Koloid dan Sifat-sifatnya
Sistem koloid (selanjutnya disingkat "koloid" saja) merupakan suatu
bentuk campuran (sistem dispersi) dua atau lebih zat yang bersifat
homogen namun memiliki ukuran partikel terdispersi yang cukup besar (1100 nm), sehingga terkena efek tyndall. Bersifat homogen berarti partikel
terdispersi tidak terpengaruh oleh gaya gravitasi atau gaya lain yang
dikenakan kepadanya; sehingga tidak dijumpai pengendapan, misalnya.
Sifat homogen ini juga dimiliki oleh larutan, namun tidak dimiliki oleh
campuran biasa (suspensi).
Koloid mudah dijumpai di mana-mana: susu, agar-agar, tinta, sampo serta
awan merupakan contoh-contoh koloid yang dpat dijumpai sehari-hari.
Sitoplasma dalam sel juga merupakan sistem koloid. Kimia koloid menjadi
kajian tersendiri dalam kimia industri karena kepentingannya.
Macam-macam koloid
Koloid memiliki bentuk bermacam-macam, tergantung dari fase zat
pendispersi dan zat terdispersinya. Beberapa jenis koloid:
 Aerosol yang memiliki zat pendispersi berupa gas. Aerosol yang
memiliki zat terdispersi cair disebut aerosol cair (contoh: kabut)
sedangkan yang memiliki zat terdispersi padat disebut aerosol
padat (contoh: asap).
 Sol
 Emulsi
 Buih
 Gel
Sifat-sifat Koloid
Efek Tyndall
Efek Tyndall ialah gejala penghamburan berkas sinar (cahaya) oleh
partikel-partikel koloid. Hal ini disebabkan karena ukuran molekul koloid
yang cukup besar. Efek tyndall ini ditemukan oleh John Tyndall (18201893), seorang ahli fisika Inggris. Oleh karena itu sifat itu disebut efek
tyndall.
Efek tyndall adalah efek yang terjadi jika suatu larutan terkena sinar.
Pada saat larutan sejati (gambar kiri) disinari dengan cahaya, maka larutan
tersebut tidak akan menghamburkan cahaya, sedangkan pada sistem koloid
(gambar kanan), cahaya akan dihamburkan. hal itu terjadi karena partikelpartikel koloid mempunyai partikel-partikel yang relatif besar untuk dapat

menghamburkan sinar tersebut. Sebaliknya, pada larutan sejati, partikelpartikelnya relatif kecil sehingga hamburan yang terjadi hanya sedikit dan
sangat sulit diamati.
Gerak Brown
Gerak Brown ialah gerakan partikel-partikel koloid yang senantiasa
bergerak lurus tapi tidak menentu (gerak acak/tidak beraturan). Jika kita
amati koloid dibawah mikroskop ultra, maka kita akan melihat bahwa
partikel-partikel tersebut akan bergerak membentuk zigzag. Pergerakan
zigzag ini dinamakan gerak Brown. Partikel-partikel suatu zat senantiasa
bergerak. Gerakan tersebut dapat bersifat acak seperti pada zat cair dan
gas( dinamakan gerak brown), sedangkan pada zat padat hanya beroszillasi
di tempat ( tidak termasuk gerak brown ). Untuk koloid dengan medium
pendispersi zat cair atau gas, pergerakan partikel-partikel akan
menghasilkan tumbukan dengan partikel-partikel koloid itu sendiri.
Tumbukan tersebut berlangsung dari segala arah. Oleh karena ukuran
partikel cukup kecil, maka tumbukan yang terjadi cenderung tidak
seimbang. Sehingga terdapat suatu resultan tumbukan yang menyebabkan
perubahan arah gerak partikel sehingga terjadi gerak zigzag atau gerak
Brown.
Semakin kecil ukuran partikel koloid, semakin cepat gerak Brown yang
terjadi. Demikian pula, semakin besar ukuran partikel koloid, semakin
lambat gerak Brown yang terjadi. Hal ini menjelaskan mengapa gerak
Brown sulit diamati dalam larutan dan tidak ditemukan dalam campuran
heterogen zat cair dengan zat padat (suspensi). Gerak Brown juga
dipengaruhi oleh suhu. Semakin tinggi suhu sistem koloid, maka semakin
besar energi kinetik yang dimiliki partikel-partikel medium
pendispersinya. Akibatnya, gerak Brown dari partikel-partikel fase
terdispersinya semakin cepat. Demikian pula sebaliknya, semakin
rendah suhu sistem koloid, maka gerak Brown semakin lambat.

Adsorpsi
Adsorpsi ialah peristiwa penyerapan partikel atau ion atau senyawa lain
pada permukaan partikel koloid yang disebabkan oleh luasnya permukaan
partikel. (Catatan : Adsorpsi harus dibedakan dengan absorpsi yang
artinya penyerapan yang terjadi di dalam suatu partikel). Contoh : (i)
Koloid Fe(OH)3 bermuatan positif karena permukaannya menyerap ion H+.
(ii) Koloid As2S3 bermuatan negatif karena permukaannya menyerap ion
S2.


Muatan koloid
Dikenal dua macam koloid, yaitu koloid bermuatan positif dan koloid
bermuatan negatif.
Koagulasi koloid
Koagulasi adalah penggumpalan partikel koloid dan membentuk endapan.
Dengan terjadinya koagulasi, berarti zat terdispersi tidak lagi membentuk
koloid. Koagulasi dapat terjadi secara fisik seperti pemanasan, pendinginan
dan pengadukan atau secara kimia seperti penambahan elektrolit,
pencampuran koloid yang berbeda muatan.

