Nanostructured films of poly(o-ethoxyaniline) (POEA) were studied by atomic force microscopy (AFM), which indicated a globular morphology for films containing one or more layers of POEA. Consistent with the nucleation and growth model for the adsorption process, the mean roughness and fractal dimension were found to increase with the time of adsorption and with the number of POEA layers in the initial stages of adsorption, reached maximum values and then decreased after 10 min of adsorption or after deposition of five POEA layers. Such behavior has
been explained in terms of the decrease in the film irregularities, with voids being filled with polymeric material leading to smoother surfaces.
Ion exchange chromatography may be defined as a reversible reaction in which free mobile ions of a solids called ion exchange are exchanged for different ions of similar charge present in solution.....................................................................
Ion pair chromatography for pharmacy studentsabhishek rai
Ion-PairChromatography
A GENERALISED OVERVIEW
Chromatography
HPLC
Reverse Phase Chromatography
Ion Pair Chromatography
Ion Pair Reagent
Mechanism of Ion Pair Chromatography
Ion Pair Wash Procedure
Ion exchange chromatography may be defined as a reversible reaction in which free mobile ions of a solids called ion exchange are exchanged for different ions of similar charge present in solution.....................................................................
Ion pair chromatography for pharmacy studentsabhishek rai
Ion-PairChromatography
A GENERALISED OVERVIEW
Chromatography
HPLC
Reverse Phase Chromatography
Ion Pair Chromatography
Ion Pair Reagent
Mechanism of Ion Pair Chromatography
Ion Pair Wash Procedure
Principles of Ion -exchange chromatography, High performance liquid chromatography (HPLC) , chromatography generally stands for a technique which separates mixtures based on different dynamic sharing of their components between two distinct physio-chemical environments called mobile and stationary phase by repeated absorption/desorption steps. Ion chromatography (IC) is a member of large family of liquid phase
chromatographic methods (that is a mobile phase is a liquid and a stationary phase is a
solid).
Layer-by-layer (LbL) films have been produced with poly(o-ethoxyaniline) (POEA), chitosan and chitosan-poly(methacrylic acid) (CS-PMAA) nanoparticles. Because the adsorption of LbL films depends on ionic interactions and H-bonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick
films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles. These nanostructured films were deposited on chromium electrodes to form a sensor array (electronic tongue) based on impedance spectroscopy. This system was used to detect copper ions in aqueous solutions.
Suspensions of white and colored nanofibers
were obtained by the acid hydrolysis of white
and naturally colored cotton fibers. Possible differences
among them in morphology and other characteristics
were investigated. The original fibers were
subjected to chemical analysis (cellulose, lignin and
hemicellulose content), X-ray diffraction (XRD)
analysis, and scanning electron microscopy (SEM).
The nanofibers were analyzed with respect to yield,
elemental composition (to assess the presence of
sulfur), zeta potential, morphology (by scanning
transmission electron microscopy (STEM)) and
atomic force microscopy (AFM), crystallinity
(XRD) and thermal stability by thermogravimetric
analysis in air under dynamic and isothermal temperature
conditions. Morphological study of several
cotton nanofibers showed a length of 85–225 nm and
diameter of 6–18 nm. The micrographs also indicated
that there were no significant morphological differences
among the nanostructures from different cotton
fibers. The main differences found were the slightly
higher yield, sulfonation effectiveness and thermal
stability under dynamic temperature conditions of the
white nanofiber. On the other hand, in isothermal
conditions at 180 C, the colored nanofibers showed
a better thermal stability than the white.
Principles of Ion -exchange chromatography, High performance liquid chromatography (HPLC) , chromatography generally stands for a technique which separates mixtures based on different dynamic sharing of their components between two distinct physio-chemical environments called mobile and stationary phase by repeated absorption/desorption steps. Ion chromatography (IC) is a member of large family of liquid phase
chromatographic methods (that is a mobile phase is a liquid and a stationary phase is a
solid).
Layer-by-layer (LbL) films have been produced with poly(o-ethoxyaniline) (POEA), chitosan and chitosan-poly(methacrylic acid) (CS-PMAA) nanoparticles. Because the adsorption of LbL films depends on ionic interactions and H-bonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick
films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles. These nanostructured films were deposited on chromium electrodes to form a sensor array (electronic tongue) based on impedance spectroscopy. This system was used to detect copper ions in aqueous solutions.
Suspensions of white and colored nanofibers
were obtained by the acid hydrolysis of white
and naturally colored cotton fibers. Possible differences
among them in morphology and other characteristics
were investigated. The original fibers were
subjected to chemical analysis (cellulose, lignin and
hemicellulose content), X-ray diffraction (XRD)
analysis, and scanning electron microscopy (SEM).
The nanofibers were analyzed with respect to yield,
elemental composition (to assess the presence of
sulfur), zeta potential, morphology (by scanning
transmission electron microscopy (STEM)) and
atomic force microscopy (AFM), crystallinity
(XRD) and thermal stability by thermogravimetric
analysis in air under dynamic and isothermal temperature
conditions. Morphological study of several
cotton nanofibers showed a length of 85–225 nm and
diameter of 6–18 nm. The micrographs also indicated
that there were no significant morphological differences
among the nanostructures from different cotton
fibers. The main differences found were the slightly
higher yield, sulfonation effectiveness and thermal
stability under dynamic temperature conditions of the
white nanofiber. On the other hand, in isothermal
conditions at 180 C, the colored nanofibers showed
a better thermal stability than the white.
The existence of conducting islands in polyaniline
films has long been proposed in the literature, which
would be consistent with conducting mechanisms based on
hopping. Obtaining direct evidence of conducting islands,
however, is not straightforward. In this paper, conducting
islands were visualized in poly(o-ethoxyaniline) (POEA)
films prepared at low pH, using Transmission Electron Microscopy
(TEM) and atomic force spectroscopy (AFS). The
size of the islands varied between 67 and 470 Å for a
pH = 3.0, with a larger average being obtained with AFS,
probably due to the finite size effect of the atomic force microscopy
tip. In AFS, the conducting islands were denoted
by regions with repulsive forces due to the double-layer
forces. On the basis of X-ray diffraction (XRD) patterns for
POEA in the powder form, we infer that the conducting islands
are crystalline, and therefore a POEA film is believed
to consist of conducting islands dispersed in an insulating,
amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasione dimensional variable range hopping (VRH) mechanism.
Layer-by-layer (LbL) films have been produced with
poly(o-ethoxyaniline) (POEA), chitosan and chitosanpoly(
methacrylic acid) (CS-PMAA) nanoparticles. Because the
adsorption of LbL films depends on ionic interactions and Hbonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles.
