Edwin L. Thomas, Ph.D. - US grants

Lactoperoxidase (LP), hydrogen peroxide (H2O2) and thiocyanate ion (SCN-) form a bacteriostatic system in human saliva. The oral "lactic-acid bacteria" release H2O2 as a by-product of carbohydrate metabolism. LP catalyzes the oxidation of SCN- by H2O2 to yield hypothiocyanite ion (OSCN-), which is in acid-base equilibrium with hypothiocyanous acid (HOSCN). HOSCN oxidizes essential sulfhydryl groups of bacterial enzymes and transport systems, resulting in inhibition of metabolism and growth. Certain bacteria such as S. mutans have a limited resistance to inhibition, due to their ability to rapidly reduce certain disulfide compounds to the sulfhydryl forms. These low-mol. wt. sulfhydryl compounds protect essential protein sulfhydryls by reacting with the inhibitor and reducing it back to SCN-. These studies will evaluate agents that may increase LP antimicrobial action in saliva: (1) by increasing the peroxide supply so as to overcome the limited resistance to inhibition, (2) by increasing the stability and/or reactivity of the inhibitor, and (3) by interfering with the activities responsible for resistance. The more promising agents will be studied with S. mutans, other oral streptococci, and streptococci that do not colonize the mouth as target microorganisms. Agents to be tested include amino sugars as substrates that result in increased H2O2 production, H2O2 and alkyl peroxides, glucose oxidase, plumbagan, iodide, sulfonamide compounds, cyanide, and inhibitors or competitive substrates of the activities involved in resistance. These studies will provide information about the interaction of the LP system with the bacteria that can survive and grow in the presence of this antimicrobial system. The studies should also provide a basis for evaluating the significance of the LP system in natural resistance to oral disease, (1) by developing methods to measure LP antimicrobial activity that could be used in the clinical environment, and (2) by identifying agents that can increase the efficacy or selectivity of antimicrobial action against oral pathogens. Such agents could then be used to compare the effect of the LP system in the normal population with the effect in a population receiving the agent.

Reaction injection molding (RIM) is a rapid process for producing large light weight plastic parts that are used for automobile and airplane parts among others. Low viscosity liquid reactants (monomers) are mixed and injected into a mold where they reach and form a solid crosslinked polymer product. The two feed streams impinge on each other at high velocity and thus achieve good mixing. Reaction proceeds as bulk copolymerization resulting in segmented block copolyers. The proposed research is aimed at elucidating the fundamental chemistry and physics involved in RIM. The PIs plan to carry out their work in six stages: (1) Model the mold filling and curing steps; (2) Study the chemistry of polyureas and polyurethanes; (3) Look at the role of phase separation during polymerization in the mold; (4) Study the effects of mixing in the mold (5) Obtain morphology measurements; and (6) Study the bubble motion and growth process in RIM due to injected nitrogen gas. The overall goal is to build a model for the RIM process. During the molding cycle the copolymers must grow into long chains and segregate nto hard and soft phases. The work in this project is the analysis of the combination of polymerization kinetics and phase separation dynamics within a flowing mixing, reacting and heat transferring system. The PIs are all very highly thought of and their laboratory is one of the best in the country for this work. The cooperation with industry provides an excellent input to help keep the project aimed in the proper direction. A three year Industry University Cooperative Research Grant is recommended at $154,682 for FY 86, $174,038 for FY 87, and $164,000 for FY 88.

