The Woodruff School

SUMMARY

Surface forces become important at small scales due to the small spacing present and high surface area to volume ratio. Liquid-mediated adhesion is defined as the adhesion between two solid surfaces in contact or close proximity in the presence of liquid film. Familiar examples in nature include: plants, which transport fluid from roots to leaves in opposition of gravity through xylem conduits; and soils whose strength characteristics depend on the way water interacts between solid particles. Among engineering systems, there are several small scale devices such as nano/micro-electro-mechanical devices (NEMS/MEMS), magnetic storage head/disk interface (HDI), the tip of atomic force microscope (AFM) for which liquid films are present in confined regions during fabrication or during operation due to condensation (humid environment), contamination, or lubrication. In many small-scale devices, the presence of the liquid film causes excessive adhesive or friction forces, and “stiction” happens. Stiction is one of the main causes of the failure in these devices. On the positive side, in the operation of nanofluidic devices, capillary forces operating in submicron channels are used to pump liquids from one location to another. In this study, liquid film adhesion within the confined region defined by the interface between contacting elastic rough surfaces is considered. The wetting liquid film entrapped within the small spacing between the contacting surfaces possess large concave curvatures at the interface, which in turn, causes large pressure drops within the liquid film. The pressure drop can be quantified using the Laplace-Young relation. This pressure drop induces tensile stresses between the contacting surfaces, which leads to reduction in spacing between the surfaces. Opposing these tensile stresses, are the compressive stresses developed at solid-solid contact spots. The interaction between these tensile and compressive stresses are studied both numerically and experimentally under 1. Static condition and 2. Capillary flow condition.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Amir Rostami

TIME:	Monday, January 9, 2017, 9:00 a.m.

PLACE:	MRDC Building, 3515

TITLE:	Liquid-mediated adhesion between contacting rough surfaces

COMMITTEE:	Dr. Jeffery L. Streator, Chair (ME) Dr. Scott Bair (ME) Dr. Itzhak Green (ME) Dr. Robert L. Jackson (ME) Dr. Michael Varenberg (ME)

SUMMARY Surface forces become important at small scales due to the small spacing present and high surface area to volume ratio. Liquid-mediated adhesion is defined as the adhesion between two solid surfaces in contact or close proximity in the presence of liquid film. Familiar examples in nature include: plants, which transport fluid from roots to leaves in opposition of gravity through xylem conduits; and soils whose strength characteristics depend on the way water interacts between solid particles. Among engineering systems, there are several small scale devices such as nano/micro-electro-mechanical devices (NEMS/MEMS), magnetic storage head/disk interface (HDI), the tip of atomic force microscope (AFM) for which liquid films are present in confined regions during fabrication or during operation due to condensation (humid environment), contamination, or lubrication. In many small-scale devices, the presence of the liquid film causes excessive adhesive or friction forces, and “stiction” happens. Stiction is one of the main causes of the failure in these devices. On the positive side, in the operation of nanofluidic devices, capillary forces operating in submicron channels are used to pump liquids from one location to another. In this study, liquid film adhesion within the confined region defined by the interface between contacting elastic rough surfaces is considered. The wetting liquid film entrapped within the small spacing between the contacting surfaces possess large concave curvatures at the interface, which in turn, causes large pressure drops within the liquid film. The pressure drop can be quantified using the Laplace-Young relation. This pressure drop induces tensile stresses between the contacting surfaces, which leads to reduction in spacing between the surfaces. Opposing these tensile stresses, are the compressive stresses developed at solid-solid contact spots. The interaction between these tensile and compressive stresses are studied both numerically and experimentally under 1. Static condition and 2. Capillary flow condition.