www.elsevier.com/locate/powtec

Powder Technology 15

General concepts in nanoparticle technology and their possible implication

on cultural science and philosophy

Wolfgang Peukert

Institute of Particle Technology, Universitat Erlangen-Nurnberg, Cauerstr. 4, 91058 Erlangen, Germany

Available online 6 June 2005

Abstract

This paper consists of two parts. The first part describes generally applicable concepts in nanoparticle technology. A key objective in

nanotechnology is to build functional structures from small building blocks, i.e. nanoparticles. Starting from the concept of product

engineering we investigate the basic preconditions for tailoring functional structures and their properties. Formation of macroscopic

structures is only possible through microscopic control of particulate interfaces, i.e. of particle interactions. Particle interactions result mainly

from the molecular properties of the respective surfaces which are governed by quantum mechanics. However, in many cases particle

interactions can be sufficiently described by classical force laws. The sum of all these forces plus external forces leads to the desired structure.

The second part of this paper draws conclusions from these physical principles and dares to apply these to philosophy and cultural sciences. It

seems that encounters between entities, in this case individuals, small groups, countries, for instance, leads to the development of social

structures and in most general sense to culture. Changing the interactions between the entities will lead to different structures. The conclusion

is straightforward but extremely complex in general: We as individuals are tailoring life and culture by our way of interacting.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Product engineering; Nanoparticles; Structure formation; Philosophy; Cultural sciences

‘‘Economy does not exist without technology, technology We use one, albeit important, aspect in nanotechnology,

not without science. True science does not exist without

philosophy, philosophy not without the essence of religion’’.

(C.F. von Weizsacker)

1. Introduction

We ask if principles originating from scientific and

technological development can also be transferred to other

fields of human culture. It is quite clear that technological

development had, and more than ever has, a strong impact on

cultural development. The technological revolution in the

19th century, the discovery of quantum mechanics and rela-

tivity in the last century, breakthroughs in biology (e.g. dis-

covery of the DNA structure by Crick and Watson, the

decoding of the human genome) and the revolution in nano-

technology all are strongly influencing human life and

culture.

0032-5910/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.powtec.2005.04.024

E-mail address: W.Peukert@lfg.uni-erlangen.de.

and apply it to cultural evolution. In this short contribution

we can only sketch some of the main ideas. A thorough

investigation of these topics is far beyond the scope of this

paper.

This paper first describes the basic concepts of product

engineering which are applicable to all types of particles.

We then introduce the new concept to tailor macroscopic

properties through microscopic control of the interfaces.

Some implications and assumptions are introduced together

with a few comments towards multiscale approaches. These

basic principles are applicable to particle production and to

formation of particulate structures. Again we first introduce

the basic principles and show the application of these

principles by specific examples. It becomes clear that the

product properties are controlled and tailored by interpar-

ticle forces.

These technological aspects are then transferred to

philosophy and cultural sciences, i.e. the basic principles

are interpreted in a much wider sense. Implicitly, we assume

that generally applicable principles which are valid in

8 (2005) 133 – 140

W. Peukert / Powder Technology 158 (2005) 133–140134

technology, should also be valid in other aspects of nature

and life in the context of human experience (if these

principles are of general applicability). This may open an

exchange between philosophy, psychology, social and

cultural sciences.

2. Concepts of product engineering

A major trend in Chemical Engineering and Particle

Technology is the shift from commodities towards high-end

products with specific properties and functionality. Whereas

in the past research was mainly directed towards better

understanding of unit operations, modern trends are

characterized by approaches for product formulation and

means to tailor specific functions and product properties.

This general trend is complemented by efforts for miniatur-

ization which led to the important development of nano-

technology. The aim to build materials from smaller and

smaller building blocks, i.e. nanoparticles, raises the

question of how to control self-assembly. Since nanoparti-

cles are controlled by surface forces rather than by volume

forces, control of particulate interfaces is the critical issue in

nanoparticle technology and in product engineering of

nanoscaled systems.

For particulate materials the product properties depend

on the chemical composition and on the dispersity of the

material. The dispersity is characterized by the particle size

distribution, the particles’ shape and morphology and their

interfacial properties. This relation was called by Rumpf [1]

‘‘property function’’, the control of the property function is

known as product engineering or product design.

