Spectroscopic study of D1-A-D2-A terpolymer films for optoelectronic applications.

Several strategies have been considered in search of more efficient organic materials for charge transfer in photovoltaic devices. Among them, the integration of donor-acceptor (D-A) functional units on a conjugated copolymer has been widely applied. In this framework, we evaluated four terpolymers made up of donor moieties derived from 9,9-dioctylfluorene and 9-(heptadecan-9-yl)-9H-carbazole combined with 2,1,3-benzothiadiazole, the acceptor moiety, in different monomer ratios and polymerization routes (block and random microstructures). The preferred molecular orientation and charge transfer dynamics of the polymeric films were assessed by near edge X-ray absorption fine structure spectroscopy (NEXAFS) and resonant Auger electron spectroscopy (RAES) around the sulfur K-edge. Charge transfer times (τCT) were estimated by the Core-Hole Clock (CHC) method. Films with a high degree of organization were identified for the block terpolymer and random terpolymers with uneven amounts of donor units, showing a preferred orientation of the benzothiadiazole (BT) molecular plane parallel to the substrate surface. The values of τCT measured for all terpolymers were higher than those for typical polymers used in photovoltaic devices, which is not desirable for this type of optoelectronic application, but this may be correlated to the strong acceptor character of BT, the unit probed. To investigate the effect of film formation on the excited state behavior, steady-state and time-resolved photoluminescence measurements were also conducted. X-ray photoelectron spectroscopy (XPS) was employed to characterize the surface chemical composition of the terpolymer films. Based on the spectroscopic data the block copolymer appears to be the most suitable for the desired application.

Synthesis of Nanocomposites of Polypropylene with Graphite Nanosheets by In Situ Polymerization Using a Fourth Generation Ziegler-Natta Catalyst.

Polypropylene nanocomposites with expanded graphite nanosheets (xGN) were synthesized by In Situ polymerization employing a Ziegler-Natta catalyst supported on particles of MgCl2 containing xGN (mass ratio 1:1) and internal electron donor to control isotacticity, and their properties were compared with those of neat polypropylene obtained using a prepared standard Ziegler-Natta catalyst. SEM micrographs showed an alteration in the morphology of the catalyst with nanoparticles when compared with the standard one. It was noted that the catalyst containing xGN was more reactive for propylene polymerization than the standard one. By thermogravimetric analyses, it was detected that the PP/xGN nanocomposites showed higher thermal stability than PP. Differential scanning calorimetry (DSC) showed that the nanocomposites presented higher crystallinity degree, indicating that the nanofillers acted as nucleating agent. Scanning (SEM) and transmission (TEM) electron microscopies showed that the nanofillers were well dispersed into the PP matrix. By dynamic-mechanical analyses (DMA) it was observed an increase in glass transition temperature and the nanocomposites moduli.

Ziegler-Natta Catalyst Based on MgCl2/Clay/ID/TiCl4 for the Synthesis of Spherical Particles of Polypropylene Nanocomposites.

In the present work, we have designed MgCl2/clay/internal donor (ID)/TiCl4 based bisupported Ziegler-Natta catalysts containing varying amounts of organoclay (montmorillonite) in order to synthesize spherical particles of polypropylene/clay nanocomposites (PCN). The organoclay was introduced into the catalyst support formulation and PCN was obtained using the in situ polymerization technique. Decreasing the reaction time, it was possible to obtain nanocomposites with high concentrations of clay (masterbatches). Micrographs of SEM confirmed the spherical morphology of the catalysts. In addition, XRD patterns show that the active sites for polymerization were inserted in the clay galleries. The catalytic performance was evaluated in slurry propylene polymerization using triethylaluminium as cocatalyst and silane as external electron donor at 70 °C, 4 bar, and different reaction times. The PCNs obtained containing different clay amounts were characterized by X-ray diffraction, thermal analyses, transmission electronic microscopy, and extractables in heptane. The results revealed that the synthesized PP/clay particles were also spherical showing that the morphological control is possible even using catalysts containing high amounts of clay. The PCN presented high degradation temperature (459 °C). The XRD peak related to the clay interlamellar distance has shifted to lower angles, and TEM images confirmed the formation of exfoliated/intercalated clay on the PP matrix and absence of microparticles of clay.