Koloid pelindung
Koloid pelindung ialah koloid yang mempunyai sifat dapat melindungi koloid
lain dari proses koagulasi.

Dialisis
Dialisis ialah pemisahan koloid dari ion-ion pengganggu dengan cara ini
disebut proses dialisis. Yaitu dengan mengalirkan cairan yang tercampur
dengan koloid melalui membran semi permeable yang berfungsi sebagai
penyaring. Membran semi permeable ini dapat dilewati cairan tetapi tidak
dapat dilewati koloid, sehingga koloid dan cairan akan berpisah.

Elektroforesis
Elektroferesis ialah peristiwa pemisahan partikel koloid yang bermuatan
dengan menggunakan arus listrik.
Posted by Veronica Chua at 11:59 PM

http://kimiaverr21.blogspot.com/2010/02/koloid-dan-sifatsifatnya.html
February 15 2011
Description
This section is from the book "Experimental Cookery From The Chemical And Physical
Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Fluidity, Viscosity, And Plasticity Of Colloidal Systems
Fluidity and viscosity. Bingham uses the term fluidity to express the opposite of viscosity. A
fluid like water yields readily to any force that tends to change its form, whereas a viscous
substance shows some resistance to flow. Viscosity is one of the important properties of
colloidal systems. As a general rule, the lyophobic colloids show a viscosity but little greater
than that of the dispersion medium, the viscosity increasing only slightly with increasing
concentration of the micelles. But the lyophilic colloids may show very high viscosities or even
plasticity with very low concentrations of the micelles.
Bingham states that "a mixture of liquids may have an indefinite number of fluidities
dependent upon the method of mixing, in other words, upon the structure of the liquid." He
also states that colloidalsolutions show differences in fluidity due to differences in structure.
Thus it is possible that cake or other batters made with the same materials and the same
proportion of materials may show differences in the structure of the finished cake on account
of different methods of mixing, giving different viscosities to the batter.
Some substances flow readily; others resist flow; and some must have weight applied to start
flow. When a substance tends to resist a shearing force it may exhibit a flow that is
characterized as viscous, turbulent, or plastic. If the substance entirely regains its original
shape, when the shearing stress is removed, it shows perfect elasticity. If the original shape is
not entirely regained and the substance is deformed to an extent directly proportional to the
shearing force, then the substance is said to show viscosity. This flow that is directly
proportional to the shearing force is called linear flow. By this is meant that if a weight of 1
pound produces a definite deformation, a weight of 2 pounds produces twice that
deformation. Turbulent flow is the flow obtained when the ratio of the shearing force to the
deformation decreases.
A pure liquid at a given temperature and pressure has a definite fluidity. The viscosity of water
is approximately six times as great at 0° as at 100°C. The viscosity of sols usually decreases
with an increase in ternperature, part of this being due to the effect of temperature upon the
intermicellar liquid. Gortner states that in "colloid systems changes due to temperature are
influenced not only by the viscosity of the dispersion medium but likewise by the effect of
temperature on solvation." Thus gelatinand agar-agar form sols with rather low viscosity at
high temperatures when compared to the viscous liquid or plastic gels they form at low
temperatures. Starch usually forms a suspension at low temperatures, and its decided
increase in viscosity or plasticity comes with rapid hydration at the gelatinization point.
Gortner states that heating a starch paste beyond the gelatinization temperature causes a
decrease in viscosity or plasticity. Electrolytes added to lyophilic systems, often even in
traces, cause great changes in the viscosity of the sol.
The factors affecting the viscosity of lyophilic systems. Gort-ner adds an eleventh factor, that
of rate of shear, pointed out by Sharp and Gortner, to the ten given by Ostwald that cause
variation in the viscosity of lyophilic systems. They are as follows: (1) concentration, (2)
temperature, (3) degree of dispersion, (4) solvation, (5) electrical charge, (6) previous thermal
treatment, (7) previous mechanical treatment, (8) the presence or absence of other lyophilic
colloids, (9) the age of the lyophilic sol, (10) the presence of both electrolytes and nonelectrolytes, and (11) the rate of shear.
Viscosity is closely related to the consistency of the finished product in food preparation. So
close is this relation in many cases that the ten factors listed by Ostwald may nearly be taken
as ten commandments of food preparation. Thus the consistency of a custard is influenced
by the concentration of egg or the protein micelles; the temperature to which it is cooked; the
degree of dispersion of the micelles, which is influenced by the reaction and other factors; the
degree of hydration, which is influenced by reaction, the kind and concentration of salts
present, etc.; the beating of the egg; the use of milk or water; how long the custard has aged
in addition to the age of the eggs and milk when used; the kinds and concentration of salts in
the egg and milk as well as the addition of sodium chloride and the non-electrolyte sugar.
Since the line of demarcation between sols and gels is not a definite one, fruit jellies, gelatin,
milk, cream, as well as egg dishes, may be added to the group of foods in which the
consistency of the finished product is related to viscosity. But this does not end
