Karen I. Winey - US grants

9305286 Winey Rheometry is the most common and reliable technique for measuring viscoelastic properties of materials. This rheometer, a Rheometrics Solids Analyzer, satisfies the sample configuration requirements of many researchers on campus, in that it can accommodate molten polymers, glassy thin films, fibers, concentrated solutions, rubber, and composites. The processing equipment, includes a melt mixer for combining a variety of components and a small extruder to form samples for subsequent structural and mechanical evaluation. Throughout the School of Engineering and Applied Science and the School of Arts and Sciences, this new equipment will compliment the experimental techniques currently used by Penn faculty. In our research laboratories we prepare copolymer/homopolymer blends by using a volatile solvent, a practice which is avoided by industry, and evaluate the morphology and phase behavior using transmission electron microscopy and small angle x-ray scattering. With the proposed equipment, blends will be prepared without using a solvent and our extensive morphological studies will be related to new rheological studies. In another example, preceramic polymers are currently studied at Penn by using synthetic techniques elemental and thermal analysis, and wide angle x-ray scattering. The new equipment will provide a means of fabricating fibers, using the extruder, and studying the mechanical properties of the preceramic polymers, using the rheometer. Other research projects include: relating the percent crystallinity and conductivity of a conducting polymer with the viscoelastic properties of the materials, comparing the molecular motion in polymer blends as measured by both diffusion and zero shear viscosity, and testing theoretical models of ionomer solutions by neutron scattering and rheology. An important goal of this project is to make the research at Penn more relevant to industrial concerns by using similar processing techniques and g iving more emphasis to the interdependence of microscopic structure and macroscopic properties. ***

We aim to establish an Undergraduate Laboratory in Polymer Science and Engineering to update the undergraduate engineering program at the University of Pennsylvania. The proposed laboratory will benefit undergraduate students by teaching important principles in polymer science and by introducing them to state-of-the-art equipment. The scope of the project involves required core courses, elective polymer courses and independent undergraduate research or design projects. The planned laboratory exercises include polymer syntheses, computer simulations, molecular and structural characterizations, morphology investigations and mechanical property measurements. Upon synthesizing their own polymers, thermodynamic, kinetic and mechanical properties will be investigated using a differential scanning calorimeter and a dynamic mechanical analyzer. This thermal analysis equipment will be a major component of the undergraduate polymer laboratory, because of the variety of polymer characteristics which these instruments can probe (e.g. glass transition, crystallization, moduli). A unique feature of the project is the incorporation of molecular modeling for illustrating chain conformations and tacticity and for predicting macroscopic properties from molecular structures. A hot stage is necessary to study the phase transitions and crystallization of polymers using an existing undergraduate light microscopy facility. This project is significant for three reasons: undergraduate laboratory facilities for the study of polymer science and engineering currently do not exist at Penn, our undergraduate engineers frequently find employment in polymer or polymer- related fields, and finally, polymeric materials are of immense commercial and scientific importance.

9307993 Winey Adhesives, photoresists, impact modifiers, packaging materials, and emulsifying agents are among the industrial uses of copolymers. Copolymers contain two or more types of monomer units covalently bonded to one another in a single polymer chain. The different monomer units of the copolymer can be arranged in a variety of sequences, for example, random, alternating, and block. Traditionally, researchers have assumed that the sequence distribution does not influence macroscopic properties, except in the case of very large sequencing differences, for example random versus block copolymers. However, a few studies, including work by the authors, have demonstrated that small differences in the sequence distribution dramatically influence blend miscibility. Given these unexpected results, a thorough investigation of the effect of sequence distribution on thermodynamics and mechanical properties will be carried out. The pertinent topics are the phase behavior in copolymer/homopolymer/homopolymer blends and the interfacial properties of copolymer confined between immiscible phases. Both blend miscibility and interfacial fracture toughness will be studied primarily as a function of the sequence distribution of the copolymer, though considerable attention will also be given to the interaction parameter and molecular weights. The sequence distribution in copolymers will be explored as a new means of effectively tailoring properties by varying the molecular structure. ***

Funds fron the Academic Research Infrastructure Program will support the acquisition of a Field Emission Transmission Electron Microscope (FE-TEM), an instrument that is specifically designed for high-resolution chemical analysis. The FE-TEM will include basic specimen stages, an x-ray flourescence spectrometer, a GATAN imaging filter, and a charge- coupled-device (CCD) camera and associated hardware. The FE-TEM will be employed in the study of: 1) structure and properties of alloy and model composite interfaces; 2) the effect of impurity segregation on the fracture mechanisms of metal/ceramic interfaces; 3) structural and compositional inhomogeneities in microwave ceramics; 4) the effects of concentration gradients near grain boundaries on the properties of electronic ceramics; 5) local structure and composition in catalytic materials; 6) morphological development of nanocrystalline ceramic composites from polymeric precursors; 7) chemistry/property relations at the interphase region in polymer/ceramic composites; 8) polymer interfaces and capillary wave formation. A field emission transmission electron microscope with associated peripheral hardware will be employed in the study of materials. A diverse range of topics from composite interfaces, fracture of metal/ceramic interfaces, microwave and electronic ceramics, catalytic materials, polymer/ceramic composities, and capillary wave formation at polymer interfaces will be studied.

