Click on research topic of interest:
- Bacteria Attachment Control and Antibacterial Properties
- Mechanically Robust Broadband Anti-Reflection Coatings
- Design and Synthesis of Mechanomutable Nanotubes via Layer-by-Layer Assembly
- Preservation of Structure and Function in Nanoparticle Thin Films
- Omni-directional structural color by layer-by-layer nanoparticle assembly
- Biocompatible Electroconductive Nanofiber Mesh
- Polymer Filtration Membranes Part 1
- Polymer Filtration Membranes Part 2
- MORE OF OUR PROJECTS COMING SOON!!!
Bacteria Attachment Control and Antibacterial Properties- Jenny Lichter
We are investigating the use of polymer coatings formed using layer by layer assembly to create coatings capable of preventing the growth of a biofilm. We are researching the effects of key surface properties, such as mechanical stiffness and surface charge, on bacteria attachment and cytotoxicity. Using the layer by layer approach and tuning synthesis and post-assembly conditions, chemically identical films can be created with different elastic moduli and chemical functional group densities. These films are then used to isolate the effects of various properties.
Left Figure: Few bacterial colonies grow on a bacteria-resistant polyelectrolyte multilayer. Right Figure: Many bacterial colonies grow on glass control. Both images are taken at 4x magnification.
Mechanically robust broadband anti-reflection coatings - Hiroomi Shimomura
Broadband anti-reflection coatings are optically useful coatings which have low reflectance and high transmittance across all visible wavelengths. One of the strategies to achieve broadband AR coatings is stacking high and low refractive index layers with precisely controlled thickness. We are researching how to produce broadband AR coatings via layer-by-layer assembly, a process which allows us to control the thickness of the films at the nanometer scale. Furthermore, we are researching technologies to provide mechanical robustness to the layer-by-layer film which allows us to apply this technique to a wide variety of commercially relevant substrates.
Design and Synthesis of Mechanomutable Nanotubes via Layer-by-Layer Assembly - Gary Chia
The ultimate goal of my thesis is to design and synthesize mechanomutable nanotubes that exhibit reversible and tunable mechanical responses to different types of external stimuli via layer-by-layer assembly. The design of such highly refined heteronanomaterials, by the incorporation of constituents from a wide range of materials as the fundamental units, provides versatility and variability in mechanical properties. Mechanomutable heteronanomaterials can be useful for the development of multi-responsive tunable sensor arrays, synthetic extracellular matrix, and dynamic armor coatings.
The layer-by layer assembly technique provides a versatile and inexpensive approach to the design and synthesis of mechanomutable heteronanomaterials. The sequential adsorption of oppositely-charged species enables the precise design and control over the molecular architectures of the film, which can be manipulated for different functionalities. The synthesis of hollow, cylindrical nanotubes using a porous-templated layer-by-layer approach is of particular interest arising from their interesting dimensions. In contrast to previously reported systems, the synthesis of mechanomutable nanotubes via layer-by-layer assembly can be designed in many different ways that result in materials that exhibit reversible and tunable mechanical responses to different types of external stimuli.
Preservation of Structure and Function in Nanoparticle Thin Films - Zekeriyya Gemici
Nanoparticle-containing thin films have been studied extensively for their optical, catalytic, barrier, and wetting properties. Many such films owe their functionalities to delicately designed nanoparticle (NP) assemblies held together by weak secondary interactions. For example, conformal coatings can be assembled layer-by-layer (LbL), where layers of positively and negatively charged polymers, NPs, or polyvalent ions can be electrostatically adsorbed on flat or textured surfaces. Such delicate assemblies can rarely endure mild rubbing with even soft cloths and readily delaminate from their underlying substrates. A few studies have addressed this problem and suggested either high-temperature calcination, which is incompatible with plastic substrates, or imbibition of polymerizable species into the NP assemblies by sol-gel or CVD. Owing to their enhanced solubilities, NPs can be stitched together in situ upon exposure to steam, without grossly altering film structure or porosity. We reinforced nanoporous all-NP and polymer-NP LbL assemblies (80-150nm) by in situ hydrothermal treatment (124-134°C) on both glass and plastic substrates. This versatile and unintrusive method can make NP-containing multilayer thin films withstand shear abrasion similar to what consumer products would experience in everyday use. 500 nm We document two types of wear: abrasive and tribochemical. While abrasive wear involves scratching under the influence of third bodies, tribochemical wear acts to flatten nanoscale surface texture by dissolving the topmost layer of oxide NP films (e.g.SiO2 ) and polishing the surface. Surface roughness and morphology are critical for both superhydrophilic and superhydrophobic surfaces; preservation of surface nanotexture is a major bottleneck in developing practical applications. While much emphasis has been placed on improving hardness and/or scratch-resistance, we point out the critical importance of avoiding tribochemical wear.
