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Quaternization of PDMAEMA into qPDMAEMA allows to subsequently hydrolyze it in an alkaline environment and obtain PMAA. Degradation of qPDMAEMA can be easily monitored via1H NMR spectroscopy by detecting a small molecule byproduct (choline iodide).

Aqueous dispersions of CNT-g-PDMAEMA and CNT-g-PMAA display opposite responses to the CO2 trigger. The addition of N2 reverts the appearance of CNTs back to the original by kicking CO2 out of the aqueous media.

Programmed formation of hierarchical graphene nanosheets, based on a combination of first and second exfoliations using the halogenated solvent ortho-dichlorobenzene (ODCB) and an adenine-functionalized supramolecular polymer (A-PPG), respectively, can be used to directly exfoliate graphite into high-quality graphene nanosheets with wide-range tunable layer thickness. In this study, we discover that natural graphite in ODCB can be directly exfoliated into well-dispersed, dozen-layer exfoliated graphite (EG) nanosheets with relatively weak interlayer interactions; this process is called first exfoliation. On subsequent addition of A-PPG into the EG solution (i.e., second exfoliation), the hydrogen-bonded adenine moieties act as indispensable key units that manipulate the self-assembly behavior of the A-PPG polymers to effectively form long-range ordered lamellar nanostructures on the surface of the graphene nanosheets. This process substantially enhances the long-term dispersion stability of EG in ODCB and achieves the production of exfoliated graphene nanosheets with the desired structural characteristics through simply adjusting the content of A-PPG in the composites. These desirable characteristics of non-covalently functionalized graphene with a supramolecular polymer are extremely rare, but highly attractive for the development of physically custom-tailored graphene based on combined first and second exfoliation processes. Thus, this development provides a facile, highly efficient graphene fabrication process for potential applications in various fields.

Water-soluble conjugated polymers (WCPs) composed of a hydrophobic polythiophene main chain with hydrophilic tertiary amine side-chains can directly self-assemble into sphere-like nano-objects in an aqueous solution due to phase separation between the hydrophilic and hydrophobic segments of the polymeric structure. Due to the presence of gas-responsive tertiary amine moieties in the spherical structure, the resulting polymers rapidly and reversibly tune their structural features, surface charge, and fluorescence performance in response to alternating carbon dioxide (CO2) and nitrogen (N2) bubbling, which leads to significantly enhanced fluorescence and surface charge switching properties and a stable cycle of on and off switching response. In vitro studies confirmed that the CO2-treated polymers exhibited extremely low cytotoxicity and enhanced cellular uptake ability in normal and tumor cells, and thus possess significantly improved fluorescence stability, distribution, and endocytic uptake efficiency within cellular organisms compared to the pristine polymer. More importantly, in vivo assays demonstrated that the CO2-treated polymers displayed excellent biocompatibility and high fluorescence enhancement in living zebrafish, whereas the fluorescence intensity and stability of zebrafish incubated with the pristine polymer decreased linearly over time. Thus, these CO2 and N2-responsive WCPs could potentially be applied as multifunctional fluorescent probes for in vivo biological imaging.

In this study, we grafted carboxymethyl chitosan (CMC) onto carbon nanotubes (CNTs), demonstrating that the CMC-grafted CNTs (CNT-g-CMCs) can disperse or aggregate in water in response to the bubbling of CO2. The CO2-switchable dispersion and aggregation of CNT-g-CMCs depend on the relative amounts of COOH to NH2 in CMC. With similar amounts of COOH and NH2 in CMC, the CNT-g-CMCs are well dispersed in water at pH 10 and exhibit no phase changes in response to the bubbling of CO2. With a higher amount of COOH than NH2 in CMC, the CNT-g-CMC dispersion in water at pH 10 becomes sensitively aggregated in response to 1 min of CO2 bubbling, but reverts to good dispersion with bubbling of N2 after 10 min. This newly developed CNT-g-CMC system with a novel CO2-responsive amphiphilic feature provides an environmentally friendly way of dispersing or aggregating CNTs in an aqueous solution without using acids and bases.

Poly(methyl methacrylate) (PMMA) nanoparticles with a sensitive CO₂‐responsive hydrophilic/hydrophobic surface that confers controlled dispersion and aggregation in water were prepared by emulsion polymerization at 50 °C under CO₂ bubbling using amphiphilic diblock copolymers of 2‐dimethylaminoethyl methacrylate (DMAEMA) and N‐isopropyl acrylamide (NIPAAm) as an emulsifier. The amphiphilicity of the hydrophobic–hydrophilic diblock copolymer at 50 °C was triggered by CO₂ bubbling in water and enabled the copolymer to serve as an emulsifier. The resulting PMMA nanoparticles were spherical, approximately 100 nm in diameter and exhibited sensitive CO₂/N₂‐responsive dispersion/aggregation in water. Using copolymers with a longer PNIPAAm block length as an emulsifier resulted in smaller particles. A higher concentration of copolymer emulsifier led to particles with a stickier surface. Given its simple preparation and reversible CO₂‐triggered amphiphilic behavior, this newly developed block copolymer emulsifier offers a highly efficient route toward the fabrication of sensitive CO₂‐stimuli responsive polymeric nanoparticle dispersions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2149–2156

In this study, we demonstrate that the amphiphilic properties of dual CO2- and temperature-responsive diblock copolymers can be switched on/off by CO2 bubbling at certain temperature and solution pH combinations to achieve oil-in-water emulsification. More importantly, phase transition studies and emulsion experiments clearly confirm that these copolymers enable efficient control of reversible emulsification processes under specific environmental conditions.

