Unidimensional Approximation of the Diffuse Electrical Layer in the Inner Volume of Solid Electrolyte Grains in the Absence of Background Ions

In this paper we continue working on our theory of electrical double layers resulting exclusively from dissociation of a solid electrolyte, which we previously proposed as a medium for catalytic interaction between solid cellulose and solid acid catalysts of hydrolysis. Two theoretical unidimensional models of the inner grain volume are considered: an infinitely long cylindrical pore, and a gel electrolyte near a grain outer surface. Despite the model simplicity, the predictions for the cylindrical pore case are in semi-quantitative agreement with literature data on electroosmotic experiments, adequately explaining high proton selectivity of sulfonic membranes, and decline of such selectivity at high background acid concentration. The gel model predicts less concentrated diffuse layer in comparison to electrolytes with impenetrable skeleton (e. g., sulfonated carbons). This suggests limited suitability of gel electrolytes as catalysts if a substrate cannot diffuse into the gel bulk and the reaction is thereby spatially limited to the near-surface region, for example if a substrate is solid like aforementioned cellulose.     

Pathway Dependence in Redox-Driven Metal–Organic Gels

Pathway dependence is common in self-assembly. Herein, the importance of pathway dependence for redox-driven gels is shown by constructing a Fe^II/Fe^III redox-based metal–organic gel system is shown. In situ oxidation of the Fe^II ions at different rates results in conversion of a Fe^II gel into a Fe^III organic gel, which controls the material properties, such as gel stiffness, gel strength, and an unusual swelling behaviour, is described. The rate of formation of Fe^III ions determines the extent of intermolecular interactions and so whether gelation or precipitation occurs.     

Adhesives to empower a manipulator inspired by the chameleon tongue

Existing grasping technologies have persistent challenges with unstructured objects and environments,highlighting an increasing demand for methods that conform to various application scenarios.Inspired by the chameleon tongue,a soft-contact grasping manipulator empowered by a class of adhesive gels has been demonstrated.The adhesives enable the manipulator to rapidly and strongly adhere to diverse substrates with varied surfaces,shapes and sizes,also to release objects under mild conditions.The robustness of such adhesive gels was highlighted with the remarkable recyclability,broad temperature tolerance and long-term stability.Furthermore,a general approach was developed to reconcile the contradiction of simultaneously enhancing their interfacial adhesion and cohesion strength that exists in conventional glues.We anticipate that this work will offer a strategy of developing adhesive materials and pave the way towards new applications of soft materials in the emerging fields of soft robotic devices and smart manufacturing.     

Characterizing the impact of thermal gels on isotachophoresis in microfluidic devices

Thermally reversible Pluronic gels have been employed as separation matrices in microfluidic devices in the analysis of biological macromolecules. The phase of these gels can be tuned between liquid and solid states using temperature to vary fluidic resistance and alter peak resolution. Although separations in thermal gels have been characterized, their effect on isotachophoresis has not. This study used fluorescein as a model analyte to evaluate isotachophoretic preconcentration as a function of thermal polymer concentration and temperature. Results demonstrated that increasing polymer concentration in microfluidic channels increased the apparent analyte concentration. A critical minimum of 10% (w/v) Pluronic was required to achieve efficient preconcentration with maximum focusing occurring in 20 and 25% polymer gels. Temperature of the thermal gel also impacted analyte focusing. Most efficient focusing was achieved at 25°C with diminishing analyte accumulation at higher and lower temperatures. Under optimal conditions, isotachophoretic preconcentration increased an additional threefold simply by including thermal gels in the system. This approach can be readily implemented in other applications to increase detection sensitivity and measure low-concentration analytes within simple microfluidic devices.     

Influence of TiO2 on the Chemical,Mechanical, and Gas Separation Properties of Polyvinyl Alcohol-Titanium Dioxide (PVA-TiO2) Nanocomposite Membranes

PVA/TiO₂ nanocomposite membranes developed were investigated for chemical, mechanical, and gas separation properties. PVA/TiO₂ dispersion offers good optical property and less aggregation, as shown by UV-vis photospectroscopy. FT-IR spectra suggest strong interaction between PVA and TiO₂. Mechanical properties of the composite membranes were enhanced by the addition of TiO₂. Permeation results show that the addition of TiO₂ up to 20 wt.% increased the selectivity of gas pairs O₂/N_2, H₂/N_2, H₂/CO₂, and CO₂/N₂ by 60%, 55%, 23%, and 26% respectively, with a corresponding decrease in the permeability. At higher loading of TiO_2, a reverse trend was observed.     

