Enhancing electrochemical preparation of polyaluminum chloride by a magnetic field

A novel effective method for preparing polyaluminum chloride (PAC) with high content of Al₁₃ polymer through conventional electrolysis coupled with rare earth Nd-Fe-B magnetic field was introduced. The content of Al₁₃ polymer in PAC synthesized by this method was highly influenced by the electrobath voltage (E), the magnetic flux density (B), the current density (i) and the distance between the two adjacent electrodes (d_adj). A total aluminum concentration (Al_T) in the PAC solution of 0.8 mol l⁻¹ was obtained when the E, B and i was 2.2 V, 0.4 T and 3.2 A dm⁻², respectively. The optimum d_adj and circulating flow (Q_f) were 20 mm and 23.7 l h⁻¹. With accelerated mass transfer rate by external magnetic field and high Q_f, this process had the advantages of forming more Al(OH)₄⁻ as the precursor of Al₁₃ polymer and inhibiting the concentration polarization more obviously than conventional electrolysis process. Under the optimum conditions, the amount of Al₁₃ polymer in PAC accounted for 82.3% of the Al_T (Al_T = 0.8 M, basicity = 2.2), which was higher than that of PAC prepared by other methods.     

The properties of a single polymer chain in solvent confined in a slit: A molecular dynamics simulation

A single polymer chain in solvent confined in a slit formed by two parallel plates is studied by using molecular dynamics simulation method. The square radii of gyration and diffusion behaviors of polymers are greatly affected by the distance between the two plates, but they do not follow the same way. The chain size decays drastically with increasing h (h is the distance between two plates), until a basin occurs, and a universal h/〈R _g〉₀ dependence for polymer chains with different degrees of polymerization can be obtained. While, for the chain’s diffusion coefficient, it decays monotonously and there is no such basin-like behavior. Furthermore, we studied the radial distribution function of confined polymer chains to explain the reason why there is a difference for the decay behaviors between dynamic properties and static properties. Besides, we also give the degree of confinement dependence of the static scaling exponent for a single polymer chain. Our work provides an efficient way to estimate the dynamics and static properties of confined polymer chains, and also helps us to understand the behavior of polymer chains under confinement.     

Hierarchical Nacre Mimetics with Synergistic Mechanical Properties by Control of Molecular Interactions in Self‐Healing Polymers

Designing the reversible interactions of biopolymers remains a grand challenge for an integral mimicry of mechanically superior biological composites. Yet, they are the key to synergistic combinations of stiffness and toughness by providing sacrificial bonds with hidden length scales. To address this challenge, dynamic polymers were designed with low glass‐transition temperature T_g and bonded by quadruple hydrogen‐bonding motifs, and subsequently assembled with high‐aspect‐ratio synthetic nanoclays to generate nacre‐mimetic films. The high dynamics and self‐healing of the polymers render transparent films with a near‐perfectly aligned structure. Varying the polymer composition allows molecular control over the mechanical properties up to very stiff and very strong films (E≈45 GPa, σ_UTS≈270 MPa). Stable crack propagation and multiple toughening mechanisms occur in situations of balanced dynamics, enabling synergistic combinations of stiffness and toughness. Excellent gas barrier properties complement the multifunctional property profile.     

Thermo‐ and pH‐Responsive Micelles of Poly(acrylic acid)‐block‐Poly(N,N‐diethylacrylamide)

Summary: The bis‐hydrophilic block copolymer, poly(acrylic acid)₄₅‐block‐poly(N,N‐diethylacrylamide)₃₆₀, was obtained after hydrolysis of poly(tert‐butyl acrylate)₄₅‐block‐poly(N,N‐diethylacrylamide)₃₆₀, synthesized by sequential anionic polymerization of tert‐butyl acrylate (tBA) and N,N‐diethylacrylamide (DEAAm) in the presence of Et₃Al. The polymer is stimuli‐sensitive with respect to both pH and temperature in aqueous solution, reversibly forming spherical crew‐cut micelles with PDEAAm‐core (〈R_h〉_z = 21.5 nm) under alkaline conditions for T > 35 °C as well as inverse star‐like micelles with an expanded PAA‐core (〈R_h〉_z = 43.8 nm) under acidic conditions for T < 35 °C, as indicated by dynamic light scattering.

