Functionalized SWNT/polymer nanocomposites for dramatic property improvement

In this paper, we present results for polymer nanocomposites of poly‐ (methyl methacrylate) (PMMA) and amide‐functionalized SWNTs. The results demonstrate that even at very low loadings, 1 wt % (0.5 vol %), the mechanical and electrical properties are significantly improved. The improvement over PMMA properties exceeds the theoretical bounds for composites with the same volume fraction loading of randomly oriented, straight, individually dispersed nanotubes. The modeling and experimental results thus suggest that the nanotube bundles are well dispersed in the polymer matrix, that the functionalization significantly improves interaction with polymer, and that the interphase formed has improved mechanical properties over that of the matrix material. Loss modulus results indicate a significant difference between functionalized and nonfunctionalized tubes in the composite. Functionalized tubes result in a composite in which relaxation mechanisms are shifted by 30 °C from that of the matrix material, indicating extensive interphase regions and absence of PMMA with bulk properties. Unfunctionalized composites demonstrate a broadening of relaxation modes, but still retain the signature of bulk PMMA properties. These data suggest a morphological difference with a discrete interphase layer in unfunctionalized composites and a fully transformed matrix in the case of functionalization. This difference is consistent with electrical and mechanical property data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2269–2279, 2005     

Use of alumina with anchored polymer coating as packing material for reversed-phase high-performance liquid chromatography

A new material with anchored polymer coating on alumina can be used as a packing material for the reversed-stationary phase of HPLC columns. The coatings are formed by in situ polymerization of maleic acid adsorbed on alumina with 1-octadecene, with cross-linking by 1,4-divinylbenzene. The chromatographic performance of this material was studied and compared with that of 20–30 μm octadecyl-bonded silica particles and a commercial column packed with 5 μm octadecyl-bonded silica. The results indicate that this new material is a promising alternative to silica-based reversed-phase packings due to its competitive performance and stability in acidic and basic media.     

Use of porous anodic alumina membranes as a nanometre-diameter column for high performance liquid chromatography

The possibility of using porous anodic alumina membranes as a column for normal-phase high performance liquid chromatography was evaluated using phenol and toluene with mobile phases having different solvent compositions.     

Characterisation and morphology of biodegradable chitosan / synthetic polymer blends

Chitosan has been used to form miscible, biodegradable blends with hydrophilic synthetic polymers as PVA and PEO. Characterisation of the blends by DSC, IR and microscopy analysis was made giving much attention to possible interactions of molecular polar group in the polymer chains. PVA/chitosan are found to be amorphous in the whole range of composition having one glass transition temperature. Molecular interactions in the pair of polymers are connected with amide group of chitosan and hydroxyl groups of PVA. PEO/chitosan blends stay amorphous up to 0.2 weight fraction of PEO. For a higher amount of PEO that polymer crystallises forming a spherulite crystalline structure. We correlate the overall kinetics of crystallisation and melting behaviour of solid, semicrystalline blends PEO/chitosan in the form of thin films for a set of PEO species of different blend composition with a morphological structure of the blends. Negative values of the Flory-Huggins interaction parameter due to specific interactions by hydrogen bonding through ether group of PEO and hydroxyl group of chitosan were evaluated. Amide groups do not participate in the molecular interaction between PEO and chitosan molecules. Avrami equation was applied to describe kinetics of crystallisation of pure PEO and PEO/chitosan blends of various compositions.     

A phosphotyrosine-imprinted polymer receptor for the recognition of tyrosine phosphorylated peptides

Hyperphosphorylation at tyrosine is commonly observed in tumor proteomes and, hence, specific phosphoproteins or phosphopeptides could serve as markers useful for cancer diagnostics and therapeutics. The analysis of such targets is, however, a challenging task, because of their commonly low abundance and the lack of robust and effective preconcentration techniques. As a robust alternative to the commonly used immunoaffinity techniques that rely on phosphotyrosine(pTyr)-specific antibodies, we have developed an epitope-imprinting strategy that leads to a synthetic pTyr-selective imprinted polymer receptor. The binding site incorporates two monourea ligands placed by preorganization around a pTyr dianion template. The tight binding site displayed good binding affinities for the pTyr template, in the range of that observed for corresponding antibodies, and a clear preference for pTyr over phosphoserine (pSer). In further analogy to the antibodies, the imprinted polymer was capable of capturing short tyrosine phosphorylated peptides in the presence of an excess of their non-phosphorylated counterparts or peptides phosphorylated at serine.     

