Colloid chemistry - Lectures 1 and 2
Transcript of Colloid chemistry - Lectures 1 and 2
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Colloid chemistry
Lectures 1 & 2: Colloidal systems.Hystory,classifications and examples.
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Colloid chemistryRecommended readings:
E. Tombácz: Colloid Chemistry for Pharmaceutical Students.Manuscript, Szeged 1988.
D. F. Evans, H. Wennerström: The Colloidal Domain: WherePhysics, Chemistry, Biology and Technology Meet.2nd Ed., Wiley-VCH, New York 1999.
D. H. Everett: Basic Principles of Colloid Science.RSC, London 1988.
R. J. Hunter: Foundations of Colloid Science. Vol. 1.,Clarendon, Oxford 1989.
D. J. Shaw: Introduction to Colloid and Surface Chemistry.4th Ed., Butterworth-Heinemann, Oxford 1992.
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2 written tests per semester: 5 October and 20 November, 20 min each(a few short questions on the fundamentals of colloid chemistry)
bank holidays: 23 and 30 October !
the slides are accessible at: http://koll1.chem.u-szeged.hu/colloids/hallgatoi.htm
Requirements
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Colloid chemistry
Lectures 1 & 2: Colloidal systems.History,classifications and examples.
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Examples of colloidal systems from daily life
CosmeticsCosmetics
DetergentsDetergents
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1. partly physical chemistry- it is not the chemical composition which is important- the state is independent of the composition
2 partly physics- the physical properties are of great importance- basic law of physics can be applied
3 partly biology- biological materials are colloids- the mechanisms of living systems are related to colloid- and interfacial chemistry
Colloid science is interdisciplinary
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size range of discontinuity:
1 nm to 500 nm (1000 nm)
1 nm = 10 Å = 10-7 cm = 10-9 m
- small particle size and small pore size implylarge interfacial area and theinterfacial properties are therefore important !
The colloidal domain
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distance x distance x
dens
ity ρ
(x)
dens
ity ρ
(x)
colloidal dispersions(incoherent systems)
porous materials; gels(coherent systems)
W. Ostwald: the colloidal state is independent of the chemical compositionA. Buzágh: colloids → systems with submicroscopic discontinuities (1-500 nm)
Colloidal discontinuities
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Classification of colloidson the basis of structure
incoherent systems coherent systems (gels)
colloidal macromolecular associationdispersions solutions colloids
liophobic liophilic liophilic
colloids
porodin reticular spongoid
corpuscular fibrillar lamellar
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TEM
HRTEM
4 ± 25 % nm cubooctahedral Pd particles224 ± 21% nmLDH particles
TEM
198 ± 17% nm SiO2 particles
TEM
SEM22 ± 20% nm O / Wmicroemulsion particles
optmicr
cryoTEM
Incoherent systems: (colloidal) dispersions
4 ± 31% nmPd particles
TEM
3.2 ± 41% µm O / Wemulsion particles
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Surface matterslamella
fibrilla
corpuscula
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Change of surface free energywith particle size
when the particle size decreases: the specific surface area increasesthe degree of dispersion increases
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Size-dependent pecific surface area: S/V(surface to volume ratio)
S / V
S / V
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Specific surface area: S/V(surface to volume ratio)
colloid
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Stability of liophilic and liophobic colloids
- liophilic (solvent loving)- liophobic (solvent hating)- hydrophilic- hydrophobic- lipophilic- lipophobic
colloidal dispersions: liophobic colloids - thermodynamically not stable; kinetically may be stable
macromolecular solutions: liophilic colloidssurfactant solutions: liophilic colloids- both thermodynamically and kinetically stable
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structure of a polypeptide molecule in aqueous solution
Non-particulate incoherent systems:macromolecular solutions
some possible comformations ofproteins in water
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Non-particulate incoherent systems:association colloids (surfactants)
chemical structure of a single surfactant molecule: sodium dodecyl sulfate
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Surfactant micellessurfactant molecule
hydrophobicalkyl chain
hydrophilichead group
self-assembling
spherical micelle
hydrophilic shellhydrophobic core
cationic surfactantanionic surfactantnonionic surfactant
orientation → energy minimumHardy-Harkins principle
30-100 moleculesd-3-5 nm(association)
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Shapes of surfactant aggregates
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Surfactants as biocolloids
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plasma membranes are primarily lipid bilayers with associated proteins and glycolipids(cholesterol is also a major component of plasma membranes)
Surfactants as biocolloids
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Surfactants as biocolloids
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Gel: it is a solid or semisolid system of at least two constituents,consisting of a condensed mass and interpenetrated by a fluid (liquid or gas)(liogel; aerogel). Network without distinct boundaries. No sedimentation.
