Inversion Behavior Research Articles

Photonic fan-out and local selectable inversion of the optical hysteresis shape

We demonstrate and elucidate the local selectable inversion of the hysteresis shape of a bistable optical signal after fan-out. This selectability is based on a hysteresis-shape transformation that yields a switching contrast over 20 dB in magnitude for both the inversion clockwise (CW) and the non-inversion counterclockwise (CCW) hysteresis shapes, while maintaining input-switching powers. This behavior leverages an initial signal whose bistability is manifested by its state of polarization; a generalized Malus’ law elucidates how selection is possible by controlling the transmittivity hysteresis through each local polarizer. The concept is demonstrated using a Fabry–Pérot semiconductor optical amplifier to produce the initial bistable polarization-rotating signal, followed by a 1 × 2 fan-out and the realization of all four hysteresis shapes at each location, independent of the other location. This fan-out and selectable inversion behavior is applicable to other nonlinear photonic systems and provides new functionality for parallel optical processing.

Reversible chirality inversion of an AuAgx-cysteine coordination polymer by pH change

Responsive chiral systems have attracted considerable attention, given their potential for diverse applications in biology, optoelectronics, photonics, and related fields. Here we show the reversible chirality inversion of an AuAgx-cysteine (AuAgx-cys) coordination polymer (CP) by pH changes. The polymer can be obtained by mixing HAuCl4 and AgNO3 with L-cysteine (or D-cysteine) in appropriate proportions in H2O (or other surfactant solutions). Circular dichroism (CD) spectrum is used to record the strong optical activity of the AuAg0.06-L-cys enantiomer (denoted as L0.06), which can be switched to that of the corresponding D0.06 enantiomer by alkalization (final dispersion pH > 13) and can be switched back after neutralization (final dispersion pH <8). Multiple structural changes at different pH values (≈9.6, ≈13) are observed through UV-Vis and CD spectral measurements, as well as other controlled experiments. Exploration of the CP synthesis kinetics suggests that the covalent bond formation is rapid and then the conformation of the CP materials would continuously evolve. The reaction stoichiometry investigation shows that the formation of CP materials with chirality inversion behavior requires the balancing between different coordination and polymerization processes. This study provides insights into the potential of inorganic stereochemistry in developing promising functional materials.

Chiroptical Response Inversion and Enhancement of Room-Temperature Exciton-Polaritons Using 2D Chirality in Perovskites.

Although chiral semiconductors have shown promising progress in direct circularly polarized light (CPL) detection and emission, they still face potential challenges. A chirality-switching mechanism or approach integrating two enantiomers is needed to discriminate the handedness of a given CPL; additionally, a large material volume is required for sufficient chiroptical interaction. These two requirements pose significant obstacles to the simplification and miniaturization of the devices. Here, room-temperature chiral polaritons fulfilling dual-handedness functions and exhibiting a more-than-two-order enhancement of the chiroptical signal are demonstrated, by embedding a 40 nm-thick perovskite film with a 2Dchiroptical effect into a Fabry-Pérot cavity. By mixing chiral perovskites with different crystal structures, a pronounced 2Dchiroptical effect is accomplished in the perovskite film, featured by an inverted chiroptical response for counter-propagating CPL. This inversion behavior matches the photonic handedness switch during CPL circulation in the Fabry-Pérotcavity, thus harvesting giant enhancement of the chiroptical response. Furthermore, affected by the unique quarter-wave-plate effects, the polariton emission achieves a chiral dissymmetry of ±4% (for the emission from the front and the back sides). The room-temperature polaritons with the strong dissymmetric chiroptical interaction shall have implications on a fundamental level and future on-chip applications for biomolecule analysis and quantum computing.

