Polymer Bridging Research Articles

Enhancing flocculation and dewatering performance of fine phosphate tailings: A sustainable approach for water resources management

The sustainable recovery of water from fine phosphate tailings (FPTs) is essential for reducing water consumption and mitigating the environmental risks associated with phosphate beneficiation operations, particularly during tailings storage. Dewatering through enhanced flocculation techniques is among the most sustainable management practices in the mining industry. However, the interactions between phosphate tailings and polymers remain insufficiently explored, particularly in the context of the flocculation process. To address this, the present study investigates the improvement of dewatering performance through optimized flocculation techniques. Fourteen flocculants, including anionic, nonionic, and cationic types, were assessed for their effectiveness in enhancing water recovery, sedimentation rates, and turbidity reduction. Among the tested flocculants, polyethylene oxide (PEO 4 M) and anionic polyacrylamide (AN923) exhibited superior performance, achieving water recovery rates exceeding 84 %, solid contents above 38 %, and settling rates over 13.9 cm/min, along with significant turbidity reductions to below 4.40 NTU. Insights into the adsorption mechanisms, derived from zeta potential measurements and Fourier-transform infrared spectroscopy, revealed that anionic polyacrylamide (APAM) induces flocculation primarily through hydrogen bonding and polymer bridging, whereas polyethylene oxide (PEO) operates via hydrophobic interactions and charge neutralization. These findings lay the groundwork for more sustainable water management strategies in phosphate mining, enhancing both resource efficiency and environmental protection.

Characterization of Surface Patterning on Polymer-Grafted Nanocubes Using Atomic Force Microscopy and Force Volume Mapping.

Atomic force microscopy (AFM), in particular force spectroscopy, is a powerful tool for understanding the supramolecular structures associated with polymers grafted to surfaces, especially in regimes of low polymer density where different morphological structures are expected. In this study, we utilize force volume mapping to characterize the nanoscale surfaces of Ag nanocubes (AgNCs) grafted with a monolayer of polyethylene glycol (PEG) chains. Spatially resolved force-distance curves taken for a single AgNC were used to map surface properties, such as adhesion energy and deformation. We confirm the presence of surface octopus micelles that are localized on the corners of the AgNC, using force curves to resolve structural differences between the micelle "bodies" and "legs". Furthermore, we observe unique features of this system including a polymer corona stemming from AgNC-substrate interactions and polymer bridging stemming from particle-particle interactions.

Axial-flow polymer bridge pump with hydrodynamic bearings.

A portable axial-flow polymer bridge pump with hydrodynamic bearings has been developed for bridge-to-bridge use. The pump is inexpensive to manufacture and disposable. It weighs 185g and was verified to have a lifetime of 3months with silent operation. For partial circulatory assist at a flow rate of 2 L/min, the clinical limit of hemolysis was verified for a rotational speed below 9000rpm, at which a pressure of 100mmHg was generated. In an anti-thrombogenic test, the pump stably operated for 6h without thrombus formation.

Spin Crossover Quenching by "Racemization" in a Family of trans-1,2-Di(tetrazol-1-yl)cyclopentane-Based Fe(II) 1D Coordination Polymers.

Optically pure (RR)- and racemic (RR/SS)-trans-1,2-di(tetrazol-1-yl)cyclopentane were synthesized and used to prepare homo- and heterochiral Fe(II) coordination compounds. [Fe((RR/SS)-C7H10N8)2(CH3CN)2](BF4)2 (1A), [Fe((RR/SS)-C7H10N8)2(C2H5CN)2](BF4)2 (2A), [Fe((RR)-C7H10N8)2(CH3CN)2](BF4)2·2CH3CN (1B·solv), and [Fe((RR)-C7H10N8)2(C2H5CN)2](BF4)2 (2B) form a family of one-dimensional coordination polymers. Fe(II) cations in these complexes are characterized by a heteroleptic coordination environment: the neighboring metal centers are bridged by two 1,2-di(tetrazol-1-yl)cyclopentane molecules, while the nitrile molecules (acetonitrile or propionitrile, respectively) occupy the axial positions. Independently of the kind of nitrile coligands, an ability to thermally induce spin crossover (SCO) is governed by chirality. 1B·solv and 2B exhibit abrupt and complete SCO occurring at T1/2 = 144 K and T1/2 = 228 K, respectively. Desolvated form, 1B (of the same stoichiometry as 2B), also exhibits SCO (T1/2 = 215 K). In contrast, an exchange within the polymeric chain of half of the RR molecules with the SS enantiomeric form results in formation of 1A and 2A, which remain in stable high-spin (HS) form down to 10 K. It has been shown that moving from a homochiral to a heterochiral system changes the structure of the polymeric unit (while maintaining the same polymer dimensionality and bridging fashion) that leads to the deep reorganization of the further coordination spheres, including the anion network.

