Effects of modified Clay on the morphology and thermal stability of PMMA/clay nanocomposites

The potential to improve the mechanical, thermal, and optical properties of poly(methyl methacrylate) (PMMA)/clay nanocomposites prepared with clay containing an organic modifier was investigated. Pristine sodium montmorillonite clay was modified using cocoamphodipropionate, which absorbs UVB in the 280–320 nm range, via ion exchange to enhance the compatibility between the clay platelets and the methyl methacrylate polymer matrix. PMMA/clay nanocomposites were synthesized via in situ free-radical polymerization. Three types of clay with various cation-exchange capacities (CEC) were used as inorganic layered materials in these organic–inorganic hybrid nanocomposites: CL42, CL120, and CL88 with CEC values of 116, 168, and 200 meq/100 g of clay, respectively. We characterized the effects of the organoclay dispersion on UV resistance, effectiveness as an O₂ gas barrier, thermal stability, and mechanical properties of PMMA/clay nanocomposites. Gas permeability analysis demonstrated the excellent gas barrier properties of the nanocomposites, consistent with the intercalated or exfoliated morphologies observed. The optical properties were assessed using UV–Visible spectroscopy, which revealed that these materials have good optical clarity, UV resistance, and scratch resistance. The effect of the dispersion capability of organoclay on the thermal properties of PMMA/clay nanocomposites was investigated by thermogravimetric analysis and differential scanning calorimetry; these analyses revealed excellent thermal stability of some of the modified clay nanocomposites.     

Thermal and optical properties of poly(methyl methacrylate)/calcium carbonate nanocomposite

The study deals with thermal and optical properties of poly(methyl methacrylate) (PMMA) containing 2wt% calcium carbonate (CaCO₃) nanofiller. It was found that the thermal conductivity increases with increasing temperatures, due to thermal activation of the phonons in the PMMA/CaCO₃ nanocomposite. This enhancement in the thermal conduction is mainly attributed to the heat transferred by lattice vibrations as major contributors and electrons as minor contributors during thermal conduction. The optical properties were investigated as a function of wavelength and photon energy of UV radiation. The optical results obtained were analysed in terms of absorption formula for noncrystalline materials. It was found that the measured optical energy gap for the pure PMMA is greater than the PMMA/CaCO₃ nanocomposite. The width of the energy tails of the localised states was calculated. Adding CaCO₃ nanofiller into PMMA matrix may cause the localised states of different colour centres to overlap and extend in the mobility gap. This overlap may give an evidence for decreasing energy gap when adding CaCO₃ nanofiller in the polymer matrix.     

聚对苯乙炔-b-聚苯乙烯刚柔嵌段共聚物的合成与自组装

在分子设计的基础上,合成了分别以CHO、OH和Br为端基的PPV低聚体,并以后者作为大分子引发剂引发苯乙烯的原子转移自由基聚合,成功合成了一种新的结构明确的PPV-b-PS二嵌段共聚物。采用IR、UV-VIS、1H-NMR和GPC等手段表征了其结构,并研究了其在CS2溶液中的自组装行为。SEM观察证明,在温度、氩气流速和湿度分别为19.2℃,0.8 m3/h和67.8%RH的条件下,PPV-b-PS在质量分数0.2%的CS2溶液中能够自组装成高度有序的六角蜂窝状结构薄膜,其空穴的平均直径为1.15μm。     

The intercalation of poly(methyl methacrylate)/aluminophosphate nanocomposites and the properties improvement

Poly(methyl methacrylate) (PMMA)/dodecylamine templated lamellar aluminophosphate (DDA-LAP) intercalated nanocomposites are prepared by in situ bulk polymerization of MMA. The intercalated structure is characterized. With the intercalation of DDA-LAP in PMMA matrix, the glass-transition temperatures of nanocomposites (T_g) are increased. The nanocomposites obtained keep relatively high transparency in optical property and have a significant improvement in mechanical properties and thermal stability. The mechanism for the properties enhancement is investigated. The strong interfacial interaction between the aluminophosphate layers and the PMMA chains, the homogeneously distribution and the graphitized char formation during heating are three key roles for the properties improvement.     

