LABORATORY OF THE MONTH

Franklin Institute Research Laboratories

Advanced analytical techniques aid the basic research programs of the Chemistry Department of The Franklin Institute Research Laboratories, Research deals chiefly with studies of the organic solid state, polymer film properties, and novel polymerization processes.

Radioact ive t racer techniques are used to investigate molecular diffusion in organic crystals. After diffu­sion anneals, crystals are sectioned and the distribution of radio­active diffusant deter­mined by means of l i q u i d s c i n t i l l a t i o n s p e c t r o m e t r y . T h i s technique is particu­l a r l y u s e f u l f o r or­ganic solids since they are readily soluble in organic solvents

IN T H E FALL of 1966, a new $5 million research center was dedicated in

Philadelphia, adjacent to The Franklin Inst i tute Science Teaching Museum. Containing 150,000 square feet of space in five floors, the new research building houses a professional staff of nearly 300, with room for expansion of both office and laboratory space to accom­modate changing programs.

Over the years, few museum visitors realized that behind certain doors in the museum itself, and in leased buildings throughout the immediate area, the In­stitute maintained one of the nation's major not-for-profit research organiza­tions. Virtually all laboratory activi­ties are now situated in the new build­ing. The 20-year-old Research Labora­tories currently performs over $6 mil­lion in R&D contracts annually, in pro­grams for both large and small in­dustries, and government agencies, Federal, state, and local. (The Insti­tu te has two other research groups: the Center for Naval Analyses, a group with headquarters in Arlington, Va., involved in operations research and evaluation for the Navy, and a fun­damental physics research group known as the Bartol Research Foundation, in Swarthmore, Pa.)

The Research Laboratories, in Phila­delphia, comprises five departments (Chemistry, Materials Science and En­gineering, Systems Sciences, Mechanical and Nuclear Engineering, and Electri­cal Engineering), and three groups of lesser scope—aerospace engineering, ap­plied physics, and science information services.

Staffed in such a variety of disci­plines, the Research Laboratories has major research programs going on in an equally wide variety of fields. A few in departments other than Chemistry a re : bio-instrumentation, telemetry, glau­coma detection, integrity of nuclear re­actor structures and components and submarine hulls, manned centrifuges and aerospace simulators, hydrostatic bearings and lubrication systems, com­mand and control systems, man-ma­chine studies for highway safety, opera­tions research study of crime predic­tion, hydraulic contamination, elec-troexplosive devices, and human fa­tigue.

Chemistry programs in basic re­search are aimed a t more complete un­derstanding of the chemistry and phys­ics of the organic solid state. Applied research programs in the Depar tment cover many problems of industrial technology, among them the problem of coatings tha t promote more efficient dropwise consideration on the condens­ing surfaces of desalinization stills.

116 A · ANALYTICAL CHEMISTRY

This new $5 million re­search center of The Franklin Institute Re­search Laborator ies, Philadelphia, Pa., was dedicated in the Fall of 1966. The 20-year-old Research Laboratories performs over $6 mil­lion in research and development annually for government and industry

Initiation of crystal growth from the vapor phase can be controlled and crystal growth observed in a special furnace which allows precise tempera­ture control. Crystals of high optical quality can be obtained in this way

The Chemistry staff is looking at several aspects of organic solids: growth and purification of organic solid crystals ; the conductivity and reactivity of crystals; photovoltaic phenomena in organic solids and solutions; molecular diffusion; novel polymerization proc­esses in solution, and the physical properties of glow-discharge polymer films.

Essential to such studies are tools for analyzing structure, composition, and puri ty of crystals and polymers. Among the tools used in these programs are infrared, visible, and UV spectro­photometry, gas-liquid chromatogra­phy, and liquid scintillation spectrome­try.

In an early study to determine the ex­tent to which a crystal lattice affects and controls the reactions of organic molecules, a relatively simple reaction was chosen—solid aromatic hydrocar-bon-perylene-with bromine. Metering the decomposition of the resultant charge-transfer complex suggested tha t the solid state can in some cases serve as a matrix to control the rate, isomer distribution, and stereochemistry of or­ganic reactions, and these phenomena are now under study.