9457997 Winey This research explores the interdependence of structure and properties in complex systems, particularly systems involving copolymers. Using a comprehensive approach involving synthesis, structure and properties, this proposal addresses the fundamental questions of sequence distribution and non-universality. With the inspiration of nature's remarkable protein engineering, it will strive to develop the technological applications of copolymers and their blends to their full capacity. %%% ***

9724486 Klein The University of Pennsylvania will acquire a confocal microscope workstation for three-dimensional imaging and micromanipulation of soft materials. The instrument will support research in the areas of colloid engineering, including colloidal crystals and particle epitaxy, vesicles and membranes, emulsions, molecular elasticity, and flow in porous media. The instrument will be part of a Center for Advanced Imaging and Micromanipulation housed in the University's Laboratory for Research on the Structure of Matter (LRSM). %%% Acquisition of this instrumentation will impact the research and research training of over 40 students and postdoctoral fellows associated with the soft materials group at the LRSM. The instrument will also be utilized by the 25 undergraduates, half of them from other colleges and universities, participating in the LRSM summer Research Experience for Undergraduates program. ***

9904127
Winey

This three-year award supports US-UK collaborative research in materials science between Karen Winey at the University of Pennsylvania and Anthony J. Ryan of the University of Sheffield in the United Kingdom. The research explores the creation and relaxation of defects in a series of soft, layered materials. In particular, it addresses an apparent lack of universality, namely that block copolymers (layered materials having short relaxation times) form focal conic defects.

The US researcher brings to this collaboration expertise in imaging and defects using electron microscopy. This is complemented by the British researcher's expertise of in-situ characterization of materials using synchrotron sources. The collaboration provides access to unique model diblock copolymers developed by the British research group and access to world class synchrotron sources - the Daresbury facility in the United Kingdom and the European Synchrotron Research Facility in Grenoble, France.

9906829
Winey

The overall objective of this research project is to resolve outstanding and disputed questions in ionomer morphology, particularly in regard to the ionic aggregates. During the first three years, the work will focus on model random ionomers in the bulk, specifically ionomers based on polystyrene, and accomplish four major scientific goals. (1) Using bright and/or annular dark field scanning transmission electron microscopy, the PI will quantitatively and completely characterized the ionic aggregates starting with size, shape and size distribution. She will use three-dimensional reconstruction from tilt series in STEM to determine the spatial distribution of the aggregates, including the distance of closest approach. In addition, an ensemble of microanalysis methods within the electron microscope (spatially resolved EELS, EDS, and quantitative ADF STEM) will quantitatively determine the compositions of the ionic aggregates and the matrix. (2) Again using electron microscopy, the PI will measure the spatial distribution of cation over a 10 - 1000 nm length scale to assess the origin of the upturn in scattering intensity at low angles. (3) Using the morphological information obtained from quantitative imaging and microanalysis, she will develop a small angle x-ray scattering model. (4) The dynamics of nano-aggregates will be studied using a heating/cooling stage and a deformation stage in the electron microscope. Throughout this project the PI will evaluate sytrenic ionomers with various materials characteristics (%acid, %neutralization, counterion type, acid type, etc.), to establish their influence on the nano-scale morphology. The integrated and unique set of tools to be used permits a more rigorous correlation between molecular parameters and morphology than previously attempted.

This work is in the technologically important area of nanoscience and nanomaterials. The PI will train one graduate student in polymer science and high resolution, chemically specific imaging, a technique, which is currently underutilized by polymer scientists and industrialists. In addition, she will also train industrial and academic scientists in these advanced techniques.

0002061
Fischer

Description: This award supports US-India Cooperative Research: Application of Carbon Nanotubes in Composites -Alignment and Adhesion Problems. US PI John Fischer, University of Pennsylvania and Rakesh B. Mathur, National Physical Laboratory (NPL), New Delhi will conduct research on critical problemsthat need solutions before nanotubes can be successfully used in high strength composites. The objective is to exploit the exceptional mechanical strength of carbon nanotubes for the fabrication of advanced composite materials.

Scope: The research groups compliment one another and each group has highly qualified senior researchers with established research records. Their collaboration is expected to produce advances that increase scientific understanding and enhance prospects for technological use of nanotube composites. The project has clear mutual benefits for the US and India, as well as potential for industrial application.

