Gregory B. McKenna - US grants

Novel experiments involving relative humidity-jumps (RH-jump) and carbon dioxide pressure-jumps (PCO2-jump) will be performed to investigate the structural recovery and physical aging responses of polymers subjected to rapid changes in plasticizing environment and chemical activity. The effects of PH or PCO2-jumps will be compared quantitatively to those induced by temperature-jumps. The comparisons will test the underlying hypothesis that changes in plasticizer content are quantitatively similar to changes in temperature for glass-changes in plasticizer content are quantitatively similar to changes in temperature for glass-forming systems. The classic TNM-KAHR models of aging and structural recovery will be extended to include plasticizer effects and compared quantitatively with the experimental data.

Modern uses of plastics demand that they show dimensional stability and moisture resistance for both short and long time durations. Electronic, automotive and infrastructure applications demand increasingly sophisticated data and model of the impact of plasticizing molecules such as water and carbon dioxide on the performance of polymers. The proposed work may provide unique and fundamental data that tests the validity of models used to describe the mechanical and dimensional behavior of plastics in such environments.

The objectives of this Product Realization and Environmental Manufacturing Innovative Systems (PREMISE) Exploratory Research project are: (1) To conduct exploratory research into the feasibility of an alternative PCB recycling process based on cryogenic decomposition of the PCBs; (2) To establish an interdisciplinary research team that can develop a long-term collaboration that builds on the understanding developed in this project; (3) To evaluate the proposed recycling process against traditional PCB recycling processes in terms of recycle rate economics, energy consumption, and environmental performance; and (4) To examine the feasibility of reusing plastics in the proposed recycling process.

The proposed recycling process is cryogenic decomposition of the PCBs. The process takes advantage of the fact that at very low temperatures, polymeric materials become highly brittle. In addition, the residual stresses set-up in the PCB resins due to thermal expansion mismatch between the polymers and other materials on the PCB is expected to lead to a better separation than might otherwise be possible simply due to the embrittlement of the plastics. Actual laboratory experiments will be performed using a cryogenic test system.

Wide diffusion of electronic equipment and shortening of product lifecycles have caused a serious problem: how to deal with large quantities of end-of-life or obsolete electronic equipment. While there are various technical challenges for electronic product recovery and recycling, this research focuses on printed circuit boards (PCBs) or printed wiring boards (PWBs). PCBs are primary components in many electronic products built for both military and commercial applications. Due to their complex construction and the consequent complicated mixture of materials, PCB recycling presents a serious challenge to today's industry. The rich content of precious metals provides a strong economic justification for materials recovery and recycling. On the other hand, large amounts of toxic components and fiber-reinforced polymers create difficulties for recycling and adverse environmental impact.