the application, for the structure or type of product in baked goods is closely related to the
viscosity of the batter or dough, which in turn is influenced by all these factors. Of course
these factors or nearly the same ones affect other properties as well as viscosity of food
materials. Thus the extensibility of gluten, the heat coagulation of proteins, etc., are
influenced by many or all of these factors.
Plasticity. Bingham defines plasticity as "a property of solids in virtue of which they hold their
shape permanently under the action of small shearing stresses but they are readily deformed,
worked or molded, under somewhat larger stresses. Plasticity is thus a complex property,
made up of two independent factors, which we must evaluate separately." Modeling clay is
plastic. Plasticity is an important property of fats used for cakes, biscuits, and pastry. A
plastic fat has a consistency such that it will form a thin sheet or layer in a batter or it will
retain air bubbles when "creamed." The enclosing of these air bubbles in the fat is an aid in
leavening cakes and may assist in obtaining a velvety texture, for the enclosing of the air
renders the fat more plastic, thus more easily distributed in the batter at lower temperatures.
http://chestofbooks.com/food/science/Experimental-Cookery/Fluidity-ViscosityAnd-Plasticity-Of-Colloidal-Systems.html
2011-03-22
Sifat-Sifat Koloid
a.
Efek Tyndall
Apabila sinar diarahkan pada sistem koloid dan larutan
sejati, contohnya koloid kanji dan larutan Na2Cr207,
maka sinar tersebut akan dihamburkan oleh sistem koloid
tetapi tidak dihamburkan oleh larutan sejati. Hal ini
ditunjukkan oleh adanya berkas sinar.
Sifat menghamburkan cahaya ini terkait dengan ukuran
partikel.
Koloid
kanji
memiliki
partikel-partikel
koloid yang relatif besar untuk dapat menghamburkan
sinar
tersebut.
Sebaliknya,
larutan
sejati
Na2Cr207 memiliki partikel-partikel yang relatif kecil
sehingga hamburan yang terjadi sangat sedikit dan sulit
diamati.
Sifat penghamburan cahaya oleh sistem koloid ditemukan
oleh John Tyndall (1820-1893), seorang ahli fisika
Inggris. Oleh karena itu, sifat ini disebut efek
Tyndall. Efek Tyndall ini dapat digunakan untuk
membedakan sistem koloid dari larutan sejati.
b.
Gerak Brown
Seorang ahli botani Inggris pada tahun 1827 yang
bernama Robert Brown (1773-1858), hal yang pertama kali
diamati di bawah mikroskop ultra adalah partikel koloid
yang tampak sebagai titik cahaya kecil sesuai dengan
sifatnya yang menghamburkan cahaya (efek Tyndall). Jika
pergerakkan
titik
cahaya
atau
partikel
tersebut
diikuti, ternyata partikel tersebut bergerak terusmenerus
dengan gerakan
zigzag.
Gerak
acak
dari
partikel koloid dalam medium pendispersinya tersebut
disebut sebagai gerak Brown. Adanya gerak Brown membuat
partikel-partikel
koloid
dapat
mengatasi
pengaruh
gravitasi
sehingga
partikel-partikel
ini
tidak
memisahkan diri dari medium pendispersinya.
Gerak Brown dari suatu partikel koloid
Partikel-partikel suatu zat senantiasa bergerak dan
gerakannya ini dapat bersifat acak seperti pada zat
cair dan gas, atau hanya bervibrasi di tempat seperti
pada zat padat. Pergerakkan partikel-partikel untuk
sistem koloid dengan medium pendispersi zat cair atau
gas akan menghasilkan tumbukan dengan partikel-partikel
koloid itu sendiri. Tumbukan tersebut berlangsung dari
segala arah. Oleh karena ukuran partikel koloid cukup
kecil, maka tumbukan yang terjadi cenderung tidak
seimbang, sehingga terjadi resultan tumbukan yang
menyebabkan perubahan arah gerak partikel sehingga
terjadi gerak Brown.
Adanya resultan tumbukan oleh partikel-partikel medium
pendispersi menyebabkan partikel-partikel koloid
bergerak secara acak.
Semakin besar ukuran partikel koloid, semakin lambat
gerak Brown yang terjadi dan sebaliknya, semakin kecil
ukuran partikel koloid, maka akan semakin cepat gerak
Brown yang terjadi. Hal ini menyebabkan mengapa gerak
Brown sulit diamati dalam larutan dan tidak ditemukan
dalam suspensi.
Suhu dapat mempengaruhi gerak Brown, jadi semakin
tinggi suhu sistem koloid, maka semakin besar energi
kinetik
yang
dimiliki
partikel-partikel
medium
pendispersinya. Akibatnya, gerak Brown dari partikelpartikel
fase
terdispersinya
semakin
cepat,
dan
sebaliknya, semakin rendah suhu sistem koloid, maka
gerak Brown semakin lambat.
c.
Adsorpsi Koloid
Jika partikel-partikel sol padat diletakkan dalam zat
cair
atau
gas
maka
partikel-partikelnya
akan
terakumulasi
pada
permukaan
zat
padat
tersebut.
Fenomena ini disebut adsorpsi yang terkait dengan
penyerapan partikel pada permukaan zat. Adsorpsi dengan
absorpsi itu berbeda. Bedanya adalah absorpsi terkait
dengan penyerapan partikel sampai ke bawah permukaan
zat.
Partikel
koloid
sol
mempunyai
kemampuan
untuk
mengadsopsi
partikel-partikel
pendispersi
pada
permukaannya, baik itu partikel netral atau bermuatan
(kation dan anion). Daya adsorpsi partikel koloid
tergolong besar karena partikel-partikelnya memberikan
suatu permukaan yang sangat luas. Sifat adsorpsi ini
telah
digunakan
dalam
berbagai
proses
seperti
penjernihan air.
d.
Muatan Koloid Sol
Sifat koloid yang terpenting adalah muatan partikel
koloid. Semua partikel koloid memiliki muatan sejenis
(positif
atau
negatif).
Dikarenakan
muatan
yang
sejenis,
maka
terdapat
gaya
tolak-menolak
antar
partikel koloid. Hal ini mengakibatkan partikelpartikel
koloid
tidak
dapat
bergabung
sehingga
memberikan kestabilan pada sistem koloid, tetapi secara
keseluruhan, sistem koloid bersifat netral karena
partikel-partikel koloid bermuatan ini akan menarik
ion-ion
dengan
muatan
berlawanan
dalam
medium
pendispersinya.
(i) Sumber Muatan Koloid Sol
Partikel-partikel koloid mendapat muatan listrik
melalui 2 cara, yaitu:
a).Proses Adsorpsi
Partikel
koloid
dapat
mengadsopsi
partikel
bermuatan dari fase pendispersinya. Akibatnya,
