Effect of Nonsolvent on the Formation of Polymer Nanomaterials in the Nanopores of Anodic Aluminum Oxide Templates

We study the effect of nonsolvent on the formation of polymer nanomaterials in the nanopores of porous templates. Water (nonsolvent) is added into a poly (methyl methacrylate) (PMMA) solution in dimethylformamide (DMF) confined in the nanopores of an anodic aluminum oxide (AAO) template. Water forms a wetting layer on the pore wall and causes the PMMA solution to be isolated in the center of the nanopore, resulting in the formation of PMMA nanospheres or nanorods after the solvent is evaporated. The formation of the polymer nanomaterials induced by nonsolvent is found to be driven by the Rayleigh‐instability‐type transformation. Without adding the nonsolvent, PMMA chains precipitate on the walls of the nanopores after the solvent is evaporated, and PMMA nanotubes are obtained.     

Investigating polymer blend miscibility with forward recoil spectrometry

We tested forward recoil spectrometry (FRES) as a method to determine miscibility by measuring coexistence compositions in binary polymer blends. In this study, equilibrium phase compositions were determined for a compositionally symmetric poly(styrene‐ran‐methyl methacrylate) random copolymer (S_0.49‐r‐MMA) and two homopolymers, deuterated polystyrene (dPS) and deuterated poly(methyl methacrylate) (dPMMA). Sample preparation, film dewetting, and beam damage were addressed, and the results for these polymer blends were in good agreement with those obtained through other experimental techniques. Deuteration had a strong effect on the miscibility of the dPS/S_0.49‐r‐MMA and dPMMA/S_0.49‐r‐MMA blends, to the extent that the asymmetric miscibility observed separately for the PS/S_0.49‐r‐MMA and PMMA/S_0.49‐r‐MMA blends was not found. Although this deuteration effect may limit the applicability of FRES for some polymer systems, the accuracy with which phase compositions can be determined with FRES makes it an attractive alternative to other less quantitative methods for investigating blend miscibility. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1547–1552, 2000     

具有一维梯度直径的金属银纳米线的制备与结构表征

Since the conceptoffunctionally graded m aterials(FG M)is proposed[1,2],m uch attention has been paid toFG M studies.Generally,FG M s were designed with thegradientdistribution ofcom position and structure,andthe graded structure of FG M is achieved by acom position gradient from one side of m aterials to theother,resulting in gradientproperties.Itis well鄄knownthat properties of nanom eter鄄sized m aterials stronglydepend on their sizes.Such size effect offers a newconcept for the design…     

Cloud point suppression in dilute solutions of model gradient copolymers with prespecified composition profiles

Gradient copolymers of 2‐hydroxyethyl methacrylate (HEMA) and 2‐(dimethylamino)ethyl methacrylate (DMAEMA) having prescribed linear, parabolic, and hyperbolic composition profiles were synthesized with the guidance of a numerical model that determines the instantaneous comonomer feed rate. These materials exhibit low polydispersity indices (<1.1); the evolution of the overall DMAEMA content and the absolute molecular weight of the copolymers are all in good agreement with the quantities predicted by our model. Compared to random copolymers of HEMA and DMAEMA, the cloud points of dilute buffered aqueous solutions of gradient copolymers decrease with increasing gradient strength; where the gradient strength is defined as the largest difference in the instantaneous composition along the copolymer. The temperature range over which the solutions transition from transparent to turbid also broadens significantly with increasing gradient strength. Both observations suggest the onset of transition to be dictated by the least soluble ends of the polymer chains. These correlations point to the importance of monomer sequence distribution in determining the macroscopic physical properties of copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Emulsion co- and terpolymerization of styrene,methyl methacrylate,and methyl acrylate. I. Experimental determination and model prediction of composition drift and microstructure in batch reactions

