The critical organic modifier aliphatic tail length for the formation of poly(methyl methacrylate)-montmorillonite nanocomposites

In this article, we report the influence of organic modifier structure (alkyl chain length C8-C20, single vs ditallow) and thereby, the effect of hydrophobicity on the structure, thermal and mechanical properties of poly(methyl methacrylate) (PMMA)-clay hybrids. Melt processed PMMA-clay hybrids were characterized using wide-angle X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The organoclays having an alkyl chain length of more than 12 CH₂ groups resulted in the formation of nanocomposites. The glass transition temperature (T_g) of PMMA increased in the presence of clay. The mean-field lattice model was used to predict the free energy for nanocomposite formation, which showed a reasonable match with the experimental results and provided a general guideline for the proper selection of polymer and organoclay (ie, organic modifier) to obtain nanocomposite. Tensile modulus showed maximum improvement of 58% for the nanocomposites compared to 9% improvement for the composites. Tensile modulus increased with increases in the alkyl chain length of the organic modifier and clay loading. The level of improvement for the tensile properties of nanocomposites prepared from primary and secondary ammonium-modified clay is the same as that obtained with the commercial organoclays.     

Preparation of P(St-NMA) microsphere inks and their application in photonic crystal patterns with brilliant structural colors

Patterned photonic crystals with structural colors on textile substrates have attracted a special attention due to the great advantages in application, which currently become a research hot-spot. This study utilized an ink-jet printing technology to prepare high-quality photonic crystal patterns with structural colors on polyester substrates. The self-assembly temperature of poly(styrene-N-methylol acrylamide) (P(St-NMA)) microspheres set to construct photonic crystals were deeply optimized. Moreover, the structural colors of prepared photonic crystal patterns were characterized and evaluated. When the mass fraction of P(St-NMA) microspheres was 1.0 wt.%, the pH value ranged from 5 to 7, and the surface tension was in the range of 63.79 to 71.20 mN/m, inks could present the best print performance. At 60 °C, prepared P(St-NMA) microsphere inks were good for printing to obtain patterned photonic crystals with regular arrangement and beautiful structural colors. Specifically, photonic crystals with different colors could be constructed by regulating the diameter of microspheres in inks, and prepared structural colors exhibited distinct iridescent phenomenon. The present results could provide a theoretical basis for the industrial realization of patterned photonic crystals by ink-jet printing technology.     

Methacrylate hydrogels reinforced with bacterial cellulose

Composite hydrogels consisting of nanofibrous bacterial cellulose (BC) embedded in a biocompatible polymeric matrix of various methacrylates were synthesized by UV polymerization using the ‘ever‐wet’ technique. The effect of monomer(s) type and ratio, system dilution at polymerization, monomer(s) hydrophilicity, crosslink density and cellulose/hydrogel ratio was investigated. The effect of BC reinforcement on equilibrium swelling depends on whether the neat gel swells more when brought into contact with water. The major improvement achieved by introduction of 1%–2% BC concerns mechanical properties. Compared with neat gels, the storage shear modulus G′ increased by a factor 10‐20, and the loss part G″ also rose significantly. The compression modulus ranged from 2 to 5.5 MPa for composites swollen to equilibrium (20‐70 wt% water). The BC‐hydrogel composites are considered for application in the tissue engineering area. Copyright © 2012 Society of Chemical Industry     

Preparation and properties of novel pH‐sensitive core−shell microspheres for enhanced oil recovery

A novel pH‐sensitive core?shell microsphere was synthesized by growing sodium acrylate as a shell on crosslinked polyacrylamide particles as the core by surface‐initiated atom transfer radical polymerization. The structures and characteristics of the microspheres were confirmed by Fourier transform infrared spectroscopy, ¹H NMR spectroscopy, SEM, transmission electron microscopy and AFM. The viscosity and size of the microspheres in response to changes in pH value were also investigated. As a kind of potential profile control and flooding agent, the performances of permeability reduction and enhanced oil recovery were studied in designed experiments. © 2017 Society of Chemical Industry     

Tristable switching of the electrical conductivity through graphene quantum dots sandwiched in multi-stacked poly(methyl methacrylate) layers

Tristable switching nonvolatile memory (NVM) devices based on graphene quantum dots (GQDs) sandwiched between multi-stacked poly (methyl methacrylate) (PMMA) layers were fabricated on indium-tin-oxide (ITO)-coated glass substrates by using a solution-processed method. Current-voltage (I-V) curves at 300 K for the silver nanowire/PMMA/GQD/PMMA/GQD/PMMA/ITO/glass devices showed tristable switching currents with high-resistance, intermediate-resistance, and low-resistance states. The device's cycling endurance of the three resistance states remained stable with a distinguishable value for each resistance state over 1000 cycles, and the obtained retention results showed well-distinguished resistance states without degradation for up to 1 × 10⁴ s. Schottky emission, Poole-Frenkel emission, trapped-charge limited-current, and ohmic conduction were proposed as the dominant conduction mechanisms for the fabricated NVM devices based on the obtained I-V characteristics. The described energy-band diagrams confirm the proposed conduction band mechanisms.     

