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Papers by juan cauich

Research paper thumbnail of Polypyrrole free-standing electrodes sense temperature or current during reaction

Polymer International, 2010

The electrochemical activity of self-supported thick (70 µm) polypyrrole films electrogenerated i... more The electrochemical activity of self-supported thick (70 µm) polypyrrole films electrogenerated in a mixed electrolyte of dodecylbenzenesulfonic acid and LiClO4 was studied in aqueous solutions of LiClO4. This material inhibits hydrogen evolution up to cathodic potentials of −3.0 V versus Ag/AgCl. During oxidation or reduction reactions under galvanostatic conditions, the electrical energy consumed for a constant charge is a function of either the working temperature or the flowing current. As a consequence any electrochemical device, moreover artificial muscles, constructed with reactive conducting polymers is expected to work simultaneously as a sensor of the working temperature. Copyright © 2010 Society of Chemical Industry

Research paper thumbnail of Sensing and Tactile Artificial Muscles from Reactive Materials

Sensors, 2010

Films of conducting polymers can be oxidized and reduced in a reversible way. Any intermediate ox... more Films of conducting polymers can be oxidized and reduced in a reversible way. Any intermediate oxidation state determines an electrochemical equilibrium. Chemical or physical variables acting on the film may modify the equilibrium potential, so that the film acts as a sensor of the variable. The working potential of polypyrrole/DBSA (Dodecylbenzenesulfonic acid) films, oxidized or reduced under constant currents, changes as a function of the working conditions: electrolyte concentration, temperature or mechanical stress. During oxidation, the reactive material is a sensor of the ambient, the consumed electrical energy being the sensing magnitude. Devices based on any of the electrochemical properties of conducting polymers must act simultaneously as sensors of the working conditions. Artificial muscles, as electrochemical actuators constituted by reactive materials, respond to the ambient conditions during actuation. In this way, they can be used as actuators, sensing the surrounding conditions during actuation. Actuating and sensing signals are simultaneously included by the same two connecting wires.

Research paper thumbnail of TEM Examination of MWCNTs Oxidized by Mild Experimental Conditions

Fullerenes Nanotubes and Carbon Nanostructures, 2012

A detailed transmission electron microscopy (TEM) examination of the surface of multi-walled carb... more A detailed transmission electron microscopy (TEM) examination of the surface of multi-walled carbon nanotubes (MWCNTs) oxidized using mild experimental conditions shows evidence of nanotube length shortening after acid treatments and important modifications at the nanostructural level, such as damage to the graphitic structure and stripping of the inner layers. It is shown that damage caused to the MWCNTs strongly depends on the acid concentration, even for short exposure times. Structural damage and fragmentation generated by a treatment based on 3.0 M HNO3 followed by H2O2 is mild compared to the severe damage caused by a combination of concentrated nitric and sulfuric acids.

Research paper thumbnail of Surface characterisation of various bone cements prepared with functionalised methacrylates/bioactive ceramics in relation to HOB behaviour

Acta Biomaterialia, 2006

This study reports the relationship between the biocompatibility and surface properties of experi... more This study reports the relationship between the biocompatibility and surface properties of experimental bone cements. The effect of hydroxyapatite (HA) or alpha-tri-calcium phosphate (alpha-TCP) incorporated into bone cements prepared with methyl methacrylate as base monomer and either methacrylic acid or diethyl amino ethyl methacrylate (DEAEMA) as comonomers was investigated. The in vitro biocompatibility of these composite cements was assessed in terms of the interaction of primary human osteoblasts grown on the materials over a period of 5 days and compared with a control surface. These results were related to the surface properties investigated through a number of techniques, namely Fourier transform infrared, contact angle measurements, X-ray photoelectron spectroscopy and energy dispersive analysis of X-rays. Complementary techniques of thermal analysis and ion chromatography were also performed. Biocompatibility results showed that the addition of alpha-TCP improves biocompatibility regardless of comonomer type. This is in contrast to HA-based cements where cell proliferation was significantly lower. Surface characterisations showed that structural integrity of the materials was maintained in the presence of the acid and base comonomers, and water contact angles were reduced particularly in DEAEMA containing materials. Furthermore, ion chromatography confirmed higher Ca2+ and PO4(3-) ion release by both types of ceramics, particularly for those containing DEAEMA. In conclusion, the incorporation of acidic and basic comonomers to either HA or alpha-TCP ceramics containing bone cements can have differential effects upon the attachment and proliferation of bone cells in vitro. Moreover, those cements consisting of alpha-TCP and containing DEAEMA comonomer indicated the most favourable biocompatibility.

Research paper thumbnail of Evaluation of mild acid oxidation treatments for MWCNT functionalization

Carbon, 2009

Acidic oxidation methods have been widely reported as an effective method to purify and functiona... more Acidic oxidation methods have been widely reported as an effective method to purify and functionalize the surface of carbon nanotubes (CNTs). Although effective, the strong acids typically employed and the high sonication power used to disperse the nanotubes in the ...

Research paper thumbnail of Degradation studies on segmented polyurethanes prepared with HMDI, PCL and different chain extenders

Acta Biomaterialia, 2010

Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft seg... more Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft segment, 4,4 0 -methylene bis (cyclohexyl isocyanate) and either butanediol (BSPU1) or dithioerythritol (BSPU2) as a chain extender. BSPU samples were characterized in terms of their physicochemical properties and their hemocompatibility. Polymers were then degraded in acidic (HCl 2 N), alkaline (NaOH 5 M) and oxidative (H 2 O 2 30 wt.%) media and characterized by their mass loss, Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Undegraded BSPU1 and BSPU2 exhibited different properties, such as the glass transition temperature T g of the soft segment (À25 vs. 4°C), mechanical properties (600% vs. 900% strain to break) and blood coagulating properties (clotting time = 11.46 vs. 8.13 min). After acidic and alkaline degradation, the disappearance of the 1728 cm À1 band of polycaprolactone (PCL) on both types of BSPU was detected by FTIR. However, the oxidative environment did not affect the soft segment severely as the presence of PCL crystalline domains were observed both by DSC (melting temperature T m = 52.8°C) and XRD (2h = 21.3°and 23.7°). By TGA three decomposition temperatures were recorded for both BSPU samples, but the higher decomposition temperature was enhanced after acidic and alkaline degradation. The formation of the porous structure on BSPU1 was observed by SEM, while a granular surface was observed on BSPU2 after alkaline degradation.

