Novel ionic polymer–metal composite actuator based on sulfonated poly(1,4-phenylene ether-ether-sulfone) and polyvinylidene fluoride/sulfonated graphene oxide

In the present work, sulfonated graphene oxide and sulfonated poly(1,4-phenylene ether-ether-sulfone) were blended with polyvinylidene fluoride to create a novel ionic polymer–metal composite actuator with enhanced performance. An ionic polymer–metal composite membrane in the protonated form was prepared by casting a composite blend of sulfonated poly(1,4-phenylene ether-ether-sulfone), polyvinylidene fluoride and sulfonated graphene oxide onto a plating of platinum metal as the electrode. The degree of sulfonation of poly(1,4-phenylene ether-ether-sulfone) was characterized using ion-exchange capacity measurements. Energy dispersive X-ray and transmittance electron microscopy analyses were carried out to analyze the chemical composition and detailed structure. Deposition of the platinum electrode and the surface morphology of the proposed ionic polymer–metal composite actuator were assessed using scanning electron microscopy analysis. The electrical properties were measured using cyclic voltammetry, linear sweep voltammetry and proton conductivity. These measurements confirmed the better actuation performance of the fabricated ionic polymer–metal composite actuator compared to other expensive ionic polymer-based actuators, in terms of its high ion-exchange capacity, good proton conductivity, high current density and large bending deflection. The robust, flexible and mechanically strong membrane actuator, fabricated via the synergistic combination of sulfonated poly(1,4-phenylene ether-ether-sulfone), polyvinylidene fluoride and sulfonated graphene oxide, has considerable potential as an actuator material for robotic, bio-mimetic and other applications.

In the present work, sulfonated graphene oxide and sulfonated poly(1,4-phenylene ether-ether-sulfone) were blended with polyvinylidene fluoride to create a novel ionic polymer–metal composite actuator with enhanced performance.     

Thermal conductivity of poly(3,4-ethylenedioxythiophene) films engineered by oxidative chemical vapor deposition (oCVD)

Oxidative chemical vapor deposition (oCVD) is a versatile technique that can simultaneously tailor properties (e.g., electrical, thermal conductivity) and morphology of polymer films at the nanoscale. In this work, we report the thermal conductivity of nanoscale oCVD grown poly(3,4-ethylenedioxythiophene) (PEDOT) films for the first time. Measurements as low as 0.16 W m⁻¹ K⁻¹ are obtained at room temperature for PEDOT films with thicknesses ranging from 50–100 nm. These values are lower than those for solution processed PEDOT films doped with the solubilizing agent PSS (polystyrene sulfonate). The thermal conductivity of oCVD grown PEDOT films show no clear dependence on electrical conductivity, which ranges from 1 S cm⁻¹ to 30 S cm⁻¹. It is suspected that at these electrical conductivities, the electronic contribution to the thermal conductivity is extremely small and that phonon transport is dominant. Our findings suggest that CVD polymerization is a promising route towards engineering polymer films that combine low thermal conductivity with relatively high electrical conductivity values.

Measuring the thermal conductivity of oxidative chemical vapor deposited poly(3,4-ethylenedioxythiophene) thin films.

