Poly(vinylidene fluoride) (PVDF) electrospun membranes are obtained from a 20% w/w solution of the polymer in dimethyl formamide. Processing parameters are systematically changed to analyze their influence on fiber morphology, fiber orientation, and on the crystallinity and crystal phase of the membranes. The PVDF concentration and travelling distance from the needle to the collector are kept fixed while the influence of the flow rate, needle diameter, applied voltage, and rotating collector speed is considered. The study allows concluding that those parameters leading to a higher stretching of the jet or straining of the fibrils during collection favor the formation of the electroactive β-phase while the total crystalline fraction depends only slightly on the electrospinning conditions.
Using computer simulations, we study the phase diagram of a two-dimensional system of disk particles with three patches distributed symmetrically along the particle equator. The geometry of the particles is compatible with a honey-comb lattice at moderately low temperature and pressure, whereas it is expected that the system forms a close-packed triangular lattice at high temperature and pressure. The effect of patch size within the single bond per patch regime was investigated, and it was found that the topology of the phase diagram changes drastically with patch size. Interestingly, in particles with small patches (with a half opening angle of 10°), the fluid transforms upon increasing the pressure into a rather exotic phase that can be understood as a honey-comb lattice whose voids are filled continuously with additional particles that remain, on average, unbound. Eventually, all the voids are occupied so that particles are located at the positions of a triangular lattice, but only two thirds of the particles are orientationally ordered whereas the remaining one third can rotate almost freely as in a plastic crystal. At moderately low temperature, the fluid transforms into a nearly empty honey-comb lattice, whereas at high temperature it transforms directly into the almost filled lattice. Interestingly, for particles with big patches (with a half opening angle of 20°), the honey-comb and triangular lattices are separated by a liquid phase that remains stable down to fairly low temperatures. Less surprisingly, only particles with big patches exhibit an equilibrium gas-liquid separation. Evolution of the solid structure of trivalent patchy particles from a honey-comb to a triangular lattice.
Over the last two decades, organogels have found tremendous use in the pharmaceutical, food, and cosmetics industries with notable developments as drug delivery matrices and trans and saturated fat replacers in processed foods. The functionality of organogels benefits from their ease of preparation, cost effectiveness, and ability to contain both hydrophilic and lipophilic constituents. This review provides thorough insight into different organogelators, their mechanisms of organogel formation, various characterization techniques and their biocompatibility when administered in vivo. Finally, a special treatise is given on the applications of organogels as controlled drug delivery vehicles for topical, dermal/transdermal, parenteral, oral, and nasal routes. In situ forming organogels and their potential for tailored release of incorporated active ingredients are also discussed.
Elastomer materials in car and truck tires require the addition of filler particles for reinforcement and durability as well as the enhancement of other properties of the final product. During the post-mixing stages the previously dispersed filler undergoes (re-)agglomeration in a process called flocculation. The resulting filler network morphology strongly influences the mechanical properties of the rubber material. This means that the structure itself, its dependence on the physicochemical properties of the underlying components, and its attendant influence on, for instance, the dynamic rubber moduli are of significant interest. In this work we discuss a modelling approach to these questions applied to binary blends consisting of natural and styrene-butadiene rubber plus filler of variable type. Our Monte Carlo flocculation simulator utilizes a lattice model of the components, whose thermodynamic development is governed by measured interface or surface tensions. The algorithm minimizes the free enthalpy while the number of MC moves provides a rough measure of time due to the local nature of the moves. We investigate two blend ratios (NR/SBR), i.e., 50/50 and 70/30, as well as two filler volume fractions ϕ, i.e., ϕ and ϕ , for variable filler surface tension (both dispersive and polar part, i.e., and ). Our results include the scattering momentum transfer characterizing the aggregate size, the fractional interface lengths between the components, and simulated transmission electron micrographs at selected conditions. We discuss how the combination of these quantities can provide information on both the storage and the loss modulus of the materials.