Our current focus is on overcoming more subtle, harder to quantify chemical-structural evolution of anti-fogging films over time. Pore size, pore fraction, and pore shape can evolve in nanoparticle thin films due to chemical stresses (e.g., humidity). Such aging presents an additional barrier to commercialization. While structure-property relationships are well- established in lithographically patterned surfaces with micron-scale textures, nanoparticle thin films defy quantitative, non-intrusive characterization with most common tools (e.g., BET). We are trying to develop new porosity characterization tools in order to establish design principles for self-assembled superwetting structures.
Omni-directional structural color by layer-by-layer nanoparticle assembly- Dr. Pinar Kurt
Some colors in nature do not come from material's inherent properties, but are as a result of light interference. This kind of color, called 'structural color,' can be seen in some species such as butterflies and beetles. We are investigating the methods and conditions for creating structural color using layer-by-layer assembly of various nanoparticles. By building alternating layers of nanoparticles with low and high refractive indices, it is possible to obtain high reflectance with any color. With optical simulation programs, we are able to design nanoparticle assembly and obtain any color with more than 90% reflectance. The ultimate goal is to control the angle-dependence of the reflectance and to create omni-directional structural color by a layer-by-layer assembly process.
This project is in collaboration with Toyota Research Institute North America (TRI-NA)
Biocompatible Electroconductive Nanofiber Mesh - Dr. Ray Turner
The solution and tissue properties of hyaluronan (HA) provide clues to how we can better engineer biocompatible products for devices and for tissue remodeling. HA, a highly versatile linear carbohydrate polymer shows a molecular mass dependent self-association in the hydrated and partially dehydrated states. HA fragments dehydrated from aqueous buffer solutions self-organize into reproducible multi-dimensional nanofiber mesh. The surface matrix patterns we create are reproducible as determined by a number of different experimental techniques, such as AFM, TEM, SEM, XPS, and optical microscopy. We explore the molecular and nanoscale properties of mesh derived from HA fragments using different application techniques. We have obtained robust and adjustable biocompatible templates, which can be modified through kinetic and thermodynamic manipulation for a number of diverse applications.
Figure: The NANOBIT (Nanoscale Biocompatible Information Transfer System) template made from pure Hyaluronic acid.
Polymer Filtration Membranes: Part 1- Ayse Asatekin
Membrane fouling, which can simplistically be described as the clogging of a membrane due to the adsorption of feed components, is one of the major obstacles faced by the membrane industry. It drives up energy consumption as well as cleaning and membrane replacement, and is especially severe in processes where the feed has high concentrations of biomolecules, such as in wastewater treatment, and in food and pharmaceutical industries. The most common way to prevent fouling is to graft a hydrophilic polymer from the membrane surface, but this is often an expensive and poorly controlled process. My project aims to develop improved membranes that resist fouling making use of the self-organization of copolymers, specifically comb copolymers with a hydrophobic backbone and hydrophilic side-chains.
Polyacrylonitrile-graft-poly(ethylene oxide) (PAN-g-PEO) is such a polymer: It has a backbone of PAN, a glassy polymer used in membrane industry, and side-chains of PEO, a hydrophilic polymer well known for its resistance to adsorption. When this copolymer is added to the casting solution during the manufacture of porous ultrafiltration (UF) membranes, the side-chains are driven to the polymer/water interface due to their hydrophilic nature. The polymer is pinned down by the PAN backbone, creating a brush of PEO chains on the membrane surface as well as lining all the pores. Membranes prepared using this method were found to resist irreversible fouling completely to a range of foulants, including protein, humic acid and alginate solutions, and oil-well produced water: The membrane can be cleaned simply by water, potentially decreasing cleaning costs and increasing membrane life. These membranes are very promising for waste-water treatment and membrane bioreactors.
Another application, this time used to prepare membranes with selectivity in the small molecule scale, relies on the microphase separation of PAN-g-PEO. In this process, a porous support membrane is coated with a thin (0.2-2 micron) film of PAN-g-PEO. The copolymer microphase separates into a bicontinuous network of each phase. The PEO phase, which is hydrophilic, allows the passage of water and molecules smaller than its diameter, acting as PEO-lined "nanochannels". The membranes produced have size-based selectivity in the nanofiltration scale, and can be used to fractionate small-molecule dyes by size. They also have a high pure water permeability, and complete resistance to irreversible fouling. Furthermore, the size cut-off of these membranes is responsive to a range of factors that affect the conformation of PEO chains, such as temperature, pressure, and ionic strength.
Polymer Filtration Membranes: Part 2 - Nathan Lovell
Amphiphilic comb copolymers impart fouling resistance to polymer membranes, an increasingly important part of the world's water supply sustainability. Research is underway to expand the application of the morphology and properties of these combs to create membranes with regenerative fouling-resistant surfaces, nanosieving membranes, and improved desalination membranes.