Molecular scale engineering tools like chemical vapor deposition (CVD) are the workhorses of the microfabrication industry. With these primarily inorganic thin film coating technologies, we can achieve multifunctional properties on the surface of a material which are different from those of the underlying substrate. CVD polymerization is a new technique that merges CVD thin film processing with the versatility of organic chemistry. This vapor phase polymerization offers a facile, solvent-free and low temperature route to simultaneously tune chemistry, morphology and functionality,¹ allowing for creative ways to engineer multiscale (thicknesses from nano to micro) and multifunctional (insulating, semiconducting, conducting) polymer films on a variety of substrates including paper, plastic, and biological tissue.¹Oxidative chemical vapor deposition (oCVD) is the vapor phase equivalent of solution-based oxidative (step growth) polymerization. oCVD enables the polymerization of thin films of electrically conducting polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT).^1,2 As depicted in Fig. 1(a), the all-dry oCVD thin film polymerization process involves subliming and reacting a solid-state oxidant like iron(iii) chloride (FeCl₃) with heated vapors of the EDOT monomer. Polymerization and thin film coating occurs simultaneously onto the surface of a temperature controlled substrate placed inside the custom-designed oCVD reactor. As we show in this work, electrical conductivity of the PEDOT films can be tailored (without affecting thermal conductivity) simply by varying the substrate temperature, synthesizing nanoscale PEDOT films whose properties can be precisely controlled in ways that are unattainable by solution processing.Open in a separate windowFig. 1(a) Schematic of oCVD reactor. Inset shows two glass substrates coated with PEDOT films of different thicknesses. (b) & (c) Cross-sectional scanning electron microscopy of polymer coatings grown by CVD polymerization on silicon trenches.Due to its high electrical conductivity, optical transparency, mechanical flexibility, and chemical and physical stability, PEDOT is one of the most widely studied conducting polymers.³ Commercially available PEDOT solutions are a mixture of PEDOT with the surfactant poly(styrenesulfonate) (PSS).²⁵ This surfactant enables the dispersion of PEDOT in polar solvents, making processing techniques such as spin coating⁴ and screen printing⁵ a viable option for depositing PEDOT thin films. However, the highly polar PSS is strongly acidic and can cause failure in devices such as polymer solar cells.⁶ Although solution processing techniques may be widespread, realizing nanoscale film thicknesses will often lead to non-uniformity due to de-wetting and surface tension effects that accompany solution processes.De-wetting and surface tension also make textured surfaces⁷ difficult to coat with the aqueous PEDOT:PSS while preserving the morphology of the structure underneath. On the other hand, CVD polymer films are uniform and pinhole free,²² exempt from de-wetting and surface tension effects. For this reason, extremely thin films are also attainable. In oCVD, reactants arrive at textured surfaces from all sides in the vapor phase, resulting in completely conformal PEDOT films that follow the contours of complex geometries.^8,9 We show in Fig. 1(b) and (c) that CVD grown polymer films uniformly cover textured surfaces like trenches cut into silicon wafers, enabling potential applications in macro and micro scale device fabrication. This vapor phase process is further compatible with substrates which would dissolve or degrade in the presence of solvents. This enables the creation of devices on fragile materials such as paper¹⁰ which would lose its structural integrity if exposed to any type of solvent. Copolymerization is also possible, providing access to functional groups which are not inherent to the specific polymer of interest.¹¹ The low cost,²³ mechanical flexibility and varied functionality offered by CVD polymerization is thus unmatched by existing solution processing methods.Herein, we use the differential 3ω method to measure the thermal conductivity of oCVD grown PEDOT films for the first time. In the oCVD process, by simply changing the substrate temperature, the conjugation length of the conducting polymer can be modified, thereby altering the electrical conductivity.¹² We studied the thermal conductivity of films grown at different substrate temperatures to determine whether a correlation exists between thermal and electrical conductivity. The transmission line method (TLM) was used to measure the electrical conductivity.¹⁶The oCVD process used to deposit PEDOT films is described in detail in ESI (S1^†).^1,12 Briefly, cleaned substrates were mounted onto a heating stage controlled from 70 °C to 130 °C. The monomer jar was heated to 130 °C while the oxidant was sublimed in a heated crucible at 225 °C. The deposition was carried out at a chamber pressure of 100 m torr for 45 min. After the deposition, the films were rinsed in methanol for 5 minutes to remove any residual monomer or oxidant. The resulting films had thicknesses ranging from 50–100 nm. The substrate used in this work was a silicon wafer with a thermally grown oxide layer. A 100 nm thick blocking layer of the electrically insulating polymer poly(divinylbenzene) (PDVB), was also deposited by CVD as described in the ESI S2.^†13 This electrically insulating layer is necessary to accurately measure the thermal conductivity of electrically conductive materials using the 3ω method.Performing temperature dependent measurements on soft, nanoscale organic layers like the oCVD grown polymer films is challenging. We describe our technique here in detail, particularly our device design and novel materials, such as the use of low temperature CVD grown PDVB blocking layer. The 3ω method used to measure the thermal conductivity of the oCVD PEDOT thin films is classified as a transient technique where a metal line acts simultaneously as a source heater and thermometer.¹⁴ When driven with a sinusoidal current at 2ω, the metal line heater causes temperature fluctuations in the sample also at 2ω. This in turn causes a small voltage signal across the heater at 3ω. The nature of the temperature fluctuation in the sample is dependent on the sample''s thermal properties, including thermal conductivity. Specifically, the differential 3ω technique was chosen because (a) knowledge of the thermal properties of the substrate and other materials deposited on the substrate are not required, and (b) the error associated with the differential 3ω method has been shown to be less than that of the slope-based 3ω method for samples with multiple films.¹⁴Fig. 2 depicts the sample structure used here. Similarly, a reference sample identical to this sample except for the oCVD PEDOT film was also fabricated. It should be noted that the thermal conductivity obtained is the effective thermal conductivity because it includes interface thermal resistance.Open in a separate windowFig. 2Device structure for 3ω measurement.A stainless-steel mask was used in conjunction with electron beam (e-beam) evaporation to fabricate the gold line heater on top of the PDVB layer. Metal lines with widths ranging from 40 μm to 70 μm were obtained. Since PEDOT is electrically conducting, the PDVB layer served to isolate the PEDOT film from the metal line heater, preventing current leakage and thus error in the measurement. Typically, processes such as sputtering or physical vapor deposition are used to deposit an electrically insulating layer such as silicon dioxide, however, sputtering may damage the polymer film and the high temperature involved will also be detrimental. In contrast, CVD polymerization of PDVB requires low substrate temperature (20 °C to 70 °C) and does not damage the PEDOT layer. The same mask and procedure was used to fabricate the line heaters on the corresponding reference samples as well.A wedge wire bonder was used to make electrical connections between the contact pads of the chip carrier and the contact pads of the line heater. However, due to the delicate and soft nature of PEDOT films, directly bonding to the line heater contact pads resulted in film damage and bond detachment. To facilitate the wire bonding process, a technique similar to the one described by Kaul et al.¹⁵ was used. A small amount of conductive epoxy was first applied to each contact pad of the gold line heater. After curing, wire bonding was then done directly from the solid epoxy to the pads on the chip carrier. This epoxy bonding technique was also utilized when measuring the electrical conductivity of the PEDOT films using TLM (Fig. 3 inset).¹⁶Open in a separate windowFig. 3Resistance vs. contact spacing of oCVD PEDOT film grown at a substrate temperature of 100 °C. Inset is an optical image of metal contacts with different spacing between pairs of electrodes.For the TLM measurements, a stainless-steel mask was first used to pattern the PEDOT film on the substrate. Gold electrodes with varying spacing between pairs of electrodes were then deposited directly onto the PEDOT film, using another stainless-steel mask and e-beam evaporation. 4-Point resistance measurements were done between each pair of electrodes to obtain a plot of resistance versus length. Fig. 3 shows results for the sample deposited at 100 °C, where the measured resistance is plotted as a function of distance between electrodes. The electrical conductivity is then inferred from the slope of the linear graph. The inset in Fig. 3 shows the gold electrodes with varying distances between pairs of electrodes on the PEDOT film. The conductive epoxy and bonded wires are also shown. The data from other samples measured were similar to that of Fig. 3. 12 Comparing the films deposited at 70 °C and 100 °C, we observe an order of magnitude increase in the electrical conductivity. However, a further increase in the substrate temperature to 130 °C only results in a 20% increase in the film''s electrical conductivity. One explanation for this result is the formation of hydrogen chloride (HCl) during the polymerization.¹² During the step growth polymerization, the oxidant initiates the reaction with the monomer to generate a radical cation, the deprotonation of the carbon–carbon coupled monomers generate the acidic HCl which acts as an inhibitor, and reduces the film''s electrical conductivity. As the substrate temperature increases the HCl content is reduced due to evaporation, resulting in a higher electrically conductive film.²⁴ Nevertheless, it appears that a saturation point was attained in our system, after which, an increase in temperature will no longer cause the HCl to evaporate. This effect could potentially explain why only a modest increase in electrical conductivity is observed for a substrate temperature increase from 100 °C to 130 °C. From 17 phonon boundary scattering effects are not expected since the thickness of the films in this study is >10 nm.Thermal and electrical conductivities of oCVD PEDOT films deposited at different substrate temperatures. Both quantities were measured at room temperature