The discovery of anomalous volume recovery in polymer glasses subjected to plasticizer-jumps through the glass transition will be explored using three new classes of experiment. First, the kinetics of mass absorption during structural recovery will be investigated. Second, the first enthalpy recovery experiments after plasticizer-jumps will be performed to determine if the observed volume anomalies are also found in the enthalpy part of the glassy structure. This will require development of a unique pressure cell for the Calvet calorimeter in the laboratories of the PI. Third, a non-resonant dielectric hole burning spectroscopy (NSHB) technique will be developed to establish how dynamic heterogeneity of the plasticizer-jump and T-jump created glasses compares. The experimental results will be interpreted within the energy landscape paradigm for glass-forming materials. The work will provide the first complete set of data that constructs the full range of macroscopic variables (volume, enthalpy and concentration) and relates them to a measure of the microscopic nature of the material (NSHB) during the evolution of glassy structure or physical aging. Finally, the development of the NSHB capabilities at Texas Tech University will be the first such apparatus in the United States.
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The graduate students and post-doctoral researcher will perform the proposed research under the direct supervision of the PI. The proposed work is expected to provide excellent training for the graduate student and post-doctoral associate in cutting edge research. As part of their training, the graduate student and post-doc will attend and present their research results at national or regional meetings. In addition to providing good training for students, the results of the project will be incorporated to the extent feasible in both undergraduate and graduate courses taught by the PI. Because the research is interdisciplinary, containing multiple aspects of polymer materials science (structural recovery and plasticization of glass forming materials) and calorimetry as well as fundamental condensed matter physics (non-resonant spectral hole burning) the work provides a rare educational opportunity for the graduate student and post-doc. They will be expected to be familiar with all aspects of the program. In addition, the work involves two significant instrument design and construction tasks (pressure vessel for calorimeter and dielectric NSHB apparatus) that are important in the education of experimental scientists.
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This NIRT award is being funded by the Polymers Program of the Division of Materials Research and the Interfacial, Transport and Thermodynamics Program of the Division of Chemical and Transport Systems. The work is aimed at understanding how spatially dynamic heterogeneity in polymeric and small molecule glass formers is influenced by confinement at the nanoscale, and how this in turn, influences the relaxation of molecular and thermodynamic properties. Dynamic heterogeneity will be systematically probed using fluorescent probe studies and solvation dynamics in nanoconfined materials as a function of confinement size. In addition, volume and enthalpy relaxation will be studied as a function of confinement with the specific aim of examining whether or not dynamic heterogeneity influences the relaxation of these properties and whether or not it is the cause of the divergence of times required to reach equilibrium. Nanoconfinement will include "soft" confinement of low molecular weight glass-formers in crosslinked rubber, "rigid" confinement of both low molecular weight glass-formers and polystyrene in nanoporous matrices, and confinement of polystyrene to ultrathin films. In addition, the macroscopic and molecular relaxation behavior of freeze-dried polystyrene glasses will be examined. The work will include many novel measurements that have not been performed previously and is anticipated to lead to an understanding of how dynamic heterogeneity is influenced by confinement, and more generally, the importance of dynamic heterogeneity on the relaxation of macroscopic properties near Tg.
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The work will provide a better understanding of the behavior of materials near their glass temperatures at the meso- or nanometer scale and is important for the ultimate usefulness and function of materials in, for example, nanocomposites and nanoelectronics applications. The program will also provide excellent training for the graduate students and post-doctoral researchers and high school students. Efforts will be made to include undergraduate researchers and high school students. Efforts will be made to include women and underrepresented minorities through special recruiting efforts at women's and minority colleges in the Texas and southwest region. In addition, an effort will be made to include undergraduate students who participate in the TTU McNair Scholars Program for first generation college students (often minorities). The work will be broadly disseminated within the scientific community by presentation at national forums and publication in both proceedings conferences and archival journals. The results of the project will also be incorporated to the extent feasible in both undergraduate and graduate courses taught by the respective PIs.
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The behavior of materials at the nanoscale is a matter of great importance due to their use in applications as diverse as particles for reinforcement of polymer composites to low k dielectric applications in micro/nano electronics. It has been widely postulated that the surface properties often dominate nanometer size materials and their interactions. In the present work, we will build upon novel nanosphere embedment experiments and develop novel nanorod embedment methods to determine the surface mechanical properties of a series of polymeric materials. The work develops atomic force microscopy methods to obtain materials data for polymers from the glassy to the rubbery states. In addition, both computational and analytical work will be used so that the time dependent modulus and Poisson's ratio can be obtained. Finally, in the proposed work, students from Texas Tech Univesity and Oklahoma State University will work in collaboration with their opposites at the relevant institutions.

TECHNICAL SUMMARY:
The behavior of ultrathin polymer films below the glass temperature is not well understood despite its importance in micro- and nano-scale engineering of polymeric structures. Research is to be performed to understand the physical aging response of ultrathin polymer films as a function of temperature and of film thickness for several different polymeric materials. The approach includes making measurements using a novel bubble inflation method of measurement developed in the labs of Texas Tech University (TTU) to perform equi-biaxial and nonequibiaxial deformation geometries. These will be the first physical aging measurements on freely standing ultrathin polymer films. In addition, the work adapts a unique dewetting method in order to perform physical aging experiments below but near to the glass transition for polystyrene films. These dewetting experiments provide completely different film constraint than do the nanobubbles and comparison of the results between the two methods provides a strong challenge to both techniques that are nominally similar, but in the literature have given different and, to-date, unreconciled results. The work also directly probes the dynamics of confined polymers and addresses unreconciled mesoscale vs. nanoscale aging responses that have been reported in the literature. Finally, material failure at the nanometer size scale has been little investigated and the TTU bubble inflation technique will be exploited to examine the rupture behavior of ultrathin polymer films.

