Aqueous Dispersions Research Articles

Physical Crosslinking of Aqueous Polymer Dispersions: A Perspective

AbstractColloidal polymers, and in particular aqueous polymer dispersions, are widely used in commercial applications such as coatings and adhesives. Historically, the solvent resistance and mechanical properties of these systems have been improved by covalently crosslinking the polymer chains after drying. More recently, work has been directed toward replacing this covalent crosslinking, which typically involves highly reactive functional groups, by physical crosslinking through the use of supramolecular interactions. While conceptually similar to the use of covalent crosslinking, physical crosslinking has a unique influence on the rheology of the polymer, which leads to substantial differences in the development of mechanical strength during drying, as well as the mechanical properties of the final polymer film. In this perspective, the advantages and challenges of this approach are outlined, and an outlook for future research in this direction is provided.

Study of Properties of Water-Dispersion Paint and Varnish Compositions with the Content of Modified Mineral Filler

This article presents the results of research work devoted to improving the characteristics of paint and varnish coatings based on aqueous dispersions of polyacrylates; it is proposed to modify them by introducing mineral raw materials as fillers and hydrated lime, with subsequent processing in a vortex layer apparatus. The introduction of activated diatomite does not cause the deterioration of covering power, adhesion or an increase in the porosity of the paint material. The modification of coatings contributes to an increase in their operational properties, which can be associated with a reduction in the free volume in the composite and the formation of polymer boundary layers with modified physical and chemical properties. The aim of this study is to obtain a water-dispersion paint and varnish composition containing modified diatomite on a polyacrylate basis and, subsequently, study its main physical and mechanical parameters. The work has been carried out by the following method: determination of porosity, adhesion, elasticity and covering power of the control composition; determination of porosity, adhesion, elasticity and covering power of the obtained composites using modified filler; investigation of the influence of radiation on the infrared spectrum of the paint coating surface using a FLIRB620 thermal imager. As a result of this research work, it was noticed that the modification of water dispersions with silica-activated diatomite helps to eliminate the main disadvantages of materials and coatings based on acrylate binders—low water resistance and low physical and mechanical characteristics. The introduction of modified diatomite into water-emulsion paint on an acrylate base does not lead to the deterioration of the main performance characteristics of paint coatings—porosity, adhesion, elasticity and covering.

Engineering the reverse micellar-templated Co(OH)2 nanospheres based Pickering emulsion and unveiling the mechanism of ambiguous phase separation

The present study employs reverse micellar-templated Co(OH)2 nanospheres, in situ hydrophobized with SDS in Pickering emulsion formulations and unlocking the mechanism of ambiguous phase separation at a certain surfactant concentration (4.3 mM). Co(OH)2 is synthesised in the core of reverse micelle: SPAN 80/1-butanol/water/toluene. Novel O/W Pickering emulsions have been developed with the help of positively charged (ς = 4.47 mV) Co(OH)2 (0.05 wt%) and an adequate amount of an anionic surfactant, SDS. An ambiguous phase separation of Pickering emulsion at 4.3 mM SDS is noticed within just 4 hr of standings, whereas, surprisingly stable O/W Pickering emulsions are found above and below these SDS concentrations. Upon addition of 2.6 mM SDS to the aqueous colloidal dispersion of Co(OH)2, the particles converted to amphiphilic one and stabilized the Pickering emulsion. However, these monolayer adsorbed surfactants face a hydrophobic interaction through tail-to-tail mode after adding 4.3 mM SDS to the colloidal dispersion. Consequently, they achieve a nanoplates-like architect and regain the extreme hydrophilic surface from both ends and eventually leads to the ambiguous phase separation through inter-droplet coalescence. The contact angle value altering from 44.9° (for 2.6 mM SDS) to 19.6° (for 4.3 mM SDS) confirms that the surface has changed from being amphiphilic to becoming extremely hydrophilic. Yet, again an increase in SDS (6.06 mM and onwards) suggest that surfactant molecules further adsorbed in either any of the two hydrophilic ends and revolving the particles to its previous amphiphilic state and eventually started to stabilise the emulsion droplets.