Light-matter interaction during and post polymerization in self-written polymer waveguide integrated with optical fibers

Self-written polymer waveguide is a polymer interconnection structure often integrated with optical fibers. The structure is fabricated by photopolymerization, through which a photon beam initiates a polymerization reaction to change liquid monomer into a solid polymer. During light-matter interaction photoinitiator molecules are excited to the singlet and then to the third state to form free radicals by attaching to the adjacent monomer molecules. The free radicals in turn form polymer chains and cross-linked structures. Photo-induced polymerization leads to a raised refractive index of the monomer and forms an optical waveguide. The change is permanent to allow the process of self-focusing and self-trapping of the propagation light beam and hence guide it to the aligned optical fiber. In this article, light matter interaction during polymer waveguide fabrication and post polymerization has been investigated. A photopolymer system of acrylate-based monomer, co-initiator amine and photo initiator is used to study the absorption of the monomer mixture at the spectral range of 450–550 nm. Then photobleaching was investigated after waveguide fabrication. The optical transmission efficiency of the polymer bridge increases as absorption ceases within the polymer structure such that optical loss reduces from 1.1 dB to about 0.65 dB.

Unexpected Molecular Sieving of Xylene Isomer Using Tethered Ligand in Polymer-Metal-Organic Frameworks (polyMOFs).

Promising advances in adsorption technology can lead to energy-efficient solutions in industrial sectors. This work presents precise molecular sieving of xylene isomers in the polymer-metal-oragnic framework (polyMOF), a hybrid porous material derived from the parent isoreticular MOF-1 (IRMOF-1). PolyMOFs are synthesized by polymeric ligands bridged by evenly spaced alkyl chains, showing reduced pore sizes and enhanced stabilities compared to its parent material due to tethered polymer bridge within the pores while maintaining the original rigid crystal lattice. However, the exact configuration of the ligands within the crystals remain unclear, posing hurdles to predicting the adsorption performances of the polyMOFs. This work reveals that the unique pore structure of polyIRMOF-1-7a can discriminate xylene isomers with sub-angstrom size differences, leading to highly selective adsorption of p-xylene over other isomers and alkylbenzenes in complex liquid mixtures (αpX/OM = 15 and αpX/OME = 9). The structural details of the polyIRMOF-1-7a are elucidated through computational studies, suggesting a plausible configuration of alkyl chains within the polyMOF crystal, which enable a record-high p-xylene selectivity and stability in liquid hydrocarbon. With this unprecedented molecular selectivity in MOFs, "polymer-MOF" hybridization is expected to meet rigorous requirements for high-standard molecular sieving through precisely tunable and highly stable pores.

Multi-scale simulation of stress transfer across ‘polymer bridge’ in graphene oxide/halloysite organic-inorganic hybrid aerogel

