Physical Sciences and Mathematics Commons^™

Molecular Engineering Of Side-Chain Liquid Crystalline Polymers By Living Polymerizations, Coleen Pugh, Alan L. Kiste

Chemistry and Biochemistry

“Living” anionic, cationic, metalloporphyrin and ring-opening metathesis polymerizations have been used to prepare well-defined side-chain liquid crystalline homopolymers, block and graft copolymers and statistical copolymers. This paper analyzes their successes and failures by reviewing the mechanistic aspects and experimental conditions of each type of polymerization, and identifies other classes of mesogenic monomers that could be polymerized in a controlled manner in the future. The emerging structure/property relationships are then identified using well-defined SCLCPs in which only one structural feature is varied while all others remain constant.

The thermal transitions of liquid crystalline polymethacrylates, polynorbomenes and poly(viny1 ether)s reach their limiting …

High-Power Broadly Tunable Picosecond Ir Laser System For Use In Nonlinear Spectroscopic Applications, D. E. Gragson, B. M. Mccarty, G. L. Richmond, D. S. Alavi

Chemistry and Biochemistry

We developed a high-power tunable picosecond IR laser system suitable for nonlinear spectroscopic investigations. We employ a Ti:sapphire regenerative amplifier that produces 1.9-ps, 17-cm⁻¹, 800-nm pulses at 1 kHz as a pump source. White-light generation in ethylene glycol and optical parametric amplification in potassium titanyl phosphate are used to produce the IR pulses. The tuning range extends from 2.4 to 3.8 μm in the idler and 1.0 to 1.2 μm in the signal. A total efficiency (signal plus idler) as high as 20% was achieved. The spatial, spectral, and temporal characteristics of the IR beam are presented along …

Critical Pressures In Multicomponent Lipid Monolayers, John P. Hagen, Harden M. Mcconnell

Chemistry and Biochemistry

Epifluorescence microscopy has been used previously to study coexisting liquid phases in lipid monolayers of dihydrocholesterol and dimyristoylphosphatidylcholine at the air/water interface. This binary mixture has a critical point at room temperature (22°C), a monolayer pressure of approx. 10 mN/m, and a composition in the vicinity of 20-30 mol% dihydrocholesterol. It is reported here that this critical pressure can be lowered, raised, or maintained constant by systematically replacing molecules of this phosphatidylcholine with molecules of a phosphatidylethanolamine, or an unsaturated phosphatidylcholine, or mixtures of the two, while maintaining the dihydrocholesterol concentration at 20 mol%. Thus, even complex mixtures of lipids …

An Improved Synthesis Of 2-(Hydroxymethyl)Indene, Hasan Palandoken, William T. Mcmillen, Michael H. Nantz

Chemistry and Biochemistry

No abstract provided.

Tunable Picosecond Infrared Laser System Based On Parametric Amplification In Ktp With A Ti:Sapphire Amplifier, D. E. Gragson, D. S. Alavi, G. L. Richmond

Chemistry and Biochemistry

A picosecond laser system that will generate high-power tunable IR pulses with bandwidths suitable for spectroscopic applications is discussed. The system is based on white-light continuum generation in ethylene glycol and optical parametric amplification in potassium titanyl phosphate. The nonlinear-optical processes are driven by a regeneratively amplified Ti:sapphire laser that produces 1.7-ps pulses at a repetition rate of 1 kHz. Energies as high as 40 and 12 µJ have been achieved over the signal (1.02–1.16-µm) and idler (2.6–3.7-µm) tuning ranges, respectively. The IR beam temporal and spatial characteristics are also presented.

Three-Phase Intersection Points In Monolayers, John P. Hagen, Harden M. Mcconnell

Chemistry and Biochemistry

Some phospholipid/dihydrocholesterol Langmuir monolayers form coexisting liquid phases. Gas domains form at the interface between the phospholipid-rich and dihydrocholesterol-rich liquid phases when these monolayers undergo expansion to low surface pressure. Analysis of the domain shapes thus formed yields the relative line tensions of the gas/phospholipid, gas/dihydrocholesterol, and phospholipid/dihydrocholesterol phase interfaces.

Sensitivity Of Second Harmonic Generation To Space Charge Effects At Si(111)/Electrolyte And Si(111)/Sio2/Electrolyte Interfaces, P. R. Fischer, J. L. Daschbach, D. E. Gragson, G. L. Richmond

Chemistry and Biochemistry

The potential dependence in the surface second harmonic response from hydrogen terminated n‐Si(111) and oxidized n‐Si(111) surfaces has been examined in aqueous NH₄F and H₂SO₄ solutions. The relative phase of the nonlinear response as measured by rotational anisotropy experiments is found to be highly sensitive to the presence of the oxide and the field applied across the Si(111)/oxide/electrolyte interface. These observations are attributed to field effects within the space–charge region of the semiconductor which vary with the presence and thickness of the insulating oxide layer on the Si(111) surface.