Development of Enteric Diclofenac Sodium Microparticles Through a Spray-Drying Process Facilitated by Different Aqueous Dispersion Systems

The objective of this study was to prepare enteric diclofenac sodium microparticles using an aqueous dispersion system via spray-drying. Two aqueous-based solvent systems, phosphate buffer at pH 7.0 and ammonium hydrogen carbonate solution, were employed as the feed dispersion media in the spray-drying process based on the solubility characteristics of Eudragit® L100. At a drug-to-polymer ratio of 1:1, the optimal solids concentration in the feed dispersion was determined to be 2% w/v, as it enabled an approximately 5-30 µm smooth-surfaced spherical microparticle with a high production yield. Diclofenac sodium was efficiently encapsulated within the microparticles, existing as solid dispersion in a partially amorphous form. Notably, the spray-drying conditions utilized in this study obviated the need for further heating for microparticles prepared using ammonium hydrogen carbonate solution, as the residual ammonium could be completely eliminated during the spray-drying process. The two-stage biorelevant drug release profile of enteric microparticles demonstrated their ability to inhibit drug dissolution under acidic conditions while facilitating drug release under basic conditions. The phosphate buffer-based microparticles exhibited greater protection efficiency under acidic conditions compared to ammonium hydrogen carbonate-based systems, despite residual alkaline salt being present in the microparticles. These results validate the potential of the developed microparticles for use as an enteric drug delivery system.

Structure and optical properties of ZnxCd1-xS and Cu:ZnxCd1-xS templated on DNA molecules

One-dimensional ZnxCd1−xS and Cu: Zn x Cd1−x S nanostructures were prepared using DNA as a template to promote growth along the molecular axis. The formation of homogeneously alloyed nanocrystals with cubic zinc blende-type structures was verified using x-ray diffraction and Raman spectroscopy. X-ray photoemission spectra revealed the presence of Cu(I) in the doped Cu: Zn x Cd1−x S nanocrystals. The effectiveness of the DNA template to direct the semiconductor growth in one dimension was demonstrated by AFM and TEM. The nanostructures displayed a granular morphology comprising nanoparticles with an average diameter of 14 nm composed of assemblies of smaller crystallites of 2.0 nm in size. Rope-like assemblies with an average diameter of 48 nm and extending in length to several hundred micrometres were obtained by evaporation-induced self-assembly. UV-Vis absorption and emission spectra indicated that the optical bandgaps (2.89–4.00eV) and photoluminescence peaks (608–819 nm) of the DNA-templated nanocrystals could be precisely controlled by modifying the molar ratios of their Zn/Cd precursors. Doping with Cu(I) gave an increase in photoluminescence intensity and a composition-independent red-shift of 0.23 eV. The preparation of DNA-templated Zn x Cd1−x S and Cu: Zn x Cd1−x S provides a simple, low-temperature route to aqueous dispersions of inorganic materials with controlled optical gap.

Dynamics of metal formation upon radiation-chemical reduction of Cd2+ ions in aqueous solutions: Morphology of cadmium precipitate

The dynamics of metal formation upon radiation-chemical reduction of Cd2+ ions in aqueous solutions in the presence of НCOONa and morphology of cadmium precipitate were studied. The dynamics process and the morphology were characterized by dynamic light scattering, photon correlation spectroscopy, scanning electron microscopy, and turbidimetry. The formation of aqueous dispersions of the metal with the initial particle size of approximately 0.20 ± 0.05 μm was demonstrated. The metal particles undergo agglomeration with time; as a result, their size increases to 2–3 μm. The process completes with the formation of the precipitate. A feature of the sediment morphology is the developed structure of its surface and high porosity. The pores (from 0.5 μm to several microns) make up 80–90% of its volume. The aggregation is accelerated with an increase in the absorbed dose (amount of reduced metal) and in the concentration of salts in the solution.

Unraveling the Complexities of Silica Nanoparticle Adsorption onto Polymer Latexes in Pickering Emulsion Polymerization.