Atomic force spectroscopy ~AFS! was used to measure interaction forces between the tip and nanostructured layers of poly~o-ethoxyaniline! ~POEA! in pure water and CuSO4 solutions. When the tip approach and retraction were carried out at low speeds, POEA chains could be physisorbed onto the Si3N4 tip
via nonspecific interactions.We conjecture that while detaching, POEA chains were stretched and the estimated
chain lengths were consistent with the expected values from the measured POEA molecular weight. The effects
from POEA doping could be investigated directly by performing AFS measurements in a liquid cell, with the
POEA film exposed to liquids of distinct pH values. For pH 6.0, the force curves normally displayed an
attractive region for POEA, but at lower pH values—where POEA is protonated—the repulsive double-layer
forces dominated. Measurements in the liquid cell could be further exploited to investigate how the film
morphology and the force curve are affected when impurities are deliberately introduced in the liquid. The
shape of the force curves and the film morphology depended on the concentration of heavy metal in the liquid
cell. AFS may therefore be used to study the interaction between film and analyte, with important implications
for the understanding of mechanisms governing the sensing ability of taste sensors.
The study and understanding of the structure and properties of styrene/vinylester (St/VE) and styrene/unsaturated polyester (St/UP) cross-linked thermosets has received technologic and scientific attention, because these resins are widely used as matrices in composites formulations, sharing advantages, such as low room temperature viscosity coupled with good mechanical properties and low cost, plus the added chemical resistance in the case of VE.
In this work, is presented the thermal behavior of polyaniline (PANI) and its derivatives poly(oethoxyaniline)
(POEA) and poly(o-methoxyaniline) (POMA), which were studied by using differential
scanning calorimetry (DSC), modulated DSC (TMDSC), respectively, and thermal gravimetric analysis
(TGA). The results from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and thermal
analysis showed the formation of crosslinking isomerization reaction during the heating process. The
results showed that the maximum weight loss and the crystallinity degree depend on the type of the
aromatic ring substituent group, i.e. hydrogen, ethoxy or methoxy.
Nanobiosensors can be built via functionalization of atomic force microscopy (AFM) tips with
biomolecules capable of interacting with the analyte on a substrate, and the detection being
performed by measuring the force between the immobilized biomolecule and the analyte.
The optimization of such sensors may require multiple experiments to determine suitable
experimental conditions for the immobilization and detection. In this study we employ molecular
modeling techniques to assist in the design of nanobiosensors to detect herbicides. As a proof
of principle, the properties of acetyl co-enzyme A carboxylase (ACC) were obtained with
molecular dynamics simulations, from which the dimeric form in an aqueous solution was
found to be more suitable for immobilization owing to a smaller structural fluctuation than
the monomeric form. Upon solving the nonlinear Poisson–Boltzmann equation using a
finite-difference procedure, we found that the active sites of ACC exhibited a positive surface
potential while the remainder of the ACC surface was negatively charged. Therefore, optimized
biosensors should be prepared with electrostatic adsorption of ACC onto an AFM tip
functionalized with positively charged groups, leaving the active sites exposed to the analyte.
The preferential orientation for the herbicides diclofop and atrazine with the ACC active site
was determined by molecular docking calculations which displayed an inhibition coefficient
of 0.168 mM for diclofop, and 44.11 mM for atrazine. This binding selectivity for the herbicide
family of diclofop was confirmed by semiempirical PM6 quantum chemical calculations which
revealed that ACC interacts more strongly with the herbicide diclofop than with atrazine,
showing binding energies of 119.04 and +8.40 kcal mol1, respectively.
This review article describes the fundamental principles of atomic force spectroscopy (AFS) and how this technique became a useful tool to investigate adhesion forces. AFS is a technique derived from atomic force microscopy (AFM) and can determine, at every location of the sample
surface, the dependence of the interaction on the probe–sample distance. AFS provides valuable information, at the nano-scale, such as, for example: (i) how the magnitude of the adhesion force depends on long- and short-range interactions and (ii) the tip–sample contact area. An overview about the theory and experiments with local force spectroscopy, force imaging spectroscopy, chemical
force microscopy and colloidal probe technique is presented. The many applications of the AFS technique for probing surface interactions open up new possibilities to evaluate adhesion, an important characteristic of materials.
In this study, the layer-by-layer technique is used to deposit nanostructured films exhibiting electrical
conductivity and magnetic behavior, from poly(o-ethoxyaniline) (POEA), sulfonated polystyrene (PSS) and
positively-charged maghemite nanoparticles. In order to incorporate the nanoparticles into the films,
maghemite nanoparticles, in the form of magnetic fluid, were added to POEA solutions, and the resulting
suspensions were used for film deposition. UV–Vis spectroscopy and atomic force microscopy images reveal
that POEA remains doped in the films, even in the presence of the maghemite nanoparticles, and its typical
globular morphology is also present. Electrical measurements show that a POEA/PSS film prepared from
POEA solution containing 800 μL of the magnetic fluid exhibits a similar conductivity to that of the control
film and, additionally, magnetic measurements indicated that nanosized maghemite phase was incorporated
within the polymeric film.
In this work, the synthetic hydroxyapatite (HAP) was studied using different preparation routes to decrease the crystal size and to study the temperature effect on the HAP nano-sized hydroxyapatite crystallization. X-ray diffraction (XRD) analysis indicated that all samples were composed by crystalline and amorphous phases . The sample with greater quantity of amorphous phase (40% of total mass) was studied. The nano-sized hydroxyapatite powder was heated and studied at 300, 500, 700, 900 and 1150 °C. All samples were characterized by XRD and their XRD patterns refined using the Rietveld method. The crystallites presented an anisotropic form, being larger in the [001] direction. It was observed that the crystallite size increased continuously with the heating temperature and the eccentricity of the ellipsoidal shape changed from 2.75 at 300 °C to 1.94, 1.43, 1.04 and 1.00 respectively at 500, 700, 900 and 1150 °C. In order to better characterize the morphology of the HAP the samples were also examined using atomic force microscopy (AFM), infrared spectrometry (IR) and thermogravimetric analysis (TGA).
