Nanoparticle Technology

Definitions

Nanotechnology wants to control the smallest

structures built of atoms and molecules. It is con-

nected with colloidal chemistry and physics, biol-

ogy, medicine, pharmacy and engineering (materi-

als and processes).

Nanoparticles (from Greek nanos – dwarf) are or-

ganic or inorganic solid particles. The dimension of

nanoparticles is not defined in a uniform manner.

a) particles in the sub micron range ( < 1 µm) ,

b) materials science : < 100 nm (nano scaled

particles)

c) pharmaceutics : < 500 nm, < 1000 nm = 1µm

Usually nanoparticles are dispersed in a continu-

ous phase ( see dispersed systems).

Historical overview – Nanotechnology and nanoparticles

2697 BC Tien-Lcheu: petroleum lamp soot for Indian ink used in China

400 BC Lycurgus cup (with gold nanoscaled particles covered glass cup, British Museum

London

1600 Manufacturing of church windows, shining red by colloidal gold nanoparticles

1857 Faraday Synthesis of colloidal gold nanoparticles, colour effects

1915 Ostwald, Wolfgang Colloids - „world of neglected dimensions“

1931 Ruska, Knoll development of an electron microscope TEM, 1938 built commercially by Siemens

1942 Knöpfer Aerosil process (Degussa) – pyrogenic silica, 1953 aluminium oxide, 1954 titanium

dioxide

1959 Feynman lecture on the prospects of miniaturisation, “There’s plenty of room at the bottom“

1968 Stöber, Fink, Bohn Synthesis of monodisperse silica, described before in 1956 by Kolbe in PhD thesis

1974 Taniguchi, Norio “Nanotechnology” for processing of separation, consolidation, and deformation of

materials by one atom or one molecule

1985 Smalley, Curl, Kroto Buckminster fullerenes, e.g. C60 carbon

1986 Binnig, Quate, Gerber construction of an atomic force microscope AFM, 1981 Binnig, Rohrer construction

of a scanning tunnelling microscope

1989 Eigler, Schweizer IBM logo written with 35 Xe-atoms on Ni

1991 Iijima Carbon nanotubes

Disperse Systems

continuous phase dispersed

phase gaseous liquid solid

gaseous bubbles porous solids

xerogels, aerogels, cryogels

liquid aerosol fog emulsion

microemulsion

porous solids with liquids

hydrogels, alcogels

solid aerosol smoke nanoparticles composite materials

Nanoparticles: Numerous fields of application

• Ceramics for membranes

• Batteries and fuel cells

• Catalysis and electrolysis reactors

• Gas storage

• Protective coating of plastic

surfaces

• Thermal and scratch protection

• Reflection avoidance in windows

• Sun creams

• Electronics, lasers, displays

• Photochromic coatings

• Automotive coatings

• Bioceramics, drug carriers

• Magnetic nanoparticles for

hydrothermal treatment of cancers

bioavailability

quantum effect

polymers

strong surface effects

aerosols

ceramics

viruses, DNA

metal powders

tobacco smoke

proteins

0.01 0.1 1µm 0.001 10-9 m 10-6 m

10 1 100 1000 nm

nanoparticle for life sciences

Sizes and properties of nanoparticle materials

Properties of nanoparticles

The outstanding importance of nanoparticles and nano

structured systems can be ascribed to :

1. particle size

bioavailability : in water non soluble substances can be

transported as nanoparticles in an organism of human

beings (application in life sciences)

2. large specific surface area

strong surface area effects (e.g. reactivity, high energy

of surface area, adsorption, higher solubility, lower melt-

ing point etc.)

3. change of electronic properties

quantum effects of particles < 10 nm, importance for

electronic and optoelectronic application

Characterisation of nanoparticles

Nanoparticles and nanopowders are characterised by :

Laser diffraction

Light scattering

Transmission electron microscopy (TEM)

Scanning electron microscopy (SEM)

Gas adsorption (BET – Brunauer, Emmett, Teller)

(BJH – Barrett, Joyner, Halenda)

Zeta - potential

particle size (1 nm – 100 nm)

large specific surface area

(electrostatic) stabilisation

Optical spectroscopy

Preparation of silica nanoparticles

Process : Sol - Gel - Synthesis - Precipitation

Chemical reactions : Hydrolysis - Polycondensation

Principles : nucleation, nucleus growth, Ostwald ripening, (agglomeration)

Controlled double jet precipitation (CDJP)

Polycondensation :

Si(OH)4 nano- SiO2 (Sol) + 2 H2O

Silicon tetra hydroxide Silica

Hydrolysis :

Si(OC2H5)4 + 4 H2O Si(OH)4 + 4 C2H5OH

Tetra ethyl orthosilicate (TEOS) Silicon tetra hydroxide Ethanol

pH 11 - 12 (NH3)

suspension in ethanol

pH 11 - 12 (NH3)

suspension in ethanol

Principle of dynamic light scattering

Optical unit of photon correlation spectroscopy

Scattering light intensity – time – function auto correlation function

correlation function

g (τ)= e-2·D·K²·τ D diffusion constant

K scattering light vector

τ delay time

Stokes – Einstein – equation

d = D3Tk B

⋅η⋅π⋅⋅

d particle diameter

kB Boltzmann constant

T absolute temperature

η dynamical viscosity

g( τ )