Modes of micelle formation for poly(acrylic acid)₄₅‐block‐poly(N,N‐diethylacrylamide)₃₆₀ in aqueous solution depending on the pH and temperature.     

Polyimides from an asymmetric hydroxyl‐containing aliphatic‐aromatic diamine synthesized via henry reaction

An aliphatic amino and an aliphatic hydroxyl group have been incorporated via Henry reaction highly efficiently toward the synthesis of a novel asymmetric aliphatic–aromatic diamine 2‐amino‐1‐[4‐(5‐aminopyridyloxy)phenyl]‐1‐ethanol (AAP_yP_hE) in three steps. AAP_yP_hE shows good copolymerization reactivity with 4,4′‐oxydianiline (ODA) toward different aromatic dianhydrides, especially 4,4′‐oxydiphthalic anhydride (ODPA). TGA measurement and mechanical test results show that all polymers maintain the inherent thermal performance and tensile properties, while the glass transition temperatures (T_g's) by DMA show moderate decrease ranging from 185.5 to 253.3 °C due to the presence of aliphatic segments. The introduction of AAP_yP_hE is found to improve the solubility of the polymers, and the polymer films' optical transparency with decreased cutoff wavelength (λ₀) ranging from 328 to 370 nm. Comparative studies reveal that the pendent aliphatic hydroxyls in the polymer chains would lead to interchain cross‐linking via condensation and secondary weak cross‐linking by hydrogen bond depending on different loading of AAP_yP_hE, which result in a fluctuation of hydrophilic–hydrophobic properties, DMA tan δ and dielectric constant of the copolymer films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3413–3423     

Localized Yielding Around Crack Tips of Double‐Network Gels

Double‐network (DN) gels, a type of interpenetrating polymer network (IPN) consisting of rigid and flexible polymer components, exhibit two outstanding mechanical behaviors: yielding deformation of the entire specimen in tensile tests and quite high fracture energy in tearing tests. In this study, atomic force microscope (AFM) measurements were conducted on DN gels to determine the local Young's moduli immediately below the fracture surfaces E_f and below the usual molded surfaces E_m, and compare the local modulus with bulk Young's moduli measured before and after the yielding deformation, denoted as E_h and E_s, respectively. E_m and E_h are around 0.1 MPa; E_f and E_s, around 0.01 MPa, one order lower than the former two moduli. The order relation indicates that yielding deformation occurred locally around the crack tip of the DN gel during fracture. This supports the basic assumption of phenomenological models recently proposed to explain high fracture energy of DN gels. (H. R. Brown, Macromolecules 2007 , 40, 3815–3818; Y. Tanaka, Europhys. Lett. 2007 , 78, 56005).

     

An optimized preparation of bismaleimide–diamine co‐polymer matrices

The main aim of this study was to develop an improved method for the preparation of a bismaleimide–diamine (BMI/DDM) polymer matrix, achieving shorter curing time, longer processing time (pot life), and good thermal mechanical properties. A matrix of BMI/DDM thermoset was prepared at optimal conditions and formulation, containing BMI and DDM in a 2:1 mol ratio with 0.1 wt% of dicumyl peroxide (DCP) as the curing accelerator. An optimal temperature of 150°C was selected for both melt‐mixing and curing processes. The mechanism of matrix preparation was also investigated using differential scanning calorimetry and quantitative Fourier transformed infrared analysis. DCP at the optimal concentration was found to accelerate cross‐linking reactions between BMI and DDM without inhibiting the chain‐extension reaction of BMI. The specified formulation exhibited longer gel time (208 s/g) and shorter post‐curing time (2 h) compared to other formulations. In addition, thermomechanical behavior and thermal stability were analyzed by dynamic mechanical analysis and thermomechanical analysis, and thermogravimetric analysis, respectively. The storage modulus (E′), glass transition temperature (T_g), and decomposition temperature (T_d) of the BMI/DDM thermosets increased with the BMI content of the formulations, while the coefficient of thermal expansion and damping behavior (tan δ) decreased in a similar manner, primarily because of an increase in the degree of cross‐linking. Copyright © 2014 John Wiley & Sons, Ltd.     