The use of agrochemicals has increased considerably in recent years, and consequently, there has been increased exposure of ecosystems and human populations to these highly toxic compounds. The study and development of methodologies to detect these substances with greater sensitivity has become extremely relevant. This article describes, for the first time, the use of atomic force spectroscopy (AFS) in the detection of enzyme-inhibiting herbicides. A nanobiosensor based on an atomic force microscopy (AFM) tip functionalised with the acetolactate synthase (ALS) enzyme was developed and characterised. The herbicide metsulfuron-methyl, an ALS inhibitor, was successfully detected through the acquisition of force curves using this biosensor. The adhesion force values were considerably higher when the biosensor was used. An increase of ~250% was achieved relative to the adhesion force using an unfunctionalised AFM tip. This considerable increase was the result of a specific interaction between the enzyme and the herbicide, which was primarily responsible for the efficiency of the nanobiosensor. These results indicate that this methodology is promising for the detection of herbicides, pesticides, and other environmental contaminants.
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Au travers de cette présentation, vous y trouverez :
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The study of intermolecular interactions at interfaces is essential for a number of applications, in addition
to the understanding of mechanisms involved in sensing and biosensing with liquid samples. There are,
however, only a few methods to probe such interfacial phenomena, one of which is the atomic force
spectroscopy (AFS) where the force between an atomic force microscope tip and the sample surface is
measured. In this study, we used AFS to estimate adhesion forces for a nanostructured film of poly(oethoxyaniline)
(POEA) doped with various acids, in measurements performed in air. The adhesion force
was lower for POEA doped with inorganic acids, such as HCl and H2SO4, than with organic acids, because
the counterions were screened by the ethoxy groups. Significantly, the morphology of POEA both in the
film and in solution depends on the doping acid. Using small-angle X-ray scattering (SAXS) we observed
that POEA dissolved in amixture of dimethyl acetamide exhibits a more extended coil-like conformation,
with smaller radius of gyration, than for POEA in water, as in the latter POEA solubility is lower. In AFS
measurements in a liquid cell, the force curves for a POEA layer displayed an attractive region for pH 5
due to van der Waals interactions, with no contribution from a double-layer since POEA was dedoped. In
contrast, for pH 3, POEA was doped and the repulsive double-layer force dominated. With AFS one is
therefore able to correlate molecular-level interactions with doping and morphology of semiconducting
polymers.
Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray
scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in
particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly(o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated
annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology—seen with atomic force microscopy and transmission electron microscopy—that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.
Light Stabilization of Polypropylene: An Independent PerspectiveJim Botkin
A review of the photodegradation and light stabilization of polypropylene with an emphasis on thick section applications. Presented at the SPE International Polyolefins Conference, Houston, TX, February 2007.
OPTUM® Technology an innovative barrier solution for polypropylene-based mate...José Luis Feijoo
Ferro, a leading supplier of specialty plastics, has recently developed OPTUM® Barrier masterbatch for a wide range of polymers. This can be incorporated by melt processing in most of the manufacturing processes involved in the developing of single and multi-layer structures in flexible and rigid packaging. In particular this is suitable for food packaging applications in order to increase product protection and shelf-life. Barrier applications can be found, however, in other in market segments such as cosmetics, industrial containers and agricultural films, where barrier to oxygen and other gases is also critical.
The present paper describes the influence of the chemical structure of two aminoalkoxysilanes: 3-
aminopropyltriethoxysilane (APTS) and N-(3-(trimethoxysilyl)-propyl)-ethylenediamine (TSPEN) on the
morphology of thin layer hybrid films with phosphotungstic acid (HPW), a Keggin heteropolyanion. X-ray
photoelectron spectroscopy analyses indicated that both silane films showed protonated amine species interacting
with the heteropolyanion by electrostatic forces as well as the presence of secondary carbamate anions.
The hybrid films have different surface morphology according to atomic force microscopy analyses.
The hybrid film with TSPEN forms flatter surfaces than the hybrid film with APTS. This effect is ascribed to
higher flexibility and chelating ability of the TSPEN on adsorbed molecules. Ultrasonication effect on surface
morphology of the hybrid film with APTS plays a fundamental role on surface roughness delivering enough
energy to promote surface diffusion of the HPW heteropolyanions. This diffusion results in agglomerate formation,
which corroborates with the assumption of electrostatic bonding between the HPW heteropolyanions
and the protonated amine surface. These hybrid films could be used for electrochemical sensor
design or to build photochromic and electrochromic multilayers.
The accurate knowledge of the size distribution of
the soil clay particles (φ ≤ 2 μm) can improve the
understanding of the soil surface chemical processes,
which, in their turn, occur mainly in this smallest
sized fraction. However, there are few available
techniques for particle size evaluation at the
nanoscale.
In this work, the synthetic Hydroxyapatite (HAP)
was studied using different preparation routes to
decrease the crystal size and was studied the
temperature effect on the nano-sized hydroxyapatite
crystallization. X-ray diffraction (XRD) analysis
indicated the all samples were composed by a
crystalline HAP phase and another amorphous part.
A low-cost sensor array system for banana ripeness monitoring is presented. The sensors are constructed by employing a graphite line-patterning technique (LPT) to print interdigitated graphite electrodes on tracing paper and then coating the printed area with a thin film of polyaniline (PANI) by in-situ polymerization as the gas-sensitive layer. The PANI layers were used for the detection of volatile organic compounds (VOCs), including ethylene, emitted during ripening. The influence of the various acid dopants, hydrochloric acid (HCl), methanesulfonic acid (MSA), p-toluenesulfonic acid (TSA) and camphorsulfonic acid (CSA), on the electrical properties of the thin film of PANI adsorbed on the electrodes was also studied. The extent of doping of the films was investigated by UV-Vis absorption spectroscopy and tests showed that the type of dopant plays an important role in the performance of these low-cost sensors. The array of three sensors, without the PANI-HCl sensor, was able to produce a distinct pattern of signals, taken as a signature (fingerprint) that can be used to characterize bananas ripeness.
