Water Expandable Polystyrene-Organoclay Nanocomposites: Role of Clay and Its Dispersion State

A published process for preparing expandable polystyrene containing water as a blowing agent was applied to synthesize water expandable polystyrene-organoclay nanocomposites (WEPS-OCN). Organoclay was uniformly dispersed in styrene monomer. During suspension polymerization, water was trapped in the polystyrene (PS) matrix through the use of starch, ending up with spherical PS-organoclay beads. By selecting organoclays with various surfactants and modifier concentrations, different distribution states of nanoclay in the PS matrix, from cluster (poor dispersion) to either intercalated (limited dispersion) or exfoliated (full dispersion) were obtained. The incorporation of organoclay led to higher water content in the expandable beads. However, as expected, the flammability of the expanded product was increased with organoclay content. Furthermore, the results showed that the average unexpanded bead size, density of preexpanded beads, foam cell morphology, and flammability were directly influenced by the dispersion status of the organoclay. The best results were obtained when full dispersion (exfoliation) of nanoclay in PS matrix occurred.     

Protein imprinting and recognition via forming nanofilms on microbeads surfaces in aqueous media

In this paler, we present a technique of forming nanofilms of poly-3-aminophenylboronic acid (pAPBA) on the surfaces of polystyrene (PS) microbeads for proteins (papain and trypsin) in aqueous. Papain was chosen as a model to study the feasibility of the technique and trypsin as an extension. Obtained core-shell microbeads were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and BET methods. The results show that pAPBA formed nanofilms (60-100 nm in thickness) on the surfaces of PS microbeads. The specific surface area of the papain-imprinted beads was about 180 m² g⁻¹ and its pore size was 31 nm. These imprinted microbeads exhibit high recognition specificity and fast mass transfer kinetics. The specificity of these imprinted beads mainly originates from the spatial effect of imprinted sites. Because the protein-imprinted sites were located at, or close to, the surface, the imprinted beads have good site accessibility toward the template molecules. The facility of the imprinting protocol and the high recognition properties of imprinted microbeads make the approach an attractive solution to problems in the field of biotechnology.     

交联型微米级聚苯乙烯粒度标准物质的研制北大核心CSCD

采用分散聚合法制备了标称粒径为3μm的单分散交联型聚苯乙烯(PS)微球。相对于线型μm级聚苯乙烯而言,交联型μm级聚苯乙烯的耐热性和耐溶剂性明显提高,其玻璃化温度提高了28.6℃,在常用溶剂中保持不溶解状态。采用扫描电子显微镜(SEM)绝对测量法对交联型μm级聚苯乙烯粒度标准物质进行定值,用美国国家标准技术研究院(NIST)的粒度标准物质校正其放大倍数。定值结果为2.84μm,扩展不确定度为0.08μm。采用F检验法和t检验法检验了样品的均匀性和稳定性。定值过程和均匀性、稳定性都符合国家二级粒度标准物质的要求。μm级交联型聚苯乙烯微球粒度标准物质,可用于高温和腐蚀等极端环境下的粒度分析。     

Synthesis and Characterization of Terpolymers of poly(L-lactide-glycolide-ε-caprolactone)

Random terpolymers of poly(L-lactide-glycolide-ε-caprolactone) (PLLGC) was prepared by ring-opening polymerization of L-lactide, glycolide and ε-caprolactone monomers initiated with stannous octanoate. Fourier transform infrared spectra, nuclear magnetic resonance and gel permeation chromatography were employed to characterize the obtained PLLGC terpolymers. The effects of polymerization temperature, reaction time, the amount of initiator and the polymerization pressure on the weight average molecular mass and polydispersity index of the PLLGC were investigated. In addition, the water contact angle of the PLLGC was also tested. The characterization of chemical structure showed that the PLLGC was successfully synthesized. For instance, a PLLGC terpolymer with a weight average molecular mass of about 12.435?×?10⁴?Da and a polydispersity index of 1.28 was obtained when the polymerization was conducted with a molar ratio of monomer to initiator ([M]/[I]) of 2000, polymerization temperature of 140?°C, polymerization pressure of 5.0?Pa and reaction time of 24?h. The random incorporation of ε-CL monomer units decreased the wettability of the PLGA copolymers.     

