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MECHANICS AND DYNAMICS OF UNDERWATER ELASTIC CONTACTS

Kumar, Nityanshu
http://orcid.org/0000-0002-4655-4653
http://rave.ohiolink.edu/etdc/view?acc_num=akron1658534196320469

Abstract Details

2022, Doctor of Philosophy, University of Akron, Polymer Science.
Mechanics and dynamics of underwater soft contacts are critical in the field of biomaterials (adhesives and sealants), soft robotics, transportation (tires and seal design) and engineering (biomimetics). From wet tire traction to underwater adhesion, the evacuation of a thin layer of water between two surfaces is essential for contact formation and subsequent interactions. This dissertation explores the effect of roughness, elastohydrodynamics and thermodynamics on water entrapment. The fact that real surfaces possess roughness on scales ranging from size of an object to atomic cut off (few angstroms) makes it challenging to study. We perform quasi-static underwater adhesion measurements between soft-elastic polydimethylsiloxane (PDMS) hemispheres of varying stiffness and rigid polycrystalline diamond surfaces with topography characterized across all length scales. The results show that the adhesion energy is lower than that predicted using the Persson’s model, indicating towards water entrapment. We developed a non-conformal contact adhesion model which requires the knowledge of real contact area and the new power spectral density (PSD) for PDMS after formation of partial contact. The real contact was determined using the Cassie-Baxter equation as the contact region is a composite of dry and water entrapment regions. We cannot measure the PSD for deformed PDMS directly and hypothesize that there exist a critical cut-off length-scale above which the surfaces are conformal, and the smaller length-scales contains entrapped water. This allowed calculation of elastic energy required to deform the PDMS and, hence, predictions of adhesion which are in excellent agreement with the experimental data. We also explored the effect of elastohydrodynamic deformation and thermodynamics/surface chemistry on contact formation. We determine the dependence of fluid evacuation on the surface wettability and elastomer modulus in underwater collision, as it is essential to any observed transient and final adhesion and friction state. We find an exponential rate of water evacuation from hydrophobic–hydrophobic (adhesive) surfaces that is 3 orders of magnitude smaller than that from hydrophobic–hydrophilic (non-adhesive) contact. This counterintuitive result comes from adhesive surfaces to more tightly sealing puddles of trapped water. These findings reveal the advantages of patterned textures observed in natural systems such as geckos and frogs.
Ali Dhinojwala (Advisor)
Mesfin Tsige (Committee Chair)
Tevis DB Jacobs (Committee Member)
Jutta Luettmer-Strathmann (Committee Member)
Hunter King (Committee Chair)
151 p.
Engineering; Mechanics; Physical Chemistry; Physics; Polymers
Underwater Adhesion; Contact Mechanics; Roughness, Topography; Real Contact Area

Recommended Citations

Citations

  • Kumar, N. (2022). MECHANICS AND DYNAMICS OF UNDERWATER ELASTIC CONTACTS [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1658534196320469

    APA Style (7th edition)

  • Kumar, Nityanshu. MECHANICS AND DYNAMICS OF UNDERWATER ELASTIC CONTACTS. 2022. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1658534196320469.

    MLA Style (8th edition)

  • Kumar, Nityanshu. "MECHANICS AND DYNAMICS OF UNDERWATER ELASTIC CONTACTS." Doctoral dissertation, University of Akron, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=akron1658534196320469

    Chicago Manual of Style (17th edition)

akron1658534196320469
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This open access ETD is published by University of Akron and OhioLINK.