Steven Ashley Snow

Laser Direct Writing of Single-Mode Polysiloxane Optical Waveguides and Devices

Using a custom-built laser direct writing system, single-mode polymer optical waveguides, and devices for board-level optical interconnects were fabricated. A novel photopatternable polysiloxane material was developed that combines low-loss, simple, and large-area processability, and reliability during manufacturing and system operation. The polysiloxane waveguides were designed with quadratic cross sections of 5.5 × 5.5 μm2 and a refractive index contrast of 0.0086 between core and cladding polymer for single-mode operation at the wavelength of 1.3 μm. A straight waveguide propagation loss of 0.28 dB/cm was achieved. A wide range of passive optical devices, including Y-splitters, directional couplers, and Mach-Zehnder interferometers were successfully fabricated and characterized. The results prove that the presented combination of material and process technology is a viable implementation for short distance board-level optical links.

LIMITING CASES OF GRAVITATIONAL DRAINAGE OF A VERTICAL FREE FILM FOR EVALUATING SURFACTANTS

The evolution of the deforming free surface of a vertically oriented thin film draining under gravity is examined for the case when there is an insoluble surfactant monolayer on a viscous, incompressible, and free liquid film with finite surface viscosity. Three coupled nonlinear partial differential equations describing the free surface shape, the surface velocity, and surfactant transport are obtained. These equations are derived at leading order and do not have inertial effects. We examine the case where the film is nearly flat so that mean surface tension is negligible; this will be in good agreement with experimental data with respect to long-time behavior of film thickness. This will be shown both analytically and computationally.We will show that in the limit of large surface viscosity, the evolution of the free surface is that obtained for the tangentially immobile case. It is verified that increasing surface viscosity slows down film drainage, thereby enhancing film stability. The Marangoni effec...

An insoluble surfactant model for a vertical draining free film with variable surface viscosity

A mathematical model is constructed to study the evolution of a vertically oriented, thin, free liquid film draining under gravity when there is an insoluble surfactant, with finite variable surface viscosity, on its free surface. Lubrication theory for this free film results in three coupled nonlinear partial differential equations describing the free surface shape, the surface velocity and the surfactant transport, at leading order. In the limit of large surface viscosity and the Marangoni effect, the evolution of the free surface is that of a rigid film. For mobile films with small surface viscosity, transition from a mobile to an essentially immobile film is observed for large Marangoni effects. It is also verified that stable aqueous films can be formed in the regime of high surfactant concentrations. The theoretical results are compared with experiment; the purpose of both is to act as a model problem to evaluate the effectiveness of surfactants for potential use in foam-fabrication processes.

The preparation of the mixed alkali metal silanolate K4Li4(OSiMe3)x(OCMe3)8−x (8⩾x⩾5.7) and the effects of mixed alkali metals on the anion induced ring opening polymerization of octamethylcyclotetrasiloxane

Abstract The novel mixed alkali metal silanolate K 4 Li 4 ( OSiMe 3 ) x ( OCMe 3 ) 8−x (x=6.8 ( 1 ), 5.7 ( 2 ), 8 ( 3 )) has been prepared via the reaction of hexamethyldisiloxane with n-butyllithium and potassium-butoxide in THF or by the reaction of KOSiMe3 with LiOSiMe3. Molecular weight studies show a partial dissociation to smaller clusters in solution. The mixed alkali metal compounds 1–3, as well as an equimolar mixture of KOSiMe3 and LiOSiMe3, serve as unique catalysts for the anion indueed ring opening polymerization of octamethylcyclotetrasiloxane in that they produce a linear polymer of relatively high molecular weight and low polydispersity.

The addition of polyoxyethylene/polyoxypropylene block copolymers to silicone surfactant systems to improve the porosity of flexible polyurethane foam

ilicone surfactants are used for the production of flexible polyurethane foam. These surfactants are commonly graft copolymers of polydimethylsiloxane (silicone) and various polyethers containing ethylene oxide and propylene oxide monomeric units. A typical structure of these copolymers is shown in Figure 1. This structure allows the copolymer to favorably orient itself at the bubble surface. The siloxane backbone is believed to reside on the air side of this interface while the polyether chains extend into the polyurethane matrix. The role of the silicone surfactant in the production of these foams appears to be complex and quite controversial. Its role in the reduction of the surface tension of the liquid mixture of polyoxypropylene glycols, toluene diisocyanates, and various additives [catalysts, blowing agent (usually methylene chloride), water] has been well documented [1-3].