This award is in response to the Nanoscience and Engineering (NSE) solicitation(NSF-00-119) and involves a nanoscience Interdisciplinary Research Team (NIRT) at the University of Pennsylvania with broad-ranging national and international collaborations. It is being co-supported by the Polymers Program of the Division of Materials Research (DMR), the Special Programs of the Division of Chemistry (CHE), and the Interfacial, Transport and Thermodynamic Processes Program of the Division of Chemical & Transport Systems (CTS).
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The ability to transition nanoscience and engineering (NSE) research to nanotechnology will depend on the development of efficient new synthetic methods to produce monodisperse nanoscale objects. To this end, the primary goal of this Nanoscale Interdisciplinary research team (NIRT) is to enable a rational approach to the design and synthesis of libraries of complex functional monodisperse objects of well-defined shapes, dimensions up to the wavelength of light, surface, and internal compartmentalized architecture. To accomplish this goal, the NIRT combines synthetic methodologies from Materials and the Life Sciences. The NIRT has assembled expertise in organic, macromolecular, supramolecular, and peptide synthesis, along with theory and modeling, and structural analysis by x-rays, TEM, and SFM. The team effort is amplified by exploiting established links with partners in industry and in Europe. Success will reveal the principles required for the construction of libraries of monodisperse self-assembling dendritic building blocks, to enable the hierarchical design of monodisperse single molecule functional nanostructures (SMN) with shape, chirality, internal and external structure, and function controlled at the level of precision currently available only in biological systems. The NIRT will investigate the structure and properties of these nanoscale objects at the level of the single molecule and in 2-D and 3-D assemblies. Novel applications of SMNs are elaborated that have potential to yield nanoscale devices for electronic, optical, chemical and medical technologies.

The proposed research will investigate the morphology of ion-containing polymers, in particular ionomers, using model materials and a variety of analytical electron microscopy (AEM) methods. Ionomers are random copolymers with a majority of non-polar monomeric units and a minority (~5-10 mol%) of polar monomeric units, typically acids such as -COOH. The acid groups can be neutralized with cations to create ionic species such as -COO-Na+ in the case of a Na-neutralized carboxylic acid. Because these ionic species are considerably more polar that the surrounding matrix, there is a driving force for the ionic species to microphase separate and form ionic aggregates although the resulting morphologies of ionic aggregates are not well understood. Controlling the morphologies of ionomers is the primary goal of the proposed research and the first step to developing both a predictive theoretical model of these materials and a robust understanding of their structure-property relationships. These ionic aggregates act as physical crosslinks to toughen the polymer and lead to both current industrial applications (chemically resistant thermoplastics, tough coatings, permselective membranes for fuel cells, and food packaging materials) and a variety of potential technological applications (e.g. protection against chemical warfare). These complex polymeric materials spur scientific interest, because (1) these amphiphilic materials have ionic interactions that mimic biological macromolecules, (2) ionomers are readily available with a wealth of chemistries that includes amorphous and semicrystalline polymers and a range of cations, and (3) high-resolution analytical tools are now available to investigate the interdependencies of chemistry, processing, morphology and properties. Winey's scanning transmission electron microscopy (STEM) studies of ionomers since 1998 provide a valuable foundation to the proposed research in which Winey endeavors to identify the materials parameters and processing conditions that have the most substantial influence on the ionomer morphologies. The proposed work seeks to uncover reliable trends in the ionomer morphology in order to provide fundamental understanding of these complex materials. As Winey determines how the various materials and processing parameters influence the ionomer morphology they will be able to control the ionomer morphology. Two hallmarks of the proposed experimental plan are (1) the use of model materials, that is materials designed to address specific scientific questions, and (2) the use of multiple characterization tools including SAXS, FT-IR, and, in particular, a range of analytical electron microscopy (AEM) methods.

Industrial, academic and military scientists have scientific interest in both the proposed research about ion-containing polymers and the development of AEM characterization tools for polymers. Winey will collaborate with the Lehigh Microscopy School to ensure that electron microscopists take full advantage of the AEM methods that are used within the proposed work to investigate complex, chemically heterogeneous polymeric materials. In addition, Winey will continue to both serve as a faculty co-advisor to the Society of Women Engineers on Penn's campus and hold an annual panel about opportunities for graduate studies and academic careers in engineering.

This grant provides funds for a shared Viscoelastic Characterization Facility (VCF) for the characterization of viscoelastic properties of soft materials at the University of Pennsylvania. The VCF has research studying materials ranging from synthetic gels and colloids to biological tissues and carbon nanotubes. The VCF will characterize soft materials by rheologic methods that assist in determining their response to mechanical deformation. The nature of viscoelastic characterization (or the field of rheology) is such that no single instrument can measure the different geometries and extent of deformation that are appropriate for desired experimental systems. Accordingly, this grant covers five instruments to span a range wide enough to be useful to the maximum number of researchers. Specifically, two complex instruments will be developed by groups with specialized needs and expertise: 1) A customized version of the ThermoHaake Rheoscope Imaging Rheometer - to be built in collaboration with MRSEC faculty that requires single molecule imaging within polymer networks. The current version of the Rheoscope will be modified to mount on a Zeiss inverted microscope with image deconvolution capability. 2) A Bohlin C-VOR-200 Rheometer modified with transparent sample housing to interface with existing scattering facilities, such as a dynamic light scattering system, allowing more powerful capabilities to relate molecular structures to macroscopic properties than possible with existing instruments. Three other instruments will serve a broad range of users whose needs are met by commercial instruments. These instruments will differ in types of samples for which they are best suited (e.g. solid versus fluid), the type of deformation they apply, the temperature range over which they operate, and the volume required for measurement.

