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Investigation by Combined Solid-State NMR and SAXS Methods of the Morphology and Domain Size in Polystyrene-b-Polyethylene Oxide-b-Polystyrene Triblock Copolymers

BONK, Fabio A.; CALDARELLI, Stefano; PHAN, Trang; BERTIN, Denis; AZEVÊDO, Eduardo Ribeiro de; MANTOVANI, Gerson Luiz; BONAGAMBA, Tito José; PLIVELIC, Tomas S.; TORRIANI, Iris L.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
744.94266%
The microphase structure of a series of polystyrene-b-polyethylene oxide-b-polystyrene (SEOS) triblock copolymers with different compositions and molecular weights has been studied by solid-state NMR, DSC, wide and small angle X-ray scattering (WAXS and SAXS). WAXS and DSC measurements were used to detect the presence of crystalline domains of polyethyleneoxide (PEO) blocks at room temperature as a function of the copolymer chemical composition. Furthermore, DSC experiments allowed the determination of the melting temperatures of the crystalline part of the PEO blocks. SAXS measurements, performed above and below the melting temperature of the PEO blocks, revealed the formation of periodic structures, but the absence or the weakness of high order reflections peaks did not allow a clear assessment of the morphological structure of the copolymers. This information was inferred by combining the results obtained by SAXS and (1)H NMR spin diffusion experiments, which also provided an estimation of the size of the dispersed phases of the nanostructured copolymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48:55-64,2010; Region Provence Alpes Cote d`Azur (PACA) - France; Region Provence Alpes Cote d`Azur (PACA) - France; ARKEMA; ARKEMA; ARCUS PACA-Bresil; ARCUS PACA-Bresil; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP

Investigation by Combined Solid-State NMR and SAXS Methods of the Morphology and Domain Size in Polystyrene-b-Polyethylene Oxide-b-Polystyrene Triblock Copolymers

BONK, Fabio A.; CALDARELLI, Stefano; PHAN, Trang; BERTIN, Denis; DEAZEVEDO, Eduardo R.; MANTOVANI, Gerson Luiz; BONAGAMBA, Tito J.; PLIVELIC, Tomas S.; TORRIANI, Iris L.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
741.9204%
The microphase structure of a series of polystyrene-b-polyethylene oxide-b-polystyrene (SEOS) triblock copolymers with different compositions and molecular weights has been studied by solid-state NMR, DSC, wide and small angle X-ray scattering (WAXS and SAXS). WAXS and DSC measurements were used to detect the presence of crystalline domains of polyethyleneoxide (PEO) blocks at room temperature as a function of the copolymer chemical composition. Furthermore, DSC experiments allowed the determination of the melting temperatures of the crystalline part of the PEO blocks. SAXS measurements, performed above and below the melting temperature of the PEO blocks, revealed the formation of periodic structures, but the absence or the weakness of high order reflections peaks did not allow a clear assessment of the morphological structure of the copolymers. This information was inferred by combining the results obtained by SAXS and (1)H NMR spin diffusion experiments, which also provided an estimation of the size of the dispersed phases of the nanostructured copolymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48:55-64,2010; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of PEO-PPO-PEO Triblock Copolymers on Phospholipid Membrane Integrity under Osmotic Stress

Wang, Jia-Yu; Chin, Jaemin; Marks, Jeremy D.; Lee, Ka Yee C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 03/08/2010 EN
Relevância na Pesquisa
545.9165%
The effects of PEO-PPO-PEO triblock copolymers, mainly Poloxamer 188, on phospholipid membrane integrity under osmotic gradients were explored using giant unilamellar vesicles (GUVs). Fluorescence leakage assays showed two opposing effects of P188 on the structural integrity of GUVs depending on the duration of their incubation time. A two-state transition mechanism of interaction between the triblock copolymers and the phospholipid membrane is proposed: an adsorption (I) and an insertion (II) state. While the triblock copolymer in state I acts to moderately retard the leakage, their insertion in state II perturbs the lipid packing, thus increasing the membrane permeability. Our results suggest that the biomedical application of PEO-PPO-PEO triblock copolymers, either as cell membrane resealing agents or as accelerators for drug delivery, is directed by the delicate balance between these two states.