Incorporating unmodified silica nanoparticles onto polymer latexes to fabricate aqueous polymer dispersions without relying on electrostatic attraction during the Pickering emulsion polymerization process still faces challenges. For negatively charged silica nanoparticles to successfully adsorb onto polymer latexes, particularly in an anionic initiator emulsion polymerization system, they have remained elusive without the use of auxiliary monomers and cationic initiators. This study investigates various experimental parameters, such as emulsion polymerization temperature, monomer solubility, salt concentration, and cation type, to elucidate the factors influencing the adsorption of unmodified silica nanoparticles in Pickering emulsion polymerization. While poly(methyl methacrylate) (PMMA)/SiO2 hybrid latexes can be obtained under pH conditions of 5-6 and at temperatures of 65 °C or below, the loading rate of silica nanoparticles decreases as the reaction temperature increases, resulting in bare PMMA latexes without silica nanoparticle adsorption at temperatures exceeding 70 °C. Introducing styrene (St) into the monomer mixture with methyl methacrylate in a ratio of up to 10 wt % leads to a gradual decrease in silica nanoparticle loading rate, from 27.3 to 8.2 wt %, attributed to the low solubility of St in water. Furthermore, the presence of sodium ions (Na+) is found to be crucial for silica nanoparticle adsorption onto PMMA latexes, as the sodium ions have a stabilizing effect on both the silica nanoparticles and the silica nanoparticle-armored latexes. These findings highlight the complex nature of Pickering emulsion polymerization in the presence of unmodified silica nanoparticles, demonstrating that the loading rate of silica nanoparticles onto polymer latexes is influenced by various factors. These insights pave the way for developing aqueous polymer dispersions with high silica nanoparticle loading rates onto polymer latexes, which is a desirable trait in the coating industry.

Construction and evaluation of a folate-mediated adriamycin phosphorene thermosensitive hydrogel delivery system against osteosarcoma

The management of osteosarcoma presents a significant challenge, and the creation of an intelligent synergistic drug delivery system is broadly acknowledged as a promising approach to therapy. Hence, in this study, a temperature-sensitive hydrogel containing DOX-loaded and folic acid-modified BPNSs that can be injected was developed to enable drug release via a pH/NIR response, aimed at synergistic photothermal‒chemotherapeutic treatment of osteosarcoma. The active targeting of BPNSs-PEG-FA/DOX involved liquid-phase stripping and electrostatic adsorption, leading to the preparation of the BPNSs-PEG-FA/DOX aqueous dispersion hybrid hydrogel matrix as a BPNSs-PEG-FA/DOX@Hydrogel through a cold method. This composite hydrogel exhibits favorable through-needle properties, superior photothermal conversion efficiency, pH/NIR intelligent responsiveness, and controlled delayed-release drug release capabilities, along with favorable in vitro cellular biocompatibility. It also demonstrates effective in vitro and in vivo active targeting, controlled delayed release, and synergistic photothermal-chemotherapeutic anti-osteosarcoma activity, showing considerable promise for the treatment of superficial tumors such as osteosarcoma.

Emergence of Amphiphilicity on Surfaces of Pure Cellulose Nanofibrils Directly Generated by Aqueous Counter Collision Process.

The present paper describes a downsizing mechanism of an aqueous counter collision (ACC) process that enables the rapid preparation of cellulose nanofibrils (CNFs) as an aqueous dispersion solely by impinging a pair of water jets containing the raw materials. Extensive studies have revealed that the resulting CNFs by ACC have amphiphilic fiber surfaces, in which two kinds of faces with different natures are present along the entire fiber axis. They therefore have superior adsorption to surfaces of various conventional polymer plastics. These characteristic adsorption behaviors, which are totally different from those for other CNFs prepared by other means, are attributable to their hydrophobic surfaces. In the present study, high-resolution microscopy, including atomic force microscopy, confocal laser scanning microscopy, and scanning electron microscopy with broad argon ion beam milling, was used to determine how the emergence of such hydrophobic characteristics in a nanofibril face occurs in relation to the ACC nanopulverization mechanism due to the collision of the pair of water jets.

