C O L L O I D

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C O L L O I D

Colored glass Paint Cheese Milk Steroform

Aerosol Cloud Cream

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S I S T E M D I S P E R S IDEFINISI: ➡ Sistem campuran terdiri dari partikel (fase terdispersi),

didistribusikan ke seluruh fase kontinyu (medium dispersi).

➡ Diklasifikasikan berdasarkan diameter partikel yang didistribusikan dalam fase kontinyu.

1 Introducing colloids

The realm of the tiny

Colloids occupy an intermediate place between [particulate] suspensions and solutions, both in terms of their observableproperties and particle size. In a sense, they bridge the microscopic and the macroscopic. As such, they possess some of theproperties of both, which makes colloidal matter highly adaptable to specific uses and functions. Colloid science is centralto biology, food science and numerous consumer products.

Solutions are homogeneous mixtures whose component particles are individual molecules whose smallest dimension isgenerally less than 1 nm. Within this size range, thermal motions maintain homogeniety by overcoming the effects ofgravitational attraction.

Colloidal dispersions appear to be homogeneous, and the colloidal particles they contain are small enough (generallybetween 1-1000 nm) to exhibit Brownian motion, cannot be separated by filtration, and do not readily settle out. But thesedispersions are inherently unstable and under certain circumstances, most colloidal dispersions can be "broken" and will"flocculate" or settle out.

Suspensions are heterogeneous mixtures in which the suspended particles are sufficiently large (> 1000 nm in theirsmallest dimension) to settle out under the influence of gravity or centrifugal force. The particles that form suspensions aresometimes classified into various size ranges.

Colloidal particles need not fall within the indicated size range in all three dimensions; thus fibrous colliods such as manybiopolymers may be very extended sizes along one direction.

The nature of colloidal particles

One phase or many?

To begin, you need to recall two important definitions:

a phase is defined as a region of matter in which the composition and physical properties are uniform. Thus ice and liquid water,although two forms of the single substance H2O, constitute two separate phases within a heterogeneous mixture.

A solution is a homogeneous mixture of two or more substances consisting of a single phase. (Think of sugar dissolved inwater).

But imagine that you are able to shrink your view of a solution of sugar in water down to the sub-microscopic level at whichindividual molecules can be resolved: you would see some regions of space occupied by H2O molecules, others by sugarmolecules, and likely still others in which sugar and H2O molecules are momentarily linked together by hydrogen bonding— not to mention the void spaces that are continually appearing and disappering between molecules as they are jumbledabout by thermal motions.

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KLASIFIKASI DISPERSI: ➡ Solution (molecular dispersion). Campuran

homogen ukuran partikel kurang dari 1 nm. Thermal motion mempertahankan homogenitas untuk mengatasi efek daya tarik gravitasi.

➡ Coloid (coloidal dispersion). Ukuran partikel umumnya antara 1-1000 nm. Menunjukkan gerak Brown. Tidak dapat dipisahkan dengan filtrasi, tetapi dispersi ini dalam keadaan tertentu tidak stabil, sebagian besar dispersi koloid dapat rusak akibat flokulasi atau koagulasi .

➡ Suspension (coarse dispersion). Campuran heterogen dengang ukuran partikel > 1000 nm. Terjadi pengendapan akibat gaya gravitasi atau sentrifugasi.

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2

Solution homogeneous particles are

molecules

Suspension heterogeneous particles settle

out

Colloid

size 1–1000 nm

particles remain suspended

What is a colloid?• Finely-divided dispersion of one phase in another• Size of dispersed (“solute-like”) entity >> ordinary molecules• Example: blood cell in water.

2

Solution homogeneous particles are

molecules

Suspension heterogeneous particles settle

out

Colloid

size 1–1000 nm

particles remain suspended

What is a colloid?• Finely-divided dispersion of one phase in another• Size of dispersed (“solute-like”) entity >> ordinary molecules• Example: blood cell in water.

2

Solution homogeneous particles are

molecules

Suspension heterogeneous particles settle

out

Colloid

size 1–1000 nm

particles remain suspended

What is a colloid?• Finely-divided dispersion of one phase in another• Size of dispersed (“solute-like”) entity >> ordinary molecules• Example: blood cell in water.

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COLLOID (COLLOIDAL DISPERSION)DEFINISI: ➡ Sistem dispersi dengan ukuran partikel antara larutan

(solution) dan suspensi (suspension), dengan ukuran partikel 1nm (10-9 m) hingga 1um (10-6 m) (mikroskopis-makroskopis). ๏ Microheterogeous Dispersion

➡ Terdiri dari fase terdispersi (terlarut) dan fase pendispersi (fase pelarut/kontinyu)

➡ Fase terdispersi dan pendispersi dapat berupa gas, cairan, ataupun padatan. ๏ Menentukan nama koloidnya

➡ Tidak mudah mengendap (sedimentation) atau mengapung (creaming).