Fracture Imaging and Response Characterization of the High-Definition Oil-Based Mud Borehole Imagers Through Modeling and Inversion

The new-generation, high-definition oil-based mud borehole imagers measure button impedances, which are often inverted to produce images of the formation resistivity, formation permittivity, and sensor standoff. These images, each reflecting a unique aspect of the downhole media, can provide a comprehensive understanding of the reservoir’s secondary porosity, i.e., fractures and vugs. To understand and validate the inversion behavior on fractures and vugs, synthetic logs of axisymmetric 2D fractures and vugs are generated and inverted. While the inverted medium properties follow the variation of the fracture-filling materials, the inverted standoff is shown to be a reliable indication of the fracture open/closed conditions. Specifically, an increased inverted standoff would always appear for mud-filled open fractures, which is further validated by laboratory measurements on artificial fractures and vugs. Numerical tests indicate that mineral-filled fractures may also lead to some variations on the inverted standoff when the resistivity contrast between the mineral-filling material and the host formation is high. Therefore, an elevated standoff may also be associated with a mineral-filled fracture. The modeling and inversion help reveal the connection between the response of the inverted parameters and the actual fracture characteristics. When the fractures are open and filled with mud, the inversion obtains an equivalent standoff at the fractures. This equivalent standoff increases not only with fracture width but also with the resistivity of the host formation. As a result, a fracture may have varying amplitudes in different formation layers. The fracture modeling and inversion also allow us to understand the prevalent existence of conductive fractures observed in the field. It is commonly thought that the resistivity of oil-based mud is always higher than that of the formation. However, this is only true at traditional operating frequencies. Because of mud dispersion, the mud resistivity is different at the two operating frequencies. For an open, mud-filled, resistive fracture to turn conductive, the formation resistivity only needs to exceed the mud resistivity at the higher operating frequency, which is typically on the order of a few 100 Ω·m instead of many 1,000 Ω·m at the lower operating frequency. As a result, an open fracture could be easily conductive in one layer but resistive in another formation layer.

Analytical and Numerical Investigations of Circular Metal Foam Sandwich Tube Under Free Inversion

Abstract The foam sandwich tube contains inner and outer tubes and filling foam. The foam sandwich tube is widely used in engineering, due to its lightweight, high specific strength, energy absorption, and other excellent characteristics. In this paper, the free inversion of the circular metal foam sandwich tube (CMFST) under axial loading is studied analytically and numerically. The plastic deformation occurs in the CMFST, and its main deformation modes include circumferential expansion, radial bending of the CMFST, and compression of the metal sandwich foam. An analytical model for the free inversion of the CMFST under axial loading is established, considering metal tube expansion, the radial bending of metal circular tube wall, and metal foam compression. The commercial abaqus software is adopted to numerically study the free inversion behavior of the CMFST. The analytical predictions agree well with the numerical ones. It is shown that the specific energy absorption (SEA) of the CMFST under free inversion is significantly better than the empty tube. When the non-dimensional foam strength is 0.05, the SEA of the CMFST under free inversion is 107.68% higher than the empty tube. Thus, the metal foam sandwich tube under free inversion is an excellent energy-absorbing device.

Effect of nonionic surfactants on the synergistic interaction between asphaltene and resin: Emulsion phase inversion and stability

Interaction between surface active components in crude oils and nonionic surfactants plays an important role in phase inversion behavior of crude oil emulsion, while the interaction mechanism is not yet fully explored. Herein, the effects of nonionic surfactants on the synergistic interaction between asphaltene and resin, emulsion stability, and emulsion phase inversion were investigated. It is shown that the addition of Span 80 and Tween 80 promotes the reduction of phase inversion point of water in oil emulsion stabilized by asphaltene and resin, as well as increases the yield strain value of the emulsion. The addition of Tween 80 to the asphaltene and resin mixture reduces the inversion point from 70 % to 30 %. The decrease of phase inversion point is attributed to the difficulty in the formation of multiple emulsions after adding nonionic surfactants. The addition of nonionic surfactants can affect the hydrogen bonding between asphaltene and resin, thereby improving the emulsion stability. Span 80 coexists with asphaltene and resin at oil-water interface, reducing the Turbiscan Stability Index (TSI) of emulsion by 15 and improving the strength of the oil-water interface membrane. In comparison, Tween 80 with stronger hydrophilic ability dissolves asphaltene and resin into bulk phase, which leads to the oil-water interface occupied by a large amount of Tween 80. Its numerous EO groups result in the strong hydrogen bonding on the oil-water interface membrane, effectively increasing the strength of the oil-water interface membrane and reducing the TSI by 19. This work contributes to a better understanding of the phase inversion of crude oil emulsion and improves crude oil recovery.