Controlled formation of Ag/poly(methyl-methacrylate) thin films by RAFT technique for optical switcher

The functional group of sulfur was introduced into the PMMA terminus by the reversible addition-fragmentation transfer (RAFT) technique and the PMMA/Ag nanocomposite film was prepared by the in situ synthetic method. The third-order nonlinear optical properties of the material were further investigated by the Z-scan technique. The result shows that the χ⁽³⁾ nonlinearity of the material depend on the doped content of Ag nanoparticles and is obtained to be 6.22 × 10⁻⁹ esu at the content of 2.4 wt%. Furthermore, it is found that the material has the potential application on optical switcher at the content of 0.8 wt%.     

Effects of molar substitution of AA pendant on poly(MMA-co-GMA) under UV curing

The molar substitution of an acrylic acid (AA) pendant group on a glycidyl methacrylate–methyl methacrylate copolymer was investigated to evaluate its affects on mechanical properties and thermal stability under UV curing. Structural analysis was conducted by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy (¹H-NMR) to study the synthetic route of the acrylate copolymer. The mechanical behaviors of AA substituted copolymers were interpreted in terms of both their loss tangent and elongation at the break point, because AA increases the cross-linking density, which is directly proportional to the degree of homopolymerization; this relationship was monitored by ¹H-NMR with various molar substitutions. In addition, the optical and mechanical properties of the copolymers were also characterized by the extent of AA molar substitution. The optimal behavior was obtained at a molar substitution of 94.3% (equivalent to an AA/GMA molar ratio of 1.4) and satisfied both the transparency (>89.3%) and elongation (>7.4%) requirements for the complex-shaped coatings.     

Compositional study and cytotoxicity of biodegradable poly(ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] and poly(ethylene glycol)

Biodegradable PHB–PEG multi-block polyurethane copolymers comprising PHB blocks (M_n: 1100, 1740 and 3240) and PEG blocks (M_n: 1960, 3250, 4150 or 7950) were synthesized followed by characterization by GPC, ¹H NMR, and FT-IR. The PHB contents ranged from 9 to 62% by weight. The copolymers displayed improved thermal stabilities compared with their respective precursors. The morphological structures of the copolymers were studied by FT-IR, DSC and XRD. FT-IR revealed the existence of amorphous and crystalline phases of PHB. Both DSC and XRD analyses showed that separate crystalline phases are formed by PEG and PHB blocks in the copolymers. Upon annealing, the melting transition temperature (T_m), melting enthalpy (ΔH_m) and the fractional crystallinity (X_c) of the PEG block increased when the length of PEG incorporated into the copolymer increased. These values were higher when the PHB block length is shorter as the shorter PHB chain does not disrupt the crystallization of PEG as much as the longer PHB chain. A similar disruptive effect on the crystallization of PHB segments was observed by varying PEG chain lengths but the effect is less pronounced compared with the PEG segments. A comparison of the swelling properties of the poly(ester urethane)s showed that the length and crystalline properties of the PHB block significantly affects the water uptake properties of the copolymers. The crystalline properties and the water uptake capacities of the copolymers could be fine-tuned by consideration of the length of the PHB and PEG block incorporated. The results of the cytotoxicity tests demonstrated that the poly(PHB/PEG) urethanes were non-cytotoxic and could potentially be used for biomedical purposes.     

Electrical and mechanical properties of PMMA/reduced graphene oxide nanocomposites prepared via in situ polymerization

We report the effect of filler incorporation techniques on the electrical and mechanical properties of reduced graphene oxide (RGO)-filled poly(methyl methacrylate) (PMMA) nanocomposites. Composites were prepared by three different techniques, viz. in situ polymerisation of MMA monomer in presence of RGO, bulk polymerization of MMA in presence of PMMA beads/RGO and by in situ polymerization of MMA in presence of RGO followed by sheet casting. In particular, the effect of incorporation of varying amounts (i.e. ranging from 0.1 to 2 % w/w) of RGO on the electrical, thermal, morphological and mechanical properties of PMMA was investigated. The electrical conductivity was found to be critically dependent on the amount of RGO as well as on the method of its incorporation. The electrical conductivity of 2 wt% RGO-loaded PMMA composite was increased by factor of 10⁷, when composites were prepared by in situ polymerization of MMA in the presence of RGO and PMMA beads, whereas, 10⁸ times increase in conductivity was observed at the same RGO content when composites were prepared by casting method. FTIR and Raman spectra suggested the presence of chemical interactions between RGO and PMMA matrix, whereas XRD patterns, SEM and HRTEM studies show that among three methods, the sheet-casting method gives better exfoliation and dispersion of RGO sheets within PMMA matrix. The superior thermal, mechanical and electrical properties of composites prepared by sheet-casting method provided a facile and logical route towards ultimate target of utilizing maximum fraction of intrinsic properties of graphene sheets.     