Hexanoyl chitosan/ENR25 blend polymer electrolyte system for electrical double layer capacitor

Single salt polymer electrolytes based on hexanoyl chitosan‐ENR25 were prepared by employing LiN (CF₃SO₂)₂ or LiCF₃SO₃ as the doping salt. Elastic property of hexanoyl chitosan was enhanced with the incorporation of ENR25. DSC studies revealed immiscibility of hexanoyl chitosan and ENR25, and dissolution of salt was favored in ENR25 phase. Conductivity enhancement was observed in the blends as compared with the neat hexanoyl chitosan. The maximum conductivities achieved for LiCF₃SO₃‐ and LiN (CF₃SO₂)₂‐comprising electrolyte systems were 1.6 × 10^?8 and 5.0 × 10^?7 S cm^?1, respectively. Deconvolution of spectra bands in the v_as (SO₂^?) mode of LiN (CF₃SO₂)₂ and v_s (SO₃^?) mode of LiCF₃SO₃ has been carried out to estimate the relative percentage of free ions and associated ions. The findings were in good agreement with conductivity results. Electrical double layer capacitor (EDLC) was fabricated with hexanoyl chitosan/ENR25 (90:10)‐LiN (CF₃SO₂)₂‐EmImTFSI electrolyte and activated carbon‐based electrodes. The conductivity and electrochemical stability window of hexanoyl chitosan/ENR25‐LiN (CF₃SO₂)₂‐EmImTFSI were ~10^?6 S cm^?1 and 2.7 V, respectively. The performance of the EDLC was analyzed by cyclic voltammetry (CV) and galvanostatic charge‐discharge (GCD). From GCD, the specific capacitance of EDLC was 58.0 F g^?1 at 0.6 mA cm^?2. The specific capacitance was found to decrease with increasing current density.     

Preparation and characterization of polymer electrolyte membrane from chloroacetate chitosan/chitosan blended with epoxidized natural rubber

Chitosan-based membranes are among the most effective and efficient PEMs for fuel cells, however their low proton conductivity needs to be improved. In this study, chitosan, chloroacetate chitosan (CCS), chitosan blend with epoxidized natural rubber (ENR), and CCS with ENR blend based membranes were prepared by solution casting, crosslinked with NaOH and H₂SO₄, and investigated for physical, chemical, electrical and ionic properties. The functional groups were identified by ATR-FTIR spectroscopy and the peaks matched improved membrane properties. The surface roughness of the membranes was determined by AFM, and it increased with the amount of ENR. The electrical properties measured with an LCR meter showed that the CCS, CS and CS-B had the highest conductance, conductivity, capacitance and dielectric constant, while the CCS10/ENR8, CS10/ENR8 and CS15/ENR3 showed the highest resistance and resistivity. Furthermore, the CCS gave the lowest dissipation factor, which indicates its suitability for use in a PEM. In addition, the contact angle was relatively high for CS-B, CS and CCS.     

Control of moisture at buried polymer/alumina interfaces through substrate surface modification

Moisture absorption in poly(4-tert-butoxycarbonyloxystyrene) (PBOCSt) films supported on Al(2)O(3) sputter coated silicon wafers is measured using neutron and X-ray reflectivity. Accumulation of water at the interface during moisture exposure results in an apparent film-thickness-dependent swelling for ultrathin PBOCSt films. The swelling of a film on Al(2)O(3) is less than the swelling of a film of the same thickness on SiO(x) for films thinner than 20 nm. This is due to comparatively less moisture accumulation at the Al(2)O(3)/PBOCSt interface. A simple, zero adjustable parameter model consisting of a fixed water-rich layer at the interface and bulk swelling through the remainder of the film describes the thickness-dependent swelling quantitatively. The influence of four different Al(2)O(3) surface treatments on the moisture distribution within PBOCSt films was examined: bare Al(2)O(3), tert-butylphosphonic acid, phenylphosphonic acid, and n-octyltrichlorosilane. Both the phenyl and the octyl surface treatments reduce the accumulation of water at the polymer/substrate interface. The tert-butyl treatment does not reduce the interfacial water concentration, presumably due to insufficient surface coverage.     