In our previous work, organic-inorganic hybrid aerogels were successfully constructed utilizing graphene oxide (GO) sheets and halloysite nanotubes (HNTs), and interesting stress transfer behavior were found. Through preliminary experimental studies, we found that the movement of polymer molecules significantly affected the stress transfer behavior of aerogels. The mechanism might involve macroscopic and microscopic scales, which were difficult to be adequately studied by conventional experimental means. Therefore, this paper investigated the stress transfer behavior of hybrid aerogels utilizing finite element analysis (FEA) combined with molecular dynamics (MD) multi-scale simulation methods. The influence of the connection angles of GO and HNTs on the stress transfer ability was studied utilizing the FEA combined with theoretical formulas. The GO polymer pull-out systems were established by MD. The pull-out processes of polymethylmethacrylate (PMMA) and polysiloxane (PSO) were compared. The effect of oxygen-containing functional group coverage of GO on interface strength was studied. The results indicated that connection angles of 60° and 30° contributed more to the stress transfer between GO and HNTs under tensile and compression stress, respectively. The interfacial enhancement effect of the GO/polymer systems reached saturation when the coverage of oxygen-containing functional groups on the GO surface was 20 %. Si–O–Si agglomeration networks were formed by silane-modified GO and PSO, which possessed stronger interfacial strength.

Mechanical reinforcement by bridging chains in polymer nanocomposites

The adsorption-induced bridging of polymer chains between adjacent nanoparticles was studied in poly(vinyl acetate)/silica nanocomposites with different polymer molecular weights, interaction strengths, nanoparticle sizes, and silica loading fractions. The polymer bridging contribution is successfully decoupled from the apparent rubbery plateau modulus by subtracting the hydrodynamic and trapped chain entanglement contributions. The bridging modulus depends on the nearest interparticle surface distance through a power-law relation with a universal exponent −3. Polymer molecular weight can enhance the bridging modulus only when nanoparticles have a high density of adsorption sites due to the emergence of direct bridging of multiple particles by one chain in addition to the regular bridging through self-similar carpets. Our results illustrate that bridging chains can dominate modulus enhancement at nanoparticle's loading at about 10 vol% in polymer nanocomposites with long polymer chains and high surface silanol density.

Effect of surface functional groups of polystyrene micro/nano plastics on the release of NOM from flocs during the aging process

Currently, the hidden risk of microplastics in the coagulation process has attracted much attention. However, previous studies aimed at improving the removal efficiency of microplastics and ignored the importance of interactions between microplastics and natural organic matter (NOM). This study investigated how polystyrene micro/nano particles impact the release of NOM during the aging of flocs formed by aluminum-based coagulants Al13 and AlCl3. The results elucidated that nano-particles with small particle sizes and agglomerative states are more likely to interact with coagulants. After 7 years of floc aging, the DOC content of the nano system decreased by more than 40%, while the micron system did not change significantly. During coagulation, the benzene rings in polystyrene particles form complexes with electrophilic aluminum ions through π-bonding, creating new Al-O bonds. NOM tends to adsorb at micro/nano plastic interfaces due to hydrophobic interactions and conformational entropy. In the aging process, the structure of PS-Al13 or PS-AlCl3 flocs and the functional groups on the surface of micro/nano plastics control the absorption and release of organic matter through hydrophobic, van der Waals forces, hydration, and polymer bridging. In the system with the addition of nano plastics, several DBPs such as TCAA, DCAA, TBM, DBCM and nitrosamines were reduced by more than 50%. The reaction order of different morphological structures and surface functional groups of microplastics to Al13 and AlCl3 systems is aromatic C-H > C-OH > C-O > NH2 > aromatic CC > aliphatic C-H and C-O>H-CO> NH2 >C-OH> aliphatic C-H. The results provided a new sight to explore the effect of micro/nano plastics on the release of NOM during flocs aging.

Architecting obliquitous and rich ion transport bridges in polymer electrolytes for room temperature long-life solid-state batteries

Solid-state lithium-metal batteries are a viable energy storage device due to their high energy density and safety features. Solid-state electrolytes are integral to maintain safety by restricting the uncontrolled growth of lithium dendrites and hindering the side reactions. However, their practical application is hampered by low ionic conductivity, undesirable interfacial contacts, severe polarization, and unbefitting operation temperature. Herein, a composite quasi-solid-state polymer electrolyte is designed via in-situ polymerization of suspension electrolyte with fumed aluminum trioxide nanoparticles and the addition of poly (ethylene glycol) diacrylate, resulting in enrichment short polymer bridges for Li ion transferring (ionic conductivity reach to 4.1 × 10−4 S cm−1 at room temperature). Remarkably, the polymer electrolyte with tortuous structural properties can afford a higher lateral Li ion diffusion, which facilitates the suppression of dendrite. Additionally, the addition of aluminum trioxide can improve the electrochemical stability, indicating a strong correlation between the electrolyte's physicochemical properties and the solvation structure of the precursor. As expected, this type of electrolyte-based Li metal batteries coupled with LiNi0.8Co0.1Mn0.1O2 and LiNi0.6Co0.2Mn0.2O2 cathodes can enable stable operation for both coin and pouch cells, paving the way for exploring a series of architectures such as flexible and custom shaped batteries.

