Search

Hollow porous silica nanospheres (HSNs) have unveiled as a potential carrier for pesticide delivery. However, HSNs mostly suffer from postsynthesis loading process of pesticides because of the tiny mesopores onto shell. To eradicate this disadvantage, it was hypothesized that developing a large through hole or pore opening on shells (>10 nm) could be effective for the postsynthesis loading of active molecules onto HSNs using a simple immersion method. We synthesized HSNs with a single large through hole or pore opening on shells (15.95 nm) in an earlier study, which was subsequently termed bowl-structured hollow porous silica nanospheres (BHSNs). In this study, the postsynthesis loading of a model pesticide, namely imidacloprid, onto BHSNs was evaluated via the simple immersion method. It was observed that the presence of a single large pore-opening on the shells of BHSNs facilitated loading of imidacloprid to the inner core or void space of BHSNs. Thermogravimetric analysis (TGA) showed that around 16% imidacloprid molecules were loaded to the BHSNs when acetone was used as a dispersing medium. It was evidenced by differences between weight losses patterns of imidacloprid loaded to BHSNs (imi@BHSNs) from pure imidacloprid. Both adsorption and entrapment mechanisms were effective during loading. FTIR analysis showed that pesticide molecules were adsorbed on BHSNs via hydrogen bonding interaction. The controlled releasing profile of imidacloprid from BHSNs was observed in distilled water at room temperature, except an initial burst release of a small amount (<5%). The controlled release composed of a faster sustained release followed by a slower conditional release due to the deposited and adsorbed imidacloprid. The non-Fickian case II transport mechanism prevailed during transportation of imidacloprid to the release media from BHSNs. We anticipate that this study could provide an important avenue for advancing practical applications of BHSNs in pesticide delivery systems. [ABSTRACT FROM AUTHOR]

To circumvent the problem of burst drug release from polymeric micelles, we designed three layered ABC micelles consisting of methoxy poly(ethylene oxide) (PEO) as the shell layer (A block); poly(lactic acid) (PLA) of different stereo-chemistries as the outer core (B block) and poly(α-benzylcarboxylate-ε-caprolactone) (PBCL) or poly(ε-caprolactone) (PCL) as the inner core (C block). The micelles were used to encapsulate a model hydrophobic drug, nimodipine. The effect of PLA (B block) incorporation and stereochemistry on the formation of semi crystalline outer cores in ABC triblock copolymer micelles, micelle stability, drug loading and release was then assessed in comparison to diblock copolymer micelles. The PLA outer core was expected to act as a barrier lowering the rate of drug diffusion out of the micellar carrier owing to a high Flory Huggins interaction parameter between nimodipine and PLA ( χ = 1.35). Introduction of PLA outer cores in ABC block copolymer micelles reduced the burst release of nimodipine from polymeric micelles without jeopardizing its high encapsulation efficiency. In ABC polymeric micelles with stereo-regular PLA blocks; semi-crystalline outer PLA cores were not formed, which was in contrast to PEO–PLA diblock copolymer micelles. Accordingly, PLA stereo-chemistry had no significant effect on drug release in ABC polymeric micelles. In contrast to diblock copolymers, no sign of stereo-complexation in mixed micelles composed of a 50:50 mixture of P d LA and P l LA containing ABC triblock copolymers was observed. The results showed the capability of properly designed ABC triblock copolymer micelles as reservoirs for drug solubilization and depot release at nanoscale dimensions. Statement of Significance Polymeric micelles are core–shell nanostructures that are widely used for drug delivery. Their hydrophobic core accommodates poor water soluble drugs and their hydrophilic shell allows the whole structure to be water soluble. A common problem with the use of polymeric micelles is leakage of the incorporated drug from these carriers. Here we have shown that a properly designed three layered (ABC) block copolymer micelle with drug compatible blocks at the inner core and drug incompatible blocks at the outer core can be used to reduce the initial fast rate of drug release while providing high amount of drug encapsulated in the core. Moreover, changes in the chemical structure of the inner core may be used to modify the stability of these systems. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) with particle size below 10 nm exhibit high catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). However, AuNPs are unstable in aqueous solution or an organic solvent in the absence of a stabilizer and a dispersion agent. In this study, we prepared highly dispersed AuNPs using the ABC triblock copolymer poly(ethylene glycol)– block -linear polyethylenimine– block -poly( ε -caprolactone) (PEG–PEI–PCL) as the stabilizer for the first time. The preparation route is very mild, convenient, and reproducible. The mean diameter of AuNPs is approximately 8 nm with a normal distribution. The as-prepared PEG–PEI–PCL-stabilized AuNPs have high catalytic activity for the reduction of 4-NP by sodium borohydride (NaBH 4 ) in aqueous solution. Compared with AB diblock copolymer PEG–PEI, ABC triblock copolymer PEG–PEI–PCL as the AuNPs stabilizer has significant advantages in stability and catalytic activity. [ABSTRACT FROM AUTHOR]