Synthesis, densification, and cation inversion in high entropy (Co,Cu,Mg,Ni,Zn)Al2O4 spinel

ABSTRACT The synthesis, densification behavior, and crystallographic site occupancy were investigated for four different spinel-based ceramics, including a high-entropy spinel (Co0.2Cu0.2Mg0.2Ni0.2 Zn0.2)Al2O4. Each composition was reacted to form a single phase, but analysis of X-ray diffraction patterns revealed differences in cation site occupancy with the high-entropy spinel being nearly fully normal. Densification behavior was investigated and showed that fully dense ceramics could be produced by hot pressing at temperatures as low as 1375°C for all compositions. Vickers’ hardness values were at least 10 GPa for all compositions. The cations present in the high-entropy spinel appear to have a stabilizing effect that led to nearly normal site occupancy compared to full cation inversion behavior of nickel aluminate spinel. This is the first report that compares cation site occupancy of a high-entropy spinel to conventional spinel ceramics.

Control of chirality inversion kinetics of triple-helical metallocryptands

Abstract Dynamic helical molecules, which can undergo a reversible chirality inversion between the P and M forms, are useful as a platform for switchable chiral functional molecules. The chirality inversion of these molecules has been extensively studied. However, it has mostly been discussed from the viewpoint of the equilibrated P/M ratios before and after the inversion; control of the response speeds or kinetic profiles has rarely been explored. In order to construct helical structures with controllable kinetic profiles, triple-helical metallocryptands, LM3, have been designed and synthesized. These molecules can undergo a relatively slow dynamic P/M chirality inversion (helicity inversion) to produce an equilibrated mixture. The P/M equilibration was accelerated or decelerated based on the following two strategies. One is based on the guest binding in the cryptand cavity. The P/M racemization kinetics of LNi3 was significantly decelerated by recognition of guanidinium ion in the cavity. The other strategy is based on the ligand exchange reactions at the octahedral cobalt(III) centers in LCo3(amine)6. The P/M chirality inversion speeds were controlled by changing the initial and entering amine ligands. In addition, a unique transient chirality inversion behavior was observed when chiral amine ligands were removed from the metallocryptand by the ligand exchange reaction with piperidine.

Thickness-dependent β/γ-NiOOH transformation of Ni-MOFs in oxygen evolution reaction

In-situ generated hydroxides and oxyhydroxides have been gradually recognized as the real active sites of metal organic frameworks (MOFs) towards the oxygen evolution reaction (OER). Nevertheless, the fine phase evolution process is still less of concern and elusive. Herein, we successfully construct serious of Ni-MOFs with differing thickness ranging from 1 nm to 270 nm through a competitive coordination strategy. Utilizing the operando resonance spectroscopy, an accurate phase inversion behavior of the Ni-MOFs has been witnessed during the OER, and demonstrated as a thickness-dependent process. Ultrathin architecture is identified as a positive factor to promote the exchange between MOFs ligands and applied electrolyte during the electrochemical test. Hence, after removing most of the internal ligands, 2D MOFs favor to be transformed as β-NiOOH, which is more active than the generated γ-NiOOH in bulky system. The density function theory (DFT) calculation alongside with the in-situ electrochemistry tests further affirm the β/γ-NiOOH transformation behavior. This work offers a new understanding of the electrocatalytic mechanism from the view point of phase evolution in 2D MOFs.

Thermodynamic Differentiation of the Two Sides of Azabuckybowl through Complexation with Square Planar Platinum(II).