Variable angle tow composites in fibre-reinforced polymer bridges

Fibre reinforced polymers are increasingly used in bridge structures for reducing their environmental impact, extending the service life and saving costs. In this work, we propose the use of composite laminates called Variable Angle Tow (VAT) to realise bridge structures. In VAT composite laminates, the fibre orientation changes pointwise over the structure, enhancing stiffness tailoring capabilities with respect to traditional straight fibre (SF) laminates. In aerospace engineering, VAT composites have been successfully used to tailor structures’ stiffness to enhance linear elastic response, reduce buckling phenomena, and optimise the postbuckling behaviour. However, VAT laminates have never been applied in civil structures. This work shows how using VAT composite laminates in a bridge girder improves its buckling and postbuckling behaviours and increases its overall stiffness. A numerical investigation is conducted to assess the benefits given by VAT composite laminates to the structural performance of bridge girders. For different spans, results of a multi-objective optimisation considering both traditional SF and VAT laminates are presented. It is found that VAT laminates exhibit a buckling load up to 80% over SF laminates, with equal or lower deflections and without adding extra material, thereby opening new design scenarios for bridge structures.

Synthesizing cationic polymers and tuning their properties for microalgae harvesting

This study reports a facile technique to synthesize and tune the cationic polymer, poly(3-acrylamidopropyl)trimethylammonium chloride (PAPTAC), in terms of molecular weight and surface change for harvesting three microalgae species (Scenedesmus sp., P.purpureum, and C. vulgaris). The PAPTAC polymer was synthesised by UV-induced free-radical polymerisation. Polymer tuning was demonstrated by regulating the monomer concentration (60 to 360 mg/mL) and UV power (36 and 60 W) for polymerisation. The obtained PAPTAC polymer was evaluated for harvesting three different microalgae species and compared to a commercially available polymer. The highest flocculation efficiency for Scenedesmus sp. and P. purpureum was observed at a dosage of 25 mg-polymer/g of dry biomass by using PAPTAC-90, resulting in higher flocculation efficiency than the commercial polymer. Results in this study show evidence of effective neutralisation of the negative charge surface of microalgae cells by the produced cationic PAPTAC polymer and polymer bridging for effective flocculation. The obtained PAPTAC polymer was less effective for harvesting C. vulgaris, possibly due to other factors such as cell morphology and composition of extracellular polymeric substances of at the cell membrane that may also influence harvesting performance.

FERRIHYDRITE-CHITOSAN NANOCOMPOSITE AS A RECYCLABLE FLOCCULANT FOR PALM OIL MILL EFFLUENT

In the present study, ferrihydrite-chitosan nanocomposite (FCN) was successfully produced by co-precipitation method and used for the first time as a recyclable flocculant for pre-treatment of palm oil mill effluent (POME). The physicochemical properties of FCN were studied using Raman spectrometer, Scanning Electron Microscope (SEM) and Thermogravimetric Analyser (TGA). The feasibility of FCN to remove total suspended solids (TSS), turbidity, chemical oxygen demand (COD), and, oil and grease (O&G) from POME was investigated using a jar test method. The optimum conditions for contaminant removal from POME were determined by varying the experimental parameters such as flocculant dosage, solution pH and settling time. The results obtained showed that FCN, at a dosage of 1.5 g/L, a contact time of 60 min and pH of 5.0 gave a highest reduction of turbidity, TSS, COD and O&G levels by 72.38%, 77.32%, 71.60% and 53.40%, respectively. Besides that, FCN exhibited a better flocculation performance as compared to alum and chitosan. After three cycles of flocculation/deflocculation process, FCN retained satisfying flocculation efficiency and flocculants recovery in the range of 80-83% and 43.2-78.6%, respectively. Combination of charge neutralisation and polymer bridging was the main key mechanism of interaction between FCN and POME contaminants. The synergy effect between iron oxide/oxyhydroxide nanoparticle and chitosan has increased the physicochemical properties and flocculation performance of the FCN nanocomposite. Overall, FCN nanocomposite can be used an alternative flocculant for POME treatment.