Coherent systems: gels
2) Macromolecules bound by strong van der Waals forces or cross-linkedby chemical bonds:
1) Floccules of small particles bound by strong van der Waals forces:
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/ / surfactant molecules + liquidsurfactant molecules + liquid
/ ”SOAP” GEL/ ”SOAP” GEL
Formation of liogels
/
/
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Coherent systems: xerogels(porous MCM-type materials)
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Xerogels: porous materials
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coherent system: gelatin (hydrogel)
Coherent systems: liogels(hydrogels and organogels)
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LiogelsLiogels show a variety of flow (rheological) behaviours:
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T= 15 0C T= 20 0C T= 25 0C T= 30 0C T= 35 0C T= 400C T= 450C
Liogels
Hydrogels may show distinct temperature and pH dependent behaviour:
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Classification of disperse systems by size
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Classification of dispersed systems
dispersed systems
amicroscopic
“true” solution
submicroscopic systems
colloids
coarse systems
micro heterogeneous
1 nm 500 nm(1000 nm)
homogeneous colloids
homogenous or heterogeneous?
heterogeneous
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• true solutions (“molecular dispersions”)• (molecules, ions) in gas, liquid (solutions) • < 1 nm, diffuse easily, pass through paper filters
• fine dispersions (colloidal dispersions )• sols (”lyophobic colloidal solutions”); • microemulsions, micelles, polymers
(”lyophilic colloidal solutions”); • smoke, films & foams• 1 to 1000 nm, diffuse slowly, separated by ultrafiltration
• coarse dispersions• most pharmaceutical suspensions and emulsions, dust,
powder, cells, sands• >1µm, do not diffuse, separated by filtration
Classification of disperse systemsby size
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Solutions
♦ Have small particles
(ions or molecules)
♦ Are transparent
♦ Do not separate
♦ Cannot be filtered
♦ Do not scatter light
Colloids♦ Have medium size particles
♦ Cannot be filtered
♦ Separated with semipermeable membranes
♦ Scatter light (Tyndall effect)
Suspensios
♦ Have very large particles
♦ Settle out
♦ Can be filtered
♦ Must stir to stay suspended
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Classification of disperse systemsby size
systemssystems
micellesmicelles
Colloid systems
fog
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Classification of colloidal dispersionsby shape
1. prolate(a>b) 2. oblate (a<b) 3 rod 4. plate 5. coil
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Classification of colloidal dispersionsin terms of the physical states of the
internal and external phases
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L/G: fog, mist, spray(liquid aerosols)
S/G: smoke, loose soot (powders)(solid aerosols)
G/L: sparkling water, foam,whipped cream
(liquid gas dispersions)
L/L: milk; mayonnaize; crude oil((micro)emulsions)
S/L: paint, ink, toothpaste(sols/suspensions)
G/S: polysterene foam,silica gel
(aerogels, xerogels)
L/S: opal, pearl(solid emulsions)
S/S: pigmented plastics(solid suspensions)
Classification of colloidal dispersionsin terms of the physical states of the
internal and external phases
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Some tidbits from thehistory of colloids
motion.
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Brownian motion
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Dynamics of colloidal particles
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Brownian motion
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The Faraday-Tyndall effect.Dark-field microscopy: the ultramicroscope.
Zsigmondy, 1903
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Ultramicroscopic images
blood red cells
Ag nanoparticles
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The Faraday-Tyndall effect
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The Faraday-Tyndall effect
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Dialysis
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Kidney and dialysis
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Artificial kidney
Water and small solute particles
pass through a semipermeable
membrane, large particles are
Retained inside.
Hemodialysis is used medically
(artificial kidney) to remove
waste particles such as
urea from blood.
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A dialysis unit
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Principle ofdialysis
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Osmotic pressure of the blood
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Osmotic Pressure of the Blood♦ Cell walls are semipermeable membranes
♦ The osmotic pressure of blood cells cannot change or damage occurs
♦ The flow of water between a red blood cell and its surrounding environment must be equal
isotonic solutions♦ Exert the same osmotic pressure as red blood cells. ♦ Medically 5% glucose and 0.9% NaCl are used their solute concentrations
provide an osmotic pressure equal to that of red blood cells
H2O
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hypotonicsolutions
♦ Lower osmotic pressure than red blood cells
♦ Lower concentration of particles than RBCs
♦ In a hypotonic solution, water flows into the RBC
♦ The RBC undergoes hemolysis;
it swells and may burst
H2O
hypertonicsolutions
♦ Has higher osmotic pressure than RBC♦ Has a higher particle concentration ♦ In hypertonic solutions, water flows out of the RBC♦ The RBC shrinks in size (crenation)
H2O
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Stability of colloidal dispersions