Dynamic Cylindrical Assembly of Triblock Copolymers by a Hierarchical Process of Covalent and Supramolecular Interactions

Li, Zhou; Ma, Jun; Lee, Nam S.; Wooley, Karen L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
542.1433%
We have developed a hierarchical process that combines linear triblock copolymers into concentric globular sub-units through strong chemical bonds and is followed by their supramolecular assembly via weak non-covalent interactions to afford one-dimensionally-assembled, dynamic cylindrical nanostructures. The molecular brush architecture forces triblock copolymers to adopt some intramolecular interactions within confined frameworks and then drives their intermolecular interactions in the mixtures of organic solvent and water. In contrast, the triblock copolymers, when not pre-connected into the molecular brush architectures, organize only into globular assemblies.

Biodegradable Nanoparticles of mPEG-PLGA-PLL Triblock Copolymers as Novel Non-Viral Vectors for Improving siRNA Delivery and Gene Silencing

Du, Jing; Sun, Ying; Shi, Qiu-Sheng; Liu, Pei-Feng; Zhu, Ming-Jie; Wang, Chun-Hui; Du, Lian-Fang; Duan, You-Rong
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 04/01/2012 EN
Relevância na Pesquisa
531.9902%
Degradation of mRNA by RNA interference is one of the most powerful and specific mechanisms for gene silencing. However, insufficient cellular uptake and poor stability have limited its usefulness. Here, we report efficient delivery of siRNA via the use of biodegradable nanoparticles (NPs) made from monomethoxypoly(ethylene glycol)-poly(lactic-co-glycolic acid)-poly-l-lysine (mPEG-PLGA-PLL) triblock copolymers. Various physicochemical properties of mPEG-PLGA-PLL NPs, including morphology, size, surface charge, siRNA encapsulation efficiency, and in vitro release profile of siRNA from NPs, were characterized by scanning electron microscope, particle size and zeta potential analyzer, and high performance liquid chromatography. The levels of siRNA uptake and targeted gene inhibition were detected in human lung cancer SPC-A1-GFP cells stably expressing green fluorescent protein. Examination of the cultured SPC-A1-GFP cells with fluorescent microscope and flow cytometry showed NPs loading Cy3-labeled siRNA had much higher intracellular siRNA delivery efficiencies than siRNA alone and Lipofectamine-siRNA complexes. The gene silencing efficiency of mPEG-PLGA-PLL NPs was higher than that of commercially available transfecting agent Lipofectamine while showing no cytotoxicity. Thus...

Multifunctional triblock copolymers for intracellular messenger RNA delivery

Cheng, C.; Convertine, A.J.; Stayton, P.S.; Bryers, J.D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
531.9902%
Messenger RNA (mRNA) is a promising alternative to plasmid DNA (pDNA) for gene vaccination applications, but safe and effective delivery systems are rare. Reversible addition-fragmentation chain transfer (RAFT) polymerization was employed to synthesize a series of triblock copolymers designed to enhance the intracellular delivery of mRNA. These materials are composed of a cationic dimethylaminoethyl methacrylate (DMAEMA) segment to mediate mRNA condensation, a hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) segment to enhance stability and biocompatibility, and a pH-responsive endosomolytic copolymer of diethylaminoethyl methacrylate (DEAEMA) and butyl methacrylate (BMA) designed to facilitate cytosolic entry. The blocking order and PEGMA segment length were systematically varied to investigate the effect of different polymer architectures on mRNA delivery efficacy. These polymers were monodisperse, exhibited pH-dependent hemolytic activity, and condensed mRNA into 86–216 nm particles. mRNA polyplexes formed from polymers with the PEGMA segment in the center of the polymer chain displayed the greatest stability to heparin displacement and were associated with the highest transfection efficiencies in two immune cell lines...

