M. Villanueva

Ionic Liquids Based on Phosphonium Cations As Neat Lubricants or Lubricant Additives for a Steel/Steel Contact

After doing several miscibility essays with eight ionic liquids (ILs) and four base oils, the ILs tri(butyl)ethylphosphonium diethylphosphate [P4,4,4,2][C2C2PO4] and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate [P6,6,6,14][(C2F5)3PF3] were selected to be studied as lubricant additives. The neat IL [P4,4,4,2][C2C2PO4], the base oils, and several blends were characterized in terms of density, viscosity, and thermal stability. The tribological performance of the miscible base oil/IL blends (1 wt %) and the neat [P4,4,4,2][C2C2PO4] were evaluated for the lubrication of an AISI 420 steel-100Cr6 steel contact pair. The friction coefficients and wear volumes obtained are also compared with those corresponding to the pure base oils and their mixtures with conventional additive zinc dialkyldithiophosphate (ZDDP). As neat lubricants, [P4,4,4,2][C2C2PO4] showed the best antifriction ability, whereas in terms of wear, better results were obtained with [P6,6,6,14][(C2F5)3PF3]. However, higher improvements in both friction and wear were found for blends containing [P4,4,4,2][C2C2PO4]. XPS analyses of the worn surfaces lubricated with these mixtures indicated the presence of phosphorus in the tribofilm formed on the wear track. However, this compound was slightly detected on tribosamples lubricated with blends containing [P6,6,6,14][(C2F5)3PF3].

Effects of diffusion on the kinetic study and TTT cure diagram for an epoxy/diamine system

The curing reactions of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n 5 0) and 1,2-diamine cyclohexane (DCH) were studied to determine a time-temperature-transformation (TTT) isothermal cure diagram for this system. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and a solubility test were used to obtain the different experimental data reported. Two models, one based solely on chemical kinetics and the other accounting for diffusion, were used and compared to the experimental data. The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre- and post-vitrification stages. The investigation was made in the temperature range 60 -100°C, which is considered optimum for the isothermal curing of the epoxy system studied.

Antimicrobial Activity of Starch Hydrogel Incorporated with Copper Nanoparticles

In order to obtain an antimicrobial gel, a starch-based hydrogel reinforced with silica-coated copper nanoparticles (Cu NPs) was developed. Cu NPs were synthesized by use of a copper salt and hydrazine as a reducing agent. In order to enhance Cu NP stability over time, they were synthesized in a starch medium followed by a silica coating. The starch hydrogel was prepared by use of urea and water as plasticizers and it was treated with different concentrations of silica-coated copper nanoparticles (Si-Cu NPs). The obtained materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, scanning electron microscopy (SEM), and rheometry. FT-IR and EPR spectra were used for characterization of Cu NPs and Si-Cu NPs, confirming that a starch cap was formed around the Cu NP and demonstrating the stability of the copper nanoparticle after the silica coating step. SEM images showed Cu NP, Si-Cu NP, and hydrogel morphology. The particle size was polydisperse and the structure of the gels changed along with particle concentration. Increased NP content led to larger pores in starch structure. These results were in accordance with the rheological behavior, where reinforcement by the Si-Cu NP was seen. Antimicrobial activity was evaluated against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial species. The hydrogels were demonstrated to maintain antimicrobial activity for at least four cycles of use. A dermal acute toxicity test showed that the material could be scored as slightly irritant, proving its biocompatibility. With these advantages, it is believed that the designed Si-Cu NP loaded hydrogel may show high potential for applications in various clinical fields, such as wound dressings and fillers.

Kinetic and thermodynamic studies of an epoxy system diglycidyl ether of bisphenol A/1, 2 diamine cyclohexane/calcium carbonate filler

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0) and 1,2-diaminecyclohexane (DCH) with a calcium carbonate filler was studied by differential scanning calorimetry (DSC) and using a scanning electronic microscope (SEM). As a first stage, the optimum content of the filler determined was 20%. From a kinetic study, in which two models were used, parameters such as reaction orders, rate constants, and activation energies were determined. A thermodynamic study allowed calculation of enthalpy (ΔH#), entropy (ΔS#), and free-energy ((ΔG#) changes. The results were compared to those obtained for the same epoxy systems without the filler.

