Russell J. Composto, Ph.D. - US grants

The "surface phase" in polymer systems is of enormous scientific and technical importance. Bonding of interfaces (weldability), friction and wear behaviour, and chemical stability depend on the structure and properties of the surface phase, but polymer science has not yet succeeded in developing a comprehensive approach to characterize and study it. This proposal requests support to expend the use of ion beams and neutron and xray scattering to probe the distribution and conformation of polymer species near surfaces so as to understand how to describe and control the behaviour of the surface phase.

This award establishes a new ion beam facility which will be used to address issues in materials research at the University of Pennsylvania. A unique opportunity exists to apply ion scattering to a variety of exciting materials problems, some of which involve new kinds of experiments which advance the state-of-the-art ion scattering techniques. A major aspect of this research is the determination of chemical composition and its variation near interfaces and in thin films. This new ion beam facility extends across a wide range of research programs, which include studies of the distribution of dopants in near-surface regions of polymer based electrolytes and conducting polymers, the composition profile across interfaces in polymers (welding) and at polymer surfaces (adhesion, surface, modification), the progression of the transformation of thin films of polymer precursors to boron-based ceramics, epitaxial growth of thin layers (metal, silicide, and metal on ceramic), hydrogen on and near the surface of metals, and surface and interface studies of surface active impurities in metals and ceramics (interface embrittlement).

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.

9417523 Composto The purpose of this U.S.-Czech research project between Dr. Russell Composto of the University of Pennsylvania and Dr. Petr Vlcek of Czech Academy of Sciences' Institute of Macromolecular Chemistry is to synthesize novel polymeric materials to study polymer adsorption at the polymer/solid interface. To do this, the researchers will use anionic-living and group-transfer polymerization techniques to prepare block copolymers and end- functionalized polymers which bind to oxide surfaces. These specialty polymers will be blended with a matrix polymer and spun-cast on an inorganic substrate. The composition profile, amount absorbed, grafting density of the adsorbed species, and the strength of adsorption will be measured. Results are expected to contribute to our basic knowledge of polymer adhesion and may have relevance to technological problems in the coatings industry. This project in materials research fulfills the program objective of advancing scientific knowledge by enabling experts in the United States and Eastern Europe to combine complementary talents and share research resources in areas of strong mutual interest and competence.

9526357 Composto The proposed resesarch on A/B:C blends will be the first attempt to study the behavior of the complex interfacial profiles and properties associated with three-component, two- phase systems. Both model and commercial systems will be studied including polystyrene blends and poly(methyl methacrylate blends. The interfacial properties will be modeled using the self-consistent field method. To complement these direct profiling measurements, neutron reflectivity experiments will be carried out at National Laboratories. In the third phase of the proposed research, the physics which underlies the wetting transition will be studied using a three-component polymer blend as a model system. %%% These studies may allow a polymer engineer to tune the morphology of complex blends by simply varying the degree of polymerization or concentration to achieve either encapsulated or separated phase domains. In addition to their intrinsic interest, the interfacial segregation and wetting studies on three-component systems will serve as a springboard for understanding more complicated systems such as those containing four-components and three-phases. ***

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. ***

9974366
Composto

The proposed research will focus on the dynamics of phase separating thin film blends. These studies aim to develop a comprehensive understanding of thin film kinetics by measuring the wetting layer growth at both the air / polymer and polymer / substrate interfaces, phase morphology immediately beneath the wetting layer, domain coarsening, surface roughness, and the roughness between the wet and non-wet phases. To probe underlying principles, dynamics will be studied as a function of materials parameters including molecular weight and composition, process dependent variables including film thickness and temperature, and substrate surface energy. To test for universal behavior, a range of model blend systems will be investigated including blends with a lower critical solution temperature and an upper critical solution temperature, in addition to copolymer blends. To directly test the interplay between phase separation and wetting, AFM will be used to directly image the near-surface morphology after selective etching of the wetting phase. Wetting layer growth will be followed using low-energy, forward recoil spectrometry, LE-FRES, and neutron reflectivity. Furthermore, LE-FRES will be developed for the analysis of laterally non-uniform samples. To quantify lateral phase composition and possibly the interfacial width at curved interfaces, analytical TEM will be developed in-house and near edge x-ray adsorption fine structure spectroscopy will be performed in collaboration with NIST. In addition to homogeneous substrates, studies will aim to control lateral profiling studies, wetting properties will be measured using a contact angle goniometer and AFM. An important component of the proposed research is to extend fundamental studies on model systems to advanced materials involving ionomer adhesion promoters and patterned dielectric materials.

