Colloidal Aspects Research Articles

COLLOIDAL ASPECTS OF YEAST FLOCCULATION: A REVIEW

In this review, areas of colloid science including the DLVO theory, flocculation kinetics and suspension rheology are outlined and their applicability to the study of yeast flocculation discussed. Specifically, fundamental methods of predicting cell-cell interaction energies, orthokinetic flocculation rates and rheological flow properties of flocculent suspensions are detailed. While the application of these theories to brewing systems is somewhat difficult, they may aid our understanding of brewing yeast flocculation. The limited information available on the colloidal nature and properties of brewing yeast cells is also summarized.

Block Copolymers - a Special Ulass of RM. Surfactants

Interfacial characteristics of block copolymers with hydrophilic and hydrophobic sequences are described. Colloidal aspects of these polymers in aqueous solution are discussed. Special attention is paid to their surfactant behaviour e.g. micelle formation, solubilization and stabilization of colloidal dispersions e.g. emulsions, foams and in dispersion polymerisation. Properties of various copolymeric surfactants are reviewed. Applications and possible areas of more recent applications are explored

Some aspects of polymer colloids I. Preparation and properties of different types of latex particles

The boundary region separating a latex particle from the surrounding medium has a great influence on the properties of latex dispersions. Four types of polystyrene and polystyrene/comonomer latices differing greatly in the structure of the boundary region were prepared. The first part of a series of papers reports on the preparation of the various latex dispersions. Mean particle sizes were obtained from simple turbidity measurements, quasi-elastic light scattering, and electron micrographs. The behavior of the particles in the centrifugal force field is a simple tool for detecting aggregation tendencies that are not directly related to salt stability. The BET-surface area agrees with the area calculated from the mean particle size when a sharp boundary and smooth surface is developed between the particle and the surrounding medium. In the case of particles with extended boundary regions (core/shell particles or particles with hairy envelopes), film formation reduces the specific surface area. Removal of soluble oligomers and polymers from the boundary region during subsequent treatments (purification and centrifugation before freeze-drying) can increase the surface area considerably.

S. G. Mason—A retrospective

Without exaggeration one can say that Professor Stanley G. Mason was one of the founders of the science of microrheology. His early interest in this field was aroused when trying to understand the complex behavior of papermaking suspensions, the obvious relevance of which became evident after joining the Pulp and Paper Research Institute of Canada (Paprican) in 1946. Besides his publications with Professor Otto Maass from his thesis work on critical phenomena, his early work deals almost exclusively with the hydrodynamic and colloidal aspects of pulp suspensions. He realized that in order to understand the complexity of such systems, it was necessary to study the properties of the individual pulp fibers that make up the suspension. In this respect the classical work of Jeffery (1922) on the motion of ellipsoidal particles in linear shear flows was extremely relevant. Mason compared a pulp fiber with a long slender spheroid and applied Jeffery's theory to the motion of single suspended fibers. Over the years a large number of papers by Mason and coworkers were devoted to the extensions of Jeffery's work. From this early work came the realization that the properties of suspensions can be understood from a knowledge of the behavior of the suspended particles, a realization which led to the science of microrheology, a term coined first by Mason himself. Mason's early work on papermaking became classical among scientists working in the field of pulp and paper. It led, among other things, to an understanding of the electrokinetic properties

Rheological and Related Colloidal Aspects of Aqueous Processing that affect the Development of Microstructure

ABSTRACTShear flow in α-A12O3 suspensions having a volume fraction of solids (φ) in the range between 0.17 and 0.50 was investigated between pH 4 and 12. It is Newtonian if the magnitude of the zeta potential exceeds a critical value which depends on φ;its value is 39 mV if φ= 0.40 and 74 mV if φ= 0.50. If this potential is less than the critical value, shear flow is pseudoplastic; its yield value markedly changes (e.g., 0 to >100 Pa) in a slightly φ-dependent, narrow pH range (<0.5 units). If a second oxide, t-ZrO2 , is present, its pH-dependent colloidal behavior governs the overall rheology, though its concentration may be only 11 % that of α-A12O3. Scanning electron microscopy of composite pieces indicates that a detrimental, rheologically detectable interaction between α-Al2O3 and t-ZrO2 can be avoided and the distribution of t-ZrO2 can be optimized during pressure casting by control of pH. Best conditions correspond to either Newtonian flow or pseudoplastic flow with a very low yield value.

