RSC 2015-NanoCoater

Tailored design of Cu2O nanocube/silicone
composites as efficient foul-release coatings†
Mohamed S. Selim,ab
Sherif A. El-Safty,*ac
Maher A. El-Sockary,b
Ahmed I. Hashem,d
Ossama M. Abo Elenien,b
Ashraf M. EL-Saeedb
and Nesreen A. Fatthallahe
Environmental concerns about the use of toxic antifoulants have increased the demand to develop novel,
environmentally-friendly antifouling materials. Silicone coatings are currently the most effective non-toxic
alternatives. This study focused on developing a model for silicone foul-release nanocomposites that were
successfully designed, fabricated, characterized, and tailored toward foul-release (FR) coatings. A series of
elastomeric polydimethyl-siloxane (PDMS)/Cu2O nanocube composites with different nanofiller
concentrations was successfully synthesized, for the first time, as FR coatings via solution casting
technique. Emphasis was given to the study of the physicomechanical and surface properties, as well as
the easy release efficiency of the elastomer PDMS enriched with Cu2O nanocubes. The bulk properties
of the nanocomposites appeared unchanged after adding low amounts of nanofillers. By contrast,
surface properties such as contact angle and surface free energy were improved, and the settlement
resistance and easy release behavior of the nanocomposites were enhanced. The surfaces were further
proven to have reversible tunable properties and are thus renewable in water. The antifouling property of
the nanocomposites was investigated by laboratory assays involving microfoulants such as Gram-positive
and Gram-negative bacteria, as well as yeast organisms, for 30 days. Exposure tests showed that lower
surface energy and elastic modulus of coatings resulted in less adherence of marine microfouling. The
most profound effect recorded was the reduction of fouling settlement with nanofiller loadings of up to
0.1% Cu2O nanocubes. Thus, the good foul release and long-term durability confirmed that the present
strategy was an attractive nontoxic and environmentally-friendly alternative to the existing antifouling
systems.
1. Introduction
Marine fouling is an extensive natural phenomenon that causes
serious problems in the marine environment and for the ship-
ping industry.1,2
Shipping accounts for approximately 90% of
global trade, and seaborne trade has nearly quadrupled over the
past four decades.3
Once attached to the hull, fouling increases
friction resistance because of surface roughness, thereby
leading to an increase in hydrodynamic weight and subsequent
top speed reduction and loss of maneuverability.4
Conse-
quently, fouling increases fuel consumption, which in turn
increases emissions of harmful compounds such as CO2, NOx,
and SOx to the atmosphere.5
The increase in fuel consumption
can be up to 40%, and the overall voyage cost can increase by as
much as 77%.6
The economic effects of hull fouling have
accelerated the development of antifouling (AF) technologies, a
global industry that has reached a worth of approximately US$ 4
billion annually.7
Traditionally, fouling is prevented through
the application of AF paints that release biocides, which are
toxic to marine organisms but may also affect non-target
species. The wide-spread use of toxicants has raised concerns
about their harmful effects on marine communities and led the
International Maritime Organization in 2001 to the universal
prohibition of further application of tributyltin compounds,
which have been widely used before the complete phase-out of
their use in 2008.8
Alternative tin-free AF coatings that employ
copper and/or booster biocides are the principal replacement
coatings. Unfortunately, their effects have been found to extend
to non-target species and present potential ecological risk to
95% of organisms in the water column even at very low
concentrations.9
a
National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukubashi,
Ibaraki-ken 305-0047, Japan. E-mail: sherif.elsay@nims.go.jp; Web: http://www.
nims.go.jp/waseda/en/labo.html
b
Petroleum Application Department, Egyptian Petroleum Research Institute, Nasr City
11727, Cairo, Egypt
c
Graduate School for Advanced Science and Engineering, Waseda University, 3-4-1
Okubo, Shinjuku-ku, Tokyo 169-8555, Japan. E-mail: sherif@aoni.waseda.jp; Web:
http://www.nano.waseda.ac.jp/
d
Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt
e
Processes Development Department, Egyptian Petroleum Research Institute, Nasr City
11727, Cairo, Egypt
† Electronic supplementary information (ESI) available. CCDC 73304. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c5ra01597a
Cite this: RSC Adv., 2015, 5, 19933
Received 27th January 2015
Accepted 9th February 2015
DOI: 10.1039/c5ra01597a
www.rsc.org/advances
This journal is © The Royal Society of Chemistry 2015 RSC Adv., 2015, 5, 19933–19943 | 19933
RSC Advances
PAPER

The substantial environmental toxicity issues that surround
the use of biocidal AF coatings have driven research in an
environment-friendly direction with a particular focus on
natural marine compounds and foul-release (FR) technology.10
Natural AF compounds also face regulatory hurdles with the
estimated cost of assembling data packages on efficacy and
environmental fate amounting to millions of dollars as well as
with the timeline for the approval process.11
Non-stick, silicone FR coatings present a feasible, cost-
effective alternative to biocidal AF coatings. Silicone coatings
rely on a technology that acts in two ways: inhibiting the
settlement of colonizing species and weakening their adhesion
strength. By providing low-friction ultra-smooth surfaces,
organisms that stick can be easily removed hydrodynamically
ideally by simply bringing the ship to speed. These coatings do
not leach and could be more durable than tin-free AF paints for
certain vessel applications.12
Silicone polymers based on
polydimethyl-siloxane (PDMS) have been the most promising
FR coating system.13
The superior properties of PDMS FR
coatings are due to their low surface energy, low surface
roughness, low porosity, and high molecular mobility.14
The O–
Si–O linkage, which presents water repellency, causes the good
thermal stability, excellent resistance to oxygen, ozone, and UV
light, anti-stickiness, and low chemical reactivity of the
coating.15
Coatings based on silicone elastomers have inher-
ently good FR properties; however, they require reinforcing
additives (usually mineral llers) to improve their specic
properties and reduce the costs. This reinforcement can be
achieved by incorporating inorganic nanoparticles (NPs) and
conventional macro- and micro-scale composites because of the
increased interaction at the polymer ller interface for the
nanocomposites.16
The extent of nanocomposite property
improvement depends on ller properties, concentration,
morphology, degree of dispersion, and degree of adhesion with
polymer chains.15,17
The use of NP-based metal oxide coatings represents a
promising approach for the development of non-toxic control
technologies for micro-fouling organisms. Surfaces can be
engineered with low-surface energy coatings that minimize
biological adhesion strength and allow FR with modest
brushing/water spray pressures or with coatings that can
prevent fouling through their photocatalytic activity. Metal
oxide NPs are stable during contact with microorganisms.18
TiO2 NPs pose a greater potential than silica in minimizing
biofouling on optical surfaces. In addition, techniques like
nano-metal oxide coatings seem to be an effective method for
combating fouling.19
Among them, Cu2O NPs are relatively easy
to make, safe, and inexpensive, and the natural abundance of
its source materials favors the fundamental and practical
research on Cu2O.20
Cu2O NPs exhibit excellent antibacterial activity against
Gram-positive and Gram-negative bacteria.18,21
A study has
proven that surface hydrophobicity/super-hydrophobicity can
be achieved on modied nano-Cu2O lms,22
which showed
potential for our eld of application. A variety of interesting
Cu2O nanostructures has been synthesized.23,24
Nanocubes
represent one of the most important structural types of Cu2O
because several other crystal morphologies of Cu2O (e.g.,
nanocages, octahedral, and more complicated structures) can
be prepared through the shape transformation of Cu2O nano-
cubes.25
Furthermore, the antibacterial activity of cubic Cu2O
NPs against Escherichia coli is superior to that of octahedral
Cu2O NPs. The polar properties of the {100} crystal planes of
Cu2O nanocubes are believed to perform an important function
in the increased antibacterial activity.26
In the present work, a series of hybrid PDMS/cubic Cu2O
nanocomposites was fabricated via solution casting technique
for use as FR coatings. The surface properties were discussed
based on the changes in water contact angle and surface free
energy. New functions of Cu2O nanocubes were introduced here
based on increasing the easy cleaning phenomena through
raising hydrophobicity and lowering surface free energy that
result in ultra-smooth surfaces with a mechanism that involves
physical anti-adhesion. This research highlights the signi-
cance of the extent of dispersion of CuO2 nanollers in deter-
mining the improvement in the physicomechanical and surface
properties of the nanocomposites. Furthermore, AF perfor-
mance was examined through biological assays to evaluate the
nanocomposite FR behavior. The ndings in this context are
attractive for their merits such as simplicity, safety, environ-
mental benignancy, commercial feasibility, and good potential
for easy-cleaning systems.