In Part I of this series the reactivity ratios of the comonomer pair methyl acrylate-methyl methacrylate were determined with low-conversion bulk polymerizations. It was shown that the binary reactivity ratios of the systems styrene-methyl acrylate, styrene-methyl methacrylate, and methyl acrylate-methyl methacrylate describe composition drift in low-coversion bulk terpolymerizations with these monomers reasonably well. A computer model was developed to simulate the composition drift in emulsion co- and terpolymerizations. The composition drift in two batch emulsion copolymerization systems (styrene-methyl acrylate and methyl acrylate-methyl methacrylate) and one emulsion terpolymerization system (styrene-methyl acrylate-methyl methacrylate) was investigated both experimentally and with the model. Experimental results were compared with model calculations. The copolymer chemical composition distributions (CCD) were determined with gradient polymer elution chromatography (GPEC®). This technique was also used for the first time to obtain information about the extent of composition drift in emulsion terpolymerizations. Cumulative terpolymer compositions were determined with ³H-NMR as a function of conversion and with this information the three-dimensional CCD was obtained. The composition drift was analyzed with respect to free radical copolymerization kinetics (reactivity ratios) and monomer partitioning. It was shown that in most emulsion copolymerizations the composition drift is mainly determined by the reactivity of the monomers and to a lesser extent by monomer partitioning, except in systems where there is a large difference in water solubility. The model predictions for cumulative terpolymer composition as a function of conversion and the three-dimensional terpolymer CCD showed excellent agreement with the experiments. The GPEC® elution chromatogram of the terpolymer was found to be in accordance with the predicted CCD and the experimentally determined CCD. © 1996 John Wiley & Sons, Inc.     

Crystallization-induced composition inhomogeneities in PVDF/PMMA blends

Composition profiles develop around growing PVDF spherulites in a blend with PMMA. These profiles assume stationary courses after a certain crystallization time provided that the overall degree of crystallinity is not too high. The composition-dependent growth rate and the diffusion-controlled remove of the surplus PMMA from the spherulite surface are then in a stationary equilibrium. The internal structure of the spherulites will then be homogeneous, too. Upon isothermal crystallization of a PVDF/PMMA = 60/40 (wt %) blend at 160°C for at least 4 h, the spherulites internal degree of crystallinity x_c as related to the PVDF fraction obeys the inequality 55 wt % ≤ x_c ≤ 84 wt %. The overall PMMA content within the spherulites as averaged over its whole inside has been determined by IR microscopy. It amounts to about 15 wt %. In contrast, the PMMA content of the amorphous phase within the spherulites (averaged again over its whole inside) ranges between 28 and 52 wt %. This composition jumps at the spherulite surface to 52 wt %. From the slope of the composition profiles outside the spherulites that have a width of more than 50 μm, the effective chain diffusion coefficient in blends as averaged over both components can be calculated to amount to (250 ± 100) μm²h⁻¹. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2923–2930, 1998     

Interfacial tension in a lower critical solution temperature blend: Effect of temperature,blend composition,and deformation of the interphase

Interfacial tension is a very important material parameter in two‐phase polymer blends. It determines the morphology development during processing, which is crucial for the end‐use properties of the material. Although different techniques for interfacial tension measurement give comparable results for immiscible polymers, the determination of the interfacial tension in lower critical solution temperature blends is not straightforward. This is illustrated for poly(α‐methyl styrene acrylonitrile)/poly(methyl methacrylate)(PαMSAN/PMMA), a slightly incompatible polymer pair. Interfacial tension has been measured with three different techniques: small‐amplitude oscillatory shear, recovery after elongation, and elongation of a multilayer sample. The large differences in these results can be attributed to the fact that most experimental techniques determine an apparent value, rather than the thermodynamic equilibrium value, of the interfacial tension. The latter is only obtained if the measurement is performed under quiescent conditions on a system that is composed of the coexisting PαMSAN‐rich and PMMA‐rich phases. The apparent interfacial tension depends on the actual composition of the phases and on the deformation of the interface. An order of magnitude approximation for such effects has been derived from theoretical considerations. Finally, each of these apparent values can be of practical importance. If a blend is prepared by melt mixing of the pure polymers, a high apparent value of interfacial tension should be considered. If, however, a blend is prepared by phase separation of a homogeneous mixture, the thermodynamic value is important. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 679–690, 2002     

电化学聚合吡咯/噻吩导电共聚物纳米纤维阵列及其表征

导电聚合物因其具有良好的空气稳定性、电化学成膜性和导电性等特点,在二次电池、电色显示及固体电容器等方面都有诱人的应用前景.近年来人们研究导电聚合物的纳米结构时发现,由于超分子效应,纳米纤维中聚合物链会以平行于纤维轴向为优先取向,这种优先取向使导电聚合物纳米纤维的电导率比块材有极大提高.     

