Christopher James Durning
810 S W Mudd, Mail Code: 4721
Phone: +1 212-854-8161
Fax: +1 212-854-3054
Our research focuses on ways of exploiting "soft" materials in a variety of new applications. The important themes in this work are to understand and control:
I Transport and diffusion in polymeric systems.
II Surface and interfacial behavior in polymeric systems.
III Association and self-assembly of soft materials.
1). Nano-structured materials, i.e. thin layers and bulk materials with organized structures on length scales in the range 1-100 nanometers. Such materials offer unique advantages in many applications, for example in high capacity magnetic storage media, in achieving ultra-small photonic and electronic devices, in graded layers and films for super-mirrors and notch filters, and in achieving "labs on a chip". We work to develop new schemes for generating nano-structures via supra-molecular chemistry and self-assembly. A particularly important specific goal is to understand and control the development of lateral (in-plane) order at surfaces, interfaces and in thin layers.
2). "Smart" or responsive materials which respond in a favorable way to external conditions. Examples include thin surface layers which promote interfacial slip at precisely predictable conditions, or chemically active surfaces engineered to exhibit thermally, electrically, photo-lytically or chemically triggered surface property changes or surface release mechanisms.
The systems we examine rely mainly on designed synthetic polymers, which are high molecular weight organic species with very specific molecular architectures. Examples include block and graft copolymers and hyper-branched or "dendritic" polymers. A few recent projects are described below.
a). ADSORPTION AND SELF-ASSEMBLY OF DENDRIMERS AT THE SOLID-LIQUID INTERFACE.
We are studying the surface activity of recently developed dendrimeric polymers and their supramolecular analogs. Dendrimers are monodisperse, branched, water-soluble polymers with an abundance of surface active end groups. They consist of a multifunctional core with "generations" of multi-functional monomers attached in tiers around the core. A homologous series can be made in ascending "generation" G (number of tiers attached to the core). Dendrimers exhibit rigidity, and thus resemble "soft-spheres" with sizes in the range 1-10 nm. Further, they exhibit "container" properties enabling delivery to surfaces of functional "cargo". These have great potential for preparation of nano-structured thin film composites if one can control particle-surface (P-S) and particle-particle (P-P) interactions well enough to promote self-assembly at an interface. We are systematically studying clustering in solution and adsorption onto solids in-situ by micro-balances, AFM and by scattering methods.
b). MOLECULAR MOBILITY IN POLYMER THIN FILMS.
Experimental studies in the past five years of the thermal and dynamic properties of ultra thin polymer films (i.e. films with thickness approaching the size of the polymer molecules) indicate that such films have significantly different properties than the corresponding bulk. This has an important impact on the preparation of ultra small photonic and electronic devices via various lithographic methods. Experimental results in the literature to date are not consistent, and in some cases, contradictory. We are systematically studying mobility of probe molecules in such films using photo-physical methods to understand the physics in detail, and develop a consistent, clear experimental picture of thin polymer film behavior.
c). STRUCTURE AND DYNAMICS OF POLYMER MELTS
AT "ENGINEERED" SOLID/LIQUID INTERFACES.
In a number of new technologies the behavior of melts of high molecular weight flexible polymers at the solid-liquid interface is critical. An example is modern recording technologies, where a thin film of polymeric lubricant plays a critical role in the mechanics of read-write operations. The goal of our work is to understand how to control the structure and dynamic behavior of the region of immediately adjacent to a solid surface, critical to lubrication and adhesion phenomena. Our study of this issue involves (i) studying the static structure of melts in contact with "engineered" solid surfaces bearing adsorbed polymers or polymeric brushes, and (ii) studying the same situation but with an imposed steady shear field. Among the techniques used, x-ray and neutron reflection is employed to study the molecular level events at the solid-melt interface.
CONTRIBUTED PAPER, "Sorption and Diffusion of n-Alkyl Acetates in Poly(methyl acrylate)/Silica Nano-composites,´ AIChE Annual Meeting, 11/8/09-11/13/09, Nashville TN, Symposium: Diffusion in Polymers I paper 651a; co-authors D. Janes, S. Harton, L. Rong.
**K.M.A. Rahman, C.J. Durning, N.J. Turro and D.A. Tomalia, "Adsorption of Poly(amido amine) Dendrimers on Gold," Langmuir, accepted.
A. Ponomarev, T. Sewell, C.J. Durning, "Adsorption of Isolated, Flexible Polymers on a Strongly Attractive Surface," Macromolecules, 33, 2662-2669 (2000).
M.M. Hassan, C.J. Durning, "Effects of Polymer Molecular Weight and Temperature on Case II Transport," J. Polym. Sci. Part B: Polym. Phys., 37, 3159-3171 (1999).*K. Tseng, N.J.Turro, C.J. Durning, "Molecular Mobility in Polymer Thin Films," Phys. Rev. E, 61, 1800-1811 (2000).
C.J. Durning, U. Sawhney, B. O'Shaughnessy, G.S. Smith, J. Majewski, D. Nguyen, "Irreversible Adsorption of Polymethylmethacrylate Melts on Quartz," Macromolecules, 32, 6772-6781 (1999).
S.J. Huang and C.J. Durning, "Nonlinear Viscoelastic Diffusion in Concentrated Polystyrene-Ethylbenzene Solutions," J. Polym. Sci.: Part B: Polym. Phys., 35, 2103-2119 (1997).