Integration of knee-shaped self-written waveguides between optical fibers by direct illumination and tip to tip coupling

Optical transmission efficiency of self-written polymer waveguide has been investigated. The polymer couplers were fabricated from a photopolymerizable monomer system by direct illumination from two pre-aligned single mode fibers, and by butt coupling of two extended long polymer tips at the end of fibers. Regarding direct illumination, the writing beams exhibit quasi-solitonic behavior and both show a tendency to attract each other to be merged at the middle point where the droplet deposited between the aligned fiber. Optical transmission gives insertion loss of 4.3 dB and 5.7 dB with total knee angles of (5° and 10°) respectively. Polymer bridges with larger deviation angles were not formed, since the induced beams were not merged properly to form a decent waveguide. Therefore, long polymer tips were fabricated separately and then they were butt coupled at different knee-angles. Optical transmission efficiency was measured over broadband from Ultraviolet to Infrared (UV-IR). In the butt-coupling approach average loss of 1.7 dB, 5.4 dB, 8.6 dB, 10.4 dB and 14.6 dB at measured wavelength 1550 nm were obtained for 300 μm- 300 μm coupling tips corresponding to knee-angles of (0°,5°,10°,15°, and 20°) respectively.

Effect of the Graphene Quantum Dot Content on the Thermal, Dynamic-Mechanical, and Morphological Properties of Epoxy Resin.

Different amounts of graphene quantum dots (CQDs) (0, 1, 2.5, and 5 wt%) were incorporated into an epoxy matrix. The thermal conductivity, density, morphology, and dynamic mechanical thermal (DMTA) properties were reused from the study of Seibert et al.. The Pearson plot showed a high correlation between mass loading, thermal conductivity, and thermal diffusivity. A poorer correlation with density and heat capacity was observed. At lower CQD concentrations (0.1 wt%), the fracture surface showed to be more heterogeneous, while at higher amounts (2.5 and 5 wt%), a more homogeneous surface was observed. The storage modulus values did not change with the CQD amount. But the extension of the glassy plateau increased with higher CQD contents, with an increase of ~40 °C for the 5 wt% compared to the 2.5 wt% and almost twice compared to the neat epoxy. This result is attributed to the intrinsic characteristics of the filler. Additionally, lower energy dissipation and a higher glass transition temperature were observed with the CQD amount. The novelty and importance are related to the fact that for more rigid matrices (corroborated with the literature), the mechanical properties did not change, because the polymer bridging mechanism was not present, in spite of the excellent CQD dispersion as well as the filler amount. On the other hand, thermal conductivity is directly related to particle size and dispersion.

Study on mechanical properties and microstructure of porous organic polymer reinforced low-grade sand under wetting–drying cycles

Polymer materials are finding increasing application in soil stabilization, but little is known about the changes in performance and microstructure of polymer membranes under wetting–drying (W-D) cycles. This paper introduced a self-developed porous organic polymer material (SPOP) to investigate the mechanical properties of treated sand under various SPOP contents (1 %, 2 %, 3 %, and 4 %) and W-D cycles (0, 4, 8, 12, 16, and 20) using uniaxial compression tests and triaxial tests. The changes in the microstructure of SPOP-sand mixtures were observed by scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The results indicated that the addition of SPOP significantly increased the mechanical strength, elastic modulus, and cohesion of natural sand under W-D cycles. The mechanical properties exhibited an upward trend before decreasing as the increment of SPOP contents and peaked at 3 % SPOP content. Specimens with high SPOP content were more susceptible to moisture. On the other hand, the mechanical properties of SPOP-sand mixtures decreased significantly for all specimens under the first 4 cycles, followed by a decrease with increasing cycles exponentially. The NMR test showed the proportion of micropores within the specimens decreased by 27.81 %–48.09 % after wetting. The micropores were transformed into mesopores and macropores, and the porosity of specimens was increased. Based on the SEM images, there were three mechanisms of polymer strengthening sand, including wrapping, pore filling, and bridging effects. Alternate W-D cycles damaged the inter-particle bridging effect, thus weakening the bonding strength between the polymer membrane and sand particles. Soil aggregates inside the specimens were loosened, and polymer membrane was softened and broken under cyclic wetting and drying, causing the unstable structure of the specimen when applied external pressure.

