Date Awarded
2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (Ph.D.)
Department
Applied Science
Advisor
Hannes C Schniepp
Committee Member
Greg C Smith
Committee Member
Mark Hinders
Committee Member
Christopher J Abelt
Abstract
Interfacial interactions play a major role in a wide range of applications from our everyday life to high-tech industrial applications. These interactions act between almost all the surfaces around us. In this work, we particularly study interfacial interactions in solid/water/liquid and solid/air/solid systems. In the first system, we mainly explored hydrophobic interactions that can take place only in a liquid medium. Long-range hydrophobic attractions between mesoscopic surfaces in water play an important role in many colloid and interface phenomena. Despite having been studied in different ways, the origin of these forces has yet to be explained. While previous research has focused on solid/water/solid and solid/water/air scenarios, we investigated a solid/water/liquid situation to gain additional insight. Here we directly measure long-range interactions between a solid and a hydrophobic liquid separated by water using force spectroscopy, where colloidal probes were functionalized with graphene oxide (GO) to interact with immobilized heptane droplets in water. We detected attractions with a range of ≈0.5 µm that cannot be explained by standard Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. When the GO was increasingly reduced to rGO to become more hydrophobic, these forces increased in strength and ranged up to 1.2 μm. This suggests that the observed attractions are indeed a result of long-range hydrophobic forces. Based on our results, we propose nanoscale air bubbles attached to the colloidal probe and molecular rearrangement at the water/oil interface as possible origins of the observed interactions. This knowledge will be useful to understand and motivate the formation of Pickering emulsions using 2D materials and other amphiphilic/hydrophobic particles. We studied interfacial interactions in solid/air/solid systems to understand attraction and adhesion between 2D materials (graphene and hexagonal boron nitride) and polymers. These 2D materials and their derivatives are widely used in nanocomposites due to outstanding mechanical, thermal, and electric properties. The interfacial bonds in the nanocomposite should be strong to transfer these properties of the nanomaterials to the polymer. In this study, we present a simple method to directly measure the interactions between different types of polymers and graphene versus hBN using force spectroscopy technique. We use polymer colloidal probes which were fabricated in the lab to carry out force spectroscopy measurements on graphene and hBN. We have studied some of the widely used polymers for nanocomposites such as polystyrene, PMMA, and epoxy. The attraction and adhesion between polymers and 2D materials were quantitatively studied. The results suggest that we cannot predict adhesive forces based on known van der Waals forces and the direct measurement of adhesive forces is required. With these two studies carried out in liquid and air media, we have uncovered interfacial phenomena that can be used in many applications such as mass production of nanomaterials, Pickering emulsions, oil/water separation, and nanocomposites.
DOI
https://dx.doi.org/10.21220/s2-dkhf-m379
Rights
© The Author
Recommended Citation
Abeywickrama, Walakulage Dona Avishi Shavindya, "Direct Measurements Of Interfacial Interactions Of 2D Materials" (2023). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1697552568.
https://dx.doi.org/10.21220/s2-dkhf-m379
