Structure and properties of biodegradable PLLA/ZnO composite membrane produced via electrospinning

These days, composite materials based on polymers and inorganic nanoparticles (NPs) are widely used in optoelectronics and biomedicine. In this work, composite membranes of polylactic acid and ZnO NPs containing 5–40 wt.% of the latter NPs were produced by means of electrospinning. For the first time, polymer material loaded with up to 40 wt.% of ZnO NPs (produced via laser ablation in air and having non-modified surface) was used to prepare fiber-based composite membranes. The morphology, phase composition, mechanical, spectral and antibacterial properties of the membranes were tested by a set of analytical techniques including SEM, XRD, FTIR, UV-vis, and photoluminescence spectroscopy. Antibacterial activity of the materials was evaluated following standard procedures (ISO 20743:2013) and using S. aureus and E. coli bacteria. It is shown that incorporation of 5–10 wt.% of NPs led to improved mechanical properties of the composite membranes, while further increase of ZnO content up to 20 wt.% and above resulted in their noticeable deterioration. At the same time, the antibacterial properties of ZnO-rich membranes were more pronounced, which is explained by a larger number of surface-exposed ZnO NPs, in addition to those embedded into the bulk of fiber material

Development and evaluation of foam-based conformance control for a high-salinity and high-temperature carbonate

Abstract The extreme heterogeneity of carbonate reservoirs in the form of fracture corridors and super-permeability thief zones present challenges to the efficient sweep of oil in both secondary and tertiary recovery operations. In such reservoirs, conformance control is crucial to ensure injected water and any EOR chemicals optimally contact the remaining oil with minimal throughput. Foam-based conformance control is a relatively new technology especially its use for deep diversion in high-salinity and high-temperature conditions. In this work, a laboratory study was conducted to develop and evaluate a foam-based conformance control technology for application in a high-salinity and high-temperature carbonate. Foaming agents (surfactants) were first screened for their suitability with regard to reservoir temperature and salinity where properties such as foamability and foam stability were measured. The best performing surfactants were then used to study the foam-induced mobility reduction across a core composite. The experiments were conducted at reservoir conditions. Foam stability and decay were also investigated in those permeability reduction experiments. Brine and crude oil were injected after foam formation where observed pressure drops allowed quantification of foam stability and decay; hence, the sustainability of mobility reduction. Finally, the potential improvement in reservoir contact and hence oil recovery were examined by oil displacement experiments conducted in specially prepared heterogeneous composites. For the studied conditions of high salinity and high temperature, foaming agents of the amphoteric family as well as one manufacturer proprietary surfactants blend were found suitable in terms of salt tolerance and foam stability. Using the proprietary blend and without oil in core, the generated foam reduced fluids mobility by a factor of 12. The attained mobility reduction was lower in presence of oil but was still acceptable for flow diversion purposes. Using the proprietary blend and with oil in core, the generated foam reduced fluids mobility by a factor of 6 (compared to 12 without oil in core). Oil recovery improvement with foam placement was also found to be significant. These results demonstrate the potential of foams for carbonates with harsh salinity and temperature conditions

Stability of Octadecyltrimethoxysilane-Based Coatings on Aluminum Alloy Surface

Long-term stability in contact with water of organosilane layers formed by octadecyltrimethoxysilane (ODTMS) on polished aluminum alloy (AA2024) through dip-coating was studied by combining SEM, water contact angle measurements, and X-ray photoelectron spectroscopy. Similar organosilane layers were formed on AA2024 coated with permanganate conversion coating, 1,2-bis(triethoxysilyl)ethane (BTSE) and hydrated SiOx as under-layers, after which their long-term durability was also tested. During immersion in water for about one month, all the samples exhibited a decrease in hydrophobicity, implying the prepared organosilane layer was not stable over time, gradually hydrolyzing and letting water interact with the underlying layer. In parallel, SEM images of one-layer samples taken after immersion showed clear signs of local electrochemical corrosion, while XPS analysis confirmed a loss of silicon from the surface layer. The highest stability over time was demonstrated by a one-layer sample prepared in an ethanol/water bath for 5 min and by a similar ODTMS layer prepared on hydrated MnOx as an under-layer

Comparative Study of Physicochemical and Antibacterial Properties of ZnO Nanoparticles Prepared by Laser Ablation of Zn Target in Water and Air

Here, we report on ZnO nanoparticles (NPs) generated by nanosecond pulsed laser (Nd:YAG, 1064 nm) through ablation of metallic Zn target in water and air and their comparative analysis as potential nanomaterials for biomedical applications. The prepared nanomaterials were carefully characterized in terms of their structure, composition, morphology and defects. It was found that in addition to the main wurtzite ZnO phase, which is conventionally prepared and reported by others, the sample laser generated in air also contained some amount of monoclinic zinc hydroxynitrate. Both nanomaterials were then used to modify model wound dressings based on biodegradable poly l-lactic acid. The as-prepared model dressings were tested as biomedical materials with bactericidal properties towards S. aureus and E. coli strains. The advantages of the NPs prepared in air over their counterparts generated in water found in this work are discussed