Luminescent and thermal properties of a novel red-emitting silicon fluoride acrylate-Eu(III) copolymer for white LEDs

A red-emitting silicon fluoride acrylate (SFA)-Eu(III) copolymer was prepared based on water-in-oil emulsion polymerization method. Its photoluminescence including the temporal decay was studied in addition to the thermal properties. Of the emissions due to the ⁵D₀ → ⁷F_J (J = 0–4) transitions of Eu³⁺ ions, an intense red emission due to ⁵D₀ → ⁷F₂ transition was observed at 618 nm under the 395 nm excitation, together with a weak ⁵D₀ → ⁷F₀ emission at 580 nm. Compared with some commercial phosphor, the SFA-Eu(III) copolymer also have a higher QE value. From the optical properties it was suggested that Eu³⁺ ions were located at the disordered non-inversion Eu³⁺ sites in the copolymer. The glass transition temperature (T_g) was estimated about −51.5 °C from a differential scanning calorimetric curve, while chemical decomposition was estimated to start from 385 °C from a thermogravimetry analysis curve. Taking into account the thermal stability in a wide temperature range from −51.5 °C to 385 °C, the SFA-Eu(III) copolymer is expected to act as a potential red component for near-UV excited white LEDs.     

Preparation and characterization of poly(methyl methacrylate)-clay nanocomposites via melt intercalation: Effect of organoclay on thermal, mechanical and flammability properties

The PMMA nanocomposites were prepared by melt processing method. The influence of organoclay loading on extent of intercalation, thermal, mechanical and flammability properties of poly(methyl methacrylate) (PMMA)-clay nanocomposites were studied. Three different organoclay modifiers with varying hydrophobicity (single tallow vs. ditallow) were investigated. The nanocomposites were characterized by using wide angle X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), and tensile tests. The intercalation of polymer chain within the silicate galleries was confirmed by WAXD and TEM. Mechanical properties such as tensile modulus (E), tensile strength, percentage elongation at break and impact strength were determined for nanocomposites at various clay loadings. Overall thermal stability of nanocomposites increased by 16-17 °C. The enhancement in T_g of nanocomposite is merely by 2-4 °C. The incorporation of maleic anhydride as compatibilizer further enhanced all the properties indicating improved interface between PMMA and clay. The flammability characteristics were studied by determining the rate of burning and LOI.     

Preparation and investigation of PVDF/PMMA/TiO2 composite film

Polyvinylidene fluoride (PVDF)/Polymethylmethacrylate (PMMA)/Titanium dioxide (TiO₂) composite, and its films was prepared and studied in detail. The structure, morphology, crystalline behavior, thermal, and mechanical properties of PVDF/PMMA/TiO₂ film were investigated through FT-IR/ATR, SEM, XRD, DSC, TGA, and Py-GC/MS, respectively. The results showed that the blended material and its film have favorable thermal and mechanical properties. The TiO₂ particles finely dispersed in the composite featured by crystalline regions of PVDF and homogeneous amorphous regions consisted of PVDF and PMMA, resulting in an advantageous properties and improvement of tensile strength and elongation at break of the PVDF/PMMA film. However, the TiO₂ can greatly narrow the thermally stable margin of PVDF in PVDF/PMMA/TiO₂ composite for at least 100 °C with catalysis decomposition effect.     