Preparation of graphene oxide/poly(vinyl alcohol) composite membrane and pervaporation performance for ethanol dehydration

Although poly(vinyl alcohol) (PVA) membranes are widely used in solvent dehydration by pervaporation, the separation factor is rather limited. Considering this, novel PVA mixed matrix membranes with graphene oxide (GO) nanosheets were prepared. poly(acrylonitrile) ultrafiltration (PAN) membrane was used as support layer. The PVA/GO composite membranes were characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy, thermogravimetric analysis and water contact angle. We also explored the pervaporation performance of the membrane for ethanol dehydration. GO slightly improves the thermal stability and crystallinity of the composite membranes. In addition, the hydrophilicity of the composite membranes is weakened after GO addition, but the crosslinking degree is increased, resulting a significant increase in the separation factor and a certain decrease in the total flux. With the amount of GO addition increases, the total flux of the PVA/GO composite membrane decreases, while the separation factor increases first and then decreases, and the preferred amount of GO addition is 2.0 wt%. Especially, the separation factor of the composite membranes with 2.0 wt% GO addition could reach 3 059, which is 16 times higher than PVA membranes, with the corresponding permeability flux is 145 g m⁻² h⁻¹.

The separation factor of the composite GOP-2.0 membranes could reach 3 059, which is 16 times higher than PVA membranes.     