2. Experimental section
2.1. Chemicals
Octamethylcyclotetrasiloxane (D4, 98%), which was used as
PDMS source, tetramethyldivinyldisiloxane (C8H18OSi2, 97%),
polymethylhydrosiloxane (PMHS; Mn ¼ 1700–3200), and plat-
inum catalyst commonly known as Karstedt catalyst (plat-
inum(0) and divinyltetramethyl-disiloxane in solution to control
catalyst concentration, stability, viscosity, and inhibition, as
well as easy dosing and formulation; Pt content: 8–11%) were
obtained from Sigma-Aldrich Company Ltd., USA. Copper
sulfate (CuSO4), which was used as copper source, and ascorbic
acid were delivered from Acros Company (Belgium). Potassium
hydroxide, sodium hydroxide, orthophosphoric acid, trichloro-
ethylene, toluene, and all solvents are analytical reagent grade
and were purchased from Merck, Mumbai, India and used as
received.
2.2. Preparation of vinyl-terminated PDMS
In a three-neck round-bottom ask tted with a condenser, a
thermometer jacket, and a nitrogen inlet and outlet, a denite
quantity of distilled D4 was introduced to remove Si–H- and Si–
OH-containing species. Finely grinded potassium hydroxide
(0.55%), which has the alkali metal counter ion K+
, was then
added. The temperature was gradually increased to 145 Æ 5
C
and was kept constant for 3 h, during which the viscosity of the
material was tremendously increased. Aerwards, tetrame-
thyldivinylsiloxane (2 Â 10À4
mol) was added, and the reaction
was continued for another 3 h. The temperature was then low-
ered gradually to RT with stirring for 8 h to stop the reaction and
19934 | RSC Adv., 2015, 5, 19933–19943 This journal is © The Royal Society of Chemistry 2015
RSC Advances Paper

complete the chain termination. The prepared polymer was
dissolved in toluene, and the unreacted KOH was neutralized by
adding concentrated H3PO4 drop wise while stirring vigorously
and detecting the pH of the resultant solution. The solution was
stirred overnight for complete neutralization and precipitation
of the salt generated and then subjected to ltration and
toluene removal.
2.3. Preparation of cuprous oxide nanocubes
Cu2O nanocubes were prepared with copper sulfate as starting
material via a simple technique. Exactly 20 mL of NaOH
aqueous solution (0.075 mol LÀ1
) was added into 10 mL of
CuSO4 aqueous solution (0.5 mol LÀ1
) with stirring (pH ¼ 10.5).
Then 25 mL of ascorbic acid aqueous solution (0.1 mol LÀ1
) was
added dropwise into the above solution with vigorous stirring at
RT. Aer 1 h, a yellow precipitate was obtained (pH ¼ 4–4.5).
The particles were separated from the solution by centrifuga-
tion (4233EC+ laboratory centrifuge, Italy) at 2000 rpm for 30
min. The product was washed by distilled water and absolute
ethanol. The nal product was dried in vacuum at 60
C for 8 h.
2.4. Curing of the prepared vinyl-terminated PDMS
The preparation of unlled PDMS lm was easily employed
through the addition curing system. It was carried out by the
addition reaction of the polyfunctional silicon hydride PMHS
with the unsaturated groups in polysiloxane chains, and the
bond-forming reaction is called hydrosilation curing. To carry
out hydrosilation curing, 10 g of the prepared polymers was
dissolved in 40 mL of toluene with continuous stirring until a
homogenous solution was obtained. Exactly 0.035 g of Karstedt
catalyst dissolved in trichloroethylene (10 mL) was then added
and stirred for 30 min. A homogenous solution of 0.3 g of PMHS
in 10 mL of toluene was added drop wise under stirring. The
resulting solution was degassed and formed air bubbles for 15
min to remove any dissolved gases from the solution. The
degassed solution was used to coat cleaned surfaces and slides,
which, upon the evaporation of the solvent, gave a smooth sheet
of cured PDMS with uniform thickness. The PDMS was
completely cured at RT for 16 h.
2.5. Preparation of PDMS/Cu2O nanocomposites
To prepare the PDMS/Cu2O nanocomposites, Cu2O NPs were
dispersed in toluene by ultrasonication (Sonics Materials,
VCX-750, USA; at 20 kHz frequency and equipped with a 13 mm-
diameter titanium probe) in an ice bath for 15 min. A solution of
the prepared vinyl-terminated PDMS resin in toluene was then
added with stirring for 10 min and sonicated for additional 10
min. The solution was subjected to hydrosilation curing as
described above.
2.6. Apparatus
Certain characterization methods for the prepared polymer,
metal oxide, and their nanocomposites are discussed; however,
the bulk of these methods provide information on the physi-
cochemical and surface properties of the nanocomposites.
The Fourier transform infrared (FTIR) spectra were recorded
using a Nicolet iS10 (Thermo Scientic, USA) with 1 cmÀ1
resolution and 4000–400 cmÀ1
range. The samples were cast on
potassium bromide (KBr) pellets (FTIR grade, Alfa Aesar,
Karlsruhe, Germany). 1
H NMR spectra were recorded on a
Varian Mercury VXR-300 NMR spectrometer at 300 MHz (Var-
ian, Inc., Palo Alto, CA, USA) using tetramethylsilane Me4Si
(TMS) as internal standard and CDCl3 as the main solvent.