Design and Synthesis of Network-Forming Triblock Copolymers Using Tapered Block Interfaces

Kuan, Wei-Fan; Roy, Raghunath; Rong, Lixia; Hsiao, Benjamin S.; Epps, Thomas H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 03/04/2012 EN
Relevância na Pesquisa
537.5601%
We report a strategy for generating novel dual-tapered poly(isoprene-b-isoprene/styrene-b-styrene-b-styrene/methyl methacrylate-b-methyl methacrylate) [P(I-IS-S-SM-M)] triblock copolymers that combines anionic polymerization, atom transfer radical polymerization (ATRP), and Huisgen 1,3-dipolar cycloaddition click chemistry. The tapered interfaces between blocks were synthesized via a semi-batch feed using programmable syringe pumps. This strategy allows us to manipulate the transition region between copolymer blocks in triblock copolymers providing control over the interfacial interactions in our nanoscale phase-separated materials independent of molecular weight and block constituents. Additionally, we show the ability to retain a desirous and complex multiply-continuous network structure (alternating gyroid) in our dual-tapered triblock material.

Nature of Interactions between PEO-PPO-PEO Triblock Copolymers and Lipid Membranes: (I) The Effect of Polymer Hydrophobicity on Its Ability to Protect Liposomes from Peroxidation

Wang, Jia-Yu; Marks, Jeremy; Lee, Ka Yee C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
527.52227%
PEO-PPO-PEO triblock copolymers have opposing effects on lipid membrane integrity- they can behave either as membrane sealants or as membrane permeabilizers. To gain insights into their biomembrane activities, the fundamental interactions between a series of PEO-based polymers and phospholipid vesicles were investigated. Specifically, the effect of copolymer hydrophobicity on its ability to prevent liposomes from peroxidation was evaluated, and partitioning free energy and coefficient involved in the interactions were derived. Our results show that the high degree of hydrophilicity is a key feature of the copolymers that can effectively protect liposomes from peroxidation and the protective effect of the copolymers stems from their adsorption at the membrane surface without penetrating into the bilayer core. The origin of this protective effect induced by polymer absorption is attributed to the retardation of membrane hydration dynamics, which is further illustrated in the accompany study on dynamic nuclear polarization (DNP)-derived hydration dynamics1.

pH-triggered self-assembly of biocompatible histamine-functionalized triblock copolymers†

Lundberg, Pontus; Lynd, Nathaniel A.; Zhang, Yuning; Zeng, Xianghui; Krogstad, Daniel V.; Paffen, Tim; Malkoch, Michael; Nyström, Andreas M.; Hawker, Craig J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
531.9902%
Histamine functionalized poly(allyl glycidyl ether)-b-poly(ethylene glycol)-b-poly(allyl glycidyl ether) (PAGE-PEO-PAGE) triblock copolymers represent a new class of physically cross-linked, pH-responsive hydrogels with significant potential for biomedical applications. These telechelic triblock copolymers exhibited abrupt and reversible hydrogelation above pH 7.0 due to a hudrophilic/hydrophobic transition of the histamine units to form a network of hydrophobic domains bridged by a hydrophilic PEO matrix. These hydrophobic domains displayed improved ordering upon increasing pH and self-assembled into a body centered cubic lattice at pH 8.0, while at lower concentrations formed well-defined micelles. Significantly, all materials were found to be non-toxic when evaluated on three different cell lines and suggests a range of medical and biomedical applications.

