Glycerol–water sessile drop elongation on PTFE inclines in relation to biochemical applications

• Slip angles of 6 μL drops on tilted PTFE had complex trends to varying glycerol–water compositions.
• As the front contact line breached first, levels of contact angle hysteresis did not match slip angle trends.
• The ratios of lengths at detachment against equilibrium corresponded with slip angle trends.
• The drops elongated in relation to angle of tilt in two distinct stages.
• Turbidity measurements show higher glycerol contents improving thermal stability of bovine serum albumin.

The movement behavior of glycerol–water mixtures as sessile drops on a tilted PTFE incline is investigated here. The slip angles found showed complex relationships in relation to the mixture composition. Since the drop was found to breach its front contact line first, the levels of contact angle hysteresis did not have corresponding trends with the slip angles. However, the ratios of the drop lengths (at the point of detachment against that at equilibrium) had corresponding trends with the slip angle. The drop elongated in a two-stage manner as it was tilted progressively. Since this could not be ascribed to a sudden change in the gravitational force acting, it implied that the drop extended first as a single body before attempting to split into two. In considering the energetics involved, the change in the solid–liquid area was mainly used by the drop to adjust to the energy supplied by gravity. Comparative experiments done with drop compression and extension on the same surface eliminated the contribution from specific characteristics associated with the liquid and solid, and inaccuracies in the contact angle measurement method used. Turbidity measurements indicate the viability of using higher glycerol content to improve thermal stability of bovine serum albumin. The findings have important implications on the manner of how heat and mass transfer occurs for drops on inclines for biochemical applications.

Figure optionsDownload as PowerPoint slide