Interfacial Particle Dynamics: One and Two Step Yielding in Colloidal Glass.

The yielding behavior of silica nanoparticles partitioned at an air-aqueous interface is reported. Linear viscoelasticity of the particle-laden interface can be retrieved via a time-dependent and electrolyte-dependent superposition, and the applicability of the "soft glassy rheology" (SGR) model is confirmed. With increasing electrolyte concentration (φ(elect)) in the aqueous subphase, a nonergodic state is achieved with particle dynamics arrested first from attraction induced bonding bridges and then from the cage effect of particle jamming, manifesting in a two-step yielding process under large amplitude oscillation strain (LAOS). The Lissajous curves disclose a shear-induced in-cage particle redisplacement within oscillation cycles between the two yielding steps, exhibiting a "strain softening" transitioning to "strain stiffening" as the interparticle attraction increases. By varying φ(elect) and the particle spreading concentration, φ(SiO2), a variety of phase transitions from fluid- to gel- and glass-like can be unified to construct a state diagram mapping the yielding behaviors from one-step to two-step before finally exhibiting one-step yielding at high φ(elect) and φ(SiO2)

Evaluation of Anionic and Cationic Pulp-Based Flocculants With Diverse Lignin Contents for Application in Effluent Treatment From the Textile Industry: Flocculation Monitoring

In wastewater treatment, flocculation is a widely used solid/liquid separation technique, which typically employs a charged polymer, a polyelectrolyte (PEL). Polyelectrolytes features, such as charge type, charge density and molecular weight, are essential parameters affecting the mechanism of flocculation and subsequent floc sedimentation. The effectiveness of the process is also influenced by the characteristics of the system (e.g., type, size, and available surface area of suspended particles, pH of the medium, charge of suspended particles). Thus, a good understanding of the flocculation kinetics, involved mechanisms and flocs structure is essential in identifying the most adequate treatment conditions, having also into consideration possible subsequent treatments. In this study, Eucalyptus bleached pulp and a cellulosic pulp with high lignin content (~4.5 wt%) obtained from Eucalyptus wood waste were used for bio-PELs production. Firstly, a pre-treatment with sodium periodate increased the pulps reactivity. To produce cationic cellulose the oxidation step was followed by the introduction of cationic groups in the cellulose chains, through reaction with Girard's reagent T. Applying different molar ratios (0.975 and 3.9) of Girard's reagent T to aldehyde groups led to cationic PELs with diverse charge density. On the other hand, to obtain anionic cellulose a sulfonation reaction with sodium metabisulfite was applied to the intermediate dialdehyde cellulose-based products, during 24 or 72 h, and anionic-PELs with diverse features were obtained. The developed water soluble, anionic and cationic bio-PELs were characterized and tested as flocculation agents for a textile industry effluent treatment. Initially, jar-tests were used to tune the most effective flocculation procedure (pH, flocculant dosage, etc.). Flocculation using these conditions was then monitored continuously, over time, using laser diffraction spectroscopy (LDS). Due to the small size of the dyes molecules, a dual system with an inorganic complexation agent (bentonite) was essential for effective decolouration of the effluent. Performance in the treatment was monitored first by turbidity removal evaluation (75–88% with cationic-PELs, 75–81% with anionic-PELs) and COD reduction evaluation (79–81% with cationic-PELs, 63–77% with anionic-PELs) in the jar tests. Additionally, the evolution of flocs characteristics (structure and size) during their growth and the flocculation kinetics, were studied using the LDS technique, applying the different PELs produced and for a range of PEL concentration. The results obtained through this monitoring procedure allowed to discuss the possible flocculation mechanisms involved in the process. The results obtained with the bio-PELs were compared with those obtained using synthetic PELs, commonly applied in effluents treatment, polyacrylamides. The developed bio-PELs can be competitive, eco-friendly flocculation agents for effluents treatment from several industries, when compared to traditional synthetic flocculants with a significant environmental footprint. Moreover, LDS proved to be a feasible technique to monitor flocculation processes, even when a real industrial effluent is being tested