Interfacial structure and properties in polystyrene/epoxy bilayer films

The interfacial structure and properties of immiscible deuterated polystyrene (dPS)/epoxy bilayer films were investigated with neutron reflectivity as functions of the composition of the epoxy layer, the thickness of the dPS layer, and the annealing time. We have found that the interfacial width and its growth rate depend strongly on the compositions of the epoxy layer but only weakly on the thickness of the dPS layer. The effect of the resin/crosslinker composition on the interfacial width and its growth rate is likely due to the different near‐surface structures that result for different epoxy stoichiometries. For an ultra‐thin dPS film (thickness = 2R_g), the data suggest a slight suppression of the growth of the interfacial width that could be due to confinement effects for the long‐chain molecules such as have been previously reported for a thickness of less than approximately 4R_g, where R_g is the radius of gyration of polymer molecules. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2653–2660, 2002     

Intercalation of water and guest molecules within Ca<Superscript>2+</Superscript>–Montmorillonite

The high potential for intercalations by water and various guest molecules is induced by the exchangeable cation inside Ca²⁺–Montmorillonite gallery. XRD peak for Mon at 2θ = 6.04° (d ₀₀₁ = 1.462 nm) shows the structural effect on the clay gallery influenced by the intercalated water layers. Further increases in the gallery height are observed with the intercalation of octadecyl ammonium cations in OMON (d ₀₀₁ = 1.840 nm) and ENR-50 matrix chains in CENR-50 (d ₀₀₁ = 1.954 nm). DSC studies on the other hand reveal the thermal behaviors of intercalated molecules that are linked to the exchangeable cations. The endothermic of Ca²⁺–Montmorillonite (H _Mon = 356.3 J/g) in low temperature range (30–100 °C) indicates the removal of free water and hydrogen bonded water molecules, while the endothermic around 150 °C is related to the induced skeletal layer of water within Ca²⁺–Montmorillonite. The OMON endothermic (H _OMON = 47.0 J/g, T _m = 36.94 °C) tells that cation exchange had modified the water structures and content inside the renewed clay. The intercalation of ENR-50 chains into OMON gallery reveals two endothermic with the T _m1 and T _m2 are at 86.24 and 113.80 °C, respectively. These T _ms confirm that the alkyl chain segment on octadecyl ammonium cation occupy the OMON interlayer space.     

Microstructure and dynamic mechanical analysis of extruded layered silicate PVC nanocomposites

The nanostructure and dynamic mechanical properties of polyvinyl chloride (PVC) and the bentonite nanocomposites have been investigated. Nanocomposites with 5 wt% concentration of bentonite were prepared by melt extrusion followed by two‐roll‐milled processing. Atomic force microscopy (AFM) and wide‐angle X‐ray scattering (WAXS) were utilized to study the micro and nanostructure of the two‐roll‐milled sheets. The nanocomposites were compounded with two types of coupling agents: KZTPP® and Tamol 2001®. Optical microscopy showed that the materials remained optically transparent, i.e. they did not show evidence of nanoclay agglomeration. The WAXS patterns of PVC‐bentonite‐KZTPP nanocomposite were anisotropic, suggesting flow‐induced preferred orientation of the nanoplates. Moreover, the 001 reflection of the bentonite was shifted toward smaller angles, suggesting that the nanoplates were intercalated by the macromolecules. On the other hand, the WAXS patterns of PVC‐bentonite‐Tamol 2001 nanocomposite remained isotropic and did not show evidence of bentonite, suggesting exfoliation of the nanoplates. The nanocomposites showed an increase in glass transition temperature T_g, with the sequence T_g,PVC < T_g,KZTPP < T_{g,Tamol 2001}. Moreover, dynamic mechanical analysis (DMA) showed an increase in mechanical moduli and activation energy (and a decrease in the intensity of the mechanical damping Tan δ) following the same sequence. Interestingly, the improvement in mechanical moduli became more pronounced above the glass transition temperature. Copyright © 2008 John Wiley & Sons, Ltd.     