NON-TECHNICAL SUMMARY:
Polymers are widely used in micro-, now becoming nano-, electronics applications. Because it is observed that polymer material properties change when feature sizes are smaller than 100 nm, this makes design and prediction of the polymer behavior at the nanoscale difficult for the electronics developer and designer. Similar effects occur in nanocomposites and other futuristic applications of polymers at the nanoscale. The present work is designed to put two different methods of measurement of nanoscale properties into direct confrontation in order to reconcile differences of nanoscale properties that have been reported in the literature. One method is the TTU nanobubble inflation test developed by the principal investigator in Lubbock, TX and the other is a nanofilm dewetting method developed by researchers at the E.S.P.C.I. in Paris, FR. The outcome of the work will provide highly important insights into the reasons for similarities and differences in reported material behaviors at the nanometer size scale. In addition to the technical work the research is to be carried out by graduate students in the Chemical Engineering Laboratories at TTU and will provide opportunities for two students to be trained and to achieve the bulk the research education to obtain their Ph.D. degrees. Finally, the results of the research will be widely disseminated through journal publication and presentations by the PI and students at national meetings.

Relaxations and diffusion play important roles in many branches of science, technology and engineering. Relaxation phenomena occur in physics, biophysics, chemistry, materials science, metallurgy, rheology, glass sciences, polymer (biopolymer) physics and engineering, fiber optics, opto-electronics and electronics. It is the primary concern in basic physics as well as in very practical applications. The 6th International Discussion Meeting on Relaxations in Complex Systems (IDMRCS) is the premier international meeting dealing with the above subjects. The funding provided in this grant by NSF will support U.S. Ph.D. students, post-doctoral fellows and junior faculty to attend the meeting and to participate through oral and poster presentations. The IDMRCS forum provides these young researchers with the opportunity to interact with internationally known researchers, which is important for career development. In addition, benefits to all supported participants can be expected from cross-field fertilisation among the multiple disciplines represented at the 6th IDMRCS.

The proposed work expands a novel nanosphere embedment experiment to the measure of the yield behavior of surfaces. The method also promises a novel, high spatial resolution method to map the surface mechanical/viscoelastic properties of polymeric and composite materials. The work builds on CMMI supported work in which it was found that nanoparticles smaller than a certain size sink into the surface and become fully engulfed by the polymer. Analysis suggests that the nanoparticles are fully engulfed only when the yield strength of the polymer surface is exceeded, which opens a route to measure the surface yield strength, as well as other properties at depths on the order of 20 nm. If successful, it will also lead to a technique to provide a surface property map of mechanical, including modulus, yield strength, and viscoelastic properties of polymer surfaces using embedment of a monolayer of clustered nanoparticles. The work also involves numerical analysis of the embedment process to include appropriate elastic-plastic, viscoplastic or viscoelastic constitutive models to extract nonlinear material properties.

By its interdisciplinary nature, the project provides a rare training opportunity for students in both chemical engineering and mechanical engineering to step into research in the thermo-mechanical behavior of polymers at the nanoscale. In addition, it is a collaborative project in which the graduate students will have the opportunity to interact with students from another institution and work with them. Part of the work in this project will be divided into smaller projects for use in term projects in courses such as viscoelasticity and polymer physics offered by the PIs in this project. All significant results will be published in journals to disseminate the findings. It is anticipated that the graduate students working on the project will present their findings at national/international conferences.