The equipment will be integrated into existing courses in the Bioengineering and Physics Departments to train both undergraduate and graduate students and will be used in the NSF Research Experience for Undergraduates Program to train additional undergraduates and provide outreach to underrepresented minorities. The management plan for the facility provides additional plans for training and outreach to both underrepresented students and industry. The VCF would also impact other communities at PENN, as seen in the range of investigators involved in this proposal which include 22 groups in 12 departments within the Schools of Arts and Sciences, Engineering and Applied Sciences, Medicine, and the Children's Hospital of Pennsylvania.

Isonomers are random copolymers with a majority of non=polar monomeric units and a minority (~5-10 mol%) of polar monomeric units, typically acids. The acid groups can be partially or fully neutralized with cations to create ionic species that self assemble to form ionic nanoaggregates. In addition to their current industrial interest as chemically resistant thermoplastics, tough coatings, permselective membranes for fuel cells, and food packaging materials, a variety of new technologies are envisioned. Wineys work with these materials focused on directly imaging the ionic aggregates using advanced electron microscopy methods, so as to provide vital insight to the interrelationships between synthesis, processing, morphology and numerous physical properties. The focus of the proposed research is to seek reconciliation between real space images collected by scanning transmission electron microscopy (STEM) and reciprocal space patterns collected by small angle x-ray scattering (SAXS). Model materials will be employed. The proposed research is divided into three segments: further STEM and SAXS technique refinements. Poly(styrene-ran-methacrylic acid) copolymers neutralized with transition metals, and poly(ethylene-ran-methacrylic acid) copolymers neutralized with transition metals.
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Ionomers are a class of plastics that are currently used as chemically resistant plastics, tough coatings (golf balls) permselective membranes for fuel cells, and food packaging materials, and a variety of new technologies are envisioned, e.g., protection against chemical warfare. Designing better ionomers for these applications requires understanding the interdependencies of structure, processing, and properties. Winey is characterizing the nanoscale structure of ionomers using advanced election microscopy and standard x-ray scattering tools. Industrial , academic and military scientists have a particular interest in Wineys efforts to reconcile microscopy and scattering data from ionomers, because in instances of successful reconciliation the wider community can subsequently rely on the faster scattering method with confidence. Providing this information will enable scientists and engineers to better establish the interdependencies and design improved materials. Winey will continue to accept speaking engagements that encourage the participation of women in science and engineering.

Non-Technical Abstract

Photography records a moment in time, but movies capture the transformations that occur from one moment to the next. Consider a chick hatching from an egg and how much more informative a movie is as compared to one photograph of the egg and another of the chick. In the study of materials, we are interested in how solids respond to various environments and stimuli. In the past we have studied transitions in materials by making many duplicate samples and stopping the transformation at a few time points to take essentially still photographs and then attempting to connect the dots between these time points. This approach is tedious and slow, not to mention riddled with uncertainties about missed information. The new instrument enables researchers to stimulate materials and record their response at the same time. Our imaging method detects chemical and topological features 500 times smaller than the thickness of a human hair, and also allows for sample manipulation on this length scale. Stimuli that are important for designing extraordinary properties into a new material include exposure to liquids and gases, temperature control, electric fields, and mechanical deformation. The materials to be studied have a wide variety of applications including membranes for fuel cells, highly sensitive chemical sensors, flexible electronics, engineered coatings, structured surfaces for tissue engineering, and high-efficiency solar cells. The instrument will be incorporated into our highly successful, professionally staffed regional facility that is open to all academic, industrial, and governmental scientists and engineers.


Technical Abstract

The new scanning electron microscope is equipped with a uniquely broad array of accessories to enable the combination of high-resolution imaging and nanoscale manipulation for powerful in situ experiments involving controlled stimuli and correlated response. In situ capabilities include nanoscale manipulation of specimens and exposure to fluids, gases, electrical fields, light, mechanical deformation, and temperature. The in situ approach enabled by this instrument is not only cleaner and more efficient than "in-and-out" procedures involving multiple instruments and exposure to air, it also makes possible entirely new, albeit high risk, initiatives to understand fundamental processes at the nanoscale. The experiments to be conducted go far beyond structural imaging, while incorporating this basic feature as an essential ingredient. We will also acquire an optical microscope with digital imaging/recording; this will serve as a "front end" for sample screening and preliminary measurements to inform and ensure the optimum use of the SEM. Seventeen faculty members associated with seven departments and representing all ranks have envisioned and planned remarkable experiments for this new instrument within four topical areas of nanoscale science: electrically responsive materials (including fuel cell membranes, flexible electronics, and nano circuitry), phase transitions (including superlattices, phase separation, and patterning), surface phenomena (including wetting, cell response, gas adsorption, and self-assembly), and mechanically responsive materials (including hard materials, proteins, and fluids). The user base will provide a focal point for initiating new collaborations, interactions and training/education initiatives. The instrument will be incorporated into our highly successful, professionally staffed regional facility that is open to academic, industrial, and governmental scientists and engineers. To encourage the full participation of local liberal arts colleges, particularly the highly selective women's college Bryn Mawr College, we will provide technical assistance and machine use to researchers from these institutions.