Chiral Azo polyurethane(urea): Preparation,optical properties and low power consumption polymeric thermo‐optic switch

Azo chromophore molecule (NPMBR) was synthesized by using 4‐nitroaniline, sodium nitrite and chiral reagent, R‐α‐methyl benzylamine. Then, NPMBR was polymerized with isophorone diisocyanate and polyether polyol to obtain novel chiral azo polyurethane(urea) (PUUR). The chemical structures of NPMBR and PUUR were characterized by FTIR and UV‐Vis spectroscopy. The UV‐induced trans/cis photoisomerization and reflex‐isomerization behaviors were investigated and the results indicated that the PUUR solution could undergo photochromism after irradiated by UV light. The measurements of refractive index and thermo‐optic coefficient (dn/dT) of PUUR were demonstrated at different wavelengths and different temperatures by ATR technique. By using CCD digital imaging devices, transmission loss of the internal waveguide was measured. The refractive index dispersions and Sellmeyer coefficients of PUUR were obtained by Sellmeyer equation. A Y‐branched switch based on thermo‐optic effect was proposed and the performance of switch was simulated. With branching angle of 0.143° and FD‐BPM method, the result showed that the power consumption of the thermo‐optic switch could be only 0.4 mW, and the response time of the switch could reach about 3 ms. It has a significant improvement in reducing the power consumption and response time compared with those of the normal Y‐branched polymer thermo‐optic switch. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Concentration dependence of the global and anisotropic dimensions of confined macromolecules

The chain dimensions 〈R²〉 of nondilute polymer solutions confined to a slit of the width D were studied using lattice simulations. It was found that the chain compression induced in good solvents by the concentration ϕ is enhanced in a slit relative to the bulk. The global dimensions of chains also change with ϕ in confined and unconfined theta solutions. At intermediate slit widths, a region was noted where coils are squeezed along all three axes. This region is manifested as a channel on the three‐dimensional surface 〈R²〉(D,ϕ) in both good and theta solvents. The coil anisotropy, given by the ratio of the parallel and perpendicular components of the chain dimensions 〈R_y²〉/〈R_x²〉, reaches high values at strong confinements, where coils form quasi‐two‐dimensional pancakes. The concentration‐induced reduction of the global chain dimensions in good solvents is almost fully transmitted to the parallel component 〈R_y²〉. The computed effects of concentration and confinement were compared with the predictions of mean‐field and scaling theories, and implications of the results to ultrathin films and layered nanocomposites were discussed. In addition, the distribution functions of the components of the end‐to‐end distance R perpendicular and parallel to the plates, W (R_x) and W (R_y), were calculated. The function W (R_x) combined with the concentration profile ϕ (x) along the pore provided details of the chain structure close to walls. A marked difference in the pace of the filling up of the depletion layer was noticed between chains in theta and good solvents. From the distribution functions W (R_x) and W (R_y), the highly anisotropic force‐elongation relations imply the deformation of chains in confined solutions and ultrathin bulk films.     

Effect of adjacent hydrophilic polymer thin films on physical aging and residual stress in thin films of poly(butylnorbornene‐ran‐hydroxyhexafluoroisopropyl norbornene)

The properties of thin supported polymer films can be dramatically impacted by the substrate upon which it resides. A simple way to alter the properties of the substrate (chemistry, rigidity, dynamics) is by coating it with an immiscible polymer. Here, we describe how ultrathin (ca. 2 nm) hydrophilic polymer layers of poly(acrylic acid) and poly(styrene sulfonate) (PSS) impact the aging behavior and the residual stress in thin films of poly(butylnorbornene‐ran‐hydroxyhexafluoroisopropyl norbornene) (BuNB‐r‐HFANB). The aging rate decreases as the film thickness (h) is decreased, but the extent of this change depends on the adjacent layer. Even for the thickest films (h > 500 nm), there is a decrease in the aging rate at 100 °C when BuNB‐r‐HFANB is in contact with PSS. In an effort to understand the origins of these differences in the aging behavior, the elastic modulus and residual stress (σ_R) in the films were determined by wrinkling as a function of aging time. The change in the elastic modulus during aging does not appear to be directly correlated with the densification or expansion of the films, but the aging rates appear to roughly scale as hσ_R^1/3. These results illustrate that the physical aging of thin polymer films can be altered by adjacent polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 992–1000     

