Christopher M. Sorensen - US grants

Photon correlation spectroscopy is a dynamic light scattering technique which measures diffusive motion of particles. It has been applied quite successfully to particulate suspensions in liquids. The application of PCS to aerosol systems, however, is still in its infancy primarily because the particles being measured are following much faster and farther than particles in liquids. The principal investigators propose to develop further and apply PCS to size and shape characterization of aerosols, and to use these abilities to study the fundamental process of coagulation.

Narrative: It is proposed to study coagulation of fine particle aerosols using static and dynamic light scattering and electron micrography inspection. The goals are: l. To determine the applicability of the fractal concept to describe aerosol particle morphology and how this fractal morphology depends on Knudsen number, particle interactions, and concurrent surface growth. 2. To test temporal scaling of the coagulative growth of aerosols in the entire Knudsen regime and determine the dependence of the coagulation kernel homogeneity and dynamic fractal dimension on Knudsen number, particle interactions, and concurrent surface growth. 3. To measure the approach of an arbitrary aerosol particle size distribution to the self-preserving form and study the effects of fractal morphology on the measurement. 4. To measure the rate of coagulation in the intermediate Knudsen regime in both liquid and solid particle aerosols. 5. To characterize the phenomenon of aerosol clumping and determine its effect on coagulative growth. Aerosols will be created from either oil droplets (DOP) or solids (NaCl, Ag) and soot from premixed flames. Sizes will be in the 5-100 nm range before coagulation. An understanding of aerosol coagulation, its rate and temporal evolution, and its effect on the resultant cluster morphology will help our fundamental understanding of aerosols and the coagulative process.

This project is in the area of the Materials Chemistry Initiative with a focus on the study of the magnetic properties of fine particles, as well as aggregates, powders, films and other bulk materials that can be created from these particles. This group will also study preparation techniques for fine particles and the physics of their aggregation and growth to bulk materials. These two intents, while they may stand alone, are complementary in that as they gain an understanding of magnetism in fine particles and their aggregates they also develop a complementary understanding of how these systems may be prepared. They will alter preparation techniques to achieve systems with unique and useful magnetic properties. More specifically, the goals are: 1. To determine how magnetic properties are dependent upon particle size, composition, and morphology. 2. To develop techniques for fine magnetic particle preparation and understand the chemistry and physics of their preparation. 3. To study aggregation and growth of magnetic particles and the resultant morphology. The results of this work will lead to creation of novel and useful magnetic materials.

Light scattering experiments are planned for supercooled water and aqueous solutions to elucidate the structural mechanisms responsible for thermodynamic anomalies in supercooled water. Raman data obtained from this work will have direct structural information for supercooled water. The OH stretch modes will yield nearest neighbor information including hydrogen bond probability, and mean O-O separation and distribution. The low frequency intermolecular modes will yield information regarding the second neighbor shell wherein the most dramatic structural changes relevant to the supercooled anomalies are thought to occur. The photon correlation spectroscopy measurements will be used to extract effective density correlation lengths due to cooperative behavior between many water molecules. Water's importance on the face of the earth cannot be overstated. This importance stems from two sources: its abundance, and its unique physical and chemical properties. In the past decade it has been found that liquid water is even more unusual in the supercooled regime below zero degrees Centigrade. Here it displays anomalies in its thermodynamic and transport properties which may be approaching a singularity. The key to water is in its hydrogen bonded structure. Raman spectroscopy can give microscopic information regarding structure and dynamics. It can determine the extent of hydrogen bonding, make decisions regarding ice-like or clathrate structures, and give information on both the first neighbor shell and molecular clustering.

This multidisciplinary project in the area of materials chemistry is jointly supported by the Inorganic, Bioinorganic and Organometallic Chemistry Program and the Solid State Physics Program. The collaborating investigators are Dr. Christopher M. Sorensen and Dr. Kenneth J. Klabunde of Kansas State University and Dr. George C. Hadjipanayis of the University of Delaware. Research will continue on the synthesis and evaluation of ultrafine magnetic particles, with the goals of learning more about the fundamental properties of these particles compared to bulk samples, to develop convenient methods for synthesis, protection and control of particle sizes and microstructure, and to gain a better understanding of the chemistry and physics of the processes by which they are formed. A broad range of synthetic approaches to the preparation of metallic, metal boride and metal oxide particles in the size range of 1-1000 nm will be investigated. Synthetic techniques will include metal atom clustering in cold matrices under inert gases and sputtering. Also to be investigated are reduction of metal ions by borohydride, hydroxide precipitation and digestion, and pyrolysis of aerosols. Reversed micelle techniques will be explored for the control of particle sizes, and the trapping of small particles in structural media, such as polymers, zeolites or vycor glass, will be investigated also. Magnetic particles will be thoroughly characterized with respect to chemical composition, morphology, magnetic ordering, magnetic moment, coercivity, and phase transformations.