2.1. Property function

Product property= f (dispersity, chemical composition)

Dispersity:

– particle size and shape and their respective

distribution

– particle morphology

– particle surface properties

The property function relates the particulate structure

(size, shape, morphology, surface) to the product properties

(structure–property correlation). Examples of property

functions are the taste of chocolate, the colour of pigments,

the strength of cements or the band gap of nanoparticles.

Particle ensembles in form of agglomerates, thin films or

filter cakes are also included in this consideration. The

process function (process–structure correlation) as defined

by Krekel and Polke [2] relates the process parameters to the

product property.

2.2. Process function

Dispersity= f (process parameters, educt concentrations)

Process parameters are the type of unit operations, their

interconnection in the process, the process conditions under

which the unit operations are operated (e.g. temperature,

pressure, mass flow rates etc.) and the materials processed.

Structure–property as well as process–structure correlations

must be known in order to run the process and to achieve the

desired goal, i.e. to produce well-defined product properties.

All nanoparticle applications have in common that the

interfacial and surface properties of the particles play a

central role. The ratio of van der Waal’s adhesion forces to

particle weight scales with particle diameter x�2 and is, for

instance at 1 Am, in the order of 106 (in case of smooth

particles). To produce well-defined property functions, the

particle interactions have to be carefully controlled. Macro-

scopic properties can only be tailored by microscopic design

of the interfaces. Surface chemistry and physics determine

on the one hand the particulate interactions with fluid or

solid phases. The types of interactions are van der Waal’s

forces, polar interactions, hydrogen bonds or even chemical

bonds. On the other hand, particle interactions control

particle and structure formation as will be discussed in this

paper. For product engineering of nanoparticulate systems,

we start conceptually at the particle surface which ‘‘trans-

ports’’ the respective particle interactions thus leading to the

desired structure. Vice versa, structure formation can only

be understood by considering the relevant interactions

which are determined by the particle surface. This concept

is illustrated in Fig. 1 for oxide particles in aqueous solution

where particle interactions can be understood in the view of

well-known DLVO-theory as a superposition of van der

Waal’s and electrostatic double layer forces.

This approach is based on some wide ranging precondi-

tions. In order to bridge the gap between the microscopic

molecular nature of a particle surface and the macroscopic

properties we need a multi-scale approach covering several

orders of magnitude in space and time. On the most basic

level quantum mechanics prevails. However, it is often

possible by using the Hellman–Feynman theorem [3] to

transfer the intrinsic quantum mechanical nature of surfaces

to the physics of molecular interactions described by

classical force laws. This theorem states that once the

electron density distributions have been determined the

intermolecular interactions can be calculated on the basis of

classical electrostatics. The contact value theorem is quite

analogous: the force between two surfaces is determined by

the density distribution of the molecules and particles in the

space between them [4]. By using these classical interaction

forces, molecular dynamics and Monte Carlo simulations

are nowadays able to describe and even predict mesoscopic

phenomena. Thus, we assume for molecular systems

(without chemical reactions) the additivity of forces.

Macroscopic properties therefore evolve from the summa-

tion of the interparticle forces plus forces from external

force fields such as gravity, centrifugal forces in sedimen-

tation and solid–liquid separation as well as electromag-

netic forces.

Fig. 2. Results of classical molecular dynamics simulation of NaCl

nanocrystals in comparison the Hertzian continuum theory.

surfaceproperties interactions

macroscopicproperties

pH

σ ζ0,

OH2+ OH O-

agglomeration

stability

crystal shape

rheology

flowability

crystal growth

filtration resistancepzc

surface modification

surfaceproperty

010

EDL repulsion

Van der Waals-attraction

Bornrepulsion

ϕmax

z / nmϕ1 min

ϕ 2 min

ϕ

ϕ

0

ion concentration

z

Fig. 1. From particle surfaces to macroscopic properties.