TECHNICAL SUMMARY
The present EAGER proposal is a collaborative effort among four U.S. institutions (Texas Tech University, Massachusetts Institute of Technology, Cornell University and Illinois Institute of Technology) and one foreign institution (Technical University of Eindhoven in the Netherlands). The technical goal is to detail the limits of validity of reported flow instabilities in entangled polymer melts and solutions. The flow of polymer fluids in conventional rheometers is generally assumed to be nearly viscometric and stable. When instability or secondary flows occur, it is generally acknowledged that such measurements cannot be used to determine material parameters. This is important in any experimental challenge to, e.g., a molecular theory such as the reptation model of polymer chain dynamics. According to a new set of results that has appeared in the literature, the basis for the experimental verification of the reptation theory is, in fact, based upon experiments from non-homogeneous flows. If this is true, it changes the paradigm for the dynamics of polymer fluids in nonlinear deformation regimes. However, much of the community is skeptical of these results and there are multiple reports in the literature of contradictory results. Hence, it is paramount to establish the range of both flow conditions (rate and magnitude of shear) and material parameters (e.g., entanglement density) for which such observations are correct and the range where errors may have been made and to do so in a way that the results are accepted by the community at large. The present proposal is constructed to do this. The groups collaborate through an innovative set of student teams having one representative from at least three institutions for all experiments. Success of the work is defined as achieving an interlaboratory consensus of the flow profiles in polymer solutions and melts. Objectivity is developed by having multiple labs with multiple students performing each type of experiment so that ?neutral eyes? have the major influence in the examination of experimental data. Three types of experiments will be performed, each will be performed in at least two labs and one will be performed in all labs. The experiments are particle tracking velocimetry, confocal microscopy fluorescence dye velocimetry and macroscopic parallel plate-cone and plate comparisons of nonlinear properties.


NON-TECHNICAL SUMMARY
The major paradigm of polymer rheology is the reptation theory. Because reptation is the present paradigm for polymer flow, it is widely used in industrial settings to understand how to change molecular parameters in making advances in polymer processing. There are several offshoots to reptation theory as well that are beginning to be adopted in industry. Yet, recent work has appeared that is being strongly advanced to challenge this paradigm. It has reported strong flow instabilities which would invalidate the reptation theory in the regime relevant to polymer processing. Hence establishing whether or not the reported flow instabilities occur in industrially relevant ranges of flow rates is important. The present proposal brings together collaborators from four U.S. and one foreign university (Texas Tech University, Massachusetts Institute of Technology, Cornell University and Illinois Institute of Technology,Technical University of Eindhoven in the Netherlands) with the goal of establishing the range of experimental conditions where such flow instabilities occur. Because the general community has not uniformly accepted the reported results, the present collaboration will provide both repeat (for validation purposes) and novel experimentation to establish the range over which the reported results are relevant and how they impact the current understanding of polymer nonlinear rheology and its basis in molecular (reptation) theory. The present proposal does this. In addition, because of its structure as a collaborative work through an innovative set of student teams having one representative from at least three institutions for all experiments. All students will participate in the collaboration with the Technical University of Eindhoven.

1133279
PI: McKenna

A fundamental investigation of the aging, dynamics and rheology of thermo-sensitive colloidal dispersions near to the glass and jamming transitions is proposed. The investigation brings the PI's expertise and experience in glassy physics, aging and rheology to bear in a novel and transformative approach to the understanding of colloidal glasses. While the relevant behaviors have been extensively studied in experiments in which the suspension has been subjected to shearing deformations at a fixed concentration, there are very few works in which the response is followed after rapid, constant volume concentration changes. The advent of thermosensitive particles, such as the poly(n isopropyl acrylamide) (PNIPAAM) systems that swell and deswell in water with temperature variation have changed this situation and offer the promise of an experimental route to investigate the glass-like behavior, and specifically, the structural recovery based behavior of colloidal dispersions near to the glass or jamming transition. In addition to the thermo-sensitivity of these particles they are also barosensitive, i.e., application of pressure can change the particle swelling, hence isotropic stresses (pressure changes) impose concentration changes. The proposed research offers a transformational outcome as it promises to validate or invalidate a frequent underlying hypothesis in colloid physics that the colloidal glass is a model system for molecular glasses. Furthermore, independent of the specific outcome of the hypothesis validation, highly novel experimental results will be obtained that are relevant to the behavior of colloidal systems in the range of concentrations that are related to glass-like or jamming behaviors. It is specifically proposed to perform the temperature- and pressure-jump experiments using responsive PNIPAAM and PS/PNIPAAM core/shell particles to cross the concentration phase boundary (liquid-to- glass) along a two different paths (T and P) using diffusing wave light scattering to probe the aging dynamics of the non-equilibrium colloids. These experiments will provide the first extensive cataloguing of the structural recovery behavior of colloidal glasses in the Kovacs catalogued signatures of structural recovery, viz., intrinsic isotherm, asymmetry of approach, and memory effect. The results will provide insights to effects of particle "hardness" or "softness?"and colloidal glass fragility on the aging dynamics. Classical physical aging experiments using torsional rheometry will also be performed in the thermosensitive response regime following the methods originally proposed by Struik for molecular glasses. While there is much work in the literature that addresses the dynamics of concentrated colloidal systems in the context of the equilibrium dynamics and their divergence with concentration, the present work is transformative in that it applies concepts related to the non equilibrium behavior of molecular glasses explicitly in concentration-jumps induced by the thermo- and baro response properties of the PNIPAAM-based colloids. Thus, new understanding of the dynamics of colloidal systems will be created.