Myeloperoxidase (MPO), hydrogen peroxide (H2O2), and chloride ion (C1-) form an antimicrobial system within phagolysosomes of neutrophils. In studies using purified MPO, antimicrobial activity was found to be modulated by certain nitrogen compounds (N-compounds). In studies on stimulated neutrophils, these N-compounds influenced the rate of neutrophil self-inactivation. The basis of these effects is MPO-catalyzed oxidation of C1- to hypochlorous acid (HOC1), which reacts with N-compounds to yield nitrogen-chlorine (N-C1) derivatives with differing antimicrobial and cytotoxic activities. The proposed studies will examine the interaction of isolated neutrophils with certain naturally occurring N-compounds that may mediate and regulate the oxidative toxicity of neutrophils in vivo. When stimulated neutrophils are studied in vitro, the major N-compounds available for reaction with HOC1 are ammonia (NH4+), taurine, and proteins that are secreted from the cytoplasmic granules. The reaction of HOC1 with NH4+ yields monochloramine (NH2C1), a lipophilic oxidizing agent with potent antimicrobial and cytotoxic activity. The role of NH2C1 in neutrophil oxidative toxicity will be studied with erythrocytes and bacteria as target cells. The reaction of HOC1 with taurine yields taurine-monochloramine (tauNHC1), a hydrophilic oxidizing agent with little or no toxicity. Formation and toxicity of tauNHC1 and related N-C1 derivatives will be studied under conditions that may promote toxicity: (a) when tauNHC1 is transported into the target-cell by a membrane transport system, and (b) when tauNHC1 reacts with NH4+ to yield NH2C1. NH4+-dependent toxicity will be studied with bacteria, erythrocytes and tumor cells as targets. Histamine is a naturally occurring N-compound that neutrophils encounter in high concentrations in vivo. The reaction of HOC1 with histamine yields histamine-monochloramine (hisNHC1), which has the unusual property of being either hydrophilic or lipophilic, depending on pH. Chlorination of histamine by stimulated neutrophils, the fate of hisNHC1, and the effect of hisNHC1 on neutrophil functions will be studied. The goal is to gain increased understanding of the regulation of neutrophil oxidative toxicity, so as to lead to new approaches to increasing resistance to infection while protecting normal tissues against oxidative attack.

This research deals with two areas of polymer materials research (1) phase transitions, morphology, and properties of block copolymers; and (2) high-resolution electron microscopy (HREM) of crystalline polymers. The first area involves the detailed study of neat linear and star diblock copolymers and block copolymer/homopolymer blends as concerns order-disorder transitions and order-order transitions. Emphasis will be placed on understanding the molecular parameters which govern phase morphology and stability. Both small and especially large-strain mechanical behavior of these model ordered microcomposites will be examined and related to the evolution of domain morphology with extent of deformation. The word in HREM will focus on understanding the details of chain packing in flexible chain-folded crystals particularly as regards regions where the chain arrangement reflects fundamental information on crystal growth (primary nucleus, twin boundaries, reentrant growth fronts). The main investigative techniques are transmission electron microscopy diffraction, small-angle x-ray scattering, digital image analysis, computer graphics of surfaces and mechanical testing. The goal of the research is to contribute to the basic understanding of structure-property relationships which can provide a basis for development of materials and improvement of their properties.

This study deals with the microstructures of block copolymer and block copolymer/homopolymer blend systems. Self-assembled neat diblock and diblock/homopolymer(s) structures will be formed from chains of various architecture, composition and molecular weight. Emphasis will be placed on novel processing so as to provide large single-crystal-like samples of various desired geometries. The evolution of the microdomain morphology during order-order phase transitions and during mechanical deformation along particular high symmetry directions will be quantitatively followed to obtain information on the fundamentals of phase transitions in block copolymer systems and on their large strain mechanical behavior. The main investigative techniques are roll casting, mechanical testing, optical microscopy, small-angle x-ray scattering, transmission electron microscopy, scanning electron microscopy, digital image analysis, and computer graphics of surfaces. The goal of the research is to contribute to the basic understanding of processing-structure-property relationships, which can provide a basis for development of polymeric materials with improved performance.

9705271 Thomas Liquid crystals hold great promise as materials in optical, barrier and structural applications. In this GOALI/Group Award, supported jointly by DMR and the MPS Office of Multidisciplinary Activities, the PIs will exploit the unique tandem interplay of domain formation and alignment in the block copolymer structure and self-organization of the mesophase by use of liquid crystal block-coil block copolymers and homopolymers in special applied processing fields. From their prior work, they have identified two general applications which will act as vehicles to exploit and test fundamental understanding of these tandem interactions: (1) to develop the knowledge and engineering expertise to produce flexible plastic liquid crystalline displays and switches and (2) to create new thermoplastic liquid crystalline polymer materials with layered structures for transparent, highly impermeable barrier film applications. To accomplish these goals they plan to exploit the interactions of microphase separation, liquid crystallinity and applied fields. A 3 year program is envisioned, with a team comprised of Superex Inc. and each university PI with 1 graduate student and 2 undergraduate researchers. Complimentary areas of expertise of the PIs will ensure a through approach to the investigation: Thomas, characterization and properties; Ober, synthesis and characterization; Muthukumar, theory and modeling. %%% Apart from the specific scientific and engineering objectives of this program, the PIs plan to use this inter- university focused research group collaboration to examine several new approaches to graduate and undergraduate education of the students connected with this program. Both graduate and undergraduate students will gain research experience outside the normal university training: graduate students will mentor undergraduates, and both groups will learn entrepreneurial skills through exchanges with our industrial partner and by taking business cou rses. Communication skills will be improved through joint seminars. Students from all three university groups will participate in special retreat-style meetings, traveling to a site chosen by the host univeristy. The location of all three universities in the Northeast makes such exchanges and visits very feasible. They will also encourage both the graduate and undergraduate students to carry out exchanges with other university teams. Each institution and research group carries with it a unique style and tradition that influences the way research is approached. By experiencing these different cultures, students at both levels (graduate and undergraduate) will benefit. The education approaches found to be most successful will be expanded at MIT, UMass and Cornell into other undergraduate programs. ***