The morphology and the phase diagram of ABC triblock copolymer thin film directed by polymer brushes are investigated by the self-consistent field theory in three dimensions. The polymer brushes coated on the substrate can be used as a good soft template to tailor the morphology of the block copolymer thin films compared with those on the hard substrates. The polymer brush is identical with the middle block B. By continuously changing the composition of the block copolymer, the phase diagrams are constructed for three cases with the fixed film thickness and the brush density: identical interaction parameters, frustrated and non-frustrated cases. Some ordered complex morphologies are observed: parallel lamellar phase with hexagonally packed pores at surfaces (LAM-HFs), perpendicular lamellar phase with cylinders at the interface (LAM-CI), and perpendicular hexagonally packed cylinders phase with rings at the interface (C-RI). A desired direction (perpendicular or parallel to the coated surfaces) of lamellar phases or cylindrical phases can be obtained by varying the composition and the interactions between different blocks. The phase diagram of ABC triblock copolymer thin film wetted between the polymer brush-coated surfaces is very useful in designing the directed pattern of ABC triblock copolymer thin film. [ABSTRACT FROM AUTHOR]

Abstract: The morphology and the phase diagram of the ABC block copolymer on the polymer-coated substrate were studied by using the self-consistent field theory. Due to the asymmetric surfaces for the block copolymer thin film, the rich hetero-structures occur, which are the combination of two different microstructures, such as perforated lamellar and lamellar phase (PL + L), cylindrical and lamellar phase (C + L). The phase diagrams were constructed for the identical interaction parameters case and the non-frustrated case. The effect of the film thickness is also considered at the fixed grafting density. Comparing the results, we found that the essence of the variation of the grafting density is the change of the effective film thickness in most cases. The relationship between the grafting density and the film thickness is constructed. Our results offer another way to tailor the phase behavior of the block copolymer thin film and obtain the hetero-structures on nanoscale. [ABSTRACT FROM AUTHOR]

Self assemblies of ABC triblock copolymer thin films on a densely brush-coated substrate were investigated by using the self-consistent field theory. The middle block B and the coated polymer form one phase and the alternating phase A and phase C occur when the film is very thin either for the neutral or selective hard surface (which is opposite to the brush-coated substrate). The lamellar phase is stable on the hard surface when it is neutral and interestingly, the short block tends to stay on this hard surface. The rippled structure forms when the cylindrical phase exists near the surface between grafted polymers and ABC block copolymers. Due to the existence of the hydrophilic brush-coated surface serving as a soft surface of the film, the energy fluctuation existing in the film confined by two hard surfaces disappears. The results are helpful for designing the nanopattern of the film and realizing the functional thin film, such as adding the functional short block A to the BC diblock copolymer. [ABSTRACT FROM AUTHOR]

A Monte Carlo simulation using the bond fluctuation and cavity diffusion algorithms was adopted to investigate the micro-phase separation of ABC triblock copolymer in ultra-thin film on simple cubic lattice. Simulations reveal that the morphologies of ABC copolymer films are dependent on not only the volume fraction of the middle block B (fB) but also on the ratio of interaction between different kinds of blocks (ε(AC)/ε(AB)). As for the molecular orientation, the copolymers stretch parallel to the flat surface at lower fB, but tend to align perpendicularly along z direction at higher fB. Furthermore, the chain configuration was discussed in detail. Smaller ε(AC)/ε(AB) is beneficial to the formation of a "loop" configuration, whereas, larger ε(AC)/ε(AB) would result in a "bridge" configuration of ABC triblock copolymer chains. The formation of micro-phase structures was illustrated intuitively by the molecular orientation and the chain configuration. [ABSTRACT FROM AUTHOR]

