F. J. Micale

PREPARATION OF LARGE-PARTICLE-SIZE MONODISPERSE LATEXES IN SPACE: POLYMERIZATION KINETICS AND PROCESS DEVELOPMENT

ABSTRACT Monodisperse polystyrene latexes are prepared by seeded emulsion polymerization; however, sizes larger than 2μm are difficult to prepare because of the creaming and settling of the particles, and their sensitivity to mechanical shear. Preparation in space would obviate the creaming and settling, and allow agitation just sufficient for good heat transfer and mixing. Three polymerizations yielding 3-5μm size particles were carried out successfully on the third flight of the “Columbia” launched March 22, 1982; however, four polymerizations yielding sizes up to 10μm on the fourth flight launched June 27, 1982, were incomplete owing to apparatus malfunction. The results of these polymerizations and the prospects of developing a preparative space process are reviewed

CONCERNING THE ORIGIN OF CHARGE AT THE POLYSTYRENE PARTICLE/WATER INTERFACE

ABSTRACT The electrophoretic mobility behavior of well-characterized polystyrene latex particles, carrying one type of surface functional endgroups, has been studied as a function of pH. At low pH, the interaction of protons with the functional endgroups increased in the order: Hydroxyl > carboxyl > sulfate; at high pH the order of interaction was reversed; and at intermediate pH no interactions were observed. The particles of the polystyrene latexes in their different forms at the intermediate pH range, dispersed in deionized water, all exhibited the same mobility irrespective of the functional endgroup. The origin of charge in these systems is explained as being the result of either the preferential adsorption of hydroxyl ions or an electron - injection mechanism due to the overlap of local intrinsic molecular - ion states in polystyrene and water. At low concentrations of functional endgroups, the surface properties of the polystyrene latexes are largely dependent upon the hydrophobic nature of the sur...

Pore structural studies of monodisperse porous polymer particles

Abstract Monodisperse polystyrene latex particles with molecular weight on the order of 106 were used as inert diluents for the preparation of monodisperse porous styrene-divinylbenzene copolymer particles via seeded emulsion polymerization techniques. Mercury porosimetry and nitrogen adsorption-desorption isotherms were used to assess pore structure and pore size distribution. Pore size distribution was very sensitive to the molecular weight of the polystyrene latex particles used as inert diluent. Qualitative evidence from the techniques used indicated that the monodisperse porous polymer particles were macroporous (average pore diameter > 500 A) in nature. As the molecular weight of the linear polymer decreased, the porous structure of the polymer particles ranged in complexity across the spectrum of macro/mesopore structures. Scanning electron microscope results indicated the existence of voids between the microspheres and their agglomerates within the porous polymer particle, and nitrogen adsorption isotherms confirmed that the pores were due to interstices between these crosslinked microspheres and agglomerates.

Surface properties of Ni(OH)2 and NiO. I. Water adsorption and heat of immersion of Ni(OH)2

Nickelous hydroxide samples were prepared from a nickelous nitrate solution with distilled ammonia gas. Particle sizes by X-ray diffraction and electron microscopy ranged from 40 to 400 nm. Water adsorption isotherms, measured gravimetrically, indicated that hydrophilicity depends upon sample preparation. The isosteric heats of adsorption calculated for one sample from multi-temperature isotherms at 25 and 39°C showed high heats of adsorption, 69 kJ/mole, at coverages below 4 molecule/nm2. The heat of immersion of the same sample of Ni(OH)2, measured by means of an adiabatic calorimeter as a function of water precoverage, showed that the heat decreased linearly from an initial zero water coverage value of 320 to 190 mJ/m2 at a coverage of 2.9 molecule/nm2. It is concluded that the surface of Ni(OH)2 is predominately hydrophobic with a limited concentration of polar sites on the crystal edges available for hydrogen bonding with polar adsorbates.

Column Electrophoresis on the Apollo-Soyuz Test Project

INTRODUCTION Electrokinetic separation techniques have been widely used for the analysis and characterization of charged materials of biological origin.3,4 Under terrestrial conditions preparative methods based on zone electrophoresis, isotachophoresis, and isoelectric focusing are prominent in the purification of charged macromolecules and small particles but have only been of limited usefulness in the separation of biological cells and larger particles. The major difficulties in the latter applications arise primarily from In the Apollo 16 experiment, a mixture of polystyrene latices was processed in an improved version of the apparatus used on Apollo 14. Whereas with such a device it is not possible to conduct the processing under terrestrial conditions without the appearance of extensive thermal convection which destroys the separation bound- aries, under microgravity conditions flight photographs showed no boundary deterioration, but did indicate that electroosmosis was a major factor in producing ov...

Surface properties of Ni(OH)2 and NiO. II. Mechanism for the thermal decomposition of Ni(OH)2 and other metal hydroxides

Abstract Nickelous hydroxide has the CdI2 structure and can be converted to NiO with the NaCl structure by thermal decomposition. It is proposed that the hexagonal plates of the hydroxide split into layers of the oxide when thermally decomposed at moderate temperatures. The relationship between the specific surface areas of the product NiO and its parent Ni(OH)2 is Σ 2 Σ 1 = 2 H 2ρ2 (1− h rn ) 1 Σ 1 + ρ 1 rρ 2 whereΣ is the specific surface area, H2 is the NiO plate thickness, ρ is the density, n is the number of layers which the parent plate will yield, h and r are crystallographic-geometric factors, and subscripts 1 and 2 refer to the hydroxide and oxide, respectively. Five Ni(OH)2 samples, which were prepared through precipitation by NH3 gas or by direct addition of NaOH, were decomposed in vacuum at 200°C. The specific surface areas of the oxide and its parent fit the above equation excellently. A review of the literature yielded surface area data for other samples of hydroxide precipitated from the ammonia-nickel complex which also fit the equation but with a higher slope and intercept. Electron micrographs provide support for the proposed splitting of the hydroxide plate. The magnesium hydroxide/magnesium oxide system is similar to the nickel system. A review of the literature yielded surface area data which also follow the above relationship. The slope provides information on the thickness of the oxide plates. Results are in excellent agreement with published X-ray broadening studies of MgO.

