The study of advanced materials using neutrons

Author

Gary W. Lynn

Date of Award

12-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Mark D. Dadmun

Committee Members

Roberto S. Benson, R. J. Hinde, L. J. Magid

Abstract

The first part of this thesis describes a new methodology based on a novel combination of x-ray reflectivity and small-angle neutron scattering to evaluate the structural properties of porous silica thin films about one micrometer thick supported on silicon wafer substrates. To complement these results, film composition was determined by high-energy ion scattering techniques. For the sample thin film presented here, the overall film density was found to be (0.55 ± 0.01) g/cm³ with a pore wall density of (1.16 ± 0.05) g/cm³ and a porosity of (53 ± 1) %. The average dimension for the pores was found to be (65 ± 1) Å. It was determined that (22.1 ± 0.5) % of the pores had connective paths to the free surface. The mass fraction of water absorption was (3.0 ± 0.5) % and the coefficient of thermal expansion was (60 ± 20) x 10^-6/°C from room temperature to 175 °C. In the second part of this thesis, we elucidate the structure of a small molecule liquid crystal/polymer interface using specular neutron reflectivity. More specifically, we examined the interfacial transition zone width of a small molecule liquid crystal/polymer interface as a function of increasing temperature. We found that the interface between a thin film (≈ 1000 Å thick) of the liquid crystal 4'-n-octyl-4-cyanobiphenyl (8CB) and a thin film (≈ 800 Å thick) of deuterated poly(methyl methacrylate) (d-PMMA) is broad and broadens with increasing temperature. It is also observed that the thin film geometry influences the mixing behavior of the PMMA/8CB system. These results may have implications on current theories of liquid crystal display devices that are formed by the phase separation of liquid crystal polymer mixtures.

Recommended Citation

Lynn, Gary W., "The study of advanced materials using neutrons. " PhD diss., University of Tennessee, 2000.
https://trace.tennessee.edu/utk_graddiss/8340