The objective of this proposal is to develop static and dynamic light scattering techniques for the characterization of fractal soot aggregates in flames. Current fractal-based theories for the optical properties of soot particles will be incorporated in the proposed techniques. The results from several static scattering/extinction measurements on soot clusters will be compared to soot clusters selected from flames and viewed by an electron micrograph. The Photon Correlation Spectroscopy, a dynamic technique to be further developed by Dr. Sorensen during this project. The research topic is important for scientist understanding of soot formation and of light scattering diagnostics, and has engineering applications in combustion and environment.

This SQUID-based sample magnetometer will perform fast, precise measurements of the magnetic properties of materials over a broad range of temperatures and applied magnetic fields. It has a complete and sophisticated computer operating system for control and analysis and allows for total automation. The proposed instrument exceeds current equipment ability in sensitivity, temperature control, and computer control. The system will be used by four faculty members of the Physics and Chemistry departments for fundamental materials research, and will aid in training of undergraduates and graduate students (20), and postdocs (3). The SQUID magnetometer is a central measurement and characterization apparatus for several projects: measurement of magnetic properties of ultrafine parcticles prepared via novel synthetic techniques having unique compositions and structures; studies of storage and relaxation processes of photoexcited charge carriers in II-VI mixed crystals and related critical phenomena; studies of magnetic anisotropy and interface exchange in multilayers of rare-earth metals and transition metals and their oxides and studies of critical phenomena in these systems; and measurements of organic ferromagnets.//

ABSTRACT CTS-9408153 C. Sorenson Static and dynamic light scattering techniques will be developed to study properties of the fractal aerosol clusters, including morphology, diffusional transport, optical scattering properties and aggregation kinetics. Aggregates of particles formed through coagulation processes are described as fractals, which allows for improved measuring techniques and overall physical understanding. The experiments will be performed with carbonaceous soot aerosols in premixed flames, and silica and titania aerosols. The proposed measuring techniques have scientific relevance, and may be applied to studies related to aerosols and colloids in industrial processes, environmental aerosol analysis, combustion, and nuclear reactor safety. ***

This project involves light scattering and absorbtion measurements on aerosol agglomerates as a function of particle size and diffraction indices. The dynamics of agglomeration at various Knudsen regimes will be measured and evaluated. The fractal optics and kinetics experiments will be compared with existing theories and a new model proposed by the P.I. A multi-angle optical diagnostic technique for size and morphology of particle and aggregate in unsteady flows will be developed, with application to turbulent flows in flames. If successful, the study will provide better understanding of the aerosol aggregation mechanisms, of light scattering and absorption processes from aggregates, and a new instrument to measure the aggregate size and composition in turbulent flows. Application range from soot formation in air pollution studies to powders synthesis in flame reactors.

pThe New Studio format for teaching introductory physics to large undergraduate classes retains the lecture format and combines traditional recitation and laboratory instruction creating an environment in which many interactive learning strategies are implemented. This New Studio, where students are taught two hours twice a week has 30 students working in groups of three at tables equipped with modern instructional technology and apparatus. The group setting allows for peer instruction and development of group skills. Instructional materials that are centered on group work, microcomputer based technology tools and problem solving are adapted and implemented in the New Studio setting. The daily sequence of the course includes the lecture to instruct economically large sections of students, but is strengthened by non-traditional classroom interactive strategies such as the use of ClassTalk and concept questions. The lecture, supported by the New Studio, engages students with simple experiments/demonstrations coordinated with the previous night's problem set. After the students explore the three to four concepts using these demonstrations, they reconsider the problem set with the guidance of their instructors and their peers. The New Studio concept is motivated by our departmental assessment of more traditional physics instruction and is based on adapting and implementing several of the interactive instructional materials and techniques demonstrated as effective in recent physics education research.