Atomic force spectroscopy, a technique derived from Atomic Force Microscopy (AFM), allowed us to distinguish nonspecific and specific interactions between the acetolactate synthase enzyme (ALS) and anti-atrazine antibody biomolecules and the herbicides imazaquin, metsulfuron-methyl and atrazine. The presence of specific interactions increased the adhesion force (Fadh) between the AFM tip and the herbicides, which made the modified tip a powerful biosensor. Increases of approximately 132% and 145% in the Fadh values were observed when a tip functionalized with ALS was used to detect imazaquin and metsulfuron-methyl, respectively. The presence of specific interactions between the atrazine and the anti-atrazine antibody also caused an increase in the Fadh values (approximately 175%) compared to those observed when using an unfunctionalized tip. The molecular modeling results obtained with the ALS enzyme suggest that the orientation of the biomolecule on the tip surface could be suitable for allowing interaction with the herbicides imazaquin and metsulfuron-methyl
Emeraldine-salt polyaniline form (ES-PANI) was chemically synthesized using hydrochloric acid at time
synthesis ranging from 0.5 to 48 h and characterized by X-ray diffraction (XRD), LeBail fit, Small-angle
X-ray diffraction (SAXD), Small-angle X-ray Scattering (SAXS) and Scanning Electron Microscopy
(SEM). Crystallinity and crystal data (a = 5.7122, b = 17.8393, c = 22.8027, a = 83.1575, b = 84.6971 and
c = 88.4419) were obtained by XRD and showed that the crystallinity did not vary with the time
synthesis. LeBail fit revealed that the crystallites were very small lamellae with global average size
around 39 Å. By SAXS it was obtained the particle Radius of Giration (Rg) of 320 Å. The maximum particle
size (Dmax) of 650 Å was obtained from the pair-distance distribution function (p(r)). SEM images showed
a fiber morphology formed by interconnected non homogeneous nanospheres. Electrical conductivity of
the samples was in 1.84 104 S/cm.
The immobilization of enzymes on atomic force microscope tip (AFM tip) surface is a crucial step in thedevelopment of nanobiosensors to be used in detection process. In this work, an atomistic modeling ofthe attachment of the acetyl coenzyme A carboxylase (ACC enzyme) on a functionalized AFM tip surface isproposed. Using electrostatic considerations, suitable enzyme–surface orientations with the active sitesof the ACC enzyme available for interactions with bulk molecules were found. A 50 ns molecular dynamicstrajectory in aqueous solution was obtained and surface contact area, hydrogen bonding and proteinstability were analyzed. The enzyme–surface model proposed here with minor adjustment can be appliedto study antigen–antibody interactions as well as enzyme immobilization on silica for chromatographyapplications.
A model HA-type polymer of para-benzoquinone synthetic humic acid (SHA) and its complexes with copper, iron and manganese metal ions were studied using atomic force microscopy (AFM). Natural humic acids (HA) and synthetic humic acids (SHA) were examined by fluorescence spectroscopy, which indicated similarity of SHA and HA spectra. The AFM images of SHA and its complexes revealed variable morphologies, such as small spheres, aggregates and a sponge-like structure. The SHA complexes displayed morphologies similar to those of natural HA. The presence of copper, iron and manganese ions led to the formation of aggregate-type structures in an apparent arrangement of smaller SHA particles.
The increasing importance of studies on soft matter and their impact on new
technologies, including those associated with nanotechnology, has brought intermolecular
and surface forces to the forefront of physics and materials science, for these are the
prevailing forces in micro and nanosystems. With experimental methods such as the atomic
force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition
to providing information on local material properties such as elasticity, hardness and
adhesion. This review provides the theoretical and experimental background of AFS,
adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution
This paper reports on the adsorption of an ultrathin chitosan layer on spin-coated films of cellulose,
where efficient attachment was induced by oxidizing cellulose which provided anionic sites for electrostatic
interaction with the positively charged chitosan. Both the cellulose oxidation and the chitosan
adsorption were confirmed with Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron
spectroscopy (XPS) measurements. The molecular-level interaction between chitosan and cellulose
involved the NAH groups, as inferred from the disappearance caused by chitosan adsorption of the amide
band at 1667 cm1 in the FTIR spectrum of cellulose. The XPS data confirmed a significant increase in the
atomic concentration of nitrogen groups, from 2.16% to 4.73% when chitosan was adsorbed on the oxidized
cellulose film, which also led to rougher films as illustrated by atomic force microscopy images.
One may now envisage applications in which the bactericide action of chitosan is combined with the biocompatibility
of cellulose
The interaction between poly(o-ethoxyaniline) (POEA) adsorbed onto solid substrates and humic substances
(HS) and Cu2+ ions has been investigated using UV–vis spectroscopy and atomic force microscopy
(AFM). Both HS and Cu2+ are able to dope POEA and change film morphology. This interaction was
exploited in a sensor array made with nanostructured films of POEA, sulfonated lignin and HS, which
could detect small concentrations of HS and Cu2+ in water.
Chemical sensors made from nanostructured films of poly(o-ethoxyaniline) POEA and poly(sodium 4-styrene sulfonate) PSS are produced and
used to detect and distinguish 4 chemicals in solution at 20 mM, including sucrose, NaCl, HCl, and caffeine. These substances are used in order to
mimic the 4 basic tastes recognized by humans, namely sweet, salty, sour, and bitter, respectively. The sensors are produced by the deposition of
POEA/PSS films at the top of interdigitated microelectrodes via the layer-by-layer technique, using POEA solutions containing different dopant
acids. Besides the different characteristics of the POEA/PSS films investigated by UV–Vis and Raman spectroscopies, and by atomic force
microscopy, it is observed that their electrical response to the different chemicals in liquid media is very fast, in the order of seconds, systematical,
reproducible, and extremely dependent on the type of acid used for film fabrication. The responses of the as-prepared sensors are reproducible and
repetitive after many cycles of operation. Furthermore, the use of an “electronic tongue” composed by an array of these sensors and principal component analysis as pattern recognition tool allows one to reasonably distinguish test solutions according to their chemical composition.
Foram investigadas as interações entre os pesticidas atrazina, imazaquin, metribuzin e paraquat com o polímero condutor poli-(o-etoxianilina)-POEA, utilizando-se as técnicas de microscopia de força atômica (AFM), espectrofotometria de ultravioleta visível (UV-Vis) e
espectroscopia de impedância eletroquímica. Os estudos de microscopia de força atômica em filmes automontados mostraram um aumento na rugosidade do filme polimérico, quando exposto aos pesticidas atrazina, imazaquin e metribuzin e uma diminuição na rugosidade do filme
polimérico exposto ao pesticida paraquat. Isso evidencia a existência de interação química, provavelmente, ligação iônica entre o nitrogênio presente na POEA e os grupos presentes nos pesticidas estudados. Os estudos de ultravioleta visível mostraram uma maior interação entre a
POEA e o pesticida imazaquin. Por meio de medidas elétricas realizadas (espectroscopia de impedância eletroquímica) com um sensor formado por filme de POEA, foi possível distinguir e determinar o limite de detecção dos pesticidas em solução aquosa, o que corrobora com os estudos por AFM e UV-Vis.