The proposed research on polymer films and coatings will provide fundamental scientific understanding that could impact advanced technological applications in the health (e.g. contact lenses, membranes) and microelectronics (e.g. dielectrics and resists) fields. Undergraduates (4/year) will continue to participate in the research program, along with public high-school teachers during the summer.

9975486
Composto

This three-year award supports US-UK collaborative research in polymer science between Russell Composto of the University of Pennsylvania and Richard A.L. Jones of the University of Sheffield in the United Kingdom. The investigators will study the thermodynamic and kinetic principles underlying polymer interfacial phenomena at the molecular level and in multi-phase systems. Complementary techniques of low-energy forward recoil spectrometry and neutron reflectivity will be used to measure interfacial excess of small molecules, and the effect of small molecule composition, chain length and polarity on interfacial properties.

Polymer interfaces play a critical role in technologically important areas including food packaging, protective coatings, adhesives, and biocompatibility. The proposed research will advance understanding for optimizing the surface, interface and bulk properties of multi-phase thin film polymer blends. The US investigator brings to this collaboration expertise in low-energy forward recoil spectrometry. This is complemented by British expertise in neutron reflectivity. The project takes advantage of unique, real time, neutron sources currently availability in the United Kingdom (Rutherford-Appleton Laboratory) and in Grenoble, France.

The proposed research will focus on the dynamics of polymer blend films and polymer blend films containing nanoparticles. Control of film properties, such as hardness and permeability, are greatly complicated by the simultaneous occurrence of phase separation and wetting. Using lateral and depth profiling techniques, the phase evolution and wetting behavior of blends with a critical composition will be investigated for films as thin as 10 nm, ca. radius of gyration. By controlling domain size and spacing, membranes with monodisperse, submicron pores will be prepared. The phase and wetting dynamics of off-critical blends will be studied to gain control over film stability, interfacial area between phases, and wetting structure. New evolutionary pathways are anticipated yielding better insight into phase separation, wetting and capillary fluctuations in confined spaces. The second project will investigate how inert fillers, in particular mobile nanoparticles, modify the rate and morphology of phase separation in polymer blend films. After evaluating silica nanoparticle diffusion and wetting, the effect of particle size, concentration and wettability on domain evolution and morphology will be evaluated using the experimental techniques developed for the previous study as well as new techniques for depth and lateral profiling of the nanoparticles within the film.
The proposed research is important because thin polymer films containing multiple components are critical to many technologies including photolithography, adhesives, and displays. In particular, experimental studies of polymer blends containing filler greatly lag both theory and commercial applications. Fundamental studies will be complimented by studies of commercial filler-polymer films of interest to the automotive coatings industry. Outreach programs including a second cable TV show on polymers, demonstrations at public and private elementary schools as well as high school teacher training will continue as will training of undergraduate students.

