DYNAMICS OF THE DEVELOPMENT OF
STRUCTURES IN COLLOIDS AND BROWNIAN
MOTION
H. Übelhack, F. Wittmann
To cite this version:
H. Übelhack, F. Wittmann. DYNAMICS OF THE DEVELOPMENT OF STRUCTURES
IN COLLOIDS AND BROWNIAN MOTION. Journal de Physique Colloques, 1976, 37 (C6),
pp.C6-269-C6-271. <10.1051/jphyscol:1976654>. <jpa-00216764>
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Submitted on 1 Jan 1976
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JOURNAL DE PHYSIQUE
Colloque C6, supplkment au no 12, Tome 37, Dkcembre 1976, page C6-269
DYNAMICS OF THE DEVELOPMENT OF STRUCTURES
IN COLLOIDS AND BROWNIAN MOTION
H. J. UBELHACK and F. H. WITTMANN
Abteilung fiir Werkstoffphysik, Technical University of Munich, Germany
RBsumB. - Le mouvement d'une particule selon Brown dans une suspension cause un Blargissement de la ligne d'absorption resonante. Au moyen de cet effet le developpement des structures
thixotropiques a et6 6tudi6. La ligne de resonance devient plus Btroite selon une fonction exponentielle et on re~oitun 6quilibre qui est dependant de la concentration du systkme. I1 est demontr6 que
le developpement de la structure thixotropique peut 8tre lie avec la viscosite des couches minces de
l'eau entre les particules. Un avantage essentiel de la spectroscopie de Mossbauer est le fait que
l'influence du temps peut 6tre 6tudiB sans dkranger le systkme.
Abstract. - The development of thixotropic gel-like structures in concentrated suspensions has
been studied by observing the broadening of the resonance lines of the Mossbauer spectrum caused
by the diffusive Brownian motion of the suspended particles. An exponential decay of the line
width to a concentration dependent equilibrium value was found. The gradual build-up of structures
in the thin separating water films being responsible for the complex stabilisation of thixotropic
systems thus could be characterized by the actual viscosity of the water films. An essential advantage
of the method described here is the non-destructive way in which the time dependent process is
studied.
1. Introduction. - Near certain solid water interfaces an ordered structure of adsorbed water films
is built up [l].In colloidal systems such as concentrated
hydrosols or suspensions this phenomenon may contribute to a complex stabilizing interaction leading to a
more or less rigid gel like structure. This structure may
be destroyed by mechanical treatment thus liquifying
the system again. Systems exhibiting this behaviour are
usually called thixotropic systems. The specific rheological characteristics of thixotropic materials are of
great interest in many areas of applied technology e. g.
in paint technology.
The time necessary for the rearrangement of thixotropic structures depends very much on the actual
system and may vary between some seconds and
several days. If the transition from the disordered
to the ordered state is slow enough it can be studied in
a nondestructive way with the help of Miissbauer
spectroscopy. During the transition period the time
dependence of the viscosity of the thin water films
separating the suspended colloidal particles strongly
influences Brownian Motion which can be observed by
a corresponding broadening of the resonance lines
of the Mossbauer spectrum.
2. Interaction between colloidal particles. - The
complex interaction of hydrophilic colloidal particles
suspended in water consists of a superposition of
several basic types of interactions. Major types of
interaction may be mentioned here : a) particles are
attracted by van der Waals forczs which depznd on the
distance between interacting surfaces, the surface
energy, and the dielectric properties of the separating
liquid, b) another attractive interaction is created by
fluctuating chains of H-bonds within separating ordered films, and c) particles immersed in water will be
charged by dissolution or adsorption processes and the
surface charge will be compensated by a diffusive layer
of ions. The electrically charged particles experience
Coulomb interaction as soon as diffusive layers overlap.
d) Near the solid-water interface water molecules
become orientated by surface forces and structured
water films are built up which may be as thick as 100 A.
The chemical potential of water molecules within these
films will be lower than in bulk water and hence the film
tends to expand creating a repulsive force. The combination of type c) and d) interactions is generally called
disjoiningpressure [2].e) In addition to above mentioned interactions in colloids some types of colloidal
particles may be linked by primary bonds which in most
cases will lead to the formation of a stable three dimensional network.
A quantitative description of the complex interaction
of combinations of type a), c) and d) is presented
within the DLVO-theory (Derjaguin, Landau, Verwey,
Overbek) [3,4]. More detailed studies of single components of the total interaction may be found in the
literature. The present paper is mainly concerned with
the structural component d ) of the disjoining pressure
and the formation of chains of H-bonds b).
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1976654
C6-270
ELH HACK
H. J.
3. Brownian motion. - The resonance lines of a
Mossbauer spectrum are broadened if colloidal particles being used as source or as absorber perform
Brownian Motion. The Brownian Motion may be
characterized by a diffusion coefficient D which governs
the line broadening [5].