Sulfonated component-incorporated quaternized poly(phthalazinone ether ketone) membranes with improved ion selectivity,stability and water transport resistance in a vanadium redox flow battery

Novel poly(phthalazinone ether ketone)-based amphoteric ion exchange membranes with improved ion selectivity, stability and water transport resistance were prepared for vanadium redox flow battery (VRB) applications. The preparation method ensured the absence of electrostatic interaction. A small amount of sulfonated poly(phthalazinone ether ketone) (SPPEK) with different ion exchange capacity (IEC) values was mixed with brominated poly(phthalazinone ether ketone) (BPPEK) to prepare base membranes with the solution casting method, and they were aminated in trimethylamine to obtain the resulting membranes (Q/S-x, x represents the IEC value of SPPEK). Compared with the AEM counterpart (QBPPEK) prepared from the amination of the BPPEK membrane, Q/S-1.37 showed lower swelling ratio and area resistance (R). The R value of Q/S-1.37 (0.58 Ω cm²) was close to that of Nafion115. The VO²⁺ and V³⁺ permeability values of Q/S-x were 96.7–97.6% and 98.5–99.2% less than those of Nafion115, respectively, demonstrating the excellent ion selectivity of Q/S-x. Compared with Nafion115 and QBPPEK, Q/S-1.37 displayed 90.0% and 92.1% decrease in the static water transport volume and 93.2% and 66.7% decrease in the cycling transport rate, respectively, revealing good water transport resistance. Compared with Nafion115, Q/S-1.37 exhibited an increase of 1.0–5.7% in the coulombic efficiency (CE) and an increase of 2.5–8.7% in the energy efficiency (EE) at 20–200 mA cm⁻². Q/S-x showed better chemical stability in VO₂⁺ solutions than QBPPEK. VRB with Q/S-1.37 could be steadily operated for 400 h without sudden capacity and efficiency drop, while VRB with QBPPEK could hold for only around 250 h. Q/S-1.37 retained higher CE, EE and capacity retention than Nafion115, displaying good long-term stability. Thus, the Q/S-x are promising for use in commercial VRBs.

Novel AIEMs were prepared through successive blending and amination processes, and they exhibited good ion selectivity, stability and water transport resistance.     

In vivo gene delivery into ocular tissues by eye drops of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) polymeric micelles.

The primary objective of this study was to investigate the feasibility of using PEO-PPO-PEO non-ionic copolymeric micelles as a carrier for eye-drop gene delivery of plasmid DNA with lacZ gene in vivo. Using pyrene fluorescence probe methods, zeta potential, and dynamic light scattering test (DLS), the ability of micelle formation of these block copolymers with plasmid was studied. Gene expressions were visualized by both the quality of enzymatic color reaction using X-gal staining and by the quantification of the substrate chlorophenol red galactopyranoside (CPRG) in enucleated eyes on day 2 after gene transfer. In addition, microscopy to identify the types of cell showing uptake and expression of the transferred gene was used. We found that the block polymeric micelles were formed above 0.1% (w/v) of block copolymer with a size of 160 nm and a zeta potential of -4.4 mV. After 2 days of topically delivery three times a day, the most intense gene expression was observed on days 2 and 3. Reporter expression was detected around the iris, sclera, conjunctiva, and lateral rectus muscle of rabbit eyes and also in the intraocular tissues of nude mice upon in vivo topical application for 48 h with a DNA/polymeric micelle formulation. Furthermore, after two enhancement treatments, the transport mechanisms of the block copolymeric micelles were found through endocytosis in tissues by enhancement through the tight junction pathway. Thus, efficient and stable transfer of the functional gene could be achieved with PEO-PPO-PEO polymeric micelles through topical delivery in mice and rabbits. These in vivo experiments indicate the possible potential use of block copolymers for DNA transfer.     

Benzothiazole appended 2,2′-(1,4-phenylene)diacetonitrile for the colorimetric and fluorescence detection of cyanide ions

A benzothiazole appended 2,2′-(1,4-phenylene)diacetonitrile derivative (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(3-(benzo[d]thiazol-2-yl)-4-hydroxyphenyl)acrylonitrile) (PDBT) has been synthesized and investigated as a novel sensor, capable of showing high selectivity and sensitivity towards CN⁻ over a wide range of other interfering anions. After reaction with CN⁻, PDBT shows a new absorption peak at 451 nm with a color transformation from colorless to reddish-brown. When yellow fluorescent PDBT is exposed to CN⁻, it displays a significant increase in fluorescence at 445 nm, resulting in strong sky-blue fluorescence emission. The nucleophilic addition reaction of CN⁻ plays a role in the sensing mechanism of PDBT to CN⁻. PDBT can distinguish between a broad variety of interfering anions and CN⁻ with remarkable selectivity and sensitivity. Furthermore, the detection limit of the PDBT probe for CN⁻ is 0.62 μM, which is significantly lower than the WHO standard of 1.9 μM for drinking water. Density functional theory simulations corroborated the observed fluorescence changes and the internal charge transfer process that occurs after cyanide ion addition. In addition, real-time applications of PDBT, such as cell imaging investigations and the detection of CN⁻ in water samples, were successfully carried out.

