential energy and surface energy is the key to realize dynamic wetting of droplets.When the characteristic radius of droplet is not more than 25 at mesoscopic scale,the larger the droplet is,the smaller the final contact angle is,and the larger the spreading coefficient is.Once the critical value of the interval is exceeded,the final contact angle and spreading coefficient will tend to be fixed.The larger the solid base surface properties,the stronger the hydrophilicity,the smaller the final contact angle,and the easier the droplets spread.The greater the absolute value of the gas-liquid interface property,the smaller the surface tension,the greater the spreading coefficient,and the better the wetting effect.