W. Peukert / Powder Technology 158 (2005) 133–140 135

How to close the gap between the molecular picture and

the macroscopic world which can only be handled by mean

field and continuum theories is still an open question. One

possible way around that problem is given in the following

example. Miesbauer et al. [5] investigated the contact

between a NaCl nanosphere and a NaCl flat surface. By

applying normal forces the validity of the Hertzian

continuum theory was tested by means of classical

molecular dynamics. The applied force law was able to

reproduce the length of unit cells of the crystal better than

2% and the bulk modulus better than 55% so that the

simulation results give almost quantitative results. From

Hertzian theory an exponent of b =1.5 in the force–

displacement curve is expected. This value is observed for

a particle radius of larger than approximately 6 nm, for

smaller particles the exponent decreases with decreasing

particle size (see Fig. 2). In the above shown concept (see

Fig. 1), we need in the first step to measure and to predict

particle interactions from the state of the particle surface.

Second, the gap between the particle level of interactions

and macroscopic phenomena can only be closed by models

based on statistical mechanics using coarse graining

approaches. Brownian and Stokesian simulations based on

the discrete element method (DEM) are examples which

point in the right direction although these models are

currently designed for ideal (e.g. often monodisperse)

systems and not yet predictive in the true sense. What is

missing are to a large extent particle properties of real

systems. From the manufacturing point of view, control

strategies must be developed—possibly coupled with inline

or at least online sensors—which allow the measurement of

surface properties and of course the dispersity and thus the

product property in the process.

Particulate surfaces may be changed through sorption of

ions, molecules, polymers or even biopolymers such as

proteins. A simple example is illustrated in Fig. 3 for

alumina particles in aqueous solution. The alumina surface

was modified through pH-adjustment, i.e. through adsorp-

tion of potential determining ions (H+ /OH�in the case of

alumina). These change the electrochemical behavior of the

suspensions as can be seen from the change in f-potentialmeasured by electroacoustics. It is not important whether

the f-potential is positive or negative, only the magnitude

counts. Higher f-potentials correspond with higher surface

charge and lead to higher repulsive forces between the

Fig. 3. Influence of surface charge and f-potential of alumina (changed by adjusting of pH) on the rheology of alumina suspensions.

W. Peukert / Powder Technology 158 (2005) 133–140136

particles. This leads in turn to a higher stability against

aggregation.

Due to the changed surface chemistry the rheology is

altered rather dramatically. The shear rate and suspension

viscosity is changed depending on the shear rate by three

orders of magnitude. In this example, the shear rate is

modified by a shift factor B which shifts all the curves in

hydrodynamic range into one single master curve. This

effect is purely due to particle interactions since the

adsorbed ions neither change particle size nor particle

shape. In accordance with particle interactions, the micro-

structure in the suspension is changed by forming more or

less aggregated particulate structures. Similar effects can be

obtained when the surface chemistry of the particles is

changed by the binding of organic molecules including

polymers. The yield stress scales with the square of the

fQpotential.

3. Structure formation

Structure formation is a key concept in product engi-

neering (see Fig. 4). In general, the formed structure

filter cake

b=zg

ener

gy

distance

pote

ntia

l

distance

diffusive transport

convective transport

field forces

van der Waals

electrostatic interactions

specific interactions

crystal

radiolaria

transport + interactions = structure

Fig. 4. Principles of structure formation.

depends on transport mechanisms and interactions. The

transport mechanisms may be diffusive or convective. In

addition, field forces such as gravity or electric fields

contribute also to the mass transfer. The study of transport

mechanisms has a long tradition in Chemical Engineering,

the book of Bird, Stuart and Lightfoot which was first

published in 1960 may serve as example [6]. This field is

well developed although many open questions still have to

be solved. Fig. 5 shows an example of controlled

aggregation and thus structure formation experiments under

Brownian motion and under controlled shear. These experi-

ments were done with 30 nm SiO2 particles. The fractal

dimensions of the obtained aggregate structures were

investigated with static light scattering (SLS) and small

angle neutron scattering (SANS). Details of these experi-

ments are described in a forthcoming publication [7]. The

fractal dimensions of the aggregates strongly depend on the

type of transport process as well as on history of the

experiments. Fractal dimensions of 2.09 were obtained

under pure Brownian motion. The aggregates can be

densified if the aggregated suspension is sheared subse-

quently. However, these values are still smaller in compar-

ison to the case where shear forces were applied from the

very beginning of the experiment. The resulting structures

are shown qualitatively in the insert of Fig. 5.