(2Z,2′Z)-2,2′-(1,4-Phenylene)bis(3-(3-(benzo[d]thiazol-2-yl)-4-hydroxyphenyl)acrylonitrile) (PDBT) has been synthesized and investigated as a novel PDBT, capable of showing high selectivity and sensitivity towards CN⁻ over a wide range of other interfering anions.     

Control of medicine release from solid dispersion composed of the poly(ethylene oxide)-carboxyvinylpolymer interpolymer complex by varying molecular weight of poly(ethylene oxide).

Solid dispersion composed of the poly(ethylene oxide) (PEO)-carboxyvinylpolymer (CP) interpolymer complex containing phenacetin (PHE) was prepared by using nine grades of PEO having different molecular weights from 2000 to 4500000. We attempted to control the medicine release from the PEO-CP solid dispersion by varying the molecular weight of PEO. The physicochemical properties of the solid dispersion were analyzed by powder X-ray diffractometry and thermal analysis. The interaction between PEO and CP was analyzed by IR spectroscopy. Transmittance of the polymer solution was measured to study the complexation between PEO and CP. The release profile of PHE varied depending on the molecular weight of PEO. The minimum release rate was observed at the PEO molecular weight of 35000. It was found that the amount of the PEO-CP complex formation by hydrogen bonding changed depending on the molecular weight of PEO. These results indicate that it is feasible to control the medicine release from the PEO-CP solid dispersion by varying the molecular weight of PEO.     

Practical,mild and efficient electrophilic bromination of phenols by a new I(iii)-based reagent: the PIDA–AlBr3 system

A practical electrophilic bromination procedure for phenols and phenol–ethers was developed under efficient and very mild reaction conditions. A broad scope of arenes was investigated, including the benzimidazole and carbazole core as well as analgesics such as naproxen and paracetamol. The new I(iii)-based brominating reagent PhIOAcBr is operationally easy to prepare by mixing PIDA and AlBr₃. Our DFT calculations suggest that this is likely the brominating active species, which is prepared in situ or isolated after centrifugation. Its stability at 4 °C after preparation was confirmed over a period of one month and no significant loss of its reactivity was observed. Additionally, the gram-scale bromination of 2-naphthol proceeds with excellent yields. Even for sterically hindered substrates, a moderately good reactivity is observed.

A practical electrophilic bromination procedure for the phenolic core was developed under efficient and very mild reaction conditions. The new I(iii)-based brominating reagent PhIOAcBr operationally easy to prepare by mixing PIDA and AlBr₃ was used.     

Enhancement of oral bioavailability of poorly water-soluble drugs by poly(ethylene glycol)-block-poly(alkyl acrylate-co-methacrylic acid) self-assemblies.

The purpose of the present study was to determine whether pH-sensitive polymeric micelles could improve the oral bioavailability of a poorly water-soluble drug. Poly(ethylene glycol)-block-poly(alkyl acrylate-co-methacrylic acid)s were synthesized by atom transfer radical polymerization and the composition of the ionizable polymer block was varied to maximize drug loading and pH-dependent release. Poorly water-soluble model drugs viz. fenofibrate (FNB) and progesterone (PRG) were incorporated in the self-assemblies by the oil-in-water emulsion or film casting methods. The pH-dependent release of several formulations was studied in vitro and the oral bioavailabilities of FNB-loaded micelles, Lipidil Micro and FNB coarse suspension were assessed in Sprague-Dawley rats at a dose of 7.5 mg/kg. Entrapment efficiency (defined as the ratio of experimental drug loading in self-assemblies to the initial amount of drug added) ranged between 55-75% and was dependent on polymer composition and drug-loading method. Hydrophobic chain composition of the polymer had tremendous impact on in vitro release kinetics, with only poly(ethylene glycol)-block-poly(n-butyl acrylate(17)-co-methacrylic acid(17)) micelles showing the desired pH-dependent drug-release profile. The oral bioavailability of FNB from these self-assemblies revealed 156% and 15% increases vs. FNB coarse suspension and Lipidil Micro, respectively. The results suggest that these pH-sensitive self-assemblies have potential for improving the oral bioavailability of poorly water-soluble drugs.     