The project will provide research training and experience to students at all levels in the methods of characterizing and synthesis of colloids and the physics of glassy colloids. The PI and his graduate students will also be involved in outreach activities of middle-school girls.

In this project funded by the Chemical Structure, Dynamics, and Mechanisms Program of the Chemistry Division, Sindee L. Simon and Gregory B. McKenna of Texas Tech University will investigate the relaxation dynamics in selenide-based chalcogenide glasses using calorimetry, dynamic heat spectroscopy, shear and bulk rheology, and nanorheology. Three important scientific issues are addressed: the stability of the glasses with respect to aging near and in the intermediate phase region, the effects of nanoconfinement and pressure on the dynamics, and the origin of the unusual mechanical stiffening of ultrathin films. Of particular interest is the measurement of enthalpy recovery and creep during aging as a function of composition, temperature, and aging time aimed at a more complete understanding of the composition dependence of the stability of these glasses. Broader impacts include training of two graduate students, incorporation of new material into courses taught by the PIs, and outreach to young students, from fifth through eleventh grades, through a "Super Saturdays" enrichment program for grade-school children and a summer "Science - It's a Girl Thing" program for junior-high and high-school girls.

The physical and chemical stability of chalcogenide glasses are important in many of their potential applications, including as memory devices, optical waveguides, and solar cells. By increasing understanding the Boolchand intermediate phase, which has enhanced stability, the results are anticipated to facilitate synthesis of stable chalcogenide glasses for such applications.

TECHNICAL SUMMARY:

The work is a fundamental investigation of the viscoelastic response of ultrathin polymer films in two different conditions. The work will compare, contrast, and seek origins of differences between the nanobubble inflation method developed by the PI at Texas Tech University and the liquid dewetting method developed by Bodiguel and Fretigny in Paris (which are the only methods currently available to measure the viscoelastic response of unsupported films). The two techniques had shown substantial differences in glass transition temperatures as functions of film thickness. The two methods differ in that one measures films with free surfaces and the other measures films floating on a mobile substrate. The planned research will examine the effects of changing substrate, molecular weight, and molecular architecture on the viscoelastic properties of ultrathin polymer films. It will explore the hypothesis that the relevant differences in confinement behavior are related to very subtle differences in surface energy/surface interactions and will provide new data focused on the understanding of how surfaces and interfaces impact the dynamics of polymers confined to the nanometer size scale.

NON-TECHNICAL SUMMARY:

The dramatic influence of nanoscale confinement on material behavior is exemplified by the response of ultrathin polymer films that show tremendous property changes, for example, in freely suspended films having nanometer thicknesses. Yet the origins of these changes are not yet elucidated. The present work probes these changes using two novel nanomechanical test methods. The work compares and contrasts mechanical properties of a series of polymers having different molecular characteristics. In addition, because there is such a strong apparent effect of the environment seen by the film surface, the work probes the behavior of the ultrathin polymer films exposed to liquids having different properties. The research provides new data in the understanding of how surfaces and interfaces impact the mechanics of polymers confined to the nanometer size scale. The project also has an important component that trains graduate students and, in addition to their scientific training, involves them in a STEM outreach program to young girls through the "Science: It's a Girl Thing" Program at Texas Tech University.