Abstract: An amphiphilic rod-coil ABC triblock copolymers using rigid oligo(para-phenyleneethynylene) (OPE) as the middle rod segment, poly(ethylene oxide)-block-oligo(para-phenyleneethynylene)-block-polystyrene (PEO-b-OPE-b-PS), was designed and successfully synthesized. In the synthetic route, a kind of macroinitiator, PEO-b-OPE-Br was achieved by stepwise coupling of iodo-terminated poly(ethylene oxide) and oligo(para-phenyleneethynylene) with amino end group, capping with 2-bromopropionyl bromide. Subsequently, from this macroinitiator atom transfer radical polymerization (ATRP) of styrene was performed to obtain PEO-b-OPE-b-PS. The resulting copolymers were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). All these novel copolymers were affirmed to have well-defined structures and narrow molecular weight distributions. [Copyright &y& Elsevier]

The synthesis of ternary semicrystalline poly(a-methylstyrene- b -isobutylene- b -pivalolactone) poly(aMeSt- b -IB- b -PVL) linear triblock copolymers has been accomplished for the first time, taking advantage of living cationic sequential block copolymerization and site-transformation technique from living cationic to anionic ring-opening polymerization (AROP). Poly(aMeSt- b -IB) diblock copolymer with ?-methoxycarbonyl group was successfully prepared by sequential addition of IB to living PaMeSt chain ends modified with p -chloro-a-methylstyrene, followed by capping with 1,1-diphenylethylene and in-situ quenching with 1-methoxy-1-trimethylsiloxy-propene. The poly(aMeSt- b -IB) diblock macroinitiator, prepared by subsequent hydrolysis of ?-methoxycarbonyl group, initiated AROP of PVL in conjunction with 18-crown-6 in THF at 60°C. Characterization by 1 H NMR spectroscopy and DSC confirmed that poly(aMeSt- b -IB- b -PVL) copolymers consisted of three microphases, low glass transition (T g ?=?-66°C) rubbery PIB, amorphous glassy PaMeSt, and high melting (T m ?=?232~235°C) PPVL with 72~92% of crystallinity normalized for the content of PPVL. [ABSTRACT FROM AUTHOR]

The self-assembly of asymmetric ABC triblock copolymers in the ordered structure is investigated using an isothermal-isobaric molecular dynamics simulation. Unlike symmetric ABC triblock copolymers, more fascinating morphologies are observed in asymmetric ones because of a larger difference of incompatibility between the components. Various modes of self-assembly in assymmetric ABC triblock copolymers are also observed depending on the block composition. When the composition of block A is changed from 0.125 to 0.25 at the same f B =0.25, the morphological transition from the “cylinder in cylinder” to “cylinders at cylinder” structure is observed in the simulation. In the case of ABC triblocks with f B =0.5, a lamellar-type structure is changed to a cylinder-type structure with increasing the length of block A. When the mid-block length increases further to f B =0.625, the “spheres on cylinder” structure is observed in both the A10B50C20 and A20B50C10 triblocks. From these results, the phase diagram of ABC triblock copolymers can be constructed. [ABSTRACT FROM AUTHOR]

The effect of block sequence on the self-assembly of ABC-type triblock copolymers in the ordered state is investigated using an isothermal-isobaric molecular dynamics simulation. The block sequence has an important effect on the morphology of ABC triblock copolymers. Different morphologies are observed depending on the block sequence as well as the block composition. The triblock copolymers with the volume fraction of 1:1:1 ( f A= f B= f C=0.33) show the three phase and four layered lamellar structures irrespective of the block sequence. The A32B16C32 triblock copolymer with f B=0.2 shows a morphology in which cylinders of midblock B are formed at the interface between A and C lamellae, whereas the morphology of triblock copolymer B16C32A32 and C32A32B16 show a cylindrical core-shell structure and a lamellar type morphology, respectively. The A20B40C20 triblock copolymer with the block B as a major component shows a tricontinuous structure, whereas both B40C20A20 and C20A20B40 triblock copolymers exhibit the lamellar structures. When the block B has larger volume fraction with f B=0.75, the matrix is composed of block B, and other two blocks A and C form spherical domains. [ABSTRACT FROM AUTHOR]