Particle size measurement based on the principles of
dynamic light scattering (DLS) was performed using a Broo-
khaven Instruments 90Plus model nanoparticle size/zeta
potential analyzer (USA). The accurate sizes of the NPs were
analyzed by TEM because DLS gives hydrodynamic nanoparticle
size. High-resolution transmission electron microscopy
(HRTEM) was conducted with an electron microscope (JEM2100
LaB6, Japan) at 200 kV accelerated voltage and with 0.14 nm
point–point resolution. In HRTEM, the solid sample was
dispersed in ethanol solution using an ultrasonicator and then
dropped on a copper grid coated with carbon lm. Prior to
inserting the samples in the HRTEM column, the grid was
vacuum dried for 10 min. The nanocomposite samples for TEM
analysis were prepared by ultra-cryomicrotomy with a Leica
Ultracut UCT (Leica Microsystems GmdH, Vienna, Austria).
Freshly sharpened glass knives with 45
cutting edges were used
to obtain cryosections with approximately 100–150 nm thick-
ness at À150
C. The cross sections were collected individually
in sucrose solution and directly supported on a 300-mesh
copper grid.
X-ray diffraction (XRD) is a versatile and non-destructive
technique that reveals detailed information about the chem-
ical composition and crystallographic structure of natural and
synthetic materials. XRD patterns were measured using a Pan-
lytical X'pent PRO (Netherlands) with monochromated CuKa
radiation with scattering reections recorded for 2q angle
between 10
and 80
corresponding to d-spacing between 1.47
and 3.26 A. To conrm the resolution of the diffraction peaks
with standard reproducibility in 2q (Æ0.005), the sample
measurement was recorded using a monochromator and
detector, which were used to generate focusing beam geometry
and parallel primary beam. The standard diffraction data were
identied according to the International Centre for Diffraction
Data (ICDD) soware with PDF-4 release 2011 database.
The optical micrographs of the samples obtained by
mechanical mixing were recorded with an Olympus BH-2
microscope (Japan) where the images were obtained using
Image J soware program. Scanning electron microscopy
images were obtained by a scanning electron microscope (JEOL
JSM530). Before insertion into the chamber, the disk-like
monolith substrates were xed on the SEM stage using carbon
tapes. Gold (Au) lms were deposited on the substrates at RT
using an ion sputter (EDWARDS S150). The distance between
the target and the disk-like monoliths substrate was 5.0 cm. The
sputtering deposition system used for the experiments consists
of a stainless steel chamber, which was evacuated down to 8 Â
10À5
Pa with a turbo-molecular pump backed up by a rotary
pump. Before sputtering deposition, the Au target (4 in. diam-
eter, 99.95% purity) was sputter cleaned in pure Ar. The Ar
Paper RSC Advances

working pressure (2.8 Â 10À1
Pa), the power supply (100 W), and
the deposition rate were kept constant throughout the investi-
gations. Moreover, to record the SEM images of the disk-like
monoliths well, the SEM micrographs were operated at 20 keV.
2.7. Test methods for the cured polymer and its
nanocomposites
2.7.1. Tensile modulus. The tensile properties of the model
FR coatings were obtained in accordance with ASTM D412
method. Dynamic mechanical analysis (DMA) was performed in
tension mode using a TTDMA (UK) from TA instruments.
Rectangular-shaped (30 mm Â 5 mm), free standing samples
were cast from the solution. The tensile modulus was assessed
at RT from stress–strain at 1 Hz single frequency, 2 N preload,
and 0.5–27 mm amplitude.
2.7.2. Swelling tests. For the swelling tests, rectangular
pieces of the synthesized unlled PDMS and PDMS/Cu2O
nanocomposites (1 cm (l) Â 1 cm (w) Â 0.5 cm (h)) were weighed
and then immersed in 100 mL of heptane for 24 h. The solution
was renewed three times during the test, and aer the allotted
time, the nal swollen weight was determined. Each point
recorded is the mean of three measurements. The swelling
degree at equilibrium, SD (%), is expressed as a percentage and
was calculated according to the literature27
and by using eqn (1).
SD (%) ¼ ((Wf À Wi)/Wi) Â 100 (1)
where Wf was the nal swollen weight of the sample at t and Wi
is the initial weight of the dry sample. The sample measure-
ments were determined at 25
C.
2.8. Contact angle measurements
Static contact angle measurements were performed on the
fabricated unlled and lled PDMS/Cu2O nanocomposites on
coated microscopic slides using a Tantec line of contact angle
meter apparatus (Germany) and the sessile drop technique. The
hydrophobic/hydrophilic character of the PDMS layer was
evaluated by measuring the contact angle between the surface
of the coating and drops of test liquids. The results are the
mean of the minimum of three determinations. The test liquids
were water (JT Baker, HPLC grade), diiodomethane, and
ethylene glycol (Aldrich products of the highest purity
available).
2.9. Wetting behavior and surface tension measurements
The measured values of contact angles were used to extract the
surface tension (gtotal
S ) of the cured polymer lms and nano-
composites following the VOCG thermodynamic approach.28
It
relies on the Fowkes's equation, which assumes the total
surface energy to be the sum of different interaction compo-
nents at the liquid–solid interface and postulates a geometric
mean relationship for both the solid–liquid and liquid–liquid
interfacial tensions.29
The total surface tension of a solid gtotal
S is composed of three
additive components: the Lifshitz–van der Waals dispersion
component, gLW
S , the polar electron-donor (Lewis base)
component, gS
À
, and the polar electron-acceptor (Lewis acid)
component, gS
+
(eqn (2) and (3)):
gtotal
S ¼ gLW
S þ 2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
gS
þgS
À
p
(2)
which results in the VOCG approach with the form
1 þ cos q
2
gL ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
gLW
S gLW
L
q
þ 2
gS
þgL
À
p
þ
gS
ÀgL
þ
p
(3)
Utilizing the surface tension gL of at least three different
liquids of known components, two polar and one nonpolar, are
necessary to obtain the three equations that can be solved for
the unknowns of the solid, gLW
S , gS
+
, and gS
À
. This research
used diidomethane as the nonpolar liquid, and water and
ethylene glycol were chosen as the polar liquids.
2.10. Biological assays
2.10.1. Microorganisms' details. Representatives of micro-
organisms that cause microbial fouling in cooling water
systems, cooling towers, and ship's hull were tested. The tested
organisms were the following:
(i) Gram positive bacteria: Staphylococcus aureus, NCTC-7447
(Gram +Ve 1) and Bacillus subtilis, NCTC-1040 (Gram +Ve 2); (ii)
Gram negative bacteria: Pseudomonas aeruginosa, NCTC-10662
(Gram ÀVe 1) and Escherichia coli, NCTC-10416 (Gram ÀVe 2);
and (iii) yeast: Candida albicans, IMRU 3669.