One-step preparation of hierarchical porous carbons from poly(vinylidene chloride)-based block copolymers

A facile self-templating and activation-free method to fabricate the hierarchical porous carbons (HPCs) from poly(vinylidene chloride) (PVDC)-based block copolymers is reported in this article. A series of block copolymers consisted of PVDC and the polystyrene (PS) blocks were prepared via RAFT living radical polymerization. Effects of molar ratio between the PVDC and the PS blocks on the microphase separation and thermal degradation of the PVDC-b-PS copolymers, and the microstructure of the as-prepared porous carbons were investigated. The results show that the PVDC block acts as a good kind of carbon precursor capable of forming micropores (0.5–0.6 nm) due to the diffusion of small molecules eliminated during the degradation of the PVDC block, and the microdispersed PS block acts as a mesopore extender to generate the mesopores (3–30 nm) by the decomposition of the PS phase. The as-prepared HPCs have the unique structures with three-dimensionally interconnected micropores and mesopores. The high Brunauer–Emmett–Teller surface area (1220 m²/g) and total pore volume (0.92 cm³/g) were achieved through controlling the composition of block copolymer. The method is facile to prepare the HPCs and suitable to the PVDC-based copolymers with other pyrolyzable block.     

Graphene/MoS2 organic glasses: Fabrication and enhanced reverse saturable absorption properties

Graphene/MoS₂ (G/MoS₂) composites were synthesized for the first time by a hydrothermal method, and then were dispersed in methyl methacrylate (MMA) to fabricate organic glass by a casting method. Here, the poly(methylmethacrylate) (PMMA) host can be obtained by the polymerization of MMA. The nonlinear absorption (NLA) properties of the G/MoS₂/PMMA organic glasses were investigated by using an open-aperture Z-scan technique. The experimental results showed that the G/MoS₂/PMMA organic glasses (the NLA coefficient β, was up to 2110 cm/GW) exhibited enhanced reverse saturable absorption (RSA) properties compared to G/PMMA (β = 242 cm/GW) and MoS₂/PMMA (β = 365 cm/GW) organic glasses. The enhanced mechanism of RSA was analyzed in terms of the energy-level diagram of graphene and MoS₂. The G/MoS₂/PMMA organic glasses have very promising applications in optical devices such as optical limiters and optical shutters.     

Temperature dependent optical properties of a synthesis blend of poly(methyl methacrylate) and vinyl rubber

The temperature dependent optical properties of a poly(methyl methacrylate) (PMMA) ethylene-co-vinylacetate (EVA) blend (PMMA-EVA) were investigated in order to study its thermo-optical behaviour in the temperature range 30–70C. The thermal coefficients of the refractive index dn/dt of PMMA-EVA, PMMA and EVA were measured as a function of the temperature. The observed trend of the, thermal coefficients is related to a first-order phase transition of the EVA component. A comparison with the results of calorimetric investigations by differential scanning calorimetry (DSC) is also reported. The possible use of this material in optics is described.     

Blends of poly(methyl methacrylate) and polyamides

The morphology of PMMA blends with different polyamides (PA-6, 6/9 and 12) was investigated by transmission electron microscopy, recognizing PA-6/PMMA as the most miscible pair. Blends of these polymers were prepared from solutions in m-cresol and formic acid and the morphology was highly dependent on the solvent. The morphology and the segregation degree of extruded PA-6/PMMA blends was investigated by scanning electron microscopy and dynamic-mechanical analysis. The compatibilization succeeded by the introduction of a block copolymer of polyamide and poly(ethylene oxide).     

Indium(III) and Gallium(III) phthalocyanines-based nanohybrid materials for optical limiting

Linear and nonlinear optical properties of a phthalocyanine (Pc)-based nanohybrid material PCIGS [Cu₂(tBu₄PcGa)(tBu₄PcIn)S₂TPP₂] are described. The overall aggregation of phthalocyanines in poly(methylmethacrylate) (PMMA) films was evident, which is indicated by the broadening of linear spectra in the Q-band region and the shift of wavelength. Upon excitation with nanosecond laser pulse at 355 nm, the transient absorption band appeared at about 500 nm is attributed to the triplet–triplet absorption of the Pcs. For PCIGS and its starting materials tBu₄PcGaCl and tBu₄PcInCl, all Z-scans exhibit a decrease in transmittance about the focus typical of an induced positive nonlinear absorption of incident light. The absorption mechanism is due to population of excited states through a multi-step nonlinear absorption. When these Pc compounds were embedded into a commercially available polymer PMMA, all the Pc/PMMA composites display much larger nonlinear absorption coefficient and lower saturable fluence for optical limiting when compared to the same Pc molecules in solution. However, in contrast to tBu₄PcGaCl and tBu₄PcInCl, PCIGS displayed decreased optical limiting response, possibly due to competing electron accepting processes in the In and Ga metals, and the highly ordered structure of the PCIGS complex itself.     