The precise control of the two faces, concave/convex faces, is an attractive challenge to realizing novel dynamic molecular systems. Herein, we report the synthesis, X-ray crystal structure, and bowl-to-bowl inversion behavior of a platinum complex with azabuckybowl as a monodentate ligand. X-ray crystallography revealed that the azabuckybowl is orthogonally coordinated to the plane containing the Pt center and other ligands. One and two-dimensional NMR studies have also confirmed that this complex was observed as mixtures of two isomers, although the isomeric ratio was highly biased. Theoretical calculations indicate that the difference in thermodynamic stability of these isomers is due to the direction of the concave/convex face of an azabuckybowl ligand.

Chiral Inversion and Recovery of Supramolecular Luminescent Copper Nanocluster Hydrogels Triggered by Polyethyleneimine and Polyoxometalates.

Construction of controllable chiroptical supramolecular luminescence systems is of great significance for developing intelligent chiral luminescence materials with precise and effective regulation and understanding chirality-switching phenomena in biological systems, which has attracted extensive attention. Because chiral metal nanoclusters (NCs) can provide facilities for the study of nanoscale chiral effects, in this study, we select chiral glutathione-stabilized copper NCs (G-SH-Cu NCs) to construct a supramolecular luminescent hydrogel with achiral branched polyethyleneimine (PEI) and polyoxometalates [Na9(EuW10O36)·32H2O, denoted as EuW10]. Thus, a chiral property precise controlled system was constructed by self-assembly. Interestingly, the addition of PEI to G-SH-Cu NC solution induced the formation of luminescent hydrogels with chiral inversion, while further addition of EuW10 not only enhanced the luminescence of the hydrogel but also recovered the chiroptical properties. The chiral inversion behavior is possibly ascribed to the hydrogen bond interaction/electrostatic interaction between G-SH-Cu NCs and PEI in the chiral inversion process, while the competition of hydrogen bonding interaction (between G-SH-Cu NCs and PEI) and electrostatic interaction (between PEI and EuW10) was accountable for the chiral recovery process. Manipulation of chirality inversion in the metal NC-containing coassemblies is rare, while this work establishes a feasible strategy to modulate the chiral inversion behavior of Cu NCs, which not only produces new physicochemical properties of metal NCs through synergistic behavior but also offers a feasible way to realize the potential application of chiroptical materials.

Enhanced sulfate ion adsorption selectivity in capacitive deionization with ball-milled activated carbon

This study interrogated straightforward ball-milling (BM) of powdered activated carbon (AC) to intensify the selective separation by capacitive deionization (CDI) primarily for SO42− with potential eco-toxicity. Depending on the BM duration (20 to 60 h) of coconut-derived AC, the prevalent shift in pore size distribution or surface charge/moieties was observed for BM-20 and BM-60, respectively, whereas synchronous modifications were noted for BM-40. In single-pass experiments (1.2/0 V) with symmetric electrodes, BM-40 notably elevated the selectivity factor of SO42− by 36 % from equimolar SO42−/Cl− mixture (2 mM each). Enumerated effective pores for SO42− (0.76–1.1 nm) and shorted diffusion length of reduced grain accelerated replacement of pre-sorbed Cl− by divalent SO42− under the alleviated ion-sieving effects. Comparison with asymmetric cells with the pristine negative electrode further evinced that ameliorated co-ion repulsion from the oxidized (with augmented potential of zero charge) negative electrode could secure driving potential on the positive electrode to strengthen the energetic-affinity-based ion swapping. In addition, quasi-absolute selectivity for NO3− sorption (with a partial inversion behavior for Cl−) was observed in the asymmetric cell receiving equimolar SO42−/Cl−/NO3− composite. Consequently, the BM effectively regulated not only the perm-selectivity, but also the surface charge and/or specific interaction.

