Download - Introduction SM
A. Interfacial phenomena and colloid chemistry
1. Basic concepts; surface energy; systems characterization.
2. Adsorption at interfaces.
3. Electrical charges at interfaces
4. Colloidal systems.
5. Wetting, foaming, detergency.
2
4
• Precipitation and chemical reduction in solutions.
• Evaporation from emulsion.• Reaction in a gas phase.• Grinding.• Polymerization in emulsion.• Syntheses in ordered systems • Sol-gel.• Reactions at the interface.• Coacervation.
B. Particles
6. Fundamental processes for theachievement of particles
5
• Organic microspheres• Microcapsules• Metallic nanoparticles• Latex
7. Representative processes for preparation of particles;
Bibliography
1. Principles of Colloid and Surface Chemistry, P.C. Hiemenez, Marcel Dekker, N.Y., 1977.
2. Physical Chemistry of Surfaces, A. Adamson, John Wiley & Sons, N.Y., 1990.
3. Surfactants and Interfacial Phenomena, M.J. Rosen, 1991.
4. Specific references indicated during class.
6
Additional books related to this course can be found in the library.
Key words: Interfaces, surfactants, colloid chemistry, adsorption, emulsions, dispersions, nanoparticles, microparticles, etc.
•Attending Classes
At the surface, attractive forces act asymmetrically.
7
Change in general energy as a result of a change in surface area.
Surface layer
dG = dA
= ( )T,V,ndGdA
GS = Surface Free Energy, erg/cm2
GS minA min
10
A change in general energy as a result of a change in surface area.
Curvature ofliquid surface
Coalescence ofof droplet
Formally, the surface tension is defined as the partial derivative of the free energy G with respect to area A.
Dispersion Systems: ExamplesDispersion Systems: Examples
Aerosols
Paints
Cement
Cosmetic Creams
Particle/Droplet Size
Surface Energy
Interactions/Stabilization
13
Colloid = Glue (Greek) 14
Acceptable nameDispersion phaseMediumAerosolLGAerosolSGFoamGLEmulsionLLSuspension, colloidal solution
SL
Solid foamGSGel, solid emulsionLS
AlloySS
Two-Phase Colloidal Systems: Definitions
Dispersion Systems – ExamplesDispersion Systems – Examples
15
ExamplesNameMediumDispersed phase
FogLiquid aerosolGLDustSolid aerosolGSSoap bubblesFoamLGMilk,cosmetic cream
EmulsionLL
Paint, inkSol, suspensionDispersion
LS
Tooth pastePasteInsulating foamSolid foamSGMargarineSolid emulsionSLDry paintSolid
dispersionSS
Self Organized StructuresSelf Organized Structures
A) A cylindrical micelleA) A cylindrical micelle
B) A bilayerB) A bilayer21
Application of Colloid-Surface Application of Colloid-Surface PhenomenaPhenomena
Detergency
Enhanced oil recovery
Emulsification
Adhesion
Ore floatation
Lubrication
Water repellency
Protein adsorption
Latex formation
Precipitation
Filtration
22
Colloid Chemistry in IsraelColloid Chemistry in Israel
Paints
Inks and printing
Resins
Cosmetics
Pharmaceutics
Agriculture
Food
Detergents
23
24
d: edge of a cube
Cube: Total number of moleculesin a cube:
(molecule length = h) = d3/h3
Number of molecules at thesurface = 6d2/h2
Ratio of surface molecules:total number: 6h/d
Surface / bulk molecules
25
20
15
10
5
Perc
enta
ge o
f mol
ecul
es in
the
surf
ace
log d/m-2 -1 0 1 2
Variation of the percentage of molecules in the surface as a function of particle size for a substance with a molar volume of 30 cm3 mol-1
Percentage of moleculesPercentage of moleculesin the surfacein the surface
26
air
liquid
Molecules will leave the interface for theinterior of the liquid.
Surface curvature
Surface Interface
Fluid Interfaces
27
Surface TensionSurface Tension
C C’
D D’
dF
A
l
B
Surface area of a film (two sides) : l d 2 W = F d
If is defined as the force acting along DC (dyne/cm) F = l 2 W = l 2 d = S = W/S
is the work in ergs necessary to generate 1cm2 of a new surface
28
The surface energy may be defined as the excess energy at the surface of a material
compared to the bulk. 29
= Surface free energy per = Surface free energy per unit areaunit area
Dyne cm erg cm cm cm2 =
32
Surface tensions of pure liquid(dynes/cm)
Water72.8Mercury485.0Nitrobenzene43.38Oleic acid32.5Benzene28.86Toluene28.4n-Octane21.77n-Hexane18.43Olive oil35.8Molten metals350-1800Ethanol22.5
Surface Tension - Solution
surfactants
NaCl/water
Water/ethanol
Isooctane/Benzene Molten Nitrates
33
Temperature EffectTemperature Effect
T
= o (1- T/TC)n
Guggenheim-Katayama
o - constant for each liquid n - empirical factor, ~1.3 organic liquidcritical temperature - TC
Pressure EffectPressure Effect
P
36
BSA
40
50
2 6
t (hrs)
0.1 mg/ml
1 mg/ml
68
72
5 15
t (msec)0.1N adipic acid
HOOC - (CH2)4 - COOH
38
Dynamic Surface Tension
12 Hexane 51.0 18.4
CCl4 48 26.9
Benzene 35 28.9
n-Octanol 8.5 27.5
n-Hexanol 6.8
n-Pentanol 4.4
n-Butanol 1.6
Ethanol
Mercury
?