Nutrient broth media were used for the cultivation and
maintenance of the tested microorganisms. The nutrient broth
composition (g LÀ1
) was as follows: peptone, 5.0 g; NaCl, 5.0 g;
yeast extract, 2.0 g; and beef extract, 1.0 g.30
Basal salt media
were used for the weight loss and biodegradability tests. The
foregoing media broth composition (g LÀ1
) was as follows:
potassium dihydrogen orthophosphate, 2.44 g; sodium dihy-
drogen orthophosphate, 5.57 g; ammonium chloride, 0.5 g;
glycerol, 6.4 mL; magnesium chloride, 2.44 g; calcium chloride,
5.57 g; ferrous sulfate, 2.00 g; yeast extract, 0.1 g; and distilled
water, 850 mL.31
2.10.2. Weight loss measurements. In weight loss experi-
ments, 100 mL of fresh culture broth of each of the tested
microorganisms was injected in 100 mL bottles that contain 30
mL of basal salt media broth. Coated samples were hung in the
medium using nylon threads. Weight loss was calculated using
eqn (4):32
Weight loss (mg cmÀ2
) ¼ ((Wbefore À Wafter)/time) (4)
where time is the duration of sample immersion in days.
2.10.3. Biodegradability test. The biodegradation study of
the prepared PDMS compounds (as painted glass slides) was
done in 100 mL batch asks that contain 30 mL of basal salts
medium with an initial pH of 7 prepared according to the
literature.33
The incubation period was 30 days at 30
C in a
shaking incubator (150 rpm). Aer the test period, the slides
were removed from the medium, washed with distilled water,
and dried. The amount of degradation was determined by
studying the weight loss according to the literature.34,35
The
RSC Advances Paper

biodegradable percentage (BD) was determined from the weight
loss measurements using eqn (5).
%BD ¼ ([WC À WS]/WS) Â 100 (5)
where WC and WS are the weight loss of the sheets in grams in
both control and sample conditions. Each value was the average
of three separate experiments.
3. Results and discussion
3.1. Prepared PDMS design characterization and curing
PDMS belongs to the water-insoluble matrix class and has
unique properties that distinguish it as a FR coating. PDMS has
methyl (–CH3) side chains that cause its low surface energy (20–
24 mJ mÀ2
) and a exible inorganic –Si–O backbone linkage that
causes its extremely low elastic modulus (z1 MPa), which are
both essential for the extremely low adhesion of fouling on
silicone coating surfaces. Thus, biolms can be easily removed
from the surface by simple mechanical cleaning or during
vessel movement.36,37
In 2000, Wynne et al. evaluated two types of PDMS coatings,
namely, the hydrosilation-cured and the condensation-cured
PDMS, and found that the unlled hydrosilation-cured PDMS
has superior properties such as hydrophobicity, roughness,
stability in water, non-shrinkage, and lower adhesion of
barnacles compared with lled condensation-cured PDMS.37
Vinyl-terminated PDMS was obtained via anionic ring
opening polymerization of D4 tetramer (because it is a less
expensive and more readily available monomer) using a strong
base catalyst (KOH), which is frequently used to ring open D4 at
common polymerization temperatures of 140–160
C (ref. 14
and 38) (see ESI, Scheme S1†). Siloxane dimers (tetramethyldi-
vinylsiloxane) are usually used as end-capping reagents to
control the molecular weight.39
Aer reaching equilibrium, the
reaction is quenched by adding a strong acid (orthophosphoric
acid). The conversion or polymerization rate of D4 is high at the
beginning and then attens out with time because of the
decrease in monomer concentration during polymerization and
because the living centers are enclosed by polymer chains in
bulk polymerization.
The FTIR spectrum of the prepared vinyl-terminated PDMS
sample revealed absorption bands at 2963 and 2905 cmÀ1
ascribed to asymmetric –CH3 stretching, at 1411 cmÀ1
assigned
to –CH3 symmetric deformation, and at 1595 cmÀ1
assigned to
Si–CH]CH2 stretching absorption. The band at 1261 cmÀ1
corresponds to CH3 symmetric deformation, that at 1096 cmÀ1
to Si–O–Si asymmetric deformation, that at 866 cmÀ1
to Si–O–Si
skeletal stretching, and that at 699 cmÀ1
to the symmetric
stretching of the Si–C bond in –Si(CH3) group. The absence of
any absorption peak at 2060 cmÀ1
and 3000–3500 cmÀ1
indi-
cates the absence of any hydrosilane (Si–H) or hydroxyl groups
(Si–OH) in the prepared polymer (see ESI, Fig. S1†).39a
The 1
H nuclear magnetic resonance (NMR) spectrum
distinguishes the signals of the chemical shi at 1.00 ppm
caused by (Si–CH3) from those at 5.94–6.2 and 5.71–5.92 ppm by
CH2]CH–Si and CH2]CH–Si. The absence of a chemical shi
at 4.6 ppm indicates the absence of Si–H and Si–OH linkages.
The DSC sample was super-cooled at À130
C and then heated
from À130
C to 50
C with a glass transition (Tg) at À122
C,
cold crystallization at À95
C, and melting (Tm) at À46
C. A
crystallization exothermal peak is observed during the cooling
step and a single melting endothermic peak during the second
heating step. The low Tg of silicones as reected in their
molecular mobility may contribute to their superior FR
characteristics.39b
The curing of the prepared vinyl-terminated PDMS follows
the hydrosilation curing mechanism where vinyl end-blocked
polymers react with the SiH groups carried by functional olig-
omers. The addition occurs mainly on the terminal carbon and
is catalyzed by organometallic compounds, preferably platinum
metal complexes, to enhance their compatibility. This reaction
has no by-product. Molded pieces made with a product from
this curing mechanism are very accurate (no shrinkage). The
mechanism of platinum hydrosilation (see ESI, Scheme S2†)
was proposed by Chalk and Harrod,40
and the catalytic cycle has
also been reported before.14
3.2. Nanoller morphology and characterization
To regulate the shape and size in wet-chemical techniques,
most synthetic strategies in preparing Cu2O NPs involve
surfactants or template reagents. However, these additives are
usually expensive, toxic, and hard to wash, and thus may affect
the performance of the products. In this work, Cu2O nanocubes
were successfully prepared and controlled without using any
template or surfactant at room temperature (RT) (Scheme 1).
The dominant factor that inuences the morphology and size of
the particles is the concentration of the NaOH used. At low
NaOH concentration, the Cu2O crystal nuclei were ineffectively
capped, remained in nanoscale, and grew randomly. In addi-
tion, OHÀ
ions affect the stability of {100}, leading to a cubic
morphology.25,41
However, continuous lowering of the NaOH
concentration may result in other forms of copper nanocubic
morphology.42
In this study, when the concentration of NaOH
solution was decreased to 0.075 M, small nanocubes with an
average side length of 70–110 nm were obtained. On the
Scheme 1 Preparation of Cu2O nanocubes (note: the picture on the
right shows the crystal structure of Cu2O oriented to show {100}
plane).
Paper RSC Advances

contrary, the nanocube size increased with increasing concen-
tration of NaOH solution. At small nanoscale, the number of
particles per unit area increases, and thus antibacterial effects
can be maximized.42
The reaction mechanism can be summarized as follows:
cupric sulfate could be dissolved in water and form a uniform
ionic solution. When NaOH is added to the solution, Cu2+
reacts
with OHÀ
and forms blue insoluble Cu(OH)2. At RT, Cu(OH)2 is
decomposed into cupric oxide and water. Ascorbic acid is then
added as reducer to reduce cupric oxide (CuO) into Cu2O. In this
process, NaOH serves not only as a reagent, but also for
adjusting the pH of the solution.