Research paper thumbnail of Characterization of bone cements prepared with functionalized methacrylates and hydroxyapatite

Journal of Biomaterials Science-polymer Edition, 2001

Bone cements prepared with methyl methacrylate and either methacrylic acid or diethyl amino ethyl... more Bone cements prepared with methyl methacrylate and either methacrylic acid or diethyl amino ethyl methacrylate as comonomers were characterized by infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, dynamic mechanical thermal analysis, and mechanical testing. Selected formulations containing these functionalized methacrylates were filled with hydroxyapatite and studied in terms of their properties in tension, compression and bending, and X-ray diffraction. It was found that residual monomer was not greatly affected by the presence of either acid or basic comonomers in the unfilled bone cements. In contrast, molecular weight, curing times, and glass transition temperature were composition dependent. For samples with acidic comonomer, a faster curing time, higher molecular weight, and higher glass transition temperatures were observed with respect to those with the basic comonomer. X-ray diffraction revealed that the crystalline structure was not affected by the nature of comonomer in the bone cement while scanning electron microscopy showed that hydroxyapatite remained as clusters in the bone cement. The mechanical properties of filled bone cements depended mainly on composition and type of testing. Hydroxyapatite-filled bone cements fullfilled the minimum compressive strength (70 MPa) required for bone cement use. However, the minimum tensile strength (30 MPa) was only fullfilled by cements prepared without comonomer and those containing methacrylic acid. The minimum bending strength requirement (50 MPa) was not satisfied by any of the formulations studied.

Research paper thumbnail of Study of crosslinking density in polydimethylsiloxane networks by DSC

Journal of Applied Polymer Science, 1995

A calorimetric study for estimating crosslinking densities of polydimethylsiloxane (PDMS) network... more A calorimetric study for estimating crosslinking densities of polydimethylsiloxane (PDMS) networks is presented. It involves the experimental determination of the heat capacities of the polymer with (C) and without (C) crosslinking. The theoretical basis of the method is described as well as the procedure used for the determination of the Cps. The crosslinking densities of PDMS networks, determined by absorbency (swelling) measurments, using the Flory-Rehner equation, and by the method described here, are compared. The PDMS, obtained by the anionic synthesis of octamethylcyclotetrasiloxane, was analyzed by gel permeation chromatography and infrared spectroscopy. Separate samples of the polymer were further crosslinked at different network densities. The Cps and the thermal stabilities were determined by DSC and TGA, respectively. The results indicate that the crosslinking density ratios of the polymer networks calculated by the relation ΔC/C are in reasonable agreement with those obtained from absorbency measurements. The crosslinking density can also be obtained from heat capacity measurments if the density of the network is known at the temperature that ΔCp is obtained. © 1995 John Wiley & Sons, Inc.

Research paper thumbnail of Comparative study on the properties of acrylic bone cements prepared with either aliphatic or aromatic functionalized methacrylates

Biomaterials, 2005

Bone cements prepared with methacrylic acid (MAA) and diethyl amino ethyl methacrylate (DEAEM) we... more Bone cements prepared with methacrylic acid (MAA) and diethyl amino ethyl methacrylate (DEAEM) were compared with formulations employing 4-methacryloyloxybenzoic acid (MBA) and 4-diethyaminobenzyl methacrylate (DEABM) as comonomer. The influence of these new aromatic monomers on various physicochemical, setting and mechanical properties was assessed. Surface characterization demonstrated that bone cements prepared with any of the functionalized monomers exhibited increasing hydrophilicity with monomer concentration and that the aromatic monomers provided more hydrophilic cements than their aliphatic counterparts for low concentrations of the functional monomer. It was also found that bone cements prepared with high amounts of the acidic aliphatic monomer provided the highest exotherm of reaction and their setting times were shorter than MBA based cements. On the other hand, DEABM containing bone cements exhibited shorter setting times than DEAEM formulations and slightly higher peak temperatures. In general, it was found that the glass transition temperature increased with the presence of acidic comonomer and decreased when alkaline comonomers were present, especially aliphatic ones.

Research paper thumbnail of Thermal degradation of commercially available organoclays studied by TGA–FTIR

Thermochimica Acta, 2007

Thermogravimetry coupled to Fourier transform infrared spectroscopy (TGA/FTIR) has been used to s... more Thermogravimetry coupled to Fourier transform infrared spectroscopy (TGA/FTIR) has been used to study the thermal decomposition products evolved during the degradation of several commercially available organoclays (Cloisites TM Na + , 10A, 15A, 20A, 25A, 93A and 30B). It was found that the decomposition pattern of the organoclays was different for each sample: Cloisite TM 10A shows three well-defined degradation stages, Cloisite TM 30B only two stages and the Cloisite TM 93A only one weight loss; Cloisites TM 15A, 20A and 25A exhibited a more complex behavior showing one main stage and a shoulder. It was also observed that the onset of the decomposition was different for each type of organoclay, being Cloisite TM 10A the lowest (160 • C) and Cloisite TM 93A the highest (212 • C). FTIR analysis of the evolved products from their non-oxidative thermal degradation showed the release of water, aldehydes, carboxylic acids, aliphatic compounds and, in some cases, aromatic compounds and CO 2 . It is suggested that the degradation of both tallow residue and unexchanged surfactant explain the presence of some products evolved during degradation of organoclays.

