Interfacial energy as an approach to designing amphipathic surfaces during photopolymerization curing.

Photopolymerization induced phase separation (PIPS) is a platform capable of creating heterogeneous materials from initially miscible resin solutions, where both the reaction's governing thermodynamics and kinetics significantly influence the resulting phase composition and morphology. Here, PIPS is used to develop materials in a single photopolymerization step that are hydrophobic on one face and hydrophilic on the other. These two faces possess a water contact angle difference of 50°, bridged by a bulk-scale chemical gradient. The impact of the PIPS-triggering inert additive is investigated by increasing the loading of poly(methyl methacrylate) (PMMA) in an acrylonitrile/1,6-hexanediol diacrylate comonomer resin. The extent of phase separation in the sample network depends on this loading, with increasing PMMA corresponding to macroscale domains that are more chemically and mechanically distinct. A significant period between the onsets of phase separation and reaction deceleration, determined using in situ FT-IR, facilitates this enhanced phase segregation in PMMA-modified samples. Spatially directed domain formation can be further promoted using multiple interface types in the sample mold, here, glass and stainless steel. With multiple interface types, interfacial rearrangements to minimize surface energy during resin photopolymerization result in a hydrophobic face that is nitrile-rich and a hydrophilic face that is nitrile-poor (e.g., acrylate-rich). Using this strategy, patterned wettability on a single face can also be engineered. This study illustrates the capabilities of PIPS for complex surface design and in applications requiring stark differences in surface character without sharp interfaces.

Polystyrene-Sepiolite Clay Nanocomposites with Enhanced Mechanical and Thermal Properties.

Polystyrene (PS)/sepiolite clay nanocomposites were prepared via the melt extrusion technique using vinyl tri-ethoxy silane (VTES) as the compatibilizer and cross-linking agent. Mechanical, thermal, and flame-retardant properties of the newly developed polystyrene-based nanocomposites were determined. Surface morphology was investigated using scanning electron microscopy (SEM), examining the distribution of the filler in various compositions of fabricated composites. Structural analysis of the samples was carried out using the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. Thermal stability was determined by thermal gravimetric analysis (TGA), showing a maximum 30.2 wt.% increase in residue by adding sepiolite clay. The results obtained from the dynamic mechanical analyzer (DMA) in terms of the storage modulus, loss modulus and damping factor exhibited better stress transfer rate and effective interfacial adhesion between the filler and the matrix. The higher filler loaded sample showed greater flame retardancy by decreasing the burning rate up to 48%.

Synthesis of Magnetic Fe3O4 Nano Hollow Spheres for Industrial TNT Wastewater Treatment.

The aim of the present work was to synthesize magnetite (Fe3O4) nano hollow spheres (NHS) via simple, one-pot, template-free, hydrothermal method. The structural, morphological, and surface analysis of Fe3O4 NHS were studied by scanning electron microscopy (SEM), x-ray diffraction technique (XRD), Fourier transform infrared spectroscopy FTIR and burner-Emmett-teller (BET). The as obtained magnetic (Fe3O4) NHS were used as an adsorbent for treating industrial trinitrotoluene (TNT) wastewater to reduce its Chemical Oxygen Demand (COD) values. Adsorption capacity (Qe) of the NHS obtained is 70 mg/g, confirming the attractive forces present between adsorbent (Fe3O4 NHS) and adsorbate (TNT wastewater). COD value of TNT wastewater was reduced to >92% in 2 h at room temperature. The adsorption capacity of Fe3O4 NHS was observed as a function of time, initial concentration, pH, and temperature. The applied Fe3O4 NHS was recovered for reuse by simply manipulating its magnetic properties with slight shift in pH of the solution. A modest decrease in Qe (5.0−15.1%) was observed after each cycle. The novel Fe3O4 NHS could be an excellent candidate for treating wastewater generated by the intermediate processes during cyclonite, cyclotetramethylene-tetranitramine (HMX), nitroglycerin (NG) production and other various environmental pollutants/species.

Gel rupture during dynamic swelling.

Hydrogels have had a profound impact in the fields of tissue engineering, drug delivery, and materials science as a whole. Due to the network architecture of these materials, imbibement with water often results in uniform swelling and isotropic expansion which scales with the degree of cross-linking. However, the development of internal stresses during swelling can have dramatic consequences, leading to surface instabilities as well as rupture or bursting events. To better understand hydrogel behavior, macroscopic mechanical characterization techniques (e.g. tensile testing, rheometry) are often used, however most commonly these techniques are employed on samples that are in two distinct states: (1) unswollen and without any solvent, or (2) in an equilibrium swelling state where the maximum amount of water has been imbibed. Rarely is the dynamic process of swelling studied, especially in samples where rupture or failure events are observed. To address this gap, here we focus on rupture events in poly(ethylene glycol)-based networks that occur in response to swelling with water. Rupture events were visualized using high-speed imaging, and the influence of swelling on material properties was characterized using dynamic mechanical analysis. We find that rupture events follow a three-stage process that includes a waiting period, a slow fracture period, and a final stage in which a rapid increase in the velocity of crack propagation is observed. We describe this fracture behavior based on changes in material properties that occur during swelling, and highlight how this rupture behavior can be controlled by straight-forward modifications to the hydrogel network structure.