William Bailey Russel - US grants

Long-term research in: Rheology of Suspensions of "Soft" Colloidal Particles. This award recommendation is made under the Program for Long and Medium-Term Research at Foreign Centers of Excellence. The program is designed to enable U.S. scientists and engineers to conduct long-term research abroad at research institutions of proven excellence. Awards provide opportunities for the conduct of joint research and the utilization of unique or complementary facilities, expertise and experimental conditions in foreign countries. Awards are selected on the basis of scientific criteria relevant to the applicant's field of science, the prospective potential of the applicant for professional growth, as well as criteria relevant to the furthering of international cooperation in science and engineering. The program is particularly directed to scientists and engineers who are embarking on their research careers. The project is under the direction of Dr. Harry J. Ploehn, Department of Chemical Engineering, Princeton, University, Princeton, NJ, in collaboration with Professor J. W. Goodwin, School of Chemistry, University of Bristol, Bristol, England. The award recommendation provides funds to cover, as appropriate, international travel, local travel abroad, stipend, dependents allowance, if applicable, language training, if required, and a flat administrative allowance of $250.00 for the U.S. home institution.

This award partially supports acquisition of instruments for measuring surface charge of colloidal particles and electrophontic mobility of colloidal particles. The instruments will be used in studies of the dielectric properties of colloidal dispersions, kinetics of floc formation and breakage, and rheology of concentrated dispersions. Better control and characterization of particles should lead to improved processing capabilities of fluids having complex microstructure.

The proposed research is a combined theoretical and experimental investigation of the structural and rheological properties of colloidal dispersions. The effective medium properties are incorporated in a statistical theory to evaluate pair of particle interactions. The calculation of the structure and rheological properties for a variety of systems is proposed. The theory will be tested via light scattering measurements, for mixtures of hard spheres, sticky spheres and spheres bearing grafted polymer layers. The statistical mechanics approach can be regarded as an alternative or complement to molecular dynamics or Stokesian simulations, covering dilute and medium concentrated dispersions. The suggested theory should be valuable for the fundamental information generated, as well as the insight gained for guiding and correlating experiments for colloidal dispersions of interest in automotive and architectural coatings, ceramic particles processed as dispersions, cosmetics, and printing inks.

9223966 Russell This award is to start a new Materials Research Group (MRG) at Princeton University on the topic of microstructured macromolecular soft materials. The goal of the research is to understand, control, and exploit these materials. The research addresses three major themes: (1) block copolymers where the meso-scale morphology is determined by block lengths and thermodynamic incompatibilities of the constituents, (2) polymer-particle dispersions where the attachment of the block copolymer at an interface leads to ordering in the colloidal phase, (3) study of the properties of complex structured fluids. These three themes involve research on dynamics of ordering, effects of shear on ordering, use of phase separated systems as templates for nano-lithography, effects of block copolymer structure on adsorption and ordering, tailoring of fluid rheology through control of microstructure. Microstructured soft materials order on the length scale of ten to hundred nanometers, where structure formation or self assembly occurs in the fluid state. Structure formation is determined by the balance among structural entropy, steric energy, and electrostatic forces. Examples of microstructured soft materials include motor oils and lubricants, colloidal additives to plastics, thermoplastic elastomers, paints and coatings, drilling fluids, nano-lithography for electronics, and nonlinear optics. The research involves collaboration with Exxon Corporate Research Laboratories. The institutional environment at Princeton University is excellent for training advanced students for careers in research and teaching. ***

9214180 Russel The Chemical Engineering department at Princeton University, noted for it's top rated research, remains as one of the leaders in the filed. In order to maintain this status, it is imperative that Princeton's chemical engineering research facilities be modernized. This ARI award provides funds to renovate and modernize the chemical engineering research facilities located in the A-wing of the Engineering Quadrangle and the G- wing of the Energy Research Laboratory. Present conditions within the laboratories are ill-suited for modern computational and experimental research. Renovations to these facilities will improve services to insure proper electrical supply, chilled and deionized water, high pressure nitrogen, compressed air and ventilation. With the refurbishment of obsolete research laboratories, efforts in the fields or ceramic processing, complex fluids catalysis and surface science, nonlinear dynamics, and polymer science and materials will significantly expand the Department;s influence in the field. Renovated facilities will sustain the momentum acquired by the Chemical Engineering department over the past decade through major senior appointments and the development and promotion of outstanding junior faculty. The department's influence on the profession through its leadership in the field, collaborations with industrial laboratories, and producing studnets who continue to pursue advance degrees will strengthen with modern facilities. ***

