Formation Kinetics of Tethered Nanolayers: Real-Time Studies with Model Polymers

University Of Kentucky Research Foundation, Lexington KY

Investigators

Abstract

ABSTRACT CTS-9911181 Lynn Penn, U. of Kentucky Tethered polymer layers provide a unique avenue for tailoring solid surfaces and the interfaces made from them. Precise control of not only the chemical structure and architecture of the tethered polymer, but also of its molecular weight, dispersity, and surface attachment density offers the possibility of similarly precise control of the physicochemical characteristics of the layer and therefore of the performance of the solid surface. Such precisely controlled layers have great potential value in additional areas, including corrosion prevention, friction and wear control, biofouling control, and waste stream purification To construct a tethered layer that has the exact characteristics needed for a particular application, the scientist or engineer must be able to manipulate the tethering process with precision. For this to be done, the kinetics and thermodynamics of layer formation must be understood and brought under experimental control. However, the tethering process is made complex by the facts that a) the process involves heterogeneous phase reactions and b) the polymer chains are being attached to a surface that is changing during the process. Furthermore, until recently, there has been no convenient way to monitor the kinetics of formation of a tethered layer. These complexities and difficulties have prevented understanding-based control of the tethering process until the present time. In this project, the kinetic and thermodynamic factors that control layer formation will be explored in terms of specific chemical and physical features of the tethering reaction. These include polymer molecular weight, polymer architecture, and end group-surface interaction. For this, model polymers that provide a wide variation of polymer architecture, molecular weight, and tethering entity will be synthesized by living anionic polymerization. Other quantities that will serve as independent variables are temperature, concentration, solvent (and there interaction between polymer backbone segments and solvent), chemistry of the reactive sites on the solid surface (and thereby interaction between reactive sites and end-functional groups of the polymer chains), and energetics of the solid surface. The tethering reactions of the model polymers to solid surfaces under different conditions will be monitored by means of a recently developed, real-time method based on size-exclusion chromatography. The data obtained from the above studies and the principles that emerge will lead to a comprehensive description of the kinetics of tethering and an evaluation of the thermodynamic factors that influence the process. From this, we will develop of a set of logical guidelines and a general applicable mathematical model of tethering kinetics that can be used for empirical control manipulation of tethered layer structure.