Nonlinear optical properties of p-(N,N-dimethylamino)dibenzylideneacetone doped polymer

A bis-chalcone derivative, p-(N,N-dimethylamino) dibenzylideneacetone was synthesized. Its third-order nonlinear susceptibility was determined to be as high as 10⁻¹² esu by employing single beam Z-scan and degenerate four wave mixing techniques using Nd:YAG 7 ns laser pulses at 532 nm. The compound was doped in to poly(methylmethacrylate) matrix and the third-order nonlinearity was investigated by using Z-scan technique. The nonlinear refractive index of the doped polymer is found to be negative, and its magnitude is of the order of 10⁻¹⁰ esu. The results show that the compound exhibits strong reverse saturable absorption and a good optical limiting property and hence may be used as a promising dopant material. The study on concentration dependence of nonlinear optical parameters has been presented.     

Luminescence Spectra of Poly(methylmethacrylate)/ZnS:Eu(III),Tb(III) Composites

Colloidal zinc sulfide solutions have been prepared by reacting zinc trifluoroacetate and thioacetamide in methyl methacrylate as a reaction medium, and europium and terbium salts have been added to the solution. Using methyl methacrylate block polymerization, we have synthesized PMMA/ZnS, PMMA/ZnS:Eu(III), PMMA/ZnS:Tb(III), and PMMA/ZnS:Eu(III),Tb(III) composites. The luminescence of the composites is due to charge recombination at energy levels of structural defects and impurities in ZnS and also to ⁵D₀ → ⁷F _j and ⁵D₄ → ⁷F _j electronic transitions of the Eu³⁺ and Tb³⁺ ions. It depends on the composition and structure of the composites, excitation wavelength, and other factors. The mutual effects of the ZnS and the Eu³⁺ and Tb³⁺ ions show up as changes in the position and relative intensity of luminescence bands in the spectra of the composites.     

The preparation and characteristic of maleic anhydride grafted polyethylene (PE-g-MA) filled CNT/PMMA composite film

ABSTRACT

In order to improve the tribological properties of PMMA, the PMMA composites incorporated with CNT powders were prepared. The effect of CNT content on tribological properties of the composites was investigated. When CNT content is 0.5 wt%, the friction coefficients of the 0.5%CNT/PMMA composite are the smallest, which are about 0.15 and are 67% less than those of the pure PMMA composite, and its wear resistance remains the same as the pure PMMA composite. Incorporating 0.5 wt% CNT into the PMMA composite may develop a continuous transferred film on the worn surface. As a result, the friction coefficients of the composite are reduced and its wear mechanism is mainly fatigue spalling. The addition of PE-g-MA improved the friction and wear properties of CNT/PMMA composite.     

Improved stability of organic light-emitting diode with aluminum cathodes prepared by ion beam assisted deposition

We have fabricated highly stable organic electroluminescent devices based on spin-coated poly-p-phenylene-vynylene (PPV) thin films. The electrical properties of aluminum cathode, prepared by ion beam assisted deposition, on PPV have been investigated and compared to those by thermal evaporation. Although energetic particles of Al assisted by Ar⁺ ion may damage the organic material, I–V–L characteristics are improved by applying thin Al buffer layer. In addition, a dense Al cathode inhibits the permeation of H₂O and O₂ into PPV film through pinhole defects, and thus retards dark spot growth. It may be deduced from highly packed structure of Al cathode with an increase in the contact area between Al and PPV that reduce the contact resistance. In conclusion, the lifetime of organic light-emitting device (OLED) has been extended effectively by dense Al film through ion beam assisted deposition process.