Surface properties of heat-treated chromia of narrow particle size distribution

Abstract Spherical particles of chromium(III) hydrous oxide having a very narrow size distribution have been prepared on a multigram scale by the sulfate process of Matijevic and characterized with regard to texture, chemical composition, and particle size distribution. Also, the surface properties have been determined as a function of activation temperature (room temperature through 1000°C) under vacuum. The unheated chromia is amorphous and hydrophilic and likely has a chain-like molecular structure. Its water sorption characteristics correlate with its bulk dehydration properties. The initial product contains considerable amounts of sulfate, i.e., the chromium to sulfate ratio in unwashed samples approaches three; this sulfate can be removed readily by washing with acid or base. Neutral water, however, is much less effective. Particle size and shape are not significantly altered by washing. The surface properties of the heat-treated chromia are reproducible and depend on the sulfate content of the original sol. The BET surface area increases progressively up to an activation temperature of ca. 450°C, mainly because of the formation of micropores. Further increase in activation temperature results in the transformation of the micropores into mesopores on account of crystallization. The analysis of argon adsorption of the micro- and mesporous samples was carried out by using the αs-method of Sing and Brunauers corrected modelless method, respectively. The estimated external area of the microporous samples agrees with the particle size estimated by electron microscopy. The volume to surface ratio of the micropores (a measure of their size) remains unchanged during their progressive growth with activation temperature (200–450°C). The mesopores formed have a very narrow size distribution. The uniformity of the micropores and the mesopores is attributed to the relatively narrow particle size distribution of the original hydrous oxide.

Rapid Measurement of Adsorption Isotherms of Emulsifiers on Latex Particles

The adsorption of emulsifier on latex particle surfaces often determines the stability of the latex. However, relatively few adsorption isotherms have been published because these experiments are difficult and time-consuming. This paper describes the determination of adsorption isotherms using a new serum replacement technique, which was developed to characterize latex particle surfaces by removing adsorbed emulsifier from the latex particle surfaces and solute electrolyte from the aqueous phase. The latex is confined in a cell with a Nuclepore filter membrane, and doubly-distilled, deionized water is pumped through the latex to replace the serum. This method allows complete recovery of the serum, as well as determination of the concentration profile of the desorbing species in the effluent stream. To determine adsorption isotherms, a known amount of emulsifier is added to a cleaned latex and the concentration profile of the emulsifier in the effluent stream is measured. A material balance between added emulsifier and desorbed emulsifier (from the concentration profile) gives the adsorption isotherm. This adsorption isotherm is correlated with the predictions of a mathematical model of the process. The adsorption of technical-grade sodium lauryl sulfate, Aerosol MA, and Aerosol OT on a Dow monodisperse polystyrene latex of 190 nm diameter determined at 23 ± 2° follows a Langmuir adsorption isotherm. The mole-r culac areas at saturation are 42 - 43 A2 , 39 - 45 A2, and 85 -100 A2, respectively. The adsorption of sodium lauryl sulfate on a monodisperse polymethyl methacrylate latex of 330 nm diameter also follows a Langmuir absorption isotherm and gives a molecular area at saturation of 57 A2. The adsorption of sodium lauryl sulfate on a monodisperse polyvinyl acetate latex of 165 nm diameter does not follow a Langmuir adsorption isotherm, but instead gives a curve characteristic of porous surfaces. The molecular area at saturation is 30 A2.

Polystyrene latex separations by continuous flow electrophoresis on the Space Shuttle

Abstract The seventh mission of the Space Shuttle carried two NASA experiments in the McDonnell Douglas Astronautics Corporation continuous flow electrophoresis system. The objectives were to test the operation of continuous flow electrophoresis in a reduced gravity environment using stable particles with established electrokinetic properties and specifically to evaluate the influence of the electrical properties of the sample constituents on the resolution of the continuous flow electrophoretic device. Polystyrene latex microspheres dispersed in a solution with three times the electrical conductivity of the curtain buffer separated with a significantly larger band spread compared to the second experiment under matched conductivity conditions. It is proposed that the sample of higher electrical conductivity distorted the electric field near the sample stream so that the polystyrene latex particles migrated toward the chamber walls where electroosmosis retarded and spread the sample.

Surface properties of Ni(OH)2 and NiO. III. Microporosity and irreversible water adsorption of NiO prepared by thermal decomposition of Ni(OH)2

Abstract The microporosity of nickel oxide (NiO) and its parent nickelous hydroxide Ni(OH2) are measured by comparison to reference isotherms. The parent Ni(OH)2 is concluded to be nonmicroporous but its thermal decomposition product NiO is 70% microporous. Exposure of freshly prepared NiO to water vapor results in irreversibly sorbed water and a subsequent decrease in micropore volume of about 29%, without appreciable change in external, nonmicroporous area. The various adsorption techniques of micropore analysis, n, t, and αs are discussed.