Synthesis and Characterization of Copper-Crosslinked Carbon Dot Nanoassemblies for Efficient Macrophage Manipulation.

Nanomedicines loaded in macrophages (MAs) can actively target tumors without dominantly relying on the enhanced permeability and retention (EPR) effect, making them effective for treating EPR-deficient malignancies. Herein, copper-crosslinked carbon dot clusters (CDCs) are synthesized with both photodynamic and chemodynamic functions to manipulate MAs, aiming to direct the MA-mediated tumor targeting. First, green fluorescent CDs (g-CDs) are prepared by a one-step hydrothermal method. Subsequently, the g-CDs are complexed with divalent copper ions to form copper-crosslinked CDCs (g-CDCs/Cu), which are incubated with MAs for their manipulation. Experimental results revealed that the prepared g-CDCs/Cu displayed good aqueous dispersibility and fluorescent emission properties. The nanoassemblies can be activated to deplete the overexpressed glutathione (GSH) and generate reactive oxygen species (ROS) in the presence of laser irradiation through the combined Cu-mediated chemodynamic therapy and CD-mediated photodynamic therapy. Furthermore, the ROS produced in MAs enabled polarization of MAs to antitumor M1 phenotype, suggesting the future potential use to reverse the immunosuppressive tumor microenvironment. These results obtained from the current study suggest a significant potential to develop g-CDCs/Cu for GSH depletion, ROS generation, and MA M1 polarization as a theransotic agent to tackle cancer.

Ice matrix composites for Cryo-ultrasonic testing

Cryo-ultrasonic testing utilizes polycrystalline ice coupling to enable the inspection of metallic components with complex shape. The relatively high velocity of compressional waves in ice (approximately 4000 m s−1) and its ability to support the propagation of shear waves, significantly strengthen the ultrasonic transmission through curved interfaces over conventional water coupling. This paper explores the possibility of further enhancing the ultrasonic properties of ice by dispersing solid particles in water before it is frozen. Complex physicochemical phenomena occur when aqueous dispersions freeze which can lead to a solid material with microstructural characteristics that may be unfavorable to the propagation of ultrasonic waves. Here, these effects are controlled to produce a composite material consisting of alumina nanoparticles in an ice matrix. The composite exhibits compressional and shear wave velocities of approximately 4800 m s−1 and 2700 m s−1 , respectively. Importantly, the mass density of the material is more than twice as large as the density of water. Finally, it is shown that a phenomenon similar to a glass transition occurs during freezing which results in low ultrasonic attenuation when the temperature approaches – 100 °C.

Impact of surface conductivity on the zeta potential determination of concentrated aqueous polymer dispersions using electroacoustics and electrokinetic standard models

Surface conductivity can have a significant impact on the determination of the zeta potential, but it is normally not accounted for when applying the Helmholtz-Smoluchowski or Henry models. In this study, we investigate concentrated polymer dispersions using electroacoustics and both standard models. We also pay particular attention to the influence of surface conductivity, which is characterized by conductivity measurements of the dispersion and dispersion medium. The Dukhin number as a measure of surface conductivity is calculated according to Maxwell–Wagner-O’Konski theory. Zeta potentials were determined by means of colloid vibration current (CVI) and electrophoretic light scattering (ELS) methods. It has been found that neglecting surface conductivity in standard electrokinetic models can lead to large measurement errors of up to 100% with increasing particle volume fraction. In this study, the surface conductivity is now correctly taken into account by using the conductivities of the dispersion and the dispersion medium. Alternatively, this influence can also be considered using the Dukhin number. The zeta potentials resulting from the CVI measurement are then in excellent agreement with ELS reference measurements over a wide volume fraction range.Graphical

Efficient Synthesis of μ-A(BC)C Miktoarm Star Polymer Assemblies via Aqueous Photoinitiated Polymerization-Induced Self-Assembly.