Nanometric TiO2 powders were obtained from low tem-perature calcination of a TiO2 resin prepared using the Pechini’s method. Firing the TiO2 resin at 500 oC/2h a powder with anatase phase was obtained, otherwise firing the TiO2 resin at 700 oC/2h a powder with rutile phase was achieved as measured by X-ray diffraction (XRD). The anatase powder presented average particle size of 60 nm observed by Scanning Electronic Microscopy (SEM-FEG) micrographs and average crystallite size of 13 nm calcu-lated from the XRD, while the rutile powder presented av-erage crystallite size of 34 nm. Nanocrystalline TiO2 films with good homogeneity and optical quality were obtained with 80 nm and 320 nm in thickness by Electron Beam Physical Vapour Deposition (EB-PVD) in vacuum on amorphous quartz substrates submitted at 350oC during the evaporation. The 80 nm-thick film presented average particle size of 140 nm and roughness (Ra) of 1.08 nm and the 320 nm-thick film showed average particle size of 350 nm and roughness (Ra) of 2.14 nm measured by Atomic Force Microscopy (AFM). In these conditions of deposi-tion the films presented only anatase phase observed by XRD and MicroRaman spectroscopy.
The fabrication of nanostructured layer-by-layer (LbL) films strives for molecular control of the film properties directly connected with modifications in the film architecture. In the present report, the photoinduced birefringence and formation of the surface-relief gratings in LbL films obtained with an azopolymer (PS119) are shown to be strongly affected by the generation of the dendrimer employed in the alternating layers. Stronger adsorption of PS119 occurred when polypropylenimine tetrahexacontaamine dendrimer (DAB) of higher generations is used, due to a larger number of sites available to interact with azochromophores in PS119. In contrast, the photoinduced birefringence for LbL films
made with the generation 1 dendrimer (DABG1) was higher, which can be explained by weaker interactions between
adjacent layers. Strong interactions in LbL films consisting of PS119 and generation 3 or 5 dendrimers restrict the
chromophore mobility, leading to a smaller birefringence. The interpretation is supported by the fact that surface-relief gratings with larger amplitudes were obtained for 35-bilayer films of DABG1/PS119 (31 nm) in comparison with films from DABG5/PS119 (5 nm). These gratings were formed with mass transport arising from a light-driven mechanism, as photoinscription was successful only with p-polarized light and not with s-polarized light.
Atomic force microscopy (AFM) was used to study the nanoscale surface chemistry and morphological
changes caused by chemical treatment of sisal fibers. Scanning Electron Microscopy (SEM)
micrographs indicated that sisal. The adhesion
force (pull-off force) between the AFM tip and the fibers surface increased after benzylation,
pointing to a decrease in the polar groups on the sisal fiber.
In attempts to reduce cost and increase sensitivity of taste sensors we have found out that a novel, inexpensive set of chrome-deposited electrodes may be used in impedance spectroscopy measurements for sensing with great performance. High sensitivity is demonstrated by detecting, reproducibly, M amounts of NaCl, HCl, sucrose, which represent basic tastes, and Cu2+ ions. This
high sensitivity can also be used to distinguish complex liquids such as wines.
More from Grupo de Pesquisa em Nanoneurobiofisica (17)
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
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Study on the adsorption of poea nanostructured films using afm
1. Study on the adsorption of poly(o-ethoxyaniline)
nanostructured films using atomic force microscopy
F.L. Leite a,b
, L.G. Paterno b
, C.E. Borato a,b
, P.S.P. Herrmann b
,
O.N. Oliveira Jr a
, L.H.C. Mattoso b,
*
a
Instituto de Fı´sica de Sa˜o Carlos, USP, CP 369, 13560-970, Sa˜o Carlos, SP, Brazil
b
Embrapa Instrumentac¸a˜o Agropecua´ria, CP 741, 13560-970, Sa˜o Carlos, SP, Brazil
Received 17 March 2005; received in revised form 24 June 2005; accepted 7 July 2005
Abstract
Nanostructured films of poly(o-ethoxyaniline) (POEA) were studied by atomic force microscopy (AFM), which indicated a globular
morphology for films containing one or more layers of POEA. Consistent with the nucleation and growth model for the adsorption process, the
mean roughness and fractal dimension were found to increase with the time of adsorption and with the number of POEA layers in the initial stages
of adsorption, reached maximum values and then decreased after 10 min of adsorption or after deposition of five POEA layers. Such behavior has
been explained in terms of the decrease in the film irregularities, with voids being filled with polymeric material leading to smoother surfaces.
q 2006 Elsevier Ltd. All rights reserved.
Keywords: Poly(o-ethoxyaniline); Adsorption; Atomic force microscopy
1. Introduction
Nanostructured films of conducting polymers have been
extensively investigated as they can be used in a variety of
applications, including sensors, optical storage, charge storage
and electrochromic devices [1]. These films may be obtained
with techniques such as the Langmuir-Blodgett (LB) [2] or the
layer-by-layer method (LbL) [3], which offer precise control of
thickness and molecular architecture. In the LbL films,
polymer adsorption is in most cases driven by ionic
interactions, with oppositely charged materials from aqueous
solutions being deposited alternately on a solid substrate.
Secondary interactions—e.g. hydrogen bonding—may also be
important for adsorption [4], as it has been shown for
polyanilines, for which H-bonding contributes even when
the molecules are protonated [5]. One consequence of the
adsorption governed by H-bonding is that multilayers of the
same material may be deposited on the same substrate, leading
also to the so-called non-self-limiting adsorption [6]. The layer
thickness can therefore be controlled by altering the
interactions responsible for adsorption, which is carried out
by changing materials and experimental conditions such as pH,
ionic strength and concentration of the solutions. For parent
polyaniline and derivatives, for instance, film properties may
vary widely due to the interplay of the adsorption mechanisms
[5], and therefore a thorough analysis of the capabilities of LbL
films requires use of several characterization techniques.
Because LbL are essentially surface films, one method that
has proven suitable for characterization is the scanning force
microscopy, especially the atomic force microscopy (AFM)
[7]. From AFM results, a number of features of LbL films of
polyanilines could be captured not only in terms of the film
properties but also of the adsorption mechanisms. For
protonated (doped) polyanilines, ionic interactions made it
possible to assemble LbL films with various water-soluble
polyanions, including sodium polystyrene sulfonate [8] and
sodium polyvinyl sulfonate [4]. Undoped polyaniline was
assembled with the nonionic water soluble polymers poly(-
vinylpyrrolidone), poly(vinyl alcohol), poly(acrylamide) and
poly(ethylene oxide) [4]. In other cases, ionic interactions and
H-bonding were found to coexist during polymer adsorption,
which depended on the pH of the solution [5]. At pHO5, for
both poly(o-methoxyaniline) (POMA) and poly(o-ethoxyani-
line) (POEA), adsorption was attributed entirely to H-bonding
since the polymers were not expected to be charged [6]. In fact,
through H-bonding POMA and POEA layers could be
adsorbed onto already deposited POMA (or POEA), with no
Polymer 46 (2005) 12503–12510
www.elsevier.com/locate/polymer
0032-3861/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2005.07.108
* Corresponding author. Tel.: C55 16 3374 2477; fax: C55 16 3372 5958.