PH-responsive water-in-oil emulsions with reversible phase inversion behavior stabilized by a novel dynamic covalent surfactant

The dynamic covalent nature of imine bonds provides a facile avenue to develop stimuli-responsive emulsifiers and has attracted considerable interest. In petroleum engineering, the development of smart emulsifiers that can be switched on demand to achieve the reversible phase inversion of the invert emulsion drilling fluid (IEDF) can effectively aid in its removal during cleanup. To this end, a novel dynamic covalent surfactant (TA-CBA) that can precisely manipulate the emulsion type by responding to acid/base stimuli was synthesized through the Schiff base reaction between 1-tetradecylamine (TA) and 4-carboxybenzaldehyde (CBA). Evaluation of the surface tension and interfacial tension (IFT) showed that the imine-bonded product TA-CBA was a surfactant with strong IFT reduction ability. At pH 7.4, the prepared water-in-oil (W/O) emulsions were stable without any separated phases after storage for 48 h and even after high-temperature aging at 210 °C. As the pH decreased from 7.4 to 4, the emulsion inverted from a higher viscosity W/O emulsion to a lower viscosity oil-in-water (O/W) emulsion. Remarkably, after the pH was adjusted back to 7.4, the rheological parameters and stability of the emulsion could be triggered at the original W/O emulsion level. 1H NMR and IFT measurements revealed that the reversible formation and breakage of covalent imine bonds led to the production of CBA and cationic amine salt (TA+), establishing the pH reversibility of the emulsion type and its rheological properties. Finally, we successfully formulated a reversible IEDF using TA-CBA as the sole emulsifier, which not only has reasonable rheological properties, filtration performance, and emulsification stability but also allows for easy cleanup. The IEDF can be phase-inverted into a water-soluble O/W emulsion drilling fluid at pH 4 and achieved a removal efficiency of 98.13 %.

Intense 2.9 µm mid-infrared emission from Dy3+/Yb3+：SrF2 crystal under 975 nm excitation

The intense 2.9 µm MIR (mid-infrared) luminescence corresponding to the Dy 3+ : 6 H 13/2 → 6 H 15/2 transition was achieved for the first time in Dy 3+ /Yb 3+ ions co-doped SrF 2 crystals. 2 at% Dy 3+ : SrF 2 ，2 at% Dy 3+ /5 at% Yb 3+ : SrF 2 , and 5 at% Yb 3+ : SrF 2 crystals were grown by Bridgman method. The influence of Yb 3+ on its spectral properties and energy transfer mechanisms has been studied. In comparison to Dy 3+ doped SrF 2 crystals, Dy 3+ /Yb 3+ co-doped crystals exhibit not only intense 2.9 µm emission but also longer high laser energy level lifetimes, favoring 2.9 µm population inversion and lasing behavior. Furthermore, the ET efficiency from Yb 3+ to Dy 3+ in Dy 3+ /Yb 3+ co-doped crystals is found to be as high as 95.34%, indicating that the ET from Yb 3+ is efficient. The results show that incorporating Yb 3+ into Dy 3+ : SrF 2 crystals improves the ability to achieve 2.9 µm lasing action, which could be used as a potential gain media for laser diode-pumped MIR lasers. • The Dy 3+ , Dy 3+ /Yb 3+ and Yb 3+ doped SrF 2 single crystals were grown by the Bridgman-Stockbarger method. • Intense 2.9 µm mid-infrared emission is observed in Dy 3+ /Yb 3+ : SrF 2 crystal under 975 nm excitation. • Detailed spectroscopic properties and energy transfer mechanisms were studied. • Dy 3+ / Yb 3+ : SrF 2 crystals are expected to achieve mid-infrared laser output.

Hybrid nanofiltration thin film hollow fiber membranes with adsorptive supports containing bentonite and LDH nanoclays for boron removal