Barrier effect of flame retardant systems in poly(methyl methacrylate): Study of the efficiency of the surface treatment by octylsilane of silica nanoparticles in combination with phosphorous fire retardant additives

In this work, flame retardant systems comprising ammonium polyphosphate (AP423) and hydrophilic (A200) or hydrophobic (R805) nanometric silica were incorporated into PMMA. The following techniques were performed to detail the fire behaviour of the composites: mass loss cone calorimetry, pyrolysis‐combustion flow calorimetry, pyrolysis‐gas chromatography–mass spectrometry, thermogravimetric analysis, X‐ray diffraction analysis, Fourier transform infrared spectroscopy and microscopic observations. The best fire behaviour was obtained with the surface‐treated silica in the presence of AP423. The formation of a new crystalline phase from the interactions between AP423 and R805 silica and a strong barrier effect due to a layered residue were the main modes of action of this system. Moreover, we have shown that the difference between the AP423 + R805 and AP423 + A200 systems was due to poor dispersion of the silica into the PMMA matrix in the latter formulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Atom transfer radical polymerization of glycidyl methacrylate followed by amination on the surface of monodispersed highly crosslinked polymer microspheres and the study of cation adsorption

The introduction of reactive groups on the surface of monodispersed highly crosslinked poly(styrene–divinylbenzene) (PSDVB) microspheres was accomplished in two steps. The first step requires immobilizing the initiating groups by a Friedel–Craft acylation between 2-chloropropionyl chlorides and the phenyl groups on the spheres. The second step requires the atom transfer radical polymerization (ATRP) of glycidyl methacrylate (GMA) to obtain spheres (PSDVB-g-PGMA) with epoxy groups on the surface. To demonstrate the feasibility of introducing functionality, the epoxy groups were ring-opened by ethylenediamines, resulting in spheres with amino functionality (PSDVB-g-PGMAEDA). The final spheres were found to have an adsorption capacity of 0.66 mmol/g in the Cu²⁺ adsorption experiments, as a preliminary application study.     

正辛胺模板法制备SiO_2空心微球及其结构表征

以正辛胺为模板、正硅酸乙酯为硅源,在盐酸的催化作用下通过溶胶-凝胶法制备出圆形度高、分散性好、结构完整的SiO2空心微球;采用SEM、XRD、FTIR、BET、TG等对不同反应时间、反应温度、搅拌速度、盐酸含量等条件下SiO2空心微球的形貌、粒径、壳层厚度和结构进行分析与表征。结果表明,SiO2空心微球的平均粒径随反应温度和反应时间的增加而缓慢增大。SiO2空心微球的平均粒径为15~28μm,壳层厚度为3.1~4.0μm;壳层表面具有孔结构,比表面积为970~1244 m2/g,可几孔径为1.5~2.4 nm。     

基于NTC微珠状热敏电阻的稳态测量方法

稳态导热系数测量方法的原理和数学模型简单,但热源均温性要求高和测量时间长限制了稳态导热系数测量方法的实际应用。提出一种测量导热系数的新型微球法稳态热测量方法,建立对应的物理模型和试验方法。通过熔融共混法制备不同质量分数的石墨烯 石蜡复合相变材料,并采用微球法对不同质量分数的石墨烯 石蜡复合相变材料的导热系数进行测量。测量得到样品的导热系数分别为0.278 W/(m·K）(0%)、0.330 W/（m·K）(0.5%)、0.402 W/（m·K）(1%)、0.524 W/（m·K）(2%)、0.604 W/（m·K）(3%)、0.654 W/（m·K）(4%)和0.711 W/（m·K）(5%)。该方法具有微球体积小、热源均匀、测量快、样品制备简单等优点,可应用于实际工程中相变材料和液体的原位导热系数测量。     

氮掺杂TiO_2中空复合微球的制备及可见光光催化性能

为了提高TiO2的可见光光催化性能,以微米级聚苯乙烯微球为模板,钛酸四丁酯为前驱体,三乙胺为氮源,采用静电吸附自组装法制备了粒径为1.20μm、壳层的厚度约为30nm且球形形貌良好的氮掺杂TiO2中空复合微球,采用SEM、XPS、XRD和紫外-可见分光光度计研究了其结构及光催化性能。结果表明:氮进入TiO2晶格内取代了部分O并改变了晶格中Ti和O的化学状态,但对TiO2晶型结构没有明显影响;氮掺杂后的TiO2中空复合微球禁带宽度变窄,氮掺杂TiO2中空复合微球不仅在紫外区有较强的光吸收能力,在可见光区也表现出较强的光响应性,对甲基橙的光催化降解率较Degussa P25型纳米TiO2的明显增强。研究结果对TiO2在光催化领域的应用具有理论指导意义。