Phase behavior, crystallization, and hierarchical nanostructures in self-organized thermoset blends of epoxy resin and amphiphilic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymers

Nanostructured thermoset blends of bisphenol A-type epoxy resin (ER) and amphiphilic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers were successfully prepared. Two samples of PEO-PPO-PEO triblock copolymer with different ethylene oxide (EO) contents, denoted as EO30 with 30 wt % EO content and EO80 with 80 wt % EO content, were used to form the self-organized thermoset blends of varying compositions using 4,4'-methylenedianiline (MDA) as curing agent. The phase behavior, crystallization, and morphology were investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). It was found that macroscopic phase separation took place in the MDA-cured ER/EO30 blends containing 60-80 wt % EO30 triblock copolymer. The MDA-cured ER/EO30 blends with EO30 content up to 50 wt % do not show macroscopic phase separation but exhibit nanostructures on the order of 10-30 nm as revealed by both the TEM and SAXS studies. The AFM study further shows that the ER/EO30 blend at some composition displays structural inhomogeneity at two different nanoscales and is hierarchically nanostructured. The spherical PPO domains with an average size of about 10 nm are uniformly dispersed in the 80/20 ER/EO30 blend; meanwhile, a structural inhomogeneity on the order of 50-200 nm is observed. The ER/EO80 blends are not macroscopically phase-separated over the entire composition range because of the much higher PEO content of the EO80 triblock copolymer. However, the ER/EO80 blends show composition-dependent nanostructures on the order of 10-100 nm. The 80/20 ER/EO80 blend displays hierarchical structures at two different nanoscales, i.e., a bicontinuous microphase structure on the order of about 100 nm and spherical domains of 10-20 nm in diameter uniformly dispersed in both the continuous microphases. The blends with 60 wt % and higher EO80 content are completely volume-filled with spherulites. Bundles of PEO lamellae with spacing of 20-30 nm interwoven with a microphase structure on the order of about 100 nm are revealed by AFM study for the 30/70 ER/EO80 blend.

Synthesis and fractionated crystallization of organic-inorganic hybrid composite materials from an amphiphilic polyethylene-block-poly (ethylene oxide) diblock copolymer

Mesostructurally ordered inorganic–organic hybrid composite materials were successfully synthesized by utilizing a low-molecular-weight amphiphilic polyethylene-block-poly(ethylene oxide) (PE–PEO) diblock copolymer as the directing agent. The hybrid composites were formed via the sol–gel reaction of inorganic precursor tetraethoxysilane (TEOS) in an acidic ethanol/water solution with various amounts of PE–PEO. In these composite materials, the hydrophobic PE block of the PE–PEO copolymer forms separate microphase on the nanoscales within the rigid matrix of silica network. The crystallization of the PE block is strictly restricted within the microphase by the rigid silica matrix and takes place through homogeneous nucleation under the nanoscale confinement environment.

Nanostructures and nanoporosity in thermoset epoxy blends with an amphiphilic polyisoprene-block-poly(4-vinyl pyridine) reactive diblock copolymer

Nanostructured thermoset blends were prepared based on a bisphenol A-type epoxy resin and an amphiphilic reactive diblock copolymer, namely polyisoprene-block-poly(4-vinyl pyridine) (PI-P4VP). Infrared spectra revealed that the P4VP block of the diblock copolymer reacted with the epoxy monomer. However, the non-reactive hydrophobic PI block of the diblock copolymer formed a separate microphase on the nanoscale. Ozone treatment was used to create nanoporosity in nanostructured epoxy/PI-P4VP blends via selective removal of the PI microphase and lead to nanoporous epoxy thermosets; disordered nanopores with the average diameter of about 60 nm were uniformly distributed in the blend with 50 wt% PI-P4VP. Multi-scale phase separation with a distinctly different morphology was observed at the air/sample interface due to the interfacial effects, whereas only uniform microphase separated morphology at the nanoscale was found in the bulk of the blend.

The miscibility of poly(d,l-lactide-co-glycolide) with amphiphilic molecules and the interaction of their mixtures with DNA at air/water interface

The miscibility of poly(d,l-lactide-co-glycolide) (PLG) with three amphiphilic molecules and the interaction of the PLG/surfactant mixtures with DNA at air/water interface are investigated by π-A isotherms, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) techniques. The π-A isotherms of the PLG mixtures with cationic C12AzoC6PyBr, and C12AzoC6N(CH3)3Br, are quite different from the π-A isotherm of pure PLG on water subphase. In contrast to the case, the π-A isotherm of PLG mixed with nonionic C12AzoC6OPy is almost identical to the pure PLG except some increasing of molecular area. Similar phenomena are observed on DNA subphase. The in situ BAM and ex situ AFM observations demonstrate that the dispersion of PLG at air/water interface becomes good when it mixes with the two cationic surfactants, whereas quite poor due to the phase separation when it mixes with the nonionic amphiphilic molecule. Based on these results we conclude that the cationic surfactants can affect the conformation change of PLG at air/water interface and figure a well miscibility with polymer whereas the nonionic amphiphilic molecule presents poor miscibility. In addition, the even mixing of the PLG and the cationic surfactants is favorable for the adsorption to DNA more effectively.

