Nanoscale Characterization of Polymer Interfaces

**UNSW Students Poster Session Preceding Seminar 10:00am 3rd Floor Atrium – EB1

Speaker: Prof. Catherine Brinson

Title: Nanoscale Characterization of Polymer Interfaces

Affiliation: Duke University

ABSTRACT:   For polymer composite, nanocomposite and polymer thin film systems, the local properties of polymers can be altered by the chemical and physical interactions with substrates and embedded particles over a substantial length scale. We utilize scanning probe methods to quantify these local property changes in the polymer region near surfaces, a regime termed “the interphase”. Understanding the behavior and underlying mechanisms of the interphase will allow robust predictive modeling and design strategies for nanocomposites, polymer coatings and electronic components. In this work, we present novel AFM experiments to characterize the elastic and viscoelastic properties of this domain. We employ simulation approaches for the experimental configuration to exclude stress interaction artifacts and explore the influence of temperature effects. First, experiments of nanoindentation via Atomic Force Microscopy (AFM) are explored to characterize the local mechanical properties (elastic and viscoelastic) of the interphase region on various modeled nanocomposite samples. The AFM studies are combined with finite element analyses of the 3d geometries in order to remove artifacts of substrate/particle interactions from the data. Results reveal a clear change in the mechanical properties of the polymers 100nm from the surface of a substrate. The effects of surface chemistry and geometric confinement have been isolated and a new method for characterizing the viscoelastic response of soft materials with AFM has been developed.  Secondly, to understand the impact of a material’s viscoelastic state on the mechanical property measurements, we conduct a set of complementary simulations of AFM indentations at increasing temperature in highly confined and unconfined films via finite element analysis (FEA) and coarse-grained molecular dynamics (CG-MD). We find that that the measured interphase length is dependent on the incompressibility and viscous dissipation of the polymer as a result of continuum level behaviour and convolutes the measurement of the interphase. Additionally, we demonstrate that the interphase length scale increases with temperature in highly confined systems but decreases if the polymer is unconfined. Overall this work provides key understanding essential to tackle materials design principles for the complex, high dimensional problems inherent in the multi-phase polymer space.

BIOGRPAHY:  L. Cate Brinson is currently the Sharon C and Harold L Yoh III Professor of Engineering with primary appointment in the Mechanical Engineering and Materials Science Department at Duke University, where she began in fall of 2017. Prior to that move, she was the Jerome B. Cohen Professor of Engineering at Northwestern University and Associate Dean in the McCormick School of Engineering with appointments in Mechanical Engineering and Materials Science and Engineering. After receiving her Ph.D. in 1990 from Caltech, Dr. Brinson performed postdoctoral studies in Germany at the DLR and began her academic career at NU in 1992. Current research investigations involve characterization of local polymer mechanical behavior under confinement, nanoparticle reinforced polymers, the phase transformation response of shape memory alloys, nano and microscale response of biomaterials, and materials genome informatics research, where investigations span the range of molecular interactions, micromechanics and macroscale behavior. Dr. Brinson has received a number of awards, including theNadai Medal of the ASME, the Friedrich Wilhelm Bessel Prize of the Alexander von Humboldt Foundation, the ASME Tom JR Hughes Young Investigator Award, and an NSF CAREER Award; she is a Fellow of the Society of Engineering Science, of the American Society of Mechanical Engineering and of the American Academy of Mechanics; and she served as a member of the Defense Science Study Group. She has given many invited technical lectures on her research and has authored one book and over 160 refereed journal publications. She has over 19000 citations and an h-index of 63 in Google Scholar. Her book has had over 50,000 chapter downloads from the e-version since publication in 2008 and a second edition published in 2015. She is a member of several professional societies and served 5 years on the Society of Engineering Science Board of Directors, including one year as President of the society. She has also been an Associate Editor of the Journal of Intelligent Material Systems and Structures and the Journal of Engineering Materials and Technology, served two terms on the National Materials Advisory Board of the National Academies and has chaired two National Research Council studies.

Refreshments served at 10:00am in 3rd Floor Atrium– EB1