Silica Nanoparticles in Xanthan Gum Solutions: Oil Recovery Efficiency in Core Flooding Tests.

Polymer flooding is one of the enhanced oil recovery (EOR) methods that increase the macroscopic efficiency of the flooding process and enhanced crude oil recovery. In this study, the effect of silica nanoparticles (NP-SiO2) in xanthan gum (XG) solutions was investigated through the analysis of efficiency in core flooding tests. First, the viscosity profiles of two polymer solutions, XG biopolymer and synthetic hydrolyzed polyacrylamide (HPAM) polymer, were characterized individually through rheological measurements, with and without salt (NaCl). Both polymer solutions were found suitable for oil recovery at limited temperatures and salinities. Then, nanofluids composed of XG and dispersed NP-SiO2 were studied through rheological tests. The addition of nanoparticles was shown to produce a slight effect on the viscosity of the fluids, which was more remarkable over time. Interfacial tension tests were measured in water-mineral oil systems, without finding an effect on the interfacial properties with the addition of polymer or nanoparticles in the aqueous phase. Finally, three core flooding experiments were conducted using sandstone core plugs and mineral oil. The polymers solutions (XG and HPAM) with 3% NaCl recovered 6.6% and 7.5% of the residual oil from the core, respectively. In contrast, the nanofluid formulation recovered about 13% of the residual oil, which was almost double that of the original XG solution. The nanofluid was therefore more effective at boosting oil recovery in the sandstone core.

Particles' Organization in Direct Oil-in-Water and Reverse Water-in-Oil Pickering Emulsions.

This paper addresses the impact of the particle initial wetting and the viscosity of the oil phase on the structure and rheological properties of direct (Oil/Water) and reverse (Water/Oil) Pickering emulsions. The emulsion structure was investigated via confocal microscopy and static light scattering. The flow and viscoelastic properties were probed by a stress-controlled rheometer. Partially hydrophobic silica particles have been employed at 1 and 4 wt.% to stabilize dodecane or paraffin-based emulsions at 20 vol.% of the dispersed phase. W/O emulsions were obtained when the particles were dispersed in the oily phase while O/W emulsions were prepared when the silica was introduced in the aqueous phase. We demonstrated that, although the particles adsorbed at the droplets interfaces for all the emulsions, their organization, the emulsion structure and their rheological properties depend in which phase they were previously dispersed in. We discuss these features as a function of the particle concentration and the oil viscosity.

Effect of Silica Nanoparticles in Xanthan Gum Solutions: Evolution of Viscosity over Time.

The effect of silica nanoparticles (NP-SiO2) in xanthan gum (XG) solutions was investigated through the analysis of viscosity profiles. First, hydrocolloid XG solutions and hydrophilic NP-SiO2 suspensions were characterized individually through rheological measurements, with and without salt (NaCl). Then, nanofluids composed of XG and NP-SiO2 dispersed in water and brine were studied through two different aging tests. The addition of nanoparticles was shown to produce a slight effect on the viscosity of the fresh fluids (initial time), while a more remarkable effect was observed over time. In particular, it appears that the presence of NP-SiO2 stabilizes the polymer solution by maintaining its viscosity level in time, due to a delay in the movement of the molecule. Finally, characterization techniques such as confocal microscopy, capillary rheometry, and Zeta potential were implemented to analyze the XG/NP-SiO2 interaction. Intrinsic viscosity and relative viscosity were calculated to understand the molecular interactions. The presence of NP-SiO2 increases the hydrodynamic radius of the polymer, indicating attractive forces between these two components. Furthermore, dispersion of the nanoparticles in the polymeric solutions leads to aggregates of an average size smaller than 300 nm with a good colloidal stability due to the electrostatic attraction between XG and NP-SIO2. This study proves the existence of interactions between XG and NP-SiO2 in solution.

Evaluation of the repartition of the particles in Pickering emulsions in relation with their rheological properties.

HYPOTHESIS: The distribution of particles in Pickering emulsions can be estimated through a percolation-type approach coupled to the evolution of their rheological features with the dispersed phase volume fraction ϕ. EXPERIMENTS: The rheological behavior of water-in-dodecane Pickering emulsions stabilized with hydrophobic silica nanoparticles is addressed. The emulsions viscosity and elastic modulus are investigated at ϕ varying from 0.1 to 0.75. Various rheological models are adjusted to the experimental data. FINDINGS: The comparison of the elastic modulus evolution of the Pickering emulsions with those of emulsions stabilized with surfactants confirms a major contribution of the particles to the rheological behavior of Pickering emulsions and supports the existence of a three-dimensional network between the droplets. The applied percolation approach allows to quantitively estimate a nanoparticles viscoelastic link between the droplets and opposes the classic vision of interfacial monolayers stabilizing the Pickering emulsions. This network of interconnected particles and droplets contributes significantly to the viscosity as well as the elastic modulus of these emulsions. To our knowledge, the applied percolation-based model is the only one capable of providing a structural explanation while describing the abrupt viscosity and elastic modulus growth of Pickering emulsions across the range of ϕ.