Probing the Association of Triblock Copolymers with Supported Lipid Membranes using Microcantilevers

Wang, Jinghui; Segatori, Laura; Biswal, Sibani Lisa
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
555.684%
Pluronics are a class of amphiphilic triblock copolymers that are known to interact with cellular membranes in interesting ways. The solubility of these triblock copolymers in free lipid membranes can be altered with temperature, allowing the possibility of tuning their membrane insertion. However, for supported lipid membranes, the asymmetric local environment and the strong influence of the solid support can alter the solubility of these triblock copolymers in lipid membranes. Here, we probe the interactions of these copolymers with supported lipid membranes using microcantilevers and fluorescence recovery after photobleaching (FRAP) measurements. We measure the solubility and interactions of triblock copolymers (F68 and F98) in supported lipid bilayers as a function of temperature and the length of the copolymer lipophilic block. A Langmuir isotherm model and a free mean area theory are applied to describe the polymer-lipid interactions at the microcantilever surface, determine association constants, and analyze the effect of triblock copolymers on lateral lipid diffusion.

Self-assembly of triblock copolymers in aqueous solution

Urbano, Bruno; Silva, Patricio; Olea, Andrés F.; Fuentes, Irma; Martínez, Francisco
Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
EN
Relevância na Pesquisa
741.9204%
Indexación: Scielo; The aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quatemization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quatemization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quatemization degree. The presence of aggregates was confirmed by transmission electronic microscopy.

Self-assembly of triblock copolymers in aqueous solution; Self-assembly of triblock copolymers in aqueous solution

Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
Relevância na Pesquisa
749.1857%
Resumen: The aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quatemization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quatemization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quatemization degree. The presence of aggregates was confirmed by transmission electronic microscopy.

Polymolecular and Unimolecular Micelles of Triblock Copolymers

GAO, YANG
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
649.02117%
Reported in this thesis are the studies of micellar aggregates of four triblock copolymers and the unimolecular micelles of a triblock copolymer. The micelles were prepared from BCF and ACF copolymers. Here A, B, C, and F denote poly(acrylic acid), poly(tert-butyl acrylate), poly(2-cinnamoyloxylethyl methacrylate), and the liquid crystalline poly(perfluorooctylethyl methacrylate) block, respectively. At room temperature (21 oC) in solvents that were selective for the A or B blocks, three of the four copolymers formed exclusively cylindrical micelles regardless of their block ratios. Cylindrical micelles were formed because their geometries best accommodated the mesogen-ordering requirement of the core-forming F block, as supported by the results from wide angle X-ray scattering and differential scanning calorimetric studies. Mesogen-driven cylinder formation was further supported by the observation of ridges formed by collapsed coronal chains on the surfaces of dried cylinders. We also observed a morphological transformation from other micellar morphologies to cylindrical micelles at 70 oC, which is near the isotropic-to-smectic A phase transition temperature for the F blocks. This inter-conversion between the vesicular and cylindrical micelles of an ACF sample could be reversed repeatly by temperature cycling. These results provided additional evidence for the mesogen-driven micellization hypothesis. Unimolecular micelles were prepared from CDC triblock copolymers...

Helices and Hamburgers from the Assembly of Linear ABC Triblock Copolymers in Block-Selective Solvents

Dupont, John
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
524.54254%
This Ph.D. thesis reports the discovery and study of several morphologies of ABC triblock copolymer assemblies in block selective solvents. One block copolymer self-assembled into helices (mostly double and some triple helices), and the other block copolymer formed a mixture of structures resembling hamburgers and striped cylinders. The helices, biomimmetic structures which are unusual from block copolymer self assembly, were prepared from the triblock copolymer poly(n-butyl methacrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(tert-butyl acrylate) (PBMA-b-PCEMA-b-PtBA). They were formed spontaneously in several binary solvent mixtures including dichloromethane/methanol, tetrahydrofuran (THF)/methanol, and chloroform/methanol. They were formed in the composition ranges where the mixtures were good for the PtBA block, poor for the PCEMA block, and marginal for the PBMA block. The structure was studied and established by TEM, AFM, DLS and 1H NMR and by TEM tomography. The mechanism and kinetics of helix formation was examined. The Hamburger and striped cylinder structures were produced from poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(succinated glyceryl monomethacrylate) or (PtBA-b-PCEMA-b-PSGMA) in mixtures of THF...