Electrochemical synthesis and corrosion protection of poly(3-aminophenylboronic acid-co-pyrrole) on mild steel

Synthesis of poly(3-aminophenylboronic acid-co-pyrrole) (p(APBA-co-Py)) is carried out potentiodynamically on a pre-passivated mild steel (MS) surface in an oxalic acid solution containing 3-aminophenylboronic acid (APBA) and pyrrole (Py) monomers. The monomer feed ratio was determined using electrochemical impedance spectroscopy (EIS) and adhesion tests. The p(APBA-co-Py) coating is characterized by electrochemically and spectroscopically comparing with poly(3-aminophenylboronic acid) (p(APBA) and polypyrrole (p(Py) homopolymers. SERS, FTIR, XPS, scanning electron microscopy-wavelength dispersive X-ray and- energy dispersive X-ray spectroscopy results indicate the presence of both APBA and Py segments in the p(APBA-co-Py) backbone. The protective properties of the coating are investigated by Tafel and EIS measurements in a 0.50 M HCl solution. The corrosion resistance of p(APBA-co-Py)-coated MS (66.8 Ω cm²) is higher than that of p(APBA)- and p(Py)-coated, passivated, and uncoated MS. The p(APBA-co-Py) coating embodies the advantageous features of both homopolymers. Py units in p(APBA-co-Py) chains improve the protective property while APBA units carrying the –B(OH)₂ group develop the adhesive property of the layer. EIS results show that the p(APBA-co-Py) coating, due to its homogeneous and compact distribution and the formation of a stable interface, enhanced corrosion resistance of MS by 87.4% for 10 hours in HCl corrosive medium.

Synthesis of poly(3-aminophenylboronic acid-co-pyrrole) (p(APBA-co-Py)) is carried out potentiodynamically on a pre-passivated mild steel (MS) surface in an oxalic acid solution containing 3-aminophenylboronic acid (APBA) and pyrrole (Py) monomers.     

Molecular orientation and stability of poly(3-hexylthiophene) nanogratings affected by the fabricated solvent vapor

During the nanoimprinting lithography (NIL) process, the role of solvent vapor in fabricating the pattern structure and inducing the molecular alignment of nanoimprinted polymer film has been attracting significant attention. We demonstrate here that the molecular orientation and thermal stability of poly(3-hexylthiophene) (P3HT) nanograting film can be affected obviously by the fabricated solvent vapor. A solvent-vapor nanoimprinting lithography (SV-NIL) technique based on a polydimethylsiloxane (PDMS) template is employed to fabricate a P3HT nanograting structure film successfully and solvent vapor is offered by chlorobenzene, chloroform and carbon disulphide, respectively. The molecular orientation of the polymer film is carefully characterized by grazing incidence wide angle X-ray diffraction (GIWAXD) measurements to investigate the effect of various solvent vapors on the molecular orientation of the P3HT nanograting film. For the P3HT nanograting film fabricated by chloroform and chlorobenzene solvent, the edge-on molecular orientation of the typical form II crystallographic structure is induced. However, this indicates that there are both the face-on molecular orientations of the form II and form I crystallographic conformation present for the P3HT nanograting film fabricated by carbon disulphide solvent. Therefore, the fabricated solvent vapor plays a significant role in determining the formation of the molecular orientation of the polymer nanostructure. Then, the role of thermal annealing in the stability of the molecular orientation was investigated for the P3HT nanograting film after a fixed temperature. As for the annealed nanograting film fabricated by chlorobenzene and chloroform solvent vapor, a single edge-on molecular orientation mode of the form I crystallographic structure has been obtained. However, for the annealed nanograting film fabricated by the carbon disulphide solvent, the edge-on and face-on molecular orientations of the form I crystallographic structure are still retained. This indicates that the stability of the form II crystallographic conformation is mainly dependent on the thermal annealing process. Therefore, after the annealing process, the final determining of the molecular alignment and crystallographic conformation depends significantly on the orientation type of the nanograting film before the annealing history, and it can be further inferred that the molecular orientation of the annealed polymer film is still affected by the fabricated solvent vapor significantly. Thus this will provide new understanding and guidance for the research of the topographical structure and molecular alignment of conjugated polymers.

Nanoimprinting-induced orientation of poly(3-hexylthiophene) nanogratings and their stability dependence on fabrication solvent.     