Microfluidic Fabrication of Pluronic Vesicles with Controlled Permeability.

Block copolymers with a low hydrophilic-to-lipophilic balance form membranes that are highly permeable to hydrophilic molecules. Polymersomes with this type of membrane enable the controllable release of molecules without membrane rupture. However, these polymersomes are difficult to assemble because of their low hydrophobicity. Here, we report a microfluidic approach to the production of these polymersomes using double-emulsion drops with ultrathin shells as templates. The small thickness of the middle oil phase enables the attraction of the hydrophobic blocks of the polymers adsorbed at each of the oil/water interfaces of the double emulsions; this results in the dewetting of the oil from the surface of the innermost water drops of the double emulsions and the ultimate formation of the polymersome. This approach to polymersome fabrication enables control of the vesicle size and results in the efficient encapsulation of hydrophilic ingredients that can be released through the polymer membrane without membrane rupture. We apply our approach to the fabrication of Pluronic L121 vesicles and characterize the permeability of their membranes. Furthermore, we show that membrane permeability can be tuned by blending different Pluronic polymers. Our work thus describes a route to producing Pluronic vesicles that are useful for the controlled release of hydrophilic ingredients.

Explorative Study on the Use of Curauá Reinforced Polypropylene Composites for the Automotive Industry.

The automotive industry is under a growing volume of regulations regarding environmental impact and component recycling. Nowadays, glass fiber-based composites are commodities in the automotive industry, but show limitations when recycled. Thus, attention is being devoted to alternative reinforcements like natural fibers. Curauá (Curacao, Ananas erectifolius) is reported in the literature as a promising source of natural fiber prone to be used as composite reinforcement. Nonetheless, one important challenge is to obtain properly dispersed materials, especially when the percentages of reinforcements are higher than 30 wt %. In this work, composite materials with curauá fiber contents ranging from 20 wt % to 50 wt % showed a linear positive evolution of its tensile strength and Young's modulus against reinforcement content. This is an indication of good reinforcement dispersion and of favorable stress transfer at the fiber-matrix interphase. A car door handle was used as a test case to assess the suitability of curauá-based composites to replace glass fiber-reinforced composites. The mechanical analysis and a preliminary lifecycle analysis are performed to prove such ability.

Synthesis of Polypropylene/Organoclay Nanocomposites via In Situ Polymerization with Improved Thermal and Dynamic-Mechanical Properties.

Preparation of polypropylene/clay nanocomposites via in situ polymerization is investigated. MgCl2/organophilic clay bi-supported Ziegler-Natta catalysts were used to prepare these nanocomposites. Three organophilic clays (Cloisite 30B, Cloisite 15A, and Claytone HY) were used as support and reinforcement agents. The nanostructure of the composites was characterized by X-ray diffraction. The results showed that the most active catalyst was that with clay having high inter-layer spacing without functional OH groups. Moreover, the silica layers of the clays (Cloisite 15A and Claytone HY) in these polypropylene/clay nanocomposites were exfoliated and well dispersed in the polypropylene matrix. Differential scanning calorimetric was used to investigate both melting and crystallization temperatures, as well as the crystallinity of the nanocomposite samples. These results showed that Cloisite 15A and Claytone HY acted as nucleating agents in the process of crystallization of polypropylene. Thermogravimetric analysis showed that Cloisite 15A and Claytone HY promoted an increase in resistance to thermal degradation. Dynamic-mechanical analysis showed that nanocomposites presented an increase in the storage modulus. Furthermore, Cloisite 15A and Claytone HY promoted an increase in glass transition temperature. Small-angle X-ray scattering analysis was used to determine how clay and its concentration influence the size of the polymer nanocrystals.