Presence Of Diblock Copolymer Research Articles

Physicochemical properties of L-alpha dipalmitoyl phosphatidylcholine large unilamellar vesicles: Effect of hydrophobic block (PLA/PCL) of amphipathic diblock copolymers

In the present work, we show how amphipathic diblock copolymers affect the physicochemical properties of the lipid bilayer of DPPC liposome. Diblock copolymers proposed for this study are focused in the difference between PLA and PCL hydrophobic block, because PLA and PCL differ in their glass transition temperature, where a higher ratio of PLA, lowers the flexibility of the diblock copolymer. On the contrary, a greater proportion of PCL makes the diblock copolymer more flexible. This flexibility difference between hydrophobic block would affect the physicochemical properties of lipid bilayer of DPPC. The difference of rigidity or flexibility of hydrophobic block and their interaction with DPPC large unilamellar vesicles (LUVs) was evaluated at low and high copolymers concentration. The copolymer concentrations used were chosen based on their respective cmc. We measure (a) Thermotropic behavior from GP of Laurdan and fluorescence anisotropy of DPH; (b) Relation between wavelength excitation and generalized polarization of Laurdan; (c) Time-resolved fluorescence anisotropy of DPH; (d) Water outflow through the lipid bilayer and (e) calcein release from DPPC LUVs. Furthermore, large unilamellar vesicles in the absence and in the presence of different copolymers were characterized by size and zeta-potential. The results show that the diblock copolymer at high PLA/PCL ratio, that is, greater rigidity of hydrophobic block produces an increase of the phase transition temperature (Tm). For DPPC LUVs, Tm increase 3.5 °C at low and about 4.5 °C at high copolymers concentration, sensed by Laurdan and DPH fluorescent probes, although the DPPC/copolymers molar ratio for Cop4 is higher than Cop3, Cop2 and Cop1. In addition, we observed a decrease in the polarity of microenvironments in the bilayer and an increase in the order of the acyl chains in the bilayer to a high proportion of PLA. Furthermore, the presence of diblock copolymer with high proportion of PLA, decreases water outflow from DPPC liposome and water efflux is slower; leading to a decrease in calcein release from DPPC liposomes. Our results clearly show that the greater the stiffness of the hydrophobic block, greater degree of packaging of the lipid bilayer, greater the order of the acyl chains, and greater retention of water and calcein inside the liposome. Therefore, the presence of AB-type diblock copolymers with a more rigid hydrophobic block, stabilizes the lipid bilayer and would allow a more controlled release of water, and encapsulated molecules inside of the DPPC liposome.

Barium sulfate crystallization dependence on upper rim calix[4]arene functional groups

Although the effects of p-sulfonated and p-phosphonated calix[4]arene on barium sulfate morphology are similar, their ability to form mesocrystals of material are markedly different. The p-phosphonated calix[4]arene results in the formation of fibre bundles similar to those previously observed during barium sulfate crystallization in the presence of di-block copolymers. The isostructural sulfonated calix[4]arene, however, affords material consistent with the initial formation of mesocrystals which subsequently fuse. This material shows significant beam damage when viewed under a transmission electron microscope (TEM) suggesting incorporation of the sulfonated calix[4]arene, although there was no evidence of this from X-ray diffraction and atomic force microscopy (AFM) studies. We hypothesise that this calixarene is incorporated without significant change in structure of the material, and that the interaction of the macrocycle with the barium sulfate lattice is sufficiently weak that surface AFM imaging is effective in removing it from the surface.

Superparamagnetic Hybrid Micelles, Based on Iron Oxide Nanoparticles and Well-Defined Diblock Copolymers Possessing β-Ketoester Functionalities

The quality of surface coating of magnetic nanoparticles destined as nanoprobes in clinical applications is of utmost significance for their colloidal stability and biocompatibility. A novel approach for the fabrication of such a coating involves the synthesis of well-defined diblock copolymers based on 2-(acetoacetoxy)ethyl methacrylate (chelating) and poly(ethylene glycol)methyl ether methacrylate (water-soluble, thermoresponsive), prepared by reversible addition-fragmentation chain transfer polymerization. Fabrication of magneto-responsive micelles was accomplished via chemical coprecipitation of Fe(III)/Fe(II) in the presence of diblock copolymers. Further to the characterization of micellar morphologies, optical and thermal properties, assessment of magnetic characteristics disclosed superparamagnetic behavior. The hybrid micelles did not compromise cell viability in cultures, while in vitro uptake by macrophage cells was significantly lower in comparison to that of the clinically applicable contrast agent Resovist, suggesting that these systems can evade rapid uptake by the reticuloendothelial system and be useful agents for in vivo applications.