Research paper thumbnail of Structure–property relationships of DEAEM-containing bone cements: effect of the substitution of a methylene group by an aromatic ring

Journal of Biomaterials Science-polymer Edition, 2007

New aromatic methacrylates were prepared by substitution of a methylene group from diethylaminoet... more New aromatic methacrylates were prepared by substitution of a methylene group from diethylaminoethyl methacrylate (DEAEM) by an aromatic ring at two different positions. Diethylamino benzyl methacrylate (DEABM) and N-methacryloyloxyethyl)-N-ethyl-m-toluidine (MEET) were polymerized and incorporated as co-monomers in bone cement formulations. Cements were evaluated in terms of curing and mechanical properties in addition to changes in their glass transition temperature by DSC and surface properties by contact angle measurements. The immediate effect of the presence of an aromatic ring within the amino methacrylate was that it modified the bone cements' physical appearance, as colored products were obtained. It was also observed that peak temperature increased and setting time decreased by the use of DEABM and MEET instead of DEAEM. Simultaneously, both tensile and compressive strength of bone cements were improved; this effect was related to a higher glass transition temperature. In addition, surface properties of cements were modified by the incorporation of the aromatic ring, being more hydrophilic at low molar fractions and more hydrophobic at high molar fractions. Based on these studies, it is concluded that the position of the aromatic ring within the amino methacrylate modified not only the cement's appearance, but also the setting and mechanical properties.

Research paper thumbnail of Synthesis of HMDI-based segmented polyurethanes and their use in the manufacture of elastomeric composites for cardiovascular applications

Journal of Biomaterials Science-polymer Edition, 2007

For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methyleneb... more For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methylenebis(cyclohexyl isocyanate) (HMDI), polytetramethylenglycol (PTMG) and 1,4-butanediol (BD) were synthesized and characterized by spectroscopy (FT-IR, (1)H-NMR) and thermal (TGA, DMA, DSC) and mechanical techniques. The segmented nature of the SPUs was not easily established by spectroscopic means; however, TGA allowed the quantification of the rigid segments content by the significant mass loss between 348 and 356 degrees C. The alpha transition was detected by DMA and related to the T(g) of the soft segments at -50 degrees C, while DSC showed the presence of an endothermic transition above 80 degrees C attributed to the melting of rigid segments. Two types of composites were prepared using the synthesized SPUs and Lycra (either T162B or T162C). The first one consisted of a two layers casting laminated while the second one was a classic unidirectional fibre-reinforced material. Laminate composites prepared with SPU containing 23.9% and 33.9% of rigid segments and Lycra T162C exhibited a higher tensile modulus but lower tensile strength than composites prepared with Tecoflex SG-80A (39.7% of rigid segments). The energy of adhesion between layers on these composites ranged from 475 to 2150 J. Fibre-reinforced SPUs exhibited higher moduli than the two layer laminated composites with increasing amounts of rigid segments in the matrix and by increasing Lycra T162C content (up to 10%). This behaviour was explained by SEM, which showed a good fibre-matrix bonding.

Research paper thumbnail of Poly(vinyl alcohol)/poly(acrylic acid) blends: Miscibility studies by DSC and characterization of their thermally induced hydrogels

Journal of Applied Polymer Science, 1993

Binary blends of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) and polyacrylamide (PAAm... more Binary blends of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) and polyacrylamide (PAAm) were characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and infrared spectroscopy (IR). Molecular weight, blend composition, and heating time at 150°C were the variables used. Results obtained by DSC indicated that PAA/PVA blends are miscible in the full range of composition. Similarly, TGA traces showed that thermal stability was higher for blends than for pure polymers. Blends of PVA with high molecular weight PAA exhibited a hydrogel behavior after drying at relatively low temperature (100°C), whereas blends containing low molecular weight PAA behaved as hydrogels only after they were heated at 150°C. Hydrogel character was increased for these two PVA/PAA blends with the heating time at higher temperature (150°C). IR spectra revealed that esterification took place in these blends after thermally treated at this temperature. In contrast, addition of glyoxal in combination with heating was necessary to produce hydrogels from PAAm/PVA blends. Furthermore, the crosslinking degree of these hydrogels was estimated from their absorbency values by applying the Flory–Rehner equation. © 1993 John Wiley & Sons, Inc.

Research paper thumbnail of A TG/FTIR study on the thermal degradation of poly(vinyl pyrrolidone

Journal of Thermal Analysis and Calorimetry, 2011

The aim of this study was to gain some fundamental knowledge on the thermal degradation pathways ... more The aim of this study was to gain some fundamental knowledge on the thermal degradation pathways of poly(N-vinyl pyrrolidone) using Thermogravimetry coupled with Fourier Transform Infrared Spectroscopy (TG–FTIR) in addition to IR and 1H NMR spectroscopic studies of the partially degraded samples. It was found that the vinyl pyrrolidone is the main volatile products of the thermal degradation of PVP which implies that the predominant mechanism during thermal degradation of this polymer is the depolymerization to monomer of the polymeric main chain; however, it is evident that simultaneous reactions may be involved yielding oligomers. FTIR and 1H NMR spectra of partially degraded samples of PVP exhibited very similar characteristics to that observed for undegraded samples although the 1H NMR spectra suggest the presence of simultaneous reactions as the fragmentation of polymeric main chain.

Research paper thumbnail of TGA/FTIR study on thermal degradation of polymethacrylates containing carboxylic groups

Polymer Degradation and Stability, 2006

In this work, the thermal degradation of polymethacrylates containing carboxylic groups namely po... more In this work, the thermal degradation of polymethacrylates containing carboxylic groups namely poly(methacryloyloxy butanoic acid), PMBA; poly(methacryloyloxy hexanoic acid), PMHA; and poly( p-methacryloyloxy benzoic acid), PMBeA was investigated by TGA/FTIR. Moreover, in order to shed more light on the reaction pathways during the thermal decomposition of these polymers, an FTIR spectroscopic study of structural changes in the degrading material was performed. By TGA it was observed that PMBA exhibited two well-defined degradation stages at 327 and 450 C; PMHA presents only one main weight loss at ca. 402 C although from DTG curve it was noted that the single step degradation was composed by two overlapped peaks located at 414 and 449 C and a small shoulder at 317 C; finally PMBeA showed three weight loss regions at 265, 353 and 468 C. From FTIR analysis of the partially degraded samples it was found that the thermal degradation of these polymers resembled that of polymethacrylic acid, i.e. anhydrides were initially formed and then the modified structure is broken to yield an aromatic structure with phenolic groups. In contrast, the analysis by FTIR of the volatile products from the studied polymers differs notably than those obtained for polymethacrylic acid: b-lactones and g-lactones were released from PMBA and PMHA, respectively, during its thermal degradation, whereas an ester derivative from benzoic acid evolves from PMBeA probably through depolymerization.

