Papers by Miguel Angel Gracia Pinilla
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The development and study of new smart materials is an emergent research area with high potential... more The development and study of new smart materials is an emergent research area with high potential applications. In this study, we have fabricated poly(ethyleneimine)/poly(acrylic acid) multilayer films on glass substrates by automated spray-layer-by-layer (spray-LbL) technique. By analyzing the changes in thickness, roughness and elasticity, with fine-tuning of the operational parameters of the spray-LbL system, evident trends of its effect on the multilayer construction were observed. In the case of its mechanical properties, the stability of Young's modulus (up to 8.25 GPa) from film thickness at this scale was detected, making it variable for other factors such as pH and molecular weight. This work also identified the healability phenomenon that is present in the exponentially grown PEI/PAA samples, based on the reduction in viscosity of the polymer complexes and the interdiffusion of polyelectrolytes at the damaged zones in the presence of water. These properties allow for the assembly of a highly electrically conductive multilay-ered film by dispersion of a top layer of silver nanowires whose sheet resistance is increased around 5% after multiple damaging events. These experimental results provide new data for the evaluation and design of polyelectrolyte multilayers assembled with a spin-assisted automated spray deposition system to serve as substrates for mechanoelectrical devices which can benefit from its self-healing and modulated mechanical capabilities.
The presence of sulfates potentialize damage on cement-based materials, leading to structural fai... more The presence of sulfates potentialize damage on cement-based materials, leading to structural failures. Therefore, structures must be designed to compensate for this effect. The mechanical properties of cement–chitin mixtures are investigated with different percentages of chitin (0.5, 1.3, and 2.1 wt.%) and aging of composite in a joint nano-scopic-and macroscopic-scale by experimental study. The objective is to increase the durability of concrete elements at coastal aquifers where concrete structures are in constant exposure to sulfate ions, chloride ions among others. Tapping mode AFM was used to characterize the surface structure and roughness of the cement pastes. To verify the chitin addition and the formation of sulfate-based aggregates Raman and IR spectra were recorded and are presented in this work. Then, force spectroscopy was used to obtain the nanomechanical properties at three different exposure times (1 day, 6 months, and 1 year) into water or a SO 4 À2 environment. Macroscopic parameters (e.g., compression strength of cylindrical probes) were assessed for comparison following standard guidelines. The results show a decrease of its mechanical properties as a function of the polymer concentration but more importantly, they correlate the elasticity and adhesion at the nanoscale with the behavior of the bulk material.
Au and Cu nanoparticles (NPs) and clusters were synthesized in aqueous media by nanosecond pulsed... more Au and Cu nanoparticles (NPs) and clusters were synthesized in aqueous media by nanosecond pulsed laser ablation (NPLA) through the irradiation of light of wavelength of 1064 nm produced by a Nd:YAG laser at a fluence of 20 mJ/cm 2 per pulse and of pulses of 5 ns. The study of the effects of the polyethyleneimine (PEI) on the Au and Cu-NPs and clusters was also performed. The capping process was performed during the irradiation of the Au or Cu targets using the laser. The procedure allows for a remarkably low range of particle sizes on the sample between 0.5 nm and 10 nm, with an average of 5 nm. The addition of the polymer (PEI) in the aqueous media inhibits the formation of aggregates or the coalescence process of the NPs, and it also produces Au-PEI and Cu-PEI clusters with sizes smaller than 2 nm; in both cases, narrow size distributions were validated by HRTEM and zeta potential (ZP) analysis. The high crystallinity (five-fold preferential orientation) of the Au-NPs-PEI(capping) compared with Au-NPs without PEI was also evidenced by microscopy analysis. Finally, a new route to produce Au-NPs, Cu-NPs and clusters functionalized with PEI was proposed.
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Papers by Miguel Angel Gracia Pinilla