Silica fumed nanoparticles were dispersed in polyacrylamide thin films by direct mixing. Atomic Force
Microscopy study was carried out in order to analyze the surface roughness. Height distribution of
surface roughness changes from Gaussian like for polyacrylamide to skew asymmetric when
increasing the silica concentration. The length of the distribution tail increases, indicating the
formation of multi-scale features that increase in number and size, as the silica increase.The authors acknowledge the financial support of the
German research foundation (DFG), French academy of
sciences and French Ministry of Foreign Affairs, Prof.
Philippe Meyer and the Meyer Foundation

Dweik, Hasan

Faroun, Maryam

Ibrahim, Imad

Makharza, Sami

Musa, Ishaq

Sowwan, Mukhles

Sultan, Wadie

English

Al-Quds University Digital Repository

 International Journal of Physical Sciences Vol. 3 (6), pp. 144-147, June, 2008 
Available online at http://www.academicjournals.org/IJPS 
ISSN 1992–1950 © 2008 Academic Journals  
 
 
 
 
Full Length Research Paper 
 
Study on the morphology of polyacrylamide – silica 
fumed nanocomposite thin films 
 
Mukhles Sowwan1, Maryam Faroun1, Ishaq Musa1, Imad Ibrahim1, Sami Makharza1, Wadie 
Sultan2 and Hasan Dweik2 
 
1The Nanotechnology Research laboratory, Materials Engineering Department, Al-Quds University, East Jerusalem- 
Palestine. 
2Department of Chemistry, Al-Quds University, East Jerusalem-Palestine. 
 
Accepted 28 May, 2008 
 
Silica fumed nanoparticles were dispersed in polyacrylamide thin films by direct mixing. Atomic Force 
Microscopy study was carried out in order to analyze the surface roughness. Height distribution of 
surface roughness changes from Gaussian like for polyacrylamide to skew asymmetric when 
increasing the silica concentration. The length of the distribution tail increases, indicating the 
formation of multi-scale features that increase in number and size, as the silica increase. 
 
Key words: Polyacrylamide, nanocompsite, surface roughness, AFM.    
 
 
INTRODUCTION 
 
In recent years, polymeric nanocomposites gained in-
creasing attention in wide range of industrial applica-tions 
including coatings, electronics, and adhesives (Alexandre 
and Dubois, 2000; Tsukruk et al., 2002; Karttunen et al., 
2008). If properly dispersed, fillers such as silica nano-
particles can substantially improve the physical proper-
ties of the resulting nanocomposites with respect to mi-
crocomposites containing the same amount of filler; the 
reason for the improvement is the higher inter-facial area 
between the polymer matrix and filler in the nanocom-
posite than in micro-composite, (Alexandre and Dubois, 
2000; Lan and Pinnavaia, 1994). But also fillers change 
the surface morphology and nanoscale rough-ness of the 
polymer films leading to change in its optical, physical 
and chemical properties (Richard and Malhotra,  2006; 
Tjong 2006). Consequently, techniques with high sensiti-
vity to the surface physical and chemical properties are 
required to reveal the nanoscale properties of nano-com-
posites. Atomic Force Microscopy (AFM) is a powerful 
technique that can provide direct spatial mapping of sur-
face topography with nanometer resolution (Cleveland et 
al., 1998). Tapping mode AFM, for example, often re-
flects differences in the properties of individual compo-
nents of heterogeneous materials  deposited  on  surface, 
 
 
 
*Corresponding authors. E-mail: msowwan@eng.alquds.edu 
and is useful for roughness measure-ments and composi-
tional mapping of polymer nanocom-posites, copolymers, 
and coatings. (Raghavan et al., 2000; Raghavan et al., 
2001; Gu et al., 2001; Bar et al., 1997; Frisbie et al., 
1994). In the present work, the surface morphology and 
nanoscale roughness of a polymer nanocomposite thin 
films, namely silica fumed-polyacr-ylamide nanocompo-
site used for coating capillary tubes (Alejandro and Jose 
1998), prepared by thin film replication method (Sowwan 
et al., 2008) were studied using AFM. 
 
