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50-592: The original estuary of the Afon Glaslyn was a dangerous place; many people were said to have died in the quicksands trying to cross the Traeth Mawr. In the late 18th century, various landowners around the edge of the estuary began to systematically reclaim land of between 50 acres (20 ha) and 100 acres (40 ha). Between 1770 and 1800 this resulted in the creation of about 1,500 acres (607 ha) of new land. Around 1798, William Madocks bought

100-428: A liquid , while others extend the definition to include substances like aerosols and gels . The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word suspension is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). The dispersed phase particles have

150-524: A local act of Parliament , Madocks' Estate Act 1807 ( 47 Geo. 3 Sess. 2 . c. xxxvi), permitting him to complete the reclamation of Traeth Mawr. Between 1808 and 1811 an embankment called the Cob was constructed from the island of Ynys Towyn (now part of Porthmadog ) to Boston Lodge in the Meirionnydd . The massive stone-lined earthwork was 1,600 yards (1,500 m) long, 90 feet (27 m) wide at

200-423: A toll . The collection of fees often caused traffic jams at peak holiday travel times: it was not exceptional for queues to back up to one mile (1.6 km) in each direction. In 2002, the highway across the Cob was widened while a separate path was added for walkers and cyclists. The pedestrian route now forms part of Lôn Las Cymru , the national cycle route from Holyhead to Cardiff . In 2010 work started on

250-432: A colloid such as milk, the colloidal particles are globules of fat, rather than individual fat molecules. Because colloid is multiple phases, it has very different properties compared to fully mixed, continuous solution. The following forces play an important role in the interaction of colloid particles: The Earth’s gravitational field acts upon colloidal particles. Therefore, if the colloidal particles are denser than

300-478: A colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond

350-539: A diameter of approximately 1 nanometre to 1 micrometre . Some colloids are translucent because of the Tyndall effect , which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color. Colloidal suspensions are the subject of interface and colloid science . This field of study began in 1845 by Francesco Selmi , who called them pseudosolutions, and expanded by Michael Faraday and Thomas Graham , who coined

400-890: A dispersed phase in this size range may be called colloidal aerosols , colloidal emulsions , colloidal suspensions , colloidal foams , colloidal dispersions , or hydrosols . Hydrocolloids describe certain chemicals (mostly polysaccharides and proteins ) that are colloidally dispersible in water . Thus becoming effectively "soluble" they change the rheology of water by raising the viscosity and/or inducing gelation. They may provide other interactive effects with other chemicals, in some cases synergistic, in others antagonistic. Using these attributes hydrocolloids are very useful chemicals since in many areas of technology from foods through pharmaceuticals , personal care and industrial applications, they can provide stabilization, destabilization and separation, gelation, flow control, crystallization control and numerous other effects. Apart from uses of

450-445: A man in four minutes and a half; but there may have been little ground for this precision. Quicksand is a trope of adventure fiction , particularly in film, where it is typically and unrealistically depicted with a suction effect that causes anyone or anything that walks into it to sink until fully submerged and risk drowning. This has led to the common misconception that humans can be completely immersed and drown in quicksand, which

500-462: A natural diffraction grating for visible light waves , particularly when the interstitial spacing is of the same order of magnitude as the incident lightwave. Thus, it has been known for many years that, due to repulsive Coulombic interactions, electrically charged macromolecules in an aqueous environment can exhibit long-range crystal -like correlations with interparticle separation distances, often being considerably greater than

550-438: A perturbation. Aggregation causes sedimentation or creaming, therefore the colloid is unstable: if either of these processes occur the colloid will no longer be a suspension. Electrostatic stabilization and steric stabilization are the two main mechanisms for stabilization against aggregation. A combination of the two mechanisms is also possible (electrosteric stabilization). A method called gel network stabilization represents

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600-445: A piece of aluminium will float on top of quicksand until motion causes the sand to liquefy. Continued or panicked movement, however, may cause a person to sink further in the quicksand. Since this increasingly impairs movement, it can lead to a situation where other factors such as exposure (i.e., sun stroke , dehydration and hypothermia ), drowning in a rising tide or attacks by predatory or otherwise aggressive animals may harm

650-500: A result of the relatively simple methods that have evolved in the last 20 years for preparing synthetic monodisperse colloids (both polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation. Colloidal phase separation is an important organising principle for compartmentalisation of both the cytoplasm and nucleus of cells into biomolecular condensates —similar in importance to compartmentalisation via lipid bilayer membranes ,