partikel
koloid
bermuatan.
Jenis
muatannya
tergantung dari jenis partikel bermuatan yang
diserap, apakah berupa kation atau anion. Untuk
dapat mengerti lebih jelas, simaklah gambar di
bawah ini.
Partikel sol Fe(OH)3 (bermuatan positif) mempunyai
kemampuan untuk mengadsorpsi kation dari medium
pendispersinya
sehingga
bermuatan
positif,
sedangkan partikel sol As2S3 (bermuatan negatif)
mengadsorpsi anion dari medium pendispersinya
sehingga bermuatan negatif.
Partikel koloid sol tidak selalu mengadsorpsi ion
yang sama tetapi dapat berbeda tergantung jenis
ion berlebih (kation atau anion) dari medium
pendispersinya. Contohnya, sol AgCl dalam medium
pendispersi
dengan
kation
Ag + berlebih
akan
+
mengadsorpsi Ag sehingga bermuatan positif dan
sebaliknya, jika anion Cl-berlebih, maka sol AgCl
akan
mengadsorpsi
ion
Cl- sehingga
bermuatan
negatif.
b).Proses Ionisasi Gugus Permukaan Partikel
Beberapa partikel koloid memperoleh muatan dari
proses
ionisasi
gugus-gugus
yang
ada
pada
permukaan partikel koloid. Contohnya adalah koloid
protein dan koloid sabun atau deterjen.
(ii)
Kestabilan Koloid
Muatan partikel-partikel koloid adalah sejenis
sehingga cenderung saling tolak-menolak. Gaya tolakmenolak
ini
mencegah
partikel-partikel
koloid
bergabung dan mengendap akibat gaya gravitasi,
sehingga muatan koloid berperan besar dalam menjaga
kestabilan koloid.
(iii)
Lapisan Bermuatan Ganda
Permukaan
partikel
koloid
mendapat
muatan
listrik
dengan
mengadsorpsi
ion
dari
medium
pendispersinya.
Lapisan
bermuatan
listrik
ini
selanjutnya akan menarik ion-ion dengan muatan
berlawanan dari medium pendispersinya. Akibatnya,
akan terbentuk 2 lapisan yang disebut lapisan
permukaan ganda. Adanya lapisan ini menyebabkan
sistem koloid secara keseluruhan bersifat netral.
(iv)
Elektroforesis
Oleh karena partikel koloid sol bermuatan
listrik, maka partikel ini akan bergerak dalam medan
listrik. Pergerakkan partikel koloid dalam medan
listrik disebut elektroforesis.
Dalam tabung U yang berisi sistem koloid sol
yang
bermuatan
positif,
dimasukkan
sepasang
elektrode dan diberi arus searah dari sumber
tegangan. Dapat diketahui bahwa partikel-partikel
koloid bermuatan positif tersebut bergerak menuju
elektrode dengan muatan berlawanan, yaitu elektrode
negatif (katode). Apabila sistem koloid tersebut
diganti dengan yang bermuatan negatif, maka akan
ditemukan
bahwa
partikel-partikel
koloid
akan
bergerak menuju elektrode positif (anode). Fenomena
eletroforesis dapat digunakan untuk menentukan jenis
muatan partikel koloid.
Muatan
beberapa
partikel
koloid
dalam
pendispersi air:
Partikel Koloid
Partikel Koloid
Bermuatan
Bermuatan
Positif
Negatif
medium
Fe(OH)3
Al(OH) 3
Pewarna dasar
Hemoglobin
As2S3
Logam seperti
Au, Ag, Pt
Tepung
Tanah liat
e.
Koagulasi
Partikel-partikel
koloid
bersifat
stabil
karena
memiliki muatan listrik yang sejenis. Apabila muatan
listrik tersebut hilang, maka partikel-partikel koloid
tersebut akan bergabung membentuk gumpalan. Proses
pengumpulan ini disebut flokulasi (floculation) dan
gumpalannya disebut flok (flocculant). Gumpalan ini
akan mengendap akibat pengaruh gravitasi. Proses
penggumpalan
partikel-partikel
koloid
dan
pengendapannya ini disebut koagulasi.
Penghilangan muatan listrik pada partikel koloid ini
dapat dilakukan dengan empat cara, yaitu :
(i)
Menggunakan prinsip elektroforesis
Proses elektroforesis adalah pergerakan partikelpartikel koloid yang bermuatan ke elektrode dengan
muatan berlawanan. Ketika partikel-partikel ini
mencapai elektrode, maka partikel-partikel tersebut
akan kehilangan muatannya sehingga menggumpal dan
mengendap di elektrode. Untuk lebih memahaminya,
lakukan kegiatan berikut.
(ii)
Penambahan koloid lain dengan muatan berlawanan
Apabila
suatu sistem koloid bermuatan positif
dicampur dengan sistem koloid lain yang bermuatan
negatif, maka kedua sistem koloid tersebut akan
saling mengadsorpsi dan menjadi netral. Akibatnya,
terbentuk
koagulasi.
Untuk
jelasnya,
lakukan
kegiatan berikut.
(iii)
Penambahan elektrolit
Jika suatu elektrolit ditambahkan ke dalam
sistem koloid, maka partikel-partikel koloid yang
bermuatan negatif akan menarik ion positif (kation)
dari elektrolit. Sementara itu, partikel-partikel
koloid yang bermuatan positif akan menarik ion
negatif (anion) dari elektrolit. Hal ini menyebabkan
partikel
-partikel
koloid
tersebut dikelilingi
oleh pasien kedua yang memiliki muatan berlawanan
dengan muatan lapisan pertama. Apabila jarak antara
lapisan pertama dan kedua cukup dekat, maka muatan
keduanya akan hilang sehingga terjadi koagulasi.
(iv)
Pendidihan
Sol, seperti belerang dan perak halida yang
terdispersi dalam air, dapat mengalami koagulasi
dengan mendidihkannya. Kenaikan suhu sistem koloid
menyebabkan jumlah tumbukan antara partikel-partikel
sol dengan molekul-molekul air bertambah banyak. hal
ini menyebabkan lepasnya elektrolit yang teradsorpsi
pada permukaan partikel koloid. Akibatnya, partikelpartikel koloid menjadi tidak bermuatan sehingga
terjadi koagulasi.
f. Koloid Pelindung
Berdasarkan
perbedaan
daya
adsorpsi
dari
fase
terdispersi terhadap medium pendispersinya yang berupa
zat cair, koloid dapat dibedakan menjadi dua jenis.
Sistem koloid di mana partikel terdispersinya mempunyai
daya adsorpsi yang relatif besar disebut koloid liofil.
Sedangkan sistem koloid dimana partikel terdispersinya
mempunyai daya adsorpsi yang relatif kecil disebut
koloid liofob. Koloid liofil bersifat lebih stabil,
sedangkan koloid liofob bersifat kurang stabil. Koloid
liofil yang berfungsi sebagai koloid pelindung.
Koloid liofil dan koloid liofob
Koloid yang memiliki medium pendispersi berupa zat
cair dapat menjadi koloid liofil dan koloid liofob.
- Koloid liofil (suka cairan) adalah koloid dimana