 
MATERIALS AND METHODS 
 
Materials 
 
Polyacrylamide (PAam) with Mw 5,000,000 and silica fumed 7nm in 
diameter were purchased from Sigma-Aldrich Co. and used as 
received. All solutions were prepared in triple distilled water.  
Mica sheets (V-5 grade) substrates were purchased from SPI 
suppliers Co, USA. Glass microscopic slides were purchased from 
Paul Marienfeld GmbH &Co, Germ. Optical grade silicon window 
(Nicodom Ltd.). 
 
 
Instruments 
 
FTIR spectroscopy measurements were performed using a 
BRUKER IFS66/S spectrophotometer .A scanning atomic force mi- 
microscope and software designed by Nanotech Electronica com-
pany (Madrid , Spain) were used for the surface roughness 
investigation (Horcas et al., 2007). A SiN  tip with  a  resonance  fre- 
  
 
 
 
 
 
Figure 1. Schematic representation of the polymer replica 
preparation procedure (a) A droplet of 5µL of polymer solution 
were deposited on a pre-cleaned glass substrate surface (b) 
the substrate and a freshly cleaved mica sheet were pressed 
(0.5 N/cm2) together for half minute (c) Sliding the mica sheet 
horizontally away from the glass surface with a constant speed 
of 0.5 cm/sec (d) Polymer replica on glass substrate. 
 
 
 
 
 
Figure 2. FTIR spectrum of 1PAam film 2 PAam-Silica 2.5% 
(wt/wt). 
 
 
 
frequency in the range 190-325 KHz and force constant in the 
range of 5.5-22.5 N/m with tip diameter 10 nm was used as the 
AFM probe. Tips were purchased from NT-MDT Company (Russia).  
A set of five frames of equal sizes of certain scale was taken from 
different areas of each sample surface, four different silica 
concentrations were tested and three samples of each silica 
concentration were measured. 
 
 
Procedure 
 
Preparation of the nanocomposite 
 
To prepare PAam-Silica nanocomposites, 0.710 g of PAam was 
dissolved in 25 ml of triple distilled water, by gradual addition of 
silica nanoparticles solution to obtain the adequate concentrations 
of polyacrylamide – Silica. Different concentrations were prepared 
2.5, 7.5, 10 and 15% (wt/wt). 
Sowwan et al.       145 
 
 
 
Preparation of thin films  
 
The nanocomposite thin films replicas were prepared in the follow-
ing way. A droplet of 5 µL of polyacrylamide solution incorporated 
with silica fumed nanoparticles was deposited on a pre-cleaned 
glass substrate surface. Afterwards, the substrate and a freshly 
cleaved Mica sheet were pressed (0.5 N/cm2) together for half 
minute, followed by sliding the Mica sheet horizontally away from 
the glass surface with a constant speed of 0.5 cm/sec, see Figure 
1. The prepared replica on the glass substrate was dried in the 
oven at 40oC for over night. As a result, thin silica- polymer  nano-
composite layers of approximately 5 µm thickness, as estimated 
from the volume of the droplet and the surface area of the com-
pressed polymer (diameter = 2.5cm), were formed between the two 
surfaces. 
 
 
RESULTS AND DISCUSSION 
 
FTIR spectroscopy results 
 
FT-IR spectrum of pure PAam film and PAam-Silica 
nanocomposites (2.5% wt/wt) are shown in Figure 2. The 
characteristic peaks of PAam and PAam-Silica  nano-
composites at different silica concentrations are shown in 
Table 1, the peaks shift  related to the NH2 stretching and 
C=O, show clear interaction between the  silica and the 
PAam. 
 