Emulsion Polymerized Polystyrene/Montmorillonite Nanocomposite and its Viscoelastic Characteristics

A novel polystyrene (PS)/clay nanocomposite was synthesized using a simple emulsion polymerization method in the presence of sodium ion exchanged montmorillonite (Na‐MMT). Prior to the radical polymerization procedure with potassium persulfate (KPS) as an initiator, the hydrophobic styrene monomer was intercalated into hydrophilic clay layers using sodium dodecyl sulfate (SDS) as a surfactant. The FTIR spectra of the products showed the characteristic absorbance peaks of both the synthesized PS and Na‐MMT. The x‐ray diffraction patterns of the products exhibited an increase in the d ₀₀₁‐spacing, pointing to the intercalation of the PS chains into the intergalleries of the Na‐MMT. The enhancement of the thermal properties of the nanocomposite materials, such as the increase in the glass transition temperature of the PS, was investigated by differential scanning calorimetry (DSC). Furthermore, based on the viscoelastic properties of the products examined using a rotational rheometer with a parallel plate geometry, the nanocomposites were found to exhibit more rapid shear thinning and increased storage (G′) and loss (G″) moduli with increasing clay content.     

Chemistry in Lasers. VI. Dimeric Luminophors in Electrogenerated Chemilumines cence

Electrogenerated chemiluminescence (ECL) provides an unusually attractive method for producing dimeric luminophors, by comparison to optical pumping of a dye laser, both in terms of dimer/monomer ratio and variety of accessible states. Several dimeric luminophors arising from the homogeneous charge transfer step are discussed, and the customary assignment of full singlet or triplet character to some of the excited moieties is shown to be unwarranted. An error in the literature concerning the kinetics of ECL-dimer formation is pointed out.     

A size-dependent microparticle capture and release chip using concentric membrane ring barriers

We present a size-dependent microparticle separation chip where different sized slit gaps are formed around a central inlet by membrane ring barriers, concentrically arranged, and adjusted with a single pneumatic source. Previous microparticle separation methods, using multiple filters with different pore sizes, require additional structures and processes to release microparticles after they are captured in the filter. In addition, those methods often result in particle loss due to clogging of the fixed pore filters. We suggest a microparticle separation chip capable of size-dependent capture and release without the particle loss. The present separation chip has four concentrically arranged membrane rings (b₁ ∼ b₄) with a thickness of 90 μm and widths of 182 μm, 188 μm, 194 μm, and 200 μm, respectively, which form slit gaps estimated to be 11.2 μm, 9.5 μm, 7.6 μm, and 5.8 μm, respectively, at the pneumatic pressure of 80 kPa. In the experiment, we demonstrated microparticle capture and release using two different sizes of PS (polystyrene) beads (diameter = 6.51 ± 0.43 μm and 10.32 ± 0.39 μm) immersed in 0.5% BSA (Bovine Serum Albumin) solution at a flow rate of 100 μl/min. At a pressure of 80 kPa, 10.32 μm and 6.51 μm-diameter beads were captured at ring barriers b₃ and b₄, respectively. Subsequently, at pressures of 65 kPa and 50 kPa, the 6.51 μm and 10.32 μm-diameter beads were respectively released from the outermost barrier (b₄). The capture and release efficiencies of 10.32 μm-diameter beads at the b₃ barrier were 91.7 ± 16.7% and 90.9 ± 8.1%, respectively. The purity of 10.32 μm-diameter beads at the b₃ barrier was 80.2 ± 6.2%. The capture and release efficiencies of 6.51 μm-diameter beads at the b₄ barrier were 100.0 ± 0.0% and 97.1 ± 4.0%, respectively. The purity of 6.51 μm-diameter beads at the b₄ barrier was 91.8 ± 2.9%. We have verified that different sizes of captured microparticles were released sequentially by gradually reducing the pressure. The present chip, having concentric membrane ring barriers which can form different sized slit gaps using a single pressure source, is simply capable of not only size-dependent microparticle capture, but also release in size order without particle clogging.     

