Fall 2018 Seminar Series - 101518 Knapp






Graduate Student Symposium

Ellen Knapp

City College of New York 


Monday, October 15, 2018

Seminar will be held in ST-160 (Lecture Hall) at 2:00 PM

Reception: 3:00 – 4:00 PM in Steinman Hall, Exhibit Room – 1st Floor


The Influence of Amphiphilicity and Orientation on Janus Particles at an Air-Water Interface 


Ellen M. Knapp1,2, Raymond R. Dagastine2, Ilona Kretzschmar1 and Raymond Tu1

(1)Chemical Engineering, City College of New York, New York, NY

(2)PFPC and the Department of Chemical and Biomolecular Engineering, The University of Melbourne, Melbourne, Australia


Well-defined anisotropic particles present unique opportunities to study directed assembly. More specifically, Janus particles allow one to precisely control the amphiphilicity of the particle and the surface wetting properties on each hemisphere. Interfacial assembly of anisotropic particles is of particular interest as these confined particles can be used to template microstructures in a bottom up fashion. The fluid-fluid boundaries can trap colloids, orienting particles in the direction normal to the surface and patterning particles in the plane of the interface(1). The ability to pattern particles at interfaces has a multitude of applications such as achieving optical properties, making antireflective surfaces, improving the resolution of E-paper displays and creating water repellant materials(2). Furthermore, anisotropic particles at interfaces can be applied as emulsion stabilizers and catalysts.(3)In all of these applications, the amphiphilicity of Janus particles plays an important role in influencing particle orientation, stability and assembly at the interface. Additionally, understanding the free-energy landscape of Janus particles at an interface can help explain and predict particle behavior under different circumstances.


The work presented studies gold capped silica Janus particles with varying degrees of amphiphilicity. A range of contact angles of the gold surface is achieved using modification with alkane thiols of various chain lengths. Colloidal AFM experiments have been conducted to elucidate how orientation and amphiphilicity of Janus particles influences their behavior at an air-water interface. In this work, Janus particles at various orientations are attached to an AFM cantilever and force is measured as the particle interacts with and is wet by the air-water interface of a surface immobilized bubble. These experiments allow for quantification of surface forces, adhesion, contact angle, and give insight as to how the energy landscape of the particle changes with orientation and amphiphilicity. Such phenomena can be compared to theory and connected to behavior of particle-laden interfaces, studied on a Langmuir trough, in order to connect microscopic and macroscopic behavior.


Works Cited:

(1)Park, Brugarolas, and Lee, Soft Matter2011, 7, 6413-6417.

(2) Walther and Muller, Chem. Rev.2013, 113, 5194-5261.

(3) Kumar et al., Soft Matter2013, 9, 6604-6617.


Ellen Knapp is a 5thyear PhD Candidate in the Chemical Engineering Department of CCNY. She is co-advised by Raymond Tu and Ilona Kretzschmar. She grew up in Rockland County New York and graduated from Villanova University in 2013 with a B.S. in Chemical Engineering. During her time at City College she has had the opportunity to collaborate with a number of institutions including University of Chicago, Argonne National Lab, University of Melbourne, and Corning Incorporated. Her thesis work focuses on the behavior of Janus particles at the air-water interface and trying to induce assembly into structures with tunable optical properties.