Research paper thumbnail of TGA/FTIR studies of segmented aliphatic polyurethanes and their nanocomposites prepared with commercial montmorillonites

Polymer Degradation and Stability, 2009

Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (C... more Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (CloisiteÔ Na þ , CloisiteÔ 15A, CloisiteÔ 30B) were studied using thermogravimetric analysis coupled with Fourier Transform Infrared Spectroscopy (TGA/FTIR). The results showed that the thermal degradation of unfilled SPU and the 4, 6 and 10 wt% hand mixed nanocomposites occurred in two stages being the first due to degradation of hard segments and the second due to the degradation of soft segments. It was also found that the thermal stability of these nanocomposites was not improved by increasing nanoclay concentration except for SPU/CloisiteÔ 15A nanocomposites were a 40 C increase was observed. In a similar manner, FTIR spectra of the evolved gases obtained after the thermal degradation of these nanocomposites were qualitatively similar to the unfilled polymer except in those containing CloisiteÔ 30B where isocyanate absorptions were detected. In contrast, SPU/CloisiteÔ 30B nanocomposites prepared by in-situ polymerization, exhibited higher thermal stability than the corresponding hand mixed nanocomposites. In addition, these nanocomposites exhibited the presence of carbon dioxide in the evolved gases during its second degradation stage which was not observed in the hand mixed nanocomposites. In this case, it can be said that the presence of clays in the nanocomposites has a significant effect on the thermal degradation pathways.

Research paper thumbnail of Thermal degradation behavior of polymethacrylates containing amine side groups

Polymer Degradation and Stability, 2008

The thermal degradation behavior of polymethacrylates containing amine groups such as poly(N,N-di... more The thermal degradation behavior of polymethacrylates containing amine groups such as poly(N,N-diethyl aminoethyl methacrylate), PDEAEM, and poly(N-ethyl-m-tolyl-aminoethyl methacrylate), PMEET, has been studied using thermogravimetry coupled with infrared ...

Research paper thumbnail of Characterization of hydrogel blends of poly(vinyl pyrrolidone) and poly(vinyl alcohol-vinyl acetate

Journal of Materials Science-materials in Medicine, 1996

Hydrogel blends were prepared from water-soluble polymers of poly(vinyl alcohol-vinyl acetate) an... more Hydrogel blends were prepared from water-soluble polymers of poly(vinyl alcohol-vinyl acetate) and poly(vinyl pyrrolidone). The method of preparation was optimized and different compositions of blends were characterized. The effect of thermal treatment and the introduction of an aldehydic crosslinking agent in the blend was also studied. The swelling characteristics of the various compositions, their thermal behaviour and the state of water was examined. Mechanical properties of the hydrogels were determined and it was observed that blends containing glutaraldehyde produced materials with good mechanical integrity and high water contents.

Research paper thumbnail of Dynamic mechanical characterization of hydrogel blends of poly(vinyl alcohol-vinyl acetate) with poly(acrylic acid) or poly(vinyl pyrrolidone

Journal of Materials Science-materials in Medicine, 1996

Transparent hydrogels were prepared by blending solutions of poly(vinyl alcohol-vinyl acetate) wi... more Transparent hydrogels were prepared by blending solutions of poly(vinyl alcohol-vinyl acetate) with either poly(acrylic acid) or poly(vinyl pyrrolidone) in the presence of glutaraldehyde as a crosslinking agent. The network obtained from the poly(vinyl pyrrolidone) system was subjected to various thermal treatments, the effects of which have been studied. Dynamic mechanical analysis was used to characterize the hydrogels and to establish the suitability of these blends for use in biomedical applications. The swelling behaviour was followed under dynamic loads as well as by mass difference. Different frequencies were used to study the dynamic properties of the hydrogel blends which showed an increase in storage modulus with increasing frequency. A comparison of modulus values obtained dynamically were in agreement with data obtained mechanically in tension.

Research paper thumbnail of Effect of cross-linking agents on the dynamic mechanical properties of hydrogel blends of poly(acrylic acid)-poly(vinyl alcohol-vinyl acetate

Biomaterials, 1996

A range of hydrogels were prepared by blending aqueous solutions of poly(vinyl alcohol-vinyl acet... more A range of hydrogels were prepared by blending aqueous solutions of poly(vinyl alcohol-vinyl acetate) with poly(acrylic acid) in various proportions. The effects of two cross-linking agents (glyoxal and glutaraldehyde) and subsequent thermal treatment on the properties of the blends are discussed. Dynamic mechanical analysis (DMA) of the xerogels indicated complete miscibility of the various blends which was evident from the appearance of a single glass transition temperature (T,) in the presence of either glyoxal or glutaraldehyde at all thermal treatments studied. A 50150% wtlwt blend was found to have the highest storage modulus and was thus selected for further study. Hydrogels prepared with glutaraldehyde without subsequent thermal treatment exhibited higher storage modulus values than those prepared using glyoxal when tested isothermally at 20°C in a water bath. A further increase in the storage modulus was observed when these hydrogels were thermally treated at 120 or 150°C. In a non-isothermal study on the cross-linked hydrogels, no variation in storage modulus was observed. Broad peaks were observed in tan 6 plots, these peaks shifting towards higher frequencies as the degree of cross-linking increased in the hydrogel. 0 1966 Elsevier Science Limited.