This research helps provide a fundamental understanding of polymer dynamics in the presence of nanoparticles using a coordinated experimental and theoretical approach. This Materials World Network team from the University of Pennsylvania and Durham University has considerable experience in polymer nancomposites and dynamic properties, and is working together in exploring polymer diffusion and rheology in these fascinating and complex materials. This team recently found a dramatic example of how polymers behave differently in the presence of nanoparticles, wherein polymer diffusion first slowed and then recovered with the addition of nanoparticles. Research efforts are focusing on three aspects of polymer nanocomposite dynamics. (1) Establishing the underlying mechanism of polymer diffusion in nanocomposites. A variety of studies are underway that explore the impact of nanoparticle / polymer interactions, nanoparticle orientation, relative size of the polymer and nanoparticle diameter, and nanoparticle shape. (2) Relating the polymer and nanoparticle diffusion studies to rheological measurements including linear viscoelastic measurements, zero-shear viscosity, plateau modulus and relaxation times. Polymer diffusion and polymer rheology are intimately related through fundamental relaxation parameters, so our goal is to reconcile these two measures of polymer dynamics in polymer nanocomposites. (3) Refining and extending our theoretical description of the polymer dynamics in the presence of nanoparticles. One critical extension is to adjust the monomeric friction coefficient near the particles to evaluate the importance of enthalpic interactions on diffusion.

The research team is well-positioned for groundbreaking insights into the physics of polymer nanocomposites that are likely to have a positive impact on the emerging industry of polymer nanocomposites. Interactions include meetings, bi-monthly teleconferences, monthly reports, data sharing via a secure website, regular international trips, and remote access to experimental equipment. This project also addresses the needs of women in science and engineering by establishing professional problem-solving groups for women faculty and graduate students as a means to collectively address the challenges and opportunities in science and engineering careers. Furthermore, undergraduates from both the University of Pennsylvania and Durham University participate in the research activities as well as consider the business aspects of launching new materials.

This Materials World Network research is supported by the DMR Polymers Program and the DMR Office of Special Programs.

TECHNICAL SUMMARY

Precise acid copolymers are novel materials having functional groups spaced exactly evenly along a linear polyethylene. For example, a phosphonic acid group can be placed on every 9th, 15th or 21st carbon. The proposed project involves nine precise acid copolymers and one random acid copolymer having carboxylic acid and phosphonic acid groups with mono- or geminal-substitution. These materials have established synthetic routes. Winey's morphological studies of the acid copolymers will use X-ray scattering, HAADF STEM, and electron diffraction to establish the crystalline structure of the polyethylene segments and the nature of the acid group assemblies. The acid copolymers will be neutralized with Li, Na, Cs, and Zn to form partially- and fully-neutralized ionomers in which Winey will probe the size, shape, spatial arrangement, and composition of the ionic aggregates. The precision of these acid copolymers and ionomers is known to yield remarkable uniformity in the morphologies, making data interpretation and comparisons with simulations more rigorous. The dynamics and mechanical properties will be studied for the first time in three precise acid copolymers and one random acid copolymer, along with their ionomers. The property measurements will include melt rheology, small-strain compression testing to explore elastic deformations, and large-strain, cyclic compression testing to study plastic deformation. The PI's group has highly specialized expertise to study the morphology, dynamics, and mechanical properties of these remarkable polymers in terms of both demonstrated prior work and existing collaborations.


NON-TECHNICAL SUMMARY

The PI will study an extraordinary set of functional polymers with the ultimate goal of knowing how the functional groups are arranged and thereby how their arrangement dictates their mechanical properties. These functional polymers have an acid group on every 9th, 15th or 21st carbon atom along a polyethylene molecule. The unprecedented precision in these molecules will lead to better structural order at both the micro- and nanoscale, which, in turn, enable improved correlations between molecular structure and properties. The PI has established collaborations with synthetic chemists, spectroscopists, and theorists to explore these remarkable materials, and within this interdisciplinary team the teaching, learning, and training of more students and researchers will be significantly enriched. These precise polymers are based on polyethylene, which constitutes the largest class of commercial polymers. This project involves the first dynamical and mechanical property measurements of these materials and in so doing will evaluate their commercial potential.