Glass transition and relaxation behavior of epoxy nanocomposites

With advances in nanoscience and nanotechnology, there is increasing interest in polymer nanocomposites, both in scientific research and for engineering applications. Because of the small size of nanoparticles, the polymer–filler interface property becomes a dominant factor in determining the macroscopic material properties of the nanocomposites. The glass‐transition behaviors of several epoxy nanocomposites have been investigated with modulated differential scanning calorimetry. The effect of the filler size, filler loading, and dispersion conditions of the nanofillers on the glass‐transition temperature (T_g) have been studied. In comparison with their counterparts with micrometer‐sized fillers, the nanocomposites show a T_g depression. For the determination of the reason for the T_g depression, the thermomechanical and dielectric relaxation processes of the silica nanocomposites have been investigated with dynamic mechanical analysis and dielectric analysis. The T_g depression is related to the enhanced polymer dynamics due to the extra free volume at the resin–filler interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3849–3858, 2004     

Contribution of Polymer‐Solvent Interactions to Dynamics of Linear Polymers in Dilute Solutions

In this work a theoretical approach to dynamics of linear vinyl polymers in dilute solutions of high viscosity solvents is presented. The calculations for the relaxation time spectra, polymer intrinsic viscosity [η (ω)], complex elastic modulus G*(ω), total intrinsic viscosity [η^T (ω)] and specific heat capacity C (ω) were carried out in the non‐free‐draining limits. The relaxation time spectrum calculated for dynamics of low frequency modes exhibits a Rouse‐like character. Its position and shape corresponds to the ultrasonic relaxation time spectrum observed in the system at 10⁶ Hz. On the other hand, the relaxation time spectrum associated with moderate frequency mode dynamics is narrower and typical for ultrasonic relaxation observed at 10⁷ Hz. The polymer intrinsic viscosity [η (ω)] and elastic modulus G*(ω) are shown to be represented by the model within a low‐frequency range. In turn, the specific heat capacity C (ω) is displayed as a representation of the model in the acoustic region mentioned above. In the high‐frequency range the dynamics is described by the total intrinsic viscosity [η^T (ω)] tending to a plateau where the value is equal to the sum of the single‐bead intrinsic viscosity [η_N] and effective solvent viscosity [η_eff].     

Spectroscopic Study of the E/Z Photoisomerization of a New Cyrhetrenyl Acylhydrazone: A Potential Photoswitch and Photosensitizer†

The new cyrhetrenyl acylhydrazone [(CO)₃Re(η⁵‐C₅H₄)‐C(O)‐NH‐N = C(CH₃)‐(2‐C₄H₂S‐5‐NO₂)] ( E‐CyAH ) has been designed, synthesized and fully characterized to study the effect of having a cyrhetrenyl fragment (sensitizer) covalently bonded to an acylhydrazone moiety (switch), on its photophysical and photochemical properties. The crystal structure reveals that E‐CyAH adopts an E‐configuration around the iminic moiety [‐N = C(CH₃)]. The absorption spectrum of E‐CyAH displays two bands at 270 and 380 nm, which are mainly ascribed to π → π* intraligand (IL) and d_π → π* metal‐to‐ligand charge transfer (MLCT) transitions, being consistent with DFT/TD‐DFT calculations. Upon 365 nm irradiation, E‐CyAH photoisomerizes to Z‐CyAH , as evidenced by UV‐Vis and ¹H‐NMR spectral changes, with a quantum yield value Φ_{E‐CyAH →Z‐CyAH} of 0.30. Z‐CyAH undergoes a first‐order thermal back‐isomerization process, with a relatively short half‐life τ_1/2 of 277 min. Consequently, E‐CyAH was quantitatively recovered after 24 h, making it a fully reversible T‐type molecular photoswitch. This remarkable behavior allows us to measure the individual photophysical properties for both isomers. In addition, E‐CyAH and Z‐CyAH efficiently photosensitize the generation of singlet oxygen (O₂ (¹Δ_g)) with good yield (Φ_Δ = 0.342).     

