Dr. Joseph B. SchlenoffDistinguished Research Professor Leo Mandelkern Professor of Polymer Science
Ph.D. (1987) University of Massachusetts, Amherst
Research InterestPOLYMERS AT SURFACES, POLYELECTROLYTES, POLYELECTROLYTE STRUCTURES
Polymer science offers many opportunities to explore the connections between basic and applied chemistry. Our laboratory is engaged in multidisciplinary research centered on the use of novel structures made from polyelectrolytes. These charged, water-soluble macromolecules, found in products from shampoos to water treatment chemicals, can be formed into ultrathin films by a very simple technique: when a substrate is exposed to oppositely charged polyelectrolytes in an alternating fashion, a thin, uniform film of polymer is deposited layer by layer. Potential applications are in several areas, including light-emitting devices, nonlinear optics, sensors, patterning, separations, enzyme active films, and bioadhesion.
Ongoing research projects are wide-ranging and follow the entire "food chain" from synthesis to functional structures. Here are some examples:
BLOCK AND RANDOM COPOLYMER MODIFICATION
We have made copolymers, charged and neutral, designed to stick to surfaces through the metal-thiol interactions. Other new materials include triblock copolymers rendered charged via selective sulfonation or alkylation to produce surface active "polysoaps."
POLYELECTROLYTE MULTILAYER CONSTRUCTION
Polyelectrolytes offer great versatility as building blocks: their conformation is a sensitive function of solution ionic strength, which also regulates interaction between the charges on the backbone. When these and other experimental variables are added to the vast palette of polyelectrolyte architectures available for multi-layer synthesis, a large parameter space for experimentation is created. We have built several computer-controlled robots that assist us in optimizing the synthesis of multilayers with desired properties. We have designed and built multilayers for patterning, programmed deconstruction, separations, and biomolecule adsorption control.
POLYELECTROLYTE MULTILAYERS IN SEPARATIONS
Multilayers used for analytical and membrane purification separations are under study. For analytical separations, fused silica capillaries coated with multilayers are particularly effective for the separation of proteins by capillary zone electrophoresis. Permeability experiments using electrodes coated with multilayers show a strong selectivity for ions of low charge. Furthermore, the membrane transport of polyvalent ions is a strong function of salt concentration in the bathing solution.
Most polyelectrolyte multilayers actually have little structure in terms of distinct stratification. One of the most important materials parameters, dictating the multilayer performance in many applications, is the mechanism by which charge is balanced and distributed throughout the multilayer. For example, a multilayer containing no salt ions has very low permeability for ion exchange and transport, but high selectivity. We are engaged in fundamental studies determining the population and location of small ("salt") counterions throughout multilayers. This knowledge is used to produce models for the structure and mechanism for multilayer buildup and propagation.
|L.Rouhana, M. Moussallem, J.B. Schlenoff Adsorption of Short-chain Thiols onto Gold Under Defined Mass Transport Conditions: Coverage, Kinetics and Mechanism J. Am. Chem. Soc. 2011, 133, 16080-16091|
|R.A. Ghostine, J. B. Schlenoff “Ion Diffusion Coefficients through Polyelectrolyte Multilayers: Temperature and Charge Dependence.” Langmuir 2011, 27, 8241-8247|
|Z.G. Estephan, P.S. Schlenoff, J.B. Schlenoff “Zwitteration as an Alternative to PEGylation.” Langmuir 2011, 27, 6794-6800|
|H.H. Hariri, J. B. Schlenoff “Saloplastic Macroporous Polyelectrolyte Complexes: Cartilage Mimics.” Macromolecules 2010, 43, 8656-8663|
|J.B. Schlenoff, A.H. Rmaile, C.B. Bucur “Hydration Contributions to Association in Polyelectrolyte Multilayers and Complexes: Visualizing Hydrophobicity.” J. Am. Chem. Soc. 2008, 130, 13589-13597|