E-mail address: mattoso@cnpdia.embrapa.br (L.H.C. Mattoso).
2. 400 500 600 700 800 900 1000
0.000
0.005
0.010
0.015
0.020
0.025
0.030
600s
180s
10s
ABS
λ(nm)
10 s
1800 s
time
1800s
(g)
Fig. 1. AFM images of POEA films produced from a pH 3 solution for distinct immersion times. (a) 0.0 min (i.e. bare glass); (b) 0.5 min; (c) 1.0 min; (d) 3.0 min; (e)
10.0 min; (f) 30.0 min. In (g) are shown the spectra with increasing absorption for increasing immersion times, from 10 up to 1800 s. Some of the curves are labeled
with the corresponding immersion time.
F.L. Leite et al. / Polymer 46 (2005) 12503–1251012504
3. intercalating polymer layer, and even reaching the nonself-
limiting process where the polymer layer grows indefinitely
[6].
The kinetics of adsorption of POMA layers has been found
to consist of a two-step process. The first, fast process is due to
nucleation while the second is attributed to a growth
mechanism described with a Johnson–Mehl–Avrami function
[9]. This is consistent with the proposal of Lvov and Decher
[10], who stated that the adsorption of polyelectrolytes is based
on two distinct stages: in the first, some polymeric segments are
anchored to the substrate, while in the second such anchored
segments serve as nucleation sites for additional polymer
adsorption. Saturation of adsorption is a result of the
equilibrium between the number of occupied sites and
the electrostatic repulsion between the ionized groups of the
polymer chains.
In this paper, we analyze the morphology and adsorption
processes for POEA layers using AFM images. Parameters
such as roughness, relative surface coverage and fractal
dimension are used to interpret the data. The analysis of
surface roughness, for instance, enables one to describe
theoretically and quantitatively real surfaces, especially at the
short-length scales [11,12].
2. Experimental section
POEA was chemically synthesized according to the method
described in Ref. [13]. The polymer obtained is a dark
precipitate, with expected weight average molecular weight
(Mw) of w41,400 g molK1
and polydispersity (Mw/Mn) of 2.3
[13]. Polymeric solutions were prepared by dissolution of
POEA in a mixture of HCl and ultra-pure water, 1:49 v/v, under
constant stirring for 18 h. The final concentration of polymer
was 0.5!10K3
mol LK1
and the pH of each solution was
adjusted to 3 by adding 0.1 M HCl solution. Substrates were
prepared with glass slides (10!10!1 mm) previously cleaned
in H2SO4/H2O2, 7:3 v/v solutions for 1 h, followed by
extensive washing in ultra-pure water. The slides were then
immersed into a H2O/H2O2/NH4OH 5:1:1 v/v solution for
40 min and again washed with large amounts of ultra pure
water. Here, we have studied two types of film. In the first one
single layer is adsorbed onto glass slides by immersing the
slides into the POEA solution for a given period of time, which
was varied to investigate the adsorption kinetics. After
adsorption, the film/substrate system was washed in an aqueous
solution of same pH and dried with a gentle nitrogen flow. In
the second set of samples, up to 10 POEA layers were adsorbed
on the same substrate by repeating the procedure above, with
no intercalating layers. Even though POEA was charged,
deposition of further POEA layers was made possible because
of H-bonding, as discussed above. The growth of the POEA
layers was monitored by measuring the UV–vis absorption
with a UV–vis spectrophotometer Shimadzu UV-1601 PC.
AFM images were taken in a Topometrix microscope,
model Explorer TMX 2010, using silicon nitride tips (V shape)
with spring constant of 0.09 N/m. Roughness and surface
fractal dimension were calculated using WS!M 4.0 software
from Nanotec Electronica S.L. (copyrightq
November 2003)
and scanning probe image processor (SPIP) version 3.1.0.1
from Image Metrology A/S 2003. All images were obtained in
the contact mode at a scan rate of 2 Hz.
3. Results and discussion
The LbL technique allows film production within short time
intervals, and therefore it is important to evaluate the kinetics
of polymer adsorption in order to optimize the time of film
fabrication. A few minutes are usually sufficient to form a
stable and continuous layer of different kinds of materials [8,
14]. Here, we shall describe the evolution of POEA film
morphology using AFM. Fig. 1 displays AFM images of a
POEA layer adsorbed at different time intervals at pH 3 on a
glass substrate. In general, the morphology of a POEA film is
characterized by small globules, ranging from 20 to 100 nm in
diameter. The number of globules increases with the time of
immersion and then reaches saturation as the substrate is
entirely coated. Since we used a pHZ3 for the POEA solution,
there should be considerable repulsion as POEA is positively
charged. The surface of POEA is expected to reflect both the
long-range morphology due to the existence of globules, and
the short-range morphology corresponding to the region inside
the globules. The last term may be dominant for thicker films
(two or more layers) [15]. The increase in the amount of
adsorbed POEA with increasing times is indicated in the
increased absorption in the UV–vis spectra of Fig. 1(g).
The evolution with time of the number of globules
(average and maximum) is depicted in Fig. 2, which basically
increases during the first minutes of adsorption and then
decreases for longer times. Before 1 min of adsorption, the
nucleation process appears to be complete, being followed by
the gradual growth of the globules without creation of new
sites. The radial growth of globules occurs as a result of the
incorporation of new polymeric chains. Finally, coalescence
101
5
10
15
20
Nucleation
Growth and Coalescence
N(10E3)
Immersion time (min.)
average number of islands
maximum number of islands
3
Aggregation
Coalescence
Fig. 2. Average and maximum number (N) of globules vs. time of immersion of
the substrate in the POEA solution. Taken from AFM images for 1 mm2
area.
F.L. Leite et al. / Polymer 46 (2005) 12503–12510 12505
4. of globules leads to a decrease in their number, these results
are according with those presented in the literature for
monolayers of octadecylphosphonic acid on mica [16]. The
size of the globules increases with time from 20 nm in the
initial stages up to 100 nm at 3 min of adsorption. It then
tends to decrease after 10 min. These conclusions were based
on images obtained from three distinct spots of the same
sample. Note that these measurements were taken for POEA
films in air. The morphology of the film as it is deposited, in
contact with the POEA solution, is different because the
domains tend to be larger, probably due to swelling of the
polymer chains [17].
