Application of Polymers in Electronic Devices

Faculty Mentor: Dr. Qiang HuangChemical and Biological Engineering

Advanced inorganic materials fabrication rely on organic polymers as additives in electrochemical deposition of thin films and nanostructures. For example, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and copolymer of imidazole and epichlorohydrin are used frequently to fabricate copper interconnect structures in integrated circuits. The purposes of using these polymers are not only to enable the formation of defect free interconnect structures but also to control the impurity, grain structures as well as resistivity of the deposited copper. Electrodeposited copper films typically have fine grains and show rapid grain coarsening at an elevated temperature. Such grain growth can be monitored with resistivity measurement or directly observed using scanning ion microscope.

REU Participants Role: The student will explore the effects of concentration and polymerization of PVP on the properties of copper (Cu). Cu films of a constant thickness, for example 500 nm, will be electrodeposited from these different solutions using the same current density of -20 mA/cm2. The sheet resistance of the films and its change upon high temperature annealing will be measured with a 4-point probe with temperature control. The student will characterize the Cu resistance change upon annealing at different temperatures, investigate the effect of PVP molecular weight on the Cu grain growth upon annealing, and explore the effect of PVP concentration on the Cu resistance change.

Bio-inspired Soft Polymer Culture of Tumor Cells

Faculty Mentor: Drs. John Kim and Shreyas Rao, Chemical and Biological Engineering

One of the ongoing challenges in oncology research is in properly mimicking the native in vivo environment for cells cultured in vitro. Cancer cells are now known to be sensitive to the mechanical properties of their culture environment24, but they are typically cultured in polystyrene (a petroleum-derived polymer) tissue culture flasks (TCPS). TCPS have a remarkably different stiffness (~3 GPa) than native tissues (e.g. 0.2-1 kPa for brain).  In Kim’s lab, it has been observed that U87-MG glioblastoma multiforme brain tumor cells assume a very different morphology depending on the biopolymer utilized to coat the TCPS. Our hypothesis is that cancer cells grown in softer hydrogel biopolymers will better mimic and model patient tumors.

REU Participants Role: The REU student will generate bio-based polymer matrices (composed of laminin, collagen, hyaluronic acid, polyethylene glycol, etc.) of varying stiffness that represent tissues of the human body (e.g., brain, breast, ovary). The student will also culture cancer cells that originate from these various organs and test for differences in cell behavior and genetic and protein-level molecular signatures. This is an excellent training opportunity for a future career/schooling in utilizing polymers for biomedical engineering research.

Experimental Studies of Bimetallic Catalysts for Sustainable Production of Amides

Faculty Mentor: Dr. James HarrisChemical and Biological Engineering

Production of chemicals from renewable feedstocks is essential to reducing our reliance on fossil fuels and emission of greenhouse gases. Molecules derived from biomass are functionalized and oxygen rich, and thus less energy dense than those from petroleum. As a result, the low energy density of biomass reduces its viability as a fuel, without costly deoxygenation. However, molecules produced from biomass are well suited to replace those currently produced by oxidation of hydrocarbons, such as alcohols, aldehydes, or acids, en route to production of functionalized chemicals. One such application is production of nylon-6,6, which requires oxidation of cyclohexane to cyclohexanol and reaction of cyclohexanol with nitric acid to produce adipic acid, which along with hexamethylenediamine acts as the monomer for nylon production. A sustainable alternative would be to use 1,6-hexanediol, which can be prepared in high yields from biomass, to generate either 1) adipic acid or 2) adipamide which could then be converted to hexamethylenediamine. Professor Harris’ group is actively studying aerobic conversion of alcohols and amines to amides as model C-N bond formation reactions.

