Highly corrosion resistant siloxane-polymethyl methacrylate hybrid coatings

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Aqueous solution behavior of thermosensitive (N-isopropylacrylamide-acrylic acid-ethyl methacrylate) terpolymers

A series of N-isopropylacrylamide (NIPAM)-acrylic acid-ethyl methacrylate terpolymers with varied monomer compositions was prepared by radical polymerization. The solution behavior of these polymers was studied in dilute aqueous solution using spectrophotometry, fluorescence spectroscopy and high-sensitivity differential scanning calorimetry. The results obtained revealed that the lower critical solution temperatures depend strongly on the copolymer composition, solution pH and ionic strength. At a high pH, the ionization of acrylic acid (AA) units leads to an increase in solution cloud points (T-c). Solutions of polymers containing 10% or less of AA display a constant T-c for pH above 5.5, with 15% there is a continuous increase in T-c with pH and, for higher AA contents, no clouding was observed within the studied temperature range. Fluorescence probe studies were conducted by following the I (1)/I (3) ratio of pyrene vibronic bands and the emission of anilinonaphtalene sulfonic acid, sodium salt (ANS), both approaches revealing the existence of hydrophobic domains for polymers with higher ethyl methacrylate content at temperatures lower than T-c, suggesting some extent of aggregation and/or a coil-to-globule transition. Scanning calorimetry measurements showed an endothermic transition at temperatures agreeing with the previously detected cloud points. Moreover, the transition curves became broader and with a smaller transition enthalpy, as both the AA content and the solution pH were increased. These broader transitions were interpreted to be the result of a wider molecular distribution upon polymer ionization, hence, displaying varied solution properties. The decrease in transition enthalpy was rationalized as a consequence of reminiscent hydration of NIPAM units, even after phase separation, owing to the presence of electric charges along the polymer chain.

Improvement of the corrosion resistance of polysiloxane hybrid coatings by cerium doping

Polysiloxane hybrid films were deposited on stainless steel by dip-coating using a sol prepared by hydrolytic co-polycondensation of tetraethoxysilane (TEOS) and 3-methacryloxy propyltrimethoxysilane (MPTS), followed by radical polymerization of methacrylic moieties. The TEOS/MPTS ratio was chosen equal to 2 and the Ce/Si ratio varied between 0.01 and 0.1. The effects of cerium concentration and valence (Ce(III) and Ce (IV)) on the structural features of polysiloxane films were studied by X-ray photoelectron spectroscopy (XPS) and (29)Si nuclear magnetic resonance (NMR). The corrosion protection of stainless steel by the hybrid coatings was investigated by XPS, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves, after immersion in saline and acid solutions. The NMR results have shown for Ce(IV) doped films a high degree of polycondensation of up to 89%. Electrochemical analysis has evidenced that hybrid films with the lowest Ce concentration act as an efficient diffusion barrier by increasing the corrosion resistance and reducing the current densities up to 3 orders of magnitude compared to bare stainless steel. The analysis of structural effects induced by Ce(III) and Ce(IV) species, performed by XPS, indicates that the improved corrosion protection of Ce(IV) doped films might be mainly related to the enhanced polymerization of siloxane groups. (C) 2010 Elsevier B.V. All rights reserved.

Application of Polysaccharide Hydrogels in Adsorption and Controlled-Extended Release of Fertilizers Processes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Corrosion protection of stainless steel by polysiloxane hybrid coatings prepared using the sol-gel process

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Carbon nanotube-reinforced siloxane-PMMA hybrid coatings with high corrosion resistance

Siloxane-polymethyl methacrylate hybrid films containing functionalized multiwall carbon nanotubes (CNTs) were deposited by dip-coating on carbon steel substrates from a sol prepared by radical polymerization of methyl methacrylate and 3-methacryloxy propyl-trimethoxysilane, followed by hydrolytic co-polycondensation of tetraethoxysilane. The correlation between the structural properties and corrosion protection efficiency was studied as a function of the molar ratio of nanotubes carbon to silicon, varied in the range between 0.1% and 5%. 29Si nuclear magnetic resonance and thermogravimetric measurements have shown that hybrids containing carbon nanotubes have a similar degree of polycondensation and thermal stability as the undoped matrix and exhibit and excellent adhesion to the substrate. Microscopy and X-ray photoelectron spectroscopy results revealed a very good dispersion of carbon nanotubes in the hybrid matrix and the presence of carboxylic groups allowing covalent bonding with the end-siloxane nodes. Potentiodynamic polarization curves and electrochemical impedance spectroscopy results demonstrate that CNTs containing coatings maintain the excellent corrosion protection efficiency of the hybrids, showing even a superior performance in acidic solution. The nanocomposite structure acts as efficient corrosion barrier, increasing the total impedance by 4 orders of magnitude and reducing the current densities by more than 3 orders of magnitude, compared to the bare steel electrode. © 2013 Elsevier B.V. All rights reserved.