Overcoming interfacial affinity issues in natural fiber reinforced polylactide biocomposites by surface adsorption of amphiphilic block copolymers

This work demonstrates that the interfacial properties in a natural fiber reinforced polylactide biocomposite can be tailored through surface adsorption of amphiphilic and biodegradable poly (ethylene glycol)-b-poly-(L-lactide) (PEG-PLLA) block copolymers. The deposition from solvent solution of PEG-PLLA copolymers onto the fibrous substrate induced distinct mechanisms of molecular organization at the cellulosic interface, which are correlated to the hydrophobic/hydrophilic ratios and the type of solvent used. The findings of the study evidenced that the performance of the corresponding biocomposites with polylactide were effectively enhanced by using these copolymers as interfacial coupling agents. During the fabrication stage, diffusion of the polylactide in the melt induced a change in the environment surrounding block copolymers which became hydrophobic. It is proposed that molecular reorganization of the block copolymers at the interface occurred, which favored the interactions with both the hydrophilic fibers and hydrophobic polylactide matrix. The strong interactions such as intra- and intermolecular hydrogen bonds formed across the fiber−matrix interface can be accounted for the enhancement in properties displayed by the biocomposites. Although the results reported here are confined, this concept is unique as it shows that by tuning the amphiphilicity and the type of building blocks, it is possible to control the surface properties of the substrate by self-assembly and disassembly of the amphiphiles for functional materials.

Synthesis and self-assembly of hybrid amphiphilic block copolymers

This thesis focused on the synthesis and self-assembly of novel block copolymers for the purpose of drug delivery. The block copolymers achieved comprise of a synthetic block and a peptide block and self-assemble into nano sized particles which can act as drug containers.

APETALA2/ETHYLENE respnse factor and basic helix-loop-helix tobacco transcription factors cooperatively mediate jasmonate-elicited nicotine biosynthesis.

Transcription factors of the plant-specific apetala2/ethylene response factor (AP2/ERF) family control plant secondary metabolism, often as part of signalling cascades induced by jasmonate (JA) or other elicitors. Here, we functionally characterized the JA-inducible tobacco (Nicotiana tabacum) AP2/ERF factor ORC1, one of the members of the NIC2-locus ERFs that control nicotine biosynthesis and a close homologue of ORCA3, a transcriptional activator of alkaloid biosynthesis in Catharanthus roseus. ORC1 positively regulated the transcription of several structural genes coding for the enzymes involved in nicotine biosynthesis. Accordingly, overexpression of ORC1 was sufficient to stimulate alkaloid biosynthesis in tobacco plants and tree tobacco (Nicotiana glauca) root cultures. In contrast to ORCA3 in C. roseus, which needs only the GCC motif in the promoters of the alkaloid synthesis genes to induce their expression, ORC1 required the presence of both GCC-motif and G-box elements in the promoters of the tobacco nicotine biosynthesis genes for maximum transactivation. Correspondingly, combined application with the JA-inducible Nicotiana basic helix–loop–helix (bHLH) factors that bind the G-box element in these promoters enhanced ORC1 action. Conversely, overaccumulation of JAZ repressor proteins that block bHLH activity reduced ORC1 functionality. Finally, the activity of both ORC1 and bHLH proteins was post-translationally upregulated by a JA-modulated phosphorylation cascade, in which a specific mitogen-activated protein kinase kinase, JA-factor stimulating MAPKK1 (JAM1), was identified. This study highlights the complexity of the molecular machinery involved in the regulation of tobacco alkaloid biosynthesis and provides mechanistic insights about its transcriptional regulators.

RGO/ZnO nanocomposite: an efficient, sustainable, heterogeneous, amphiphilic catalyst for synthesis of 3-substituted indoles in water

A nanocomposite consisting of reduced graphene oxide and zinc oxide nanoparticles (RGO/ZnO) with unique structural features was developed as an efficient, sustainable, amphiphilic, heterogeneous catalyst for the synthesis of various 3-substituted indoles in water. The catalyst was recycled six times without significant loss in catalytic activity. The higher environmental compatibility and sustainability factors such as smaller E-factor and higher atom economy make the present methodology a true green and sustainable process for the synthesis of various biologically important 3-substituted indoles.

Self-assembled multimicellar vesicles via complexation of a rigid conjugated polymer with an amphiphilic block copolymer

A viable method of encapsulating block copolymer micelles inside vesicles using a conjugated polymer is reported in this study. Self-assembly and complexation between an amphiphilic block copolymer poly(methyl methacrylate)-b-poly(acrylic acid) (PMMA-b-PAA) and a rod-like conjugated polymer polyaniline (PANI) in aqueous solution were studied using transmission electron microscopy, atomic force microscopy and dynamic light scattering. The complexation and morphology transformation were driven by electrostatic interaction between PANI and the PAA block of the block copolymer. Addition of PANI to PMMA-b-PAA induced the morphology transformation from micelles to irregular vesicles through vesicles, thick-walled vesicles (TWVs) and multimicellar vesicles (MMVs). Among the observed morphologies, MMVs were observed for the first time. Morphology transformation was studied as a function of aniline/acrylic acid molar ratio ([ANI]/[AA]). Micelles were observed for the pure block copolymer, while vesicles and TWVs were observed at [ANI]/[AA] = 0.1 and 0.3, respectively. MMVs were observed at [ANI]/[AA] = 0.5 and irregular vesicles were observed for molar ratios at 0.7 and above. Clearly, a conjugated polymer like polyaniline can induce a morphology transformation even at its lower concentrations and produce complex morphologies.