AND F. WITTMANN
could be observed. The equilibrium value was reached
again within some days (see Fig. 1 and 2). The equilibrium value of line width r has been found to be different for the two samples under investigation. The
If the diffusive motion of Brownian particles is governed by the Einstein-Stokes relation the diffusion constant D can be expressed as a function of particle radius
R and the viscosity q of the liquid in which they are
immersed :
Viscous flow of liquids may be described as an activation energy controlled process [6]. From the change of
the linewidth a change of activation energy Q can be
evaluated :
FIG. 1. - Time dependent change of the width of the resonance
lines as measured on sample (A). At t = 0 the ordered structure
has been mechanically destroyed.
4. Experimental. - In a suspension of hydration
products of cements calcium-ferrite hydrates
(CaOFe,O, .(H,O),) having a mean radius of about
100 ,.& are fixed to bigger agglomerations (103-104,.&)
and they may serve as marker particles for FeS7Mossbauer spectroscopy. The Mossbauer spectrum of the
marker particles consists of a quadrupol split line
(IS = 0.62 mm/s against Na,Fe(CN), N0.2 H,O,
AEQ = 0.7 mmls). Spectra have been recorded using a
2. - Time dependent change of the width of the resonance
constant acceleration drive system with a ~o~~ in Pt FIG.
lines as measured on sample (B). At t = 0 the ordered structure
source. The line width has been determined by a fit with
has been mechanically destroyed.
two Lorentzian lines.
Two samples with different waterlhydrate ratio have
been studied :
characteristic time for the exponential decay was
- suspension (A) with 60 Vol % water and 40 % nearly the same for both thixotropic suspensions,
i. e. 1.7 days for suspension (A) and 2 days for suspenhydrates and
- suspension (B) with 67 Vol % water and 33 % sion (B). The extension of the measurements to higher
water contents (80 Vol X)shows, that this applies only
hydrates.
to the concentrated systems. In dilute suspensions the
The agglomerations (microgels) are known to have undisturbed state is reached more slowly because
50 % microporosity. Therefore a corresponding pro- geometrical rearrangement becomes increasingly
portion of the water is taken up by the gel and a remai- important.
ning 20 Vol % for suspension (a) and 37 Vol % for suspension (B) can be considered to be free water. Hence
5. Discussion. - In colloidal suspensions with a
from geometrical considerations it becomes clear that low waterlsolid ratio the thin liquid films separating
the particles are nearly in contact and are separated individual gel particles may exhibit a high degree of
by very thin water films onIy.
ordering. These structured layers are often formed in
The samples have been sealed in a PVC foil to pre- the vicinity of solid surfaces. By mechanical treatment
vent loss of water during the experiment. Before testing relative movement of colloidal particles may be caused.
they have been stored for a week so that mechanical In this way the structured layers are disturbed and the
equilibrium could be reached. At t = 0 the thixotropic viscosity of the films and as a consequence of the total.
structure has been destroyed by mechanical treatment. system sharply decreases. In thixotropic systems gra-,
A pronounced and immediate increase of the line width dual rearrangement of the ordered structure is observed
.
DYNAMICS OF THE DEVELOPMENT OF STRUCTURES IN COLLOIDS AND BROWNIAN MOTION
and in this way Brownian motion is increasingly
hindered 171.
It has been shown that Mossbauer spectroscopy may
be used to study the rearrangement of thixotropic
colloidal structures [8, 91. The systems studied in this
investigation, once being disturbed, reach their equilibrium position according to an exponential law. The
characteristic relaxation time depends on the water
content. As may have been anticipated thicker liquid
films require more time to become rearranged. The
major advantage of the approach described here is the
non-destructive way in which the gradual
decrease
of Brownian motion in collodial systems can beystudied.
As
above viscous
may be
rized by introducing a n activation energy. As the degree
of order within thin liquid films increases the activation
energy increases as well. The average potential barrier
of the elementary process of viscous flow increases. By
applying eq. (3) the time-dependent ncrease of activation energy may be calculated. Results obtained in this
C6-271
3. - Increase of the activation energy of viscous flow
as function of time after the thixotropic structure has been
mechanically destroyed.
nG,
way are shown on figure 3. It may be concluded that
thixotropic systems can be successfully investigated
with the help of Mossbauer spectroscopy.
References
[l] DROST-HANSEN,
W., Ind. Eng. Chem. 61 (1969) 10.
[2] DERJAGUIN,
B. V., J. Coll. Interf. Sci. 49 (1974) 249.
..
[3] DERJAGUIN,
B. V., LANDAU,L., Acta Phys. Chim. USSR 14
(1941) 633.
[41 VERWEY,
E. J. W., OVERBECK,
J. Th. G.,] Theory 'of the Stabflity of Lyophobic Colloids (Elsevier, Amsterdam)
1948.
[5] SINGWI,K. S., SJOLANDER,
A., Phys. Rev. 120, Nr. 4 (1960)
1093.
[6] FRENKEL,
J. I., Kinetic Theory of Liquids (Dover) 1945.
l71 HAUSER, E. A., Xolloid-Z. 98 (1929) 57.
[S] HAN~EL,
D. and SEVSEK,
F., A study of thixotropic 8-FeOOH
by Mossbauer Effect (to be published).
[9] ~ ~ B E L H AH.
CK
J.,, PhD-Thesis, Technical University Munich
1976.