Research paper thumbnail of Polypyrrole free-standing electrodes sense temperature or current during reaction

Polymer International, 2010

The electrochemical activity of self-supported thick (70 µm) polypyrrole films electrogenerated i... more The electrochemical activity of self-supported thick (70 µm) polypyrrole films electrogenerated in a mixed electrolyte of dodecylbenzenesulfonic acid and LiClO4 was studied in aqueous solutions of LiClO4. This material inhibits hydrogen evolution up to cathodic potentials of −3.0 V versus Ag/AgCl. During oxidation or reduction reactions under galvanostatic conditions, the electrical energy consumed for a constant charge is a function of either the working temperature or the flowing current. As a consequence any electrochemical device, moreover artificial muscles, constructed with reactive conducting polymers is expected to work simultaneously as a sensor of the working temperature. Copyright © 2010 Society of Chemical Industry

Research paper thumbnail of Sensing and Tactile Artificial Muscles from Reactive Materials

Sensors, 2010

Films of conducting polymers can be oxidized and reduced in a reversible way. Any intermediate ox... more Films of conducting polymers can be oxidized and reduced in a reversible way. Any intermediate oxidation state determines an electrochemical equilibrium. Chemical or physical variables acting on the film may modify the equilibrium potential, so that the film acts as a sensor of the variable. The working potential of polypyrrole/DBSA (Dodecylbenzenesulfonic acid) films, oxidized or reduced under constant currents, changes as a function of the working conditions: electrolyte concentration, temperature or mechanical stress. During oxidation, the reactive material is a sensor of the ambient, the consumed electrical energy being the sensing magnitude. Devices based on any of the electrochemical properties of conducting polymers must act simultaneously as sensors of the working conditions. Artificial muscles, as electrochemical actuators constituted by reactive materials, respond to the ambient conditions during actuation. In this way, they can be used as actuators, sensing the surrounding conditions during actuation. Actuating and sensing signals are simultaneously included by the same two connecting wires.

Research paper thumbnail of TEM Examination of MWCNTs Oxidized by Mild Experimental Conditions

Fullerenes Nanotubes and Carbon Nanostructures, 2012

A detailed transmission electron microscopy (TEM) examination of the surface of multi-walled carb... more A detailed transmission electron microscopy (TEM) examination of the surface of multi-walled carbon nanotubes (MWCNTs) oxidized using mild experimental conditions shows evidence of nanotube length shortening after acid treatments and important modifications at the nanostructural level, such as damage to the graphitic structure and stripping of the inner layers. It is shown that damage caused to the MWCNTs strongly depends on the acid concentration, even for short exposure times. Structural damage and fragmentation generated by a treatment based on 3.0 M HNO3 followed by H2O2 is mild compared to the severe damage caused by a combination of concentrated nitric and sulfuric acids.

Research paper thumbnail of Surface characterisation of various bone cements prepared with functionalised methacrylates/bioactive ceramics in relation to HOB behaviour

Acta Biomaterialia, 2006

This study reports the relationship between the biocompatibility and surface properties of experi... more This study reports the relationship between the biocompatibility and surface properties of experimental bone cements. The effect of hydroxyapatite (HA) or alpha-tri-calcium phosphate (alpha-TCP) incorporated into bone cements prepared with methyl methacrylate as base monomer and either methacrylic acid or diethyl amino ethyl methacrylate (DEAEMA) as comonomers was investigated. The in vitro biocompatibility of these composite cements was assessed in terms of the interaction of primary human osteoblasts grown on the materials over a period of 5 days and compared with a control surface. These results were related to the surface properties investigated through a number of techniques, namely Fourier transform infrared, contact angle measurements, X-ray photoelectron spectroscopy and energy dispersive analysis of X-rays. Complementary techniques of thermal analysis and ion chromatography were also performed. Biocompatibility results showed that the addition of alpha-TCP improves biocompatibility regardless of comonomer type. This is in contrast to HA-based cements where cell proliferation was significantly lower. Surface characterisations showed that structural integrity of the materials was maintained in the presence of the acid and base comonomers, and water contact angles were reduced particularly in DEAEMA containing materials. Furthermore, ion chromatography confirmed higher Ca2+ and PO4(3-) ion release by both types of ceramics, particularly for those containing DEAEMA. In conclusion, the incorporation of acidic and basic comonomers to either HA or alpha-TCP ceramics containing bone cements can have differential effects upon the attachment and proliferation of bone cells in vitro. Moreover, those cements consisting of alpha-TCP and containing DEAEMA comonomer indicated the most favourable biocompatibility.

Research paper thumbnail of Evaluation of mild acid oxidation treatments for MWCNT functionalization

Carbon, 2009

Acidic oxidation methods have been widely reported as an effective method to purify and functiona... more Acidic oxidation methods have been widely reported as an effective method to purify and functionalize the surface of carbon nanotubes (CNTs). Although effective, the strong acids typically employed and the high sonication power used to disperse the nanotubes in the ...

Research paper thumbnail of Degradation studies on segmented polyurethanes prepared with HMDI, PCL and different chain extenders

Acta Biomaterialia, 2010

Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft seg... more Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft segment, 4,4 0 -methylene bis (cyclohexyl isocyanate) and either butanediol (BSPU1) or dithioerythritol (BSPU2) as a chain extender. BSPU samples were characterized in terms of their physicochemical properties and their hemocompatibility. Polymers were then degraded in acidic (HCl 2 N), alkaline (NaOH 5 M) and oxidative (H 2 O 2 30 wt.%) media and characterized by their mass loss, Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Undegraded BSPU1 and BSPU2 exhibited different properties, such as the glass transition temperature T g of the soft segment (À25 vs. 4°C), mechanical properties (600% vs. 900% strain to break) and blood coagulating properties (clotting time = 11.46 vs. 8.13 min). After acidic and alkaline degradation, the disappearance of the 1728 cm À1 band of polycaprolactone (PCL) on both types of BSPU was detected by FTIR. However, the oxidative environment did not affect the soft segment severely as the presence of PCL crystalline domains were observed both by DSC (melting temperature T m = 52.8°C) and XRD (2h = 21.3°and 23.7°). By TGA three decomposition temperatures were recorded for both BSPU samples, but the higher decomposition temperature was enhanced after acidic and alkaline degradation. The formation of the porous structure on BSPU1 was observed by SEM, while a granular surface was observed on BSPU2 after alkaline degradation.