The competition between crystallization and demixing in polymer blends. V. Numerical modeling and quantitative evaluation of crystallization-induced composition inhomogeneities

It is well known that crystallization of one component in a polymer blend causes composition profiles around the growing spherulites. Amplitude and width of these profiles, respectively, depend on the ratio between the rates of diffusion and of spherulite growth. They can be determined by suitable experimental means. In the present article, the profiles are modeled, starting from Frank's solution of the diffusion equation in spherical coordinates under the boundary condition of moving walls that simultaneously are sources of the diffusing material. Modeled and experimentally determined profiles in PVDF/PEA and PCL/PS blends agree well. The analysis yields estimates for the diffusion coefficient D in polymeric melts as D ≅ (50 ··· 500) μm²/h. Finally, the interference of the composition profiles around several adjacent spherulites can be demonstrated. © 1996 John Wiley & Sons, Inc.     

Separation of poly-3-hydroxyvalerate-co-3-hydroxybutyrate through gradient polymer elution chromatography

Polyhydroxyalkanoates are biodegradable polyesters produced by bacteria that can have a wide distribution in molecular weight, composition of monomers, and functionalities. This large distribution often leads to unpredictable physical properties making commercial applications challenging. To improve polymer homogeneity and obtain samples with a clear set of physical characteristics, poly-3-hydroxyvalerate-co-3-hydroxybutyrate copolymers were fractionated using gradient polymer elution chromatography (GPEC) as opposed to extensively used bulk fractionation. Separation was achieved using a reversed-phase column with chloroform and ethanol as the solvent and non-solvent, respectively. A separation was also conducted on a normal-phase column to compare elution patterns between columns of varied polarity. The fractions were analyzed using Size Exclusion Chromatography (SEC) and NMR to determine the percentage of 3-hydroxyvalerate in the copolymer as well as its molecular weight. It was found that as the percentage of "good" solvent was increased in the mobile phase, the polymers eluted with decreasing percentage of 3-hydroxyvalerate and increasing molecular weight which indicates the importance of precipitation/redissolution in the separation. The elution pattern of the polymer remained unchanged when using both a normal- and reversed-phase column which also illustrates the dominance of precipitation/redissolution in GPEC of polyhydroxyalkanoates. As such, GPEC is shown to be an excellent choice to provide polyhydroxyalkanoate samples with a narrower distribution in composition than the original bulk copolymer sample.     

Critical micelle concentrations of block and gradient copolymers in homopolymer: Effects of sequence distribution,composition, and molecular weight

The critical micelle concentrations (CMCs) of styrene–methyl methacrylate (S-MMA) block and gradient copolymers present in a homopolymer poly(methyl methacrylate) (PMMA) matrix were determined using an intrinsic fluorescence technique based on the ratio of excimer to monomer fluorescence from styrene repeat units. The homopolymer molecular weight (MW) and copolymer MW, composition, and sequence distribution were varied to determine their effects on the CMC, and comparisons were made to theory. Although the effects of these parameters on micelle formation have been the focus of significant theoretical study, few experimental studies have addressed these issues. The MW of the S block (forming the micelle core) has a strong effect on the CMC. For example, an order of magnitude reduction in the CMC (from ∼ 1 to ∼ 0.1 wt %) is observed when the S block MW is increased from 51 to 147 kg/mol while maintaining the MMA block and PMMA MWs at 48–55 kg/mol. Increasing the PMMA matrix MW also has a strong an effect on the CMC, with the CMC for a nearly symmetric S-MMA block copolymer with each block MW equal to 48–51 kg/mol decreasing by a factor of 5 and by several orders of magnitude when the matrix MW is increased from 55 to 106 kg/mol and 255 kg/mol, respectively. In contrast, similar changes in the MMA block MW have little effect on the CMC. Finally, when present in a 55 kg/mol PMMA matrix, a 55 kg/mol S-MMA gradient copolymer with a styrene mole fraction of 0.51 exhibits a factor of 6 larger CMC than a block copolymer of similar MW and composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2672–2682, 2008     

