Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Template Synthesis and Micellization of Block Copolymers with Interacting Blocks  [cached]
Permyakova N.M.,Zheltonozhskaya T.B.,Klymchuk D.O.,Poliyan M.Ya.
Proceedings of the International Conference Nanomaterials : Applications and Properties , 2013,
Abstract: It is known that А-В and А-В-А block copolymers with interacting blocks are related to the class of intramolecular polycomplexes. Such block copolymers form a stable micellar structures in dilute aqueous solutions due to hydrophobic interactions between non-polar bound segments of the blocks. Given micellar structures have attracted a considerable attention due to their possible applications as different templates, drug delivery systems, nanoreactors. Here we presented peculiarities of a template synthesis of the block copolymers consisting interacting poly(ethylene oxide) and poly(acrylic acid) blocks and also its self-assembly to micelles in acidic aqueous solutions, which was confirmed by Transmission Electron Microscopy (TEM).
Chain Diffusion in Lamellar Block Copolymers  [PDF]
Michael Murat,Gary S. Grest,Kurt Kremer
Physics , 1997,
Abstract: Diffusion of symmetric diblock copolymer chains in macroscopically oriented lamellar block copolymers are studied in a molecular dynamics simulation. Results for diffusion constant both parallel $D_\parallel$ and perpendicular $D_\perp$ to the lamellar planes are compared to results in the disordered one phase region. For diblocks of length N=40 (1.1 N_e) and $100 (3N_e)$, where $N_e$ is the entanglement length of a homopolymer melt at the same density, $D_\parallel$ is nearly independent of $\chi$, while $D_\perp$ is strongly suppressed as $\chi$ is increased. These results are in agreement with theoretical predictions based on the Rouse model. The isotropic diffusion constant of quenched disordered systems is approximated fairly well by $(2D_\parallel+D_\perp)/3$ of the corresponding lamellar system.
Soft particle model for block copolymers  [PDF]
F. Eurich,A. Karatchentsev,J. Baschnagel,W. Dieterich,P. Maass
Physics , 2007, DOI: 10.1063/1.2787007
Abstract: A soft particle model for diblock (AB) copolymer melts is proposed. Each molecule is mapped onto two soft spheres built by Gaussian A- and B-monomer distributions. An approximate analytical expression for the joint distribution function for the distance between both spheres and their radii of gyration is derived, which determines the entropic contribution to the intramolecular free energy. Adding a mean-field expression for the intermolecular interactions, we obtain the total free energy of the system. Based on this free energy, Monte Carlo simulations are carried out to study the kinetics of microphase ordering in the bulk and its effect on molecular diffusion. This is followed by an analysis of thin films with emphasis on pattern transfer from walls with a periodic structure. It is shown that the level of coarse graining in the soft particle model is suitable to describe structural and kinetic properties of copolymers on mesoscopic scales.
Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents  [PDF]
Galder Cristobal,Jean-Francois Berret,Cedrick Chevallier,Ruela Talingting-Pabalan,Mathieu Joanicot,Isabelle Grillo
Physics , 2008, DOI: 10.1021/ma702249w
Abstract: We have studied the phase behavior of the poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible solvents, water and tetrahydrofuran (THF). The techniques used to examine the different polymers, structures and phases formed in mixed solvents were static and dynamic light scattering, small-angle neutron scattering, nuclear magnetic resonance and fluorescence microscopy. By lowering the water/THF mixing ratio X, the sequence unimers, micron-sized droplets, polymeric micelles was observed. The transition between unimers and the micron-sized droplets occurred at X = 0.75, whereas the microstructuration into core-shell polymeric micelles was effective below X = 0.4. At intermediate mixing ratios, a coexistence between the micron-sized droplets and the polymeric micelles was observed. Combining the different aforementioned techniques, it was concluded that the droplet dispersion resulted from a solvent partitioning that was induced by the hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the droplets were rich in THF and concentrated in copolymers and that they were stabilized by the hydrophilic poly(acrylic acid) moieties.
Multifunctional nanoassemblies of block copolymers for future cancer therapy  [cached]
Horacio Cabral and Kazunori Kataoka
Science and Technology of Advanced Materials , 2010,
Abstract: Nanoassemblies from amphiphilic block copolymers are promising nanomedicine platforms for cancer diagnosis and therapy due to their relatively small size, high loading capacity of drugs, controlled drug release, in vivo stability and prolonged blood circulation. Recent clinical trials with self-assembled polymeric micelles incorporating anticancer drugs have shown improved antitumor activity and decreased side effects encouraging the further development of nanoassemblies for drug delivery. This review summarizes recent approaches considering stimuli-responsive, multifunctionality and more advanced architectures, such as vesicles or worm-like micelles, for tumor-specific drug and gene delivery.
Orienting Ion-Containing Block Copolymers Using AC Electric Field  [PDF]
Y. Tsori,F. Tournilhac,L. Leibler
Physics , 2003, DOI: 10.1021/ma034026x
Abstract: We consider orientation mechanisms for block copolymers in an electric field. Theoretical and experimental studies have shown that nonuniformity of the dielectric constant gives rise to a preferred orientation of the melt with respect to the applied field. We show that the presence of ions, as found in anionically prepared copolymers, may increase the alignment effect markedly. Time-varying (ac) and static (dc) fields are considered within a unified framework. We find that orientation of block copolymers can in principle be achieved without a dielectric contrast if there is a mobility contrast. The presence of ions is especially important at small field frequencies, as is in most experiments. Unlike the no-ions case, it is found that orienting forces depend on the polymer chain lengths. The mobile-ions mechanism suggested here can be used to reduce the magnitude of orienting fields as well as to discriminate between block copolymers of different lengths.