TECHNICAL SUMMARY:
Nanoparticles can impart polymers with unique mechanical and functional properties while also having dramatic effects on how nanoparticles and polymers move. Unlike traditional polymer composites, nanocomposites contain nanoscale particles that are smaller than the radius of gyration of the polymers and this presents a variety of new underlying questions in polymer physics. The dynamics of nanoparticles and polymers are fundamentally important to the processability, dispersion and properties of polymer nanocomposites. Recent reports have found a variety of unexpected, and even inconsistent, results about dynamics in polymer nanocomposites as measured by rheology, neutron scattering methods, and polymer melt diffusion. This Materials World Network project will provide fundamental understanding of dynamics in the presence of spherical nanoparticles (3-100 nm) using complementary experimental and simulation tools. Three research aims correspond to three classes of nanoparticles: hard nanoparticles with just surface functionalization, soft nanoparticles with grafted polymer chains, and mobile nanoparticles. This US and United Kingdom team has expertise spanning polymer science, including nanoparticle functionalization, synthesizing grafted nanoparticles, nanocomposite fabrication and morphology characterization, polymer diffusion studies, neutron scattering, self-consistent field calculations, and simulations by molecular dynamics and dissipative particle dynamics. The team will participate in monthly teleconferences and exchange visits to both institutions by the PI, CoPIs, and their students, as well as joint trips to neutron scattering facilities in Europe.

NON-TECHNICAL SUMMARY:
Nanoparticles can impart polymers with unique mechanical and functional properties, while also having dramatic effects on how nanoparticles and polymers move in polymer nanocomposites. Brownian motion describes the random motion of gases that is dominated by collisions between gas molecules. Polymer molecules can be thousands of times larger much gas molecules and when surrounded by and entangled with other polymers they typically move by the reptation mechanism, a snake-like motion that involves moving along the contour of the polymer. This widely accepted mechanism is insufficient to describe the dynamics in polymer nanocomposites. The motions of nanoparticles and polymers are fundamentally important to the processability, dispersion and properties of polymer nanocomposites. This Materials World Network (MWN) project seeks to provide a fundamental understanding of how nanoparticles and polymers move using complementary experimental and simulation methods. Given the growing industrial importance of polymer nanocomposites, the MWN team will develop a short course to present the fundamentals and the latest research in this rapidly expanding field. The MWN team will have regular scientific exchanges with industrial scientists. The US and United Kingdom researchers all routinely have undergraduates performing research in their groups and this will extend to this project. Finally, the three senior personnel are active in improving the status of women in science and engineering and this international collaboration will enable information exchanges regarding best practices pertaining to identifying, recruiting, developing and retaining women students and faculty.

This project is supported by the Polymers Program and the Office of Special Programs in the Division of Materials Research.

PART 1: NON-TECHNICAL SUMMARY

Polyethylene is ubiquitous in modern life from plastic bags to milk jugs to gas pipes. Modifying polyethylene by attaching acid and ionic groups to the molecule transforms polyethylene into a substantially tougher and more abrasion resistant material with better chemical resistance. These improved properties stem from the presence of nanoscale aggregates that contain the acid group and metal ions. These ionic aggregates have long been thought to be spherical, and polymer scientists know how to manipulate this structure to tune mechanical properties.

In this research, the PI plans to engineer these nanoscale aggregates to promote ion or proton transport. New plastics with fast and highly selective ion or proton transport will contribute to breakthroughs in water treatment, energy storage, and energy conversion. Prof. Karen Winey along with her graduate and undergraduate students at the University of Pennsylvania have been studying precise polyethylenes where the acid or ionic groups are evenly spaced along the molecular chains. They found that these precise copolymers exhibit new, and as yet untested, types of ionic aggregates. By selecting different polymers and ions, the ionic aggregates can be transformed from spherical nanoscale aggregates to aggregates in the shape of sheets and percolated networks. Both of these new structures are particularly promising for ion transport, because the aggregates are more extensive than discreet spherical aggregates. This award will explore the properties afforded by these new types of ionic aggregates with the intent of identifying polymers with substantially improved ion or proton transport. Polymer synthesis and quasi-elastic neutron scattering experiments will use national facilities.



PART 2: TECHNICAL SUMMARY

Poly(ethylene-co-acrylic acid) precise copolymers are model polymers with a linear backbone and pendant carboxylic acid groups separated by exactly 9, 15 or 21 carbons. Previous morphology studies of these precise acid copolymers and their neutralized ionomers have identified a variety of aggregate shapes of which two morphologies are particularly interesting with respect to conductivity. The layered morphologies consist of functional groups assembled into planar aggregates and the percolated morphologies have stringy, branched aggregates that span the sample to make a co-continuous structure. Relative to single-ion conductors with spherical aggregates, the layered and percolated aggregates possess greater connectivity that is expected to provide faster ion transport. Ion conductivity will be studied in precise acid copolymers neutralized with Li, Na, or Cs. Proton conductivity will be studied in hydrated precise acid copolymers and precise acid copolymers mixed with various imidazoles. These precise copolymers and ionomers provide unprecedented molecular control that produces well-defined morphologies and thereby facilitate the improved understanding of structure-property relationships pertaining to ion and proton transport. By comparing conductivities for different morphology types, the proposed project will provide design rules for making specific morphology types with improved conductivity.