Intermolecular and interparticle interactions are much

less understood than transport phenomena but of key

importance in evolving fields such as nanoparticle technol-

ogy. In the case of purely thermodynamically determined

systems, the transport mechanisms can be neglected. The

structure is then only dependent on the interactions and can

in principle be determined by minimizing the total energy of

the system. The equilibrium shapes of crystals, the

crystalline structure of highly charged colloidal suspensions

or ordered arrays of optical micro-lenses or photonic

crystals may serve as examples. The types of interactions

are: dispersive, electrostatic, magnetic forces, structural

(entropic) forces in fluids as well as forces due to material

bridges. Material bridges form between particles in close

contact in the presence of supersaturation and due to

time /h

0 1 2 3 4

app

aren

t fr

acta

l dim

ensi

on

1.0

1.5

2.0

2.5

3.02.75

2.0

SANS (shear rate 100s-1)light scattering (shear rate 100s-1)calculation (shear rate 100s-1)SANS (shear rate 1000s-1)light scattering (shear rate 1000s-1)calculation (shear rate 1000s-1)

increasing shear rate

SANSlight scatteringcalculation

perikinetic agglomeration

SANS: shear rate 1000s-1

orthokinetic agglomeration

Fig. 5. Fractal dimensions of aggregated silica nanoparticles.

W. Peukert / Powder Technology 158 (2005) 133–140 137

ripening or sintering depending on solubility in the liquid

phase or the temperature in gas phase systems, respectively.

4. Structure formation in thin films

As a special case of structure formation, we are studying

the formation of thin films by dip coating [8,12]. Depending

on the application there is demand for open or dense

structures with defined pore size distributions. Dense

coatings are necessary for passivation purposes, highly

percolated structures are needed for electronic and opto-

electronic devices whereas coatings with defined pore size

distributions are required as a carrier matrix in catalytic

applications. Therefore the question is to what extent the

microstructure can be influenced by means of tailored

particle interactions. The microstructure of dip-coated

samples is influenced by the rate of evaporation and the

rate of aggregation. The former depends on the selection of

process parameters such as withdrawal velocity and drying

conditions. The latter is associated with the stability and

dispersity of the sol, thus with the physical–chemical

properties of the coating bath. A water-based sol containing

SiO2 particles is used. Its stability can be controlled by

adjusting solely pH, electrolyte concentration and by

selecting the type of electrolyte. Before conducting coating

procedures the sol is characterized with respect to its particle

size distribution and stability behavior. The median particle

size of the volume distribution, determined by both photon

correlation spectroscopy and acoustic spectroscopy, is

measured to x50,3=60 nm. The width of the size distribution

given by j5/95=x5 /x95 amounts to 0.3. Stability character-

ization is done by electroacoustic spectroscopy. The f-potential is measured under variation of pH and electrolyte

concentration. Furthermore, electrolytes of different

valences are used (NaCl, CaCl2, LaCl3). Despite high

electrolyte concentrations and pH values near the isoelectric

point, the sol has been stable for weeks. This unusual

stability does not correspond to the conventional DLVO

theory, but to structuring of solvent water in the vicinity of

the solid-liquid interface. There are few experimental

investigations revealing that water structuring is an inherent

property of colloidal silica leading to an additional repulsive

contribution to the net force. For theoretical treatment, the

conventional DLVO-theory is superimposed by this so-

called hydration force. To determine the magnitude of the

hydration force photometric measurements are carried out.

Under certain preconditions it is possible to determine the

stability factor W which is correlated to the overall

interaction energy.

Throughout the coating experiments process parameters

are kept constant. The withdrawal velocity is 1 m/min.

Environment is conditioned by a defined steam-laden

nitrogen stream of a relative humidity (rh) of 60%. The

solid mass content of the bath is cm=10%. For structure

formation in the drawn film not only the bath properties

have to be considered but also the change of interaction

properties during the drying process. Stability behavior

within the film changes because of increasing solid content

and electrolyte concentration. This dynamic process is an

essential aspect in generating defined pore geometries. To

study the obtained structures we apply different character-

ization methods. With illustrating methods such as AFM

and REM surface structure can be quantified by determining

surface roughness.