Colloidal aspects of pesticidal and pharmaceutical formulations—An overview

AbstractIn this overview, the colloidal aspects of pesticidal and pharmaceutical formulations of the dispersion type are described. The nature and magnitude of the interaction forces between particles or droplets in a dispersion are briefly described. These include double‐layer, steric and van der Waals' interactions. Combinations of these interaction energies govern the stability/instability of dispersions. The various states of suspensions and emulsions can be described in terms of energy‐distance curves. Particular attention is given to the various break‐down processes, such as flocculation, coalescence, Ostwald ripening and phase inversion. Some guidelines for the stabilisation of suspensions and emulsions are given. The following practical aspects of dispersion and emulsion formulation are discussed: (a) creaming, sedimentation and their prevention; (b) the assessment of the state and long term physical stability of suspensions, including particle and droplet size analysis and rheology. In the latter case, both steady‐state shear stress–shear rate and low deformation (oscillatory, constant stress and shear wave propagation) are very useful in the control and assessment of the long term physical stability; (c) mixed suspensions and emulsions i.e. suspoemulsions. The possible interactions between suspension particles and emulsion droplets are briefly described; (d) multiple emulsions that can be applied for sustained release; (e) microemulsions, their formation and characterisation illustrating the potential application of these systems in formulations: (f) microencapsulation, describing the most common procedures for preparation of such systems. These include interfacial polymerisation and condensation and coacervation techniques.

ON THE NUCLEATION OF SYNTHETIC DIAMOND

Based on the colloid aspects and the model of the structure transformations in diamond synthesis under the action of a solvent-catalyst, it is suggested that the coalescence of the puckered dimers of diamond as crystallized units is the main way of diamond nucleation. From experiments, a curve representing the qualitative relationship between the number of diamond nuclei and the temperature as well as the relationship between the diamond nucleation and the pressure are obtained. The roles of the above mentioned nucleation mechanism on directing the practice of diamond synthesis are discussed.

Microemulsions: Colloidal aspects

Microemulsions: Colloidal aspects

Symposium on colloid and surface chemical aspects of lubrication and lubricants

Symposium on colloid and surface chemical aspects of lubrication and lubricants

The future of cancer research

To forecast development in the future is a thankless job--for who can tell? I was once asked to write a prophecy for placement in a corner stone as to the state of biological investigation fifty years in the future. I refused, saying that if I could know what it was to be in two years I would be satisfied. My only excuse is that I have now been at the job of cancer research for 52 years, interrupted it is true by a couple of wars and other interludes. Still, that time included a lot of experiences, particularly as three-fifths of it included directing others in cancer research. Looking back on this time I wonder how slow was the progress of thought and experiment. During this time, I followed many leads: Fibiger's work (1) in 1927 on experimental production of transplantable cancer; the colloidal aspects of the vital system; tissue culture or the growing of cells for which we transplanted a pupil of Fischer's from the Kaiser Wilhelm Institute in Berlin; enzyme studies in 1931 (2) for which we transplanted a complete enzyme laboratory from the old German University in Prague, headed by a pupil of Willstaetter, for few in the United States knew anything about enzymes and certainly none about enzymes in cancer. All this was without any real leads to the future of cancer research. I began to think that I was accumulating a lot of isolated uncorrelated facts about cancer and finding that the research was upon experiment-and-error basis and not on scientific method. As a mat ter of fact it still is on the experiment-and-error basis as may be seen from the late meeting of the Association for Cancer Research at Chicago with its hundreds of papers. Experiment-and-error type of work is all right if enough experiments are done but sometimes it takes awful lot of them and then may not hit the right one, whereas the scientific method is to go from step to step and eventually arrive at a solution. So I began to consider the process of cancer. It had to have something to grow on and to support it like a plant needs soil and fertilizer-a growth factor as expressed by Fildes (a) an essential metabolite which cannot be synthesized. And what was the growth factor in cancer : it would be the same as in all young growing cells because cancer cells are immature cells--glucose of course for the main source but

Some colloidal aspects of the gluten problem

Some colloidal aspects of the gluten problem

Journal of Colloid Science

MANY readers will by this time have seen the first numbers of the Journal of Colloid Science, which is being published by the Academic Press of New York. From the international composition of its editorial board and consulting committee, however, it should also have a wide appeal outside the country of its origin. Publication is to be bi-monthly, and the yearly subscription is 10 dollars. This new journal should perform a useful service in bringing together a great number of related papers now scattered throughout the chemical and biological literature. The first number (January 1946) contains nine papers upon topics ranging over the biological and physical aspects of colloids.