terdapat gayatarik menarik yang cukup besar antara
fase
terdispersi
dan
medium
pendispersinya.
Contohnya, dispersi kanji, sabun, deterjen, dan
protein dalam air.
- Koloid liofob (tidak suka cairan) adalah koloid di
mana terdapatgaya tarik menarik yang lemah atau
bahkan tidak ada gaya tarik menarik antara fase
terdsipersi dan medium pendispersinya. Contohnya,
dispersi emas, Fe (OH)3, dan belerang dalam air.
Jika medium pendispersi koloid ini adalah air, maka
istilah yang digunakan adalah koloid hidrofil dan
koloid hidrofob.
Gaya tarik menarik koloid hidrofil yang lebih kuat
dibandingkan
koloid
hidrofob
disebabkan
oleh
keberadaan ikan hidrogen yang terbentuk antara fase
terdispersi
dan
air
(medium
pendispersi).
Sebagai contoh ikatan hidrogen antara gugus amino (NH2 atau - NH-) molekul protein dan molekul air,
ikatan hidrogen antara gugus -OH molekul kanji dan
molekul air. Ikatan hidrogen ini tidak ditemukan
dalam koloid liofob seperti dispersi emas atau
belerang dalam air.
Beberapa perbedaan sifat -sifat koloid liofil /
hidrofil dan liofob / hidrofob, khususnya sol dalam
medium pendispersi cair diberikan berikut ini.
Sifat - sifat
Sol liofil /
Sol liofob /
1.
Pembuatan
2. Muatan
Partikel
3. Adsorpsi
medium
pendispersi
(proses solvasi
/ hidrasi)
4. Viskositas
(kekentalan)
hidrofil
Sol liofil dapat
dibuat langsung
dengan
mencampurkan fase
terdispersi
dengan medium
pendispersinya.
Pembuatannya
dapat melibatkan
konsentrasi yang
relatif besar.
Partikel-partikel
sol hidrofil
mempunyai muatan
yang kecil atau
tidak bermuatan
Partikel partikel sol
hidrofil
mengadsorpsi
medium
pendispersinya.
Akhirnya,
terbentuk lapisan
medium
pendispersi yang
teradsorpsi di
sekeliling
partikel. Lapisan
ini yang
menyebabkan
partikel partikel sol
hidrofil tidak
saling bergabung.
Proses ini
disebut solvasi /
hidrasi.
Viskositas sol
liofil lebih
besar
dibandingkan
viskositas medium
pendispersinya.
Hal ini
hidrofob
Sol liofob tidak
dapat dibuat
hanya dengan
mencampur fase
terdispersi dan
medium
pendispersinya.
Perkecualian adalah
pada konentrasi yang
kecil.
Partikel-partikel
sol hidrofob
memiliki muatan
positif atau
negatif.
Muatan ini
memberikan
kestabilan bagi
sistem koloid.
Partikel-partikel
sol hidrofob tidak
mengadsorpsi medium
pendispersinya.
Muatan partikelpartikel sol
diperoleh dari
adsorpsi partikelpartikel ion yang
bermuatan listrik.
Viskositas sol
hidrofob hampir sama
dengan viskositas
medium
pendispersinya. Oleh
karena itu, sol
liofob tidak
5.
Penggumpalan
6. Sifat
reversibel
7.
Efek Tyndall
disebabkan ukuran
partikel
meningkat akibat
proses solvsi dan
karenanya jumlah
medium
pendispersinya
yang bebas
berkurang. Sol
liofil yang
hangat akan
membentuk gel
jika
didinginkan.
Tidak mudah
menggumpal dengan
penambahan
elektrolit. Untuk
menggumpalkan sol
liofil diperlukan
elektrolit dengan
konsentrasi
tinggi, dimana
elektrolit ini
dapat memecah
lapisan medium
pendispersi yang
melindunginya dan
menyebabkan
penggumpalan.
Sol liofil
bersifat
reversibel.
Artinya, fase
terdispersi sol
liofil dapat
dipisahkan dengan
koagulasi atau
penguapan medium
pendispersinya,
dan kemudian
dapat diubah
kembali menjadi
sol dengan
penambahan medium
pendispersinya.
Sol liofil
memberikan efek
Tyndall yang
lemah. Hal ini
membentuk gel.
Mudah menggumpal
dengan penambahan
elektrolit. Sol
liofob akan
menggumpal bahkan
dengan penambahan
elektrolit dengan
konsentrasi rendah.
Hal ini disebabkan
sol liofob tidak
memiliki lapisan
pelindung seperti
halnya sol liofil.
Sol liofob bersifat
tidak reversibel.
Artinya, fase
terdispersi sol
liofob yang telah
digumpalkan atau
dipisahkan dari
medium pendispersiny
a, tidak dapat
diubah kembali
menjadi sol.
Sol liofob dapat
memberikan efek
Tyndall yang jelas.
Hal ini disebabkan
8. Migrasi
dalammedan list
rik
disebabkan ukuran
partikelpartikelnya
relatif kecil.
Partikel-partikel
sol liofil dapat
bermigrasi ke
anode, katode,
atau tidak
bermigrasi sama
sekali
dalammedan listri
k. Contohnya
protein.
ukuran partikelpartikelnya cukup
besar.
Partikel-partikel
sol liofob akan
bergerak ke anode
atau ke katode. Hal
ini tergantung jenis
muatan partikel
apakah negatif atau
positif.
http://www.freewebs.com/leosylvi/sifatsifatkoloidsol.htm
2011-03-22
What is a Colloidal Dispersion?
Colloidal system or colloidal dispersion is a heterogeneous system which is made up of
Dispersed phase and Dispersion medium. In colloidal dispersion one substance is dispersed
as very fine particles in another substance called dispersion medium. In case of dust, solid
particles are dispersed in air as dispersion medium.
Types of Colloidal Dispersions
Dispersed phase and dispersion medium can be solid, liquid or gas. Depending upon the
state of dispersed phase and dispersion medium, eight different types of colloidal
dispersions can exist.
Eight Different Types of Colloidal Dispersions are:
1.
Foam
2.
Solid foam
3.
Liquid Aerosol
4.
Emulsions
5.
Gels
6.
Solid Aerosol
7.
Sol (Colloidal suspension)
8.
Solid sol (Solid suspension)
Dispersed
Phase
Gas
Gas
Gas
Liquid
Liquid
Liquid
Dispersion
Medium
Liquid
Solid
Gas
Gas
Liquid
Solid
Type of Colloidal
Dispersions
Foam
Solid foam
Does not exist
Liquid Aerosol
Emulsions
Gel
Solid
Gas
Solid
Liquid
Solid
Solid
Solid Aerosol
Sol or Colloidal
Suspension
Solid sol(solid
suspension)
It is important to note that when one gas is mixed with another gas, a homogeneous
mixture is formed i.e. gases are completely miscible into each other. Colloidal dispersions
are heterogeneous in nature and gas dispersed in another gaseous medium does not form
colloidal system.
When the dispersion medium is gas, the solution is called Aerosol and when the dispersion
medium is liquid, the colloidal dispersion is known as Sol. Sols can further be classified into
different types depending upon the liquid used.