Polyvinylidene fluoride (PVDF) is a significant polymer in the formation of nanofiber webs via the electrospinning technique. In this paper, three PVDF-wrinkled fiber webs with different molecular weights (M W s) (180000, 275000, and 530000) were generated via the electrospinning method by using tetrahydrofuran/N,N-dimethylformamide at the solvent ratio of 1:1 as a mixed solvent. The formation mechanism of the wrinkled electrospun PVDF fibers is demonstrated. Furthermore, the relationships between the M W and the surface structure, mechanical properties, crystalline phases, and piezoelectric properties of electrospun PVDF fibers are comprehensively investigated. The results reported that the surface structure, mechanical properties, crystalline phases, and piezoelectric properties of wrinkled electrospun PVDF fibers can be affected intensely by maneuvering the M W . We believe this study can be served as a good reference for the effect of M W on the morphology and properties of electrospun fibers.
Surface functionalization is an important chemical task that allows to manipulate graphite's physical and chemical properties. It helps improve graphite's processability, giving it new properties, which may be important for solving specific problems. The graphite surface functionalization may be based on physisorption and chemisorption. In turn, the chemisorption-based functionalization may be edge-selective and non-selective. This review discusses the edge-selective functionalization of the graphite surface and reports the recent studies that take graphite and its different types as a source material. The paper also touches upon other functionalization possibilities, i.e. physisorption and non-selective chemisorption.
A new symmetrical dihydrazide derivative organogelator (MBH-10) with two dihydrazide units was synthesized. The gelation property and the self-assembly behavior were researched by FE-SEM, XRD, rheology, FT-IR, concentration-dependent 1 H NMR, etc. Gels could be formed in acetonitrile and n-octanol with good mechanical properties. Quadruple hydrogen bonds between the dihydrazide units were viewed as the main driving force in the self-assembly process. The MBH-10 gelator which showed both anion-response (F − , H 2 PO 4 − ) property and relatively green, efficient toxic dyes removal property might be used in the field of anion sensing and environment remediation in the future.
Increasing water pollution is a major concern for the global community. So, purification and reuse of wastewater are very much urgent. In this work, methyl ester of phenylalanine (Phe-OMe), a non-gelator, has been successfully applied to produce two-component charge transfer-induced organogel and metallohydrogel using picryl chloride and Cu(II) respectively. These gels and their gelation processes were utilized to mop up different toxic metal ions and ionic dyes (especially zwitterionic dye) from wastewater. Phe-OMe can drop down these metal concentrations below the permissible limit of WHO within 10 min. Interestingly, the organogel instantly turns into sol upon the addition of either base or acid. This property makes the gel act as sensors of harmful acidic and basic vapors like HCl, ammonia, and so on in the laboratories and in different industries.
In this study, two isotactic polypropylene (PP) samples (PP-A, PP-B) with similar molecular weights and average isotacticities but different stereo-defect distributions were used to prepare the isotactic polypropylene/cellulose nanocrystals (PP/CNC) composites, the crystallization structures and crystallization kinetics were studied using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and non-isothermal crystallization kinetics, so as to provide understandings concerning the influences of CNC and stereo-defect distribution on the crystalline structure and crystallization kinetics the PP/CNC composites. The results showed that as the content of CNC increased, the crystallization temperature and crystallization rate of PP/CNC composites increased gradually, the crystallization peak width became narrower, the crystallite sizes decreased, and the saturated concentration of CNC was found to be 0.5 wt%. On the other hand, results showed that PP-A (whose stereo-defect distribution was less uniform than PP-B) and its PP/CNC composites still possessed higher crystallization rate, stronger crystallizability and smaller crystallite size compared with their counterparts of PP-B, suggesting that the stereo-defect distribution is the first factor determining the crystallization kinetics of PP/CNC composites.