REU Participants Role: the student will synthesize bimetallic particles supported on metal oxides using wet chemistry techniques, and may perform hydrothermal zeolite synthesis. The student will characterize the resultant materials using XRD and N2 adsorption. The student will perform oxidative coupling reactions in liquid phase batch reactors, initially the reaction between methanol and dimethylamine to form dimethylformamide in the presence of oxygen, for comparison to the results of the same reaction in the gas phase performed by a graduate student. The student will learn to collect liquid samples as a function of time, inject these to GCMS, and analyze GC data. Additional oxidation reactions may be performed throughout the course of the summer.

Functionalization of Membranes for Selective Removal of Contaminants from Water

Faculty Advisor: Dr. Milad Esfahani, Chemical and Biological Engineering

Per- and polyfluoroalkyl substances (PFAS) are current threats to human and environmental health and pose a risk to the safety of groundwater, surface water, and drinking water. The main adverse properties of PFAS can be listed as being highly toxic, bioaccumulate, do not degrade readily in the environment, and are known to be endocrine disruptors and carcinogenic. Polymeric nanofiltration  (NF) membranes are used for water treatment; however, they do not provide complete removal of all short- and long-chain PFAS from water. NF membranes surface hydrophilicity, roughness, and surface charge can be functionalized by metal organic frameworks (MOFs) for selective adsorption and complete removal of PFAS compounds from water.

Role of Student: REU students will learn how to synthesis polymeric membranes and characterize their structure (pore size, pore morphology, porosity, contact angle, roughness, etc.). The student will also learn the functionalization of membrane surface using different types of MOFs. The student will also help the graduate student study and evaluate the functionalized membrane performance (permeation, rejection, and fouling) at various operational conditions.

Investigation of Stretchable Electronic Polymers

Faculty Mentor: Dr. Evan WujcikChemical and Biological Engineering

Stretchable electronic polymers (SEPs) are crucial in a number of areas including healthcare, medical diagnosis, athletic gear, artificial skin, robotics, prosthetics and orthotics, and virtual reality; particularly the relatively new research area of electronic skins, or “e-skins.” Though great efforts and huge advancements have been made in SEPs, the successful design and fabrication of an ideal electronic material with the electro-mechanical properties and self-healing ability matching that of human skin eludes researchers. The intrinsic conductive and stretchable polymer or its composite route is considered a superior strategy for SEPs. The homogenous and isotropic nature of polymer film preparation has made these materials more repeatable, reliable, and with more response linearity. However, for recent reported conductive polymer based SEPs, the sensitivity, stretchability, and linearity are still not satisfactory—with few being truly self-healable.  Here, an advanced SEP system will be investigated resulting in polyaniline/acidic polyacrylamide/small molecule dopant (PANI/A-PAM/SMD) films. As these polymer systems have never been realized previously, there is necessity in developing a methodology for predicting the structure-property relationships behind these materials. Through this work, the SEP synthesis route will be explored and the self-healing, mechanical, and electronic properties will be studied and evaluated.

REU Participants Role: The REU student will put initial effort on understanding basic synthesis and characterization of these new polymer systems working in conjunction with a graduate student already skilled in these areas. The student will delve further into the study by developing and examining the influence of the system components on the structure-property relationships of these novel advanced polymer sensors. Through this project, the REU student will study fundamental aspects of polymer systems synthesis & characterization (SEM, EDX, TGA, DSC, XPS, XRD), as well as, applied sensor design & fabrication.