τ

I(t)

time

small particle

large particle

small particle

large particle

Laser Optics Sample

Photo multiplier correlator Optical Unit

Particle size distribution of titanium dioxide nanoparticles

method: dynamic light scattering method

instrument : Zetamaster (Malvern)

detector angle 90 °

wave length 630 nm

temperature 25 °C

Particle size distribution of titanium

dioxide after peptization within 24 hours

Mean particle diameter:

dm, 3 = 18.6 nm (volume density)

dm, 0 = 12.0 nm (number density) 5 10 50 100

Particle diameter in nm

1.0

2.0

3.0

4.0

Part

icle

size

freq

uenc

y di

stri

butio

n q 0

(log

d) i

n nm

-1

Determination of the zeta – potential for nanoparticle characterisation

Charge distribution around a moving particle in an electrical field

Detection of particle velocity in an interference pattern system of two lasers

particle

laser beams interference pattern scattering light detector

anode cathode

Stabilisation of titanium dioxide nanoparticles in suspension

0,0 0,5 1,0 1,5 2,0 2,50

10

20

30

40

Zeta - Potential in mV

Zeta

- Po

tent

ial i

n m

V

pH - value of suspension

Zeta potential of TiO2 ranging from + 20 mV to + 40 mV for a pH < 3.0

Stabilisation of titanium dioxide nanoparticles in suspension

Zeta potential of TiO2 ranging from + 20 mV to + 40 mV for a pH < 3.0

OH2+OH2

+ Ti O-

O-

O-

+ H+

TiOH OH

OH

base

+OH-

OH2+

O-

OH2+ OH

Tiacid

Processes for the production of nanoparticles

Production processes

in a liquid phase in a gaseous phase

Precipitation process

• in homogeneous solution

• in surfactant based systems

Sol - gel process

Hydrothermal process

Aerosol process

• Flame hydrolysis

• Spray pyrolysis

Ag+ + Br - AgBr

Silver bromide

Chemical and physical processes for nano particle synthesis Process: precipitation – in homogeneous solution

synthesis of silver bromide

Chemical reaction:

Principle: precipitation (Controlled double jet precipitation CDJP - technique)

Precipitation homogeneous solution - controlled double jet precipitation CDJP

nucleus formation, followed by growth

reaction and Ostwald ripening

Particle size: AgBr : 7 nm - 60 nm, particle system dependent

a lot of syntheses on a laboratory scale T. Sugimoto : J. Colloid Interface Sci. 150 (1992) 208 - 225

(gelatine)

KBr AgNO3

ions

embryos

nuclei

primary particle

growth, coagulation, ...

growth

cluster formation

complex and cluster formation

colloids

Precipitation reactions in homogeneous solution

AgBr – nanoparticle, produced by CDJ - technique at pBr 2,0 (a), 2,8(b), 4,0 (c)

Images (scanning electron microscopy) of typical monodisperse nanoscale

oxides by conversion of metal alkoxides in alcoholic solution

Precipitation reactions in homogeneous solution

Images (transmission electron microscopy left - scanning electron microscopy right) of

CdS – nanoparticles, produced in homogeneous solution at 26°C by CDJ - technique

Image (scanning electron microscopy) of PbS – nanoparticles, produced in homo-

geneous solution at 26°C by CDJ - technique

Precipitation reactions in homogenous solutions

Scanning electron microscopy image of aluminium(III)-oxide, 100°C, left

Transmission electron microscopy image of chromium(III)-oxide, 75°C, right,

produced by precipitation reaction in homogeneous solution Images (scanning electron microscopy) of zinc oxide, 90°C, pH 8,8 (left) and

150°C, pH 13,3 (right), produced by precipitation reaction in homogeneous

solution

Precipitation reactions in surfactant based systems

Images (scanning electron microscopy) of mullite (aluminium silicate) and barium

titanate, produced by precipitation in surfactant based systems (microemulsion)

Image (transmission electron microscopy) of silica, produced by precipitation in

surfactant based systems (microemulsion)

Chemical and physical processes for nanoparticle synthesis

process: sol - gel process / precipitation

synthesis of silica (Kolbe (1956), Stöber, Fink, Bohn (1968))

chemical reaction :

principle: nucleus formation, followed by growth reaction and Ostwald ripening,

controlled double jet precipitation CDJP

products : titanium (IV) – oxide , aluminium oxide, zirconium (IV) - oxide

nuclear power materials ThO2, UO2, PuO2

advantages: often mono disperse, spherical particles of controlled size

disadvantages: reactions have to be carried out with low particle

concentrations, low production output

hydrolysis :

Si(OC2H5)4 + 4 H2O Si(OH)4 + 4 C2H5OH

tetraethylorthosilicate silicon tetra hydroxide ethanol

ethanolic suspension

polycondensation :

Si(OH)4 SiO2 + 2 H2O silicon tetra hydroxide silica

ethanolic suspension

0,2 M tetraethylorthosilicate

ethanol

particle 500 nm – 10 μm

ammonia / water

ethanol

tetraethylorthosilicate / ethanol

pH 11 – 12 (NH3)

pH 11 – 12 (NH3)

Sol - gel synthesis / precipitation reaction

Image (transmission electron microscopy) of Stöber particles (silica)

Image (scanning electron microscopy) of Stöber particles (silica)

Si(OH)4

Dimers

Cycles

Particles

1 nm

5 nm

10 nm

30 nm

100 nm

pH 7 – 10 without salts

Sol (Stöber – Particles)

Morphology of nanoparticles

pH < 7 or

pH 7 - 10 with salts

3 – dimensional gel network

Brinker, C.J.; Scherer, G.W. : Sol-Gel-Science, The Physics and Chemistry of Sol-Gel-Science, Academic Press, San Diego, 1990

Sol - gel process

Precursor Sol Gel Aerogel

spherical particle in gel structure Xerogel

thin layer structure powder ceramics

C.J. Brinker, G.W. Scherer : Sol - Gel Science

Aerosil chemical reaction

dehydratisation

chemical reaction drying

drying

Calcination Calcination Calcination

coating

dipping organic suspension

surfactants

Aerosol processes

Images (transmission electron microscopy) of different

oxides, produced by direct oxidation in an arc