Engineering - Materials Science (57)
Based on knowledge and skills developed in a previous CCLI grant we intend to develop CD-ROM based tutorials on functional materials. These CD-ROM based tutorials are designed, using a blackboard analogy, to support important classes of functional materials that are currently missing from introductory material science curricula. The tutorials will be contained on CD-ROMs that will receive international distribution. They, along with an included interactive Glossary and an Animation/Video player will be available for
instructors who wish to use them to support traditional lecture courses. The tutorials, along with the textbook being written to accompany them, could be used in a number of other learning situations, including distance learning, continuing education, and courses at institutions that do not have an engineering curriculum. The topics covered will include dielectric, piezoelectric, ferroelectric, magnetostrictive, and optical properties of materials. In this project we plan to create a new set of interactive, self-paced, multimedia tutorials for a new sophomore engineering course being developed at the University of Pennsylvania. The subject matter will be structured using a case study approach. Our new tutorials are designed to enhance student learning before a lecture is given. The material in these tutorials will be used to introduce students to specific materials concepts that they will be tested on before the lecture. We plan to use these materials in conjunction with a textbook. Our long range goal is to create a collection of online instructional materials that serve as the core for a one semester freshman level course.

TECHNICAL SUMMARY:

The proposed research on "Regulation of Polymer Blend Morphology Using
Nanospheres and Nanorods, "aims to understand how phase separation in polymer blend
films affects the dispersion of nanoparticles (NP) and how NP affect phase evolution,
wetting and film stability. Whereas prior studies focus on neat blends, the current study
will investigate how particle characteristics, in particular, surface chemistry and shape,
influence how NP disperse and organize in a multi-phase morphology. Nanospheres of
silica and nanorods of CdSe will be investigated. To control their location, NP are
functionalized by acid-groups, neutral brushes, and attractive brushes. By tuning the
surface properties, which control partitioning and organization, NP can be driven into one
domain or towards the interface between phases. The location of NP dictates film
characteristics including wetting layer growth rate, mprphology, phase evolution, and
film stability. By controlling the location of NP, a new route for engineering phase size is
expected from these systematic studies. For example, stable biocontinuous structures can
be produced by NP "jamming" resulting in highly efficient photovoltaic devices. The
proposed research requires a palette of complementary depth and lateral profiling
techniques including ion beam etching combined with scanning electron microscopy.

NON-TECHNICAL SUMMARY:

Polymer nanocomposites (PNC) are foundin everyday materials such as tires and
golfballs as well as high technology devices for energy conversion and sensor
applications. PNC are examples of nano-based materials, which are driving the
revolution in nanotechnology. This exploding field has received worldwide investments
totaling $8 billion in 2004 with an anticipated impact of $2.6 trillion by 2014. Although
highly versatile and widely used, a fundamental understanding of PNC is lacking and
basic science is necessary to produce PNC based devises that are reliable, efficient and
economical.

During the past 3.5 years, this NSF project has provided research training for 25
engineering undergraduates (10 females) and 6 high school teaching (2 female, 2
minority). Two of these have received NSF Graduate Fellowships. Lectures about
polymer science to teachers in the Philadelphia School District has lead to great
enthusiasm about developing laboratories for a Science Van that will reach out to
underrepresented nimorites in middle school. With University encouragement, the
Science Van project is in the planning stages. International collaborations with scientists
from the United Kingdom and the Czech Republic will provide students with a better
understanding about research in these countries.

TECHNICAL SUMMARY

The aim of the proposed research on ?Nanorod Assembly in Polymeric Matrices? is to understand the fundamental principles that drive nanorod assembly when spatially confined. An underlying theme is controlling the location, alignment and packing of nanorods to optimize targeted properties. The work to be undertaken during this project involves
(1) orienting gold nanorods in homopolymer thin films and lamellar block copolymer films that confine the nanorods, and measuring their polarization dependent optical properties;
(2) applying thermodynamic principles to design systems that incorporate and align gold nanorods within cylindrical domains of block copolymers, and then studying nanorod induced phase transformations in block copolymer morphologies; and
(3) investigating unique nanorods including TiO2, silica with a gold nanoshell and Janus nanorod systems to explore how rod diameter, surface functionality, and biphasic surfaces direct the location of nanorods in block copolymers.
A successful outcome of the proposed research will be precise control over assembly of functional nanorods in polymer films using spatial confinement. As a proof of concept, a nanorod/polymer device will be fabricated and its polarization-dependent optical properties tested to demonstrate that these coating can be used as color polarizing filters.