Water-soluble conjugated polymers (WCPs) composed of a hydrophobic polythiophene main chain with hydrophilic tertiary amine side-chains can directly self-assemble into sphere-like nano-objects in an aqueous solution due to phase separation between the hydrophilic and hydrophobic segments of the polymeric structure. Due to the presence of gas-responsive tertiary amine moieties in the spherical structure, the resulting polymers rapidly and reversibly tune their structural features, surface charge, and fluorescence performance in response to alternating carbon dioxide (CO

Carboxymethyl chitosans (CMC) with various degrees of carboxymethyl substitution were prepared and investigated on their changes in water solubility in response to bubbling of CO

We have successfully synthesized ternary CdxZn1-xSe alloy quantum dots (QDs) and CdxZn1-xSe/ZnS core/shell nanocrystals. In order to be used as a fluorescent/paramagnetic bi-functional probe, the ZnS shell was doped with 0.1% and 5% of paramagnetic manganese ions. The compositions of Cd, Zn, and Se in the CdxZn1-xSe core QDs were identified by energy-dispersive X-ray spectroscopy (EDS), and the crystal structures of the alloy nanocrystals were identified by wide angle X-ray diffraction (WAXD). The particle size and distribution of nanocrystals were determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). By varying the ratio of Cd:Zn in the CdxZn1-xSe core, the band gaps of CdxZn1-xSe nanocrystals became adjustable and were in the range of 1.92 eV to 2.72 eV. Hence, the fluorescent color of nanocrystals varied from red to blue in the visible light region. The CdxZn1-xSe/ZnS core/shell nanocrystals exhibited superior photoluminescence (PL) quantum yield up to 50%. Compared with CdxZn1-xSe cores, the PL emission peaks of CdxZn1-xSe/ZnS core/shell QDs are red-shifted. Electron paramagnetic resonance (EPR) measurements for manganese-doped CdxZn1-xSe/ZnS nanocrystals showed paramagnetic properties at both low and high Mn2+ concentrations.

In this study we investigated the effects of the sequence length distributions in random and block copolymers of N-isopropylacrylamide and methacrylic acid (MAA)—PNIPAm-co-PMAA and PNIPAm-b-PMAA, prepared through free radical copolymerization and reversible addition fragmentation chain transfer (RAFT) polymerization, respectively—on their lower critical solution temperature (LCST), glass transition temperatures (Tg), and CO2-responsiveness. The insertion of the PMAA segment into PNIPAm enhanced the thermal properties (e.g., higher values of Tg) because of strong hydrogen bonding between the carboxylic acid units of the PMAA segment and the amide units of the PNIPAm segment, as determined using Fourier transform infrared and 1H NMR spectroscopy. The LCST increased upon increasing the pH for both the random and block copolymers, because the COOH units of the PMAA segments dissociated to form COO− groups, which improved the solubility in aqueous solutions. Furthermore, the variation in the LCST of PNIPAm93-b-PMAA7 with respect to pH was greater than that of PNIPAm-co-PMAA, due to the sequence length distribution effect. Treatment with supercritical CO2 (scCO2) also caused the values of Tg to increase for PNIPAm-co-PMAA but decrease for PNIPAm93-b-PMAA7, presumably because CO2 in the micelle structure of the block copolymer had a plasticization effect. Reversible CO2-responsiveness of the block copolymer in aqueous solution was evidenced by the appearance and disappearance of cloudy aqueous solutions upon alternating bubbling with CO2 and N2; this behavior was not observed for the random copolymers.

CO2-switchable multi-stimuli-responsive polymer nanoparticles (MSPNs), a combination of protonated poly(2-dimethylamino-ethyl methacrylate) (PDMAEMA) and hydrophobic poly(methyl methacrylate) (PMMA), were prepared by carbon-dioxide-assisted (CO2-assisted) emulsion polymerization. These MSPNs exhibited excellent thermal properties and unique temperature-/pH-responsive and CO2-/nitrogen-switchable (CO2-/N2-switchable) abilities, making them highly attractive multifunctional polymer nanoparticles with potential for many applications. Importantly, dispersion experiments and morphological studies clearly confirmed that these newly developed nanoparticles not only possess efficient, reversible CO2-/N2-switchable aggregation/redispersion ability, but also can remain in stable colloidal dispersion at low pH and promote rapid precipitation of nanoparticles at high pH. With simple preparation and high reproducibility, this approach provides a potentially novel pathway for the development of next-generation multifun...

Radical copolymerizations of N-isopropylacrylamide (NIPAm) with acrylic acid (AA) initiated by azobisisobutyronitrile in supercritical carbon dioxide (scCO2, 55 °C, 27.6 MPa) were compared with those performed in MeOH at 55 °C. The AA compositions of the copolymers in scCO2 were lower than those of the copolymers in MeOH and they increased upon decreasing the pressure of scCO2 from 27.6 to 13.8 MPa. The glass transition temperatures of these copolymers deviated positively from those of respective homopolymers prepared in both media, with the copolymer obtained at a 50/50 feed ratio exhibiting the highest value of Tg. FTIR spectroscopy revealed enhanced H-bonding between the amide group of the NIPAm and the carboxyl group of the AA in the copolymers in scCO2, suggesting that the much higher values of Tg of these copolymers, relative to those in MeOH, arose presumably from the more highly alternating sequences of their NIPAm and AA units.