The FTIR spectrum of the prepared Cu2O NPs revealed a
strong absorption band at 626 cmÀ1
attributed to the Cu–O
linkage of Cu2O, which agrees with previous literature.43
Therefore, the as-prepared products were pure Cu2O because no
infrared-active mode of CuO around 530 cmÀ1
appeared (see
ESI, Fig. S2†).
The high morphological uniformity of these Cu2O crystals
is reected in their XRD patterns shown in Fig. 1. The strong
and sharp diffraction peaks suggest that the resultant prod-
ucts were well crystallized. The characteristic peaks for Cu2O
(2q ¼ 29.69, 36.52, 42.41, 61.68, 73.61) marked by indices
[(110), (111), (200), (220), (311)] showed that the resulting
Cu2O was essentially crystalline. All the peaks of the prepared
Cu2O NPs match well with that of standard Cu2O, and no
diffraction peaks from metal copper or cupric oxide appear in
the XRD patterns.
The size of the Cu2O crystallites was estimated from the
Debye–Scherrer eqn (6):
D ¼ (Kƛ/b1/2)cos q (6)
where K is the Scherrer constant, which is related to the crys-
tallite shape; ƛ and q are the radiation wavelength and Bragg's
angle, respectively; and b1/2 is the full width at half maximum of
the diffraction peak. The crystal sizes of the product were
calculated and proven to be in the nanosize range.
Fig. 1 XRD pattern of the as-synthesized Cu2O nanocubes, inside DLS
of the as-synthesized Cu2O nanocubes, and schematic of a liquid
droplet on the surface of coated glass slide.
Fig. 2 (A), (B), and (C) are the TEM images of the prepared Cu2O
nanocubes at low and high magnifications; (D) corresponding SEM
images of the as-synthesized Cu2O nanocubes; (E) corresponding
SAED patterns of the as-synthesized nanocubic Cu2O; (F) corre-
sponding crystal lattice, which is consitent with XRD results; and (G)
and (H) are the TEM images of the PDMS/Cu2O nanocomposites (0.1%
nanofillers) at low and high magnification powers.
RSC Advances Paper

DLS is a non-invasive technique that measures the size and
size distribution of NPs dispersed in a liquid, as shown in Fig. 1.
The size distribution prole of the synthesized NPs showed an
average particle size of 90 nm. The polydispersity index of Cu2O
NPs was 0.236, which indicates that the particles are poly-
dispersed in nature. These results matched with the results
from the XRD analysis.
The transmission electron microscopy (TEM) analysis
(Fig. 2A–C) and SEM analysis (Fig. 2D) of the prepared Cu2O NPs
showed that they have approximately uniform size, cubic shape,
clean surface, and particle sizes between 70 and 110 nm. The
inset shows the selected area electron diffraction (SAED)
patterns (Fig. 2E) obtained by directing the electron beam
perpendicular to the square faces of the cube. The square
symmetry of this pattern indicates that each Cu2O nanocube
was a single crystal bounded mainly by {100} facets. Further-
more, it exhibits individual NPs and clear lattice fringes with d
spacing of 0.25 and 0.30 nm, corresponding to the {111} and
{110} reections of the cubic Cu2O structure, respectively
(Fig. 2F).
3.3. Nanocomposite design and physicomechanical
characterization
For the fabrication of PDMS/Cu2O nanocomposites appropriate
for marine easy-release coatings, investigating various concen-
trations of Cu2O nanocubes to be embedded into the PDMS
matrix is crucial. The detailed fabrication process of the PDMS/
Cu2O nanocomposites is shown in Scheme 2. The TEM obser-
vations of the PDMS/Cu2O nanocomposites (Fig. 2G and H)
demonstrate that a complete disagglomeration of low concen-
trations of Cu2O nanocubes is achieved in the nanocomposites,
whereas high concentrations show a different trend. The bright
background shows the polymer matrix, whereas the dark cubic
structures are the structure of Cu2O NPs, and their diameter is
approximately 90 nm. In terms of concentration (0.1% nano-
llers), individual cubes are well dispersed and separated from
one another. Thus, the nest extent of dispersion is achieved,
and the samples exhibit high-quality dispersion without any
remaining aggregate, thereby causing signicant improvement
in the nanocomposite properties.
The FTIR spectra of the PDMS/Cu2O nanocomposites
provide evidence for the interaction between the polymer and
the NPs. The shis in the absorptions for Si–O–Si asymmetric
deformation and Si–O–Si skeletal deformation are less vivid for
low concentrations but are well observed when the nanoller
content was increased up to 5% loading. The peak for Si–O–Si
asymmetric deformations shis from 1034 cmÀ1
for vinyl-
terminated PDMS to 1020 cmÀ1
for the nanocomposites, and
the peak for Si–O–Si skeletal stretching shis from 805 cmÀ1
to
792 cmÀ1
for the 5% loading sample. The increase in the
intensity of the peak at 3500 cmÀ1
, which is due to the OH
stretching of the H-bond of the adsorbed water on the surface of
Cu2O, did not appear at low concentrations but was observed on
high ller loadings (see ESI, Fig. S3†).
The tensile modulus of the prepared nanocomposites is
illustrated in Fig. 3. It is not affected by the incorporation of a
small amount of Cu2O NPs (up to 0.1%) in the nanocomposites
Fig. 4 Water contact angle of the unfilled and filled PDMS/Cu2O
nanocomposites.Scheme 2 Synthesis of PDMS/Cu2O nanocomposites.
Fig. 3 Tensile modulus of the unfilled and filled PDMS/Cu2O nano-
composites with different loadings.
Paper RSC Advances

with an average value remaining at 3.6 Æ 0.5 MPa. In other
words, the stiffness of the silicone-based materials remains
constant. A progressive increase of up to 8 MPa is observed for
high concentrations (5% nanoller loadings), which may be
explained by aggregation and agglomerations that cause the
increase in stiffness. For the PDMS/Cu2O nanocomposites and
within the limited content of nanollers (less than 0.5 wt%), the
dynamic stress was unchanged with an average value of 1300 Æ
185 Pa and then increased up to 3315.5 Pa (for the high content
in Cu2O at 5 wt% nanollers), which may be caused by the
presence of aggregates at high concentrations.
3.4. Surface and AF investigation of the nanocomposite
lms
Biofouling is a dynamic process that spans numerous length
scales and involves a complex variety of molecules and organ-
isms. Surface chemistry is a signicant factor in the formation,
stability, and release of the fouling organisms' adhesion to
surfaces.44
The hydrophobicity of the surface of hybrid nano-
composites was evaluated using static contact angle measure-
ments, as shown in Fig. 4. The measurements were performed
before and aer immersion in demineralized water for 7
days.15,45
The unlled PDMS contact angle obtained before
immersion was 102 Æ 2
, indicating a hydrophobic character,
whereas the contact angle aer immersion dropped to 90
,
indicating the decrease in surface hydrophobicity. With
different loading concentrations of Cu2O nanollers before and
aer immersion, the wettability of the coatings shows an
increase in the hydrophobic behavior with 0.1% nanollers.