Assisting and eliminating memory effects of paste by adding polysaccharides.

A densely packed colloidal suspension, called a paste, is known to remember the direction of its motion because of its plasticity. Because the memory in the paste determines the preferential direction for crack propagation, the desiccation crack pattern morphology depends on memory of its motions (memory effect of paste). Two types of memory effects are memory of vibration and memory of flow. When a paste is dried, it usually shows an "isotropic and random cellular" desiccation crack pattern. However, when a paste is vibrated before drying and it remembers the direction of its vibrational motion, primary desiccation cracks propagate in a direction perpendicular to its vibrational motion before drying (memory of vibration). Once it flows and remembers the direction of its flow motion, primary desiccation cracks propagate in the direction parallel to its flow motion (memory of flow). Anisotropic network formation via interparticle attraction among colloidal particles in a suspension is the dominant factor affecting a paste's memory of its motion. Calcium carbonate (CaCO_{3}) paste remembers the direction of its vibrational motion, but not its own flow direction because Coulombic repulsion among charged CaCO_{3} colloidal particles prevents the formation of a network structure in a flow. For this study, we strove to assist and eliminate CaCO_{3} paste memory effects by adding polysaccharides. First, to characterize memory in paste, we propose a method of image analysis to quantify the strength and the direction of the anisotropy of desiccation crack patterns using Shannon's information entropy. Next, we conduct experiments to add polysaccharide to CaCO_{3} paste, revealing that the addition of a small amount of polysaccharide to CaCO_{3} paste assists the paste in remembering its own flow motion. Findings also indicate that the addition of a large amount of polysaccharide prevents the formation of both memories of its flow and vibrational motion and eliminates the memory effects of paste. We then perform "flocculation and sedimentation" experiments to investigate the interaction among CaCO_{3} colloidal particles in a solution. Results show that, in an aqueous solution with low polysaccharide concentration, CaCO_{3} colloidal particles flocculate each other and quickly form a sediment in a short time, whereas, in an aqueous solution with high polysaccharide concentration, a longer time is necessary for flocculation and sedimentation. Because the addition of small amounts of polysaccharides to CaCO_{3} paste induces polymer bridging between colloidal particles as interparticle attraction, it helps to produce a macroscopic network structure which retains memory of its flow motion and thereby assists the formation of memory of flow, whereas the addition of large amounts of polysaccharides induces interparticle repulsion, which prevents the formation of memory effects of all types.

Differently charged polyacrylamides (PAMs) significantly affect adsorption affinity and associated floc growth behaviors during ballasted flocculation: Performance and mechanism

