Nano Materials – Synthesis, Characterisation and Properties Prof. Dr. Johann Plank Department Chemie Technische Universität München Germany
Nano Sized Particles Sun tan lotion
TiO2 nano particles
Desinfection of drinking water
Ag nano particles
National Nanotechnology Initiative
Nanostructured Surfaces - Examples Self-cleaning roof shindles
Self-cleaning blue jeans Self-cleaning car coating
Nano Particles
Magnetite nano crystals in bacteria
Nanos as catalysts for:
Nano particles showing particle size dependent light absorption and luminescence
car exhaust gases (Pt) decontamination (TiO2) electrodes for fuel cells (Pt)
Nanostructured Surfaces in Nature Colours of butterfly wings originate from nanostructure, and not pigments
Inorganic Nano Particles Star-shaped Anatase nano crystals
Organic nano particles possessing raspberry morphology
Content of Lecture I Definition of Nano Particles and Colloids II Nano Particles and Colloids – General Behaviour a b c d
Brown´s molecular movement light scattering theories on colloidal stability (DLVO theory) surface charge of colloids (zeta potential, streaming potential) e impact of salts and electrolytes on surface charge f coagulation, flocculation and aggregation
Content of Lecture III Synthesis of Nano Particles a Physical processes – Break down methods b Chemical processes - Bottom up processes c Chemical synthesis in gaseous phase (flame pyrolysis, CVD) IV Industrial Nano Particles a Carbon black b Pyrogenic silica V Sol-Gel Process a Fundamentals b Xerogels and aerogels VI Organic Nano Particles a Latex particles and dispersions
Content of Lecture VII 3D Nanostructured Materials a b c d
Nanoporous materials Nano crystals Core-shell particles Nano capsules
VIII Nano TiO2 a Photo catalysis b Superhydrophilic properties c Nano structured selfcleaning surfaces IX Carbon Nanotubes a SWCTs, DWCTs, MWCTs b Self-assembly of CNTs c Crystal-like CNTs X SiOx Nano Wires
II Colloids and Nano Particles
Comparison of scales
Typical Colloidal Systems - - - -++ + - - - - -+ - + -- - + - + - - +- + + + +- - - - Dispersion colloid
Cement in water
Latex dispersion
Methyl cellulose
Xanthan gum
Molecule colloid
Association colloid
Emulsifier micelles
Definition of Colloids Thomas Graham (1805-1869, President of Chemical Society of London) introduced the term „colloid“ Colloids possess a size which is between the size of molecules and that of macroscopically discernible heterogeneities of matter colloidal size: 1 - 500 nm
colloid science studies colloidal particles, their synthesis, properties and interfaces
Types of Colloidal Systems
3 types of colloidal systems: a two-phase systems (emulsions, dispersions) b macro molecules in solution (polymers) c association colloids (surfactant micelles)
Examples of Colloids in Daily Life
Two-phase colloidal systems Examples:
milk, mayonnaise, Bailey´s liquor aqueous bentonite or cement slurries (concrete) colloidal gold (Rubin glass) zeolites latex paints
Definition of Nano Particles 3 definitions: a) particles possessing a diameter of 1 - 1000 nm (nano scale) b) particles possessing a diameter of 1 - 100 nm c) particles which below a certain size show a discontinuous change of their properties = quantum size effect
II Behavoir of Colloids and Nano Particles
Number of surface atoms increases exponentially with decreased particle size Surface atoms exhibit unsaturated bonds and coordination spheres, Thus their behavior differs from that of bulk atoms inside the particle Consequence: Completely different physico-chemical behavior of the particle
Comparison of scales
Brown´s Molecular Movement First observed by Robert Brown, a Scottish botanicologist, in 1827 Temperature-dependent independent movement of molecules and particles
Diffusion:
R ⋅T σ = L ⋅ 3 ⋅ r ⋅ π ⋅η 2
30 μm Spontaneous movement of colloids under a microscope
Diffusion and Sedimentation Particles of different size: a size-dependent equilibrium between sedimentation and Brown´s molecular movement is established
Sedimentation equilibrium of colloids and nano particles:
− M i ⋅ g ⋅ dh d ln ci = RT
c= M= g= h= R= T=
concentration molar mass gravitational constant height Gas constant temperature
Brown´s Molecular Movement of Colloids and Nano Particles Application of Brown´s molecular movement in analysis of clay: Atterberg analysis of clays (Atterberg cylinder): Separation of colloidal from coarse particles
Light Scattering Potential interactions of particles with light: a Absorption b Transmission c Scattering d Deflection e Reflection
Theory from Prof. Mie
deflection transmission absorption scattering/reflection
Light Scattering For colloidal systems: particle size ~ wavelength of light Æ Colloids and nano particles exhibit strong light scattering effect
Calculated light scattering pattern of a spherical particle according to Mie´s theory
3D pattern of light scattered by colloidal particles
Light Scattering Particles size analysis by light scattering:
Schematic of a laser granulometer
Light Scattering: Tyndall Effect
Experiment: Tyndall Effect
Stabilization of Colloidal Systems Electrostatic repulsion
electrostatic repulsion ⇒ dispersing effect
Steric hindrance
steric hindrance ⇒ dispersing effect
Surface Charge, Zeta Potential and Charge Density Surface charge of a SiO2 particle
10 0 0
1
2
3
4
5
6
Zetapotential [mV]
-10 -20
7
8
9
10
11
12
Zeta potential of SiO2 Isoelectric point at ~ pH 1.5
-30 -40 -50 -60 pH-Wert
Surface Charge, Zeta Potential and Charge Density Surface charge of inorganic nano / colloid particles
e.g. Al2O3, SiO2, MgO
Isoelectric point (IEP)
Silver iodide
Development of Surface Charge
Surface charge of colloidal and nano particles comes from:
- Incomplete coordination / bond sphere of surface atoms
colloid particle
- Incongruent dissolution behavior of ions located on the surface (example: cement) - Adsorption of anions or cations onto the surface - Protonation and deprotonation of functional groups present on the surface
Surface Charge of a Cement Particle
Clinker phases: C3S, C2S, C3A, C4AF .