Colloidal Structure of Rubber in Solution. Colloidal Aspects of Vulcanization

Abstract Colloidal changes in solutions of purified rubber due to a vulcanizing system consisting of piperidinium pentamethylenedithiocarbamate, sulfur, and zinc propionate have been followed by means of measurements of the depolarization and intensity of the transversely scattered light and by viscosity measurements. A study was made of the time required for vulcanization of benzene solutions of rubber with the above vulcanizing agents. The temperature coefficient of vulcanization was approximately the same as that for cures of solid stocks. The light scattering results are interpreted as showing that, upon the addition of the vulcanizing agents to the solutions, the colloidal units become larger. The decrease in viscosity is explained as being due to a diminished “interlocking” of the units. In the vulcanization of the solutions, an equilibrium of colloidal processes occurs which results in a constant viscosity for the larger part of the time required for vulcanization, although the light scattering measurements show a continuous change. The magnitude of the light scattering changes indicates that the molecular clusters in the gelled solution are probably not very different from those in the original solution. The viscosity measurements show that the forces between the clusters have been radically strengthened.

The Influence of Catalysts in the Reaction of Sulfur on Unsaturated Organic Substances. I. A Study of Vulcanization at Elevated Temperature

Abstract From these results it might be thought that in the presence of potassium xanthate or hexamethylenetetramine there is formed a compound of sulfur and cinnamate containing one atom of sulfur per molecule of the ester. This compound would not be identical to that found by Baumann and Fromm, which was mentioned in Section 1. It has been seen that it is formed at a higher temperature and that it contains two atoms of sulfur per molecule of the ester. We attempted to isolate the compound containing one atom of sulfur, the existence of which we suspected. To this end, we distilled under reduced pressure (13 mm.) the product extracted with acetone. However, at 143° C. the ethyl cinnamate distilled almost quantitatively, whereas the sulfur remained in the residue from the distillation. Moreover, we observed a very intense Tyndall effect in the acetone solution. Several reasons for these phenomena suggest themselves: 1. The compound formed is stable only in equilibrium with its components. By distillation the cinnamate is eliminated, equilibrium is destroyed, and the compound is quantitatively decomposed during distillation. 2. Upon the addition of acetone, with a view to extracting the substance, the compound is destroyed and the sulfur which is precipitated in the colloidal state is dissolved with ethyl cinnamate in the acetone. In the acetone solution, therefore, the cinnamate and colloidal sulfur are found in stoichiometric proportion. This would explain both the equivalence which was found and the colloidal aspect of the acetone solution. 3. A definite chemical compound is not formed, purely colloidal natural phenomena are involved, and the stoichiometric relations must he due purely to chance. We shall not pay any particular attention at this time to experiments which would lead to a choice among these explanations. They will be the object of a future work. Nevertheless it seems of interest to us to note the parallelism between the vulcanization of rubber and the sulfuration of a well-defined unsaturated compound, and particularly the action of catalysts of vulcanization. Finally another important similarity may be pointed out. In the case of vulcanized rubber, a definite compound has not been isolated. It is likewise known that sulfur, which alone is insoluble in acetone, passes over in large quantity when extractions are made with this solvent. The question has always arisen whether this is a case of phenomena of a colloidal nature or of the formation of chemical compounds. We shall continue our work with a study directed particularly to simple cases where the starting compounds are well-known ones. Our efforts will be especially directed to the existence or non-existence of definite compounds. We have pointed out in this first article the difficulties before us. We shall then continue with studies of isoprene and methylbutadiene. It is conceivable that by the progressive polymerization of these products the complex case of rubber will finally be reached.