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ReferencesHunter, Robert: Introduction to Modern Colloid Science. Oxford U. Press, 1993

Some interesting notes on the history of colloids can be found near the end of this Web page by D.H. Everett of U. Bristol.

A cook's guide to emulsions

Concept Map

© 2008-2017 by Stephen Lower

This document is licensed under a Creative Commons Attribution 3.0 Unported License

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Types of Colloid Dispersion

5

More examples

opalsolid solsolidsolid

buttersolid emulsionliquidsolid

meringuesolid foamgassolid

paint, blood, inksolsolidliquid

milkemulsionliquidliquid

whipped creamfoamgasliquid

smokeaerosolsolidgas

fogaerosolliquidgas

exampletypedispersed phasecontinuous phase

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(Liquid) Foam [gas/liquid]

(Liquid) Aerosol [liquid/gas] (Solid) Aerosol. [liquid/gas]

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(Solid) Foam [gas/solid]

(Liquid) Emulsion [liquid/liquid] (Liquid) Sol [solid/liquid]

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Gel. [liquid/solid]

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➡ Sifat koloid:

๏ Optical properties — Tyndall Scattering ๏ Optical properties — Ultramicroscope ๏ Brownian Motion — Balance Force

➡ Colloid Science bersifat multi disiplin (fisika dan kimia). ๏ Fisika dan kimia permukaan dan antar muka

(Surface Science). ➡ Ciri utama dari dispersi koloid adalah rasio luas

permukaan terhadap volume yang besar. ๏ Menentukan sifat permukaan partikel terdispersi

(lapisan permukaan, adsorpsi, dan muatan listrik). ➡ Sifat permukaan partikel juga menentukan

hubungannya dengan partikel lainnya dan dengan pendispersi (fase continu atau pelarut).

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Tyndall Scattering (Effect): ➡ Cahaya disebarkan oleh partikel yang terdispersi. ➡ Kemampuan penyebaran cahaya berbanding lurus

dengan ukuran partikel. ➡ Menyebabkan warna colloid lebih putih (susu, asap,

awan). ➡ Ditemukan pertama kali oleh John Tyndall.

-John Tyndall (1820-1893) was anIrish-born scientist whose interestsspanned a remarkably widescope, ranging from the nature ofradiant heat to the flow of glaciers.

Are colloids macroscopic or microscopic?

Colloidal dispersions behave very much like solutions in that they appear to be homogeneous on a macroscopic scale. Theyare often said to be microheterogeneous. The most important feature that distinguishes them from other particulate matter isthat

Colloids dispersed in liquids or gases are sufficiently small that they do notsettle out under the influence of gravity.

This, together with the their small sizes which allows them to pass through most filters, makes it difficult to separatecolloidal matter from the phase in which it is dispersed.

Optical properties of colloidal dispersions

Colloidal dispersions are distinguished from true solutions by their light-scattering properties. The nature of this scatteringdepends on the ratio of the particle size in the medium to the wavelength of the light.

A collimated beam of light passing through a solution composed of ordinarymolecules (r) tends retain its shape. When such a beam is directed through acolloidal dispersion, it spreads out (left container).→

John Tyndall discovered this effectin 1869. Tyndall scattering (as it iscommonly known) scatters allwavelengths equally. This is incontrast to Rayleigh scattering, whichscatters shorter wavelengths more, bringingus blue skies and red sunsets.

Tyndall scattering can be seen even indispersions that are transparent. As thedensity of particles (or the particle size)increases, the light scattering may becomegreat enough to produce a "cloudy" effect,as in this image of a smoke-filled room → .

This is the reason that milk, fog, and cloudsthemselves appear to be white.The individual water droplets in clouds (orthe butterfat droplets in milk) are actually

transparent, but the intense light scattering disperses the light in all directions,preventing us from seeing through them.

Visualizing colloids: the Ultramicroscope

Colloidal particles are, like molecules, too small to be visible though an ordinary optical microscope. However, if one looksin a direction perpendicular to the light beam, a colloidal particle will "appear" over a dark background as a tiny speck dueto the Tyndall scattering. A microscope specially designed for this application is known as an ultramicroscope. Bear in mindthat the ultramicroscope (invented in Austria in 1902) does not really allow us to "see" the particle; the scattered lightmerely indicates where it is at any given instant.