Barrier properties of polymer/alumina nanocomposite membranes fabricated by atomic layer deposition

Novel polymer/ceramic nanocomposite membranes were fabricated, characterized and tested for their barrier performance. Atomic layer deposition (ALD) was used to deposit alumina films on primary, micron-sized (16 and 60 μm) high-density polyethylene (HDPE) particles at a rate of 0.5 nm/cycle at 77 °C. Well-dispersed polymer/ceramic nanocomposites were obtained by extruding alumina coated HDPE particles. The dispersion of alumina flakes can be controlled by varying the number of ALD coating cycles and substrate polymer particle size. The diffusion coefficient of fabricated nanocomposite membranes can be reduced to half with the inclusion of 7.29 vol.% alumina flakes. However, a corresponding increase in permeability was also observed due to the voids formed at or near the interface of the polymer and alumina flakes during the extrusion process, as evidenced by electron microscopy. The low surface wettability of the alumina outerlayers was believed to be one of the main reasons of void formation. Particle surface wettability was improved using 3-aminopropyltriethoxysilane (APS) to coat the particle ALD surface modified polymer particles prior to extrusion. The diffusion coefficient and permeability of the membrane using surfactant-modified particles decreased by 20%, relative to the non-modified case.     

Functionalization of chitosan polymer and their applications

The deacetylated derivative of chitin i.e. chitosan is an advantageous and interesting bioactive polymer. Despite its biodegradability, it consists of many reactive primary and secondary hydroxyl (–OH) and amino (–NH₂) functional groups which allow the possibilities of chemical modifications. The several chemical modifications such as alkylation, acylation, quaternization, phthaloylation, sulfation, thiolation, carboxymethylation, graft copolymerization etc. carried out. The chemical modification results various types of derivatives with modified properties for specific applications in varied area mainly of pharmaceutical, biomedical, biotechnological, cosmetic, agricultural, food and non-food industries as well as in water treatment, paper, and textile industry. The ability of chitosan to undergo versatile modifications and applications presents a great opportunity to scientific community and to industry.     

Conducting polymer/alumina composites as viable adsorbents for the removal of fluoride ions from aqueous solution

The polyaniline/alumina (PANi-AlO) and polypyrrole/alumina (PPy-AlO) composites were prepared and characterized by FT-IR, SEM and X-ray diffraction studies and were employed as adsorbents for the removal of fluoride ions from aqueous solution by the batch sorption method. The amount of fluoride ions adsorbed per unit mass of the adsorbents was observed to be higher than that by the individual constituents. The maximal amount of adsorption is 6.6 mg/g for PANi-AlO and for PPy-AlO it is 8 mg/g. The Langmuir and Freundlich isotherms were used to describe adsorption equilibrium. The kinetics of the adsorption process was investigated using Natarajan-Khalaf equation and intraparticle diffusion model. FT-IR and XRD pattern of the adsorbent, before and after the adsorption is recorded to get better insight into the mechanism of the adsorption process. The results of equilibrium and spectral investigations revealed that the mechanism of fluoride ion removal by these composites involve both the formation of aluminium-fluoro complexes on the alumina surface and doping/dopant-exchange of fluoride ions in the polymer.     

Thermal stability of polymer compositions with modified alumina

Thermal stability and combustibility of polymer compositions: foam plastic (trade mark PEN-I) based on an epoxide novolak block copolymer, and poly(methyl methacrylate, containing modified alumina of various dispersion as a filler, were investigated.     

Removal of heavy metals by using adsorption on alumina or chitosan

The removal of heavy metals from wastewater by using activated alumina or chitosan as adsorbers was evaluated. Cd(II) and Cr(III) were employed as models of the behaviour of divalent and trivalent metal ions. The adsorption of Cd(II) and Cr(III) onto the adsorbers evaluated was studied as a function of pH, time, amount of adsorber, concentration of metal ions and sample volume. A 0.4-g portion of activated alumina can retain 0.6 mg Cr(III) and 0.2 mg Cd(II) from 20 mL sample adjusted at pH 4 and stirred for 30 min. It is therefore possible to totally decontaminate 500 mL of a waste containing 5 mg L(-1) Cd(II) and Cr(III) with 10 g alumina. On the other hand, 0.4 g chitosan can totally decontaminate 20 mL of a pH 5 solution containing up to 50 mg L(-1) Cd(II) and Cr(III). A 99.2+/-0.1% retention of Cd(II) and 83+/-1% retention of Cr(III) was obtained from 500 mL of a laboratory waste. The aforementioned strategies were applied for the minimization of analytical chemistry teaching laboratories and atomic spectrometry laboratory wastes. On comparing both adsorbers it can be concluded that chitosan is more preferable than alumina due to the reduced price of chitosan and the absence of side-pollution effects.     

壳聚糖改性的高分子表面活性剂的合成与性能

以商品壳聚糖(CTS)为原料,通过对-NH_2的化学改性,合成制备了壳聚糖改性的水溶性两性离子表面活性剂.采用正交试验法对合成反应工艺作了优化;通过红外光谱(IR)、核磁共振(H-NMR)及元素分析(EA)等方法对烷基壳聚糖中间体(RCTS)与最终产物,即烷基壳聚糖磺酸季铵盐(SRCTS)的分子结构进行了表征,并对SRCTS的水溶性、表面张力以及泡沫性能作了初步的探索.结果表明:经改性的SRCTS具有良好的表面活性与泡沫稳定性,其最低表面张力值可降至29.1mN/m;泡沫半衰期可提高65%.     