The water contact angle analysis (i.e., at 130
) shows a lm
surface that is simultaneously hydrophobic and lipophobic due
to the well dispersion of ller NPs, leading to (1) increased
surface area and chemical bonding, and (2) reduced the surface
roughness of polymer-NPs patterns, as shown in Table S1.†
Results shows a decrease in the hydrophobicity at high NPs
concentrations for both the un-immersed and immersed
Table 1 Contact angle (q) measurements for various solvents (ethylene glycol and diiodomethane); total surface tensions (gtotal
S ) of the
chemically synthesized PDMS and filled PDMS/Cu2O nanocomposites controls before (dry) and after (wet) immersion in distilled water for 7 days
in various solvents according to VOCG equation; and the percentage degree of swelling SD (%) in n-heptane as a good solventa
Sample design
q Ethylene glycol q Diiodomethane gtotal
S (mN mÀ1
)
Swelling degree
in n-heptane (SD (%))Dry Wet Dry Wet Dry Wet
PDMS blank 84
Æ 2
78
Æ 2
75
Æ 1
70
Æ 2
20.23 23.06 93.6 Æ 1%
PDMS/Cu2O (0.01%) 95
Æ 2
88
Æ 3
80
Æ 2
75
Æ 3
17.85 21.32 90.3 Æ 2%
PDMS/Cu2O (0.05%) 104
Æ 3
97
Æ 3
84
Æ 2
79
Æ 2
16.22 19.6 88.5 Æ 1.5%
PDMS/Cu2O (0.1%) 120
Æ 2
112
Æ 2
89
Æ 1
85
Æ 2
14.096 16.39 89.9 Æ 1%
PDMS/Cu2O (0.5%) 106
Æ 1
96
Æ 3
85
Æ 1
80
Æ 1
15.47 18.55 88.6 Æ 2.6%
PDMS/Cu2O (1%) 98
Æ 3
89
Æ 2
81
Æ 2
76
Æ 2
17.37 20.2 88.4 Æ 1.8%
PDMS/Cu2O (3%) 91
Æ 2
87
Æ 2
76
Æ 2
72
Æ 1
20.38 23.11 87.5 Æ 1.2%
PDMS/Cu2O (5%) 83
Æ 4
79
Æ 4
71
Æ 1
67
Æ 2
23.31 31.31 85.9 Æ 2.5%
a
Note: gtotal
S calculated with van oss–Chaudhury–Good approach, Lifshitz–van der Waals component gLW
S , lewise base component gS
À
and lewise
acid component gS
+
.
Fig. 5 (A) and (B) present the weight loss and biodegradability measurements, respectively, of the unfilled and filled PDMS/Cu2O nano-
composites with different microorganisms [Gram (+Ve 1), Gram (+Ve 2), Gram (ÀVe 1), and Gram (ÀVe 2) bacteria and yeast].
RSC Advances Paper

samples, indicating the effect of agglomeration and aggregation
of NP nanollers. As a result, the absence of the chemical
boding interactions between the polymer and agglomerated
ller NPs onto surface pattern may occur with the high-
concentration of NP llers.46
Table S1† shows that with high-
concentrations of NPs used, the ne Cu2O NPs may tend to
combine together and form strongly bonded aggregates onto
surfaces, leading to drastically decrease in surface area and
hydrophobic character. The enhanced surface hydrophobicity
increases the surface roughness and facilitates the fouling
adhesion. Our nding also shows that the contact angle reaches
to a value close to that obtained before immersion under drying
condition. Therefore, the unlled and lled silicone surfaces
appear to have reversibly tunable properties.46
Surface energy measurements on the PDMS/Cu2O nano-
composites were performed according to the van Oss–Chaud-
hury–Good (VOCG) model by measuring the surface contact
angle with both polar (water, as in Fig. 4, and ethylene glycol)
and nonpolar (diiodomethane) liquids, as shown in Table 1.
The calculated surface free energy values of the unlled and
lled PDMS are summarized in Table 1. The results illustrate
low surface free energy for the 0.1% Cu2O nanollers and thus
low adhesion of microorganisms. By contrast, the surface free
energy gradually increases with increasing ller loadings of up
to 5% because of the roughness caused by agglomerations and
aggregation.
Swelling measurements represent a technique of choice for
the characterization of the polymer network. This test consists
of immersing a piece of composite in a good solvent (heptane)
and monitoring the evolution of the swelling mass at regular
intervals. The swelling degree of the lled PDMS was lower than
that of the unlled, as shown also in Table 1. A low swelling
degree is typical of a more important crosslinking density.
Thus, Cu2O NPs can be seen as additional (physical) cross-
linking points, acting positively during network formation
because of the excellent affinity between components.
Biodegradation can be dened as the process in which
substances are broken down by the action of microorganisms.
The microorganism's growth in the material increases the size
of pores and induces cracks. As a result, the structure of the
material is destabilized.47
The biodegradation of PDMS in
natural or living organisms has been poorly examined.39
PDMS
has been treated as nonbiodegradable and inert. At the turn of
1970s, the possibility of their biodegradation has been
proven.48,49
Only few studies that focus on the biodegradation of
various siloxanes have been reported. Nevertheless, the lack of
studies did not affect the general assessment that polysiloxanes
are a group of polymers that is difficult to biodegrade.49
In this
work, AF and biodegradation analysis was performed on the
prepared PDMS/Cu2O nanocomposites as follows.
Weight loss tests were carried out on the unlled and lled
PDMS nanocomposites from 0.1% PDMS/Cu2O (which wasFig. 6 Optical microscope images (A), (B), (C), and (D) of the unfilled
PDMS; (E), (F), (G), and (H) of the 0.01% nanofillers in the PDMS/Cu2O
nanocomposites; (I), (J), (K), and (L) of the 0.05% nanofillers in the
PDMS/Cu2O nanocomposites; (M), (N), (O), and (P) of the 0.1% nano-
fillers in the PDMS/Cu2O nanocomposites; (Q), (R), (S), and (T) of the
0.5% nanofillers in the PDMS/Cu2O nanocomposites; (U), (V), (W), and
(X) of the 1% nanofillers in the PDMS/Cu2O nanocomposites; (Y), (Z),
(AA), and (AB) of the 3% nanofillers in the PDMS/Cu2O nano-
composites; (AC), (AD), (AE), and (AF) of the 5% nanofillers in the PDMS/
Cu2O nanocomposites; all images were recorded before and after
immersion in microorganisms for 30 days.