375 485
מתח בין-פנים : נוזל/מים
WaterWater
Hexane Butanol
41
1. Antonoff’s Rule 12 = 1 - 2
(1,2 at saturation)
2. Girifalco & Good
12 = 1 + 2 - 2(12)1/2
= 4V11/3 V2
1/3
(V1 1/3 + V2 1/3)2 V - molar vol.
Estimation of Interfacial Tension
42
3. Owens & Wendt
Surface tension value is composed of polar (P) and non-polar (d) parts
12 = 1 + 2 - 21d 2
d - 21p 2
p
w =h + d = p + d
Estimation of Interfacial Tension
http://www.firsttenangstroms.com/pdfdocs/OwensWendtSurfaceEnergyCalculation.pdf
43
oil (dwater oil)1/2
(dwater oil)1/2 water
Schematic representation of the contributions to an oil-water interfacial tension.
Oil phase
Water phase
44
Data:
12 hexane water : 51.1 dyne/cm
hexane = 18.4 dyne/cm
H2O = 72.8 dyne/cm
phexane = 0
51.1 = 18.4 + 72.8 - 2wd 18.4
wd = 21.8 dyne/cm
wh = 72.8 - 21.8 =51 dyne/cm
Adhesion p,d
45
An Example for Calculating d p
Surface CurvatureSurface Curvature
R
gas
G1 = 4R2, G2 = 4(R2 - 2Rdr + dr2)
G 8 Rdr
P 4R2dr = 8 Rdr Work against pressure difference.
P = 2 (/R) ( P = 4 (/R) for two surfaces )
Young & Laplace : P = (1/r1 +1/r2 )
48
Sphere: r1 = r2
Flat surface: r1 = r2 =
Δp for water drops of different radii at
Droplet radius1 mm0.1 mm1 μm10 nm
Δp (atm)0.00140.01441.436143.6
49
r
h
Capillary rise
Wetting
P=0
r
h
non-Wetting
Capillary depression
P = 2/r P = gh hydrostatic pressure
= (rhg )/2 ( = 0o, 180o)
Liquids in Capillaries
50
= (rhg )/2
Chloroform: d = 1.476 g/cm3 h = 3.67 cm r = 0.01 cm = ?
= 0.50.013.671.476981 = 26.6 (g·cm/sec2·cm)
Water: = 72 dynes/cm h = 9.9 cm
Water, r = 0.1 cm h = 0.99 cm
Surface Tension Measurementby a Capillary
52
= 26.6 dynes/cm
Surface Tension Measurements Methods
R >> rf = 2·2R ( =0 ) = f/4 R
f
For i, ring must be wetted (=0 ) by the lowerLiquid. If CCL4/H2O, ring must be hydrophobic54
Ring Method (Du Nouy)
59
Interfacial Tension ofClean and Dirty Engine Oils
Inte
rfac
ial T
ensi
c
Time(s)
Synth-CSynth-DNat-CNat-DSunOil
Wilhelmy Plate MethodWilhelmy Plate Method
Wtotal = Wplate + 2( w + t )
Wtotal = Wplate + 2( w + t ) ·cos
0 = 0
(for complete wetting (=0)
w : width t : thicknessW : weight
platinum, glass, mica
60
Drop weight method (drop and tip enlarged)2r = mg
= (mg/ 2r)
mg: max. weight which can be supported by surface forces. : empirical tables.
Drop Weight MethodDrop Weight Method
63
Controlling Surface Tension by Surfactants
RCOO-Na+ R8-18c
log C
cmc
wettingmicellesemulsionflocculation
74
O
1. Anionic
2. Cationic
3. Zwitterionic
4. Nonionic
R C OO() Na(+)
R (+)N(CH3)3 Cl()
R (+)NH2CHCH2 COO()
C OH
C O C R
C O C R’
O
75
Surfactants Classification
77
Usage of Surface Active Agents
Micellization – solubilizationProduction and stabilization of emulsions
Production and stabilization of dispersionsFoaming
FluctulationFloatationWetting
Products: Detergents, medical and cosmeticemulsifiers, inks and paints.