Radiation effects on SBR–EPDM blends: A correlation with blend morphology

The effect of γ radiation on the morphological and physical properties of Styrene–butadiene rubber (SBR) and Ethylene–propylene–diene monomer (EPDM) blends has been investigated. An attempt has been made to establish a correlation between various parameters like Gordon–Taylor parameter (k), hydrodynamic interaction parameter (Δ[η]_mix), chemical shift factor (b), Charlesby–Pinner parameter (p₀/q₀) and polymer–polymer interaction parameter (χ). The results showed a close dependence of mechanical and physical properties of irradiated blends on these parameters. The probability of spur overlap has been found to increase with the increase in EPDM content in the blends, which in turn results in significant improvement in the mechanical properties of the irradiated SBR–EPDM blends with higher EPDM fraction. The efficiency of four multifunctional acrylates as crosslinking aid for the radiation‐induced vulcanization of SBR–EPDM blend was also studied. The results established lower efficiency of methacrylates over acrylates in the process and indicated that among the crosslinking agents studied trimethylolpropane triacrylate is the most efficient one. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1676–1689, 2006     

Application of interface distribution functions to the evaluation of the small angle x-ray scattering of multicomponent polymer systems

A method for correcting the small angle x-ray intensity of multi-component polymer systems to compute the interface distribution function is presented. The resolution of this function can be improved to a great extent by evaluating the interference function from the measured intensity corrected for fluctuation scattering by use of a function which is proportional to the gas scattering of the investigated system. The method is applied successfully to polymer blends composed of components having similar morphology.Presented at the Spring Meeting of the Deutsche Physikalische Gesellschaft, Hamburg, March 14–16, 1988.     

铝基阳极氧化铝模板水热法制备TiO2纳米管阵列

在(NH4)2TiF6的水溶液中,以铝基阳极氧化铝为模板,采用水热法制备了TiO2纳米管阵列. 使用场发射扫描电镜和X射线衍射对水热合成产物进行了表征. 实验结果表明,水热处理所得TiO2纳米管阵列具有特殊的形貌,其表面为连续的多孔状,断面为不连续、相互分离的管状;管口和管壁分别由平均粒度约45和25 nm的微细TiO2颗粒紧密堆积而成. 采用本方法制备的TiO2纳米管阵列无需热处理便已具有明显的锐钛矿型晶相特征.     

Eco-friendly synthesis of ZnO nanorods using Cycas pschannae plant extract with excellent photocatalytic,antioxidant, and anticancer nanomedicine for lung cancer treatment

The tunable ZnO nanorods (NRs) are produced due to the phytochemicals present in Cycas pschannae leaves which act as reducing and stabilizing agents. The confirmations of the ZnO NRs were validated using different characterization techniques: X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer, Emmett and Teller (BET), scanning electron microscopy–Energy Dispersive X-Ray Analysis (EDX), UV–visible spectroscopy, Raman spectroscopy, and transmission electron microscopy. The ZnO NRs show unique surface area and low particle size. Photocatalytic activity was measured and found to be 50.75% at low concentrations and 78.33% at high concentrations. The antioxidant activity of the ZnO NRs also showed promising results for their use in free radical scavenging. In vitro toxicity studies using zebrafish embryos was performed to evaluate the toxic nature of it and the obtained result confirmed its non-toxic nature. In addition, ZnO anticancer potential was verified using the A549 lung cancer cell line. Cytotoxic assessments of ZnO NRs were performed via 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), and neutral red uptake assays to examine the cell death cycle on the A549 lung cancer cell. Dose-dependent apoptosis and necrosis were confirmed by Lactate dehydrogenase (LDH) assay. It was also confirmed that ZnO NRs induce Reactive oxygen species (ROS) and apoptosis inside cancer (A549) cells via different intrinsic gene expression. Thus, based on this research it is evident that an effective ecofriendly, nontoxic potential anticancer drug can be synthesized using C. pschannae leaf extract.     

