Hunter: Foundations of Colloid Science 2e. Resources. Solutions for exercises within the book. reset; + A; - A. Hunter: Foundations of Colloid Science 2e. This is a completely revised, reorganised, and updated second edition of the classic textbook on colloid science, provided for the first time in a. Following an introduction by the editors, the book contains nine chapters, covering the following topics: Structure and. Properties of Biosurfactants (S. Lang, .
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by Robert J. Hunter: Foundations of Colloid Science. ISBN: # | Date : Description: PDF-1b3e8 | This is a completely revised. Dispersion and electrokinetics of scattered objects in ethanol-water mixtures. Role of hydration energy and co-ions association on monovalent and divalent cations adsorption at mica-aqueous interface. Discover more publications, questions and projects in Colloid Science. Oxford [Oxfordshire]: Clarendon Press ; New York: Oxford University Press, - Oxford science publications. Solutions to exercises in volume 1 / by Robert J. Hunter. Vol.2 / Robert J. Hunter written in collaboration with Derek Y. C.
Volume 1 Interfacial Phenomena and Colloid Stability- Basic Principles deals with the fundamental aspects of interfacial phenomena, which form the basis of applications of interface and colloid science to various disperse systems. These include suspensions, emulsions, nano-dispersions, wetting, spreading, deposition and adhesion of particles to surfaces. This book is valuable for research scientists and PhDs. Volume 2 Interfacial Phenomena and Colloid Stability- Industrial Applications provides the knowledge that is essential for the composition of the complex multi-phase systems used varied areas of application. It enables the chemist as well as the chemical engineer in designing the formulation on the basis of a rational approach, and the formulation scientist to better understanding the factors responsible for producing a stable product with optimum application conditions. Demonstrate the importance of the fundamental aspects of interfacial phenomena in various industrial applications Interdisciplinary approach: Enabled only by enough insights in all involved disciplines surface chemistry, materials science, physics Improving selectivity and activity: Through operating on the interface level Tharwat F. He works as a consultant in multiple applied fields of colloid and interface science and is actively engaged in research work.
The bile itself consists of of salts of a variety of bile acids, all of which are derived from cholesterol. The cholesterol-like part of the structure is hydrophobic, while the charged end of the salt is hydrophilic.
Microemulsions Ordinary emulsions are inherently unstable; they do not form spontaneously, and once formed, the drop sizes are sufficiently large to scatter light, producing a milky appearance.
As time passes, the average drop size tends to increase, eventually resulting in gravitational separation of the phases.
Microemulsions, in contrast, are thermodynamically stable and can form spontaneously. The drop radii are at the very low end of the colloidal scale, often nm or smaller. This is too small to appreciably scatter visible light, so microemulsions appear visually to be homogenous systems. Microemulsions require the presence of one or more surfactants which increase the flexibility and stability of the boundary regions.
This allows them to vary form smaller micelles than surface tension forces would ordinarily allow; in some cases they can form sponge-like bicontinuous mixtures in which "oil" and "water" phases extend throughout the mixture, affording more contact area between the phases. The uses of microemulsions are quite wide-ranging, with drug delivery, polymer synthesis, enzyme-assisted synthesis, coatings, and enhanced oil recovery being especially prominent.
Build up molecular-sized particles atoms, ions, or small molecules into aggregates within the colloidal size range. Condensation Dispersion processes all require an input of energy as new surfaces are created. For solid particles, this is usually accomplished by some kind of grinding process such as in a ball- or roller-mill. Solids and liquids can also be broken into colloidal dimensions by injecting them into the narrow space between a rapidly revolving shaft and its enclosure, thus subjecting them to a strong shearing force that tends to pull the two sides of a particle in opposite directions.
The application of ultrasound at about 20 kHz to a mixture of two immiscible liquids can create liquid-in-liquid dispersions; the process is comparable to what we do when we shake a vinegar-and-oil salad dressing in order to create a more uniform distribution of the two liquids. Condensation Numerous methods exist for building colloidal particles from sub-colloidal entities. For example, a sample of paraffin wax is dissolved in ethanol, and the resulting solution is carefully added to a container of boiling water.