If the liquid used is water, the solution is Hydrosol or Aquasol.

If liquid used is Benzene, the solution is Benzosol

If liquid used is Alcohol, the solution is Alcosol

If any organic compound is used, the solution is Organosol
Example of Colloidal Dispersions
Different Types of Colloidal Dispersion and their examples are summarized in table
below.
Type of Colloidal Dispersions
Foam
Solid foam
Does not exist
Liquid Aerosol
Emulsions
Gel
Solid Aerosol
Sol or Colloidal Suspension
Solid sol(solid suspension)
Examples
Soap, beer, lemonade
Pumice stone
Fog, dust
Milk, rubber
Butter, Cheese
Dust
Paste, ink
Pearls, gem stones
http://www.xamplified.com/colloidal-dispersions/
2011-03-22
http://old.iupac.org/goldbook/C01174.pdf
2011-03-22
A colloid is a substance microscopically dispersed evenly throughout another substance. [1]
A colloidal system consists of two separate phases: a dispersed phase (or internal phase)
and a continuous phase (or dispersion medium). A colloidal system may be solid, liquid,
or gaseous.
Many familiar substances are colloids, as shown in the chart below. In addition to these
naturally occurring colloids, modern chemical process industries utilize high shear mixing
technology to create novel colloids.
The dispersed-phase particles have a diameter of between approximately 5 and
200 nanometers.[2] Such particles are normally invisible in an opticalmicroscope, though
their presence can be confirmed with the use of an ultramicroscope or an electron
microscope. Homogeneous mixtures with a dispersed phase in this size range may be
called colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersions,
or hydrosols. The dispersed-phase particles or droplets are affected largely by the surface
chemistry present in the colloid.
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 systems (also called colloidal solutions or colloidal suspensions) are the subject
of interface and colloid science. This field of study was introduced in 1861
by Scottish scientist Thomas Graham.
Contents
[hide]