Research paper thumbnail of Characterization of bone cements prepared with functionalized methacrylates and hydroxyapatite

Journal of Biomaterials Science-polymer Edition, 2001

Bone cements prepared with methyl methacrylate and either methacrylic acid or diethyl amino ethyl... more Bone cements prepared with methyl methacrylate and either methacrylic acid or diethyl amino ethyl methacrylate as comonomers were characterized by infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, dynamic mechanical thermal analysis, and mechanical testing. Selected formulations containing these functionalized methacrylates were filled with hydroxyapatite and studied in terms of their properties in tension, compression and bending, and X-ray diffraction. It was found that residual monomer was not greatly affected by the presence of either acid or basic comonomers in the unfilled bone cements. In contrast, molecular weight, curing times, and glass transition temperature were composition dependent. For samples with acidic comonomer, a faster curing time, higher molecular weight, and higher glass transition temperatures were observed with respect to those with the basic comonomer. X-ray diffraction revealed that the crystalline structure was not affected by the nature of comonomer in the bone cement while scanning electron microscopy showed that hydroxyapatite remained as clusters in the bone cement. The mechanical properties of filled bone cements depended mainly on composition and type of testing. Hydroxyapatite-filled bone cements fullfilled the minimum compressive strength (70 MPa) required for bone cement use. However, the minimum tensile strength (30 MPa) was only fullfilled by cements prepared without comonomer and those containing methacrylic acid. The minimum bending strength requirement (50 MPa) was not satisfied by any of the formulations studied.

Research paper thumbnail of Study of crosslinking density in polydimethylsiloxane networks by DSC

Journal of Applied Polymer Science, 1995

A calorimetric study for estimating crosslinking densities of polydimethylsiloxane (PDMS) network... more A calorimetric study for estimating crosslinking densities of polydimethylsiloxane (PDMS) networks is presented. It involves the experimental determination of the heat capacities of the polymer with (C) and without (C) crosslinking. The theoretical basis of the method is described as well as the procedure used for the determination of the Cps. The crosslinking densities of PDMS networks, determined by absorbency (swelling) measurments, using the Flory-Rehner equation, and by the method described here, are compared. The PDMS, obtained by the anionic synthesis of octamethylcyclotetrasiloxane, was analyzed by gel permeation chromatography and infrared spectroscopy. Separate samples of the polymer were further crosslinked at different network densities. The Cps and the thermal stabilities were determined by DSC and TGA, respectively. The results indicate that the crosslinking density ratios of the polymer networks calculated by the relation ΔC/C are in reasonable agreement with those obtained from absorbency measurements. The crosslinking density can also be obtained from heat capacity measurments if the density of the network is known at the temperature that ΔCp is obtained. © 1995 John Wiley & Sons, Inc.

Research paper thumbnail of Comparative study on the properties of acrylic bone cements prepared with either aliphatic or aromatic functionalized methacrylates

Biomaterials, 2005

Bone cements prepared with methacrylic acid (MAA) and diethyl amino ethyl methacrylate (DEAEM) we... more Bone cements prepared with methacrylic acid (MAA) and diethyl amino ethyl methacrylate (DEAEM) were compared with formulations employing 4-methacryloyloxybenzoic acid (MBA) and 4-diethyaminobenzyl methacrylate (DEABM) as comonomer. The influence of these new aromatic monomers on various physicochemical, setting and mechanical properties was assessed. Surface characterization demonstrated that bone cements prepared with any of the functionalized monomers exhibited increasing hydrophilicity with monomer concentration and that the aromatic monomers provided more hydrophilic cements than their aliphatic counterparts for low concentrations of the functional monomer. It was also found that bone cements prepared with high amounts of the acidic aliphatic monomer provided the highest exotherm of reaction and their setting times were shorter than MBA based cements. On the other hand, DEABM containing bone cements exhibited shorter setting times than DEAEM formulations and slightly higher peak temperatures. In general, it was found that the glass transition temperature increased with the presence of acidic comonomer and decreased when alkaline comonomers were present, especially aliphatic ones.

Research paper thumbnail of Thermal degradation of commercially available organoclays studied by TGA–FTIR

Thermochimica Acta, 2007

Thermogravimetry coupled to Fourier transform infrared spectroscopy (TGA/FTIR) has been used to s... more Thermogravimetry coupled to Fourier transform infrared spectroscopy (TGA/FTIR) has been used to study the thermal decomposition products evolved during the degradation of several commercially available organoclays (Cloisites TM Na + , 10A, 15A, 20A, 25A, 93A and 30B). It was found that the decomposition pattern of the organoclays was different for each sample: Cloisite TM 10A shows three well-defined degradation stages, Cloisite TM 30B only two stages and the Cloisite TM 93A only one weight loss; Cloisites TM 15A, 20A and 25A exhibited a more complex behavior showing one main stage and a shoulder. It was also observed that the onset of the decomposition was different for each type of organoclay, being Cloisite TM 10A the lowest (160 • C) and Cloisite TM 93A the highest (212 • C). FTIR analysis of the evolved products from their non-oxidative thermal degradation showed the release of water, aldehydes, carboxylic acids, aliphatic compounds and, in some cases, aromatic compounds and CO 2 . It is suggested that the degradation of both tallow residue and unexchanged surfactant explain the presence of some products evolved during degradation of organoclays.