700-404: A sudden decrease in its viscosity (" sol " form). After an initial disturbance—such as a person attempting to walk on it—the water and sand in the quicksand separate and dense regions of sand sediment form; it is because of the formation of these high volume fraction regions that the viscosity of the quicksand seems to decrease suddenly. Someone stepping on it will start to sink. To move within

750-430: A trapped person. Quicksand may be escaped by slow movement of the legs in order to increase viscosity of the fluid, and rotation of the body so as to float in the supine position (lying horizontally with the face and torso facing up). The quicksands were of great extent at low water, and had an infamous reputation in the country. Close in shore, between the islet and the promontory, it was said that they would swallow

800-877: A type of liquid crystal . The term biomolecular condensate has been used to refer to clusters of macromolecules that arise via liquid-liquid or liquid-solid phase separation within cells. Macromolecular crowding strongly enhances colloidal phase separation and formation of biomolecular condensates . Colloidal particles can also serve as transport vector of diverse contaminants in the surface water (sea water, lakes, rivers, fresh water bodies) and in underground water circulating in fissured rocks (e.g. limestone , sandstone , granite ). Radionuclides and heavy metals easily sorb onto colloids suspended in water. Various types of colloids are recognised: inorganic colloids (e.g. clay particles, silicates, iron oxy-hydroxides ), organic colloids ( humic and fulvic substances). When heavy metals or radionuclides form their own pure colloids,

850-434: Is a colloid consisting of fine granular material (such as sand , silt or clay ) and water . It forms in saturated loose sand when the sand is suddenly agitated. When water in the sand cannot escape, it creates a liquefied soil that loses strength and cannot support weight. Quicksand can form in standing water or in upward flowing water (as from an artesian spring ). In the case of upward-flowing water, forces oppose

900-481: Is defined by particles remaining suspended in solution and depends on the interaction forces between the particles. These include electrostatic interactions and van der Waals forces , because they both contribute to the overall free energy of the system. A colloid is stable if the interaction energy due to attractive forces between the colloidal particles is less than kT , where k is the Boltzmann constant and T

950-489: Is directly proportional to the average particle size and volume fraction of the dispersed phase. Therefore, local changes in concentration caused by sedimentation or creaming, and clumping together of particles caused by aggregation, are detected and monitored. These phenomena are associated with unstable colloids. Dynamic light scattering can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards

1000-425: Is impossible. According to a 2010 article by Slate , this gimmick had its heyday in the 1960s, when almost 3% of all films showed characters sinking in clay, mud, or sand. Colloid A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in

1050-416: Is shaken by an earthquake or similar forces. The movement combined with an increase in pore pressure (of groundwater) leads to the loss of particle cohesion , causing buildings or other objects on that surface to sink. Quicksand is a shear thinning non-Newtonian fluid : when undisturbed, it often appears to be solid (" gel " form), but a less than 1% change in the stress on the quicksand will cause

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1100-648: Is the absolute temperature . If this is the case, then the colloidal particles will repel or only weakly attract each other, and the substance will remain a suspension. If the interaction energy is greater than kT, the attractive forces will prevail, and the colloidal particles will begin to clump together. This process is referred to generally as aggregation , but is also referred to as flocculation , coagulation or precipitation . While these terms are often used interchangeably, for some definitions they have slightly different meanings. For example, coagulation can be used to describe irreversible, permanent aggregation where

1150-421: Is the sedimentation or creaming velocity. The mass of the colloidal particle is found using: where and ρ 1 − ρ 2 {\displaystyle \rho _{1}-\rho _{2}} is the difference in mass density between the colloidal particle and the suspension medium. By rearranging, the sedimentation or creaming velocity is: There is an upper size-limit for

1200-956: Is used to control colloid suspensions. A colloidal crystal is a highly ordered array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear analogous to their atomic or molecular counterparts. One of the finest natural examples of this ordering phenomenon can be found in precious opal , in which brilliant regions of pure spectral color result from close-packed domains of amorphous colloidal spheres of silicon dioxide (or silica , SiO 2 ). These spherical particles precipitate in highly siliceous pools in Australia and elsewhere, and form these highly ordered arrays after years of sedimentation and compression under hydrostatic and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of interstitial voids , which act as

1250-506: The Cob. After a number of trials and some modifications, the line was upgraded to a narrow gauge railway in 1863. In 1927 the Cob was breached again, and took several months to repair. A carriageway was also constructed at a lower level on the inland side to take a public highway. Until September 2003, when the Cob was bought by the Welsh Assembly Government , all vehicles crossing the embankment were required to pay

