Role of Vertical Component of Surface Tension of the Droplet on the Elastic Deformation of PDMS Membrane

摘要

Poly(dimethylsiloxane)(PDMS)has been widely used in lab-on-a-chip and micro-total analysis systems(u-TAS),thus wetting and electrowetting behaviors of PDMS are of great importance in these devices.PDMS is a kind of soft polymer material,so the elastic deformation of PDMS membrane by a droplet cannot be neglected due to the vertical component of the interfacial tension between the liquid and vapor,and this vertical component of liquid-vapor surface tension is also balanced by the stress distribution within the PDMS membrane.Such elastic deformation and stress distribution not only affect the exact measurement of contact angle,but also have influence on the micro-fluidic behavior of the devices.Using ANSYS code,we simulated numerically the elastic deformation and stress distribution of PDMS membrane on a rigid substrate due to the liquid-vapor surface tension.It is found that the vertical elastic deformation of the PDMS membrane is on the order of several tens of nanometers due to the application of a droplet with a diameter of 2.31 mm,which is no longer negligible for lab-on-a-chip and u-TAS.The vertical elastic deformation increases with the thickness of the PDMS membrane,and there exists a saturated membrane thickness,regarded as a semi-infinite membrane thickness,and the vertical elastic deformation reaches a limiting value when the membrane thickness is equal to or thicker than such saturated thickness.