In this study, multiwalled carbon nanotubes (CNT), ball-milled CNT (bmCNT), and acid-treated CNT (CNT-COOH) were assessed as thermal stabilizers in poly(vinyl chloride) (PVC). Films of pure PVC, CNT/PVC, bmCNT/PVC, and CNT-COOH/PVC cast from tetrahydrofuran were subjected to thermal aging in N 2 in a test tube submerged in an oil bath maintained at 180 °C for a certain time. FTIR and UV-Vis spectra and discoloration of aged PVC composites were investigated on the formation of conjugated polyene structure in PVC. The results found that all three types of CNT of small amounts (0.1 or 0.3 phr) could stabilize PVC against thermal degradation by retarding the rate of formation of a conjugated polyene structure, with the stabilizing efficacy in the order of bmCNT > CNT > CNT-COOH. Moreover, Congo red and dehydrochlorination (pH measurement) tests were investigated on the degradation of PVC to HCl during the thermal aging as a function of time, CNT type and content. Thermal degradations of PVC to HCl were promoted by all three types of CNT in the initial 30 min of aging but were clearly stabilized against degradation over prolonged aging (for instance, 120 min) by bmCNT followed by CNT-COOH, both exhibiting the optimal stabilizing efficacy at 1 phr. The bmCNT was the most effective thermal stabilizer among the three types of nanotubes studied in PVC to resist both its discoloration and degradation of HCl. This newly-developed PVC composite with CNT as an additive provides an efficient route towards the development of highly thermal-stabilized PVC.

Chitosan- g -poly[(2-dimethylamino)ethyl methacrylate] was investigated as a CO 2 -switchable emulsifier in this study. Poly(2-dimethylamino)ethyl methacrylate (PDMAEMA) was prepared by atom transfer radical polymerization followed by grafting to chitosan (CS). The CO 2 -responsiveness and reversible CO 2 -switchable temperature- and pH-sensitive behavior of PDMAEMA and CS- g -PDMAEMA were investigated as emulsifiers via simple CO 2 and N 2 bubbling. The lower critical solution temperatures (LCSTs) of PDMAEMA and CS- g -PDMAEMA aqueous solutions both increased as pH decreased to about pH 7.3, at which point the LCSTs disappeared. At elevated temperatures (e.g. 60 °C), CO 2 bubbling removed the turbidity in CS- g -PDMAEMA aqueous solution and N 2 bubbling restored turbidity. The presence of CS- g -PDMAEMA in a two-phase solution of n -butanol/deionized water enabled the formation of a completely emulsified single phase after CO 2 bubbling, which reverted to a two-phase solution on N 2 bubbling. Overall, CS- g -PDMAEMA has potential as a CO 2 -switchable emulsifier.

Multiple stimuli-responsive amphiphilic block copolymers of poly(methacrylic acid) (PMAA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) were used as emulsifiers to prepare two-way CO2 stimuli-responsive poly(methyl methacrylate) (PMMA) latex particles via aqueous emulsion polymerization. The polymerization at pH 2 and 50 °C produced mainly PDMAEMA-surfaced PMMA latex particles, whereas the polymerization at pH 12 and 50 °C produced mainly PMAA-surfaced particles. Both types of latex particles appeared to precipitate at higher pH values from the emulsifier of a longer PDMAEMA block length. The direction from precipitation to dispersion for PDMAEMA-surfaced particles or from dispersion to precipitation for PMAA-surfaced particles in response to CO2 bubbling of the pH 12 dispersion of particles depended on the PDMAEMA block length. Together, this study reveals that—by tuning the PDMAEMA block length in PMAA-b-PDMAEMA used as an emulsifier and polymerization at pH 2 or 12—PMMA latex particles can exhibit two-way CO2 responsiveness between dispersion and precipitation. Thus, due to their simple preparation and unique dual pH and CO2 responsiveness, these newly developed PMAA-b-PDMAEMA emulsifiers provide a highly efficient approach for the development of smart PMMA latex nanoparticles with desirable multifunctional properties.

Diblock copolymers of poly(tert-butyl methacrylate) (PtBuMA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) of four different block lengths were prepared by sequential two-step reversible addition-fragmentation chain transfer radical polymerization, followed by hydrolysis of the PtBuMA blocks to obtain poly(methacrylic acid)-b-PDMAEMA (PMAA-b-PDMAEMA). The effect of the PDMAEMA block length on the multistimuli-responsive amphiphilic features of both types of diblock copolymers was investigated as CO2-switchable emulsifiers for emulsification/demulsification of n-octane (an oil) in water in response to CO2/N2 bubbling. The amphiphilicity of PtBuMA-b-PDMAEMA was switched on, and the amphiphilicity of PMAA-b-PDMAEMA was switched off by CO2 bubbling at pH 12 and 25 °C to achieve emulsification/demulsification. A longer PDMAEMA block length in PMAA-b-PDMAEMA conferred more sensitive CO2-responsive amphiphilicity but reduced the extent of recovery of emulsification ability on N2 bubbling. This newly developed diblock copolymer system could potentially serve as a "multifunctional surfactant" for CO2-switchable emulsification/demulsification of oil-in-water and water-in-oil mixtures.

Carbon nanotubes (CNTs) that were first grafted with vinyl trimethoxysilane (VTMS) and then with methacryloxypropyl trimethoxysilane (MATMS) could result in well dispersion in thermosetting vinyl ester/styrene resin and exhibit significant enhancement in storage modulus of the composite. If the VTMS-grafted CNTs were grafted with VTMS, rather than MATMS, in the second step of grafting, significant phase separation was found in the composite. The scavenging efficiencies of the silane-grafted CNTs for hydroxyl (OH.) radicals measured by electron paramagnetic resonance (EPR) were investigated as a function of the step and degree of grafting. The EPR data revealed that the radical scavenging efficiency of a given CNTs exhibited a significant decrease after the first step of grafting with VTMS but exhibited insignificantly further decrease after the second step of grafting with MATMS. The radical scavenging efficiency of a given silane-grafted CNTs was decreased with increasing degree of the silane grafting, an indication that the radical scavenging mechanism involved the reactions of radicals with the CNTs, rather than with the silane grafts. The radical-initiated crosslinking of the vinyl ester/styrene composite was significantly retarded by the silane-grafted CNTs; this should be taken into consideration when producing thermoset polymer/CNT composites having highly enhanced moduli.