In this study, green light-activated photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization of glycerol methacrylate was performed using an ω,ω-heterodifunctional macro-RAFT agent. Because of the different RAFT controllability of two RAFT groups toward methacrylic monomers, only one RAFT group was activated under green light irradiation, leading to the formation of a diblock copolymer macro-RAFT agent with one RAFT group located at the chain end and the other RAFT group located between two blocks. The obtained diblock copolymer macro-RAFT agent was then used to mediate aqueous photoinitiated RAFT dispersion polymerization of diacetone acrylamide (DAAM), which formed μ-A(BC)C miktoarm star polymer assemblies with a diverse set of morphologies. Comparing with the ABC triblock copolymer, it was found that the architecture of the μ-A(BC)C miktoarm star polymer facilitated the formation of higher-order morphologies. Kinetic studies indicated that the aqueous photoinitiated RAFT dispersion polymerization exhibited ultrafast polymerization behavior, with quantitative monomer conversion being achieved within 5 min. Size exclusion chromatography analysis confirmed that good RAFT control was maintained during the polymerization. A morphological phase diagram for μ-A(BC)C miktoarm star polymer assemblies was constructed by varying the monomer concentration and the [DAAM]/[Macro-RAFT] ratio. We expect that this study not only develops an approach for the preparation of miktoarm star polymer assemblies but also provides mechanistic insights into the polymerization-induced self-assembly of nonlinear polymers.

Self-assembled rectorite films with remarkable mechanical performance: preparation, structural characterization, and properties

Cohesive flexible rectorite clay films with good mechanical performance were prepared by a simple casting method through the self-assembly of exfoliated natural clay from aqueous dispersions. The multi-layered microstructure of the films consisted of continuous layers of aligned clay platelets parallel to the casting surface. Layers overlap randomly in the lateral direction (plane) and join vertically in an irregular manner by edge-to-face cross-linkages (bridging) to form coherent multi-layered nanostructured films with platelet-void microstructure. The films with the highest mechanical properties had thicknesses below 30 µm. Overall films from rectorite clay with monovalent interlayer content exhibited a higher experimental tensile strength ranging up to 44 MPa and Young’s modulus up to 56 GPa. The corresponding experimental values for films with divalent interlayer cations were 23 MPa for strength and 25 GPa for modulus. The highest experimental values for strength and modulus for neat Na–Ca–rectorite films were 25 MPa and 50 GPa respectively. These two mechanical property values of the best rectorite-based clay films compare favorably with values featured by polymer films typically used for packaging applications.

Healable Supracolloidal Nanocomposite Water-Borne Coatings.

Water-borne coatings often contain nanofillers to enhance their mechanical or optical properties. The aggregation of these fillers may, however, lead to undesired effects such as brittle and opaque coatings, reducing their performance and lifetime. By controlling the distribution and structural arrangement of the nanofillers in the coatings and inserting reversible chemical bonds, both the elasticity and strength of the coatings may be effectively improved, while healing properties, via the reversible chemistry, extend the coating's lifetime. Aqueous dispersions of polymer-core/silica-corona supracolloidal particles were used to prepare water-borne coatings. Polymer and silica nanoparticles were prefunctionalized with thiol/disulfide groups during the supracolloid assembly. Disulfide bridges were further established between a cross-linker and the supracolloids during drying and coating formation. The supracolloidal nanocomposite coatings were submitted to intentional (physical) damages, i.e., blunt and sharp surface scratches or cut through into two pieces, and subsequently UV irradiated to induce the recovery of the damage(s). The viscoelasticity and healing properties of the coatings were examined by dynamic, static, and surface mechanical analyses. The nanocomposite coatings showed a great extent of interfacial restoration of cut damage and surface scratches. The healing properties are strongly related to the coating's viscoelasticity and interfacial (re)activation of the disulfide bridges. Nanocomposite coatings with silica concentrations below their critical volume fraction show higher in situ healing efficiency, as compared to coatings with higher silica concentration. This work provides insights into the control of nanofillers distribution in water-borne coatings and strategies to increase the coating lifetime via mechanical damage recovery.