An array of experimental methods will be applied to probe the structure, dynamics and conductivity of these materials including electrochemical impedance spectroscopy, quasielastic neutron scattering (QENS), dielectric relaxation spectroscopy, X-ray scattering, DSC, FTIR, NMR and mechanical properties. Direct comparison of the QENS results with atomistic molecular dynamics simulations will elucidate the mechanism of conduction within the percolated aggregates and explore whether or not the ion motion is decoupled from the chain dynamics.

This award supports the purchase of a state-of-the-art X-ray scattering instrument that will be operated as an open-access facility within the Laboratory for Research on the Structure of Matter (LRSM), host of an NSF-funded MRSEC at the University of Pennsylvania (Penn). The Xeuss 2.0 from Xenocs allows the structural characterization over length scales from 0.09 to 600 nm and thus facilitates study of hierarchical structures in a wide range of hard and soft materials. The anticipated scope of materials to be studied includes metals, ceramics, plastics, biological tissue, and novel combinations of these. The instrument will also play a vital role in the materials education and training of the many high school, undergraduate and graduate students, visiting scientists, post-doctoral associates and local high school teachers who participate in LRSM programs. The facility will also develop and administer workshops and online training materials to promote its broad use by beginners and to fully develop expert-users and thus promote knowledge exchange and technology transfer. The open-access facility will be used by scientists and engineers from local companies and colleges/universities to advance their research. Besides providing unique training in fields critical for US technological competitiveness, the discoveries and understanding facilitated by the new instrumentation will underpin future technologies, thereby informing industry, stimulating the economy, and offering benefits to society at large.

This grant enables the purchase of a state-of-the-art X-ray scattering instrument for an open-access facility within the Laboratory for Research on the Structure of Matter (LRSM), host of an NSF-funded MRSEC at the University of Pennsylvania (Penn). The Xeuss 2.0 by Xenocs enables materials characterization across an extraordinarily wide range of cutting-edge research programs at Penn and in the Philadelphia/Delaware-Valley region. The dual Cu-Mo source and adjustable sample to detector distances provide structural information at both high and low spatial resolution across a wide range of length scales (0.09 to 600 nm). An assortment of sample environments enables materials to be manipulated in situ and operando to probe their structural evolution in response to temperature, tensile stress and electric/magnetic fields, even in humid and liquid environments. Thus, the instrument will advance research on the synthesis, fabrication, processing, and assembly of a wide range of materials systems, and will provide crucial insight about structure relevant to their chemical, electrical, magnetic, mechanical, optical, thermal, and transport properties. The anticipated materials usage portfolio includes nanoporous metals for catalysis and energy storage; nanocrystals, nanorods, and nanocrystal superlattices for light harvesting; polymer nanocomposite films for thermal management, optical properties, and scratch resistance; acid- and ion-containing polymers displaying micro-phase separation for ion transport; dendrons, dendrimers, and their self-assembled structures; hierarchical polymer-based films for controlled wetting; chromonic liquid crystals with novel self-assembled structures and phase transitions; inorganic microlaminated thin films wherein fabrication methods control magnetic properties; thin film molecular glasses with controlled stability and toughness; hierarchical protein structures in squid lenses and other tissues; polycarbonates in ionic liquids to manipulate chemical reactivity; and oriented protein films for electromechanical coupling. The new instrumentation is critical for at least 17 research groups, including 12 from Penn spanning 7 academic departments, and 3 from local universities. Additionally, the instrument will advance proprietary/open-publication research of nearby industrial partners. The Xeuss 2.0 will play a vital role in the materials education and training of the many high school, undergraduate and graduate students, visiting scientists, post-doctoral associates and local high school teachers who participate in LRSM programs.

CBET - 1706014
PI: Winey, Karen I.

Many polymeric materials are modified with nanoparticles to provide special mechanical, electronic, or optical properties. Controlling the distribution of the nanoparticles throughout the polymeric material is essential for achieving these desired properties. Nanoparticles can diffuse through polymers or gels, and in some cases diffusion during processing or during use of the material leads to a maldistribution of nanoparticles and nanoparticle aggregation that degrade product performance. This award will support research into the diffusion of nanoparticles in polymers and gels. It will focus specifically on the regime where the nanoparticle sizes are comparable to the size of mesh formed by entanglements in polymers and by crosslinks in gels. In this regime, nanoparticle diffusion depends on the both the movement of the nanoparticles and fluctuations in the polymer mesh through which the nanoparticles diffuse. Effects of the nanoparticle shape, interactions between the nanoparticles and the polymeric matrix, and spatial variations in the structure of the polymer matrix will also be examined and compared with existing theories. Results from this award will be disseminated to industrial practitioners through an annual symposium organized by the researchers. In addition, the research team will lead hands-on demonstrations of nanoscience for the public at Philly Materials Day and the University of Pennsylvania's annual Nano Day.