Effect of carbon nanotubes (CNT) on free radical polymerization of N -isopropylacrylamide (NIPAAm) initiated by azobisisobutyronitrile at 55 °C in supercritical carbon dioxide (scCO 2 ) of 27.6 MPa and in methanol (MeOH) was investigated. The weight average molecular weight (M w ) of PNIPAAm polymerized in scCO 2 for 10 h was 1.2 × 10 6 g/mol but that of PNIPAAm in MeOH was 0.3 × 10 6 g/mol as determined by the intrinsic viscosity. Yield of the polymerization for 10 h in scCO 2 was higher than that in MeOH. Gel permeation chromatography was not effective for molecular weight characterization of PNIPAAm, with a higher M w giving a larger discrepancy as compared to the viscometric method. PNIPAAm of higher M w as prepared in scCO 2 giving more chain entanglements that could enhance formations of intrachain and interchain hydrogen bonds resulted in a decrease of the lower critical solution temperature of PNIPAAm. CNT reduced yield but raised M w of PNIPAAm much more in scCO 2 than in MeOH, an indication that radical scavenging efficiency of CNT in the precipitation polymerization of NIPAAm in scCO 2 was higher than that in the solution polymerization of NIPAAm in MeOH.

The effects of atmospheres of CO2 and N2 on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAAm) in aqueous solution have been investigated using high-pressure differential scanning calorimetry (HP-DSC). In the absence of CO2 and N2, the phase transition—from the hydrated to dehydrated state—of PNIPAAm in aqueous solution was characterized by an endothermic peak near 30.5 °C, namely the LCST. This endothermic peak shifted to relatively lower temperature upon increasing the pressure of CO2, but shifted slightly to higher temperature under a higher pressure of N2. This behavior appears to be associated with the CO2 molecules displacing the H2O molecules from around the amide groups of PNIPAAm upon increasing the pressure, thereby enhancing the formation of intramolecular hydrogen bonds between the amide groups; in contrast, increasing the N2 pressure strengthened the interactions of H2O with the apolar isopropyl and amide groups. Despite the difference in the effects of CO2 and N2 on the LCST, higher pressures of CO2 and N2 both led to more positive changes in enthalpy (ΔH) for the phase transition per mole of NIPAAm units. The higher values of ΔH at higher CO2 pressures presumably resulted from the formation of strong intramolecular hydrogen bonds. For a given CO2 pressure, the value of ΔH was less positive at higher concentrations of PNIPAAm, suggesting a lesser degree of disruption of hydrogen bonds during its HP-DSC heating scans. Under a given pressure of CO2, the addition of a salt (NaCl, KCl, KBr) led to a further decrease in the LCST and the value of ΔH of the aqueous PNIPAAm solution, due to the salt ions coordinating H2O molecules.

Carboxymethyl chitosans (CMC) with various degrees of carboxymethyl substitution were prepared and investigated on their changes in water solubility in response to bubbling of CO2 or N2 as a function of the relative concentrations of COOH and NH2 side groups. When having similar concentrations of COOH and NH2, the produced CMC was water soluble at pH 10 and consecutively experienced peculiar dissolution-to-precipitation-to-dissolution during bubbling of CO2, and experienced reverse dissolution-to-precipitation-to-dissolution process during subsequently bubbling of N2. With the concentration of COOH much higher than that of NH2, the water soluble CMC at pH 10 exhibited no phase changes in response to bubbling of CO2 and N2. This newly developed CMC solution system with novel CO2 responsive amphiphilic feature has a potential use as a CO2 switchable surfactant to control interface of mixtures of hydrophilic and hydrophobic species in emulsification/demulsification applications.

A new adenine-functionalized polythiophene (PAT) has been developed which allows the incorporation of multiple self-complementary hydrogen-bonded groups into micelles. After the encapsulation of fullerene derivatives (PCBM) into PAT, their excellent electrochemical storage capacities make the PAT/PCBM micelle a promising candidate for an electron storage/transport layer in the fabrication of high-performance electrochemical devices.

Graphene oxide (GO) and carbon nanotubes (CNT) were dispersed in chitosan (CS) or sulfonated chitosan (sCS) aqueous solution followed by casting films on glassy carbon electrodes (GCE) for investigations on the electrocatalytic activities of the films by cyclic voltammetry (CV) for developments of electrochemical sensors for dopamine (DA), uric acid (UA), and ascorbic acid (AA). The impacts of the water soluble GO and sCS on the electrocatalytic activity of the modified electrodes and the detection capacities for the three analytes were especially investigated. CV curves revealed that GO/CNT/CS/GCE exhibited much higher electrocatalytic activity and selective detection capacity for DA, UA, and AA than CNT/CS/GCE, GO/CS/GCE, CS/GCE, and bare GCE. The GO-assisted dispersion of the conductive CNT in the GO/CNT/CS film was attributed for the observed high electrocatalytic activity. By replacing CS with sCS, the GO/CNT/sCS/GCE exhibited much more enhanced electrocatalytic activities than the GO/CNT/CS/GCE toward the oxidations of the three analytes. The expandable sCS in aqueous solutions of analytes leading to enhanced porosity in the GO/CNT/sCS film was attributed for its much more enhanced electrocatalytic activities. For selective detections of DA, UA, and AA, the GO/CNT/sCS/GCE had wider linear concentration ranges, higher sensitivities, and shorter response times for detections of DA and UA than the GO/CNT/CS/GCE. For detection of AA, the two modified GCEs were insignificantly different.

