We report the first ever photon correlation spectroscopy performed on single alkali and mixed alkali metaphosphate glasses at refractory temperatures above the glass transition. We find not only a significant decrease in the glass transition temperature but also a decrease in fragility for the mixed alkali composition as compared with the single akali glasses. We argue that structural relaxatio...

Materials Research Group (CMRG) at the University of Mississippi (UM) have recently begun a research study supported by the U. S. Department of Agriculture (NRICSREES-USDA Award number 2003-35504-13627) examining natural fiber reinforcements (NFR). The objectives of this research are to demonstrate the feasibility of using the cost-effective pultrusion process to manufacture high quality polyme...

We have measured the relaxation to equilibrium in the supercooled nematic phase upon approach to Tg of a fragile liquid-crystalline photosensitive polymeric glass former. Perturbation is introduced in a non-conventional way by optical pumping (orientation) of the nematic polydomain phase. Relaxation back to equilibrium is followed both on the microscopic scale, by means of depolarized time-reso...

In this letter we employ null ellipsometry on Langmuir Blodgett multilayers of a glass forming photosensitive side chain polymer to investigate both the structural changes and the related time relaxation as a function of temperature and sample thickness following isothermal optical perturbation. Below a thickness of a few layers the glassy multilayer system collapses to a smecticlike crystal. T...

We briefly review our findings on the relationship between the fragility of glass formation and cooperative motion, focusing on a simple glass-forming polymer melt. We identify string-like cooperative motions with the hypothetical ‘cooperatively rearranging regions’ of the Adam-Gibbs (AG) description, thereby providing a molecular basis for this interpretation. Moreover, these strings can be de...

Cyclic olefin copolymers comprise a new class of polymeric materials showing properties of high glass-transition temperature, optical clarity, low shrinkage, low moisture absorption, and low birefringence. There are several types of cyclic olefin copolymers based on different types of cyclic monomers and polymerization methods. In this work, we have analyzed the chemical structure of the curren...

The role of substrate modulus on critical loads to initiate and propagate radial cracks to failure in curved brittle glass shells on compliant polymeric substrates is investigated. Flat glass disks are used to drive the crack system. This configuration is representative of dental crown structures on dentin support in occlusal contact. Specimens are fabricated by truncating glass tubes and filli...

We perform molecular dynamics simulations of the glass transition through isobaric and isochoric cooling of a model polymeric material. In general, excellent agreement between the simulation results and the existing experimental trends is observed. The glass transition temperature (Tg) is found to be a function of pressure under isobaric conditions and specific volume under isochoric conditions...