In Fig. 3(a) we depict a possible model for thin film growth,
which includes nucleation, aggregation and coalescence
processes—with the corresponding AFM images for a POEA
film in Fig. 3(b). The rationale is based on a computer
simulation model according to which polymer molecules
adsorb from the bulk at a rate R and then suffers a 2D random
walk on the surface with a surface diffusion constant D [18].
Collisions between these (2D) diffusing molecules result in the
formation of clusters or globules, which then grow due to
the accumulation of additional material [19]. With diffusion,
the nucleus not only grows from its initial position but also
triggers the formation of other, smaller nuclei, with the
morphology becoming flatter. The process of growth and
coalescence depends largely on the diffusion rate. If D is large,
molecules adsorbed on the surface will probably collide with
existing globules. If R is large, there will also be the formation
of large globules. Consistent with this explanation is the
observation that the growing globules are compact in shape
instead of fractal and this implies that desorption from globules
and rearrangement into more favorable configuration occurs
after than 10 min of adsorption.
The images shown in Fig. 3(b) bring only some
snapshots of the growth process. In the upper image,
corresponding to the initial stage of growth, a number of
scattered domains are seen, which is consistent with a
nucleation regime. Considering other images (not shown),
we know that this regime lasts up to ca. 60 s. For
immersion times higher than 60 s and up to ca. 180 s,
aggregation is observed, as can be seen in the image in the
middle of Fig. 3(b), where the substrate is practically fully
covered. Coalescence occurs for longer periods of immer-
sion, which is denoted by a smaller number of larger
domains.
Another important issue in the POEA film formation is the
change in roughness with the time of adsorption. The simplest
way to characterize the surface roughness is to determine the
roughness parameters RMS (root-mean-square average) and Ra
(arithmetic average). Both are functions of the height deviation
Fig. 3. (a) Typical model of progressive nucleation, growth and coalescence; (b) AFM images of POEA on muscovite mica for initial, intermediate and final stages of
adsorption.
F.L. Leite et al. / Polymer 46 (2005) 12503–1251012506
5. from the mean surface level, as follows:
RMS Z
1
N
XN
iZ1
Z2
i
" #1=2
(1)
and
Ra Z
1
N
XN
iZ1
jZij (2)
where N is the number of data points and Zi is the distance from
the mean surface level.
The mean surface level is defined as a reference, being
parallel to the general direction of the profile within the limits
of the sampling length, such that the sum of the areas contained
between this line and those parts of the profile that lie on either
side are equal [20]. Fig. 4 shows that the roughness tends to
increase with the time of adsorption and then reaches a
maximum at 10 min. For longer periods, there is a small
decrease and the roughness stabilizes after 20 min. In the first
minutes of adsorption, the glass surface is covered with few
globules and consequently, the roughness, which is basically
the ratio between the height of ‘peaks’ and ‘valleys’ on the
sample surface, is rather large. As the number of globules
increases the roughness becomes a result of the presence of
POEA film exclusively, and therefore, it tends to reach a
constant value, higher than the bare glass. The small decrease
in roughness with the time of adsorption can be related to
rearrangements of polymeric chains and globules on the film
surface [21]. At longer times, the polymeric chains are able to
assume more favorable conformations, which usually tend to
be flatter in consequence of the surface energy minimization.
The same has been observed in other polyelectrolyte systems,
where the surface morphology becomes more compact as the
time of adsorption increases [16].
For a globular morphology as observed for the POEA films
the concept of fractals is useful for the description of the
irregularities on the film surface. Fractal geometry is a branch
of mathematics that describes disordered objects using
fractional dimensions. The dimension of Euclidian geometry
are given as the integers 0, 1, 2, and 3 corresponding to dots,
lines, planes, and 3D bodies, respectively [22]. This
classification, however, is inadequate for the irregular shapes
of numerous natural and artificial geometrical objects. One can
intuitively assign intermediate dimensional values to such
objects. A fractal is a measure of how ‘complicated’ a self-
similar figure values to such objects and determine the relative
amounts of the surface irregularities for different distance
scales [23]. In a rough sense, it measures ‘how many points’ lie
in a given set and is characterized by a scaling law such as
Llwl1Kf
is the value of the curve measured with the unit l and
f is the fractal dimension. The fractal dimension can be
experimentally evaluated through the Minkowski dimension.
In this work, though, f was estimated using a different
approach, taking into account that an intersection of a plane
with a self-similar or a self-affine fractal surface generates self-
similar lakes (with less materials). This approach is depicted in
Fig. 5, where the voids in the image of a POEA film are ‘filled’
until a certain level. The perimeter L and the area A of the lakes
formed were estimated with the WS!M 4.0 software and
using the relation LZaf0
Af0
/2
, where a is a constant and f0
ZfK
1 is the fractal dimension of the void perimeter. In order to
avoid errors in the fractal dimension measurements, several
height thresholds were analyzed, varying G3 nm, from which
the f0
values were obtained independently of the surface depth.
We have used for ‘filling’ of the void volumes a height value
corresponding to 50% of the maximum height for each image.
Fig. 5. AFM images of POEA (2!2 mm) showing (a) topography and (b)
topography with the empty spaces assumed to be filled.
0 3 6 9 12 15 18 21 24 27 30 33
0
1
2
3
4
5
6
7
Ra
RMS
Immersion Time (min.)
Ra
1
2
3
4
5
6
RMS
Fig. 4. Roughness vs. immersion time for 1 mm2
area.
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
1.256
1.264
1.272
1.280
1.288
1.296
1.304
1.312
1.320
1.328
RSC
f
Immersion time (min.)
Relativesurfacecoverage
2.0
2.5
3.0
3.5
4.0
FractalDimension
Fig. 6. Fractal dimension (f) and relative surface coverage (RSC) for POEA on
glass vs. immersion time.
F.L. Leite et al. / Polymer 46 (2005) 12503–12510 12507
6. The variation of this level does not significantly affect the final
results.