类特异性分子印迹聚合物微球的识别机理及其光谱学研究

以氯磺隆为模板分子,甲基丙烯酸二乙氨基乙酯为功能单体,三甲氧基丙烷三甲基丙烯酸酯为交联剂,乙腈为致孔剂,在60℃温度下,采用热引发沉淀聚合方法制备了一种能同时吸附氯磺隆、噻吩磺隆、单嘧磺隆的类特异性分子印迹微球,并运用紫外光谱、红外光谱法等手段对其识别机理进行研究。结果表明,该聚合物微球对氯磺隆及其分子结构类似物噻吩磺隆、单嘧磺隆具有类特异性吸附能力,同时揭示了分子印迹微球是通过氢键作用特异性地识别模板分子及其类似物。     

Polystyrene/multi-wall carbon nanotube composites prepared by suspension polymerization and their electrorheological behavior

Polystyrene and polystyrene/multi-wall carbon nanotube composites, PS/MWNT, with MWNT content up to 1 wt.% were prepared in the form of microspheres through in situ suspension polymerization. The morphology of the fraction of 32–64 μm was examined by SEM and TEM microscopy. On the surface of the spheres the presence of MWNT was not observed. The microspheres intersections showed the structure of aggregates of sintered beads a few micrometers in size with heterogeneous interface. No MWNT material was observed inside the beads; it seemed to be situated in the heterogeneous phase of microspheres. Suspensions of PS/MWNT in silicone oil show electrorheological effect, whose intensity strongly depends on MWNT content in composite microspheres.     

Effect of interfacial tension on propagating polymerization fronts

This paper is devoted to the investigation of polymerization fronts converting a liquid monomer into a liquid polymer. We assume that the monomer and the polymer are immiscible and study the influence of the interfacial tension on the front stability. The mathematical model consists of the reaction-diffusion equations coupled with the Navier-Stokes equations through the convection terms. The jump conditions at the interface take into account the interfacial tension. Simple physical arguments show that the same temperature distribution could not lead to Marangoni instability for a nonreacting system. We fulfill a linear stability analysis and show that interaction of the chemical reaction and of the interfacial tension can lead to an instability that has another mechanism: the heat produced by the reaction decreases the interfacial tension and initiates the liquid motion. It brings more monomer to the reaction zone and increases even more the heat production. This feedback mechanism can lead to the instability if the frontal Marangoni number exceeds a critical value. (c) 2000 American Institute of Physics.     

Electrorotation of beads of immobilized cells

Electrorotation spectra were recorded for single yeast cells, microbeads (<90 μm) containing different concentrations of immobilized yeast cells within a κ-carrageenan matrix, and yeast clumps obtained by flocculation. It was found that, at the low medium conductivities used, the electrorotation spectra of κ-carrageenan beads containing immobilized yeast cells had a single peak, and were essentially the same as the electrorotation spectra of cell-free microbeads. Increasing the yeast concentration had no effect on the spectra. In contrast, the electrorotation spectra of clumps of flocculated yeast had a clockwise as well as an anti-clockwise peak, and were similar to those of single yeast cells. It is proposed that in beads with flocculated cells the cell–cell contacts cause the cells to form effectively a continuous cell layer with medium dispersed between the cells. This is in contrast with the gel beads, where little cell–cell contact occurs, and the gel forms a continuous phase between the yeast cells. Based on these assumptions a simple model is described based on Maxwell–Wagner's theories of interfacial polarization, in which the continuous and dispersed phase are reversed.     