1300-697: The Porthmadog, Minffordd and Tremadog bypass to reduce the amount of through traffic in the town. On completion the original course of the A487 across the Cob was renumbered as the A4971 . In 2012, 260 m (850 ft) of the embankment were widened on the seaward side of the Porthmadog end to allow a second platform to be constructed at the Ffestiniog & Welsh Highland Railway's Harbour Station. Quicksand Quicksand (also known as sinking sand )

1350-542: The Tan-yr-Allt estate near Penmorfa Marsh. Soon afterwards he reclaimed an area of sand from the sea and the river by building a 2 mi (3.2 km) earthen bank from Prenteg to Clog-y-Berth (now Porthmadog). The township of Tremadog was founded within the new area. A wooden-tracked railway was used in the dyke's construction. The rails were later used by the Croesor Tramway . In 1807 Madocks obtained

1400-561: The bottom, tapering to 18 feet (5.5 m) at the top, which was 21 feet (6.4 m) above the level of the river. The work completed the reclamation of 1,500 acres (607 ha) of Traeth Mawr. Soon after completion in 1812, the embankment was breached in a violent storm. Repairs were completed by the end of September 1814. Although the original estimate to complete the Cob was £ 23,500 (£16.9million in 2014), it eventually cost Madocks £ 60,000 (£43.3million in 2014) to finish. At its seaward end, Traeth Mawr joins "Traeth Bach" ("little sands"),

1450-417: The case of non-ionic surfactants or more generally interactions forces inside the system. Storing a dispersion at high temperatures enables to simulate real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times. Mechanical acceleration including vibration, centrifugation and agitation are sometimes used. They subject

1500-446: The chemical conditions of the soil sample, i.e. soil pH . Colloid solutions used in intravenous therapy belong to a major group of volume expanders , and can be used for intravenous fluid replacement . Colloids preserve a high colloid osmotic pressure in the blood, and therefore, they should theoretically preferentially increase the intravascular volume , whereas other types of volume expanders called crystalloids also increase

1550-626: The control of rheology and the physical modification of form and texture. Some hydrocolloids like starch and casein are useful foods as well as rheology modifiers, others have limited nutritive value, usually providing a source of fiber. The term hydrocolloids also refers to a type of dressing designed to lock moisture in the skin and help the natural healing process of skin to reduce scarring, itching and soreness. Hydrocolloids contain some type of gel-forming agent, such as sodium carboxymethylcellulose (NaCMC) and gelatin. They are normally combined with some type of sealant, i.e. polyurethane to 'stick' to

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1600-413: The diameter of colloidal particles because particles larger than 1 μm tend to sediment, and thus the substance would no longer be considered a colloidal suspension. The colloidal particles are said to be in sedimentation equilibrium if the rate of sedimentation is equal to the rate of movement from Brownian motion. There are two principal ways to prepare colloids: The stability of a colloidal system

1650-541: The estuary of the River Dwyryd . In 1836, the Ffestiniog Railway began using the Cob when it built a tramroad to transport slate from the quarries around the inland town of Blaenau Ffestiniog to Porthmadog , where it was loaded onto ships . Empty wagons were hauled back up to the quarries by horses . Loaded dandy waggons used gravity to run downhill from Blaenau Ffestiniog to the port across

1700-407: The fluid. Quicksand has a density of about 2 grams per cubic centimeter, whereas the density of the human body is only about 1 gram per cubic centimeter. At that level of density, sinking beyond about waist height in quicksand is impossible. Even objects with a higher density than quicksand will float on it if stationary. Aluminium, for example, has a density of about 2.7 grams per cubic centimeter, but

1750-409: The force of gravity and suspend the soil particle. The cushioning of water gives quicksand, and other liquefied sediments, a spongy, fluid-like texture. Objects in liquefied sand sink to the level at which the weight of the object is equal to the weight of the displaced soil/water mix and the submerged object floats due to its buoyancy. Soil liquefaction may occur in partially saturated soil when it

1800-400: The forces holding the particles together are stronger than any external forces caused by stirring or mixing. Flocculation can be used to describe reversible aggregation involving weaker attractive forces, and the aggregate is usually called a floc . The term precipitation is normally reserved for describing a phase change from a colloid dispersion to a solid (precipitate) when it is subjected to