Fig. 6 displays how f and relative surface coverage (RSC)
for POEA films varies with the immersion time. The RSC
which is represented by the ratio between the RMS and Ra, is
also presented. If the height ratio is x and the degree of
coverage with smaller globules is q, then we can express the
RMS/Ra ratio as [15]:
RMS
Ra
Z
½x2
ð1KqÞ CqŠ1=2
xð1KqÞ Cq
(3)
The fractal dimension f remains between 2 and 3. Since fZ2
for a Euclidian surface, an increase above 2 means an increase
in film roughness. The highest value for f is observed at 10 min
of adsorption. The coverage factor is stabilized after 10 min of
adsorption which means that the surface is covered with a
continuous film right after equilibrium between adsorption and
desorption. With the increase in immersion time up to 30 min,
the fractal dimension is approximately 2.6. Generally, if a
surface is sufficiently flat, both RMS and RA roughness are
similar. However, if a surface is rather rough containing a
considerable number of islands and voids, the value of RMS is
larger than RA. Indeed, for 1 min of adsorption a greater value
of f is observed, i.e. there are more irregularities at this stage. In
fact, few sites on the glass surface are occupied with POEA
globules at this time; as the adsorption continues, more sites are
occupied and the coverage of the surface with POEA film
increases.
For immersion times up to 10 min a slight decrease of fractal
dimension is accompanied by a considerable change (increase)
in the RSC due to the characteristic flatness of surface and
more polymers chains adsorbed after 10 min. The surfaces of
these irregularities are not taken into account in the calculation
of ‘real’ surface areas. To a certain extent this is confirmed by
comparison of fractal dimension values for the same film
obtained for different scan lengths (Fig. 7). The results show
that the fractal dimension of the sample increases with the scan
length and smaller immersion times. For long immersion times,
e.g. 30 min, the film exhibits a self-similar behavior with
almost no change in f with the scan length being varied by 1–2
orders of magnitude. However, for shorter immersion times,
Fig. 8. AFM images of POEA in pHZ3 for distinct number of layers. (a) Glass surface; (b) one layer; (c) three layers; (d) five layers; (e) seven layers and (f) nine
layers.
1000 2000 3000 4000 5000
2.34
2.36
2.38
2.40
2.42
2.44
2.46
2.48
2.50
2.52
2.54
2.56
2.58
2.60
FractalDimension
Scan Length (nm)
0.5 Min.
3 Min.
30 Min.
Fig. 7. Fractal dimension for distinct immersion times vs. scan length (one
layer).
F.L. Leite et al. / Polymer 46 (2005) 12503–1251012508
7. Fig. 7 indicates that distinct morphologies are observed at
different length scales.
We have also investigated the morphology of films
containing more layers of POEA, with the multilayer being
produced by successive immersion of a glass slide into the
POEA solution during 3 min. After each immersion, the
deposited film was washed in aqueous solution of the same pH
and dried with nitrogen flow. Fig. 8 presents AFM images for
films containing different numbers of POEA layers, indicating
a globular morphology in all cases. This result is in agreement
with the model proposed for POEA adsorption, where small
nuclei are first adsorbed and then serve as nucleation sites for
further polymer deposition. For multilayer films of POEA
alternated with sulfonated lignin (SL) layers, however, the
globular morphology is absent when SL is adsorbed on top of
POEA layers. In fact, the surface roughness for LbL films of
POEA and SL depends on the topmost layer, since the films are
much rougher when POEA is the top layer in comparison to
those with SL in the top layer [24].
With a globular morphology, regardless of the number of
POEA layers, one could expect a continuous increase in
surface roughness. However, this expectation is not fulfilled, as
indicated in Fig. 9. The roughness is related to the presence of
islands and voids on the substrate surface. For the first POEA
layers, the roughness increases, since the flat surface of glass
exhibits a very low roughness when compared to POEA layers.
However, as the number of POEA layers increases, the voids
from a previous layer are filled with the additional POEA and
as a consequence the surface roughness tends to decrease.
Fig. 10 shows f increasing with the number of POEA layers
deposited, until five layers, and then decreasing. Analogously
to the roughness, at the first layers deposited a greater number
of irregularities appear. With additional layers, such irregula-
rities are filled with polymeric material and the film surface
tends to be flatter, i.e. the fractal dimension tends toward 2. In
the 3D growth, the growth rates of nuclei are essentially equal
or comparable in the direction perpendicular to the substrate
surface. However, in the 2D growth, the nuclei grow more
quickly in the parallel direction than in the perpendicular
direction until they meet each other and overlap.
4. Conclusions
Layer-by-layer films of poly(o-ethoxyaniline) POEA were
studied by AFM and morphological parameters such as grain
size, roughness, fractal dimension and relative surface coverage
were evaluated. Overall, a globular morphology was observed,
typical of a nucleation adsorption process, where the first
polymer chains are anchored to the substrate and serve as nuclei
for further polymer adsorption. The roughness of the layers
increases within the first minutes reaches a maximum value and
then remains constant after 20 min of adsorption. At the
beginning, few globules are adsorbed and therefore the
roughness is large. As the adsorption continues, the voids
between globules are filled with more polymeric material and
consequently roughness decreases. We find that the kinetics
theory, developed to explain thin film growth, provides a
qualitative explanation of the time dependence of island
nucleation and growth in the late-growth regime and also the
island density in the aggregation regime. A similar behavior is
observed for the fractal dimension, which increases for the first
minutes of adsorption and then tends towards an average value
between 2 and 3. For the multilayer films, the globular
morphology appears for all the POEA layers deposited. Film
roughness increases up to five layers and then decreases as the
number of POEA layers deposited increases. The irregularities,
such as voids and islands, are constantly filled with polymeric
material and the film surface becomes smoother. The fractal
dimension behaves in the same manner, reaching its maximum
with five layers and then decreasing to a value between 2 and 3,
typical of a planar surface containing irregularities. The study of
polymer adsorption by atomic force microscopy is of key
importance to understand the adsorption mechanism and surface
properties of thin film produced by layer-by-layer deposition.
Acknowledgements
Financial assistance from CNPq, CNPq/CT-Hidro,
IMMP/MCT, FAPESP, Rede Nanobiotec/CNPq/MCT (Brazil)
is gratefully acknowledged.
0 1 2 3 4 5 6 7 8 9 10
0
1
2
3
4
5
6
7
8
9
10
Roughness(nm)
Number of layers
Ra
RMS
Fig. 9. Roughness vs. number of layers for POEA.
0 1 2 3 4 5 6 7 8 9 10
2.50
2.55
2.60
2.65
2.70
2.75
2.80
Number of Layers
FractalDimension(f)
115
120
125
130
135
140
145
150
155
160
sizeofglobules(nm)
Fig. 10. Fractaldimensionandsizeoftheglobulesvs.numberoflayersforPOEA.
F.L. Leite et al. / Polymer 46 (2005) 12503–12510 12509
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