A human endogenous retrovirus-derived gene that can contribute to oncogenesis by activating the ERK pathway and inducing migration and invasion.

Endogenous retroviruses are cellular genes of retroviral origin captured by their host during the course of evolution and represent around 8% of the human genome. Although most are defective and transcriptionally silenced, some are still able to generate retroviral-like particles and proteins. Among these, the HERV-K(HML2) family is remarkable since its members have amplified relatively recently and many of them still have full length coding genes. Furthermore, they are induced in cancers, especially in melanoma, breast cancer and germ cell tumours, where viral particles, as well as the envelope protein (Env), can be detected. Here we show that HERV-K(HML2) Env per se has oncogenic properties. Its expression in a non-tumourigenic human breast epithelial cell line induces epithelial to mesenchymal transition (EMT), often associated with tumour aggressiveness and metastasis. In our model, this is typified by key modifications in a set of molecular markers, changes in cell morphology and enhanced cell motility. Remarkably, microarrays performed in 293T cells reveal that HERV-K(HML2) Env is a strong inducer of several transcription factors, namely ETV4, ETV5 and EGR1, which are downstream effectors of the MAPK ERK1/2 and are associated with cellular transformation. We demonstrate that HERV-K(HML2) Env effectively activates the ERK1/2 pathway in our experimental setting and that this activation depends on the Env cytoplasmic tail. In addition, this phenomenon is very specific, being absent with every other retroviral Env tested, except for Jaagsiekte Sheep Retrovirus (JSRV) Env, which is already known to have transforming properties in vivo. Though HERV-K Env is not directly transforming by itself, the newly discovered properties of this protein may contribute to oncogenesis.

The HERV-K human endogenous retrovirus envelope protein antagonizes Tetherin antiviral activity.

UNLABELLED: Endogenous retroviruses are the remnants of past retroviral infections that are scattered within mammalian genomes. In humans, most of these elements are old degenerate sequences that have lost their coding properties. The HERV-K(HML2) family is an exception: it recently amplified in the human genome and corresponds to the most active proviruses, with some intact open reading frames and the potential to encode viral particles. Here, using a reconstructed consensus element, we show that HERV-K(HML2) proviruses are able to inhibit Tetherin, a cellular restriction factor that is active against most enveloped viruses and acts by keeping the viral particles attached to the cell surface. More precisely, we identify the Envelope protein (Env) as the viral effector active against Tetherin. Through immunoprecipitation experiments, we show that the recognition of Tetherin is mediated by the surface subunit of Env. Similar to Ebola glycoprotein, HERV-K(HML2) Env does not mediate Tetherin degradation or cell surface removal; therefore, it uses a yet-undescribed mechanism to inactivate Tetherin. We also assessed all natural complete alleles of endogenous HERV-K(HML2) Env described to date for their ability to inhibit Tetherin and found that two of them (out of six) can block Tetherin restriction. However, due to their recent amplification, HERV-K(HML2) elements are extremely polymorphic in the human population, and it is likely that individuals will not all possess the same anti-Tetherin potential. Because of Tetherin's role as a restriction factor capable of inducing innate immune responses, this could have functional consequences for individual responses to infection. IMPORTANCE: Tetherin, a cellular protein initially characterized for its role against HIV-1, has been proven to counteract numerous enveloped viruses. It blocks the release of viral particles from producer cells, keeping them tethered to the cell surface. Several viruses have developed strategies to inhibit Tetherin activity, allowing them to efficiently infect and replicate in their host. Here, we show that human HERV-K(HML2) elements, the remnants of an ancient retroviral infection, possess an anti-Tetherin activity which is mediated by the envelope protein. It is likely that this activity was an important factor that contributed to the recent, human-specific amplification of this family of elements. Also, due to their recent amplification, HERV-K(HML2) elements are highly polymorphic in the human population. Since Tetherin is a mediator of innate immunity, interindividual variations among HERV-K(HML2) Env genes may result in differences in immune responses to infection.