In Fig. 6a AFM scans demonstrate the almost

negligible influence of drying conditions. In this experi-

ment a different silica sol is used which is composed of

00

1

1

2

2

m00

1

1

2

2

m

rh = 0% rh = 60%

SiO100nm

2

U = 100cm/min

0 1 2length / µ

µ µ

µµ

µ

µ

µ

m

heig

ht /

nm

75

-75

RMS = 7.37nm

0 1 2length / m

heig

ht /

nm

75

-75

RMS = 6.91nm

00

1

1

2

2

m 00

1

1

2

2

m

0 1 2length / m

heig

ht /

nm

75

-75

I = 10 M -4 I = 0,1M

0 1 2length / m

heig

ht /

nm

75

-75

RMS = 3,95nm RMS = 12,14nm

Levasil100

rh = 60%

U = 100cm/min

a)

b)

Fig. 6. Surface structure of SiO2 thin films made from a) 100 nm

monospheres and b) 60 nm particles.

W. Peukert / Powder Technology 158 (2005) 133–140138

100 nm monospheres. The left image shows a coating

drawn at rh=0% (pure nitrogen) whereas on the right

image the relative humidity had been set to 60%.

Comparing the rms-roughness images does not differ

significantly and the coatings appear to be very uniform.

The difference is revealed regarding the order. Order is

more pronounced at the right image showing up small

domains of hexagonal structure. In Fig. 6b the left surface

scan is taken from a coating that was dipped with the pure

sol, that means without any addition of electrolyte, while

the right scan is taken from the sol with addition of NaCl

resulting in a 0.1 M sol. The f-potential of the pure sol is

f =�50 mV at pH 8.5 whereas for the 0.1 M sol the value

decreases to f =�18 mV. The rms-roughness of the latter

sample is 3 times higher than that of the pure sol. This

indicates a more open coating structure in the first case.

The observed results can be explained both with the

reduced electrostatic repulsion and the breakdown of the

structured water layers due to introduced ions. This leads

to a reduced potential barrier which gives rise to a higher

probability of particle agglomeration in the primary

minimum. It is pointed out that ordered structures as

shown in Fig. 6a can only be reached if the particle size

distribution is sufficiently narrow and can never be

reached with the sol used in Fig. 6b because of its

polydispersity.

In order to get volume structure information, N2-

porosimetry as well as SAXS was used. SAXS experiments

were done using the Jusifa beamline at DESY in Hamburg,

Germany. By inverting the measured radial intensity

distribution structural information can be extracted. These

experiments lead to pair correlation functions which are

correlated with particle interactions. The macroscopic

properties of the thin films change accordingly. For instance,

the extinction of the thin film can be altered by a factor of 30

for the same film drawing conditions, i.e. similar film

thickness, but varying particle interactions.

5. Possible implications for cultural development and

philosophy

In the preceding sections we did show that structure

formation can be understood in terms of interactions

between small entities of the considered ensemble. In the

case of nanotechnology, these entities are nanoparticles. The

interactions originate from the intrinsic properties of the

particles, i.e. mostly from their surface properties, but to

some extent also from internal (volume) properties,

although these may be screened by short-range surface

effects.

Nanotechnology and nanoparticles are an integral part of

the hierarchy in nature which spans from the atomic nuclei

to the cosmos. As part of this hierarchy nanotechnology

follows the same laws which control the hierarchy of the

cosmos. We can thus assume the existence of generally

applicable laws and rules. In a philosophical sense, we

assume unity of all being. Being means in that sense the

outer and inner world in which we are living. The outer

world is the cosmos whereas the inner world refers to our

feelings, dreams and imaginations, i.e. to our psyche and the

spiritual world.

This hierarchy involves nature starting with elementary

particles which comprise atoms, atoms are a part of

molecules, molecules build all materials in the non-living

and living world. In each step forward the constituents of

the lower level are integrated into the higher level where

they become part of a larger entity at the expense of their

individuality. Each level has the capabilities of the lower

level plus some additional features. Upon integration,

however, we easily may loose sight of some of the

components of lower levels. Nanotechnology is just one

section or aspect in this hierarchical evolutionary process.

However, it is a manmade process.