TECHNICAL AND NON-TECHNICAL ABSTRACT
Funds in the amount of $4,000 are requested to provide for partial support (travel, registration) for approximately 10 junior faculty, post-docs and students to attend the day-and-a-half TDPOLY Short Course on ?Polymer Glasses? to be held Feb. 28-March 1, 2015) under the auspices of the Division of Polymer Physics (DPOLY) of the American Physical Society (APS) in conjunction with the Society?s March 2-6, 2015 meeting in San Antonio, Texas. The purpose of the short course is to provide an advanced survey of the present state of knowledge of polymer glasses. It is designed for advanced graduate students, faculty and industrial researchers who are working in the general area of polymer physics and who have a need to deepen their understanding of glass-forming polymers and their extensive applications.

CBET - 1506072 McKenna, Gregory B.
CBET - 1506079 Zia, Roseanna N.

Colloids are dispersions of particles in a liquid, such as water, and the particles are so small that they do not separate for very long times. The materials are widely used in commercial products such as paints and inks. They are also believed to be a good model materials for glasses. The present work is a collaborative study that combines experiment and large scale computer simulations that will provide novel scientific understanding of the behavior of colloidal glasses and comparisons will be made with knowledge from the literature concerning molecular glasses in similar conditions. Graduate and high school students will participate in the research activities at both PIs' institutions.

Understanding dynamical arrest in complex matter is a great challenge in soft matter science. Most study of colloidal systems near jamming assumes parity with corresponding behavior in molecular glasses. Yet, recent studies reveal non-equilibrium responses in colloids that differ qualitatively from glassy dynamics as monitored via the Kovacs signatures, viz., the intrinsic isotherm, the asymmetry of approach, and the memory effect. The proposed study will illuminate the structural underpinnings of such differences through a novel combination of experiment and dynamic simulation. The structure and dynamics will be determined in experiments analogous to the Kovacs experiments for molecular glass-forming systems. Here stimulus-responsive particles will change diameter at constant number density to create concentration-jump conditions to mimic the temperature-jumps of the Kovacs signature experiments. Concurrent simulations will effect similar conditions in silico. Experiment and simulation will inform and validate each other and the joint interrogation of the colloid dynamics near to the jamming transition will potentially create a transformative understanding of arrested states in soft matter. In a broader sense, this is a collaboration of two very different PIs. One is an expert in the experimental physics of molecular glasses, especially aging. The other is an expert in large scale computer simulation, with emphasis on colloidal systems. The result provides unique cross-disciplinary training to graduate students in both computational and experimental physics, deepening their knowledge of the fundamentals of dynamics and aging of molecular and colloidal glasses. Further, women and under-represented minorities will play a central role as undergraduate and graduate researchers.

NON-TECHNICAL SUMMARY:

The technological infrastructure that provides science and engineering solutions to the rapidly growing nanotechnology area is of considerable national interest. The present work addresses fundamentals of the nanoconfinement behavior of materials that form the basis of the relevant enabling technologies. One important set of problems addressed relates to the engineering properties (such as stiffness and yield strength) of nanometer-thick films that are in freely standing form and, consequently, cannot be readily measured. The only method available for making such measurements in such materials is a bubble-inflation method developed in the PI's laboratory that allows testing of extremely small quantities of material, especially nanometer-thin polymer films. The work investigates the engineering properties of freely standing polymer films deep in the glassy state with particular emphasis on yield behavior. These studies will be the first to provide film thickness and temperature dependence of yield in freely standing films. Also, in the freely standing films, a large enhancement in the material stiffness is observed and, recently, conflicting theoretical models of the stiffening behavior have appeared to explain the phenomenon. Such predictions are, of course important to nanomaterial design and use, and the present work will establish the range of validity of these theories. Molecular architecture effects will also be investigated. Finally, the nanobubble inflation experiment permits investigations of novel materials that were previously unachievable due to their extremely small quantities. In this case, the investigators will study ultrastable polymer glasses made by physical vapor deposition (PVD) and that can be made more stable than even a 20 million year old amber glass. This high stability allows the interrogation of a long-standing question whose resolution is fundamental to theories of glasses and, in particular, how to make long-term predictions of their behavior in applications to important areas such as advanced composites and adhesives.