9310603 Saville Under the aegis of this equipment grant proposal, funds are sought to purchase a set of devices (a high frequency impedance analyzer, computer, and auxiliary equipment - hereafter to be called the High Frequency Dielectric Spectrometer) to characterize colloidal dispersions, emulsions and thin films via measurements of the (complex) impedance of dielectric constant. The instrument will be used in several research projects including: (i) Dielectric Spectroscopy of Colloidal Dispersions - Research on the electrical nature of the particle-fluid interface and the properties of adsorbed polymer layers using electrokinetic measurements, (ii) Microemulsions - Research on the relationships between structures and bulk properties. (iii) Dielectric Properties of Thin Film and Emulsions - Characterization of thinning processes in single films and emulsions. ***

9809483
Russel
The Materials Research Science and Engineering Center (MRSEC) at Princeton University addresses fundamental problems in the science and engineering of complex materials. Research in this Center, which has been named the Princeton Center for Complex Materials, is organized into four interdisciplinary research groups. The Center also provides seed funding for new opportunities in materials research. The Center supports efforts in materials education at all levels including summer undergraduate research experiences, a topical summer institute for graduate students working on materials-related areas, and outreach to the pre-college level via an internet-based software developed by the Center and prototyped in a nearby science museum. The MRSEC also supports shared experimental facilities that are accessible to center participants and to outside users, and has strong research collaborations with industry and national laboratories.

A common theme in the four interdisciplinary research groups of the MRSEC is fundamental understanding of the links between molecular structure or mesoscopic texture and macroscopic properties with the goal of rationally designing materials for technological purposes. One group investigates the unusual phases and excitations in low-dimensional electronic materials, including high temperature superconductors and semiconductor heterostructures. A second group explores engineered structures based on semiconducting organic thin films for application to optoelectronic devices. A third group pursues the materials science of organic molecules that order spontaneously in solutions or melts with an outlook on advanced lubricant and novel lithographic applications. A fourth group emphasizes the development of nanostructured composites with improved mechanical and dielectric properties by mimicking biological composite materials. Participants in the Center currently include 26 senior investigators, 8 postdoctoral associates, 16 graduate students, 14 undergraduates, and 3 technicians and other support personnel. Professor William B. Russel directs the MRSEC.

ABSTRACT CTS-9521662 The interparticle forces colloidal microstructure and rheological properties of two types of stable dispersions of spheres containing either polymeric stabilizers grafted to the particles or soluble associative three-block co-polymers will be investigated. Non- equilibrium statistical mechanics equations are used to described the colloidal microstructure. For the polymer-stabilized spheres, a new potential of the mean force, hydrodynamic functions accounting for the polymer layer and a method for generating the equilibrium distribution functions, are proposed. For the associative polymeric suspension, a non-equilibrium interparticles force similar to that in reversible network theories will be introduced in analysis. The proposed work has relevance to rheological characterization of polymer-stabilized suspensions, with particular relevance to advanced materials processing coatings. ***

Abstract CTS-9812409 W.B. Russel, Princeton University The objective of this proposal is to develop a theoretical basis supported by experiments for the formulation of concentrated dispersions with tailored rheology by investigating the relationship among interparticle forces, microstructure and rheological properties. Examples will include stable dispersions of spheres containing end block and chain associative polymers. Experiments combine rheological measurements with dynamic light scattering and rheo-optical techniques. The data will be interpreted using non-equilibrium statistical mechanics and including the treatment of micelles and brushes form the polymer literature. A conservation equation describes the microstructure of a dispersion of Brownian spheres interacting through pairwise additive potentials, short range hydrodynamical interactions, and subjected to shear or other external fields. The proposed research has relevance to materials and chemicals industries where the connection between composition, microstructure and rheological behavior are important. ***