The colloid aspects of textile materials and related topics. A general discussion

The colloid aspects of textile materials and related topics. A general discussion

The Colloid Aspects of Textile Materials

EIGHT years ago, the Faraday Society made an interesting experiment in devoting one of its discussions to “Physical and Physico-Chemical Problems Relating to Textile Fibres”. At that time the study of fibres was in its infancy, with an uncertain future, and all workers in the subject owe the Society a debt of gratitude for early encouragement during difficult years. Courageous patronage deserves a rich reward, and this the Society achieved in the outstanding success of the second discussion on “The Colloid Aspects of Textile Materials”, which was held in the Chemistry Department of the University of Manchester on Sept. 21–23. The meeting was noteworthy for the number and distinction of its overseas visitors and contributors, among whom were included E. H. Büchner (Amsterdam), E. Elöd (Karlsruhe), R. O. Herzog (Berlin), G. van Iterson (Delft), J. R. Katz (Amsterdam), P. Krais (Dresden), H. Mark (Ludwigshafen), M. Mathieu (Paris), O. Roehrich (Paris), S. E. Sheppard (Rochester, N.Y.), H. de Witt Smith (New York), H. Staud-inger (Freiburg), and J. J. Trillat (Paris).

The Faraday Society

The Faraday SocietyPublished Online:29 May 2014https://doi.org/10.1259/0007-1285-5-57-676-bSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail AboutAbstractThe Colloid Committee of the Faraday Society has arranged a general discussion on the colloid aspects of textile materials, to be held in the Department of Chemistry of the University of Manchester from September 21 to 23 next. Previous article Next article FiguresReferencesRelatedDetails Volume 5, Issue 57September 1932Pages: 673-736 © The British Institute of Radiology History Published onlineMay 29,2014 Metrics Download PDF

Colloid Aspects of Textile Materials

A GENERAL discussion on “The Colloid Aspects of Textile Materials” has been arranged by the Faraday Society to be held in the Department of Chemistry of the University of Manchester on Sept. 21–23, under the presidency of Sir Robert Mond. An introductory address will be given by Prof. F. G. Donnan. The general subjects to be discussed include cellulose and its derivatives, lignin and keratin fibre particles, their production, deformation, and degradation and manufacturing processes. Among the foreign guests who will speak at the discussion are: Prof. H. Mark (Ludwigshafen), Prof. H. Staudinger (Freiburg), Dr. S. E. Sheppard (Rochester, U.S.A.), Dr. J. J. Trillat (Paris), Prof. K. Freudenberg (Heidelberg), Prof. O. Roehrich (Paris), Prof. Herzog (Berlin), Prof. J. R. Katz (Amsterdam), Mr. C. R. Nodder (Lambeg), Prof. E. El¶d (Karlsruhe), and Prof. P. Krais (Dresden). Further particulars of the meeting can be obtained from The Secretary, Faraday Society, 13 South Square, Gray's Inn, London, W.C.1.

Colloid Aspects of Food Chemistry and Technology

WE start life as a quivering lump of jelly, and most of our foodstuffs are colloids. Food chemistry and food technology have passed beyond the stage of mere analysis into a field of science which engages all the important physico-chemical problems of colloids. Hence the need for a textbook which summarises the voluminous and scattered literature. Such problems as the staling of bread, the foaming of milk, the homogenisation of cheese, the sandiness in ice-cream, the froth on beer, the fining of wine, the clarification of water, to name but a few, all involve colloidal chemistry. Such a work will soon be found invaluable in the food laboratory, and the author's reputation ensures its thoroughness.

THE SIZE OF THE PROTEIN MOLECULE

The chemist and the biologist have attached a mysterious dignity to the proteins ever since these compounds were recognized as distinct components of living matter. The very name proteins was selected by Mulder nearly a century ago to indicate their primary importance. Even before those details of structure were known that represent the molecule as a complex of eighteen or more amino-acids united into an elaborate polypeptid arrangement, the unusually large size of the molecular units had impressed itself on students of the albuminous compounds. This characteristic seems to endow them with a sort of sluggishness in reaction and a stability that adapts them to become part of the fundamental structure of cells. A recent writer¹has remarked that the large molecular weights of the proteins must be considered one of their outstanding characteristics, in great part responsible for such colloidal aspects of their behavior as their failure to