Desenvolvimento de revestimentos híbridos do sistema siloxano-PMMA com aplicações anticorrosivas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Obtenção e caracterização de hidrogéis de poliacrilamida-co-metilcelulose como sistemas carreadores de cloridrato de propranolol

Matrizes poliméricas como os hidrogéis são sistemas de liberação controlada que estão sendo largamente utilizados na indústria farmacêutica. Neste trabalho os hidrogéis de PAAm-co-MC foram obtidos e caracterizados afim de carrear o propranolol, fármaco anti-hipertensivo. Os hidrogéis compostos pelos monômeros AAm e MC foram sintetizados por polimerização via radical livre, sendo investigada quatro concentrações de AAm (3,6%; 7,2%; 14,7% e 21,7% m/v). A caracterização dos hidrogéis foi realizada com os estudos de grau de intumescimento, potencial zeta, IR-FT, MEV e análises térmicas (TG, DTA, DTG e DSC). O hidrogel 3,6% apresentou maior grau de intumescimento em todos os meios de análise. O potencial zeta revelou que todos os hidrogéis permanecem próximo do ponto isoelétrico. O espectro de absorção do infravermelho permitiu identificar bandas características, tanto do hidrogel como do propranolol. As curvas de TG dos hidrogéis evidenciaram a degradação dos mesmos em dois estágios, sendo observado na curva DTG a maior perda de massa em torno de 400ºC e as curvas DTA e DSC confirmaram os três eventos endotérmicos. Já o propranolol apresentou um único estágio de degradação e seu pico de fusão foi em 163,4ºC. As microfotografias relevaram a disposição da rede tridimensional dos hidrogéis. A relação da adsorção propranolol/hidrogel foi de 573 mg/g, seguindo o modelo da isoterma de Langmuir. No estudo da cinética de liberação in vitro a liberação do propranolol a partir da matriz do hidrogel foi de aproximadamente 80% do fármaco em 424 horas, apresentando um modelo bimodal. A realização deste trabalho demonstrou que o hidrogel de PAAm-co-MC é um grande promissor para aplicação em sistemas carreadores de fármacos.

Desenvolvimento de sistemas multifuncionais baseados em híbridos orgânico-inorgânicos dopados

Pós-graduação em Química - IQ

Desenvolvimento de revestimentos siloxano-PMMA reforçados por nanotubos de carbono, óxido de grafite e óxido de grafite reduzido para aplicações anticorrosivas

Pós-graduação em Química - IQ

Structural properties of cerium doped siloxane-PMMA hybrid coatings with high anticorrosive performance

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Filmes híbridos PMMA-siloxano modificados com nanotubos de carbono para proteção de materiais metálicos contra corrosão

Using the sol-gel process, organic-inorganic hybrid coatings were synthesized by incorporation of different concentrations of functionalized carbon nanotubes, to improve their mechanical strength and thermal resistance without changing its passivation character. The siloxane-PMMA hybrids were prepared by radical polymerization of methyl methacrylate (MMA) with 3-methacryloxipropiltrimethoxisilane (MPTS) using the thermal initiator benzoyl peroxide (BPO), followed by acid catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS). The analysis of pristine and functionalized carbon nanotubes was carried out using Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy and Raman Spectroscopy. Structural analysis of hybrids was performed by Nuclear Magnetic Resonance, Atomic Force Microscopy and Raman Spectroscopy. For analysis of mechanical strength and thermal stability were performed mechanical compression tests and thermogravimetric analysis, respectively. Electrochemical Impedance Spectroscopy was used to evaluate the corrosion resistance in saline environment. The results showed an effective functionalization of carbon nanotubes with carboxyl groups and conservation of its structure. The hybrids showed high siloxane network connectivity and roughness of approximately 0.3 nm. The incorporation of carbon nanotubes in the hybrid matrix did not change significantly their thermal stability. Samples containing carbon nanotubes exhibit good corrosion resistance (on the order of MΩ in saline environment), but the lack of complete dispersion of carbon nanotubes in the hybrid, resulted in a loss of mechanical and corrosion resistance compared to hybrid matrix.