Surface Charge of a Cement Particle ++ +
Surface charge: - Can not be measured directly - Indirectly accessible via zeta potential - Average of different surface charges Phase C3S C2S C3A C3A + CaSO4 . xH2O C4AF C4AF + CaSO4 . xH2O
+ ++ + + ++ + ++ + + + ++ + + + + ++ +++ +
Zeta Potential - 5 mV - 7 mV + 12 mV + 7 mV + 5 mV + 5 mV
from Yoshioka et al., Cem. Concr. Res. 32 (2002), 1507
+ ++ + + + + +
Dispersion of Cement in Water
+ SP
- -+ - - + + + + - + - - + - - + -- + -- + + + +- + -+ -- + + -- - + + --- - + + - - + + + + + + + + + + + -+ + + + - - --+ -+ + + - - + + -- + + + - + + + + + + - - + ++ + + - - + - ++ +
-
- - +-- + - + + -- -++- - -- + - -+ - - + -- - - +-+ +-- - -+ -- +-- + - - -+- + -+ + -+ + -+ - -- -+- - -++ - - -+ + -- + -- - - +--- - -+ - +- + -- ++ + -+ +- - - - - + - -- - +- -+ - - - -+- + --+- +- - + - - -++ - - -+ --+ - + -+- + + - -+ -+ - + - -- + - - --++ - +--- - - +
+ SP
.
.
Electrostatic and Steric Stabilisation of Collodial Suspensions
Polycondensate +
+ + +
-
O3S
Zement -korn
+ -
-
O3S
+ - O3S + +O3S
Polycarboxylate +
+ + +
Zement -korn
+ + + +
O3S
• Electrostatic Repulsion
• Steric Effect
Steric Stabilization of Colloidal Suspensions The concept of „steric“ hindrance
Steric Stabilisation from: - osmotic effect - gain in entropy - enthalpic effect
Electrostatic Stabilization: DLVO Theory DLVO theory, developed by Derjaguin, Landau (1941) and Verwey, Overbeek (1948) describes the electrostatic stabilization of colloidal suspensions Repulsion of droplets possessing same electrical charge in an emulsion. Total interaction potential
VT = VA + VR + VB Attractive Forces = Van der Waals attraction (approximation for spherical particles at distance d « a)
A⎛a⎞ VA = − ⎜ ⎟ 12 ⎝ d ⎠
A = Hamaker constant (material specific) a = radius of particle D = distance between particles
Electrostatic Stabilization: DLVO Theory Electrostatic repulsive forces
a 32 ⋅ ε ⋅ ε 0 ⋅ (R ⋅ T ) 2 2 −κ⋅H VR = ⋅ ⋅γ ⋅e 2 ν F where
⎛ 2z ⎞ ⎜ e − 1⎟ ⎜ ⎟ ν ⋅ F ⋅ ψ0 ⎝ ⎠ γ= z mit z = R ⋅T ⎛ 2 ⎞ ⎜ e + 1⎟ ⎜ ⎟ ⎝ ⎠
a = particle radius H = distance between spherical particles ν = charge of ion 1/κ = Debye Hückel length (describes extension of diffuse ion layer) ε = dielectricity constant ε0 = dielectricity constant in vacuum F = Faraday´s constant ψ0 = surface potential
Born´s Repulsive Forces (only occur at almost direct contact between particles)
VB
Electrostatic Stabilization: DLVO Theory Total Interaction Potential: VR= electrostatic repulsion VB= Born´s repulsion VA= van der Waals attraction VT= total interaction potential
A dispersion is stable when Vm is particularly high The distance between particles at which Vm attains a maximum represents the particle distance in a stable dispersion
Electrostatic Stabilization: DLVO Theory Total interaction potential between particles: Dispersion a) stable b) almost stable c) unstable
Electrochemical Double Layer Around a Colloidal Particle
STERN layer of adsorbed anions/cations
-
Anions always adsorb first on particle surface because of van der Waals attractive forces