Emulsifying properties of sugar beet pectin microgels

Particle stabilized (‘Pickering’) oil-in-water (O/W) emulsions were fabricated using sugar beet pectin (SBP) microgel particles (SBPM) that differed in their crosslinking density and therefore elasticity. Droplet size distributions and emulsion microstructures were investigated via light scattering and complimentary imaging techniques: light microscopy, confocal laser scanning microscopy and scanning electron microscopy. Comparisons to emulsions stabilized by native (i.e., non-microgelled) SBP at equivalent overall SBP content were made throughout. The SBPM-stabilized emulsions (20 and 40 vol% oil) were shown to have an improved physical stability compared to those stabilized by SBP. For example, droplet coarsening on prolonged (9 week) storage at ambient temperature (25 °C) and on temperature cycling (75 °C) was substantially reduced for SBPM-stabilized emulsions. This is attributed to the greater steric barrier provided by SBPM particles and their higher energy of displacement. Furthermore, the higher viscoelasticity of the SBPM-stabilized emulsions (particularly at 40 vol% oil) retarded droplet creaming. This higher viscoelasticity could be due to weak flocculation of the SBPM-stabilized droplets or the strong influence of the SBPM on the viscoelasticity of the intervening aqueous phase, even at relatively low SBPM concentrations

Linear ABC Amphiphilic Triblock Copolymers for Complexation and Protection of dsRNA

We herein report the synthesis and characterisation of linear ABC triblock copolymers, investigation of their self-assembly in aqueous solution, and complexation and protection with double stranded-RNA (dsRNA). The amphiphilic triblock copolymers were synthesised via reversible addition–fragmentation chain transfer (RAFT) polymerisation. The precisely controlled polymerisation allowed for modification of the degree of polymerisation of quaternised 2-(dimethylamino)ethyl methacrylate (QDMAEMA, Q), tert-butyl acrylamide (tBAA, B) and N,N-dimethyl acrylamide (DMA, D) blocks, tailoring hydrophobicity. The Q homopolymer was synthesised as a macromolecular chain-transfer agent. The cationic functionality provides the ability for electrostatic interaction of the triblock copolymers with anionic biomolecules, such as dsRNA, for therapeutic or agrochemical delivery applications. The B second block was designed to provide strong anchoring of the assembled structures for enhanced stability. As illustrated by 1H NMR spectroscopy, Q-b-B-b-D linear ABC triblock copolymers were prepared with molecular weights 30, 37 and 44 kDa. The self-assembly of these amphiphilic triblock copolymers in aqueous solution was confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Furthermore, the potential of these tailored block copolymers as vehicles for dsRNA delivery was demonstrated through complexation and protection of the anionic biomolecule dsRNA against destabilisation at high salt concentration and enzymatic degradation by RNase A, confirmed by ethidium bromide exclusion and agarose gel electrophoresis assays

Recent Advances in Engineered Nanoparticles for RNAi-Mediated Crop Protection Against Insect Pests

Since the discovery of RNA interference (RNAi) in the nematode worm Caenorhabditis elegans in 1998 by Fire and Mello et al., strides have been made in exploiting RNAi for therapeutic applications and more recently for highly selective insect pest control. Although triggering mRNA degradation in insects through RNAi offers significant opportunities in crop protection, the application of environmental naked dsRNA is often ineffective in eliciting a RNAi response that results in pest lethality. There are many possible reasons for the failed or weak induction of RNAi, with predominant causes being the degradation of dsRNA in the formulated pesticide, in the field or in the insect once ingested, poor cuticular and oral uptake of the nucleic acid and sometimes the lack of an innate strong systemic RNAi response. Therefore, in the last 10 years significant research effort has focused on developing methods for the protection and delivery of environmental dsRNA to enable RNAi-induced insect control. This review focuses on the design and synthesis of vectors (vehicles that are capable of carrying and protecting dsRNA) that successfully enhance mRNA degradation via the RNAi machinery. The majority of solutions exploit the ability of charged polymers, both synthetic and natural, to complex with dsRNA, but alternative nanocarriers such as clay nanosheets and liposomal vesicles have also been developed. The various challenges of dsRNA delivery and the obstacles in the development of well-designed nanoparticles that act to protect the nucleic acid are highlighted. In addition, future research directions for improving the efficacy of RNA-mediated crop protection are anticipated with inspiration taken from polymeric architectures constructed for RNA-based therapeutic applications

A Facile Method for Generating Worm-like Micelles with Controlled Lengths and Narrow Polydispersity

This work shows that highly uniform worm micelles formed by polymerisation induced self-assembly can be obtained via simple postsynthesis sonication. Importantly, this straightforward and versatile strategy yields exceptionally monodisperse worms with tunable aspect ratios ranging from 7.2 to 17.6 by simply changing the sonication time

pH-responsive polymer microcapsules for targeted delivery of biomaterials to the midgut of Drosophila suzukii

Drosophila suzukii or spotted wing Drosophila is an economically important pest which can have a devastating impact on soft and stone fruit industries. Biological pesticides are being sought as alternatives to synthetic chemicals to control this invasive pest, but many are subject to degradation either in the environment or in the insect gut and as a result require protection. In this study we identified a sharp change in pH of the adult midgut from neutral to acidic (pH 6, but underwent rapid dissolution at pH < 4.2. In vivo studies showed that the natural acidity of the midgut of D. suzukii also induced the breakdown of the responsive P2VP microcapsules to release FITC-dextran which was taken up into the body of the insect and accumulated in the renal tubules