Lifetime prediction of the epoxy system badge n = 0/1,2 DCH by thermogravimetric analysis

Lifetime of the system diglycidyl ether of bisphenol A (BADGE n 5 0)/1,2- diamine cyclohexane (DCH) was predicted by thermogravimetric analysis. Lifetime was considered when either 5% weight loss or 5% conversion was reached. Experimental results were treated using two different methods: The first method was independent of the degradation mechanism and the second was based on the thermodegradation kinetic mechanism. The activation energy of the reaction, determined using the Flynn- Wall-Ozawa method, was 148.51 kJ/mol. This value is in a good agreement with that of 144.01 kJ/mol obtained using Kissinger9s method. From the experimental results, it was found that the optimum temperature of service for this material is in the range of 100 -140°C, at which the corresponding lifetime range is from 27 to 2633 years.

Effects of diffusion on the kinetic study of an epoxy system diglycidyl ether of bisphenol A/1,2-diamine cyclohexane/calcium carbonate filler

The curing reactions of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0), 1,2-diamine cyclohexane (DCH) with calcium carbonate filler, were studied to determine different kinetic parameters. Two models-one based solely on chemical kinetics and the other accounting for diffusion-were used and compared to experimental data both for systems with and without filler. It was found that 100°C is the optimum service temperature, and also that the presence of the filler has no influence on the optimal service temperature range (60-100°C) of the epoxy system.

Long-term thermal stabilities of ammonium ionic liquids designed as potential absorbents of ammonia

Searching for potential absorbents in working pairs with NH3, a series of new ammonium ionic liquids related to choline were designed and synthesized. In order to explore their applicability in refrigeration by absorption, their thermal stabilities were studied. For this proposal, a thermogravimetric analyzer, TGA 7 – Perkin-Elmer, was used in dynamic mode from 100 °C to 800 °C at 10 °C min−1 under dry air atmosphere. From the ionic liquids TG curves, the onset temperatures (Tonset) were determined, as well as the loss of mass at these Tonset. Significant decomposition was detected at lower temperatures than Tonset in all cases, meaning that the true ionic liquids stability is lower than that provided by the dynamic TG. Isothermal studies at lower temperatures than Tonset were also carried out to estimate the long-term thermal stabilities at different temperatures.

Comparative study of the thermal stability of the epoxy systems badge n=0/1, 2 dch and badge n=0/1, 2 DCH/CaCO3

The thermal degradation of the epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) and diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diaminecyclohexane (DCH) containing calcium carbonate filler immersed and not immersed in hydrochloric acid have been studied by thermogravimetric analysis in order to compare their decomposition processes and to determine the reaction mechanism of the degradation processes. The value of the activation energies, necessary for this study, were calculated using various integral and differential methods. Analysis of the results suggests that hydrochloric acid does not affect the decomposition of the epoxy network and that the reaction mechanisms produce sigmoidal-type curves for the systems not immersed in HCl and deceleration curves for the same systems immersed.

TTT Cure Diagram

Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied to calculate time-temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were measured as a function of temperature using solubility test. Differential scanning calorimetry (DSC) was used to calculate the vitrification times. DSC data show a one-to-one relationship between Tg and fractional conversion, a independent of cure temperature. As a consequence, Tg can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from the gel times obtained using the solubility test (41.5 kJ mol-1). This value is similar to the results obtained for other similar epoxy systems. Isoconversion contours were calculated by numerical integration of the best fitting kinetic model.

New insight into the environmental impact of two imidazolium ionic liquids. Effects on seed germination and soil microbial activity

The next generation of ionic liquids must be synthetized taking into account structures that guarantee the suitable properties for a defined application as well as ecological data. Thus, searching of the right methodologies to know, quickly and efficiently, the ecological effects of these compounds is a preliminary task. The effects of two imidazolium based ionic liquids with different anions, 1-butyl-3-methylimidazolium tetrafluoroborate, [C4C1Im][BF4], and 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C3C1Im][NTf2], on seedling emergence of six tree species and on the microbial behaviour of two soils were determined in this work. Results showed that the highest doses of both ionic liquids caused the total inhibition of germination for almost all the species studied and that the seeds are more sensitive to the presence of these compounds than soil microbial activity. Nevertheless, signals of stress and death are observed from the results of heat released by microorganisms after the addition of the highest doses of both ionic liquids. The novelty of this work resides in the enlargement of knowledge of toxicity of ILs on complex organisms such as arboreal species and microbial activity of soils studied for the first time through a microcalorimetric technique.