-John Tyndall (1820-1893) was anIrish-born scientist whose interestsspanned a remarkably widescope, ranging from the nature ofradiant heat to the flow of glaciers.

Are colloids macroscopic or microscopic?

Colloidal dispersions behave very much like solutions in that they appear to be homogeneous on a macroscopic scale. Theyare often said to be microheterogeneous. The most important feature that distinguishes them from other particulate matter isthat

Colloids dispersed in liquids or gases are sufficiently small that they do notsettle out under the influence of gravity.

This, together with the their small sizes which allows them to pass through most filters, makes it difficult to separatecolloidal matter from the phase in which it is dispersed.

Optical properties of colloidal dispersions

Colloidal dispersions are distinguished from true solutions by their light-scattering properties. The nature of this scatteringdepends on the ratio of the particle size in the medium to the wavelength of the light.

A collimated beam of light passing through a solution composed of ordinarymolecules (r) tends retain its shape. When such a beam is directed through acolloidal dispersion, it spreads out (left container).→

John Tyndall discovered this effectin 1869. Tyndall scattering (as it iscommonly known) scatters allwavelengths equally. This is incontrast to Rayleigh scattering, whichscatters shorter wavelengths more, bringingus blue skies and red sunsets.

Tyndall scattering can be seen even indispersions that are transparent. As thedensity of particles (or the particle size)increases, the light scattering may becomegreat enough to produce a "cloudy" effect,as in this image of a smoke-filled room → .

This is the reason that milk, fog, and cloudsthemselves appear to be white.The individual water droplets in clouds (orthe butterfat droplets in milk) are actually

transparent, but the intense light scattering disperses the light in all directions,preventing us from seeing through them.

Visualizing colloids: the Ultramicroscope

Colloidal particles are, like molecules, too small to be visible though an ordinary optical microscope. However, if one looksin a direction perpendicular to the light beam, a colloidal particle will "appear" over a dark background as a tiny speck dueto the Tyndall scattering. A microscope specially designed for this application is known as an ultramicroscope. Bear in mindthat the ultramicroscope (invented in Austria in 1902) does not really allow us to "see" the particle; the scattered lightmerely indicates where it is at any given instant.

-John Tyndall (1820-1893) was anIrish-born scientist whose interestsspanned a remarkably widescope, ranging from the nature ofradiant heat to the flow of glaciers.

Are colloids macroscopic or microscopic?

Colloidal dispersions behave very much like solutions in that they appear to be homogeneous on a macroscopic scale. Theyare often said to be microheterogeneous. The most important feature that distinguishes them from other particulate matter isthat

Colloids dispersed in liquids or gases are sufficiently small that they do notsettle out under the influence of gravity.

This, together with the their small sizes which allows them to pass through most filters, makes it difficult to separatecolloidal matter from the phase in which it is dispersed.

Optical properties of colloidal dispersions

Colloidal dispersions are distinguished from true solutions by their light-scattering properties. The nature of this scatteringdepends on the ratio of the particle size in the medium to the wavelength of the light.

A collimated beam of light passing through a solution composed of ordinarymolecules (r) tends retain its shape. When such a beam is directed through acolloidal dispersion, it spreads out (left container).→

John Tyndall discovered this effectin 1869. Tyndall scattering (as it iscommonly known) scatters allwavelengths equally. This is incontrast to Rayleigh scattering, whichscatters shorter wavelengths more, bringingus blue skies and red sunsets.

Tyndall scattering can be seen even indispersions that are transparent. As thedensity of particles (or the particle size)increases, the light scattering may becomegreat enough to produce a "cloudy" effect,as in this image of a smoke-filled room → .

This is the reason that milk, fog, and cloudsthemselves appear to be white.The individual water droplets in clouds (orthe butterfat droplets in milk) are actually

transparent, but the intense light scattering disperses the light in all directions,preventing us from seeing through them.

Visualizing colloids: the Ultramicroscope

Colloidal particles are, like molecules, too small to be visible though an ordinary optical microscope. However, if one looksin a direction perpendicular to the light beam, a colloidal particle will "appear" over a dark background as a tiny speck dueto the Tyndall scattering. A microscope specially designed for this application is known as an ultramicroscope. Bear in mindthat the ultramicroscope (invented in Austria in 1902) does not really allow us to "see" the particle; the scattered lightmerely indicates where it is at any given instant.

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Brownian Motion:

➡ Pergerakan partikel terdispersi secara acak (random) dalam sistem dispersi.

➡ Diakibatkan oleh tumbukan antar partikel terdispersi. ➡ Ditemukan pertama kali oleh Robert Brown.