Chain Entropy and Polymerization Thermodynamics: Quantifying Nanoconfinement Effects

Texas Tech University, Lubbock TX

Investigators

Abstract

NON-TECHNICAL SUMMARY: The chemistry used to create polymeric materials is called polymerization. For many applications it is important to make such polymeric materials within extremely tight spaces, even down to the nanoscale (i.e. to thicknesses about 10,000 times smaller than the thickness of a human hair). This process is called nanoconfinement. In this project, polymerization under nanoconfinement will be studied and theoretical predictions will be tested. The results of the research are important for a fundamental understanding of confined polymerization in nanoelectronic and nanolithography processes, and thus could facilitate technological advances important to these industries. In addition, the results have implications for understanding biopolymers and proteins in biological systems where, for example, protein polymerization can occur in confined environments. The project includes the training of one graduate student, one postdoctoral researcher, and an undergraduate researcher in cutting-edge research involving polymer chemistry and physics at the nanoscale. Ethics training will be incorporated into the training of the students. The PI has a strong track record working with minority and female students, and a vigorous effort will similarly be made to include underrepresented students in this project. Outreach will include organization of two one-week-long polymer modules for the TTU program, "Science -- It's a Girl Thing," for girls in junior high school, and the development of four two-hour modules for the TTU Super Saturdays science program for 4th to 6th graders. TECHNICAL SUMMARY: The fundamental question of entropy loss on confining a chain to a nanopore is addressed, and theories for the scaling of confinement entropy with chain size and nanoconfinement size and dimension will be tested. The entropy loss on confining a chain to a nanopore will be directly determined from the difference in the entropy change on reaction in nanoconfined and bulk conditions. The research focuses on nanoconfined free radical n-alkyl methacrylate polymerizations since the thermodynamics of these systems in the bulk case are well understood. Monomer/polymer equilibria will be studied using calorimetry as a function of reaction temperature and confinement conditions, ranging from weak confinement for dilute solutions in large cylindrical pores to strong confinement for undiluted monomer in small spherical cavities. Monomer and initiator concentrations will be varied to change molecular weight independent of pore size and reaction temperature, whereas pore surface chemistry and monomer structure will be varied to change interfacial interactions. In addition, comparisons will be made with nanoparticle-filled systems having similar surface to volume ratios as the nanoporous matrices but without the chain confining constraints.