1 Classification of colloids

2 Hydrocolloids

3 Interaction between colloid particles

4 Stabilization of a colloidal dispersion (peptization)

5 Destabilizing a colloidal dispersion (flocculation)
o
5.1 Technique monitoring colloidal stability
o
5.2 Accelerating methods for shelf life prediction

6 Colloids as a model system for atoms

7 Colloidal crystals

8 Colloids in biology

9 Colloids in the environment

10 Use in intravenous therapy

11 See also

12 References

13 Further reading

14 External links
[edit]Classification
of colloids
Because the size of the dispersed phase may be difficult to measure, and because colloids
have the appearance of solutions, colloids are sometimes identified and characterized by
their physico-chemical and transport properties. For example, if a colloid consists of a solid
phase dispersed in a liquid, the solid particles will not diffuse through a membrane, whereas
with a true solution the dissolved ions or molecules will diffuse through a membrane. Because
of the size exclusion, the colloidal particles are unable to pass through the pores of an
ultrafiltration membrane with a size smaller than their own dimension. The smaller the size of
the pore of the ultrafiltration membrane, the lower the concentration of the dispersed colloidal
particules remaining in the ultrafiltred liquid. The exact value of the concentration of a truly
dissolved species will thus depend on the experimental conditions applied to separate it from
the colloidal particles also dispersed in the liquid. This is, a.o., particularly important
for solubility studies of readily hydrolysed species such as Al, Eu, Am, Cm, ... or organic
matter complexing these species.
Colloids can be classified as follows:
Medium / Phas
Dispersed phase
es
Gas
Continu
Liqu
ous
id
medium
Gas
Liquid
Solid
NONE
(All gases are
mutually miscible)
Liquid aerosol
Examples: fog, mist, hair
sprays
Solid aerosol
Examples: smoke, clo
ud, air particulates
Foam
Example: whipped
cream, Shaving cream
Emulsion
Sol
Examples: milk, mayonnais Examples: pigmented
e, hand cream
ink, blood
Gel
Solid foam
Solid Examples: aerogel, styrofoam, Examples: agar, gelatin, jel
pumice
ly, opal
Solid sol
Example: cranberry
glass
In some cases, a colloid can be considered as a homogeneous mixture. This is because the
distinction between "dissolved" and "particulate" matter can be sometimes a matter of
approach, which affects whether or not it is homogeneous or heterogeneous.
[edit]Hydrocolloids
A hydrocolloid is defined as a colloid system wherein the colloid particles are dispersed
in water. A hydrocolloid has colloid particles spread throughout water, and depending on the
quantity of water available that can take place in different states, e.g., gel or sol (liquid).
Hydrocolloids can be either irreversible (single-state) or reversible. For example, agar, a
reversible hydrocolloid of seaweedextract, can exist in a gel and sol state, and alternate
between states with the addition or elimination of heat.
Many hydrocolloids are derived from natural sources. For example, agaragar and carrageenan are extracted from seaweed, gelatin is produced by hydrolysis of
proteins of bovine and fish origins, andpectin is extracted from citrus peel and
apple pomace.
Gelatin desserts like jelly or Jell-O are made from gelatin powder, another effective
hydrocolloid. Hydrocolloids are employed in food mainly to
influence texture or viscosity (e.g., a sauce). Hydrocolloid-based medical dressings are
used for skin and wound treatment.
Other main hydrocolloids are xanthan gum, gum arabic, guar gum, locust bean gum,
cellulose derivatives as carboxymethyl cellulose, alginate and starch.
[edit]Interaction
between colloid particles
The following forces play an important role in the interaction of colloid particles:

Excluded volume repulsion: This refers to the impossibility of any overlap between
hard particles.

Electrostatic interaction: Colloidal particles often carry an electrical charge and
therefore attract or repel each other. The charge of both the continuous and the dispersed
phase, as well as the mobility of the phases are factors affecting this interaction.

van der Waals forces: This is due to interaction between two dipoles that are either
permanent or induced. Even if the particles do not have a permanent dipole, fluctuations
of the electron density gives rise to a temporary dipole in a particle. This temporary dipole
induces a dipole in particles nearby. The temporary dipole and the induced dipoles are
then attracted to each other. This is known as van der Waals force, and is always present
(unless the refractive indexes of the dispersed and continuous phases are matched), is
short-range, and is attractive.

Entropic forces: According to the second law of thermodynamics, a system
progresses to a state in which entropy is maximized. This can result in effective forces
even between hard spheres.

Steric forces between polymer-covered surfaces or in solutions containing nonadsorbing polymer can modulate interparticle forces, producing an additional steric
repulsive force (which is predominantly entropic in origin) or an attractive depletion force
between them. Such an effect is specifically searched for with tailormade superplasticizers developed to increase the workability of concrete and to reduce
its water content.
[edit]Stabilization
of a colloidal dispersion (peptization)
Stabilization serves to prevent colloids from aggregating. Steric stabilization and electrostatic
stabilization are the two main mechanisms for colloid stabilization. Electrostatic stabilization
is based on the mutual repulsion of like electrical charges. In general, different phases have
different charge affinities, so that a electrical double layer forms at any interface. Small
particle sizes lead to enormous surface areas, and this effect is greatly amplified in colloids. In
a stable colloid, mass of a dispersed phase is so low that its buoyancy or kinetic energy is
too weak to overcome the electrostatic repulsion between charged layers of the dispersing
phase. The charge on the dispersed particles can be observed by applying an electric field:
All particles migrate to the same electrode and therefore must all have the same sign charge.
[edit]Destabilizing
a colloidal dispersion (flocculation)
Unstable colloidal dispersions form flocs as the particles aggregate due to interparticle
attractions. In this way photonic glasses can be grown. This can be accomplished by a
number of different methods:

Removal of the electrostatic barrier that prevents aggregation of the particles. This
can be accomplished by the addition of salt to a suspension or changing the pH of a
suspension to effectively neutralize or "screen" the surface charge of the particles in
suspension. This removes the repulsive forces that keep colloidal particles separate and
allows for coagulation due to van der Waals forces.