Role of sequential adsorption of polymer/surfactant mixtures and their conformation in dispersion/flocculation of alumina

The role of sequential adsorption of a non-interacting pair of polymer (polyacrylic acidPAA) and surfactant (sodium dodecyl sulfate-SDS) on alumina particles and in determining the stability of their suspensions was studied with particular attention to the conformation of the polymer. It was found that the sequence of addition is of critical importance in determining the dispersion/flocculation of this system. When SDS was added first, both PAA conformation and suspension stability varied with SDS concentration. Whereas when PAA was added first, the subsequent adsorption of SDS molecules had no effect on either the polymer conformation or the suspension stability. This is attributed to masking of SDS species by the larger polymer chains. SDS can not however be completely masked by PAA chains once the PAA concentration is decreased below the optimal concentration for flocculation. When the stirring duration was increased, the mode of addition showed no effect suggesting that the system then reaches equilibrium. Interestingly, a small amount of pre-adsorbed PAA was found to facilitate the adsorption of SDS.     

Synthesis and performance of proton conducting chitosan/NH4Cl electrolyte

The polymer electrolytes based on chitosan and ammonium chloride were prepared by solution casting technique and the properties were studied. The addition of ammonium chloride results in: (1) the enhancement of the amorphous nature of the polymer electrolytes; (2) the shift of the absorption bands of amino group at 1566 cm^?1 and the carbonyl group at 1640 cm^?1 towards lower wave number, and the appearance of a new absorption band at 1759 cm^?1; (3) a decrease of the glass transition temperature. The 20 wt % ammonium chloride doped polymer electrolyte has the best room temperature electric property, the lowest activation energy and the highest ionic conductivity. Placing the as‐prepared polymer electrolyte in a dryer is adverse for the sample's moisture content, and results in higher activation energy and lower ionic conductivity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 260–266, 2010     

Photorefractive performance of a CdSe/ZnS core/shell nanoparticle-sensitized polymer

We report the photorefractive performance of a polymer composite sensitized by CdSe/ZnS core/shell nanoparticles, and also comprising poly(N-vinylcarbazole) and an electro-optic chromophore. The nanoparticles are characterized by absorption and photoluminescence spectroscopy, elemental analysis, transmission electron microscopy, and powder x-ray diffraction. The electro-optic response of the composite is measured independently of the photorefractive effect by transmission ellipsometry. An asymmetric two-beam coupling gain of 30.6+/-0.4 cm(-1) is obtained, confirming photorefractivity. Degenerate four-wave mixing is used to assess photorefractive performance and, at a poling field of 70 V microm(-1), yields a diffraction efficiency of 4.21%+/-0.03%, a holographic contrast of 3.05 x 10(-4)+/-1 x 10(-6), a space-charge rise time of 25+/-2 s, and a sensitivity of 4.7 x 10(-5)+/-4 x 10(-6) cm3 J(-1). These results constitute a significant improvement on the performance of previous nanoparticle-sensitized photorefractive polymer composites.     

Micelle-induced multiple performance improvement of fluorescent probes for H2S detection

In this paper, two colorimetric and turn-on fluorescent probes N-[2-(2-hydroxy)-ethoxy] ethyl-4-azido-1,8-naphthalimide (SS1) and N-butyl-4-azido-1,8-naphthalimide (SS2) for selective recognition of H₂S were designed and synthesized. The probes were constructed by incorporating an azido group into the naphthalimide fluorophore as a specifical reaction group for sulfide utilizing its reducing property. Once treated with H₂S, the azido groups of the probes were converted to amino groups and the solutions’ color changed from colorless to yellow companied with a strong yellow-green fluorescence. Rapid and sensitive responses of the probes towards H₂S were achieved in the presence of cationic surfactant cetyltrimethyl ammonium bromide (CTAB): the reaction was completed within 10 min in CTAB compared to more than 4 h in buffer solution, and the detection limit decreased from 0.5 μM to 20 nM. High selectivity and good competition of both probes towards H₂S over other 11 ions and 2 reducing agents were realized in CTAB micelle. An overall linear concentration range of 0.05 μM to 1 mM was achieved with the assistance of differently charged surfactants CTAB and sodium dodecyl sulfate (SDS). The probes were applied to rapidly and sensitively detect H₂S levels in fetal bovine serum without any pretreatment of the sample.