Characterizing and controlling adhesion between rough deformable solids.

Format:

Book

Thesis/Dissertation

Author/Creator:

Quon, Roger Allan.

Contributor:

Vanderlick, T. Kyle, advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Materials science.

Chemical engineering.

Mechanics.

0346.

0542.

0794.

Penn dissertations--Chemical engineering.

Chemical engineering--Penn dissertations.

Local Subjects:

Penn dissertations--Chemical engineering.

Chemical engineering--Penn dissertations.

0346.

0542.

0794.

Physical Description:

236 pages

Contained In:

Dissertation Abstracts International 60-07B.

System Details:

Mode of access: World Wide Web.

text file

Summary:

This thesis describes the study of adhesion between rough solids from a contact mechanics approach using the surface forces apparatus. Specifically, the adhesion and deformation of microscopically rough gold and molecularly smooth mica is considered. Unique to this experimental investigation is the ability to simultaneously monitor changes at the interface and in the bulk as the contacting bodies deform. The observed behavior is analyzed primarily in the context of contact mechanics theory by Johnson, Kendall and Roberts (Johnson, Kendall et al. 1971). This experimental advantage and analytical framework provides a means of evaluating the influence of surface chemistry, thin films and operating environments on adhesion between rough bodies.

To this end, a relation between microscopic deformations of asperities at the interface to macroscopic deformations in the bulk is established. Surface forces and applied loads plastically deform metallic asperities trapped at the contact interface. Little deformation is recovered when applied loads are removed until just prior to separation. This behavior is demonstrated to be the basis behind observed adhesion hysteresis, as reflected in bulk deformations. This study also establishes the sensitivity of the contact mechanics approach, in conjunction with the surface forces apparatus, to detect minor changes in surface preparation and/or energies.

Adsorption of a chemically well-defined monolayer to the rough gold surface demonstrates the importance of chemistry and film structure to the adhesion and separation of solids. In this study, deformations at the interface are partially reversible, but adhesion hysteresis is again observed. The hysteresis is attributed to the capacity of the bound monolayer to absorb some of the energy placed into deforming the contacting solids. The compressibility of bound monolayers were also determined and found to be on the order of 25 to 50 MPa, the same magnitude as Langmuir-Blodgett films.

The humidity in which rough solids contact strongly influences adhesion, particularly at saturation. Adhesion between rough solids may be predicted by meniscus theory derived for contact between smooth surfaces if the wettabilities are similar. Meniscus theory, however, inadequately predicts the adhesion force at saturation between rough solids if the wettabilities are significantly dissimilar. Complementary adsorption studies suggest the propensity of a surface to form a surface film is important to the adhesion between rough solids in humid environments.

Finally, a method of obtaining a very smooth gold surface for contact mechanics studies against mica is described. An adhesion measurement between this smooth gold and smooth mica is found to be, on average, five-fold greater than the rough gold/smooth mica typically employed in this thesis. Foundations for further investigations of the impact of roughness, surface chemistry, film structure and operating environment are established.

Notes:

Thesis (Ph.D. in Chemical Engineering) -- University of Pennsylvania, 1999.

Source: Dissertation Abstracts International, Volume: 60-07, Section: B, page: 3418.

Adviser: T. Kyle Vanderlick.

Local Notes:

School code: 0175.

ISBN:

9780599390331

Access Restriction:

Restricted for use by site license.