Polymer Molecular Weight Dependence on Lubricating Particle-Particle Interactions

Using ultrathin surface coatings of water-soluble polymers to modify interfacial friction is relatively new, but may offer routes to form beneficial coatings while using significantly lower polymer concentrations. In the current study, silica surfaces were modified by the physisorption of poly(vinylpyrrolidone) (PVP) from water solution. Four polymer samples with different molecular weights, ranging from 8 to 1300 kDa, were examined here. Optical reflectivity measurements showed that the saturated surface excess for each PVP sample was ∼1 mg/m2. The amount of trapped water within the 8 kDa PVP film (∼10 wt %) was found to be much less than the trapped water (40–55 wt %) in films formed from higher molecular weight PVPs (40, 360, and 1300 kDa). In addition, QCM dissipation values for the 8 kDa PVP film was more than four times smaller than those measured for the higher molecular weight PVPs, suggesting that the 8 kDa PVP conforms to a flat film (predominantly train orientation), whereas the high molecular weight PVPs slowly reorganize resulting in more lossy films (increased Sauerbrey film thickness). Colloid-probe AFM lateral force measurements showed that 8 kDa PVP films exhibited similar lateral resistance to that seen for uncoated silica surfaces in water, whereas higher molecular weight PVP films showed significantly reduced lateral forces. This lubrication effect, induced by the adsorbed higher molecular weight PVP samples was explored further by measuring the rheology of concentrated particle suspensions. Suspension yield stress data for PVP-coated particles showed a reduction by a factor of 2 in the yield stress when compared to the uncoated particles for suspension concentrations above 60 vol %, i.e., approaching the close-packed limit of spheres

Pre-treatment of industrial olive oil mill effluent using low dosage health-friendly cationic polyelectrolytes

Olive oil production involves a significant annual release of industrial olive oil mill effluent (OME) to the environment. These discharges bring serious environmental problems since they are extremely hazardous for the aquatic environment due to their organic matter and high turbidity levels. The present study comprises the development of new, hydrophobically modified, cationic flocculants directed to oily effluents application. A health-friendly formulation was used in their synthesis process, performed by inverse-emulsion. In particular, Poly(AAm-MAPTAC) was synthesized in two different polymer compositions and, as well, with the presence of a hydrophobic monomer (Poly(AAm-MAPTAC-SMA)) at several compositions up to 8wt%. The obtained polyelectrolytes were characterized in terms of final composition, hydrodynamic diameter, zeta potential and molecular weight. Their flocculation performance was evaluated in an industrial oily effluent from an olive oil mill. Results revealed that the hydrophobic modification improves noticeably the flocculation performance of cationic polyelectrolytes in the treatment of olive oil mill effluents. In the best conditions, it was possible to achieve 90% turbidity reduction, 47% COD removal and 34% total solids removal with only 53mg/L of flocculant. Moreover, 79% of turbidity was reduced after addition of 13mg/L

Evaluation of Anionic Eco-Friendly Flocculants Prepared from Eucalyptus Pulps with Diverse Lignin Contents for Application in Effluent Treatment

Modification of cellulosic-rich materials for the production of cellulose-based polyelectrolytes (PELs) can bring several benefits, such as high biodegradability and low or no toxicity, for numerous applications, when compared with the use of traditional, synthetic PELs. Moreover, cellulose-based PELs originating from wood wastes, contribute to the valorisation of such wastes. In this work, Eucalyptus pulps with diverse lignin contents, extracted from Eucalyptus wood wastes, were anionized by a two–step reaction procedure (periodate oxidation followed by sulfonation). Applying different reaction times (24–144 h) in the sulfonation step allowed for producing a range of cellulose-based anionic PELs with different characteristics. PELs obtained after 24 and 72 h of sulfonation were thoroughly characterized (Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies, anionic group content (elemental analysis), zeta potential and hydrodynamic diameter (dynamic light scattering)) and subsequently evaluated as flocculants in decolouration processes of model effluents (Methylene Blue and Crystal Violet) and an industrial effluent from a textile industry. Furthermore, possible flocculation mechanisms induced by the use of the various PELs are discussed. Results are compared with those obtained with a commonly applied, synthetic flocculant (polyacrylamide). It is demonstrated that it was possible to obtain water-soluble lignocellulosic PELs starting from raw materials with different degrees of purity and that those PELs are promising eco-friendly alternative flocculation agents for the decolouration of effluents