Addition of a charged polymer flocculant. Polymer flocculants can bridge individual
colloidal particles by attractive electrostatic interactions. For example, negatively-charged
colloidal silica or clay particles can be flocculated by the addition of a positively-charged
polymer.

Addition of non-adsorbed polymers called depletants that cause aggregation due to
entropic effects.

Physical deformation of the particle (e.g., stretching) may increase the van der Waals
forces more than stabilization forces (such as electrostatic), resulting coagulation of
colloids at certain orientations.
Unstable colloidal suspensions of low-volume fraction form clustered liquid suspensions,
wherein individual clusters of particles fall to the bottom of the suspension (or float to the top if
the particles are less dense than the suspending medium) once the clusters are of sufficient
size for the Brownian forces that work to keep the particles in suspension to be overcome by
gravitational forces. 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 the toothbrush after it is applied.
[edit]Technique
monitoring colloidal stability
Measurement principle of multiple light scattering coupled with vertical scanning
Multiple light scattering coupled with vertical scanning is the most widely used technique to
monitor the dispersion state of a product, hence identifying and quantifying destabilisation
phenomena.[3][4][5][6] It works on concentrated dispersions without dilution. When light is sent
through the sample, it is backscattered by the particles / droplets. The backscattering intensity
is directly proportional to the size and volume fraction of the dispersed phase. Therefore, local
changes in concentration (e.g.Creaming and Sedimentation) and global changes in size
(e.g.flocculation, coalescence) are detected and monitored.
[edit]Accelerating
methods for shelf life prediction
The kinetic process of destabilisation can be rather long (up to several months or even years
for some products) and it is often required for the formulator to use further accelerating
methods in order to reach reasonable development time for new product design. Thermal
methods are the most commonly used and consists in increasing temperature to accelerate
destabilisation (below critical temperatures of phase inversion or chemical degradation).
Temperature affects not only the viscosity, but also interfacial tension in 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 the product to different forces that pushes the particles /
droplets against one another, hence helping in the film drainage. However, some emulsions
would never coalesce in normal gravity, while they do under artificial gravity.[7] Moreover
segregation of different populations of particles have been highlighted when using
centrifugation and vibration.[8]
[edit]Colloids
as a model system for atoms
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 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. In addition, phase
transitions in colloidal suspensions can be studied in real time using optical techniques, and
are analogous to phase transitions in liquids.
[edit]Colloidal
crystals
Main article: Colloidal crystal
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.[9] 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-packeddomains
of amorphous colloidal spheres of silicon dioxide (or silica, SiO2).[10][11] 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 interstitialvoids, which act as a natural diffraction grating for visible light waves,
particularly when the interstitial spacing is of the same order of magnitude as
the incident lightwave.[12][13]
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 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 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.
[edit]Colloids
in biology
In the early 20th century, before enzymology was well understood, colloids were thought to
be the key to the operation of enzymes; i.e., the addition of small quantities of an enzyme to
a quantity of water would, in some fashion yet to be specified, subtly alter the properties of the
water so that it would break down the enzyme's specific substrate,[citation needed] such as a
solution of ATPasebreaking down ATP. Furthermore, life itself was explainable in terms of
the aggregate properties of all the colloidal substances that make up an organism. As more
detailed knowledge of biology andbiochemistry developed, the colloidal theory was
replaced by the macromolecular theory, which explains an enzyme as a collection of
identical huge molecules that act as very tiny machines, freely moving about between the
water molecules of the solution and individually operating on the substrate, no more
mysterious than a factory full of machinery. The properties of the water in the solution are not
altered, other than the simple osmotic changes that would be caused by the presence of
any solute. In humans, both the thyroid gland and the intermediate lobe (pars intermedia)
of the pituitary gland contain colloid follicles.
[edit]Colloids
in the environment
Colloidal particles can also serve as transport vector[14] of diverse contaminants in the surface
water (sea water, lakes, rivers, fresh water bodies) and in underground water circulating in
fissured rocks[15] (limestone, sandstone, granite, ...). Radionuclides and heavy metals
easily sorb onto colloids suspended in water. Various types of colloids are recognised:
inorganic colloids (clay particles, silicates, iron oxy-hydroxides, ...), organic colloids
(humic and fulvic substances). When heavy metals or radionuclides form their own pure
colloids, the term "Eigencolloid" is used to designate pure phases, e.g., Tc(OH) 4, U(OH)4,
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[16] because of the process of ultrafiltration occurring in dense clay
membrane.[17] The question is less clear for small organic colloids often mixed in porewater
with truly dissolved organic molecules.[18]
[edit]Use
in intravenous therapy
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,[19] and therefore, they should theoretically
preferentially increase the intravascular volume, whereas other types of volume expanders
called crystalloids also increases the interstitial volume andintracellular volume.
However, there is still controversy to the actual difference in efficacy by this
difference.[19] Another difference is that crystalloids generally are much cheaper than
colloids.[19]Recently, however, it has been determined that the use of colloids was bolstered
by faked research studies [1]
http://en.wikipedia.org/wiki/Colloid
2011-03-22