A similar evolution is taking place in human develop-

ment. Cultural history can be described as an evolution of

human consciousness. Each person lives through some of

the stages of this process during childhood. The evolution of

human culture and consciousness can be understood along

the same lines. Each level is transcended at the higher level

with a gain in consciousness. The decisive aspects of the

lower level are integrated at the higher level and there lose

Fig. 7. Carlo Crivelli, Maria Verkundigung 1486 (Mysterium der

Erreichbarkeit).

W. Peukert / Powder Technology 158 (2005) 133–140 139

their autonomy. At the higher level, new capabilities

become available. To give just one example: on the magical

level an individual believes that the outer world can be

influenced by magic power; on the mythological level the

personal identity is transformed to a role or group identity

where the group follows a mythological leader who gets his

power from a god; this aspect is transcended on the rational

level where the ruling power is the ratio(Descartes: I am

being because I am thinking). This led to the industrial

revolution and is the current level. It has to be mentioned

that these levels are valid for many people and therefore

represent some average or collective states. In almost all

times and many cultures, individuals did live whose

consciousness was far more developed than that of the

average person. Plato or Plotin may serve as examples for

higher levels of consciousness in cultures which were more

or less at the mythological level.

After the manifestation of one level the main concepts of

this specific level tend to integrate the concepts of the

former level. After some time, these aspects become

deficient and a new level evolves. This led, for instance,

to the industrial revolution and is the current level. Thinkers

and philosophers like Gebser [9], Habermas [10], Sloterdijk

[12] or Wilber [11] describe these developments in great

detail.

We might conclude from the lesson of nanotechnology

where we said that structure is determined by interactions,

that relationships in a general sense exist prior to all things.

Things in this context mean both material and immaterial

entities. We may then proceed by saying that the field of

relationships forms a network from where inner space and

outer space and relations come into existence. The interac-

tions between two entities, e.g. two human beings, can be

understood as an inner relationship or inner space whereas

both human beings do act as an ensemble to the outside. I do

not want to anticipate that both humans necessarily act in a

well coordinated way. Also the opposite, namely their fights

in the inner space will have some influence on the

appearance of both to the outer world.

In that sense we might further conclude that all cultural

development starts from interactions. The interactions may

evolve from only two persons, from a larger group, from a

city, a nation and so on. It would be quite worthwhile to

further elucidate the evolution of human cultures as well

as the structures formed in the living and non-living

nature.

In this short communication I want to highlight the

possibility to deduce concepts of wider applicability also

from general laws in the basic and applied sciences. In this

sense it is quite interesting for engineers who do often

believe that wisdom comes from philosophy and religion

and that science (here the natural sciences biology,

chemistry, and physics) and technology are those disciplines

which are only responsible for the external world. It seems

to me, however, that implications valid for the non-living

world seem to be transferable to spiritual and cultural life.

Fig. 7 presents a painting of Carlo Crivelli which shows

impressively views into inner and outer spaces. It may serve

thus as illustration for the evolution of cultures and human

consciousness in history.

6. Conclusions

This paper first describes basic concepts for product

engineering. Nanoparticulate systems are mostly controlled

by surface rather than volume forces. Therefore, macro-

scopic properties have to be tailored through microscopic

control of particulate interfaces. We recognize structure

formation in nanoparticulate systems as a self-organization

process which can be understood as part of the hierarchical

evolution process of nature. Similar evolutionary processes

are active in the psychological and social development of a

human being.

Nanotechnology as an inherently interdisciplinary field

needs for its development interactions between disciplines.

To say it with Werner Heisenberg: Probably, one can

generally say that the most fruitful developments of human

thinking often did occur in history when two different kinds

of thinking have met [13]. Nanotechnology is this field in

science where biology, chemistry, engineering and physics

meet. It is interesting that conclusions drawn from basic

concepts in nanotechnology point directly to consequences

for research strategies in nanotechnology, namely that

interdisciplinary interactions between scientists are an

important precondition for research in this field. Further,

interactions in a wider sense may be considered as a ‘‘driving

force’’ for the evolution of cultural sciences as well.

W. Peukert / Powder Technology 158 (2005) 133–140140

Interactions in a more general sense lead to cultural

development and thus to a network of outer and inner space.

Space is related to geometry and topology. These multidi-

mensional topologies have been described by Sloterdijk by

the acrynom of foams [12].

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