Synthesis and characterization of hafnium and molybdenum bifunctional initiators for the preparation of triblock copolymers

Gabert, Andrea Jennifer
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 202 p.
ENG
Relevância na Pesquisa
563.0467%
Chapter 1. Three monofunctional mixed alkyl hafnium complexes containing the (MesNpy)2 ligand ([(MesitylNCH2)2CMe(2-CsH4N)]2) were synthesized. (MesNpy)Hf(Neo)R ((2b), R = Me; Neo = CH2CMe2Ph) and (MesNpy)Hf(CH2TMS)(R), ((3b), R = Me and (4b), R = i-Bu)) were activated with {Ph3C} {B(C6F5)4} and one alkyl group was selectively removed in all cases. The kinetics of activated 4b were studied and the resulting complex was an initiator for the living polymerization of 1-hexene, with the exception of a slight initiation effect. Five linker molecules were investigated for the preparation of bifunctional hafnium mixed alkyl complexes. One complex synthesized, disilyl[(MesNpy)HfMe]2 (disilyl(X)2 = X-CH2SiMe2(CH2)5SiMe2CH2-X) was activated with {Ph3C} {B(C6F5)4} and the methyl groups were successfully removed to form {disilyl[(MesNpy)Hf]2} {B(C6F5)4}2. This complex was also a living catalyst for the polymerization of a-olefins.; Chapter 2. Addition of p-divinylferrocene to Mo(CHCMe2Ph)(NAr)(ORF6)2 (ORF6 = OCMe(CF3)2; Ar = 2,6-diisopropylphenyl) produced the bimetallic species [Mo(NAr)(ORF6)2(=CHC5H4)]2Fe (6), which upon treatment with lithium tert-butoxide produced the related tert-butoxide complex (7). X-ray crystallography studies of 6 and 7 showed them to be "syn/syn " bimetallic species. In solution...

SELF-ASSEMBLY OF TRIBLOCK COPOLYMERS IN AQUEOUS SOLUTION

Olea, Andrés F.; Martínez, Francisco; Fuentes, Irma; Silva, Patricio; Urbano, Bruno
Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
EN
Relevância na Pesquisa
741.9204%
The aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4- vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quaternization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quaternization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quaternization degree. The presence of aggregates was confirmed by transmission electronic microscopy.; This work was supported by FONDECYT 1070371...

Enhancing Composition Window of Bicontinuous Structures by Designed Polydispersity Distribution of ABA Triblock Copolymers

Li, Yue; Qian, Hu-Jun; Lu, Zhong-Yuan; Shi, An-Chang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/10/2013
Relevância na Pesquisa
549.02117%
The phase behavior of polydisperse ABA triblock copolymers is studied using dissipative particle dynamics simulations, focusing on the emergence and property of bicontinuous structures. Bicontinuous structures are characterized by two separate, intermeshed nanoscopic domains extending throughout the material. The connectivity of polymeric bicontinuous structures makes them highly desirable for many applications. For conventional monodisperse diblock and triblock copolymers, regular bicontinuous structures (i.e., gyroid and Fddd) can be formed over a narrow composition window of ~3%. We demonstrate that the composition window for the formation of bicontinuous structures can be regulated by designed polydispersity distributions of ABA triblock copolymers. In particular, introducing polydispersity in both A and B blocks can lead to a significant enhancement of the composition window of bicontinuous structures with both continuous A and B domains. The mechanism of the bicontinuous structure enhancement is elucidated from the distribution of the long and short blocks. Furthermore, it is shown that the polymeric bicontinuous structures from polydisperse ABA triblock copolymers possess good continuity throughout the sample, making them ideal candidates for advanced applications.; Comment: 8pages...