Paper RSC Advances

proven to enhance characteristics with low nanoller loading of
0.01% and 0.05%, as described in the aforementioned tests)
and up to 5% llers. A comparison of the weight loss results of
the unlled and lled PDMS nanocomposites at various load-
ings were carried out and shown in Fig. 5A, which suggests that
the weight loss is higher for the unlled PDMS and decreased to
nearly zero with 0.1% loadings in PDMS/Cu2O. As shown in
Fig. 5B, the biodegradability percentages for 30 days were
calculated, where the blends with low nanoller concentrations
degrade slowly, whereas those with high nanoller concentra-
tions degrade rapidly in 30 days. This nding indicated that the
signicant FR characteristics were found with design patterns
that have well dispersion of Cu2O NP llers at loading amount
up to 0.1%. In such patterns, the Cu2O NPs may lead to increase
surface area, chemical bonding, and surface smoothness of
polymer-NPs surfaces (see Table S1†). Consequently, the
enhancement in the surface properties and the adhesion
resistance of microorganisms is achieved, thereby preventing
surface deterioration. On the contrary, with the surface design
patterns fabricated at high concentrations of up to 5% ller
NPs, the gradual increase in the fouling adhesion is due to the
agglomeration and aggregation of the NPs at high ller
concentrations.
Generally, the resistance of Gram-negative bacteria toward
antibacterial substances is related to the hydrophobic surface of
their outer membrane rich in lipopolysaccharide molecules.
The membrane acts as barrier to the penetration of numerous
antibiotic molecules associated with the enzymes in the peri-
plasmic space, which are capable of breaking down the mole-
cules introduced from outside.50
The biolm coverage on the surface of silicone was roughly
determined through the biolm formation images in the optical
microscope for the unlled and lled PDMS specimens before
and aer immersion in the used microorganisms, as shown in
Fig. 6. For the unlled PDMS, given that the silicone and glass
slide are transparent, the picture background was white if no
bacteria are attached to the silicone surface. The surface
coverage of the dark area (fouled area) relative to the total area
was assumed to be the surface coverage of the bacteria. The
well-dispersed NPs observed, which are related to the low
concentrations of Cu2O NPs up to 0.1%, were the reason for the
homogeneity and immunity of the surface. By contrast, the non-
homogeneity observed for the blank samples were due to the
fouling settlement on its surface, which is observed for the
characteristics achieved from the failure mechanism technique.
With increasing nanoller concentrations of up to 5%, the
specimens were also densely fouled. The SEM micrographs for
the unlled and lled polymer nanocomposites (see ESI,
Fig. S4†) were obtained and showed Cu2O NPs as white spots. A
good dispersion and homogeneity of NP distributions is
observed for concentrations up to 0.1%, thus affords improved
surface characteristics and enhanced immunity against micro-
organisms. By contrast, additional loadings up to 5% of Cu2O
NPs lead to aggregation and agglomerations and consequently
increased surface roughness. Thus, air voids may be trapped
between the agglomerates and reduce the surface properties
and immunity of the coatings against fouling.
4. Conclusions and outlook
A series of PDMS/cubic Cu2O nanocomposites with advanced
surface properties was successfully fabricated for use as FR
coatings. The XRD and TEM results of the prepared Cu2O NPs
exhibit truncated nanocubes bounded by {100} facets with an
average diameter of 90 nm. These nanocomposites were
synthesized with various ller concentrations, and conventional
hydrosilation curing mechanism was employed using platinum
catalyst and Si–H functional cross-linker. The inclusion of small
concentrations (0.1%) of NPs can signicantly enhance the
surface properties and, to a lesser degree, the phys-
icomechanical performance of the nanocomposites because of
well dispersion. However, high NP concentrations (5%) tend to
strongly agglomerate (particle clustering) because the inter-
molecular attraction forces of the NPs are high given their large
surface area, thus reducing the nanocomposite properties. The
surface characteristics of the prepared nanocomposites were
studied from a mathematical viewpoint using appropriate
mathematical tools. At low levels, an increase in hydrophobic
character and a decrease in surface tension were achieved
because of the well dispersion of nanollers. The surface is
homogenous such that sessile drops of test liquids assume a
hemispherical shape with maximum increase in contact angle
for 0.1% nanollers, which enhance the easy cleaning
phenomena. The results obtained from the present investiga-
tion revealed that the AF potential of PDMS/Cu2O gradually
increased with increasing ller loadings up to 0.1% but
decreased at high loading levels because of agglomerations. The
presence of Cu2O nanocubes in the PDMS matrix endows it with
various properties that make the polymer nanocomposite a
promising candidate as an environment-friendly FR coating.
Notes and references
1 (a) M. P. Schultz, J. A. Bendick, E. R. Holm and W. M. Hertel,
Biofuels, 2011, 27, 87–98; (b) S. Krishnan, C. J. Weinman and
C. K. Ober, J. Mater. Chem., 2008, 18, 3405–3413; (c)
Md. S. Rahaman, H. Thérien-Aubin, M. Ben-Sasson,
C. K. Ober, M. Nielsen and M. Elimelech, J. Mater. Chem. B,
2014, 2, 1724–1732.
2 D. Carteaua, K. Vallée-Réhela, I. Linossier, F. Quiniou,
R. Davy, C. Compère, M. Delbury and F. Faÿ, Prog. Org.
Coat., 2014, 77, 485–493.
3 ICSISF, Overview of the international shipping industry,
International Chamber of Shipping and International
Shipping Federation, 2009, http://www.marisec.org/
shippingfacts/keyfacts/, accessed 14.12.2009.
4 K. A. Dafforn, J. A. Lewis and E. L. Johnston, Mar. Pollut.
Bull., 2011, 62, 453–465.
5 (a) N. D. Hoa and S. A. El-Say, Chem.–Eur. J., 2011, 17,
12896–12901; (b) B. Dahlback, H. Blanck and M. Nyden,
Coast. Mar. Sci., 2010, 34/1, 212–215; (c) N. D. Hoa and
S. A. El-Say, J. Phys. Chem. C, 2011, 115, 8466–8474.
6 D. M. Yebra, S. Kiil and K. Dam-Johansen, Prog. Org. Coat.,
2004, 50, 75–104.
RSC Advances Paper

7 T. Wright, Marine Coatings Market, 2009, http://
coatingsworld.com/articles/2009/05/marine-coatings-
market.php/, accessed 20.06.2009.
8 T. Bolam, J. Barry, R. J. Law, D. James, B. Thomas and
S. G. Bolam, Mar. Pollut. Bull., 2014, 79, 326–332.
9 M. Lejars, A. Margaillan and C. Bressy, Chem. Rev., 2012, 112,
4347–4390.
10 (a) V. A. Ganesh, A. Baji and S. Ramakrishna, RSC Adv., 2014,
4, 53352–53364; (b) F. Fay, D. Carteau, I. Linossier,
M. Delbury and K. Vallée-Réhel, Colloids Surf., B, 2013,
102, 569–577.
11 D. Rittschof, Biofuels, 2000, 15, 119–127.
12 (a) M. Lejars, A. Margaillan and C. Bressy, Polym. Chem.,
2013, 4, 3282–3292; (b) R. T. Carson, M. Damon,
L. T. Johnson and J. A. Gonzalez, J. Environ. Manage., 2009,
90, 2460–2468.
13 (a) X. Liu, W. Tong, Z. Wu and W. Jiang, RSC Adv., 2013, 3,
4716–4722; (b) D. Feng, D. Rittschof, B. Orihuela,
K. W. H. Kwok, S. Stafslien and B. Chisholm, Aquat.
Toxicol., 2012, 110–111, 162–169.