This study focused on removal of boron from water via hybrid nanofiltration (NF) thin film composite (TFC) hollow fiber (HF) membranes. To do so, nanocomposite polyvinyl chloride (PVC) HF membranes containing bentonite and layered double hydroxide (LDH) nanoparticles as natural and synthetic adsorbents were fabricated as the adsorptive support layers with high efficiency in boron removal. The phase inversion behavior of dope solutions and mechanical strength of the adsorptive nanocomposite PVC HF membranes were investigated and the results showed that LDH interacts better with PVC polymeric chains than bentonite. It was found that LDH with smaller pores and better adsorption capability in comparison with bentonite results in more hydrophilic membranes with better performance. On the other hand, bentonite tends to become agglomerated at above 1.5 wt%. Moreover, the fabricated membranes containing LDH have lower MWCO and more uniform pore size distribution which make them better options as support for the TFC layer formation to fabricate NF TFC membranes. The selective TFC layer was then fabricated via interfacial polymerization of m-phenylenediamine (MPD) and 1,3,5- benzenetricarbonyl trichloride (TMC) on the outer layer of the nanocomposite PVC HF membranes. Boron removal, and recovery and reusability of the fabricated NF TFC membranes were investigated by Na₂CO₃ solution. It was found that the NF TFC membranes containing LDH with boron removal of more than 83.6% and water flux of 16.1 L/m2.h at 4 bar operational pressure exhibit better performance than the NF TFC membranes containing bentonite.

Aqueous three-phase systems formed by poly(vinylpyrrolidone) + poly(ethyleneglycol) + lithium sulfate + water: Phase behavior and partition data

Aqueous three-phase systems (A3PSs) have been used to extract and separate several strategic analytes; however, there are several gaps in the characterization and theoretical principles of this technique. Therefore, an A3PS made up of 10,000 g‧mol−1 of polyvinylpyrrolidone (PVP), 10,000 g‧mol−1 of polyethylene glycol (PEG), lithium sulfate (Li2SO4), and water was characterized in this study. The results revealed that PEG, PVP, and Li2SO4 were concentrated in the top, middle, and bottom phases, respectively, whereas water was the main component in all phases. The three-dimensional coordinates of the phase composition points generated a plane with an area that increased as the difference in the phase compositions increased. The tie-plane area (TPA) decreased as the global composition and temperature decreased, indicating a strong temperature effect. Moreover, at relatively low overall concentrations, a phase inversion behavior between the electrolyte-rich phase and the PVP-rich phase was observed at 308.15 K. HE-4R dye molecules preferentially partitioned to the PVP-rich phase, and this trend increased as the TPA and temperature increased. A similar partition behavior was observed for Cu(II) ions, but they preferred to concentrate in the salt-rich phase. At relatively low overall concentrations, the Cu(II) ions promoted phase inversion at 298.15 K, a phenomenon similar to that observed in the temperature study. Thus, the phase diagram for a new A3PS was obtained, and as far as we know, this is the first work that quantitatively describes the TPA.

Design of Ru‐aqua complex possessing potential inversion behavior

AbstractWe attempted to design Ru‐aqua complexes that possess potential inversion behavior for sequential proton‐coupled oxidation (PCO) reactions. Standard reduction potentials for [RuIII(T)(B)(OH)]m+ + H+ + e− → [RuII(T)(B)(H2O)]m+ (E°(RuIII/II)), [RuIV(T)(B)(O)]m+ + H+ + e− → [RuIII(T)(B)(OH)]m+ (E°[RuIV/III]) reactions as well as ΔE° values (ΔE° = E°(RuIII/II) − E°(RuIV/III)) of newly designed 41 Ru‐aqua complexes along with those of previously reported 13 known ones were calculated using the DFT method with PBE1PBE/def2SVP/SDD combination. Four complexes with negative ΔE° values and nine complexes with ΔE° values smaller than 0.1 V were found by this screening work. The calculated ΔE° values had a close relationship with E°(RuIII/II). Complexes possessing large ΔE° values showed relatively small E°(RuIII/II) that gave rise to the increased gap with E°(RuIV/III). It was found that the distortion of electronic structures during progressing two PCO reactions is mostly responsible for the potential inversion.