TECHNICAL SUMMARY:

The behavior of ultrathin polymer films remains an intense area of investigation, but most studies have been limited to the case of substrate-supported films even though studies suggest much larger effects occur in the freely standing state. The present work tests three aspects of freely standing ultrathin films using the TTU bubble inflation method and takes advantage of the method's capability of making viscoelastic measurements on extremely small quantities of material to study the response of an ultrastable polymer glass made by physical vapor deposition (PVD). One important set of problems addressed relates to the engineering properties, such as modulus and yield strength of nanometer thick films that are in freely standing form and, consequently, not readily measured. The only method available for making such measurements in such materials is a bubble inflation method that allows testing of extremely small quantities of material, especially ultrathin or nano-metric polymer films. The work investigates the engineering properties of freely standing polymer films deep in the glassy state with particular emphasis on yield behavior. Also, in freely standing films, a large modulus enhancement is observed and, recently, conflicting theoretical models of the stiffening behavior have appeared to explain the phenomenon. Such predictions are, of course important to nanomaterial design and use and the present work will establish the range of validity of these theories. Branched polymers have been shown to exhibit different nanoscale behavior from linear counterparts upon confinement on a supporting layer and the TTU bubble inflation method will be used to examine the effects of branching and unentangled polymer chain length on the viscoelastic properties of freely standing ultrathin films. Finally, it remains controversial whether or not the dynamics (relaxation time or viscosity) in glass-forming liquids, including polymers, diverge at a finite temperature. The PI's group has now demonstrated the first PVD ultrastable polymer glass that can be used to determine the upper bound relaxation times in a fashion similar to prior work with a 20 million year old amber but over a larger "window" of temperatures because the PVD polymer has a fictive temperature at least 50 K below the glass transition temperature, and optimization of the PVD conditions offers the possibility of an even larger testing window. Should the experiment be successful, it will provide further experimental data that can challenge theories of the behavior of glass-forming systems.

PI: McKenna, Gregory B. / Schroeder, Charles / Anderson, Rae
Proposal Number: 1603943/ 1604038 / 1603925

The goal of this proposal is to explore the behavior of polymer molecules that form large rings, instead of the usual linear polymer molecules. Such polymers, an example of which can be the DNA molecule, behave in a different way than linear molecules when processed or when they flow in a solution, because there are no ends in the chains. Results of this work can lead to improved polymer materials, to understanding in detail the behavior of bio-molecules, and to new technologies for DNA sequencing.

Circular polymers are fascinating materials that have inspired polymer theorists and experimentalists for decades. The dynamics of circular chains differ fundamentally from their linear counterparts due to the absence of chain ends. Despite recent progress, however, the effects of circular topology on polymer dynamics remain a key unresolved problem in the field. In this proposal, the PIs are poised to make major progress in our understanding by preparing circular and linear DNA molecules that are monodisperse and of high topological purity. The assembled team has the expertise to synthesize and characterize circular and linear DNA, and will study the rheological behavior of these materials over a wider range of concentrations and molecular weights than previously achieved. A comprehensive approach is proposed that will include macroscopic and micro-rheology, single molecule polymer dynamics, and DNA synthesis, to provide new information regarding the dynamics of linear and circular DNA. Beyond providing a point of departure for understanding their circular counterparts, the parallel study of linear entangled DNA will provide unprecedented data using perfectly monodisperse DNA samples to directly test predictions from reptation theory, such as the cross-over to reptative behavior at extremely high entanglement densities. In addition to graduate student participation, educational activities are proposed in all three collaborating institutions, ranging from underrepresented minority student involvement at Texas Tech, to high school teacher engagement at Illinois and undergraduate student participation at the U of San Diego, a mainly undergraduate institution.

