Colloidal Particles In Solution Research Articles

Utilization of polymeric materials in laser fusion target fabrication

A variety of coating techniques are described that are used for depositing uniform films of a predetermined thickness and high surface quality of a laser fustion target ( LFT). The first coating method involves the thermal cleavage of di- p-xylylene. The product of this thermal treatment polymerizes readily to poly( p-xylylene). Addition of pendent groups onto the dimer di- p-xylylene extends the usefulness of this coating method. The modified dimers deposit films at significantly higher rates and with improved surface quality compared to films produced from the unmodified dimer. Spherulitic morphology is eliminated and the degree of crystallinity is decreased with the addition of pendent moieties on the phenylene ring. This reduction in the size of the morphological units significantly reduces the surface perturbations caused by these structures, giving rise to target coatings with the required smoothness. Complete elimination of all spherulites and also all lamellae (i.e., crystallinity) occurs with the glow discharge polymerization technique. The glow discharge polymerization of p-xylene is used to coat a LFT rapidly with a highly crosslinked, amorphous, transparent film having a high surface quality. The system is designed to eliminate powders from depositing on the target's surface. Finally, a technique is described for depositing inorganic and/or organic coatings using dilute aqueous solutions of colloidal particles. This method is unique in that the films are composed of layers of particles with each layer possessing the identical surface charge and chemical makeup.

Pseudo-exfoliation material. Electron microscopy after the application of lanthanum as tracer particles and ionic stain.

Lenses with pseudo-exfoliation (PE) were suspended in a solution of lanthanum, which was present partly in ionic form, partly as electron-dense tracer particles in colloidal solution, dependent on pH and on the concentration of lanthanum. By electron microscopy the tracer particles were found in a narrow zone along the surface of the PE excrescences. Only a few of the smallest particles had penetrated into their most superficial layer. In the specimens treated with ionic lanthanum, the effect was an electron-dense staining of the PE material within a 1-2 micrometer thick superficial layer. The PE fibrils as well as parts of the interfibrillar spaces were stained. These results indicate the presence of proteoglycans, and confirm the concept of an interfibrillar matrix which excludes other macromolecules and particles from penetrating into the material.

Thermal Motion and Forced Migration of Colloidal Particles Generate Hydrostatic Pressure in Solvent

A colloidal solution of ferrite particles in an osmometer has been used to demonstrate that the property that propels water across the semipermeable membrane is the decrease in hydrostatic pressure in the water of the solution. A magnetic field gradient directed so as to force the ferrite particles away from the semipermeable membrane of the osmometer and toward the free surface of the solution enhanced the colloidal osmotic pressure. The enhancement of this pressure was always exactly equal to the augmentation of the pressure as measured by the outward force of the particles, against the area of the free surface. Contrariwise, directing the magnetic field gradient so as to force the ferrite particles away from the free surface and toward the semipermeable membrane diminished the colloidal osmotic pressure of the solution. For a sufficiently forceful field gradient, the initial colloidal osmotic pressure could be negative, followed by an equilibrium pressure approaching zero regardless of the force of the particles against the membrane. Thus, the osmotic pressure of a solution is to be attributed to the pressure in the solvent generated in opposition to the pressure of the solute particles caused by their interaction with the free surface (Brownian motion and/or an external field force), or by their viscous shear when they migrate through the solvent, or both.

Mechanical and surface coagulation

Abstract A quantitative theory is developed for the kinetics of a coagulation at surfaces or interfaces. It is tested on aqueous colloidal solutions of hydrophobic particles coagulated by bubbling N2 through them. The theory is found to satisfy the experimental data quantitatively. An additional successful test is carried out on the same sols coagulating, in almost complete absence of turbulence, in rotating circular tubes under maintenance of a quasi stationary twin liquid meniseus against air. The sols used exhibited, if left standing quietly, a “shelflife”, without noticeable coagulum formation, in excess of several years.

Some possible phase transitions in dilute colloidal solutions

The relation between the molecular interaction of colloidal particles in solution and the formation of an anisotropic phase is examined in two special cases. It is shown that for an asymmetrical potential a continuous transition from the unordered to the nematic state is possible, while for a symmetrical interaction potential the most stable transition is discontinuous.

The Effect of Dissolved Substances on the Deposition of Colloidal Particles From a Solution by Means of an Electric Current

Effect of Various Dissolved Substances on Porcelain Slip (a Colloidal Solution of Particles of Clay, Flint, and Feldspar in Water).---(1) Effect on compactness of deposit produced by an electric current. It was found that the addition of only from 0.1 to 0.3 per cent. of any one of a number of substances, including ${\mathrm{Na}}_{2}$Si${\mathrm{O}}_{3}$, ${\mathrm{Na}}_{2}$S${\mathrm{O}}_{4}$, ${\mathrm{Na}}_{3}$P${\mathrm{O}}_{4}$, ${\mathrm{Na}}_{2}$HP${\mathrm{O}}_{4}$, H tartrate, Na tartrate, NaOH and KOH, resulted in a deposit which, though not quite dry, was solid instead of being semi-liquid. The compactness does not depend on the current density. As the amount of substance added is increased, the compactness increases less and less and soon reaches a limiting value. The full effect of the substance does not appear at once but only after a period which varies up to several hours. (2) Effect on the fluidity of the slip is to increase it markedly. From the relative action of different substances this effect is intimately related to the first one. Although the result of adding the substance is first to precipitate some of the particles, when more solid material is added the precipitate is redissolved so that for the same fluidity the proportion of solid dissolved is much greater with the added substance than without. (3) Suggested explanation. Both effects may be explained if we assume that the radii of the spheres of action of the particles of the slip are diminished by the dissolved substance. Particles will go into colloidal solution if no combinations result from encounters. This property is expressed in terms of the interfacial surface tension of the particles. The equations of distribution of colloidal particles under the action of gravity are obtained and with their help an explanation of the effect mentioned above, the precipitation and re-solution of the particles of the slip, is suggested. From a consideration of the experimental results it is concluded that the volume of the spheres of action of a particle in porcelain slip is about double the actual volume of the particle.