Microgel Capsules Tailored by Droplet‐Based Microfluidics

Microgel capsules are micrometer‐sized particles that consist of a cross‐linked, solvent‐swollen polymer network complexed with additives. These particles have various applications, such as drug delivery, catalysis, and analytics. To optimize the performance of microgel capsules, it is crucial to control their size, shape, and content of encapsulated additives with high precision. There are two classes of microgel‐capsule structures. One class comprises bulk microcapsules that consist of a polymer network spanning the entire particle and entrapping the additive within its meshes. The other class comprises core–shell structures; in this case, the microgel polymer network just forms the shell of the particles, whereas their interior is hollow and hosts the encapsulated payload. Both types of structures can be produced with exquisite control by droplet‐based microfluidic templating followed by subsequent droplet gelation. This article highlights some early and recent achievements in the use of this technique to tailor soft microgel capsules; it also discusses applications of these particles. A special focus is on the encapsulation of living cells, which are very sensitive and complex but also very useful additives for immobilization within microgel particles.     

Chitosan‐PEG Hydrogel with Sol–Gel Transition Triggerable by Multiple External Stimuli

Smart hydrogels play an increasingly important role in biomedical applications, since materials that are both biocompatible and multi‐stimuli‐responsive are highly desirable. A simple, organic solvent‐free method is presented to synthesize a biocompatible hydrogel that undergoes a sol–gel transition in response to multiple stimuli. Methoxy‐poly(ethylene glycol) (mPEG) is modified into carboxylic‐acid‐terminated‐methoxy‐poly(ethylene glycol) (mPEG‐acid), which is then grafted onto chitosan via amide linkages yielding mPEG‐g‐chitosan. Grafting of mPEG onto hydrophobic chitosan imparts hydrophilic properties to the resultant polymer. The mPEG‐g‐chitosan gel exhibits a controllable multi‐stimuli‐responsive property. The balance between hydrophilicity and hydrophobicity is believed to confer mPEG‐g‐chitosan with stimuli‐responsive behavior. The effect of salt concentration, solute concentration, temperature, and pH on the sol–gel transition of mPEG‐g‐chitosan is evaluated and the underlying mechanisms of mPEG‐g‐chitosan polymer packing and gelation property is discussed.

     

Thermo‐responsive gels in the presence of monovalent salt at physiological concentrations: A Monte Carlo simulation study

In this work, slightly charged thermo‐responsive gels in the presence of salt at concentrations close to physiological conditions have been simulated within a coarse‐grained model widely used in the last decade. These simulations allow differentiate charge and salt effects, which are antagonist and coupled in many real systems because the degree of ionization might depend on the electrolyte concentration. An analysis in terms of the different contributions to osmotic pressure is also presented, which highlights the role played by excluded volume effects. In addition, our results also permit us to test some predictions based on the ideal Donnan equilibrium, a common assumption made to justify the swelling behavior of gels and microgels in the presence of salt. More specifically, simulations show that, for the slightly charged gels simulated here, such an assumption overestimates the concentration of salt inside collapsed gels and underestimates the excess of osmotic pressure associated to the additional electrolyte. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1403–1411     

Investigation of sequence isomer effects in AB‐polybenzimidazole polymers

In the present work, a unique series of random polybenzimidazole (PBI) copolymers consisting of the recently reported novel isomeric AB‐PBI (i‐AB‐PBI) and the well known AB‐PBI were synthesized. The i‐AB‐PBI incorporates additional linkages (2,2 and 5,5) in the benzimidazole sequence when compared with AB‐PBI. Random copolymers, varying in composition at 10 mol % increments, were synthesized to evaluate the effects of sequence isomerism in the polymer main chain without altering the fundamental chemical composition or functionality of a polymer chain consisting of 2,5‐benzimidazole units. Polymer solutions were prepared in polyphosphoric acid (PPA) and cast into membranes using the sol–gel PPA process. The resulting polymers were found to have high inherent viscosities (>2.0 dL/g) and showed elevated membrane proton conductivities (～0.2 S/cm) under anhydrous conditions at 180 °C. Fuel cell performance evaluations were conducted, and an average output voltage ranging from 0.5 to 0.60 V at 0.2 A/cm² was observed for hydrogen/air at an operational temperature of 180 °C without applied backpressure or humidification. Herein, we report for the first time glass transition (T_g) temperatures for AB‐PBI, i‐AB‐PBI, and an anomalous T_g effect for the series of randomized PBIs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 619–628