Chitosan-g-poly[(2-dimethylamino)ethyl methacrylate] was investigated as a CO

Radical scavenging efficiencies of various modified multiwalled carbon nanotubes (CNT) including ball-milled CNT, benzoyl peroxide-treated CNT, acid-treated CNT, and microwave-treated CNT were investigated in this study. Raman spectrometry, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive spectrometry were used to characterize these modified CNT. Electron paramagnetic resonance (EPR) and ultraviolet/visible spectrophotometer (UV/Vis) were used to measure radical scavenging efficiencies of the modified CNT for hydroxyl (OH ) radical and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, respectively. EPR, UV/Vis, and Raman spectra revealed that the radical scavenging efficiencies for both radicals increased with increasing contents of defect sites on the modified CNT. The DPPH radical scavenging efficiencies of the modified CNT were found to be relatively low as compared to the OH radical scavenging efficiencies; the rankings in the scavenging efficiencies, however, were similar for both radicals. The findings in this study that the modified CNT were effective radical scavengers suggested that these CNT have potential applications as antioxidants.

Free-radical polymerization kinetics of N-isopropylacrylamide (NIPAAm) using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator in supercritical carbon dioxide (scCO2) was investigated. A high-pressure differential scanning calorimeter revealed that the melting temperatures of NIPAAm and AIBN were both decreased with increasing CO2 pressure in a linear fashion and the polymerization could occur in CO2 at 55 °C. The polymerization kinetics of NIPAAm in scCO2 was compared with that in methanol (MeOH). At 55 °C, the induction periods of polymerizations in scCO2 of 27.6 MPa were much longer (up to 6 h) than those in MeOH (about 30 min) for similar feed concentrations. The monomer conversions reached and molecular weights produced were much higher in scCO2 than in MeOH. The reaction orders for initial monomer and initiator concentrations, [NIPAAm]0 and [AIBN]0, in initial stage of polymerizations were respectively 1.48 and 0.79 in scCO2 and 1.27 and 0.51 in MeOH.

A series of side-chain-tethered copolymers containing the N-(2-ethylhexyl)-N′-(thiophene-3-yl)-3,4:9,10-perylenebis(dicarboximide) (thiophene-PDI) moieties and 4,4-diethylhexyl-cyclopenta[2,1-b:3,4-b′]dithiophene unit were synthesized via Grignard metathesis polymerizations. With the incorporation of pendent perylenebis(dicarboximide) (PDI) moieties as acceptor side chains and thiophene as the donor backbone, the copolymers exhibited the intramolecular donor–acceptor characteristic and displayed a panchromatic absorption ranging from 290 to 1100 nm and ideal bandgaps of 1.49 to 1.52 eV. Due to the coplanarity of PDI moieties, the charge separation and transfer process were more effective and enhanced after photoexcitation. When increased the weight ratio of PC61BM:polymer to 3, the Jsc could be raised significantly. The value of bandgap decreased slightly, and both Voc and Jsc showed an upward trend with the increase of molar ratio of thiophene-PDI unit from 50% (the copolymer P11) to 75% (the copolymer P13). The polymer/PC61BM devices have shown a significant improvement from 0.45 to 1.66% with a judicious modulation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1978–1988

Nitrogen-doped graphene (NDG)/titanium dioxide (TiO2) nanoparticles were coated on indium-tin oxide (ITO) glass substrates to fabricate NDG-TiO2 nanocomposite electrodes. 3-methylthiophene (3MT) was electrochemically deposited on the NDG-TiO2 films to form poly(3-methylthiophene) (P3MT/NDG/TiO2) composite electrochromic electrodes. The introduction of NDG and TiO2 mesoporous films significantly increased the initial maximum optical contrast (ΔT%) to 70% as compared 41% of pure ITO electrodes, whereas the P3MT/NDG/TiO2 composite electrodes enhanced the adhesion of P3MT polymers to the NDG/TiO2/ITO substrate, thereby increasing the long-term stability of the corresponding electrochromic devices. Experimental results reveal that P3MT/NDG/TiO2 composite electrodes retained up to 90% of ΔT%, relative to 70% remaining ΔT% of pure ITO electrodes. This illustrates the enhanced long-term stability achieved through the introduction of a NDG-TiO2 nanocomposite films in electrochromic devices. These devices demonstrated excellent response time characteristics and ΔT% value of 6 s and ca. of 70%, respectively. This work has shown that conductive polymer/NDG/TiO2 composite electrodes are well suited to electrochromic devices for the promotion of performance and stability.

Composites of Nafion, COOH-capped CdSe, and self-doped polyaniline (SPAN) were used to prepare novel chemical modified glassy carbon electrodes (Nafion/CdSe/SPAN/GCE). The electrocatalytic activities of the modified GCE to the redox reactions of dopamine (DA), uric acid (UA), and ascorbic acid (AA) were investigated by cyclic voltammetry (CV). CV curves revealed that the electrocatalytic activities of Nafion/CdSe/SPAN/GCE to oxidations of the analytes in solution of pH 7 were in the order of DA > UA > AA. This order was consistent with the strong-to-low extent of interactions between the modified GCE and the analytes. These interactions were consistent with the observations that the oxidation rate of DA followed a diffusion-controlled process whereas that of UA followed a surface adsorption-controlled process. The composites of casting at higher pH levels were found to exhibit better CdSe and SPAN dispersions in films and higher electrocatalytic activities. CdSe and SPAN exhibited insignificant synergistic effects on the oxidations of DA when cast from Nafion solutions of both low and high pHs whereas CdSe and SPAN exhibited much synergistic effects on the oxidations of UA when cast from the Nafion solution of high pH at 12.