Dynamic Monte Carlo simulation of aggregation of nanoparticles in the presence of diblock copolymer

The aggregation of hydrophobic nanoparticles in the presence of diblock copolymers is investigated using dynamic Monte Carlo simulation on a simple cubic lattice. One nanoparticle occupies one lattice site, one block copolymer (A m B m ) occupies 2 m sequentially linked sites with m segments of A and m segments of B, and solvents are represented by any unoccupied sites. All of them are self-avoiding and nearest-neighbor interactions are considered. A compact big aggregate, dispersed aggregates wrapped by polymer chains, and an ordered lamellar structure are obtained by varying the concentration of copolymer. The structures are seen to be controlled by competing forces between the interaction of copolymer with nanoparticles and the self-assembly of copolymer in solution. The critical concentration of copolymer needed to form the lamellar structure, C p , L , decreases with the chain length. It is also found that C p , L decreases roughly linearly with the concentration of nanoparticles C n , which can be approximately expressed as C p,L = 0.764 – 0.857 C n when m = 2 . The simulation demonstrates that addition of diblock copolymer can effectively control the aggregation of nanoparticles and lead to the formation of a variety of nanostructures.

An Interfacial Curvature Map for Homopolymer Interfaces in the Presence of Diblock Copolymers

An Interfacial Curvature Map for Homopolymer Interfaces in the Presence of Diblock Copolymers

Suppression of Lateral Phase Separation in Thin Polyolefin Blend Films

The effectiveness of a compatibilizer in suppressing lateral phase separation in thin polyolefin blend films is investigated as a function of film thickness and temperature. Neutron and X-ray reflectivity measurements were made on spun-cast thin blend films of partially deuterated and hydrogenated polyolefin blends with and without diblock compatibilizer. We use an extended silicon surface passivating treatment. Under these biased symmetric wetting conditions (air vs hydrophobic Si), binary blend films are stabilized against both dewetting from the substrate and roughening of the surface due to phase separation when the film thickness (25 nm) is on the order of the molecular radius of gyration. However, thicker (100 nm) films exhibit lateral phase separation that can be suppressed by the addition of block copolymer compatibilizer. This stabilization effect can be attributed to the reduction of interfacial tension leading to a broadening of interfaces, and additionally, the presence of diblock copolymer in both phases alters their surface interactions. On longer time scales, optical micrographs show the development of large-scale features over the course of a year in the molecularly thin blend films and in the ternary thin film (stored under vacuum). A droplet morphology is observed for molecularly thin blend films, and an interconnected domain structure characteristic of the early and intermediate stages of phase separation is observed for the ternary thin blend film. The phase separated structure obtained for the binary thin blend film does not evolve with time. Our results indicate that one also needs to account for kinetics in order to develop a comprehensive understanding of the structure of thin blend films. In general, temperature has a weak effect on the profile development of compatibilized blend films.

Elastic properties of homopolymer-homopolymer interfaces containing diblock copolymers

We study the elastic properties of homopolymer/homopolymer interfaces containing diblock copolymers by means of a theory of Gaussian fluctuations. The interfacial tension and the bending rigidity of the interface in the two-phase coexistence region are calculated from the power spectrum of capillary modes. Our theory shows that in the limiting case of a pure binary homopolymer mixture, while the interfacial tension increases monotonically with increasing χN (where χ is the Flory-Huggins parameter and N is the homopolymer molecular weight) the bending rigidity does not. The bending rigidity increases rapidly at first for small values of χN, but then decreases with further increase of χN. In the presence of diblock copolymers, the interfacial tension always decreases with increasing diblock copolymer volume fraction at a given χN. However, the bending rigidity can show either a decrease or an increase depending on χN and the ratio γ between the molecular weights of a diblock copolymer and that of a homopolymer. Our results for the surface pressure and the bending rigidity are further compared with results based on scaling arguments of wet polymer brushes.