Abstract
CTS-0120421
Russel

It is important to understand and quantitatively model the linear and nonlinear rheology of highly concentrated micellar and colloidal systems. The goal of the proposed research is to reproducibly formulate two types of systems with prescribed rheology. These are the highly viscous and viscoelastic micellar solutions of telechetic polymers, as well as nanosize particles bearing terminally grafted chains that form brushes. Although considerable work has been done to understand the behavior of associative polymers, this study will provide the fundamental understanding of the underlying structure of the micelles. There is little information on the rheology of the nanosized brush-like particles. Therefore, this study should provide new and exciting insight in the rheology of soft particles with the potential for unusual variations with concentration and the stress field.

CBET-0754078, Russel

Our recent work offers a solid understanding of the mechanics controlling consolidation and cracking of immobilized, i.e. close packed, colloidal dispersions that deform nonlinearly and viscoelastically due to contact or interfacial forces. Our model identifies, in terms of appropriate dimensionless groups, the conditions under which air-water, polymer-water, or polymer-air interfacial energies suffice to form homogeneous void-free or porous films as thin layers of aqueous dispersions dry on a rigid substrate. The model also predicts the capillary pressure above which cracking becomes favorable, when deformation is too slow to keep up with evaporation, as the elastic energy recovered when a crack opens exceeds the additional surface energy expended. Complementary experiments with polymer latices and inorganic oxide colloids in a pressure filtration cell permit direct measurement of the negative capillary pressures required for cracking, demonstrating that many packings do not crack until the capillary pressure exceeds significantly the minimum predicted for an infinite crack. Further experiments and theory establish the importance of flaws to nucleate cracks, as for linearly elastic solids under tension. This work provides a foundation for addressing a remaining puzzle and two related challenges.
First, crack tips following a drying front in a thin film develop a characteristic spacing and often advance in the direction of the gradient in capillary pressure in a stick-slip fashion. This suggests an additional dynamical process, which some attribute to the flow of water driven through the particle packing by gradients in the capillary pressure. To elucidate the pattern selection process we propose two experimental geometries with controlled propagation of gradients, complemented with analysis of the dynamic process through an extension of the existing model. A thin rectangular channel confines evaporation to the open ends and allows cracks propagating in from the ends to be viewed through the flat faces via a microscope. Alternatively, the pressure filtration cell mentioned above can be tilted slightly to create a gradient in thickness of a thin layer with a free surface but without the lateral flows caused by nonuniform evaporation. Cracks nucleated by notches at the thick edge then should propagate toward the thin edge with increasing capillary pressure.
Second, some technologies require highly porous films that cannot be dried at the desired thickness without cracking, raising the question of how to maintain capillary pressures for cracking above those attainable with menisci at the surface of the film. For this purpose we propose to study films formed with colloidal rods for which random packing creates pores larger than the rod diameter, thereby reducing the maximum capillary pressure relative to random close packing of spheres of the same diameter. Success will depend on whether the effective modulus of the packing, which controls cracking, does not fall enough to negate the benefit. Experiments with colloidal rods of boehmite, either bare or stabilized with a silica coating, in the pressure filtration cells will determine the critical capillary pressures as a function of film thickness to assess the potential.
Third, we intend to explore film formation and cracking in the pressure filtration cell for binary mixtures of hard and soft spheres with interactions tuned to delay percolation of the hard phase to as high a volume fraction as possible. This effort, using the same experimental tools as above, will be guided by theory being developed to understand the recently discovered ?halo? effect due to electrostatic attractions between small highly charged polymer latices and larger electrically neutral inorganic spheres.
The intellectual merit lies in the creation of a solid fundamental basis of understanding and using that to devise new avenues for the technology. Success in understanding these phenomena should benefit drying processes important to technologies ranging from conventional (but always improving) architectural coatings, through tape casting processes for fabricating ceramic substrates and multilayer devices, to carefully tailored particulate coatings for inkjet papers. The research provides broader impact by posing a stimulating vehicle for educating graduate students and undergraduates for careers in the chemical and related industries.