Journal of Materials Science and Chemical Engineering, 2013, 1, 53-56
http://dx.doi.org/10.4236/msce.2013.15011 Published Online October 2013 (http://www.scirp.org/journal/msce)
Could Nanoparticles Reinforce Polymer Matrices?
G. Schrodj, M.-P. Hirn, B. Haidar*
Institut de Science de Materiaux de Mulhouse, CNRS-UMR 7361, Mulhouse, France
Received August 2013
ABSTRACT
In this work, we challenge the idea that “introducing nanoparticles in polymer matrices enhance properties” which is
assumed spreading almost dogmatically. Two series of compounds were prepared: one based on elastomers (solu-
tion-SBR) filled with conventional carbon black particles, CB, the other used the same polymer but filled with carbon
nanotubes, CNT. The results of two types of experiments were compared on the two series. The first is physical based
on the non linear response of filled materials to static deformation, th e second physicochemical, stands on calorimetric
measurements of the polymer heat of adsorption on the solid. Static deformation effect on dynamic mechanical modulus
shows the behavior of the CB filled elas tomers was qualitatively identical to that of glassy polymer reflecting the exi s-
tence of an immobilized fraction of the polymer at the intephase, while that of CNT was found identical to unfilled p o-
lymer indicating a poor filler-polymer interactions. Polymer adsorption measured by flow micro calorimeter showed a
substantial amount of heat exchange on the surface of CB while no heat of adsorption was detected on CNT. The lack
of interaction between the polymer and the CNT, except for a small domain of a narrow polymer molecular weight,
prevent any enhancements of mechanical properties. Other applications may be improved.
Keywords: Polymer; Nanoparticle; Dynamic Modulus; S tatic Deformation; Adsorption; Calorimeter; Interphase
1. Introduction
Expectations of nanoparticles benefits in polymer based
materials rose out of proportion, as it is very often the
case when a new technology immerges. All kind of for-
tunes, and miss fortunes, were attributed to the nano-
aspect of this kind of particles: reinforcing and tough-
ening effects; electrical, thermal and acoustical virtues;
transport properties optical and aging enhancements... [1]
However, when useful real products were late to the
market or appeared less exciting than what it had been
announced, expectations fell as rapidly as it had des-
cended to an overwhelming low level. Only then, thoughts
go back to basics: chemistry, physics and polymer sci-
ence. We most likely are for the time being at this stage
of nanoparticles development in polymer science.
For instance, the driving force behind any effect of
solid particles on the behavior of polymer matrix is the
way polymer chains get in contact with the solid surface.
Adsorption, affinity, interactions, immobilization, inter-
phase buildup… are only a few of many concepts devel-
oped in the literature to emphasize the importance of
polymer/filler contact-adjustment on the properties and
behaviors of the compound.
In this work, we tempted to compare the effect if par-
ticles size-scale on two of the polymers prominent prop-
erties: Dynamic-mechanical and physicochemical.
2. Nonlinear Behavior of Filled Polymer as
Detected by Dynamic Mechanical
Behavior
Nonlinear response of polymer material do deformation
can be demonstrated by different means. One of the most
elegant is that of TL. Smith [2] which consists of apply-
ing at a time, t0, à constant macroscopic strain, λ, on the
polymer specimen (as in relaxation test) and superim-
poses every now and th en on λ a dynamic deformation of
constant frequency, f, and amplitude, ε, small enough be
considered as affiliated to the linear defor ma tion.
2.1. Behavior of Glassy Polymers
In the case of glassy polymers such as polycarbonate,
Poly (methyl methacrylate), polystyrene… dynamic mod-
ulus, e.g. E’ schematically presented in Fig u r e 1, de-
creases suddenly upon deformation from its original val-
ue, E’0, to an undetectable level. Results show linear
modulus-time dependency in a log-log scale, the slope of
which is µ. This behavior was attributed to the nonequi-
librium stat of glassy polymers, the so called “physical
aging” phenomenon and its consequences as a decrease
of the modulus (increase of the polymer segmental mo-
bility, “des-aging”) upon deformation thereafter, and
*Corresponding a uthor.

G. SCHRODJ ET AL.
54
Figure 1. Schematic presentation of the dynamic mechani-
cal experimen t .
under relaxation conditions, a continues increase of the
modulus because of the decrease of segmental mobility,
“aging” anew. µ therefore is considered as an assessment
of the physical aging rate.