New processing methods will be developed to combat a major technological problem of many pharmaceuticals, namely that of stability. Pharmaceuticals that are in the molecularly-disordered, or amorphous, state are advantageous compared to molecularly-ordered, or crystalline, forms of the same drug because the amorphous material has higher solubility in water and higher bioavailability. Consequently, lower doses can be used, decreasing both cost and the probability of toxic side effects. However, amorphous pharmaceuticals are generally not stable and can crystallize, albeit slowly, from the amorphous state. The aim of this Grant Opportunity for Academic Liaison with Industry (GOALI) collaborative research project is to gain a fundamental understanding of crystallization from the amorphous state and to develop new processing strategies to make stable forms of amorphous pharmaceuticals. The results are anticipated to facilitate development of new amorphous drug formulations and to, thus, benefit the U.S. economy and society. The graduate students on the project will be trained in this multidisciplinary scientific research that involves manufacturing engineering, amorphous and crystal physics, and pharmaceutical science. The collaboration with the industrial partner will ensure commercial consideration and provide a unique and broad-perspective training opportunity for the students.

Fundamental knowledge related to amorphous pharmaceuticals will be pursued in this project. The crystallization or devitrification from the glassy state will be addressed using as a framework, the time-temperature-transformation diagram for crystallizing materials. The research is based on the hypothesis that one can create more stable amorphous pharmaceutical glasses if the nucleation nose of the diagram and the crystallization nose are both avoided, with the former occurring at shorter times. Flash scanning calorimetry will facilitate exploration of a wide range of very high cooling rates or short isothermal crystallization/nucleation times in order to establish the bounds of the potential for making specific compounds into stable glasses. Spray drying, vapor deposition, and melt extrusion methods will also be investigated as processing paths to create stable glassy pharmaceuticals. Crystallization kinetics from the glassy state will be studied by calorimetry, and the relationship to glassy dynamics, as obtained from dielectric spectroscopy and viscoelastic methods, will be established.

This award supports research to characterize the nonlinear viscoelastic behavior of glassy polymers. Understanding the long-term mechanical behavior of glassy polymers is critical for assurance of the durability of glassy polymers in their use as stand-alone materials, or as matrix materials for advanced composites, in applications that require low-density and high specific strength materials, such as in automotive, sports, and aerospace industries. This project will take steps to address the challenge from a fundamental perspective using a novel nonlinear fingerprinting methodology that promises to bring important advances for development of premier products, hence benefiting US industry and society. In the past, the fingerprinting methodology has been used to characterize polymeric fluids. This award extends the method to polymer glasses, both through novel experiments and through appropriate nonlinear constitutive modeling and validation. The graduate students on the project will be trained in this cutting edge research, which involves experimental and computational mechanics of time-dependent materials, glassy polymer physics, and structure-property relations for engineering polymers. The project will also leverage STEM outreach programs at both Texas Tech University and University of Texas Dallas to excite K-12 students about science and engineering.

Fundamental knowledge related to the nonlinear viscoelastic behavior of solid polymers will be pursued in this project. This requires a general scheme to classify the variety of observed behaviors and use these observations to challenge the relevant constitutive equations. The research will use the combined Large Amplitude Oscillatory Shear and Mechanical Spectral Hole Burning fingerprinting methodology to provide fingerprints of the nonlinear viscoelastic behavior of a series of glassy polymers and to challenge them against a set of nonlinear constitutive law predictions from several leading models from the literature. Not only will the work show that the method can be applied to glassy polymers, but by choosing to examine polymers with different degrees of heterogeneity, as estimated by the strength of the beta-relaxation, the method can differentiate among different types of nonlinear behavior and, in principle, determine how the details of the dynamic heterogeneity impacts the fingerprints and the constitutive model parameters. This provides an important advance in ideas of structure-property relations in the nonlinear mechanics of polymers. Furthermore, the work provides a critical evaluation of the fingerprinting paradigm, currently developed for shearing deformations in nonlinear fluids, by making measurements in non-volume preserving conditions, viz., tension and compression to develop material fingerprints as a function of said deformation geometries and comparing them to the shearing results.