Polyacrylamide/sodium alginate (PAM/SA) hydrogel was prepared from sodium alginate (SA) and acrylamide (AM) by covalently cross-linking. Temporary shape double network PAM/SA hydrogels were obtained by ionic cross-linking formed by complexation of SA and six metal cations (Fe 3+ , Cu 2+ , Ag + , Ca 2+ , Ni 2+ , and Co 2+ ), among the PAM/SA-Fe 3+ hydrogels has the best shape fixity ratio (83%). When the hydrogel is placed in different recovery liquids (sodium citrate, EDTA, sulfuric acid, and potassium carbonate), the shape recovery ratio (98.9%) is the best in sodium citrate solution, and the recovery time (182 s) of the hydrogel is the shortest. In general, Fe 3+ , Cu 2+ , and Ag + are suitable for the construction of ionic-shape memory hydrogels. The PAM/SA hydrogels also exhibited excellent adjustable mechanical properties by changing metal cations and soaking time. The strategy could broaden the construction of ion-responsive shape-memory hydrogels.
The characteristics of ion beam (IB) irradiated polyethylene glycol (PEG) films were analyzed to determine their potential use as a liquid crystal (LC) alignment layer. The transmittance of the PEG films at various IB intensities was measured to verify the possibility of using it as an alignment layer. Anti-parallel cells with the PEG film were fabricated to examine the LC alignment characteristics. Perfectly dark cross-polarized microscopy images were obtained at an intensity of 700 eV, which indicates uniform LC alignment, and pre-tilt angle measurements supported this finding. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses were conducted to determine the effect of the IB irradiation on the PEG film on the surface modification. After exposure at an IB intensity of 700 eV where uniform LC alignment was achieved, remarkable chemical composition modification of the PEG film, including the reduction of C-O bonds that affected the uniform LC alignment, was observed via the XPS analysis. Furthermore, the AFM analysis revealed that low kurtosis value was obtained at this IB intensity. Therefore, we are convinced that the PEG films irradiated at this low IB intensity show potential as alternative alignment layer in LC applications.
The influence of carbon nanotubes (CNTs) in antiferroelectric liquid crystals (AFLCs) is studied using Landau phenomenological theory. A Landau model is developed to describe the effect of CNTs in the mixture of nematic liquid crystal and AFLCs. The effects of CNTs on the AFLCS and the isotropic to chiral smectic-A* (I-SmA*) transition are studied. Theoretical results indicate the decrease of the helical pitch in the SmC* A phase and the decrease of the I-SmA* transition temperature with the increase of the concentration of CNTs. Theoretical results are compared with experimental results.
As soft materials represent new features that offer long-range orders, they have received considerable interests in optoelectronic fields. In this contribution, the assembly and characterization of soft materials incorporated by lanthanide complex have been reported. The polymeric hosts are derived from polyvinyl alcohol and polyacrylamide-co-polyacrylic acid. As for the metal complexes, the organic chromophore can sensitize europium or terbium ions simultaneously and green/red emissions are achieved. In the aqueous solution phase, the europium complex generates luminescence quenching effect upon the addition of Cu 2+ ions and the detection limit has been determined to be 3.6 μM. In addition, the "on-off" changes can be also observed based on the complex-loaded hydrogels and the mechanical properties are discussed. This responsive soft material will demonstrate great potentials in optical devices, biological analysis, and medical diagnosis fields.
Efficient buildup of carbon nanomaterial network with isotropic structure and performances in viscous polymer bulk has been of intense interest for abundant range of applications. Herein, a conductive and elastoplastic carbon nanohybrid preform is prepared. The strategy for assembling structurally intact carbon nanotubes (CNTs) and amphiphilic graphene oxide (GO) into integral carbon nanohybrid framework is implemented by using 2-ethyl-4-methylimidazole (EMI) during an undisturbed reaction. The as-synthesized porous carbon nanohybrid preform with sandwich cell wall was characterized with respect to wettability, electrical conductivity, and structural robustness to evaluate the structural and functional synergies from GO sheets and CNTs. Significantly increased conductivity is ascribed to the networking sp 2 -hybridized carbon domains interconnected by CNT bridges. The hydrogen-bonded EMI chains functioning as physical cross-linking are responsible for the elastoplasticity of carbon nanohybrid preform. A mechanism underlying is proposed for the conversion from common carbon nanomaterials to three-dimension multifunctional reinforcement.