Interfacial Phenomena of Solvent-diluted Block Copolymers  [PDF]
Shai Cohen,David Andelman
Physics , 2013, DOI: 10.1021/ma401479f
Abstract: A phenomenological mean-field theory is used to investigate the properties of solvent-diluted di-block copolymers (BCP), in which the two BCP components (A and B) form a variety of phases that are diluted by a solvent (S). Using this approach, we model mixtures of di-block copolymers and a solvent and obtained the corresponding critical behavior. In the low solvent limit, we find how the critical point depends on the solvent density. Due to the non-linear nature of the coupling between the A/B and BCP/solvent concentrations, the A/B modulation induces modulations in the polymer-solvent relative concentration with a double wavenumber. The free boundary separating the polymer-rich phase from the solvent-rich one is studied in two situations. First, we show how the presence of a chemically patterned substrate leads to deformations of the BCP film/solvent interface, creation of terraces in lamellar BCP film and even formation of multi-domain droplets as induced by the patterned substrate. Our results are in agreement with previous self-consistent field theory calculations. Second, we compare the surface tension between parallel lamellae coexisting with a solvent phase with that of a perpendicular one, and show that the surface tension has a non-monotonic dependence on temperature. The anisotropic surface tension can lead to deformation of spherical BCP droplets into lens-shaped ones, together with re-orientation of the lamellae inside the droplet during the polymer/solvent phase separation process in agreement with experiment.
Photo-Induced Micellization of Block Copolymers  [PDF]
Eri Yoshida,Satoshi Kuwayama
Polymers , 2010, DOI: 10.3390/polym2040623
Abstract: We found novel photo-induced micellizations through photolysis, photoelectron transfer, and photo-Claisen rearrangement. The photolysis-induced micellization was attained using poly(4- tert-butoxystyrene)- block-polystyrene diblock copolymer (PBSt- b-PSt). BSt- b-PSt showed no self-assembly in dichloromethane and existed as isolated copolymers. Dynamic light scattering demonstrated that the copolymer produced spherical micelles in this solvent due to irradiation with a high-pressure mercury lamp in the presence of photo-acid generators, such as bis(alkylphenyl)iodonium hexafluorophosphate, diphenyliodonium hexafluorophosphate, and triphenylsulfonium triflate. The 1H NMR analysis confirmed that PBSt- b-PSt was converted into poly(4-vinylphenol)- block-PSt by the irradiation, resulting in self-assembly into micelles. The irradiation in the presence of the photo-acid generator also induced the micellization of poly(4-pyridinemethoxymethylstyrene)- block-polystyrene diblock copolymer (PPySt- b-PSt). Micellization occurred by electron transfer from the pyridine to the photo-acid generator in their excited states and provided monodispersed spherical micelles with cores of PPySt blocks. Further, the photo-Claisen rearrangement caused the micellization of poly(4-allyloxystyrene)- block-polystyrene diblock copolymer (PASt- b-PSt). Micellization was promoted in cyclohexane at room temperature without a catalyst. During micellization, the elimination of the allyl groups competitively occurred along with the photorearrangement of the 4-allyloxystyrene units into the 3-allyl-4-hydroxystyrene units.
Thermodynamics of Surfactants, Block Copolymers and Their Mixtures in Water: The Role of the Isothermal Calorimetry  [PDF]
Rosario De Lisi,Stefania Milioto,Nicola Muratore
International Journal of Molecular Sciences , 2009, DOI: 10.3390/ijms10072873
Abstract: The thermodynamics of conventional surfactants, block copolymers and their mixtures in water was described to the light of the enthalpy function. The two methodologies, i.e. the van’t Hoff approach and the isothermal calorimetry, used to determine the enthalpy of micellization of pure surfactants and block copolymers were described. The van’t Hoff method was critically discussed. The aqueous copolymer+surfactant mixtures were analyzed by means of the isothermal titration calorimetry and the enthalpy of transfer of the copolymer from the water to the aqueous surfactant solutions. Thermodynamic models were presented to show the procedure to extract straightforward molecular insights from the bulk properties.
Design and Application of Nanoscale Actuators Using Block-Copolymers  [PDF]
Joshua M. G. Swann,Paul D. Topham
Polymers , 2010, DOI: 10.3390/polym2040454
Abstract: Block copolymers are versatile designer macromolecules where a “ bottom-up” approach can be used to create tailored materials with unique properties. These simple building blocks allow us to create actuators that convert energy from a variety of sources (such as chemical, electrical and heat) into mechanical energy. In this review we will discuss the advantages and potential pitfalls of using block copolymers to create actuators, putting emphasis on the ways in which these materials can be synthesised and processed. Particular attention will be given to the theoretical background of microphase separation and how the phase diagram can be used during the design process of actuators. Different types of actuation will be discussed throughout.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.