2.2. Behavior of Elastomers
A solution-SBR specimen was crosslinked using 2 phr of
dicumil peroxide. The effect of a static deformation, λ =
l/l0 = 1.03 on dynamic modulus when tested at −100˚C, T
< Tg, de-aging followed by aging processes were clearly
observed, Figure 2. In contrast to the glassy state, the
high segmental mobility of the polymer at the rubbery
state places it in a quasi-thermodynamic equilibrium.
Therefore measurements made at 30˚C under similar
relaxation conditions, the modulus E’ of the same cros-
slinked elastomers is virtually unaffected by a static de-
formation, at least as long as such a deformation remains
moderate as shown also in Figure 2.
2.3. Behavior of Polymer Filled with
Conventional Particles
The same solution-SBR was filled with 45 phr carbon
black N-330 before crosslinking.
CB filled SBR showed a clear de-aging followed by ag-
ing processes, just as the unfilled po lymer behaves at the
glassy state, Figur e 2. This behavior was attributed to the
presence, in filled rubber, of a rubber/filler interfacial
region with a specific behavior [3]. The polymer within
this “interphase” has a low segmental mobility compared
to the free rubber matrix and present, therefore, a glassy
like behavior. Such interphase results most likely form
the interactions that polymer most exchange with the
solid surface. Such a specifically low segmental behavior
of the rubber at the filler interface was already detected
especially by 1H solid NMR mea s ure ments [4] .
2.4. Behavior of Polymer Filled with
Nanoparticles
When filler particles are replaced in SBR based matrix
Figure 2. E’ before, E’0, and after static deformation for
differe nt compounds précis ed on the graph.
by nanoparticles (carbon nanotubes, diameter 25 - 12 nm,
1 - 2 µ length), while all other conditions are kept iden-
tical to the ones adopted for conventional filler, we ob-
tain the same behavior as for unfilled polymer, Figure 3.
This may be a strong indication that no interphase is
created at the nano tubes/polymer interface which pre-
sumably due to a lack of interactions exchange between
the two actors. Under these circumstances one would not
expect a substantial “reinforcing” effect beyond the hy-
drodynamic resulting from the filler addition which is
noticed by the increase of the modulus compare Figures
2 and 3.
3. Calorimetric Evaluation of Polymer-Filler
Interactions
Previous results stress the need for a direct measurement
of filler-polymer interactions. Calorimetric approach
using a flow calorimeter appeared as well adapted to
achieve this goal.
A Flow Micro Calorimeter (FMC) was used to meas-
ure the polymer solution heat of adsorption on the filler.
It operated under a constant flow rate (3.3 ml/h) of carri-
er solvent, THF, at 25˚C. In a pulse mode, a known
amount of the polymer dissolved in the carrier solvent
was injected in the flow path through a calibrated sample
loop. If any thermal exchange occurs when the solute
λ
σ
E’
E’
0
time
t
0

G. SCHRODJ ET AL.
55
comes into contact with the particles being studied, a
peak was registered (positive or negative corresponding
to exo- or endothermic events respectively, as schema-
tized in Fig u r e 4). The unadsorbed or/and desorbed frac-
tion of the solute, if any, was then detected by a down-
stream detector. The polymer concentration was fixed at
10 g/l. The FMC principles and the experimental setup
were described elsewhere [40-43].
3.1. Heat of SSBR Adsorption on CNT and CB
The peaks of adsorption of a solution of SSBR of CB and
CNT areas presented in Figur e 5.
Figure 3. Effect of static deformation on E’ for CNT filled
SSBR.
Figure 1. Schematic presentation of FMC.
Figure 5. FMC thermogrammes of SSBR solution on CB
and CNT.
In the case of CB we observe an exothermic peak in-
dicating an irreversible adsorption resulting from a clear
interaction exchanged between the polymer and the solid
surface, while in the case of CNT, although a similar
exothermic peak appears first, it is followed right after by
an equivalent endothermic one reflecting reversible ad-
sorption or two successive processes of adsorption and
desorption; the final balance of the two processes is quite
close to zero while for CB the balance is largely exo-
thermic. The estimation of the molar heat of adsorption
on CB gives a value in the range of chemical bounding,
several hundreds of kJ/mol which may explain the irre-
versible aspect of the adsorption in this case.
3.2. The Effect of the Molecular Weight of
Polybutadien on Its Heat of Adsorption on
CNT
The absence of a permanent adsorption on CNT in con-
trast with CB is unexpected and requires more investiga-
tion. The most important difference between CB and
CNT is their forms: aspect ratio and size scale; although
chemical defects and edges of graphite plan are more
prominent in CB than in CNT, both solid surfaces are
essentially formed out graphite plans. Under theses cir-
cumstances it was legitimate to question the reticence of
CNT to adsorb polymer on the base of scale size match-
ing of the two substances. In fact, the size of a CB ag-
gregate is quite huge compared to CNT diameter, which
approaches the radius of gyration of a long polymer
chain itself. The behavior of the polymer chain toward
the two kinds of surfaces might be quite different.