9807591 Thomas This proposal describes a research program aimed at developing novel macromolecular materials for technological applications. The first area is traditional: morphology and mechanical properties; and the second is completely new: block copolymer photonic band gap (PBG) materials. Both areas depend critically on the ability to organize block copolymers into well ordered microdomain morphologies using composition, molecular architecture, and careful processing. Tailored self assembly into new microdomain structures such as the double gyroid tricontinuous structure in ABA triblocks is exemplary for understanding how the microdomain structure of a glassy continuous (polystyrene end blocks) and a rubber continuous (polyisoprene mid block) system evolves with increasing deformation and substantially recovers upon release of the applied load. The continued exploration of ABC terpolymers, both linear and miktoarm stars, will undoubtedly reveal additional new microdomain structures. The object is to gain an overall understanding of how composition, number of components and chain architecture govern the resultant structure of the intermaterial dividing surface of the periodic microdomains. In the second area, a new field will be explored, of potentially huge significance for block copolymer materials and their interesting topologically connected microdomains by using them in combination with high dielectric contrast nanoparticles to create novel photonic band gap materials. PBG materials are a new class of materials with enormous potential to revolutionize electroptical and all optical applications. Up to the present, this new field has been pioneered using microlithography to pattern periodic dielectric structures. By sequestering nanoparticles into one of the components of an appropriately high Mw block copolymer, structures with excellent dielectric contrast and appropriate length scale can b produced to control the flow of U.V. and visible li ght. %%% These two projects are in the areas of polymer-based structures for technological applications. In addition to the basic science and new technology, both graduate students and undergraduate students will be exposed to multidisciplinary training in these exciting project thrust areas. ***

This two-year award provides support for US-France cooperative research aimed at understanding how to control super and molecular level structures of liquid crystalline polymers and liquid crystalline block copolymer materials. The project involves the research groups of Edwin L. Thomas at Massachusetts Institute of Technology and Jean- Claude Wittman and Bernard Lotz at the Institut Charles Sadron in Strasbourg, France. The investigators will characterize and process these materials. Thin films of polymer will be processed to undergo microphase separation and liquid crystal formation on highly oriented polytetrafluoroethylene substrates and under an applied electric or magnetic field. The US research group brings to this collaboration expertise in applied advanced electron microscopic techniques. This is complemented by French expertise in crystal physics and orientational processing. The project will advance understanding of substrate and field processing of liquid crystalline polymeric materials and their optical applications.

The research proposed will further the possibility that block copolymers gain entry into higher value, high technology applications, such as chemically patterned surface coatings, lithographic masks and improved optical components. To this end, the investigator proposes two broadly related fundamental research areas: (1) creation of nanopatterns with surface-reactive rod/coil diblock copolymers and (2) fabrication of tunable magneto-optical materials from nanoparticle-filled block copolymers. In both these projects, the PI's previous experience with block copolymer processing and structure-property characterization will provide a firm base to build structure and chemical interactions between the host copolymer and a substrate and/or an applied field, or between the host polymer and surface engineered nanoparticles determines the resultant nanocomposite morphology will permit attainment of new and enhanced physical properties. Improved insight into the principles of how to best create ordered block copolymer based systems will have broad applicability to a host of emerging technologies. Key to this will be knowledge of how the processing conditions interplay with chemical structure to achieve desirable end states and thus afford superior materials based on BCPs.