纳米铝粉/聚苯乙烯包覆粒子的制备及表征

利用超声波的分散和粉碎作用,对纳米Al粒子进行了表面疏水处理。然后,以无水乙醇为反应介质,苯乙烯为单体,偶氮二异丁腈为引发剂,聚乙烯吡咯烷酮为分散剂,在氮气保护环境下,利用超声波的活化和引发作用,引发苯乙烯单体在纳米Al粒子表面进行分散聚合反应,制备出了纳米铝粉/聚苯乙烯包覆粒子。最后,运用多种测试手段对纳米Al/PS包覆粒子形貌、粒径大小及分布、表面特性、化学组成及结构等进行了表征。测试结果表明,所制备的纳米Al/PS包覆粒子已经形成了完整的球型核壳包覆结构,表面完整无缺陷,粒径大小约为2.0 m。     

Magnetic properties and energy transfer in the luminophors CaS:Eu,Cl

Studies have been performed on the magnetic properties and electron paramagnetic resonance (EPR) spectra of the small-crystal luminophors CaS:Eu,Cl. By comparing the EPR and magnetic susceptibility data we have determined that Eu enters into the CaS matrix primarily in the trivalent state Eu³⁺. We have found that the magnetic susceptibility of the sample with the lowest europium content (5×10⁻³ at. %) has a sharp peak at T≈5 K. A model is proposed of clusters into which the europium ions in these luminophors can associate. On the basis of this model an explanation is given for the anomalous temperature dependence of the magnetic susceptibility as well as a long list of other experimental facts (including peculiarities of the thermal luminescence). Zh. éksp. Teor. Fiz. 113, 1698–1707 (May 1998)     

Fibrin-based matrix for stem cell isolation and as a basis for new technologies for tissue regeneration

Fibrin microbeads (FMB) are made by moderate-heat condensation of fibrin drops in oil to obtain beads in the range of 100–200 μm. This procedure yields protein-based hard stable beads with high binding capability of the matrix dependent cell. Therefore, the FMB could serve for high yield isolation of mesenchymal stem cells (MSC) from different sources in higher yield than that obtained by conventional methods. The cells could be expanded on the FMB in suspension culture without the need for trypsinization and passages. Cell differentiation into different phenotypes, such as bone and cartilage, can be induced in cells loaded on FMB. When implanted, the cells on FMB survive the implantation and can download to become integrated with the target organs for tissue regeneration. This makes the use of FMB a simple technique for cell-based tissue regeneration without the need for implanting bulk scaffolds on which the cells have a low rate of survival. FMB technology provides a simple and highly effective fibrin-based method for cell separation, expansion in suspension and delivery to assist tissue regeneration.     

PS/Ag核壳结构复合微球的制备与性能

以乳液聚合法制备的平均粒径1.2~1.5μm单分散聚苯乙烯(PS)微球为核,经过超声敏化、化学镀、还原等过程制备了PS/Ag核壳结构复合微球。采用透射电镜、X射线衍射、红外光谱、紫外可见光谱对其形貌、物相、结构与光学性质进行了表征与分析。结果表明:PS/Ag复合微球粒径相对均一;通过多次敏化、控制二次银氨溶液浓度(0.002~0.006 mol/L),可实现对纳米银壳层厚度的调控;纳米银壳层沉积生长过程中,随着PS微球表面银粒子的增多、增大,复合微球的光学等离子体共振吸收峰产生显著的展宽与红移。     

Synthesis,Photophysical, Electrochemical and Thermal Investigation of Anthracene Doped 2-Naphthol Luminophors and their Thin Films for Optoelectronic Devices

A series of novel luminophors of 2-naphthol by doping anthracene were prepared using conventional solid state reaction technique. The photophysical, electrochemical and thermal properties were studied by Fluorescence spectroscopy, XRD, SEM, TGA-DSC and by Cyclic Voltammetry techniques. The thin films were characterized by Fluorescence spectroscopy. XRD study of fine grained powders exhibited sharp peaks which specify crystallinity and homogeneity of the doped luminophors. The fluorescence spectra of doped 2-naphthol exhibited emission of anthracene at 413 nm i.e. blue emission with instantaneous fluorescence quenching of 2-NP due to excitation energy transfer (EET). Electrochemical data specify that the HOMO and LUMO energy levels of the synthesized luminophors are in the range of 5.55–5.71 eV and 3.03–3.24 eV, respectively. TGA-DSC study confirmed thermal stability of prepared luminophors. Hence, overall study proposes that these luminophors seems applicable to be used as n-type materials for Optoelectronic devices.     