This study presents a two-stage hydrothermal process to synthesize anatase TiO 2 nanoparticles. The first stage formed sodium titanate (Na 2 Ti 9 O 19 ). Octahedral TiO 6 in Na 2 Ti 9 O 19 shares crystal edges similar to those of octahedral TiO 6 in anatase TiO 2 . This study used Na 2 Ti 9 O 19 as an intermediary to generate pure anatase TiO 2 . The second stage involves disintegrating the structure of the Na 2 Ti 9 O 19 crystals through an ion exchange of Na + in Na 2 Ti 9 O 19 with H + in HNO 3 , resulting in the formation of pure anatase TiO 2 nanoparticles (7 to 10 nm). The static (acid addition) and space repulsion (binder addition) methods (surface area with BET = 81.594 m 2 g −1 ) were used to hinder the coalescence of TiO 2 nanoparticles. The proposed approach produces well-dispersed nanoparticles compared to the method using only static repulsion (surface area with BET = 68.071 m 2 g −1 ). These two TiO 2 materials were used to prepare photoelectrodes with a film thickness of approximately 6 μm in dye-sensitized solar cells (DSSCs), which achieved device efficiencies of 6.23% and 4.66%, respectively.

Composites of self-doped polyaniline (SPAN), chitosan (CS), and carbon nanotubes (CNT) (or COOH-functionalized CNT, denoted by fCNT) were cast on glassy carbon electrodes (GCE) via different casting procedures for investigations on their apparent electrocatalytic activities in buffer solutions of pH 2, 7, and 11 using the Fe(CN) 6 3-/4- redox couple as a probe by cyclic voltammetry (CV). CV curves revealed that the cast CS–CNT and CS–fCNT composites both exhibited apparent electrocatalytic activities to the reactions of the probe at pH 2 and 7. The SPAN was found to exhibit synergistic effects with (f)CNT on the apparent electrocatalytic activity, with CNT exhibiting higher synergism than fCNT. SPAN in the outer layer of the SPAN/CS–(f)CNT/GCE exhibited more enhanced apparent electrocatalytic activity than that in the inner layer of the CS–(f)CNT/SPAN/GCE or that being mixed in the CS–(f)CNT–SPAN/GCE. At pH 7, the layered SPAN/CS–CNT/GCE and CS–CNT/SPAN/GCE that exhibited fairly high apparent electrocatalytic activities to the redox reactions of the probe exhibited also high apparent electrocatalytic activities to the oxidation reactions of dopamine (DA) and uric acid (UA) and were suitable for their detections. The layered SPAN/CS–fCNT/GCE and CS–fCNT/SPAN/GCE, and the non-layered CS–(f)CNT–SPAN/GCE exhibited low anodic peak current densities and were not suitable for the detections of both analytes.

A systematic analysis for mixed dyes of D131, D149, and N3 ternary components on performance of dye-sensitized solar cells (DSSCs) has been performed. Using an experimental design of mixture, empirical models are fitted and plotted as contour diagrams, which facilitate revealing the synergistic/antagonistic effects between these mixed dyes. Dye co-sensitization effects in DSSCs are proved by the photo-physic properties, efficiency of the DSSC devices, and kinetic parameters of photo-electron transfer. The performance of DSSCs is significantly affected by the composition of dyes. The optimal efficiency (ca. 9.5%) of these mixed-dye DSSCs exists at the composition of 1/2 D149–1/2 N3. This composition appears to help conveying the charge transfer from the excited dye molecules to the conduction band of TiO 2 , leading to a higher efficiency of the assembled devices. Supplementary study of the electrochemical impedance are in support of enhancing charge transfer of TiO 2 (e − ) with the co-sensitized dyes.

A conjugated alternating copolymer as the donor material of the active layer in polymer solar cells has been designed and synthesized via Stille coupling reaction. The alternating structure consisted of 3,5-didecanyldithieno[3,2-b:2',3'-d]thiophene (DDTT) donor unit and 5,6-bis(tetradecyloxy)benzo-2,1,3-thiadiazole (BT) acceptor unit. Since both units have been attached pendant chains, the polymer was soluble in common organic solvents. UV-vis spectrum exhibited a broad absorption band in the range of 270–780 nm and a low bandgap of 1.83 eV. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the polymer were estimated to be –5.10 and –3.27 eV, respectively. Based on the ITO/PEDOT:PSS/PDDTTBT:PCBM/Al device structure, the power conversion efficiency (PCE) under the illumination of AM 1.5 (100 mW/cm2) was 0.127%. The effects of annealing temperature (50–150°C) for 30 min on the device performance were studied. It was found that PCE of 0.292% could be acquired under the annealing condition at 50°C for 30 min. The improved device efficiency under the optimal condition was confirmed by the higher light harvest in UV-vis spectra, the enhanced quenching of photoluminescence (PL) emission, and the improved nanoscale morphology by atomic force microscopy (AFM) examination.

An extremely low bandgap donor–acceptor copolymer has been designed and synthesized as the donor material of the polymer solar cells via Stille coupling reaction. The donor–acceptor alternating structure consisted of 4,4-diethylhexyl-cyclopenta[2,1- b :3,4- b ′]dithiophene (CPDT) donor unit and 2,3-bis(2-ethylhexyl)thieno[3,4- b ]pyrazine (TP) acceptor unit. Since both units have attached branched alkyl chains, the polymer was well dissolved in common organic solvents. UV–vis spectrum of the polymer film exhibited a panchromatic absorption ranging from 280 to 1285 nm and a low bandgap of 1.20 eV. Compared to that in solution, solid-state UV–vis absorption spectrum of the polymer showed a strong bathochromic shift, indicating more efficient π-stacking and stronger intermolecular interactions. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the polymer were estimated to be 5.07 and 3.87 eV, respectively. Based on the ITO/PEDOT:PSS/Polymer:PC 61 BM/Al device structure, the power conversion efficiency (PCE) under the illumination of AM 1.5 (100 mW/cm 2 ) was 0.149%. The effects of annealing temperature (100–200 °C) for 30 min on the device performance were studied as well. It was found that PCE of 0.264% could be acquired under the annealing condition at 175 °C for 30 min. The improved device efficiency under the optimal condition was confirmed by the higher light harvest in UV–vis spectra, the enhanced quenching of photoluminescence (PL) emission, and the increase in external quantum efficiency.