Smectic ordering in athermal systems of rod-like triblock copolymers

Varga, Szabolcs; Fraden, Seth
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/10/2007
Relevância na Pesquisa
524.54254%
The phase behavior of the system of parallel rigid triblock copolymers is examined using the second-virial density functional theory. The triblock particle consists of two identical infinitely thin hard rods of finite lengths on the opposite ends of one central hard cylinder with nonzero length and diameter. Stability analyses and free energy calculations show that the system of parallel particles can form not only uniform nematic and smectic A phases, but a smectic-C phase too. The stability and structure of the tilted structure is controlled by only the diameter and the length of the central cylinder segment. Interestingly, the diameter effects only the layer tilting and the periodicity, but not the packing fraction of the nematic to smectic-C transition. For all values of cylinder length the usual smectic-A and smectic-C transitions compete with each other and no nematic-columnar transition is observed. At low and high cylinder length the smectic-A phase is stabilized first, while the smectic C is the most stable for intermediate length values.

Weak Segregation Theory and Non-Conventional Morphologies in the Ternary ABC Triblock Copolymers

Erukhimovich, Igor Ya.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/06/2005
Relevância na Pesquisa
535.89152%
The Leibler weak segregation theory in molten diblock copolymers is generalized with due regard for the 2nd shell harmonics contributions defined in the paper and the phase diagrams are built for the linear and miktoarm ternary ABC triblock copolymers. The symmetric linear copolymers with the middle block non-selective with respect to the side ones are shown to undergo the continuous ODT not only into the lamellar phase but also into various non-conventional cubic phases (depending on the middle block composition it could be the simple cubic, face-centered cubic or non-centrosymmetric phase revealing the symmetry of space group No.214 first predicted to appear in molten block copolymers). For asymmetric linear ABC copolymers a region of compositions is found where the weakly segregated gyroid (double gyroid) phase exists between the planar hexagonal and lamellar or one of the non-conventional cubic phases up to the very critical point. In contrast, the miktoarm ABC block copolymers with one of its arm non-selective with respect to the two others are shown to reveal a pronounced tendency towards strong segregation, which is preceded by increase of stability of the conventional BCC phase and a peculiar weakly segregated BCC phase (BCC3)...

Effects of Adsorption of Low-Molecular-Weight Triblock Copolymers on Interactions between Hydrophobic Surfaces in Water

Eskilsson, K; Ninham, Barry; Tiberg, F; Yaminsky, Vassili
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
632.8693%
In this work, we report on the interaction forces between hydrophobed silica surfaces immersed in polymer solutions. The polymers studied were a series of poly(ethylene oxide)-polytetrahydrofuran-poly(ethylene oxide) (PEO-PTHF-PEO) triblock copolymers and a poly(ethylene oxide) homopolymer. The interaction forces were measured by the interfacial gauge technique. We show how the interactions are changed by the adsorbed state of the copolymers. This depends on both the copolymer concentration and the adsorption time. Above a critical surface coverage, the interaction between approaching surfaces at first shows a steric repulsion due to overlap of the adsorbed polymer layers. This repulsion increases as the distance between the surfaces decreases. In this regime the energy-distance curve could be accounted for by the theory of grafted polymer brushes of de Gennes. However, for small surface-to-surface distances the interaction curves do not follow this prediction. Instead, the repulsion stabilized at a more or less constant level with decreasing intersurface separation. Finally, however, hard wall contact was established between the two surfaces. We infer that adsorbed copolymers to a large extent are expelled from the gap between the surfaces in this small surface-to-surface distance range. The force needed to expel copolymers from the intersurface gap was shown to be equal to the surface pressure at the solid-liquid interface. We also studied the influence of the rate of approach and the separation of the surfaces on the energy-distance curves. The process of expelling polymers from the surface-to-surface gap was shown to depend on the velocity of the approaching surfaces and the surface coverage. For high approach rates and/or large surface coverages...