Complex fluids are a wide class of materials that flow like liquids but have finite structures. Common examples are oil/water emulsions or polymers dissolved in solvents, which exhibit fascinating and useful properties. We study these fluids to understand how their structure on the nanoscale affect their bulk properties.
Schematic of polymer grafted nanoparticles dispersed in a polymeric matrix
Nanocomposites are materials comprised of nanoparticles dispersed in a polymeric matrix and exhibit enhanced mechanical, electrical, and optical properties. We aim to understand the changes happening on the nanoscale when particles and polymers are mixed to understand these enhanced properties.
Atomic force microscopy image of polymer-grafted nanoparticles
We investigate how polymers deform and move near surfaces. Understanding their structure and dynamics will allow us to design and develop novel materials with enhanced properties.
Schematic showing confined relaxations of grafted polymer
Many applications require particles or other species to be delivered to a specific location, often through a crowded or complex material. We study how to control this delivery process by tuning the size and shape of the particles in relation to the surrounding fluid.
Schematic showing viral nanoparticles flowing through and attaching to a porous lateral flow assay
Soft interactions modify the diffusive dynamics of polymer-grafted nanoparticles in solutions of free polymer
Accepted: May 31, 2019
R. Poling-Skutvik, A. H. Slim, S. Narayanan, J. C. Conrad, and R. Krishnamoorti. ACS Macro Lett. 2019, 8, 917-922.
Polymer-grafted nanoparticles diffuse faster than expected in polymer solutions. These dynamic deviations arise from soft interaction potentials and cannot be explained using current theories derived for hard-spheres.
Structure dominates localization of tracers within aging nanoparticle glasses
R. Poling-Skutvik, R. C. Roberts, A. H. Slim, S. Narayanan, R. Krishnamoorti, J. C. Palmer, and J. C. Conrad. J. Phys. Chem Lett. 2019, 10, 1784-1789.
Accepted: March 27, 2019
Tracer particles undergoing Brownian motion in a colloidal glass are spatially localized according to their size. This localization length does not change with sample age, indicating the importance of matrix structure on tracer dynamics.
Techniques and Skills
Neutron scattering is an extremely powerful technique to probe the structure and dynamics of soft materials. Specifically, we use neutron spin echo spectroscopy (NSE) to study dynamics and small-angle neutron scattering (SANS) to study structure, with experience at both NIST and ORNL neutron sources.
Scattering pattern of polymer in presence of contrast-matched silica nanoparticles
X-rays are highly sensitive and intense. Using lab-scale and synchrotron sources at Argonne National Lab, we probe the structure and dynamics of many materials, often complementing neutron scattering data. With x-rays we can connect the physics on a nanoscale to the bulk material properties.
Scattering pattern of silica nanoparticles with long-range electrostatic interactions
Optical microscopy gives invaluable information about the behavior of individual particles. Using particle tracking algorithms, we can quickly and directly measure the dynamics of particles to understand transport mechanisms or bulk mechanical properties.
Silica model of porous media used in collaboration with Martin Fernø to study oil recovery
Differential Dynamic Microscopy
Differential dynamic microscopy (DDM) combines the benefits of scattering with those of optical microscopy. With this technique, we can probe the dynamics of materials below the optical resolution of a microscope or in concentrated suspensions, where particle tracking is difficult.
Series of image differences of M13 filamentous bacteriophage diffusing in a polymer solution
Rheology is the study of how materials respond to stresses and deformations. To probe these mechanical properties, we use standard rheometers as well as microrheology techniques, which relate the motion of particles to the bulk material properties.
The ability to synthesize our own polymers allows us to tailor their morphology to study specific properties. We use atom-transfer radical polymerization (ATRP) and anionic polymerization to prepare polymers with narrow molecular weight distributions and graft them to surfaces.
Schematic of polymer grafted nanoparticles dispersed in semidilute polymer solutions.
Conferences and Presentations
May 31, 2019
University of Pennsylvania Polymer Symposium
I presented an invited student talk at the 4th Annual Penn Polymer Symposium detailing some recent work on the dynamics of polymer-grafted nanoparticles in polymer solutions. This work was conducted near the end of my Ph.D. research. The presentation continued into some exciting preliminary results on the
March 5-9, 2018
AMERICAN PHYSICAL SOCIETY MARCH MEETING
Los Angeles, CA
At the APS March Meeting in Los Angeles, I was selected to present my research investigating the confined dynamics of grafted polymer chains (F55.07, Presentation) in the Frank J. Padden Jr. Award Award Symposium for excellence in polymer physics research. My colleague, Ryan C. Roberts, also presented our work detailing investigations of tracer dynamics through colloidal glassy liquids (R53.04).
June 10-13, 2018
ACS COLLOID AND SURFACE SCIENCE SYMPOSIUM
State College, PA
I presented a talk in the Directed Assembly of Molecules and Particles session on our recent work investigating how to produce three-dimensional porous nanomaterials simply and controllably using semidilute polymer solutions (Talk #352, Presentation). This presentation described work recently published in ACS Applied Nanomaterials. My colleague, Maxwell Smith, also presented a poster describing our research on the transport of anisotropic viral nanoparticles through complex materials (# 196).