Enhanced β‐phase in PVDF polymer nanocomposite and its application for nanogenerator

Harvesting energy from the ambient mechanical energy by using flexible piezoelectric nanogenerator is a revolutionary step toward achieving reliable and green energy source. Polyvinylidene fluoride (PVDF), a flexible polymer, can be a potential candidate for the nanogenerator if its piezoelectric property can be enhanced. In the present work, we have shown that the polar crystalline β‐phase of PVDF, which is responsible for the piezoelectric property, can be enhanced from 48.2% to 76.1% just by adding ZnO nanorods into the PVDF matrix without any mechanical or electrical treatment. A systematic investigation of PVDF‐ZnO nanocomposite films by using X‐ray diffractometer, Fourier transform infrared spectroscopy, and polarization‐electric field loop measurements supports the enhancement of β‐phase in the flexible nanocomposite polymer films. The piezoelectric constant (d₃₃) of the PVDF‐ZnO (15 wt%) film is found to be maximum of approximately −1.17 pC/N. Nanogenerators have been fabricated by using these nanocomposite films, and the piezoresponse of PVDF is found to enhance after ZnO loading. A maximum open‐circuit voltage ~1.81 V and short‐circuit current of 0.57 μA are obtained for 15 wt% ZnO‐loaded PVDF nanocomposite film. The maximum instantaneous output power density is obtained as 0.21 μW/cm² with the load resistance of 7 MΩ, which makes it feasible for the use of energy harvesting that can be integrated to use for driving small‐scale electronic devices. This enhanced piezoresponse of the PVDF‐ZnO nanocomposite film‐based nanogenerators attributed to the enhancement of electroactive β‐phase and enhanced d₃₃ value in PVDF with the addition of ZnO nanorods.     

Organomagnesium clusters: Structure, stability, and bonding in archetypal models

We have studied the molecular structure and the nature of the chemical bond in the monomers and tetramers of the Grignard reagent CH₃MgCl as well as MgX₂ (X = H, Cl, and CH₃) at the BP86/TZ2P level of theory. For the tetramers, we discuss the stability of three possible molecular structures of C_2h, D_2h, and T_d symmetry. The most stable structure for (MgCl₂)₄ is D_2h, the one for (MgH₂)₄ is C_2h, and that of (CH₃MgCl)₄ is T_d. The latter is 38 kcal/mol more stable with chlorines in bridge positions and methyl groups coordinated to a Mg vertex than vice versa. We find through a quantitative energy decomposition analysis (EDA) that the tetramerization energy is predominantly composed of electrostatic attraction ΔV_elstat (60% of all bonding terms ΔV_elstat + ?E_oi) although the orbital interaction ?E_oi also provides an important contribution (40%).     

Photocatalytic properties of CuO/(001)‐TiO2 composites synthesized by the vapor–thermal method

Composites of (001)‐face‐exposed TiO₂ ((001)‐TiO₂) and CuO were synthesized in water vapor environment at 250°C with various Cu/Ti molar ratios (R_Cu/Ti). The resulting CuO/(001)‐TiO₂ composites were characterized using a variety of techniques. The synthesis under high‐temperature vapor allows close contact between CuO and (001)‐TiO₂, which results in the formation of heterojunctions, as evidenced by the shift of valence band maximum towards the forbidden band of TiO₂. An appropriate ratio of CuO can enhance the absorption of visible light and promote the separation of photogenerated carriers, which improve the photocatalytic performance. The degradation rate constant K_app increased from 5.5 × 10^?2 to 8.1 × 10^?2 min^?1 for R_Cu/Ti = 0.5. Additionally, the results showed that superoxide radicals (^?O₂^?) play a major role in the photocatalytic degradation of methylene blue.