Ionic Polyamides as New Engineering Polymers

Faculty Mentor: Dr. Jason E. BaraChemical and Biological Engineering

The hybridization of ionic liquids (ILs) with high performance “engineering” para-aramid and meta-aramid polyamide architectures associated with Kevlar™ and Nomex™, respectively, presents opportunities to create vast new arrays of polymer materials to address needs in energy-efficient separation of CO2 and other gases, weight reductions in automotive and aerospace vehicles and diversifying the types of polymers that can be used in additive manufacturing (3-D printing). Bara’s lab has developed ionic polyamides (i-PAms) that experience unique intermolecular interactions through both H-bonding and Coulombic forces. Thermal, mechanical and transport properties of i-PAms important for engineering design (e.g. glass transition and melting temperatures, tensile modulus, gas permeability, etc.) can be controlled by selection of the requisite building blocks. Given the great number of possible structures suggested by changing the ‘R’ group and anion (X) within the repeat unit structure, there is a need to understand structure-property relationships associated with the i-PAm motif so as to design materials with desirable properties to address modern engineering challenges. Initially, the scope of the work will be limited to simple ‘R’ groups (e.g, linear alkyl chains) and the bistriflimide (Tf2N) anion so as to allow the student to elucidate structure-property relationships that arise from changing a single variable at a time.

REU Participants Role: The REU student will first focus on characterization and processing of materials already prepared by the PI’s group. There will also be ample opportunity for the student to learn polymer synthesis and produce some new i-PAm materials with systematic variations to backbone structure (i.e., vary the ‘R’ group). The student will also study the solubility of the structurally-varied i-PAms in both conventional organic solvents (e.g., acetone, ethanol, etc.) and also in ILs. The REU student will learn fundamental aspects of condensation (step-growth) polymer synthesis, characterization (DSC, XRD, NMR, GPC, SEM) and polymer processing techniques such as film casting, extrusion and molding.

Mass Spectrometry Studies of Peptides

Faculty Mentor: Dr. Carolyn CassadyChemistry and Biochemistry

Mass spectrometry (MS) has become an important tool for obtaining the amino acid sequences of peptides and proteins. Students working on this project will employ state-of-the-art tandem mass spectrometry (MS/MS) techniques such as collision-induced dissociation (CID), in-source decay (ISD), and electron transfer dissociation (ETD) to explore the fragmentation pathways of protonated, deprotonated, and metallated peptide ions. An emphasis will be placed on studying acidic peptides, which are difficult to sequence by standard techniques and which have been the focus of recent NSF- and NIH-funded research by the Cassady group. The locations and identities of amino acid residues in the peptide chains will be varied in order to observe how these factors affect dissociation, which in turn affects the structural information obtained from mass spectrometry. Students will synthesize their own model peptides to test hypotheses about peptide fragmentation mechanisms and will learn procedures for MS/MS spectral interpretation. The effects of additives such as Cr(III) on the ability of peptides to ionize and protonate will be studied by electrospray (ESI) and matrix-assisted laser desorption ionization (MALDI).

REU Participants Role: REU students will study and sequence acidic peptides by generating MS and MS/MS spectra using various mass spectrometers.

Modification and Characterization of Membrane Adsorbers

Faculty Mentor: Dr. Steven WeinmanChemical and Biological Engineering

Heavy metals, such as chromium, lead, mercury, copper, and iron, are dominant contaminants in wastewater produced from mining processes. They are known to be toxic, are not biodegradable, unlike organic contaminants, and will accumulate in living organisms posing a threat to human health as they enter into environmental waters through leaching and disasters. Environmental regulations are becoming more stringent and thus require new technologies to meet these needs. Functionalized polymeric membranes offer an efficient way to remove these heavy metals. Unlike technologies that rely on pore diffusion for mass transport (e.g. resin beads), membrane adsorbers use convective flow through the membrane pores for mass transport to the adsorption sites. This increases the productivity (volume/time) of water that can be processed, making membrane adsorbers more commercially viable than their resin analogs. Polyethersulfone (PES) membranes can be easily modified via UV graft photopolymerization with polymer ligands capable of complexing with heavy metals. Membrane adsorber capacity, productivity, and selectivity can be optimizing by changing the ligand grafting density and degree.