To add to our understanding of me­chanical strength, electrical properties, and reactions of organic solids, molecu­lar diffusion studies have been in prog­ress for four years. The prime objec­tives have been to obtain diffusion pa­rameters for organic molecular crystals, an area which has received little a t ten­

tion, and to gain insight into the role of crystal defects in the physical proper­ties of such crystals. Diffusion from a thin layer of radioactive material and subsequent sectioning of the crystal make it possible for the investigator to determine the penetration profiles from which diffusion parameters can be evaluated. Permeation techniques allow the measurement of gas diffusion through thin (50-100 μ) single crystal membranes.

I n their work on the electrical proper­ties of organics, staff members are seek­ing to elucidate mechanisms of conduc­tion in organic solids. Ul t rapure solids are prepared, for studies on charge-car­rier injection, trapping, and t ransport by a variety of steady state and t ran­sient measurement techniques. Zone refining and crystal growth from the melt by means of the Bridgeman meth­od are techniques routinely used to sup­ply samples for these studies. Con­trolled initiation and growth of crystals from the vapor phase is also employed to provide crystals of high physical per­fection and purity.

The production of photovoltages in thin layers of organic solids, glow dis­charge polymer films, and solutions con­taining electron donors and acceptors is currently under investigation in a pro­gram to explore the potentialities of or­ganic materials in photocells. Organic materials generally show maximum photo-response in the spectral region where solar energy output is a t a maxi­mum, in contrast to silicon solar cells.

VOL. 39, NO. 4, APRIL 1967 · 1 1 7 A

L A B O R A T O R Y O F T H E M O N T H

Power outputs are much less in organic systems investigated so far, however, being in the microwatt region or lees.

Unusual physical and chemical prop­erties are demonstrated by the dense, thin, pinhole-free polymer films that are formed by glow-discharges in or­ganic, metallorganic, and inorganic va­pors. By collecting such films on vari­ous substrates, and examining them by infrared and electron spin resonance spectroscopy, it is possible to determine their molecular bonding and reactivi­ties. Recently, reactive film species have been collected from the Crookes dark space on a surface cooled by liquid nitrogen, and grafted to polymeric sub­strates of known composition. Anal­ysis of the products reveals information about polymerization reactions.

Investigation of charge-transfer chemistry led to the discovery of a new type of cationic polymerization of N-

vinylcarbazole catalyzed by quinones and similar electron acceptors which, heretofore, were viewed mainly as in­hibitors of free radical polymerizations. The initiating mechanism is believed to involve formation of a charge-transfer complex between monomer and catalyst followed by redox-dissociation to form the radical-cation of the monomer and the radical-anion of the catalyst. Pres­ent investigations are concerned with further elucidation of the mechanism, and expanding the scope of applications of this polymerization to the prepara­tion of other polymers and copolymers. A related finding was that 7V-vinylcar-bazole can be polymerized by 40 ppb or less of a protonic acid, which probably is the lowest concentration of a catalyst ever known to catalyze an addition pol­ymerization. This effect can be used to detect minute traces of acidic contami­nants in the atmosphere or in solution.

Electronic equipment to measure transient photo-currents in photo-conduc­tive organic crystals al­lows the evaluation of such defect and impurity sensitive properties as charge carrier generation and trapping

The Measurement of small conductivity changes produced in high resistance organic crystals by ambient vapor-crystal interactions can be used to de­tect low levels of ambient vapor. Meas­urable conductivity changes can be produced in anthracene crystals, for example, by iodine vapor at the ppm level

Zone-refining techniques are applied in the preparation of high purity organic solids. Single crystals are grown from the melt by means of a Bridgeman furnace

Many ordinarily unreactive organic mate­rials may be induced to polymerize when bombarded by electrons. The reaction is accompanied by a glow discharge at reduced pressure and results in the formation of a polymer film of high density. Electrical prop­erties of such fi lms are evaluated and related to physical and chemical structure

118 A · ANALYTICAL CHEMISTRY See ACS Laboratory Guide for All Products/Sales Office

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