This award will support research to measure nanoparticle diffusion in hydrogels and entangled polymer melts that are characterized by their mesh size and tube diameter, respectively. The research will explore systems where the nanoparticle diameter and mesh size or tube diameter are comparable, because models predict strong deviations from conventional Stokes-Einstein diffusion in these cases. Single particle tracking methods will be used to measure nanoparticle diffusion in tetra-poly(ethylene oxide) and polyacrylamide hydrogels. Tetra-poly(ethylene oxide) hydrogels form a model network with nearly monodisperse mesh size. Polyacrylamide hydrogels form a network with a mesh size and heterogeneity that can be manipulated by varying solvents. Rutherford Backscattering Spectrometry will be used to measure nanoparticle diffusion coefficients for phenyl-capped, brush grafted, and hydroxyl-terminated nanoparticles (spherical and cylindrical) in polystyrene and poly(2-vinylpyridine) to explore both athermal and attractive nanoparticle-polymer interactions. Quantitative comparisons will be made with models and theories across a critical range of the ratio of nanoparticle to mesh size, as defined as the tube diameter in the reptation model. Finally, one nanoparticle-polymer system has been specially designed to facilitate measuring nanoparticle diffusion by both single particle tracking and Rutherford backscattering methods to compare complementary information provided by individual nanoparticle motion and ensemble averages from a single system.

PART 1: NON-TECHNICAL SUMMARY

Batteries, particularly those for portable electronic devices, can contain flammable liquids, such that when a battery is damaged a fire can ensue. To mitigate this safety risk, batteries include additional housing and safety features, and while this improves safety during operation, this strategy also increase the size and weight of the battery. An alternative strategy is to replace the flammable liquid with a plastic membrane that allows ions, such as lithium, to pass through without allowing electrons to pass. Prof. Winey's group has been studying single-ion conducting polymers that could be valuable for battery applications and for other membrane applications. In previous NSF-funded work they have uncovered a variety of new nanoscale structures that arise when the active chemical groups are evenly placed along a linear polymer molecule. One of these nanoscale structures, an alternating layered arrangement of ions and crystalline polymer, was recently found to have exceptional proton transport properties when hydrated. To capitalize on this finding, the PI has established new design rules for polymer membranes and built multiple collaborations with synthetic chemists who are incorporating these design concepts into new polymers. Winey's group will explore the nanoscale structures and conductivities of these newly designed polymers as a function of their polymer chemistry and processing to refine and extend their design rules for single-ion conducting polymer membranes. Given the current societal challenges related to clean water, energy storage and energy conversion, the fundamental understanding afforded by this project will have an important societal impact.


PART 2: TECHNICAL SUMMARY

A strong interest in ionomers and other polymers with acid, ionic and polar groups is fueled by their potential ability to selectively transport charged species, which is relevant to batteries, water purification technologies, and fuel cells. The prevailing research directions in the field of solid polymer electrolytes have consolidated around two general classes of homogeneous materials wherein the ions are uniformly distributed throughout the material: polymers mixed with salts and single-ion conductors. The ubiquitous design strategy in these materials systems is based on the understanding that ion conductivity is associated with chain dynamics and ions must be dissociated from their counterion. Unfortunately, these approaches have only limited success in developing suitable polymer-based electrolytes. Winey's group is exploring an alternative hypothesis, namely that efficient ion conductivity in polymers can be broadly achieved when the ions are sequestered into spatially-continuous nanoscale aggregates and the ions dissociate from their counterions. This project builds upon a promising result from the PI and collaborators wherein proton conductivity of a hydrated precise polyethylene with sulfonic acid groups on exactly every 21st carbon is somewhat higher than a commercial membrane. This precise polyethylene self-assembled into nanoscale layers lined with the acid groups and separated by a crystalline alkyl spacer. The high proton conductivity is evidence that the conducting protons are decoupled from the motion of the much slower polymer backbones. The proposed project will expand upon this singular finding to establish the merits of the proposed alternative hypothesis. The planned research combines conductivity measurements, structural characterization, and molecular dynamics simulations to rigorously interrogate this hypothesis using new nanostructured precise polymers. The proposed alkyl polyester sulfonates and telechelic oligomers are expected to have crystalline domains that direct the assembly of layered aggregates; these layered morphologies will be aligned in thin films on interdigitated electrodes to explore the fundamentals of conductivity. Random percolated structures in precise polyethylenes with short carbon spacers will also be investigated. The PI and her group will undertake this project with a set of unfunded collaborators: Prof. Stefan Mecking (Konstanz), Prof. Justin Kennemur (Florida State University), Prof. Paul Nealey (U Chicago), Dr. Amalie Frischknecht (Sandia), and Dr. Mark Stevens (Sandia).
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This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.