REU Participants Role: There will be ample opportunity for the REU student to learn about modification, characterization, and testing of membranes. Emphasis will be placed on changing the ligand grafting degree to allow the student to optimize the capture of copper from solution. The student will also study the integrity of the membrane adsorber when exposed to low pH solutions (like those from acid mine drainage) and the capability of the chosen ligand(s) to capture other heavy metals common in copper ore mine drainage such as zinc, lead, and mercury. The REU student will learn fundamentals of UV graft photopolymerization, characterization (AFM, ATR-FTIR, Contact Angle, ICP-OES, SEM), and membrane water purification techniques such as direct flow filtration, static binding capacity, and dynamic binding capacity.

Molecular Simulation of Ionic Polyimides and Composites as Gas Separation Membranes

Faculty Mentor: Dr. Heath TurnerChemical and Biological Engineering

Polyimides are at the forefront of advanced membrane materials for CO2 capture and gas purification. Recently, “ionic polyimides” (i-PIs) have been reported as a new class of condensation polymers which combine structural components of both ionic liquids (ILs) and polyimides through covalent linkages. The experimental realization of the first generation of i-PI + IL composite materials have already been reported, but the fundamental insight and underlying molecular-level behavior of these systems are not well understood. Molecular simulations can be used to provide this information, and this creates an excellent opportunity for a collaborative investigation. Moreover, the Turner and Bara groups have a long history of developing comprehensive experimental+simulation approaches for investigating these types of soft matter adsorbents, involving well over a dozen undergraduate researchers (several ultimately winning Barry M. Goldwater Scholarships and NSF Graduate Fellowships for graduate studies).

REU Participants Role: In this project, an REU student will be trained in the basic principles of molecular dynamics and Monte Carlo simulations. The student will acquire hands-on training with model development protocols, advanced simulation packages, structural analysis techniques, parallel computing concepts, and a deeper appreciation for the potential linkages between simulations and experiments. While the primary focus will be on understanding the gas adsorption properties of composites of i-PI polymers + ILs, the molecular-level structure of these composites can be used to understand and help develop protocols for identifying the next generation of membrane designs. In the past, we have identified elevated productivity and increased engagement of our REU students that are involved in computational research projects that involve strong experimental collaborations.

Nanocomplex for MRI-enabled Cell Tracking

Faculty Mentor: Dr. Yuping BaoChemical and Biological Engineering

Imaging-guided cell tracking is critically important for the verification of accuracy and efficacy in cell-based therapy.28 To enable in vivo MRI tracking, efficient contrast agents with desirable resolution and tracking time are critical. The objective of this project is to develop effective MRI contrast agents with high resolution and elongated circulation time by encapsulating ultrasmall (< 4 nm) iron oxide nanoparticles, a newly developed T1 contrast agent, inside a polymer matrix (alginate). The ultrasmall nanoparticles offer positive contrasts with high resolution while the polymer matrix can be tuned with optimal size and surface for elongated circulation time.

REU Participants Role: REU students will synthesize the nanoclusters with different sizes, various nanoparticle loading, and drug encapsulation. The student will also perform various characterization techniques to evaluate the success of the synthesis, including dynamic light scattering for size and surface charge and relaxometery for the relaxivities. The student will also assist the graduate student to study the cellular uptake behavior and cellular MRI effectiveness. This project provides a great platform for students who are interested in the application of polymers and their role drug delivery, bioimaging, and nanomedicine.

Polymerization of Sulfonyl Aziridines

Faculty Mentor: Dr. Paul RuparChemistry & Biochemistry

Polyethyleneimine (PEI) is a polymer with a -(CH2CH2NH)n– repeat unit. Because of its high amine content, PEI finds use in many applications, from CO2 capture to non-viral gene transfections. PEI is normally synthesized from the cationic ring opening polymerization of aziridine, which exclusively affords branched PEI (b-PEI) rather than the more desired linear form (l-PEI). The Rupar group has recently shown that sulfonylaziridines undergo living, anionic ring opening polymerization to form poly(sulfonylaziridines) (PSAz) of precise molecular weight and narrow molecular weight distributions. Importantly, PSAz can be converted to l-PEI (Figure 2). The Rupar group is currently exploring the use of sequential anionic polymerizations with sulfonylaziridines as a route to l-PEI containing block copolymers. We are especially interested in the application of the block copolymers for the templating of surfaces with inorganic materials.