+
-
+
- ++ - -- -+ + + -- + -- - - + -- - - + +-+ + + Diffuse ion layer in pore solution
Cement particle
Surface Charge, Zeta Potential and Charge Density Definition of Zeta potential Ψi Ψa Ψ0
ζ
S dehydr. anion hydr. anion hydr. cation
}
-
SternStern-layer Ψ0 = Nernst-Potential Ψi = Potential der inneren Helmholtz-Schicht -Schicht Stern-Schicht mit Ψa = ΨS Ψa = Potential der äußeren Helmholtz-Schicht ζ = Potential an der Scherebene = Zetapotential S = Scherebene (Teilabriss der diffusen Schicht)
}
Water Layer on Surface of Colloidal/Nano Particles Molecular condensator after BOCKRIS
Principle of Zeta Potential Measurement Electroacoustic method:
+ + + - - + + + - - + +
+ Dipolmoment
Strömungsrichtung der Flüssigkeit
Schicht adsorbierter Wassermoleküle
Colloid Vibration Potential
Surface Charge, Zeta Potential and Charge Density Electrophoretic measurement of zeta potential
verschobene Gegenionenwolke
bewegtes Teilchen
-
-
-
-
-
-
-
-
-
E Elektrophoretic behavior of colloids in an electrical field
Surface Charge, Zeta Potential and Charge density
Instrument for electrophoretic measurement of zeta potential
Factors Impacting the Surface Charge of Colloids
Particle surface
Impact of electrolyte concentration (ionic strength) on surface charge
ζ1 ζ2
Shear plane of zeta potential
-
ΨS
Electrolyte concentration
10-6 M
ζ3
0,1 M
} Stern layer
10-2 M
Flussdelta durch Ton-Ausflockung MississippiDelta (Louisiana/USA)
Golf von Mexiko
Mündung des Yukon (Alaska/USA)
Factors Impacting the Surface Charge of Colloids
Zetapotential (mV)
Impact of pH value on surface charge 50
SiO2-Sol
40
TiO2
30
Fe2O3
20
Al2O3-Sol
10 0 -10
0
1
2
3
4
5
6
7
pH-Wert -20 -30 -40 -50 -60
isoelektrischer Punkt
8
9
10
11
12
13
Surface Charge, Zeta Potential and Charge Density Surface charge of a latex dispersion Experimental determination of surface charge of colloidal particles via streaming potential
++ ++ ‐‐ ‐ ++ ‐ ‐ ‐‐ ‐‐ ++ ‐ + + ‐‐‐‐‐+ ++++ ‐ + ‐‐‐‐‐ +++ ‐ ‐ ‐‐‐‐ ‐‐+++++ ‐‐ ‐‐ +++ ‐‐ ‐‐‐ ++ + ‐‐ + ++ +++
++‐ ++ ‐ ‐‐+ ‐‐ ‐‐‐‐+ + + ‐‐‐‐‐++ ‐ ‐‐‐‐‐ +++ ‐ ‐ ‐ ‐ ‐ + ++ ‐‐‐‐‐‐ ‐ ++ ++++ ‐‐ ‐‐‐ ++ ++ ‐‐ ++ +++++ ++ +
Surface Charge, Zeta Potential and Charge Density Charge determination of silica by titration with cationic polymer (Poly-DADMAC) 200
Zugabe PDADMAC 1 mmol (mL)
0 -200
0
2
4
6
8
10
12
14
16
18
20
22
24
Ladungsmenge (mV)
-400 -600 -800 -1000 -1200 -1400 -1600 -1800 -2000
Streaming potential is measured
Ludox TM 0,1% (28 nm) Ludox LS 0,1% (12 nm) Ludox SM 0,1% (7 nm)
Relatives Potential
Factors Impacting the Surface Charge of Colloids -
S1
S2
Zetapotential ohne Polymer Zetapotential mit Polymer
Schichtdicke des adsorbierten Polymers
Impact of adsorbed positively charged polymer on zeta potential of a negatively charged particle Æ Charge reversal
Impact of adsorbed nonionic polymer on zeta potential Æ Decrease of zeta potential measured
Electrochemical Double Layer after Adsorption of Anionic Polymers
Potential Adsorbed Conformations of Polyelectrolytes on a Charged Surface
Train
Loop
Tail