Polymerization rate and mechanism of ultrasonically initiated emulsion polymerization of n-butyl acrylate

The factors affecting the induction period and polymerization rate in ultrasonically initiated emulsion polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymerization of BA without any added initiator by enhancing the N2 flow rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced polymerization rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymerization rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical polymerization mechanism for ultrasonically initiated emulsion polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of polymerization and the polymerization process. Compared with conventional emulsion polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster polymerization rate, and higher molecular weight of the polymer prepared.     

Properties of Absorbent Acrylic Foam Prepared Based on the Method of High Internal Phase Emulsion

Acrylate and methacrylate monomers absorbent acrylate foams were prepared based on the method of high internal phase emulsion (HIPE). The influence of reaction conditions on liquid absorption by acrylate foams was studied. The reaction conditions included monomer ratio, cross-linker amount, initiator amount, emulsifier amount, emulsion concentration, emulsification temperature, and the curing time. The reaction conditions were determined to achieve the best liquid absorption by acrylate foams. Acrylate foams were analyzed with Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that when the monomer ratio was 9:1, cross-linking agent was 30% of monomer amount, initiator amount was 4% of the reactants amount, emulsifier amount was 8% of the reactants amount, the ratio of aqueous phase to oil phase was 32:1, emulsification temperature was 75°C, and curing time was 1.5 h, we could prepare the acrylate foam material with the best liquid absorption. Reaction of monomer and cross-linking agent was confirmed by FTIR analysis. The pore sizes of acrylate foam were between 1 μm and 8 μm according to SEM analysis. This material was very suitable to absorb aqueous fluids.     

Variable morphology of PTFE-like polymer nanocrystals fabricated by oriented plasma polymerization at atmospheric pressure

Rapid formation of PTFE-like polymer nanocrystals was achieved by a novel synthesis method—oriented plasma polymerization (OPP) at atmospheric pressure. The entire process was completed within a short period of time ranging between a few seconds to several minutes through dielectric barrier discharge (DBD) at atmospheric pressure. The surface morphology of the coated organic crystal film was observed through scanning electronic microscope (SEM) and different morphology nanocrystals were found such as nanorods and nanotubes. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the single-crystalline phase of these nanocrystals. The sizes of the nanosingle crystals were from 10 nm to 1 μm. The effects of discharge conditions such as discharge time, ratio of the monomer to carrier gas and power on the nanocrystalline morphology and crystallinity were investigated. As a result, the physical morphology and structures could be controlled through the conditions of the oriented plasma polymerization to some extent. This novel polymerization method opened a new way to nanofabricate polymeric crystallines fast and effectively.     

Surface modification and characterization of magnesium hydroxide sulfate hydrate nanowhiskers

In order to enhance the compatibility with plastic polymers, magnesium hydroxide sulfate hydrate (MHSH) nanowhiskers were modified through grafting methyl methacrylate (MMA) on the surface of the nanowhiskers by emulsion polymerization. The influences of the reaction time, MMA monomer content, adding speed of monomer and the reaction temperature on the grafting ratio were investigated. Thermogravimetry (TG), Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy and surface contact angle measurement were used to characterize the effect of surface modification. The results showed that the MHSH nanowhiskers were uniformly coated by polymethyl methacrylate (PMMA), and a well-defined core-shell hybrid structure of MHSH/PMMA was obtained. The surface contact angle of the hybrid whiskers increased to 87.32° from 12.71° and the whiskers surface was changed from hydrophilic to lipophilic.