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The use of Raman and FTIR Spectroscopy for the Analysis of Silica-based Nanofillers
C. Yeung, G. Gherbaz and A. S. Vaughan
University of Southampton, Southampton, UK
Results and Discussion
The interest in nanocomposites has grown exponentially since the early 1990s. With an
increase in understanding of nanoparticle-matrix interactions, the ability to engineer
materials and optimise desired properties became well established. However, detailed
studies on the fundamental concept of varying surface functionalisations and how this can
aid mixing, seems to have been neglected. A possible reason for this is that any such
systematic study requires the surface chemistry to be quantitatively characterized.
For fillers such as nanosilica, the surface chemistry can easily be changed using
commercial silanes. By using such technologies, it is possible to modify the chemistry and
extent of the interphase regions, as well as modifying dispersion. Here we present the first
step towards the design and quantification of nanoparticle surface chemistry in
nanodielectrics.
Raman Spectroscopy
Extended scans from 1300 cm-1 to 850 cm-1 for
500 accumulations at 10 s were acquired using a
x50 lens.
Figure 1. shows Raman spectra obtained from
the silane coupling agent Z-6040, the nanosilica
and micro-silica.
A selection of Raman spectra obtained from
nanosilica samples treated with the indicated
quantities of Z-6040 are shown in Figure 3.
Intensity
Introduction
400 mg silane
200 mg silane
100 mg silane
 The epoxide peak is shown at ̴ 910 cm-1.
 The intensity of the epoxide peak increases
monotonically with the concentration of the Z6040 in the initial processing solution.
Raman and FTIR Spectroscopy
Raman Spectroscopy
 Although it is possible that some signal
emanates from adsorbed molecules, the
repeated washing process suggests that the
signal is dominantly from covalently bonded
chemical groups.
 The variations in vibrational and rotational
energy of a system causes inelastic energy
exchanges between incident electromagnetic
radiation and matter.
Intensity
Confocal Raman spectroscopy is a technique that
takes advantage of the Raman effect.
Nanosilica
 The changes in frequency between incident
and detected radiation is determined by the
chemical composition of the system.
 The intensity of Raman photons are detected
and plotted as a function of frequency.
 The spectrum observed allows the qualitative
identification of the material.
FTIR Spectroscopy
Micro-silica
1200
1100
1000
1200
1100
1000
900
Wavenumber / cm-1
Figure 3. Variation in absorbance as a function
of functionalised nanosilica loading level.
 The results demonstrate strongly that the
chosen chemical processing method has been
successful in introducing epoxide an other
organic groups into the system.
900
Wavenumber / cm-1
Figure 1 : Raman spectra of untreated
nanosilica, untreated micro-silica and Z-6040
coupling agent.
FTIR Spectroscopy
Each spectrum was collected from 400 cm-1 to
7800 cm-1 over 32 scans at 4 cm-1 resolution.
Figure 2. represents data for 10mg and 20mg of
functionalised nanosilica in the carrier oil.
Fourier Transform Infrared (FTIR) spectroscopy is
a method of absorption spectroscopy which
analyses the vibrational modes of a system in the
infrared region of the electromagnetic spectrum.
 The amount of scattering increases with the
amount of nanosilica present in the specimen.
 Molecules absorb resonant frequencies that
are specific to certain bonds within the system.
Figure 4. Raw FTIR absorbance for
functionalised and unfunctionalised micro-silica
and the derived difference spectrum
Figure 4. shows raw FTIR data for micro-silica.
 The 10/400 line represents functionalised
micro-silica.
 The amount of absorbance is detected and
plotted as a function of frequency.
 The 10/0 line represents the unfunctionalized
micro-silica.
 The spectra produced allow the quantitative
identification of a material.
The above types of spectroscopy complement
each other, one analysing a system qualitatively
with great spacial resolution, whilst the other
provides, in principle, a more quantitative
approach.
1300
 In addition, the results show that Raman
spectroscopy is a viable means of probing the
chemistry of such materials.
Silane Z6040
1300
0 mg silane
 The solid line represents the difference.
Figure 5. shows absorbance spectra for 10mg of
functionalised nanosilica with different loading
levels of Z-6040.
Figure 2 : FTIR data showing variation in
specimen absorbance as a function of
functionalised nanosilica loading level.
 At this loading level the absorbance was
dramatically reduced compared to the
equivalent micro-silica case.
Experimental procedure
 The epoxide peak can no
distinguished from the noise.
Functionalising silica
 The major feature around 1100 cm-1 increases
monotonically
with
the
degree
of
functionalisation.
Both nanosilica and micro-silica were functionalised for this experiment. Functionalised
specimens were prepared by:
 Dissolving the required quantity of the silane coupling agent (100 mg, 200 mg or 400
mg) in 3.0 g of methanol.
 Adding 200 mg of the appropriate silica.
longer
be
Figure 5. Variation in specimen absorbance as a
function of functionalised nanosilica loading
level.
Conclusions
 Samples were stirred to provide basic dispersion and left for 24 h to allow surface
reactions to occur.
 Vibrational spectroscopy can provide information concerning the chemical state of
functionalised silica.
 Excess silane was removed by repeated washing of the functionalised silica using
methanol and evaporated in an oven.
 In the case of Raman spectroscopy, the magnitude of the characteristic peaks scales with
the degree of functionalisation
Raman Spectroscopy
 However, the approach is not easily adapted to provide absolute concentration data.
 The resulting product was pressed to form a compacted disk-shape.
 In the case of FTIR spectroscopy, optical scattering appears to compromise the simplistic
application of the classical Beer Lambert equation
 Data from these samples were obtained using a Renishaw Raman RM1000
spectrometer with a 785 nm CW diode laser of maximum operating power 25 mW.
 At present the FTIR technique is only capable of providing semi-quantitative data.
FTIR Spectroscopy
 After functionalising, the required mass of silica (10 mg, 20 mg or 40 mg) was dispersed
into 90 mg of Nujol oil.
 FTIR studies were performed using a Perkin Elmer Spectrum GX spectrometer with a
liquid nitrogen cooled mercury cadmium telluride (MCT) detector.
Contact details :
[email protected]
University of Southampton, Highfield, Southampton, SO17 1BJ, UK