Jeffamine-based diblock copolymer nanoparticles via reverse sequence polymerization-induced self-assembly in aqueous media

Jeffamines® are commercially available amine-capped poly (alkylene oxides) that have been used for various applications. In this study, a weakly hydrophobic monoamine-capped propylene oxide-rich Jeffamine® (M2005) is derivatized to introduce a trithiocarbonate end-group via amidation. This precursor is then dissolved using N,N′-dimethylacrylamide (DMAC), 2-(N-acryloyloxy)ethyl pyrrolidone (NAEP) or N-acryloylmorpholine (NAM) as a co-solvent to produce a concentrated aqueous reaction mixture containing 20 % w/w water. Subsequently, reversible addition-fragmentation chain transfer (RAFT) polymerization is used to prepare Jeffamine®-core diblock copolymer nanoparticles by reverse sequence polymerization-induced self-assembly (PISA). At intermediate conversion, additional degassed water is added and each polymerization continues to almost full conversion (>99 %) within 4 h at 60 °C, resulting in a 10–20 % w/w aqueous dispersion of sterically-stabilized Jeffamine®-core nanoparticles. Efficient chain extension of the Jeffamine® precursor is achieved in most cases and relatively narrow molecular weight distributions are obtained (Mw/Mn < 1.30) as judged by GPC analysis. Transmission electron microscopy studies confirm a polydisperse spherical morphology and dynamic light scattering studies report hydrodynamic diameters ranging from 145 to 312 nm. Finally, aqueous electrophoresis studies indicate essentially neutral nanoparticles over a wide range of solution pH, as expected for the three types of non-ionic steric stabilizer chains selected for this study.

Microwave Investigation of DMSO‐Doped PEDOT:PSS Patch Resonators Under Varying Relative Humidity

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a conductive polymer widely used in various microwave sensing components. Enhancing the efficiency of PEDOT:PSS‐based microwave structures relies on improving the polymer's conductivity, achievable by adding secondary solvents such as dimethyl sulfoxide (DMSO), which significantly boosts the electrical conductivity. However, the performance of DMSO‐doped PEDOT:PSS films in microwave regime requires investigations. Herein, patch resonators are fabricated using solution processing of aqueous dispersion of PEDOT:PSS doped with varying concentrations of DMSO from 0 to 8 wt.% to investigate their microwave behavior within the frequency range of 4.5–6.5 GHz. The PEDOT:PSS patch structures are implemented on a glass substrate and their resonant characteristics, including resonant frequency and amplitude, are studied in response to varying relative humidity (RH) levels ranging from 0% to 70%. The significant variations in the microwave responses are observed at the resonant amplitude, confirming the main impact of humidity on the conductivity of the films. According to the measured results, the 2 wt.% doped patch shows greater sensitivity to the changes to the RH in contrast to the 8 wt.% doped patches, where the response shows less sensitivity to the humidity variation. The results indicate that a lower percentage of DMSO enhances sensitivity to the humidity at the cost of increased electromagnetic loss in the resonant patch structures for humidity sensing applications.

Brief Report: Can a Fraction of the Dolutegravir Dispersible Tablet Solution be Used to Dose Neonates?

Background: The smallest dolutegravir (DTG) dose approved is 5 mg once-daily in infants ≥4 weeks and weighing ≥3 to &lt;6 kg using a dispersible tablet (DT). Neonates (&lt;28 days of life) may require a lower dose due to immature organ development. We evaluated the aqueous dispersibility of the generic DTG-DT 10-mg scored tablets (Viatris Inc.) to determine the possibility of uniform concentrations that could allow for lower daily doses in neonates. Methods: Each 5-mL polypropylene tube had DTG-DT 5 mg dissolved in 5-mL ultrapure water. Tubes were labeled with 3 “zones” (bottom: 0–1 mL; middle: 1–3 mL; top: 3–5 mL). Suspensions were mixed by swirling or swirling with a syringe pump, vortexing, or sonication. DTG concentration in each zone was determined using high-performance liquid chromatography. Tubes were rinsed with 1-mL acetonitrile to determine the residual drug. Acceptable criterion for percentage difference was set at ≤20% according to the European Medicines Agency guidelines. Results: Dispersion of DTG-DT in water did not remain homogeneous, resulting in DTG concentrations that varied by over 50% across the 3 zones within the tubes. Rapid sedimentation was observed shortly after mixing. Furthermore, it was found that 24%–35% of the DTG residue remained adhered to the tube after the aqueous dispersion had been eluted, highlighting the importance of the rinse step. Conclusions: Aqueous dispersion of the DTG-DT is not uniform and displays a high degree of sedimentation. It is therefore not possible to administer a fraction of the dispersion (lower DTG dose) to neonates by using this formulation.