The concept of tourist flows and the geography of tourism

The critical analysis of the main concepts of the geography of tourism was carried out. It was found that the most popular among them are devoted to the destinations of tourists, which is correct for recreation, and for tourism only half is adequate because of the one-sidedness, since the usual environment where the tourist comes from is ignored, where, in fact, recreational needs are formed that only afterwards will be satisfied in the destination. In order to avoid this drawback, it is proposed to consider tourism as a form of population migration through tourist flows connecting the places of origin and destination of tourists, which makes it possible to see this phenomenon holistically. As a theoretical and methodological foundation, the paradigm of behavioral geography was chosen, which considers the territorial behavior of people through their life lines, which appear in tourism as tourist trips. At the same time, it matters mass behaviors as unidirectional numerous trips that form tourist flows. The dialectical nature of the tourist flow is revealed, when the places of origin and destination of tourists are united by the mechanical movement of people, based on the opposition of temporary stay in a destination to permanent residence in the usual environment. As the main author's vision, a conceptual model of the formation and distribution of international tourist flows in the geographical space, which is also relevant for domestic tourism, is proposed and substantiated. It is built on the illumination of the apperception of the usual environment through the formation of dynamic stereotypes, as well as on the basis of the proposed basic tourist motives. These include the motives of migration, comfort, contrast, and aesthetics. The motive of migration that pushes tourists out from the usual environment is consistent with the well-known concept of escapism as a break from the routine of everyday life. The motive of contrast that attracts to destinations different from people’s usual environment is described by the tourist’s inversion behavior suggested by Graburn. All these motives have found their substantiation on the basis of I. Pavlov’s dynamic stereotypes which were helpful in disclosure of one lacking link in understanding the motive of comfort. Basing on all aforesaid motives combined into motivational system structured according to such geographical components of tourism flows as usual environment and destinations, and against the background of such properties of geographical space as length and heterogeneity, a conceptual model of territorial behavior of people in the modus of tourists was suggested.

Fate of Photoinduced Electron Transfer Reactions with Temperature- and pH-Induced Assembly/Disassembly of Star Block Copolymer Micelles.

The assembly/disassembly of star block copolymers induced by changes in temperature or pH of the medium is anticipated to have interesting implications for hosting/releasing drugs and tuning chemical reactions. This study investigates the possibility of employing the dually sensitive self-assembly of an ethylene oxide-propylene oxide star block copolymer, Tetronic T904, to influence photoinduced electron transfer (ET) reactions, on switching from the assembled state (micelle) when temperature is above the critical micelle temperature (CMT) and pH of the medium is above the pKa of T904 to the dissociated (unimer) state when either the temperature is below the CMT or the polymer is protonated. Steady-state and time-resolved fluorescence techniques have been used to characterize the microenvironments of the reactants in T904 solutions under different temperature and pH conditions and to determine ET rate constants. Interestingly, the bimolecular ET rate constants in both assembled and disassembled states of T904 depict a bell-shaped correlation with the driving force of the reaction, in accordance with Marcus inversion behavior instead of the usual Rehm-Weller behavior seen in conventional solvents. The assembly/disassembly of T904 stimulated by temperature or pH affects the micropolarity in the reactant environment, the magnitude of ET rate constants, and the position of inversion on the exergonicity scale.

Mechanical Property of Polypropylene Gels Associated with That of Molten Polypropylenes.

This study aims to understand the fundamental mechanical relationship between polypropylene (PP)-gels and solid PPs without solvent through mechanical and thermal analyses, by which the mechanical similarities between molten PPs and PP gels were found, leading to the reliable estimate of the mechanical properties of semi-crystalline gels. The gelation of syndiotactic and isotactic polypropylenes (sPP and iPP) was found when PPs were dissolved in 1,2,3,4-tetrahydronaphthalene (tetralin). Interestingly, it was found that the storage modulus of sPP-gel became higher than that of iPP-gel at low PP concentration (<~40 wt%). The result was distinctly different from the result of neat solid PPs (without solvent), where the modulus of solid sPP is generally significantly lower than that of solid iPP. Such inversion behavior in the mechanical property of semi-crystalline gels had not been reported and discussed before. By further investigation of the storage moduli of neat sPP and iPP, it was found that the storage modulus of sPP became higher than that of iPP above the melting points of PP, which was similar to the behavior of the storage moduli observed in the diluted PP-gels. Such similarity between PP-gels and PP melts was also observed within iPP samples with different molecular weights.