Rod/coil BCPs and their blends with both coil- and rod-homopolymers are largely unexplored and present an opportunity to learn about the role of liquid crystallinity on microphase separation. Emphasis will be on rod/coil - coil blends to investigate rod BCP micelles, and on the presence of reactive groups on the rod block to provide means for locking-in morphologics, for tuning substrate interaction, and to create synthetic anistropic organic nano-objects, which can then be employed as unique building blocks in hierarchical self assembly. Self assembled nanocomposites based on polymer-inorganic materials with magnetic field tunable optical properties will be produced by spatially templating superparamagnetic nanoparticles in BCPs. Surface engineering nanoparticles will be sequestered in the BCP and should display superior properties over the corresponding bulk materials due to their small size (single domain particles). By choosing a BCP that has sufficient molecular weight so that the microdomains' periodicity provides a visible wavelength photonic ban gap (PBG), these researchers will fabricate a magnetic field tunable PBG materials. Such materials have potential as polarization rotators and optical isolators ("one way light valves") via the field dependent Verdet constant of the composite. In addition, the experimental data set of nanoparticle-BDP morphologies will be used to compare to recent theoretical models of the geometry of nanoparticle-BCP self-assembly.

This project has several ways to impact society. Visits of graduate students to other universities and to industry are envisioned to give them a broader experience, as well as to access to novel instrumentation. The PI has several highly productive collaborations: C. Ober and S. Gruner (Cornell) - block copolymer synthesis and synchrotron scattering (routine visits by 3-4 students to CHESS and short (one week) periods to Ober lab; S. Margel (Var-Llan, Israel) - nanoparticle synthesis (due to the present situation in Israel, no students have yet visited his lab) and B. Lotz Strasbourg) - TEM and electron diffraction characterization (month long visit to CNRS). The PI has recent experience co-founding a start up (Omni Guide Communications, Inc.) with another professor and a former graduate student, affording a perspective on how to undertake tech transfer from the university into the market place. Over the past 12 years, the PI has filed a total of 15 patent disclosures and 5 patents have been issued. In addition, the PI's group has always hosted several undergraduates, called UROPs, at MIT. Their successful participation in research is attested by co-authorzship of several publications.

This project is aimed at constructing two optical instruments in order to measure novel optical and acoustic properties of periodic polymeric materials. Specifically scientists at the MIT are interested in measuring both photonic and phononic dispersion relationships in self assembled block copolymers and photopolymers created by 3d interference lithography using high resolution magnetooptical rotation measurements and Brillouin light scattering. These two complementary types of measurement jointly rely on common physics (wave propagation in periodic media). Specifically the researchers will construct a high resolution Faraday polarization rotation apparatus comprised of an electromagnet system and a photoelastic modulator for the magnetooptical measurements and purchase a Brillouin light scattering apparatus, consisting of a Fabry-Perot interferometer and avalanche photodetector to enable the phononic dispersion curves to be measured. The realization of such experimental setups will enable scientists to test very exciting predictions of recent modeling studies conducted concerning 1D chiral photonic crystals containing magnetooptical nanoparticles being performed under NSF grant DMR#0308133 and to further recent work on phonon dispersion in 1D lamellar block copolymer crystals and 3d bicontinuous cubic network crystals made via interference lithography. The scientists have found a nondispersive optic-like mode related to the periodic variations in the mechanical properties, a clear indication of the behavior of a phononic crystal.


Photonic crystals (materials that can guide the propagation of light, and in particular reflect certain colors) and phononic crystals (materials that can guide the propagation of sound, and in particular, reflect certain frequencies) both present basic scientific and potentially very technologically interesting materials. In this project scientsists at MIT will develop two related instruments to make new measurements of these interesting phenomena. Interactions between electromagnetic waves (light) or elastic waves (sound) in periodic materials can be surprising and useful. The researchers will make appropriate patterned polymeric crystals, model/simulate their properties using well developed theories and use the newly acquired instruments to access never before measured data for critical comparison to theory and for fundamental insight into to potentially revolutionary new devices: super thin prisms to spread out the colors of white light and open structures that one can see through but not hear through.

TECHNICAL SUMMARY
Periodic and quasiperiodic polymeric structures at the sub-micron and nano scale offer many interesting scientific opportunities for fundamental studies of material behavior at these length scales. This proposal describes a unified approach for the experimental investigation and theoretical modeling of periodic polymer materials which can simultaneously act as hypersonic phononic crystals and visible wavelength photonic crystals. Structures will be fabricated using block polymer self-assembly and interference and electron beam lithography. We plan to explore novel photonic bandgap structures fabricated via double inversion techniques as well as through direct fabrication with unique organic-inorganic hybrid monomers. Brillouin light scattering is an ideally suited method for the direct experimental measurement of phonon dispersion relations while transmission and reflection measurements of incident light will be employed to assess the optical dispersion relations. FEM modeling provides the ability to model elastic wave propagation in a wide range of bicomponent periodic structures and numerical techniques are well established for modeling light wave propagation. The combination of these tools and approaches constitutes a complete methodology for fabrication and characterization, measurement and modeling of this exciting new class of materials.