REU Participants Role: REU students will participate in the block copolymer synthesis and study their self-assembly behavior. In addition, students will learn many state-of-the-art polymer characterization techniques including GPC/SEC, MALDI-TOF MS, and NMR.

Self-Assembly Behavior of Linear-Hyperbranched Block Copolymers

Faculty Mentor: Dr. Chao ZhaoChemical and Biological Engineering

Hyperbranched polymers (HBPs), comprising of dendritic units, linear units and terminal units, are highly branched macromolecules with a three dimensional dendritic architecture.  Given the great number of possible parameters involved, including polymer architecture, polymer composition, polymer concentration, solvent selectivity, and others, the systematic study of the self-assembly behavior in solution of HBP is extremely challenging. There is a need to develop a easy, robust, and potentially fast methodology for investigating the self-assembly behavior of HBP. Zhao‘s lab introduced an amphiphilic hyperbranched polyglycerol-polypropylene glycol-hyperbranched polyglycerol (HPG-PPG-HPG) copolymer, consisting of two hydrophilic hyperbranched HPG stars linked by a linear PPG chain. The self-assembly behavior of HPG-PPG-HPG copolymers can be induced and studied in a water environment by adjusting parameters such as f-value (the ratio of the hydrophilic part to the total mass of the copolymers), hydrophobic linear block length, hydrophobic linear block property (hydrophobicity, rigidity, glass transition temperature), and molecular weight. The copolymer allows the effect of each parameter listed on the self-assembly behavior of HBPs to be studied at a time.

REU Participants Role: REU students will begin the research with the synthesis and characterization of HPG-PPG-HPG copolymers. Students will have ample opportunity to learn fundamental aspects of anionic polymerization, learn to control the molecular weight and chemical composition by tuning the feed ratio of PPG to glycidol, and learn to examine and confirm the polymer chemical structure using NMR, FTIR, GPC, and other methods. Students will learn techniques to characterize the phase transition of HPG-PPG-HPG in water, including monitoring the phase transition using DLS, and observing the aggregates morphology using a microscope. The REU student will learn basic concepts of polymer self-assembly, and understand structure-property relationships associated with the self-assembly process.

Surfmers for effective, stable polymer foams

Faculty Mentor: Dr. Amanda KohChemical and Biological Engineering

One route to polymer foams is through emulsion-templated polymerization through the creation of an emulsion, wherein voids are created within a polymer continuous phase. Control over the void size and volume is critical to achieving the final overall material performance desired. Small-molecule surfactants are the interfacial additive that is most capable of producing microemulsions that are kinetically stable through the reduction of interfacial tension and yield foams with high internal surface area. Surfactants, however, must be removed from the porous material after polymerization (potentially causing problems in downstream applications), and can have unforeseen effects on the foam structure and mechanical properties. Dr. Koh’s previous work has shown that not only can a library of surfactants be developed to specifically target a desired application, but that modifications on the head and tail of the molecule allow it to both stabilize an interface while interacting with both phases.  In the case of a polymer foam, an ideal surfactant would be a surfactant monomer or “surfmer.” The surfmer structure must be chosen to optimize foaming and reactivity with the polymeric continuous phase.

REU Participants Role: The REU student will focus on surfmers common to forming commercial latexes such as those based on styrenic and acrylic sulfonates. The student will evaluate interfacial performance against internal phases such as air and ethanol thus determining the ability of each surfmer to stabilize foam and form an understanding of surfmer interfacial tension structure-property relationships. The student will then form polymer foams using the surfmers identified and determine material properties such as internal pore size, foam type (open- vs. closed-cell), and structure of polymer foam voids. The REU student involved with this project will be exposed to the interfacial and materials science required for