Research in the Shaw group pushes state of the art analytical techniques to their cutting edge in order to develop novel understanding of chemical behavior at interfaces. Project areas are based on polymer surfaces, biofouling, and environmental corrosion processes.

Research

Autophobing SurfacesBiofilm Resistance
Carbon Dioxide RecyclingFluid Flow at Structured Surfaces
Ionic Liquid InterfacesUrban Film Studies

Autophobing Surfaces

Figure
Optical images (6x zoom) of liquid droplets on surfaces of
varying hydrobphobicity.

Fluids on surfaces generally spread into thin layers or collapse into droplets.  In special cases, we can observe both of these phenomena as the chemical system matures over time. This is known as autophobing, and it makes for a visually intriguing example of surface science in action. Our group is developing expertise in this area as it will aid us in developing a more detailed understanding of the creation and annihilation of solid-liquid and liquid-gas interfaces.

 


Biofilm Resistance

Figure 2
Top: Human biofilms are readily found on the surface of teeth,
as well as on surfaces of medical implants which can lead to
failure.
Bottom: Marine biofilms form on virtually any surface
that is left stationary in the ocean environment.

Biofilms are made of sticky proteins and bacterial plaques that adhere to surfaces. In humans, these films can lead to failure of medical implants, including tenacious infections. Biofilms affect marine systems by increasing drag on ships' hulls and clinging to expensive measurement instruments, degrading performance in many ways. 

The National Institute of Health estimates that 80% of all human infections are caused by biofilms, and the control of marine biofilms is a $5 billion business annually. Our interest in this area lies in describing role of chemical and physical surface interactions that control the binding events of a nascent biofilm. Some evidence suggests that very smooth surfaces (at the atomic level) will, in effect, be so slippery that a bacterial cell or adhesive molecule will not be able to anchor. This slippery behavior is thought to be due to increased nano to micro scale fluid motion on surfaces that continuously acts to sweep the would-be biofilm materials away, before they have time to anchor. 

Our research program uses very sensitive spectroscopic techniques and probe microscopy to investigate the fluid flow at these surfaces as a potentially innovative mechanism to reduce, or eliminate, biofilm formation in marine environments, and in humans.


Carbon Dioxide Recycling

Reduction Current Enhancement of Pyridinium in Carbon Dioxide
Cyclic voltammograms showing reduction current enhancement of pyridinium in CO2 environment.

The goal of this work is to capture atmospheric carbon dioxide and develop an environmentally responsible technology to recycle it back into valuable materials or fuels. The electrochemical reduction of CO2 in ionic liquids holds several distinct advantages, including a high solubility of CO2, an extended range of electrochemical stability,  and nearly infinite tunablity of the ionic liquid as a solvent / charge carrier. This work will involve a multi-pronged approach including advanced spectroscopic methods, electrochemical analysis, theoretical simulations, and synthesis of new electrodes and ionic liquid materials.

Lucio, Anthony J.; Shaw, Scott K. Pyridine and Pyridinium Electrochemistry on Polycrystalline Gold Electrodes and Implications for CO2 Reduction. Journal of Physical Chemistry C. 2015, 119 (22), 12523-12530. DOI: 10.1021/acs.jpcc.5b03355


Fluid Flow at Structured Surfaces 

Slip Boundary Conditions
Top: Schematic of no slip, partial slip, and complete slip boundary conditions present at the
solid liquid interface. In the no slip boundary condition, the velocity of the fluid at the solid
interface matches the velocity of the surface. In a partial or complete slip boundary condition,
the fluid’s velocity at the solid interface can oppose the velocity of the surface. Bottom: AFM
images of 1 x 1 um sections of rough and smooth silver substrates with 7.1 ± 2.7 nm and
2.3 ± 0.3 nm average RMS roughness. These surfaces correspond to the rough and smooth
(right most) figures in the schematic.

This project aims to develop the understanding of complex chemical and physical interactions between fluid molecules surfaces. For many years, empirical evidence has shown that a fluid will flow more slowly (or not at all) as it approaches a solid wall, such as the inside of a garden hose. This research project aims to discover exactly what the relationship is between fluid flow and wall roughness. To do this we will press the limits of nanofabrication techniques to create ultra-smooth surfaces and slowly increase roughness on a sub-nanometer scale while monitoring the fluid behavior. We predict (as do some others) that a critical threshold of roughness exists below which a fluid will flow as freely near the wall as it does far away from the wall. However, we are also cautious to consider the strength of possible intermolecular interactions between the fluid and the solid wall. The outcomes of this work will impact fundamental surface science as well as the foundations of fluid mechanics and the hydro-dynamic theory. The insights to be gained in surface-fluid and fluid-fluid interactions, the role of van der Waals forces, hydrogen bonding, and micro-viscocity, will be immediately useful to all areas involving fluid flow, particularly water filtration, microfluidics, biomedical devices, and countless surface preparation techniques.

Nania, Samantha L.; Shaw, Scott K. Analysis of fluid film behaviour using dynamic wetting at a smooth and roughened surface. Analytical Methods Advance Article. DOI: 10.1039/C5AY00574D


Ionic Liquid Interfaces

IL IRRAS Spectra
IRRAS spectra of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide while the film is
being formed compared to spectra of 60 min old static film. It shows the anion reorients over
the span of 60 min.

IL Interface Density Profile
Oscilatory density profile at the interface compared to the bulk.

Ionic liquids exhibit low vapor pressure, high thermal stability and electrical conductivity. They are of interest for applications in electrochemistry, catalysis, lubrication, photovoltaics etc. Their macroscopic properties in the above mentioned application environments are governed by their orientation and behavior at the solid surface. This study aims at studying IL films on silver substrate using spectroscopic techniques.

Previous studies on IL interface show ordering at the solid -liquid interface which extends upto few tens of nanometers and is characterized by oscillatory density profiles as shown in the above figure. Beyond this region bulk isotropic characteristics of the fluid are observed. Our results indicate high molecular ordering throughout the film which extends upto few microns. This is found to be a result of rearrangement of bis(trifluoromethylsulfonyl)imide anion as evidenced by the change in the IRRAS spectra.


Urban Film Studies

Figure 4
Beijing smog contributes to the accumulation of urban films on every solid
surface in a one-hundred mile radius.

Urban Films are found on virtually every surface in a city’s landscape, and act as sponges for volatile (sometimes very toxic) chemicals. The films are generally composed of soot, water, and ‘grime’ that is emitted from various natural and man-made sources.

Our interest in these films is two-fold: to investigate the molecular level interactions that makes them efficient as chemical sponges, and to learn how these films interact with their environments to accumulate, mature, and release problematic chemicals into the environment. Our expertise in surface analysis will allow for ground breaking research in this area relevant to atmospheric science, environmental chemistry, and corrosion science.

Urban Film Formation and Maturation Schematic
     Schematic illustrating urban film formation and maturation.