Formation of precipitates under controlled conditions The trick here is to prevent the initial colloidal particles of the newly-formed compound from coalescing into an ordinary precipitate, as will ordinarily occur when solutions of two dissolved salts are combined directly.
An alternative that is sometimes useful is to form the sol by a chemical process that procedes more slowly than direct precipitation: Sulfur sols are readily formed by oxidation of thiosulfate ions in acidic solution: Sols of oxides or hydrous oxides of transition metals can often be formed by boiling a soluble salt in water under slightly acidic conditions to prevent formation of insoluble hydroxides: Addition of a dispersant usually a surfactant can sometimes prevent colloidal particles from precipitating.
Thus barium sulfate sols can be prepared from barium thiocyanate and NH4 2SO4 in the presence of potassium citrate. Ionic solids can often selectively adsorb cations or anions from solutions containing the same kinds of ions that are present in the crystal lattice, thus coating the particles with protective electric charges. How Dispersions are Broken That oil-in-vinegar salad dressing you served at dinner the other day has now mostly separated into two layers, with unsightly globs of one phase floating in the other.
This is surface chemistry in action! Emulsions are fundamentally unstable because molecules near surfaces i. The resulting repulsions between like and unlike exact an energetic cost that must eventually be repaid through processes that reduce the interfacial area. The consequent breakup of the emulsion can proceed through various stages: Coalescence - smaller drops join together to form larger ones; Flocculation - the small drops stick together without fully coalescing; Creaming - Most oils have lower densities than water, so the drops float to the surface, but may not completely coalesce; Breaking - the ultimate thermodynamic fate and end result of the preceding steps.
The time required for these processes to take place is highly variable, and can be extended by the presence of stabilizer substances.
Thus milk, an emulsion of butterfat in water, is stabilized by some of its natural components. Coagulation and flocculation The processes described above that allow colloids to remain suspended sometimes fail when conditions change, or equally troublesome, they work entirely too well and make it impossible to separate the colloidal particles from the medium; this is an especially serious problem in wastewater settling basins associated with sewage treatment and operations such as mining and the pulp-and-paper industries.
Coagulation is the general term that refers to the "breaking" of dispersions so that the colloidal particles can be collected, usually by settling out. The term Flocculation is often used as a synonym for coagulation, but it is more properly reserved for a special method of effecting coagulation which is described further on.
Most coagulation processes act by disrupting the outer diffuse part of the electric double layer that gives rise to the electrostatic repulsion between them. Not likely something you would want to drink! You will see "Do not freeze" labels on many foodstuffs and on colloidal consumer products such as latex house paint.
Freezing disrupts the double layer by causing the ions within it to combine into neutral species so that the particles can now approach closely enough for attractive forces to take over, and once they do so, they never let go: coagulation is definitely an irreversible process!
Addition of an electrolyte Coagulation of water-suspended dispersions can be brought about by raising the ionic concentration of the medium.
The added ions will migrate to the oppositely-charged regions of the double layer, thus neutralizing its charges; this effectively reduces the thickness of the double layer, eventually allowing the attractive forces to prevail.
Rivers carry millions of tons of colloidal clay into the oceans. If you fly over the mouth of a river such as the Mississippi shown here in a satellite image , you can sometimes see the difference in color as the clay colloids coagulate due to the action of the salt water.
The coagulated clay accumulates as sediments which eventually form a geographical feature called a river delta. The latter may start out as a powdery or granulated material such as natural gelatin or a hydrophilic polymer, but once the gel has formed, the "solid" part is less a "phase" than a cross-linked network that extends throughout the volume of the liquid, whose quantity largely defines the volume of the entire gel.
The "solid" components of hydrogels are usually polymeric materials that have an abundance of hydrophilic groups such as hydroxyl —OH that readily hydrogen-bond to water and also to each other, creating an irregular, flexible, and greatly-extendable network. These polymers are sometimes synthesized for this purpose, but are more commonly formed by processing natural materials, including natural polymers such as cellulose.
Gelatine is a protein-like material made by breaking down the connective tissues of animal skins, organs, and bones. The many polar groups on the resulting protein fragments bind them together, along with water molecules, to form a gel. A number of so-called super-absorbant polymers derived from cellulose, polyvinyl alcohol and other materials can absorb huge quantities of water, and have found uses for products such as disposable diapers, environmental spill control, water retention media for plants, surgical pads and wound dressings, and protective inner coatings and water-blockers in fiber optics and electrical cables.