Electrode modified with a composite film of ZnO nanorods and Ag nanoparticles as a sensor for hydrogen peroxide

A conducting fluorine-doped tin oxide (FTO) electrode, first modified with zinc oxide nanorods (ZnONRs) and subsequently attached with photosynthesized silver nanoparticles (AgNPs), designated as AgNPs/ZnONRs/FTO electrode, was used as an amperometric sensor for the determination of hydrogen peroxide. The first layer (ZnONRs) was obtained by chemical bath deposition (CBD), and was utilized simultaneously as the catalyst for the photoreduction of Ag ions under UV irradiation and as the matrix for the immobilization of AgNPs. The aspect ratio of ZnONRs to be deposited was optimized by controlling the number of their CBDs to render enough surface area for Ag deposition, and the amount of AgNPs to be attached was controlled by adjusting the UV-irradiation time. The immobilized AgNPs showed excellent electrocatalytic response to the reduction of hydrogen peroxide. The resultant amperometric sensor showed 10-fold enhanced sensitivity for the detection of H₂O₂, compared to that without AgNPs, i.e., only with a layer of ZnONRs. Amperometric determination of H₂O₂ at −0.55 V gave a limit of detection of 0.9 μM (S/N = 3) and a sensitivity of 152.1 mA M⁻¹ cm⁻² up to 0.983 mM, with a response time (steady-state, t₉₅) of 30-40 s. The selectivity of the sensor was investigated against ascorbic acid (AA) and uric acid (UA). Energy dispersive X-ray (EDX) analysis, transmission electron microscopic (TEM) image, X-ray diffraction (XRD) patterns, cyclic voltammetry (CV), and scanning electron microscopic (SEM) images were utilized to characterize the modified electrode. Sensing properties of the modified electrode were studied both by CV and amperometric analysis.     

Monolithic stationary phases with a longitudinal gradient of porosity

The duration of the hypercrosslinking reaction has been used to control the extent of small pores formation in polymer‐based monolithic stationary phases. Segments of five columns hypercrosslinked for 30–360 min were coupled via zero‐volume unions to prepare columns with segmented porosity gradients. The steepness of the porosity gradient affected column efficiency, mass transfer resistance, and separation of both small‐molecule alkylbenzenes and high‐molar‐mass polystyrene standards. In addition, the segmented column with the steepest porosity gradient was prepared as a single column with a continuous porosity gradient. The steepness of porosity gradient in this type column was tuned. Compared to a completely hypercrosslinked column, the column with the shallower gradient produced comparable size‐exclusion separation of polystyrene standards but allowed higher column permeability. The completely hypercrosslinked column and the column with porosity gradient were successfully coupled in online two‐dimensional liquid chromatography of polymers.     

Molecular weight distribution in composition controlled emulsion copolymerization

The effect of different strategies for copolymer composition control on the molecular weight distribution (MWD) and gel fraction in the emulsion copolymerization of methyl methacrylate and butyl acrylate was investigated. Starved and semistarved processes for copolymer composition control were both considered. For gel‐forming systems it was found that the starved process gave more gel and lower molecular weights than the semistarved process. The feasibility of simultaneous control of the copolymer composition and the MWD was assessed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1100–1109, 2000     

Template-synthesized Protein Nanotubes with Controlled Size Based on Layer-by-layer Method

The protein nanotubes fabricated by a layer‐by‐layer deposition method using the porous alumina membrane as the template were described. The combination of the template method and the layer‐by‐layer assembly technique for the fabrication of protein nanotubes presented simplicity and versatility. The nanotubes composed of two kinds of proteins (bovine serum albumin and hemoglobin lyophilized bovine erythrocytes) with different sizes could be synthesized through this method. The outside diameter of the obtained nanotubes was determined by the diameter of the pores of the template. And the wall thickness of the protein nanotubes increased with the increase of the number of protein layers that made up of the walls of nanotubes. Such biodegradable nanotubes with good biocompatibility should be useful for in vivo applications.