14 N. Roy and A. K. Bhowmick, Polymer, 2010, 51, 5172–5185.
15 I. Mohoric and U. Sebenik, Polymer, 2011, 52, 4423–4428.
16 A. Beigbeder, P. Degee, S. L. Conlan, R. J. Mutton, A. S. Clare,
M. E. Pettitt, M. E. Callow, J. A. Callow and P. Dubois,
Biofuels, 2008, 24/4, 291–302.
17 G. Momen and M. Farzaneh, Rev. Adv. Mater. Sci., 2011, 27,
1–13.
18 (a) J. Hrenovic, J. Milenkovic, N. Daneu, R. Matonickin
Kepcija and N. Rajic, Chemosphere, 2012, 88, 1103–1107;
(b) S. A. El-Say, N. D. Hoa and M. Shenashen, Eur. J.
Inorg. Chem., 2012, 33, 5439–5450; (c) M. Khairy and
S. A. El-Say, Chem. Commun., 2014, 50, 1356–1358.
19 (a) M. A. Shenashen, S. A. El-Say and E. A. Elshehy, Particle,
2014, 31, 93–316; (b) R. Dineshram, R. Subasri,
K. R. C. Somaraju, K. Jayaraj, L. Vedaprakash, K. Ratnam,
S. V. Joshi and R. Venkatesan, Colloids Surf., B, 2009, 74,
75–83; (c) M. Khairy and S. A. El-Say, Sens. Actuators, B,
2014, 193, 644–652.
20 (a) C.-H. Kuo and M. H. Huang, Nano Today, 2010, 5, 106–
116; (b) M. Khairy, S. A. El-Say and M. Ismael, Chem.
Commun., 2012, 48, 10832–10834.
21 S. C. Ling, L. Y. Fang, Q. W. Jing and H. C. Zhi, Sci. China, Ser.
B: Chem., 2009, 52, 1028–1032.
22 Y. Ding, Y. Li, L. Yang, Z. Li, W. Xin, X. Liu, L. Pan and
J. P. Zhao, Appl. Surf. Sci., 2013, 266, 395–399.
23 M. J. Siegfried and K.-S. Choi, J. Am. Chem. Soc., 2006, 128,
10356–10357.
24 X. Liu, RSC Adv., 2011, 1, 1119–1125.
25 (a) X. Zhang, J. Song, J. Jiao and X. Mei, Solid State Sci., 2010,
12, 1215–1219; (b) M. Khairy and S. A. El Say, RSC Adv.,
2013, 3, 23801–23809.
26 (a) Y.-J. Lee, S. Kim, S.-H. Park, H. Park and Y.-D. Huh, Mater.
Lett., 2011, 65, 818–820; (b) N. D. Hoa and S. A. El-Say,
Nanotechnology, 2011, 22, 485503.
27 A. Goyal, A. Kumar, P. K. Patra, S. Mahendra, S. Tabatabaei,
P. J. J. Alvarez, G. John and P. M. Ajayan, Macromol. Rapid
Commun., 2009, 30, 1116–1122.
28 R. J. Good, M. K. Chaudhury and C. J. van Oss, Langmuir,
1988, 4, 884–891.
29 F. M. Fowkes, Ind. Eng. Chem., 1964, 56, 40–52.
30 R. M. Atlas, Handbook of microbiological media, CRC Press
LLC, New York, 3rd edn, 2004.
31 C. S. Piddington, B. R. Kovacevich and J. Rambosek, Appl.
Environ. Microbiol., 1995, 61/2, 468–475.
32 X. Sheng, Y. B. Ting and S. O. Pehkonen, Corros. Sci., 2007,
49, 2159–2176.
33 W. Hole Oceanographic Institution (WHOI), Marine Fouling
and its Prevention, United States Naval Institute, Annapolis,
Maryland, 1952.
34 G. F. Moore and S. M. Saunders, Advances in Biodegradable
Polymers, Smithers Rapra Technology Ltd, 1998.
35 G. C. Sonal, G. C. Sachin, P. R. Bhosale, D. B. Nakade and
P. D. Raut, Int. J. Environ. Sci., 2012, 2/3, 2435–2442.
36 E. Yilgör and I. Yilgör, Prog. Polym. Sci., 2014, 39, 1165–1195.
37 K. J. Wynne, G. W. Swain, R. B. Fox, S. Bullock and J. Uilk,
Biofuels, 2000, 16, 277–288.
38 R. T. Ragheb, M.Sc. thesis, Virginia Polytechnic Institute and
State University, 2005.
39 (a) S. A. El-Say, A. Shahat, W. Warkocki and M. Ohnuma,
Small, 2011, 7, 62–65; (b) S. A. El-Say, M. Mekway,
A. Yamaguchi, A. Shahat, K. Ogawa and N. Teramae, Chem.
Commun, 2010, 46, 3917–3919; (c) G. G. Bausch and
J. S. Tonge, Proc. Waterborne, High-Solids, Powder Coat.
Symp., 1996, 23, 340–353.
40 A. J. Chalk and J. F. Harrod, J. Am. Chem. Soc., 1965, 87, 16–
21.
41 (a) H. Sekhar and D. N. Rao, J. Nanopart. Res., 2012, 14, 976;
(b) S. A. El-Say, M. A. Shensahen and A. Shahat, Small, 2013,
9, 2288–2296.
42 (a) Y. Cao, Y. Xu, H. Hao and G. Zhang, Mater. Lett., 2014,
114, 88–91; (b) S. A. El-Say, M. Khairy, M. Ismael and
H. Kawarada, Appl. Catal. B Envir., 2012, 123–124, 162–173;
(c) M. Khairy, S. A. El-Say, M. Ismael and H. Kawarada,
Appl. Catal. B Envir., 2012, 127, 1–10.
43 H. Yang, J. Ouyang, A. Tang, Y. Xiao, X. Li, X. Dong and Y. Yu,
Mater. Res. Bull., 2006, 41, 1310–1318.
44 D. W. Goupil, V. A. DePalma and R. E. Baier, Presented at the
Marine Industries: Problems Opportunities, Washington,
D.C., 1973, unpublished.
45 M. Nosonovsky and B. Bhushan, J. Phys.: Condens. Matter,
2008, 20, 395005.
46 M. ˇSupov, G. S. Martynkov and K. Barabaszov, Sci. Adv.
Mater., 2011, 3, 1–25.
47 S. Bonhomme, A. Cuer, A.-M. Delort, J. Lemaire,
M. Sancelme and G. Scott, Degrad. Stab., 2003, 81/3, 441–452.
48 H. J. Lukasiak1, A. Dorosz, M. Prokopowicz, P. Rosciszewski
and B. Falkiewicz, Biodegradation of silicones
(organosiloxanes), in Biopolymers, Wiley, New York, 2002,
vol. 9, pp. 539–568.
49 P. Rosciszweewski, J. Lukasiak, A. Dorosz, J. Galinski and
M. Szponar, Macromol. Symp., 1998, 130, 337–346.
50 Y. Gao, M. J. van Belkum and M. E. Stiles, Appl. Environ.
Microbiol., 1999, 65, 4329–4333.
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