Research paper thumbnail of Structure–property relationships of DEAEM-containing bone cements: effect of the substitution of a methylene group by an aromatic ring

Journal of Biomaterials Science-polymer Edition, 2007

New aromatic methacrylates were prepared by substitution of a methylene group from diethylaminoet... more New aromatic methacrylates were prepared by substitution of a methylene group from diethylaminoethyl methacrylate (DEAEM) by an aromatic ring at two different positions. Diethylamino benzyl methacrylate (DEABM) and N-methacryloyloxyethyl)-N-ethyl-m-toluidine (MEET) were polymerized and incorporated as co-monomers in bone cement formulations. Cements were evaluated in terms of curing and mechanical properties in addition to changes in their glass transition temperature by DSC and surface properties by contact angle measurements. The immediate effect of the presence of an aromatic ring within the amino methacrylate was that it modified the bone cements' physical appearance, as colored products were obtained. It was also observed that peak temperature increased and setting time decreased by the use of DEABM and MEET instead of DEAEM. Simultaneously, both tensile and compressive strength of bone cements were improved; this effect was related to a higher glass transition temperature. In addition, surface properties of cements were modified by the incorporation of the aromatic ring, being more hydrophilic at low molar fractions and more hydrophobic at high molar fractions. Based on these studies, it is concluded that the position of the aromatic ring within the amino methacrylate modified not only the cement's appearance, but also the setting and mechanical properties.

Research paper thumbnail of Synthesis of HMDI-based segmented polyurethanes and their use in the manufacture of elastomeric composites for cardiovascular applications

Journal of Biomaterials Science-polymer Edition, 2007

For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methyleneb... more For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methylenebis(cyclohexyl isocyanate) (HMDI), polytetramethylenglycol (PTMG) and 1,4-butanediol (BD) were synthesized and characterized by spectroscopy (FT-IR, (1)H-NMR) and thermal (TGA, DMA, DSC) and mechanical techniques. The segmented nature of the SPUs was not easily established by spectroscopic means; however, TGA allowed the quantification of the rigid segments content by the significant mass loss between 348 and 356 degrees C. The alpha transition was detected by DMA and related to the T(g) of the soft segments at -50 degrees C, while DSC showed the presence of an endothermic transition above 80 degrees C attributed to the melting of rigid segments. Two types of composites were prepared using the synthesized SPUs and Lycra (either T162B or T162C). The first one consisted of a two layers casting laminated while the second one was a classic unidirectional fibre-reinforced material. Laminate composites prepared with SPU containing 23.9% and 33.9% of rigid segments and Lycra T162C exhibited a higher tensile modulus but lower tensile strength than composites prepared with Tecoflex SG-80A (39.7% of rigid segments). The energy of adhesion between layers on these composites ranged from 475 to 2150 J. Fibre-reinforced SPUs exhibited higher moduli than the two layer laminated composites with increasing amounts of rigid segments in the matrix and by increasing Lycra T162C content (up to 10%). This behaviour was explained by SEM, which showed a good fibre-matrix bonding.

Research paper thumbnail of Poly(vinyl alcohol)/poly(acrylic acid) blends: Miscibility studies by DSC and characterization of their thermally induced hydrogels

Journal of Applied Polymer Science, 1993

Binary blends of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) and polyacrylamide (PAAm... more Binary blends of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) and polyacrylamide (PAAm) were characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and infrared spectroscopy (IR). Molecular weight, blend composition, and heating time at 150°C were the variables used. Results obtained by DSC indicated that PAA/PVA blends are miscible in the full range of composition. Similarly, TGA traces showed that thermal stability was higher for blends than for pure polymers. Blends of PVA with high molecular weight PAA exhibited a hydrogel behavior after drying at relatively low temperature (100°C), whereas blends containing low molecular weight PAA behaved as hydrogels only after they were heated at 150°C. Hydrogel character was increased for these two PVA/PAA blends with the heating time at higher temperature (150°C). IR spectra revealed that esterification took place in these blends after thermally treated at this temperature. In contrast, addition of glyoxal in combination with heating was necessary to produce hydrogels from PAAm/PVA blends. Furthermore, the crosslinking degree of these hydrogels was estimated from their absorbency values by applying the Flory–Rehner equation. © 1993 John Wiley & Sons, Inc.

Research paper thumbnail of A TG/FTIR study on the thermal degradation of poly(vinyl pyrrolidone

Journal of Thermal Analysis and Calorimetry, 2011

The aim of this study was to gain some fundamental knowledge on the thermal degradation pathways ... more The aim of this study was to gain some fundamental knowledge on the thermal degradation pathways of poly(N-vinyl pyrrolidone) using Thermogravimetry coupled with Fourier Transform Infrared Spectroscopy (TG–FTIR) in addition to IR and 1H NMR spectroscopic studies of the partially degraded samples. It was found that the vinyl pyrrolidone is the main volatile products of the thermal degradation of PVP which implies that the predominant mechanism during thermal degradation of this polymer is the depolymerization to monomer of the polymeric main chain; however, it is evident that simultaneous reactions may be involved yielding oligomers. FTIR and 1H NMR spectra of partially degraded samples of PVP exhibited very similar characteristics to that observed for undegraded samples although the 1H NMR spectra suggest the presence of simultaneous reactions as the fragmentation of polymeric main chain.

Research paper thumbnail of TGA/FTIR study on thermal degradation of polymethacrylates containing carboxylic groups

Polymer Degradation and Stability, 2006

In this work, the thermal degradation of polymethacrylates containing carboxylic groups namely po... more In this work, the thermal degradation of polymethacrylates containing carboxylic groups namely poly(methacryloyloxy butanoic acid), PMBA; poly(methacryloyloxy hexanoic acid), PMHA; and poly( p-methacryloyloxy benzoic acid), PMBeA was investigated by TGA/FTIR. Moreover, in order to shed more light on the reaction pathways during the thermal decomposition of these polymers, an FTIR spectroscopic study of structural changes in the degrading material was performed. By TGA it was observed that PMBA exhibited two well-defined degradation stages at 327 and 450 C; PMHA presents only one main weight loss at ca. 402 C although from DTG curve it was noted that the single step degradation was composed by two overlapped peaks located at 414 and 449 C and a small shoulder at 317 C; finally PMBeA showed three weight loss regions at 265, 353 and 468 C. From FTIR analysis of the partially degraded samples it was found that the thermal degradation of these polymers resembled that of polymethacrylic acid, i.e. anhydrides were initially formed and then the modified structure is broken to yield an aromatic structure with phenolic groups. In contrast, the analysis by FTIR of the volatile products from the studied polymers differs notably than those obtained for polymethacrylic acid: b-lactones and g-lactones were released from PMBA and PMHA, respectively, during its thermal degradation, whereas an ester derivative from benzoic acid evolves from PMBeA probably through depolymerization.