Abstract
CTS-0080017
C. M. Sorensen, Kansas State University


The PI proposes to extend the results he has obtained in the development of static light scattering diagnostics of aerosol aggregation kinetics. These measurements will be extended to include large particles (including some in the turbulent range), and also some cases in need of time resolution. Some needed theoretical work is planned, to characterize the fractal aggregate scattering, and also to generalize these assessments to homogeneous spherical aerosols. Fast microphotography will give an insight of the particles size and morphology. These quantitative results will make possible the kinetics characterization of aerogelation and turbulent aggregation.

A special effort will be to establish the validity limits of the Smoluchovski equation, which does not seem to fit some of the earlier measured kinetics in dilute or turbulent systems. Cluster fractal data will yield the evolution beyond the diffusional (laminar) regime, while density fields will identify deviations from mean-field behavior.

Physics (13). This project creates an interactive studio instruction for the first semester of a junior / senior level, three-semester, optics course. It adapts and implements hands-on, interactive, peer-instruction methods developed successfully by others and aspects of Paradigms in Physics developed at Oregon State University. Application of interactive studio instruction to an upper level physics course is novel. An important aspect of the optics studio is a mini-exploration / mini-lecture / mini-lab combination for instruction. This involves a very brief acquaintance (mini-exploration) followed by a short lecture (mini-lecture) over some aspect of optics. This is followed by a similarly short period of experimentation with optical equipment (mini-lab) that illustrates and amplifies the mini-lecture. Students work on the mini-lab in groups of four, which encourages peer instruction while the lecturer visits the student groups to provide direct, interactive instruction. Many of the mini-labs are related to homework problems which helps to combine conceptual and problem solving skills. A few mini-exploration / mini-lecture / mini-lab combinations with associated problems are performed each two-hour studio period.

National Science Foundation - Active Nanostructure and Nanosystems (ANN) (NSF 05-610)
Nanoscale Interdisciplinary Research Teams (NIRT)

ABSTRACT
Proposal Number: 0609318
Principal Investigator: Sorenson, Christopher M.
Affiliation: Kansas State University
Proposal Title: NIRT: Nanometer Stoichiometric Particle Compound Solutions and Control of their Self-Assembly into the Condensed Phase

This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 05-610, category NIRT. The goal is to create a new family of nanometer "stoichiometric particle compounds," or what could also be called nanoparticles of all the same size, and to control their active assembly into condensed phases. In order to do this, understanding and control of solution phase and interfacial properties is needed. Understanding of particulate self-assembly to yield two and three dimensional superlattices, films and gels is also needed. To achieve this goal a series of nanomaterials will be synthesized in large amounts and will be "nanomachined" (digestively ripened) to molecular stoichiometry and stabilized with selected surface ligands. The ligands will be chosen for their tendencies to be hydrophobic or hydrophilic, their ability to form ordered monolayers, and to hydrogen bond and/or interdigitate with neighbors. In this way solution phase behavior, aggregation, crystallization to form superlattices, and assembly into various structures will be controlled. The physical chemistry of solutions, their phase diagrams, interfacial phenomena, and transitions to other phases is very well understood. Moreover, much is known about colloid phase stability and what happens when the colloid is destabilized. The new nanometer size stoichiometric particle compounds to be studied lie between solutions and colloids, and their phase behavior, interfacial phenomena, transitions to other phases, and controlled assembly have not been explored with experiment or theory. This research will attempt to rectify this lack of experimental data and understanding, and hence bind all these systems with one universal description. Therecently developed supramolecular building techniques will be extended to assembly of particles rather than molecules. The idea is to view these nearly uniform in size and composition nanoparticles as stoichiometric compounds with behavior, perhaps in some novel manner, analogous to "normal" atomic and molecular systems. Creation of materials based on single-sized nanoparticles, rather than atoms and molecules that actively assemble into superlattices, films, gels and supermolecular entities would yield a whole new class of materials with which it could rebuild or recreate all our modern marvels. Stoichiometric particle compounds can produce a particle-based world. Thus, from a broad perspective, this is an attempt to develop and then use the concept of a three-dimensional periodic table where size is the third dimension. The PIs will develop a streamlined set of course options to allow our students to achieve a broad training across physics, chemistry, materials science and engineering without significantly adding time to their training experience. The program will introduce teen women to nanoscience and technology through a recently established and very successful summer workshop series. The PIs will include undergraduates in the research year round.