NON-TECHNICAL SUMMARY

Polymer nanocomposites (PNCs) are utilized in applications ranging from sports (golf balls) to transportation (tires) because they combine materials with synergistic properties. Presently, PNCs are attracting interest for information storage as well as electronic and energy applications. The proposed research will provide scientists with the rules for selecting the materials that will lead to optimum efficiency in PNCs. The broader impacts include laboratory experience for middle and high school students, high school teachers and undergraduates including those from underrepresented groups. An annual science day for middle school students (6th ? 8th grade) will continue at the University of Pennsylvania. In addition, female elementary school students are introduced to a summer camp called Girls in Engineering Math & Science Camp (GEMS). A successful partnership with Central High School (CHS) in Philadelphia that has already resulted in a new innovative Materials Science course will continue. Future plans include extending the course from one to two sections, developing laboratories, exposing students to new characterization tools, and facilitating joint research projects. The first materials science textbook aimed at high school students is also planned. Because CHS draws academically talented, multicultural and diverse (32% African American, 5% Latino, 50% female) students, this partnership will have a profound and lasting impact on the scientific and technological literacy of underrepresented groups.

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:
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:
This Partnership in Research and Education (PIRE) project addresses critical research challenges for the development of Active Coating Technologies (ACTs) through an international research and educational platform with an aim to transform the human habitat and our ability to respond to disasters. These ACTs will generate fundamental scientific understanding that enables the design of novel materials and properties for the robust collection and purification of water, elimination/reduction of disease transmission, and efficient generation and storage of energy, and hence, will address societal needs that have high relevance for the world and the U.S. To this aim, the University of Pennsylvania has formed an international partnership with fourteen collaborators from six institutions within the Grenoble Innovation for Advanced New Technologies (GIANT) in Grenoble, France. The collaboration with Giant provides the complementary expertise and resources critical for the research. The domestic partners, namely, Alabama State University, Villanova University and Bryn Mawr College further increase the research depth and diversity of participants, who will take part in every aspect of the project including research and education at GIANT. Through the planned research programs every summer, the US team consisting of a post doc, an early career faculty, and graduate and undergraduate students from these domestic institutions and UPenn, will gain invaluable international research experiences at Grenoble. Other important educational components include industrial internships at Salvoy, a world leader in the area, as well as workshops to develop broader career skills, training for the communication of technical information, and the opportunity to innovate on a prototype "Relief Tent" that will showcase ACT research. The research will address fundamental and up-to-now unsolved, materials-related scientific problems that will be applicable to engineering better human habitats and emergency response structures. The integrated research and educational components of the project will contribute to preparing a globally-engaged science and engineering workforce and a new cadre of US scientists poised to be international scientific leaders.

Part 2:
To enable coatings that transform the human habitat, each ACT utilizes the versatility afforded by polymers, nanoparticles and their mixtures to create coatings with tailored chemistry, surface texture and function. ACT 1 (water management) seeks to understand how the size, geometry, and surface energy of hierarchically structured coatings influence wetting and water transport. GIANT adds expertise in photoreactive nanomaterials that, when combined with Penn's structured coatings, open new opportunities to manage water. US scientists can investigate wetting of structured coatings using micro beam x-ray scattering tools at GIANT. ACT 2 (suppression of disease transmission) will relate the mechanics and texture of nanobilayer and layer-by-layer coatings to bacteria adhesion and proliferation. GIANT's expertise in synthesis and visualization of biomacromolecules is critical for understanding how bacteria interact with novel surfaces. ACT 3 (energy conversion and storage) will design multilayered coatings to efficiently collect and convert light using textured surfaces from ACT 1 in combination with unique nanoparticles. These photovoltaic cells will be coupled with solid polymer electrolytes designed with fast ion pathways for next generation lithium ion batteries. GIANT's expertise in interrogating energy materials in-situ and in-operando is particularly unique. Five unifying principles and methods integrate the ACTs, including commonality of materials and approaches, the unifying role of theory and simulation, a need for mechanical characterization and robustness, novel methods for structure/property studies at GIANT, and the translation of basic research into applications in collaboration with industry.