1850-513: The forces that govern the structure and behavior of matter, such as excluded volume interactions or electrostatic forces, govern the structure and behavior of colloidal suspensions. For example, the same techniques used to model ideal gases can be applied to model the behavior of a hard sphere colloidal suspension. Phase transitions in colloidal suspensions can be studied in real time using optical techniques, and are analogous to phase transitions in liquids. In many interesting cases optical fluidity

1900-444: The individual particle diameter. In all of these cases in nature, the same brilliant iridescence (or play of colors) can be attributed to the diffraction and constructive interference of visible lightwaves that satisfy Bragg’s law , in a matter analogous to the scattering of X-rays in crystalline solids. The large number of experiments exploring the physics and chemistry of these so-called "colloidal crystals" has emerged as

1950-486: The medium of suspension, they will sediment (fall to the bottom), or if they are less dense, they will cream (float to the top). Larger particles also have a greater tendency to sediment because they have smaller Brownian motion to counteract this movement. The sedimentation or creaming velocity is found by equating the Stokes drag force with the gravitational force : where and v {\displaystyle v}

2000-673: The principal way to produce colloids stable to both aggregation and sedimentation. The method consists in adding to the colloidal suspension a polymer able to form a gel network. Particle settling is hindered by the stiffness of the polymeric matrix where particles are trapped, and the long polymeric chains can provide a steric or electrosteric stabilization to dispersed particles. Examples of such substances are xanthan and guar gum . Destabilization can be accomplished by different methods: Unstable colloidal suspensions of low-volume fraction form clustered liquid suspensions, wherein individual clusters of particles sediment if they are more dense than

2050-416: The process of ultrafiltration occurring in dense clay membrane. The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules. In soil science , the colloidal fraction in soils consists of tiny clay and humus particles that are less than 1μm in diameter and carry either positive and/or negative electrostatic charges that vary depending on

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2100-536: The product to different forces that pushes the particles / droplets against one another, hence helping in the film drainage. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity. Segregation of different populations of particles have been highlighted when using centrifugation and vibration. In physics , colloids are an interesting model system for atoms . Micrometre-scale colloidal particles are large enough to be observed by optical techniques such as confocal microscopy . Many of

2150-408: The quicksand, a person or object must apply sufficient pressure on the compacted sand to re-introduce enough water to liquefy it. The forces required to do this are quite large: to remove a foot from quicksand at a speed of 1 cm/s would require the same amount of force as that needed to lift a car. It is impossible for a human to sink entirely into quicksand, due to the higher density of

2200-470: The skin. A colloid has a dispersed phase and a continuous phase, whereas in a solution , the solute and solvent constitute only one phase. A solute in a solution are individual molecules or ions , whereas colloidal particles are bigger. For example, in a solution of salt in water, the sodium chloride (NaCl) crystal dissolves, and the Na and Cl ions are surrounded by water molecules.  However, in

2250-471: The soluble forms some of the hydrocolloids have additional useful functionality in a dry form if after solubilization they have the water removed - as in the formation of films for breath strips or sausage casings or indeed, wound dressing fibers, some being more compatible with skin than others. There are many different types of hydrocolloids each with differences in structure function and utility that generally are best suited to particular application areas in

2300-401: The suspension medium, or cream if they are less dense. However, colloidal suspensions of higher-volume fraction form colloidal gels with viscoelastic properties. Viscoelastic colloidal gels, such as bentonite and toothpaste , flow like liquids under shear, but maintain their shape when shear is removed. It is for this reason that toothpaste can be squeezed from a toothpaste tube, but stays on

2350-401: The term colloid in 1861. Colloid : Short synonym for colloidal system. Colloidal : State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order. Colloids can be classified as follows: Homogeneous mixtures with

2400-480: The term " eigencolloid " is used to designate pure phases, i.e., pure Tc(OH) 4 , U(OH) 4 , or Am(OH) 3 . Colloids have been suspected for the long-range transport of plutonium on the Nevada Nuclear Test Site . They have been the subject of detailed studies for many years. However, the mobility of inorganic colloids is very low in compacted bentonites and in deep clay formations because of

2450-436: The toothbrush after it is applied. The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple light scattering coupled with vertical scanning. This method, known as turbidimetry , is based on measuring the fraction of light that, after being sent through the sample, it backscattered by the colloidal particles. The backscattering intensity

2500-559: The typical size range for colloidal particles. The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, it is often required for the formulator to use further accelerating methods to reach reasonable development time for new product design. Thermal methods are the most commonly used and consist of increasing temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only viscosity, but also interfacial tension in

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