Research paper thumbnail of TGA/FTIR studies of segmented aliphatic polyurethanes and their nanocomposites prepared with commercial montmorillonites

Polymer Degradation and Stability, 2009

Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (C... more Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (CloisiteÔ Na þ , CloisiteÔ 15A, CloisiteÔ 30B) were studied using thermogravimetric analysis coupled with Fourier Transform Infrared Spectroscopy (TGA/FTIR). The results showed that the thermal degradation of unfilled SPU and the 4, 6 and 10 wt% hand mixed nanocomposites occurred in two stages being the first due to degradation of hard segments and the second due to the degradation of soft segments. It was also found that the thermal stability of these nanocomposites was not improved by increasing nanoclay concentration except for SPU/CloisiteÔ 15A nanocomposites were a 40 C increase was observed. In a similar manner, FTIR spectra of the evolved gases obtained after the thermal degradation of these nanocomposites were qualitatively similar to the unfilled polymer except in those containing CloisiteÔ 30B where isocyanate absorptions were detected. In contrast, SPU/CloisiteÔ 30B nanocomposites prepared by in-situ polymerization, exhibited higher thermal stability than the corresponding hand mixed nanocomposites. In addition, these nanocomposites exhibited the presence of carbon dioxide in the evolved gases during its second degradation stage which was not observed in the hand mixed nanocomposites. In this case, it can be said that the presence of clays in the nanocomposites has a significant effect on the thermal degradation pathways.

Research paper thumbnail of Thermal degradation behavior of polymethacrylates containing amine side groups

Polymer Degradation and Stability, 2008

The thermal degradation behavior of polymethacrylates containing amine groups such as poly(N,N-di... more The thermal degradation behavior of polymethacrylates containing amine groups such as poly(N,N-diethyl aminoethyl methacrylate), PDEAEM, and poly(N-ethyl-m-tolyl-aminoethyl methacrylate), PMEET, has been studied using thermogravimetry coupled with infrared ...

Research paper thumbnail of Characterization of hydrogel blends of poly(vinyl pyrrolidone) and poly(vinyl alcohol-vinyl acetate

Journal of Materials Science-materials in Medicine, 1996

Hydrogel blends were prepared from water-soluble polymers of poly(vinyl alcohol-vinyl acetate) an... more Hydrogel blends were prepared from water-soluble polymers of poly(vinyl alcohol-vinyl acetate) and poly(vinyl pyrrolidone). The method of preparation was optimized and different compositions of blends were characterized. The effect of thermal treatment and the introduction of an aldehydic crosslinking agent in the blend was also studied. The swelling characteristics of the various compositions, their thermal behaviour and the state of water was examined. Mechanical properties of the hydrogels were determined and it was observed that blends containing glutaraldehyde produced materials with good mechanical integrity and high water contents.

Research paper thumbnail of Dynamic mechanical characterization of hydrogel blends of poly(vinyl alcohol-vinyl acetate) with poly(acrylic acid) or poly(vinyl pyrrolidone

Journal of Materials Science-materials in Medicine, 1996

Transparent hydrogels were prepared by blending solutions of poly(vinyl alcohol-vinyl acetate) wi... more Transparent hydrogels were prepared by blending solutions of poly(vinyl alcohol-vinyl acetate) with either poly(acrylic acid) or poly(vinyl pyrrolidone) in the presence of glutaraldehyde as a crosslinking agent. The network obtained from the poly(vinyl pyrrolidone) system was subjected to various thermal treatments, the effects of which have been studied. Dynamic mechanical analysis was used to characterize the hydrogels and to establish the suitability of these blends for use in biomedical applications. The swelling behaviour was followed under dynamic loads as well as by mass difference. Different frequencies were used to study the dynamic properties of the hydrogel blends which showed an increase in storage modulus with increasing frequency. A comparison of modulus values obtained dynamically were in agreement with data obtained mechanically in tension.

Research paper thumbnail of Effect of cross-linking agents on the dynamic mechanical properties of hydrogel blends of poly(acrylic acid)-poly(vinyl alcohol-vinyl acetate

Biomaterials, 1996

A range of hydrogels were prepared by blending aqueous solutions of poly(vinyl alcohol-vinyl acet... more A range of hydrogels were prepared by blending aqueous solutions of poly(vinyl alcohol-vinyl acetate) with poly(acrylic acid) in various proportions. The effects of two cross-linking agents (glyoxal and glutaraldehyde) and subsequent thermal treatment on the properties of the blends are discussed. Dynamic mechanical analysis (DMA) of the xerogels indicated complete miscibility of the various blends which was evident from the appearance of a single glass transition temperature (T,) in the presence of either glyoxal or glutaraldehyde at all thermal treatments studied. A 50150% wtlwt blend was found to have the highest storage modulus and was thus selected for further study. Hydrogels prepared with glutaraldehyde without subsequent thermal treatment exhibited higher storage modulus values than those prepared using glyoxal when tested isothermally at 20°C in a water bath. A further increase in the storage modulus was observed when these hydrogels were thermally treated at 120 or 150°C. In a non-isothermal study on the cross-linked hydrogels, no variation in storage modulus was observed. Broad peaks were observed in tan 6 plots, these peaks shifting towards higher frequencies as the degree of cross-linking increased in the hydrogel. 0 1966 Elsevier Science Limited.