Chitosan was extracted by supercritical carbon dioxide (scCO 2 ) containing 1 wt% acetic acid (AC) aqueous solution as a cosolvent at 35, 45, 50 °C and 20, 30, 40 MPa for 1 h. Effects of operating conditions on the extraction yield and on the degree of deacetylation (DD), molecular weight (MW), and polydispersity (PD) of the extract were investigated. Without the AC cosolvent, chitosan could scarcely be extracted by pure scCO 2 whereas, with the AC in scCO 2 , 1.65–3.04% by weight of chitosan could be extracted with the conditions studied. The extraction yield was increased by increasing density of scCO 2 . The extract had lower MW and PD but higher DD than the untreated chitosan. The DD data revealed that in chitosan the amount of the amino groups (NH 2 ) other than the carbonyl (C O) in the residual acetyl groups (CH 3 CO ) governed the extraction process. The DD, MW, and PD of the extract were higher as extracted by scCO 2 (+1 wt% AC solution) of higher densities. By tuning density of scCO 2 in the presence of AC via controls of temperature and pressure, chitosan could be fractionated by the method established here.

This study investigates the electrocatalytic activities of carbon nanotubes (CNTs) in temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) composites with a low critical solution temperature of about 32 °C. The composite cast on a glassy carbon electrode (GCE) as working electrode was investigated by cyclic voltammetry (CV) using potassium ferricyanide as a probe. The factors examined included the temperature (25 and 37 °C, denoted as 25f and 37f) at which GCE was modified, content of CNT in the composite, acid treatment of CNT, and working temperature (25 and 37 °C, denoted as 25aq and 37aq) of GCE. The CV data revealed that a higher content of CNT and COOH-functionalized CNT (fCNT) in the composite exhibited a higher electrocatalytic activity. The electrocatalytic activity of the modified GCE was also found to be significantly temperature dependent. The fCNT/PNIPAAm composite with the 25f–37aq temperature combination exhibited strong electrocatalytic activity and highly selective detection ability for the three analytes (dopamine, uric acid, and ascorbic acid). In contrast, the same composite with the other three combinations (25f–25aq, 37f–25aq, and 37f–37aq) and the CNT/PNIPAAm composite with all four combinations exhibited insignificant electrocatalytic activity and no selective detection ability.

Poly(N-isopropylacrylamide)(PNIPAAm) with a lower critical solution temperature of about 32 °C was used as matrix to prepare temperature responsive carbon nanotubes (CNT) and functionalized CNT (fCNT) composites to modify glassy carbon electrode (GCE) as working electrode for electrochemical selective detection of dopamine, uric acid, and ascorbic acid. The GCE modification temperature (25 and 37 °C, denoted as 25f and 37f), working temperature (25 and 37 °C, denoted as 25aq and 37aq), and the type of CNT (CNT and fCNT) were found to significantly affect the electrocatalytic activity of the composites toward redox reactions of Fe(CN) 6 3−/4− as a probe and the selective detection ability for the three analytes. The fCNT/PNIPAAm composite with the 25f–37aq temperature combination exhibited strong electrocatalytic activity and highly selective detection ability for the three analytes. In contrast, the same composite with the other three combinations (25f–25aq, 37f–25aq, and 37f–37aq) and the CNT/PNIPAAm composite with all four combinations exhibited insignificant electrocatalytic activity and no selective detection ability.

Self-doped conducting polyaniline-modified indium tin oxide (ITO) electrodes were prepared by cyclic voltammetry on ITO substrates in aniline (AN) and o-aminobenzene sulfonic acid (OSA) mixed monomer solutions with AN/OSA mole ratios of 25/75, 50/50, and 75/25, followed by investigations on electrocatalytic activities of the copolymers to redox reactions of Fe(CN)63−/4− as a probe in aqueous solutions of different pH using cyclic voltammetry. For a given pH, the P(25AN-co-75OSA)-modified ITO electrode demonstrated the highest current density, followed by the P(50AN-co-50OSA)- and by the P(75AN-co-25OSA)-modified ITO electrodes. It can be concluded that a higher content of OSA (sulfonate) in the copolymer exhibited a higher extent of self-doping in the copolymer, leading to a higher electrocatalytic activity to redox reactions of the probe. The electrocatalytic activities of the copolymers decreased with increasing pH. The P(25AN-co-75OSA)-modified ITO electrode was electroactive for sensing the redox reactions of the probe in aqueous solutions of up to pH 7, the P(50AN-co-50OSA)-modified ITO electrode was electroactive for up to only pH 5, but the P(75AN-co-25OSA)-modified ITO electrode was not electroactive in aqueous solution of pH even as low as 2.

Organic dyes are synthesized containing bridging ethylenedioxythiophenes (EDOT) between the electron donors and electron acceptors (2-cyanoacetic acid) on carbazole–triphenylamines. These compounds are then characterized by photophysical, electrochemical, and theoretical computational methods. Nanocrystalline TiO 2 -based dye-sensitized solar cells (DSSCs) are fabricated using these dye molecules as light-harvesting sensitizers. The overall efficiency of the sensitized cells is high (5.20%) compared to the efficiency of a cis-di(thiocyanato)-bis(2,2′-bipyridyl)-4,4′-dicarboxylate ruthenium (II) (N3 dye)-sensitized device (7.57%) fabricated and measured under the same conditions. The dye (ETPA3) containing one carbazole, two EDOT bridges, and two 2-cyanoacetic acid groups appears to assist in the charge transfer from the excited dye molecules to the conduction band of TiO 2 , leading to the higher efficiency of the devices using assembled with this dye. A supplementary study of the electrochemical impedance supports the enhancement of the charge transfer of TiO 2 (e − ) with the ETPA3 dye. A computational examination of the ETPA3 compound also indicates higher charge transfer efficiency in the electronically excited state.