 
AFM results 
 
Figure 3a shows an AFM topography image of polyacry-
lamide thin film surface with a scan size of 2.5 m2. The 
corresponding surface roughness distribution is shown in 
Figure 3b. The Y axis represents the number of events 
(pixels in the image, 1 pixel ~ 5nm) while the X-axis 
represents the height of these events. For simplicity, 
Random Gaussian roughness were assumed, the distri-
bution is symmetric Gaussian (blue), this can be seen 
from the excellent fit. 
Figure 4 shows an AFM topography images of fumed 
silica-polyacrylamide nanocomposite thin films with (a) 
2.5% (b) 7.5% (c) 10% (d) 15% (wt/wt) respectively. The 
corresponding surface roughness distribution is shown in 
Figure 5. The root mean square roughness (RMS) as a 
function of silica concentration is shown in Figure 6. The 
RMS roughness increase as silica increase. However, 
while the RMS roughness value of a sample surface can 
be useful, it can be also misleading (Figure 6 -pointers).  
Two surfaces can have the same RMS roughness, but 
different topographies. A study of the surface roughness 
distribution shape can be effective tool in understanding 
and characterizing of nano-scale surface roughness. The 
distribution shape is changing from symmetric, for the 
pure polyacrylamide, into positively skewed asymmetric 
when adding the silica nanoparticles. The length of the 
distribution tail increase, which indicates the formation of 
multi- scale features that increase in size and number, as 
the silica increase. This result is consistent with the AFM 
topography  images  shown   in   Figure 4a-d.  The  Multi- 
 146          Int. J. Phys. Sci. 
 
 
 
Table 1. FTIR Characteristic peaks of PAam and PAam – Silica nanocomposite. 
 
Materials as (cm-1) 
NH2 
s (cm-1) 
CH2 

 
(cm-1) 
(C=O) 

 
 (cm-1) 
CH bending
 
 (cm-1) 
CH wagging
 

  
(cm-1) 
NH rocking of NH2 
PAam 3353 2936 1658 1452 1324 1125 
PAam-Si 2.5% 3347 2948 1676 1451 1323 1124 
PAam-Si 7.5% 3344 2945 1665 1451 1323 1124 
PAam-Si 10% 3344 2945 1658 1451 1323 1124 
PAam-Si 15% 3344 2936 1659 1451 1323 1124 
 
 
 
 
 
Figure 3a. AFM topography image 2.5 µm2 scan of pure 
polyacrylamide thin film on glass substrate (b) Surface 
roughness height distribution (blue) and the Gaussian fit (Red). 
The Y axis represents the number of events (pixels in the image, 
1 pixel ~ 5nm) while the X-axis represents the height of these 
events. 
 
 
 
 
 
Figure 4. AFM topography images 2.5 µm2 scan of PAam-Silica 
nanocomposite thin films surface with different Silica 
concentrations (wt/wt) (a) 2.5% (b) 7.5% (c) 10%   (d) 15%. The 
Multi-Scale features are marked with small black arrows. 
 
 
Figure 5. Surface roughness shape distribution of PAam-Silica 
nanocompsite thin film surface as a function of Silica 
concentration (wt/wt). The Y axis represents the number of 
events (pixels in the image, 1 pixel ~ 5nm) while the X-axis 
represents the height of these events. 
 
 
 
 
 
Figure 6. Root Mean Square roughness of PAam-Silica 
nanocompsite thin film surface as a function of Silica concentration 
(wt/wt). 
  
 
 
 
Scale features are marked with small black arrows. 
 
 
Conclusion 
 
AFM study of PAam-Silica nanocomposite thin film repli-
ca surfaces on glass substrate showed that the surfaces 
tend to have a multi scale relief structure. The main 
component of this structure is the low scale Gaussian 
roughness. The surface roughness distribution analysis 
revealed various large-scale features, their size and 
number increase as a function of silica concentration and 
hence increase the root-mean-square roughness. 
 
 
ACKNOWLEDGEMENT 
 
The authors acknowledge the financial support of the 
German research foundation (DFG), French academy of 
sciences and French Ministry of Foreign Affairs, Prof. 
Philippe Meyer and the Meyer Foundation. 
 
 
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Study on the morphology of polyacrylamide – silica fumed nanocomposite thin films

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Study on the morphology of polyacrylamide – silica fumed nanocomposite thin films

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