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)

ABSTRACT
Proposal Number: CTS-0627929
Principal Investigator: Sorenson, Christopher M
Affiliation: Kansas State University
Proposal Title: Support for Students to Attend Nanoaerosol Characterization Symposium

Intellectual Merit

Scattering is a powerful way to characterize the structure of material. With the advent of nanotechnology it has become more important to characterize nanoparticles and aerosols, and new techniques need to be utilized to these ends. This conference will report on the results of efforts over recent years to discover new techniques on projects as diverse as soot formation in combustion, material synthesis in aerosol reactors, and the structure of aqueous nanodroplets.

Broader Impact

The participation of US students and post-docs in this symposium will provide an opportunity to interact with leading international experts and become familiar with the current state of the art of this field world-wide, exchange ideas and develop collaborative projects. Graduate students will also have the opportunity to learn how national facilities can play an important role in their research.

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Edgar

Funds are requested to support the acquisition of a state-of-the-art field emission environmental scanning electron microscope (FESEM) to improve the quality and expand the scope of the research, training and education activities at Kansas State University (KSU). This instrument offers higher resolution imaging, electron-beam-lithography (EBL), energy-dispersive spectroscopy (EDS) and a broader range of operating conditions that will significantly enhance the research capabilities at the University. The new FESEM will be housed in the central KSU Microscopy Laboratory which serves as the core, multi-user microscopy facility for five Colleges, 20 Departments, and a private company. This equipment is a critical part of a broader effort of the University to improve its microscopy and imaging capabilities to provide a well-equipped, integrated research and education environment. The FESEM-instrument requested is the FEI NovaNanoSEM 230 with EDS & EBL.

The goal of this project is to develop a complete, comprehensive and quantitative description of light scattering by irregularly shaped particles. A device for simultaneous multi-angle, calibrated scattering matrix measurements over essentially all angles from 0.1 degrees to 180 degrees will be designed and built. An important characteristic of the device, not found in previous studies of irregularly shaped particles, is the ability to go to very small angles necessary to detect the Guinier and Rayleigh scattering regimes. With this device, scattering by a wide variety of irregular particles including soot aggregates, humidified soot aggregates and then dried soot aggregates, mineral dusts and humidified dusts, and crystalline solids with geometric shapes will be studied. Such particles are of significance for atmospheric aerosols and the global environment. The combined experimental and theoretical work will yield a quantitative yet physical description of scattering by all types of particles. This description will be both accurate and straightforward to implement into global climate models.

Intellectual Merit:
The study will apply and test broadly the q-space analysis method to both the experimental data and systematic theoretical calculations. The method is a completely new way of analyzing light scattering that past work indicates will be broadly applicable. With this q-space perspective, the systematic studies should yield a new physical picture of scattering that will give an unprecedented intellectual intuition on how scattering works.

Broader Impacts:
One of the most significant problems facing humanity today is global climate change. The results of this research will have direct bearing on the problem of how aerosols affect our global environment. The goal of this study is to understand and accurately describe light scattering from any kind of particle including the wide variety of non-spherical shapes that occur in the atmosphere. With such knowledge, the direct impact of aerosols on the environment can be predicted and the aerosol content in the atmosphere can be accurately detected and measured.

There are a number of projects regarding education, outreach and curriculum development that will directly result from or be significantly related to this work including: a summer workshop for teen women, involvement of undergraduates in research, an upper level undergraduate course on light scattering, talks at high schools, mentorship of graduate students, and writing of a monograph on light scattering.

The scattering of incoming sunlight by atmospheric particles has a significant impact on the radiation balance of the Earth. The pattern and impact of light scattering by spherical particles is well-known, but atmospheric particles such as dust, soot, and biological particles are irregularly shaped and interact with light differently. In this award, the researchers will conduct experimental and theoretical studies to build a collection of general rules that describe how light scatters by particles of any shape. The results of the project are likely to have an impact on the understanding of how aerosols affect the global environment. Teaching and training will be emphasized, with graduate and undergraduate student involvement in the project and well as various outreach activities. The research also has the potential to impact other scientific fields.

The overarching perspective used in this proposal is the Q-space analysis which provides a means for a universal, quantitative description of the scattering that leads to new physical insights into the scattering process. The emphasis of the proposal will be on coarse mode aerosols, such as mineral dusts and soot that have a large impact on the direct radiative forcing of Earth's climate. The project includes both experimental components, making use of a light scattering device, and theoretical components with an end goal of deriving a general description of scattering for any particle shape or size.