In this study, we first investigated dispersion of the COOH functionalized carbon nanotubes (fCNT) in polyethylenimine (PEI) aqueous solution of pH 1–13 by solubility observation, zeta potential, and transmission electron microscopy. The fCNT/PEI dispersions of different pH were then cast on ITO electrode to investigate electrochemical behavior of the composites by cyclic voltammetry (CV) and electrochemical impedance spectroscopy. Solubility data found that the fCNT well dispersed in PEI aqueous solutions of pH 1–11 except 13 but precipitated in pure aqueous solutions of pH 1, 3, and 13. The fCNT dispersion improved by PEI in low pH solutions could be attributed to the interactions of the NH 3 + of PEI and the COO− of fCNT. At a pH in the range of 3 to 11 at which ITO electrode was modified by the cast composite, the dispersed fCNT was found to electrocatalyze the redox reactions of the Fe ( CN ) 6 3 - / 4 - probe and the PEI matrix could enhance the catalytic ability of fCNT leading to strong redox current intensity in CV curves. The fCNT/PEI composites cast from solutions at pH 1 and 13 exhibited no redox signals of the Fe ( CN ) 6 3 - / 4 - probe. The pH variational fCNT dispersions in the fCNT/PEI composites and the interactions of Fe ( CN ) 6 3 - / 4 - and NH 3 + of PEI could be used to justify the CV curves. The fCNT/PEI composite cast from aqueous solution of pH 11 exhibited the least oxidation potential, the most reversible redox reactions, and the largest oxidation current intensity of the Fe ( CN ) 6 3 - / 4 - probe.

Hybrid thin films containing nano-sized inorganic domains were synthesized from UV-curable acrylate-modified waterborne polyurethane (WPU-AC) and monodispersed colloidal silica with coupling agent. The coupling agent, 3- (trimethoxysilyl)propyl methacrylate (MSMA), was bonded onto colloidal silica first, and then mixed with WPU-AC to form a precursor solution. This precursor was spin coated, dried and UV-cured to generate the hybrid films. The silica con- tent in the hybrid thin films was varied from 0 to 30 wt%. Experimental results showed the aggregation of silica particles in the hybrid films. Thus, the silica domain in the hybrid films was varied from 30 to 50 nm by the different ratios of MSMA- silica to WPU-AC. The prepared hybrid films from the crosslinked WPU-AC/MSMA-silica showed much better thermal stability and mechanical properties than pure WPU-AC.

CdSe–poly(N-vinylcarbazole) (CdSe–PVK) nanocomposite was synthesized and utilized as the electron acceptor in the active layer of polymer solar cells. The photovoltaic properties of the polymer solar cells based on poly(3-hexylthiophene) (P3HT):CdSe–PVK as the active layer were investigated in detail. The effects of annealing temperature (100–200 °C) and time (5–60 min) on the device performance were studied. At annealing temperature of 150 °C for 30 min, the device demonstrated an optimal efficiency of 0.235% under AM 1.5 (100 mW cm−2) solar simulated light irradiation. The improved efficiency under the optimal conditions was confirmed by the highest light harvest in UV–vis spectra due to the increased crystallinity of P3HT after thermal annealing. Photoluminescence of these devices also exhibited that the quench effect increases with the increasing of annealing temperature, indicating that the charge separation between electron-donating (P3HT) and electron-accepting (CdSe–PVK) molecules was increased after heat treatment. Atomic force microscopy (AFM) images showed that the phase segregation and 3D interpenetrating networks of P3HT:CdSe–PVK were responsible for the enhancement of the device efficiency.

A new donor–acceptor alternating copolymer as the donor material of the active layer in polymer solar cells has been synthesized. The alternating structure consisted of dithieno[3,2-b:2′,3′-d]thiophene (DTT) donor unit and 5,6-bis(tetradecyloxy)benzo-2,1,3-thiadiazole (BT) acceptor unit. Both units were confirmed by 1 H NMR and elemental analysis. Since the BT unit has long alkyoxyl side chains, the polymer was soluble in common organic solvents. Optoelectronic properties of the copolymer (PDTTBT) were investigated and observed by UV–vis, photoluminescence (PL) spectra, and cyclic voltammogram (CV). UV–vis spectrum exhibited a broad absorption band in the range of 300–750 nm and a low bandgap of 1.83 eV. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of PDTTBT could be determined from the data of CV and UV–vis spectrum. Based on the ITO/PEDOT:PSS/PDTTBT:PCBM/Al device structure, the power conversion efficiency (PCE) under the illumination of AM 1.5 (100 mW/cm 2 ) was 0.113%. It was found that PCE of 0.301% could be acquired under the annealing condition at 150 °C for 30 min. In addition, solar cells fabricated with the 1,8-octanedithiol (OT) additive in the mixture solvent or adding TiO x optical spacer show efficiencies significantly improved over 15%.

The dispersion of three kinds of acid-treated carbon nanotubes (CNTs) in poly(acrylic acid) (PAA) aqueous solution of different pH and ionic strengths (varied by NaCl, KCl and ZnCl2) was investigated by visual observation, zeta potential, particle size analysis, transmission electron microscopy and scanning electron microscopy. Visual observation revealed that the dispersion of CNTs acid treated at 60 °C for 3 h and at 80 °C for 2 h was poor in aqueous solutions with pH 12. The poor dispersion of acid-treated CNTs may be improved by adding PAA. In particular, PAA improved the dispersion of CNTs with greater COOH content. In a low pH solution (pH 1.5), a higher PAA content resulted in poorer CNT dispersion while in a high pH solution (pH 12.5), a higher PAA content led to better CNT dispersion. For superior dispersion in a basic aqueous solution (pH 12.5), experimental data showed that a greater atomic radius or a higher cationic charge of the added salt may result in faster aggregation and thus precipitation of CNTs. Copyright © 2011 Society of Chemical Industry