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RD Miller

Publications and source records attributed to RD Miller.

14 recordsLinked to original sources
PubMed1999

Ordered bicontinuous nanoporous and nanorelief ceramic films from self assembling polymer precursors

Three-dimensional ceramic nanostructured films were produced from silicon-containing triblock copolymer films exhibiting the double gyroid and inverse double gyroid morphologies (space group Ia3d). A one-step room-temperature oxidation process that used ozonolysis and ultraviolet irradiation effected both the selective removal of the hydrocarbon block and the conversion of the silicon-containing block to a silicon oxycarbide ceramic stable to 400 degrees C. Depending on the relative volume fraction of the hydrocarbon block to the silicon- containing block, either nanoporous or nanorelief structures were fabricated with calculated interfacial areas of approximately 40 square meters per gram and pore or strut sizes of approximately 20 nanometers.

Journal Article↗
PubMed1998

Segmental Dynamics of Solid-State Poly(methylphenylsilane) by 1D and 2D Deuterium NMR.

The segmental dynamics of solid-state poly(methylphenylsilane) were probed with deuterium solid-echo and two-dimensional exchange (2D-X) NMR via a methyl-d3 label. Between 25 and 50 degreesC, the spectra indicated that the polymer consisted of two fractions-a fast fraction with correlation times (tauc) below 10(-5) s and one with tauc's above 10 s. Above 50 degreesC, motion with tauc's around 10(-3) s was also detected. A minimization routine was developed to fit the 2D-X spectra to a model of isotropic rotational diffusion with a distribution of tauc's. The best fits were obtained with trimodal stretched-exponential distributions. The trimodal distributions consisted of a fast mode with tauc's around 10(-5) s, an intermediate mode with tauc's between 10(-4) and 0.3 s, and a slow mode with tauc's generally above 10 s. As the temperature increased from 56 to 90 degreesC, the fast fraction steadily increased from 21% to 50% while its average tauc remained around 10(-5) s; the intermediate fraction remained relatively constant at 23% while its average tauc decreased from 125 to 8 ms, and the rigid fraction decreased from 55% to 32% with an average tauc around 40 s. The fast fraction was attributed to amorphous segments, the rigid fraction to crystalline segments, and the intermediate fraction to segments that formed an interphase between the two.

Journal Article↗
PubMed1996

Structure in Thin and Ultrathin Spin-Cast Polymer Films

The molecular organization in ultrathin polymer films (thicknesses less than 1000 angstroms) and thin polymer films (thicknesses between 1000 and 10,000 angstroms) may differ substantially from that of bulk polymers, which can lead to important differences in resulting thermophysical properties. Such constrained geometry films have been fabricated from amorphous poly(3-methyl-4-hydroxy styrene) (PMHS) and semicrystalline poly(di-n-hexyl silane) (PD6S) by means of spin-casting. The residual solvent content is substantially greater in ultrathin PMHS films, which suggests a higher glass transition temperature that results from a stronger hydrogen-bonded network as compared with that in thicker films. Crystallization of PD6S is substantially hindered in ultrathin films, in which a critical thickness of 150 angstroms is needed for crystalline morphology to exist and in which the rate of crystallization is initially slow but increases rapidly as the film approaches 500 angstroms in thickness.

Journal Article↗