The law of distribution of particles in colloidal solution

The work of Perrin and his collaborators (1) on the experimental and theoretical application of the results of the kinetic theory to colloidal solutions is probably the most complete exposition of this very interesting phase of modern work. In the course of the work, Perrin (2) shows that we should expect a law of distribution of the particles in a colloidal suspension analogous to that regulating the distribution of the molecules of air in the atmosphere. By balancing the osmotic pressure of the particles in solution against the effect of gravity, he deduces the equation RT/N log n / n 0 = V (ρ 1 - ρ 2 ) g (h - h 0 ) , (1) where n and n 0 are the numbers of particles per cubic centimetre, at depths h and h 0 from the top of the solution, V is the volume of each particle, ρ 1 and ρ 2 , the densities of the material of the particles and the medium respectively, and R, T, N, and g the ordinary constants.

Societies and Academies

LONDON. Royal Society, November 3.—Prof. C. S. Sherrington, president, in the chair.—T. R. Merton: The spectra of lead isotopes. Comparison of the wave-lengths of five lines in the spectra of ordinary lead and lead from Australian carnotite shows differences wrhich are not constant, but vary for the different lines. The difference in wave-length observed for the principal line, λ= 4058 Å., is about two hundred times as great as that expected on theoretical grounds.—G. I. Taylor; Experiments with rotating fluids. Methods are described by which experiments pa spheres, cylinders, and vortex rings moving through rotating fluids can be projected in a lantern and instantaneous photographs taken. If any small motion be given to a rotating fluid, the resulting flow will be such that concentrated masses of coloured liquid should be drawn out into thin films, parallel to the axis of rotation. Photographs taken by a camera placed vertically above a rotating basin of water show that the liquid moves in this way.—L. Bairstow, Miss B. M. Cave, and Miss E. D. Lang: The two-dimensional slow motion of viscous fluids. In its restricted form the equation of motion of a viscous fluid is ∇4ψ = 0, where ψ is Stokes's stream function. If the molecular rotation in the fluid be defined by ξ≡∇2ψ the equation of motion may be expressed alternatively as ∇2ξ=0. The equation ∇4ψ=0 is transformed by means of Green's theorem to a form in which the only unknown is the distribution of the ξ doublets on the boundaries. The strengths of the doublets are found by solving the resulting integral equation. An example shows the motion of fluid past a circular cylinder in an infinite parallel-walled channel. If d be the diameter of the cylinder, ρ the density of the fluid, v the kinematic coefficient of viscosity, and U the velocity of the fluid in the centre of the channel at infinity, then, when the width of the channel is 5d, the resistance per unit length of cylinder is R=7.10ρvdU. The value of Ud/v to which this formula applies is not to exceed 0.2.—H. C. H. Carpenter and Constance Elam: The production of single crystals of aluminium and their tensile properties. The parallel portion of the test pieces of the sheet was 4 in. × 1 in.×0.125 in., consisting of about 1,687,000. The conversion of this area into a single crystal involved heat treatment for six hours at 550° C., tensile stress of 2.4 tons per square inch, producing an average elongation of 1.6 per cent. on 3 in., and final heat treatment beginning at 450° and extending up to 600° C. On an average, one test piece in four produces a single crystal over its parallel portion, which frequently grows up into the shoulders of the test piece. The tenacity of single crystals varied from 2.8 to 4.08 tons per sq. in., while the extension on 3 in. varied from 34 to 86 per cent., according to the orientation of crystal relative to stress. Five types of specimens were recognised. Stress tests of test pieces consisting of two and three crystals show the strengthening influence of one crystal upon another. Experiments on round bars resulted in the production of single crystals in the parallel portion pf bars 0.564 and 0.798 in. in, diameter. The total volumes of the crystals were more than 1 cb.in., and more than 2 cb.in. respectively. The tensile properties were determined, and in every case a wedge-shaped fracture was produced, the bar diminishing principally, in one dimension only. Remarkable twinning effects were observed in certain cases.—C. V. Raman and B. Ray: The transmission colours of sulphur suspensions. When a few drops of sulphuric acid are added to a dilute solution of sodium thiosulphate and a precipitate of sulphur gradually forms in the liquid, the suspension becomes practically opaque to the shorter wave-lengths first and the longer wave-lengths later, and afterwards regains its transparency partially, the shorter wave-lengths re-appearing first and later the longer wave-lengths. A theoretical explanation is offered.—E. F. Burton and Miss E. Bishop: The law of distribution of particles in colloidal solution.