Plasma treatments had emerged as a useful technique to improve seed germination. In this work we investigate the influence of different irrigation conditions and plasma treatments on the germination of nasturtium seeds. During plasma treatment, seeds experience a progressive weight loss as a function of treatment time that has been associated to water release, a process that is more pronounced after longer plasma treatment times. Seeds treated for short times (<30 s) are able to germinate more efficiently than untreated specimen under hydric stress (drought conditions), while plasma treatments for longer times (up to 300 s) impaired germination independently on irrigation conditions. Characterization analysis of plasma treated seeds by FTIR-ATR, SEM/EDX and XPS showed that plasma treatment affected the chemical state of pericarp while, simultaneously, induced a considerable increase in the seeds water uptake capacity. The decrease in germination efficiency found after plasma treatment for long times, or for short times under optimum irrigation conditions, has been attributed to that the excess of water accumulated in the pericarp hampers the diffusion up to the embryo of other agents like oxygen which are deemed essential for germination.
Thermo-sensitive hydrogels from free radical copolymerization of NIPAAm and crosslinking monomer MBA (p(NIPAAm-co-MBA)) using in situ liquid atmospheric DBD plasma are successfully synthesized as revealed by FTIR and solid state 13 C-NMR analysis, despite a rather short polymerization time of 10 min. The addition of MBA crosslinking monomer exerts a positive influence on the p(NIPAAm-co-MBA) copolymerization process, particularly at higher monomer concentrations and incident plasma power as suggested by GPC analysis. The swelling capacity of the p(NIPAAm-co-MBA) hydrogels declines significantly when the MBA concentration increased due to better crosslinking efficiency during the copolymerization process. The decrease in swelling capacity of p(NIPAAm-co-MBA) is also displayed by cryo-SEM analysis as smaller pore sizes and higher pore density of hydrogels were detected. The thermo responsiveness of p(NIPAAm-co-MBA) hydrogels is confirmed by DSC analysis with LCST values similar to the LCTS value of p(NIPAAm) around 32 8C. Enthalpy /J/g : 58,5924 (Endothermic effect) Exo Peak: 32.8140 o C Onset point: 26.5695 o C Enthalpy: 26.4631 J/g Peak: 33.2749 o C Onset point: 30.6265 o C Enthalpy: 69.6224 J/g Peak: 33.5454 o C Onset point: 21.9078 o C Enthalpy: 58.5924 J/g Peak: 33.0978 o C Onset point: 30.6117 o C Enthalpy: 59.0967 J/g Figure 6. DSC thermograms of the p(NIPAAm-co-MBA) hydrogels obtained at 30 W plasma power with (a) 10% NIPAAm with 0.1% MBA, (b) 10% NIPAAm with 1% MBA, (c) 20% NIPAAm with 0.2% MBA, and (d) 20% NIPAAm with 2% MBA (heating rate of 1.5 8C min À1 from 5 to 50 8C).
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