Influence of reduced graphene oxide on flow behaviour,glass transition temperature and secondary crystallinity of plasticized poly(vinyl chloride)

Understanding the rheological behaviour of thermoplastic nanocomposites is important to obtain a concrete knowledge of their processability. The viscoelastic properties of nanocomposites are a reflection of their morphology. The study of flow and deformation of nanocomposites provides essential information related to prevalent interactions in the system as well as contribution from the dispersion of incorporated nanofillers. In the present study, plasticized polyvinyl chloride/reduced graphene oxide nanocomposites (PPVC/RGO) were fabricated using melt mixing technique with different filler concentration. Flow behaviour of the nanocomposites was analyzed using small amplitude oscillatory shear (SAOS) measurements and it indicated an enhancement in the storage modulus (G′), loss modulus (G′′) and complex viscosity (η*) with RGO content. This can be attributed to very good dispersion and reinforcing effect of RGO in PPVC matrix as supported by TEM and FTIR results. Weak gel model is used to fit the rheological parameters and is found to be in excellent agreement with the SAOS experiments. Thermal history of the prepared nanocomposites was learned using differential scanning calorimetry. A shift in glass transition temperature (T_g) to higher temperature region could be seen, that manifest the effect of RGO in the amorphous portion of PPVC. An interesting property called secondary crystallinity was also found in these materials.

Understanding the rheological behaviour of thermoplastic nanocomposites is important to obtain a concrete knowledge of their processability.     

Prodrug modification increases potassium tricyclo[5.2.1.0(2,6)]-decan-8-yl dithiocarbonate (D609) chemical stability and cytotoxicity against U937 leukemia cells

Potassium tricyclo[5.2.1.0(2,6)]-decan-8-yl dithiocarbonate (D609) is a selective antitumor agent, potent antioxidant, and cytoprotectant. It has the potential to be developed as a unique chemotherapeutic agent that may provide dual therapeutic benefits against cancer, e.g., enhancing tumor cell death while protecting normal tissues from damage. However, D609 contains a dithiocarbonate (xanthate) group [O-C(=S)S(-)/O-C(=S)SH], which is chemically unstable, being readily oxidized to form a disulfide bond with subsequent loss of all biological activities. Therefore, we developed the synthesis of a series of S-(alkoxyacyl) D609 prodrugs by connecting the xanthate group of D609 to an ester via a self-immolative methyleneoxyl group. These S-(alkoxylacyl)-D609 prodrugs are designed to release D609 in two steps: esterase-catalyzed hydrolysis of the acyl ester bond followed by conversion of the resulting hydroxymethyl D609 to formaldehyde and D609. Three S-(alkoxyacyl) D609 prodrugs were synthesized by varying the steric bulkiness of the acyl group. These prodrugs are stable to ambient conditions, but readily hydrolyzed by esterases to liberate D609 in a controlled manner. More importantly, the lead prodrug methyleneoxybutyryl D609 is biologically more effective than D609 in inhibiting sphingomyelin synthase, thereby increasing the level of ceramide and inducing apoptosis in U937 leukemia cells. The prodrug has a significantly lower LD(50) value than that of D609 (56.6 versus 117 microM) against U937 cells. These findings demonstrate that prodrug modification of the xanthate moiety with an alkoxyacyl group can improve D609 oxidative stability and enhance its antitumor activity.     

Novel design of microreservoir-dispersed matrices for drug delivery formulations: Regulative drug release from poly(ethylene oxide)- and poly(tetramethylene oxide)-based segmented polyurethanes

Drug release from the monolithic devices of segmented polyether-poly(urethane-urea) (PEUU)s based on both poly (tetramethylene oxide) (PTMO) and poly (ethylene oxide) (PEO) as their soft segments were thoroughly investigated in terms of the relationship between their microdomain structure and the drug release profiles. These PEUUs exhibited diverse microdomain structure depending upon the differences in the solubility parameter of constituting segments and their weight fractions in the polymers. The drug release profiles of these PEUUs were closely connected with the mode of microdomain structure composed of the PTMO, PEO, and hard segments. That is, the formation of distinct microdomains of the PTMO and hard segments dispersed in the PEO matrices allowed the definite regulation of both release rate and transport mode of drug release in the monolithic devices of highly water-swollen PEUUs. These results indicate that the design consisting of microdomains has distinct function as a drug reservoir and transport channel and is a promising way for regulating the release profile of drugs with a variation of solubility parameters from highly water swollen polymeric formulations.     

Partially quaternized poly(tertiary amine) as pH-dependent drug carrier for solubilization and temporary trapping of lipophilic drugs in aqueous media

Deprotonated macro molecules of partially quaternized poly(tertiary amine) of the poly-[thio-1-(N,N-diethyl aminomethyl) ethylene] type with less than 20% quaternized repeating units take globular conformations which form a molecularly dispersed organic microphase in water. It is shown that drugs reputedly insoluble in water can be dissolved and temporarily trapped in this lipophilic microphase. Because of pH-dependent destabilization, occurring through an all-or-none cooperative mechanism, instantaneous release can be obtained in a very narrow pH range. Factors affecting trapping and release are considered in regard to characteristics of body fluids and use of these polymers as drug carriers.     