Gels are essential components of a huge variety of consumer products ranging from thickening agents in foods and personal care products to cushioning agents in running shoes. Gels can be fragile! You may have noticed that a newly-opened container of yogurt or sour cream appears to be smooth and firm, but once some of the material has been spooned out, little puddles of liquid appear in the hollowed-out depressions.
As the spoon is plunged into the material, it pulls the nearby layers of the gel along with it, creating a shearing action that breaks it apart, releasing the liquid. Anyone who has attacked an egg yolk with a cook's whisk, written with a ball-point pen, or spread latex paint on a wall has made use of this phenomenon which is known as shear thinning.
Our bodies are mostly gels The interior the cytoplasm of each cell in the soft tissues of our bodies consists of a variety of inclusions organelles suspended in a gel-like liquid phase called the cytosol. Dissolved in the cytosol are a variety of ions and molecules varying from the small to the large; among the latter, proteins and carbohydrates make up the "solid" portion of the gel structure.
Embedded within the cytosol is the filament-like cytoskeleton which controls the overall shape of the cell and holds the organelles in place. In free-living cells such as the amoeba, changes in the cytoskeleton enable the organism to alter its shape and move around to engulf food particles. Be thankful for the gels in your body; without them, you would be little more than a bag of gunge-filled liquid, likely to end up as a puddle on the floor!
The individual cells are bound into tissues by the extracellular matrix ECM which — on a much larger scale, holds us together and confers an overall structure and shape to the body. The ECM is made of a variety of structural fibers collagens, elastins embedded in a gel-like matrix. Toothpastes, lotions, lubricants, coatings are common examples. Most of the additives that confer desirable flow properties on these products are colloidal in nature; in many cases, they also provide stabilization and prevent phase separation.
Since ancient times, various natural gums have been employed for such purposes, and many remain in use today. More recently, manufactured materials whose properties can be tailored for specific applications have become widely available. Examples are colloidal microcrystalline cellulose, carboxymethyl cellulose, and fumed silica.
Fumed silica is a fine nm , powdery form of SiO2 of exceptionally low bulk density as little as 0. It is made by spraying SiCl4 a liquid into a flame. It is used as a filler, for viscosity and flow control, a gelling agent, and as an additive for strenghthening concrete. Food colloids Most of the foods we eat are largely colloidal in nature.
The function of food colloids generally has less to do with nutritional value than appearance, texture, and "mouth feel". The latter two terms relate to the flow properties of the material, such as spreadability and the ability to "melt" transform from gel to liquid emulsion on contact with the warmth of the mouth. Dairy products Milk is basically an emulsion of lipid oils "butterfat" dispersed in water and stabilized by phospholipids and proteins.
Most of the protein content of milk consists of a group known as caseins which aggregate into a complex micellar structure which is bound together by calcium phosphate units. Homogenizer The stabilizers present in fresh milk will maintain its uniformity for hours, but after this time the butterfat globules begin to coalesce and float to the top "creaming". In order to retard this process, most milk sold after the early 's undergoes homogenization in which the oil particles are forced through a narrow space under high pressure.
This breaks up the oil droplets into much smaller ones which remain suspended for the useful shelf life of the milk. The structures of cream, yogurt and ice cream are dominated by the casein aggregates mentioned above. Whereas milk is an oil butterfat -in-water dispersion, butter and margarine have a "reversed" water-in-oil arrangement.
This transformation is accomplished by subjecting the butterfat droplets in cream to violent agitation churning which forces the droplets to coalesce into a semisolid mass within which remnants of the water phase are embedded.
The greater part of this phase ends up as the by-product buttermilk. Eggs: colloids for breakfast, lunch, and dessert A detailed study of eggs and their many roles in cooking can amount to a mini-course in colloid chemistry in itself.
The raw eggwhite is basically a colloidal sol of long-chain protein molecules, all curled up into compact folded forms due to hydrogen bonding between different parts of the same molecule.
Upon heating, these bonds are broken, allowing the proteins to unfold. The denuded chains can now tangle and bind to each other, transforming the sol into a cross-linked hydrogel, now so dense that scattered light changes its appearance to opaque white.