Therefore, we synthesized a series of polybutadienes
with identical micro-structure (1,2-PB content equal to
about 80%, same Tg), various molecular weights (from
thousand to several hundred-thousand g/mol) and a very
narrow molecular weight distribution (Ip ≈ 1.1). Results
obtained by the application of FMC experimental ap-
proach on CNT are show in Figure 6.
Figure 6. Molar heat of adsorption as a function of molecu-
lar weight of polybutadiene.
1.13
1.15
1.17
1.19
1.21
-1 135
log E', MPa
aging time, log s
E'0
E' carbon nanotubes filled SBR at 30°C
measurement cell
4 thermistors
solutefluid
sa mple
thermogramme
refractogramme
050
Time (min)
CB
050
Time (min)
CNT
0
300
600
900
100100010000 100000 1000000
Heat of Adsorption, kJ/mol
MW, g/mol

G. SCHRODJ ET AL.
56
It is clear that for linear amorphous polymer adsorp-
tion takes place exclusively in a relatively small window
of MW ’s. Adsorption, within this window, is ir reversible
and associated with substantial amount of heat, whereas
outside its limits adsorption is reversible and heat ex-
change is low. Low molecular weight polymer and oli-
gomers are, expectedly, not adsorbed because of their too
small size which unables them to create a sufficient
number of contact to ensure permanent adhesion; heat of
adsorption in this case is too low to overcome thermal
agitation, kT.
High MW’s molecules do not adsorb either, presumably,
because of their failure under our experimental condi-
tions to wind around the nanotube, contradicting model-
ing predictions [5] or, most likely, because its incapacity
to yield a sufficient number of adsorption contact-points
to guarantee permanent adhesion. In order to do so a po-
lymer chain should undergo a defolding process of its
coiled conformation all along the tube axis. Such process
is highly disadvantaged from an entropic viewpoint.
Therefore, only an intermediate MW’s chain can meet
the compromise of being short enough to defold over the
tube surface without too much entropic penalty but still
able to create enough contact-points to offer an enthalpic
gain high enough to link it permanently to the surface of
the nanotube.
4. Conclusions
As many other new technologies, carbon nanotubes
unique structure and characters have attracted excessive-
ly so much attention so fast that they can hardly live up
to all our earliest expectations namely in polymer appli-
cations. The main reason hides in the fact that the way a
long macromolecule come within reach of nano-sized
solid differs fundamentally from the way it approaches
conventional, relatively “unlimited” surface.
This is clearly demonstrated by the absence of adsorp-
tion of polybutadienes on CNT except through MW’s
narrow window in which the size of the macromolecule
matches the size of the exposed surface. The conse-
quence of such a lack in the establishment of the neces-
sary interactions is to restrain adsorption and therefore,
exclude the formation of a valuable interphase, which is
responsible for the emergence of most of the reinforce-
ment observable facts. This is evidenced by the non- ef-
fect of static deformation on dynamic modulus for CNT
filled SSBR while CB filled one show first, a decrease
then, an increase of the dynamic modulus upon deforma-
tion. The immobilized nature of the interphase is in this
case presumably responsible for such a nonlinear deag-
ing/physical aging behaviors.
REFERENCES
[1] K. Friedrich, S. Fakirov and Z. Zhang, “Poly mer Compo-
sites: From Nano- to Macro-Scale,” Springer, 2005.
[2] B. Haida and T. L. Smith, “Dependance of Segmental
Mobility in Polycarbonate on Time and Deformation,”
Polymer, Vol. 31, 1990, p. 1904.
[3] B. Haida, H. Deradji, A. Vidal and E. Papirer, “Polymers
and Surfaces. A Versatil Combination in Recent Research
Developments in Polymer Science,” In: H. Hommell, Ed.,
(Research Signpost, Trivandrum, India), 1990.
[4] V McBrierty and K. Packer, “Nuclear Magnetic Reso-
nence in Solid Polymers,” Cambridge, 1993.
http://dx.doi.org/10.1017/CBO9780511525278
[5] I. Gurevitch and S. Srebnik, “Conformational Behavior of
Polymers Adsorbed on Wrapping of Nanotubes,” Chemi-
cal Physics Letters, Vol. 444, 2007, p. 96.
http://dx.doi.org/10.1016/j.cplett.2007.06.112