Mechanically tough and highly stretchable poly(acrylic acid) hydrogel cross-linked by 2D graphene oxide

The mechanical performances of hydrogels are greatly influenced by the functionality of cross-linkers and their covalent and non-covalent interactions with the polymer chains. Conventional chemical cross-linkers fail to meet the demand of large toughness and high extensibility for their immediate applications as artificial tissues like ligaments, blood vessels, and cardiac muscles in human or animal bodies. Herein, we synthesized a new graphene oxide-based two-dimensional (2D) cross-linker (GOBC) and exploited the functionality of the cross-linker for the enhancement of toughness and stretchability of a poly(acrylic acid) (PAA) hydrogel. The 2D nanosheets of GO were modified in such a way that they could provide multifunctional sites for both physical and chemical bonding with the polymer chains. Carboxylic acid groups at the surfaces of the GO sheets were coupled with the acrylate functional groups for covalent cross-linking, while the other oxygen-containing functional groups are responsible for physical cross-linking with polymers. The GOBC had been successfully incorporated into the PAA hydrogel and the mechanical properties of the GOBC cross-linked PAA hydrogel (PAA-GOBC) were investigated at various compositions of cross-linker. Seven times enhancement in both toughness and elongation at break has been achieved without compromising on the modulus for the as-synthesized PAA-GOBC compared to the conventional N,N′-methylenebis(acrylamide) (MBA) cross-linked PAA hydrogel. This facile and efficient way of GO modification is expected to lead the development of a high-performance nanocomposite for cutting-edge applications in biomedical engineering.

Incorporation of a novel GO based cross-linker into the conventional poly(acrylic acid) hydrogel remarkably enhances the toughness and stretchability.     

Self-aggregates of poly(2-hydroxyethyl aspartamide) copolymers loaded with methotrexate by physical and chemical entrapments.

Amphiphilic copolymers based on poly(2-hydroxyethyl aspartamide) (PHEA) formed self-aggregates for the entrapment and release of methotrexate (MTX) by physical entrapment and chemical conjugation. In physical entrapment, MTX was partitioned into hydrophobic domains in self-aggregates of PHEA grafted with octadecyl chains (PHEA-C18) and the amount of the entrapped drug increased linearly by 3.39 mg per the degree of substitution of grafted octadecyl groups. The amphiphilic nature of the drug induced a large initial release in the buffer medium, irrespective of the amount of octadecyl chains. However, PEG-grafted PHEA-C18 copolymers conjugated with MTX, ConG, formed a micelle-like structure by self-association of the conjugates and suppressed the initial large release. The alkyl grafting lowered the CAC, meaning enhancement of aqueous stability. The release was accelerated in pH 10.0 by rapid hydrolysis of ester linkage by base-catalyzed cleavage, while it was significantly reduced at pH 5.0.     

Optical properties and ionic conductivity studies of an 8 MeV electron beam irradiated poly(vinylidene fluoride-co-hexafluoropropylene)/LiClO4 electrolyte film for opto-electronic applications

The influence of 8 MeV energy electron beam (EB) irradiation on optical properties and ionic conductivity of PVDF–HFP/LiClO₄ (90 : 10 PHL10) electrolyte film with 40, 80 and 120 kGy doses. The FT-IR results show that C O bond stretching at 1654 cm⁻¹ is due to the degradation of polymer chains and the CH₂ bond wagging intensity at 1405 cm⁻¹ corresponds to C–H bond scissioning in the 120 kGy dose irradiated film. ¹H and ¹³C NMR spectroscopy was performed and the ¹³C NMR spectra confirm the effect of EB irradiation of the PHL10 polymer electrolyte by sharpening and splitting the spectral lines with increasing EB dose and revealing a new spectral line at 162.80 ppm with a 120 kGy EB dose. The size and shape of the porous morphology was drastically changed, becoming deeply porous with a visible inner hollow shaped structure, suggesting increased amorphous character upon irradiation. The absorption band of the unirradiated film observed at 202 nm in the ultraviolet region is shifted to 274 nm after irradiation due to inter band transition of electrons from the valence band to the conduction band and the optical band gap decreasing from 3.49 eV in the unirradiated film to 2.64 eV with a 120 kGy EB dose. Segmental motion in the polymer matrix leads to a decrease in the local viscosity by increasing the mobility of ions upon irradiation. Nyquist plots show semicircles at high frequency due to Li-ion migration through the porous surface of the electrolyte film. A maximum ionic conductivity of 8.28 × 10⁻⁴ S cm⁻¹ was obtained with a 120 kGy EB dose and the observed cyclic voltammetry of the irradiated polymer electrolyte suggests it is electrochemically stable.

A study into the effect of 8 MeV energy electron beam irradiation on the optical properties and ionic conductivity of a PVDF–HFP/LiClO₄ electrolyte film.