Inkjet-Printed Bio-Based Melanin Composite Humidity Sensor for Sustainable Electronics.

A lack of sustainability in the design of electronic components contributes to the current challenges of electronic waste and material sourcing. Common materials for electronics are prone to environmental, economic, and ethical problems in their sourcing, and at the end of their life often contribute to toxic and nonrecyclable waste. This study investigates the inkjet printing of flexible humidity sensors and includes biosourced and biodegradable materials to improve the sustainability of the process. Humidity sensors are useful tools for monitoring atmospheric conditions in various fields. Here, an aqueous dispersion of black soldier fly melanin was optimized for printing with a cosolvent and deposited onto interdigitated silver electrodes on flexible substrates. Impedance spectroscopy demonstrated that adding choline chloride increased the ion concentration and AC conductivity by more than 3 orders of magnitude, resulting in a significant improvement in sensing performance and reduced hysteresis. The devices exhibit fast detection (0.8 ± 0.5 s) and recovery times (0.8 ± 0.3 s), with a 170 ± 40-fold decrease in impedance for relative humidity changes from 30% to 90%. This factor is lowered upon prolonged exposure to high humidity in tests over 72 h during which a stable operation is reached. The low embodied energy of the sensor, achieved through material-efficient deposition and the use of waste management byproducts, enhances its sustainability. In addition, approaches for reusability and degradability are presented, rendering the sensor suitable for wearable or agricultural applications.

Single-walled Carbon Nanotubes Wrapped with Charged Polysaccharides Enhance Extracellular Electron Transfer.

Microbial electrochemical systems (MESs) rely on the microbes' ability to transfer charges from their anaerobic respiratory processes to electrodes through extracellular electron transfer (EET). To increase the generally low output signal in devices, advanced bioelectrical interfaces tend to augment this problem by attaching conducting nanoparticles, such as positively charged multiwalled carbon nanotubes (CNTs), to the base carbon electrode to electrostatically attract the negatively charged bacterial cell membrane. On the other hand, some reports point to the importance of the magnitude of the surface charge of functionalized single-walled CNTs (SWCNTs) as well as the size of functional groups for interaction with the cell membrane, rather than their polarity. To shed light on these phenomena, in this study, we prepared and characterized well-solubilized aqueous dispersions of SWCNTs functionalized by either positively or negatively charged cellulose-derivative polymers, as well as with positively charged or neutral small molecular surfactants, and tested the electrochemical performance of Shewanella oneidensis MR-1 in MESs in the presence of these functionalized SWCNTs. By simple injection into the MESs, the positively charged polymeric SWCNTs attached to the base carbon felt (CF) electrode, and as fluorescence microscopy revealed, allowed bacteria to attach to these structures. As a result, EET currents continuously increased over several days of monitoring, without bacterial growth in the electrolyte. Negatively charged polymeric SWCNTs also resulted in continuously increasing EET currents and a large number of bacteria on CF, although SWCNTs did not attach to CF. In contrast, SWCNTs functionalized by small-sized surfactants led to a decrease in both currents and the amount of bacteria in the solution, presumably due to the detachment of surfactants from SWCNTs and their detrimental interaction with cells. We expect our results will help researchers in designing materials for smart bioelectrical interfaces for low-scale microbial energy harvesting, sensing, and energy conversion applications.