NON-TECHNICAL SUMMARY:

To promote the progress of polymer science, this project is focused on polymer nanocomposites. Because they underlie so many applications, polymer-nanocomposite research impacts and improves technologies ranging from complex devices, such as energy producing solar cells, to everyday materials, such as lighter packaging. The fundamental issues that the project seeks to address are those that govern the assembly of anisotropic particles in block copolymers. Specifically, the project will produce vertically-oriented, anisotropic particles with controlled regular separations, and in so doing will advance understanding of nanorods and nanoplates in polymeric materials having special geometries such as nanocylinders in a matrix or alternating nanosheets. The resulting insights about how to self-assemble vertically oriented nanoparticles will enable the scientific community to explore a variety of anisotropic properties including molecular, electrical, and thermal transport. A successful outcome of the proposed research will be precise control over the vertical orientation and lateral spacing of nanorods and nanoplates in polymer nanocomposite films, which have potential benefits to society in areas of nanofiltration, sensing, barrier coatings and lighting. Besides producing a well educated, scientifically skilled work force, the integration of research and education benefits society at several levels. Besides graduate education, undergraduates from the US and abroad as well as local Philadelphia high school participants will benefit from research and mentoring. To reach a broad audience, researchers will participate annually in Nanoday@Penn and Philly Materials Day, which attract over 200 high school students and 2000 attendees, respectively. Furthermore, the annual Teachers Materials Science Workshop will continue as well as a unique partnership with Central High School, Philadelphia, which exposes a large minority student population to opportunities in STEM fields.



TECHNICAL SUMMARY:

The thermodynamic and dynamic principles that control vertical alignment of nanorods and nanoplates in block copolymer (BCP) films will be investigated. Anisotropic particles will be grafted with polymer brushes to control their interactions with other particles and BCP. Research objectives are to:
(1) Vertically align nanorods in perpendicular cylindrical domains of block copolymers. Metallic, nanophosphor and semiconducting nanorods will be investigated in poly(styrene-b-2-vinyl pyridine) (PS-b-P2VP) and P2VP films. The effect of nanorod diameter and length on vertical orientation is of particular interest, as well as using binary mixtures of nanorods to direct them to specific microdomains.
(2) Vertically align nanoplates in perpendicular lamella domains of block copolymers. Graphene oxide, nanophosphor and laponite nanoplates will be investigated in poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and PS films.
(3) Investigate the dynamics of nanorod assembly in homopolymer and block copolymer films during solvent annealing. Single particle tracking will be used to measure nanorod mobility. Field theoretic simulations modified to include dynamics will guide experiments and provide insight into the balance between thermodynamics and dynamics that differentiates the final morphology.
The research leverages new and continuing collaborations to create novel particle-polymer assemblies, perform in situ characterization, and model vertically aligned polymer nanocomposites. Specifically, dispersion will be studied as a function of particle shape, size and surface chemistry, film thickness and interface interactions, and BCP composition and size. Three-dimensional field theoretic simulations will guide the choice of experimental parameters and provide a thermodynamic framework for understanding the interplay between particle and BCP orientation. BCP morphology will be determined by TEM, AFM and SAXS, particle location by TEM, FIB-SEM and depth profiling by RBS. GISAXS will be used to follow in situ structural evolution during solvent annealing. Optical properties will be characterized by UV-vis spectroscopy. This research benefits from unfunded collaborations with Sandia National Laboratories and the Advanced Light Source.

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.