Síntese e caracterização de matrizes híbridas para aplicação em sistemas de liberação controlada

Pós-graduação em Ciência dos Materiais - FEIS

Application of Polysaccharide Hydrogels in Adsorption and Controlled-Extended Release of Fertilizers Processes

This article studied the applicability of poly(acrylamide) and methylcellulose (PAAm-MC) hydrogels as potential delivery vehicle for the controlled-extended release of ammonium sulfate (NH(4))(2)SO(4) and potassium phosphate (KH(2)PO(4)) fertilizers. PAAm-MC hydrogels with different acrylamide (AAm) and MC concentrations were prepared by a free radical polymerization method. The adsorption and desorption kinetics of fertilizers were determined using conductivity measurements based on previously built analytical curve. The addition of MC in the PAAm chains increased the quantities of (NH(4))(2)SO(4) and KH(2)PO(4) loaded and extended the time and quantities of fertilizers released. Coherently, both loading and releasing processes were strongly influenced by hydrophilic properties of hydrogels (AAm/MC mass proportion). The best sorption (124.0 mg KH(2)PO(4)/g hydrogel and 58.0 mg (NH(4))(2)SO(4)/g hydrogel) and desorption (54.9 mg KH(2)PO(4)/g hydrogel and 49.5 mg (NH(4))(2)SO(4)/g hydrogel) properties were observed for 6.0% AAm-1.0% MC hydrogels (AAm/MC mass proportion equal 6), indicating that these hydrogels are potentially viable to be used in controlled-extended release of fertilizers systems. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2291-2298, 2012

Liquid crystal polymers: macromolecular design for enhanced performances

During this work, done mainly in the laboratories of the department of Industrial Chemistry and Materials of the University of Bologna but also in the laboratories of the Carnegie Mellon University in collaboration with prof. K. Matyjaszewski and at the university of Zaragoza in collaboration with prof. J. Barberá, was focused mainly on the synthesis and characterization of new functional polymeric materials. In the past years our group gained a deep knowledge about the photomodulation of azobenzene containing polymers. The aim of this thesis is to push forward the performances of these materials by the synthesis of well defined materials, in which, by a precise control over the macromolecular structures, better or even new functionality can be delivered to the synthesized material. For this purpose, besides the rich photochemistry of azoaromatic polymers that brings to the application, the control offered from the recent techniques of controlled radical polymerization, ATRP over all, gives an enormous range of opportunity for the developing of a new generation of functional materials whose properties are determinate not only by the chemical nature of the functional center (e.g. azoaromatic chromophore) but are tuned and even amplified by a synergy with the whole macromolecular structure. Old materials in new structures. In this contest the work of this thesis was focused mainly on the synthesis and characterization of well defined azoaromatic polymers in order to establish, for the first time, precise structure-properties correlation. In fact a series of well defined different azopolymers, chiral and achiral, with different molecular weight and highly monodisperse were synthesized and their properties were studied, in terms of photoexpansion and photomodulation of chirality. We were then able to study the influence of the macromolecular structure in terms of molecular weight and ramification on the studied properties. The huge amount of possibility offered by the tailoring of the macromolecular structure were exploited for the synthesis of new cholesteric photochromic polymers that can be used as a smart label for the certification of the thermal history of any thermosensitive product. Finally the ATRP synthesis allowed us to synthesize a total new class of material, named molecular brushes: a flat surface covered with an ultra thin layer of polymeric chain covalently bond onto the surface from one end. This new class of materials is of extreme interest as they offer the possibility to tune and manage the interaction of the surface with the environment. In this contest we synthesized both azoaromatic surfaces, growing directly the polymer from the surface, and mixed brushes: surfaces covered with incompatible macromolecules. Both type of surfaces acts as “smart” surfaces: the first it is able to move the orientation of a LC cell by simply photomodulation and, thanks to the robustness of the covalent bond, can be used as a command surface overcoming all the limitation due to the dewetting of the active layer. The second type of surface, functionalized by a grafting-to method, can self assemble the topmost layer responding to changed environmental conditions, exposing different functionality according to different environment.