What happens next depends very much on the skill of the cook. The idea is to drive out enough of the water entrapped within the gel network to achieve the desired density while retaining enough gel structure to prevent it from forming a rubbery mass, as usually happens with hard-boiled eggs.
This is especially important when the egg structure is to be incorporated into other food components as in baked dishes. The temperature limit required to avoid this disaster can be raised by adding milk or sugar; the water part of the milk dilutes the proteins, while sugar molecules hydrogen-bond to them, forming a protective shield that keeps the proton strand separated. This is essential when baking custards, but incorporating a bit of cream into scrambled eggs can similarly help them retain their softness.
Whipped cream and meringues The other colloidal personalities eggs can display are liquid and solid foams.
Instead of applying heat to unfold the proteins, we "beat" them; the shearing force of a whisk or egg-beater helps pull them apart, and the air bubbles that get entrapped in the mixture attract the hydrophobic parts of the unfolded proteins and help hold them in place.
Sugar will stabilize the foam by raising its viscosity, but will interfere with protein folding if added before the foam is fully formed. Sugar also binds the residual water during cooking, retarding its evaporation until after the proteins not broken up by beating can be thermally coagulated. Paints and inks Paints have been used since ancient times for both protective and decorative purposes.
They consist basically of pigment particles dispersed in vehicle — a liquid capable for forming a stable solid film as the paint "dries". The earliest protective coatings were made by dissolving plant-derived natural polymers resins in an oil such as that of linseed.
The double-bonds in these oils tends to oxidize when exposed to air, causing it to polymerize into an impervious film. The colloidal pigments were stabilized with naturally-occurring surfactants such as polysaccharide gums.
Present-day paints are highly-engineered products specialized for particular industrial or architectural coatings and for marine or domestic use. For environmental reasons, water-based "latex" vehicles are now preferred. Inks The most critical properties of inks relate to their drying and surface properties; they must be able to flow properly and attach to the surface without penetrating it — the latter is especially critical when printing on a porous material such as paper.
Many inks consist of organic dyes dissolved in a water-based solvent, and are not colloidal at all. The ink used in printing newspapers employs colloidal carbon black dispersed in an oil vehicle. The pressure applied by the printing press forces the vehicle into the pores of the paper, leaving most of the pigment particles on the surface. The inks employed in ball-point pens are gels, formulated in such a way that the ink will only flow over the ball and onto the paper when the shearing action of the ball which rotates as it moves across the paper "breaks" the gel into a liquid; the resulting liquid coats the ball and is transferred to the paper.
As in conventional printing, the pigment particles remain on the paper surface, while the liquid is pressed into the pores and gradually evaporates. Water and wastewater treatment Turbidities of 5, 50, and units. Even "pristine" surface waters often contain suspended soil sediments that can harbor infectious organisms and may provide them with partial protection from standard disinfection treatments.
The sulfates of aluminum alum and of iron III have long been widely employed for this purpose. Synthetic polymers tailored specifically for these applications have more recently come into use. The usual method of removing turbidity is to add a flocculating agent flocculant. These are most often metallic salts that can form gel-like hydroxide precipitates, often with the aid of added calcium hydroxide quicklime if pH of the water must be raised.
The flocculant salts neutralize the surface charges of the colloids, thus enabling them to coagulate; these are engulfed and trapped by fragments of gelatinous precipitate, which are drawn together into larger aggregates by gentle agitation until they become sufficiently large to form flocs which can be separated by settling or filtration. Soil colloids The four major components of soils are mineral sediments, organic matter, water, and air. The water is primarily adsorbed to the mineral and organic materials, but may also share pore spaces with air; pore spaces constitute about half the bulk volume of typical solid.
The principal colloidal components of soils are mineral sediments in the form of clays, and the humic materials in the organic matter. In addition to influencing the consistency of soil by binding water molecules, soil colloids play an essential role in storing and exchanging the mineral ions required by plants. Because these ions are loosely bound, they constitute a source from which plant roots can draw these essential nutrients.
Conversely, they can serve as a sink for these same ions when they are released after the plant dies. Clays These are layered structures based on alumino-silicates or hydrous oxides, mostly of iron or aluminum.
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