Various organic polymers have been widely used to provide inter-particle bridging between microsand and microflocs for producing ballasted floc aggregates during ballasted flocculation. However, it is not yet clear how differently charged polymers will determine predominant mechanisms of ballasted floc growth at diverse coagulant dosages. In this study, three representative aluminum sulfate (AS) coagulant dosages (where microfloc aggregates formed after coagulant addition possessed negative, zero and positive zeta potentials, respectively) were prearranged, and then the role of cationic, anionic and nonionic polyacrylamides (PAMs) in ballasted flocculation of clay suspensions was comparatively evaluated at each AS dosage. As expected, the temporal evolution of floc average size at stages of ballasted floc maturation and regrowth (following breakage) was dependent upon both AS coagulant dosage and PAM selection. Also, the selection of differently charged PAMs produced maturated floc aggregates with different shear-resistant and recovery abilities at a fixed AS dosage, presumably owing to the predominant mechanism of ballasted floc growth. Differently from the removal efficiency of water turbidity after sedimentation, the involvement of nonionic PAM (rather than the case of “without adding PAM”) gave rise to the lowest removal percentage of UV254 at the same AS dosages. This finding was probably attributed to the role of possible flocculation mechanism(s) in the transformation of dissolved humic acid (HA) complexes into insoluble HA composites at the maturation stage. Based on the experimental results, a conceptual model of ballasted floc growth process induced by differently charged polymers was proposed to vividly explore the possible floc-growth mechanism (such as charge neutralization, polymer bridging, and/or electrostatic patch) occurring for each combination of coagulant dosage and PAM type. This research may contribute to gaining a deep insight into the combined effects of coagulant dosage and differently charged polymer selection on the interaction between polymer-enhanced floc cohesion and ballasted floc formation.

Ballasted flocculation pretreatment for mitigating ultrafiltration membrane fouling: Role of differently charged polyacrylamides at typical coagulant dosages

In this work, ballasted flocculation (without sedimentation) was suggested as a potential pretreatment for ultrafiltration to improve cake layer microstructure and mitigate membrane fouling. First, three representative aluminum sulfate (AS) coagulant dosages (including 1.0, 2.5 and 8.0 mg Al/L) were determined during preliminary testing to produce microfloc aggregates with negative, zero and positive zeta potentials at the coagulation stage of ballasted flocculation. Regardless of the applied coagulant dosage, not only ballasted floc size but also their strength and recovery abilities (following breakage) were dependent upon the selection of differently charged polyacrylamides (PAMs), likely due to the effect of PAM selection on polymer bridging and associated flocculation mechanisms. Second, comparisons of membrane flux decline and resistance distribution were performed to evaluate the importance of coagulant dosage and PAM type to cake layer formation and membrane fouling potential in the ballasted flocculation and ultrafiltration integrated process. The results demonstrated that the ballasted floc aggregates formed by ballasted flocculation pretreatment contributed to diverse structural characteristics of the fouled layer during their accumulation on the membrane surface, thereby affecting the degree of membrane fouling for various combinations of AS dosage and PAM type. Besides, the microsand particles involved in the formed layer could act as a skeleton of the cake layer structure, so their spatial distribution within the layer interior played a critical role in cake layer microstructure improvement, ultrafiltration efficiency enhancement and membrane fouling mitigation. In other words, the extent of steric-hindrance effects by ballasted floc aggregates should be emphasized in the formation of cake layer.

Mechanical reinforcement of waterborne latex pressure‐sensitive adhesives with polymer‐grafted nanoparticles

AbstractWaterborne pressure sensitive adhesives (PSAs) consisting of polymer microparticle emulsions (i.e. latex) are more commonly used in commercial applications than solvent‐borne alternatives, as the use of water as a suspension medium provides better consumer safety and reduces environmental impact. However, the lower mechanical performance of waterborne PSAs prevents their use in applications requiring permanent adhesion or strong bonding between substrates. This reduction in mechanical strength is often attributed to void spaces that form during water evaporation and coalescence of the latex particles, and thus a potential strategy to improve PSA strength would be to add filler materials to occupy these voids. Fundamental studies investigating how interfacial interactions between the latex and fillers affect the collective strength of the films would enable better design of adhesive compositions to tailor PSA mechanical properties. Here we report the use of polymer brush‐grafted nanoparticles (PGNPs) as a means of mechanically reinforcing the PSAs, and determine how different aspects of the particle and polymer brush designs enable this improvement in adhesive performance. The PGNPs investigated here are intentionally designed to phase segregate into the aqueous phase of the initial latex suspension, which allows them to both fill free pore volume and also form multivalent supramolecular interactions with the latex particles to form polymer bridges that improve the interconnectivity of the final film. These studies provide insight into potential design strategies for tuning PSA properties with PGNPs, and enable up to 32% improvements to the cohesive strength of the PSAs without the typical deterioration of adhesive strength observed in PSAs using non‐brush‐coated particle fillers.