NON-TECHNICAL SUMMARY
Dual band gap materials for sound and light (?Deaf and Blind Materials?) are a step towards creation of material systems with unusual properties. Success in the present endeavor will provide a pathway forward for construction of multicomponent, hierarchically structured materials designed to provide a set of key properties. This work will help us understand the basic nature of the propagation of light and sound through nanostructured polymeric materials. This work promises to enhance the foundations for experimental studies of phononic, photonic and importantly dual band gap photonic-phononic crystals and open new pathways towards achieving new material properties (e.g.tailored thermal conductivity, significantly enhanced acousto-optical coupling) that can have important technological applications since the properties of the periodically structured material are no longer just due to the inherent material properties, but can be dominated by the role of wave interference within the structure to give novel and indeed revolutionary properties (e.g. localization of sound and light to specific places in the material) that are simply unattainable otherwise. Our efforts will develop both experimental techniques and skilled people to use them at the cutting edge of what is really the emerging new field of ?periodic materials.?
Moreover, working with sound and light waves is a tremendous advantage for inspiring young minds to the wonders of science. This is because light waves and sound waves are ubiquitous ? we are essentially immersed in them every day and are continually receiving and sending such waves. The non-intuitive interactions of these waves with periodic structures elicits genuine awe. We plan to provide block copolymer films on substrates that can be readily manipulated by ?kitchen chemistry? using various stimuli such as vinegar and salt solutions. Motivated by our interests to introduce students to the interesting ways that waves interact with periodically structured materials at the micro- and nano- scale to create new properties as well as to highlite/motivate the study of certain topics in freshman year math, including Fourier series, we have just completed a monograph, ?Periodic Materials and Interference Lithography: photonics, phononics and mechanics,? to be published in summer, 2008 by Wiley-VCH.

NON-TECHNICAL SUMMARY

The detailed structure of defects in soft materials like polymers has received relatively little attention compared to the vast literature on defects in hard crystalline materials (metals, ceramics and semiconductors), where high-resolution electron microscopy and other techniques have quantitatively imaged the new arrangements of the atoms caused by the various kinds of defects, thus enabling a very detailed understanding of the key role of different kinds of defects on controlling important material properties such as mechanical strength and electrical conductivity. This research will explore the use of new, highly advanced electron microscopic and tomographic techniques in an attempt to provide valuable data for comparison to theoretical simulations of the morphology of microdomain interface morphology in important classes of polymeric materials called A-B diblock copolymers. For these materials the interplay of minimization of interfacial area between the A and B domains versus the stretching of the polymer molecules within the respective domains controls the shape of the interface. Additionally, the PI will extend and verify advanced microscopy techniques to explore the 3D nature of grain boundary and line defects that can frequently occur in technologically important diblock polymeric materials and can limit their performance. This research will also contribute to the training of postdoctoral scholars and graduate and undergraduate students in advanced electron microscopic and tomographic techniques. Results from this project will also be incorporated into relevant graduate-level courses.



TECHNICAL SUMMARY

This research seeks to image the 3D shape of the microdomain interface in network phases and around grain boundary and dislocation defects in block copolymers (BCPs). In noncrystalline BCPs, the order is not in the atoms but in the interfaces separating the component blocks (the so called Intermaterial Dividing Surface, IMDS). Previous limitations to 3D reconstructions will be overcome via incoherent imaging using high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). Computational work will define the limitations of the reconstruction techniques by simulations using ideal morphological models combined with the known technique limitations (missing data wedge, strong oscillations in the contrast transfer function for bright-field imaging, defocus across tilted specimens). 3D imaging of the morphology is crucial but very challenging -- the inherent lack of contrast and the susceptibility of organic materials to electron beam damage are formidable obstacles. For some morphologies, reliable reconstructions may not be realizable due to experimental limitations. The few literature studies featuring 3D reconstructions of BCPs display some seemingly unrealistic features of the microdomain interface. Should the approaches turn out to be unable to overcome such experimental limitations, the focus will shift to setting limits on "interpretable resolution" and cautioning that the reconstructions in the published literature to date may have been "overinterpreted". No matter what the outcome, these results will be important for the polymer materials community to view and to understand. For ordered materials, the presence of defects can contribute positively or negatively to material performance. With such fundamental understanding, it should be possible to eventually learn to manipulate the defect types and their numbers in BCP systems and accordingly influence transport properties applicable to fuel cells, battery membranes, etc., where the light weight, flexibility, and low cost of polymers makes them highly attractive.