Role Of Molecular Architecture Research Articles

The role of molecular architecture on the viscoelastic properties of thermoreversible polyurethane adhesives

New polyurethane (PUR) adhesives containing covalent Diels-Alder (DA) bonds that can break and form with temperature have been recently developed for sustainable multilayer packaging. The understanding of the mechanical properties and in particular of creep in terms of molecular architecture appears of outmost importance in view of their applications and potential reutilization. Oscillatory shear rheometry shows a modulus decrease with temperature associated to bond breakage and the enhancement found upon cooling can be associated with network reconstruction. Analysis of storage modulus values above the glass transition and below the retro-DA reaction suggests a lower network crosslinking density with increasing adduct content. Room temperature indentation and shear rheometry tests reveal that DA bonds improve the modulus and reduce the resistance to linear viscoelastic flow. The modulus improvement can be associated to the enhanced chain rigidity introduced by the DA moieties and the reduced creep resistance seems to be related to the decrease of crosslinking density.

Role of molecular architecture and temperature on extrusion melt flow instabilities of two industrial LLDPE and LDPE polyethylenes investigated by capillary rheology, high‐pressure sensitivity slit die and optical analysis

AbstractThe characteristic time periodicity and the spatial characteristic wavelength of extrusion flow instabilities of a linear and a branched commercial polyethylene (PE) are characterized via capillary rheology, optical analysis and modeled. The two investigated polyethylenes have the similar weight average molecular weight (Mw). The characteristic time periodicity is obtained and compared using three methods: (i) a highly sensitive pressure slit die, (ii) a new online optical analysis method based on the construction of a space–time diagrams, and (iii) an offline transmission polarization microscopy. In addition, the spatial characteristic wavelength λ is quantified by offline transmission polarization microscopy. The characteristic time periodicity of the extrusion flow instabilities follows a power law behavior as a function of apparent shear rate to a power of −0.7 for both materials,. A qualitative model is used to predict the spatial characteristic wavelength of extrusion flow instabilities as well. It is found that the characteristic spatial wavelength λ and the characteristic time periodicity have an Arrhenius temperature‐dependent behavior.

Role of Molecular Architecture on Ion Transport in Ethylene oxide-Based Polymer Electrolytes

This work aims to develop a detailed mechanistic understanding of the role of a graft polymer architecture on lithium ion (Li+) transport in poly(ethylene oxide)-based polymer electrolytes. Specifically, we compare Li+ transport in poly(ethylene oxide) (PEO) versus poly(oligo oxyethylene methacrylate) (POEM) polymers doped with lithium bis(trifluoromethanesulfonyl) (LiTFSI) salts, using both experimental electrochemical characterization and molecular dynamics (MD) simulations. Our results indicate that POEM exhibits a range of relaxation processes that cannot be interpreted solely in terms of glass-transition temperature (Tg) effects. Due to its side-chain architecture, the segmental relaxation of POEM is nonuniform across ether oxygens (EOs) and shows a more pronounced sensitivity to temperature above Tg compared to PEO. Moreover, POEM also exhibits a nonuniform Li+ coordination behavior, in which Li+ is primarily solvated by two different chains in POEM, compared to a single chain in PEO. Li+ transport in POEM occurs via two events with distinct characteristic times: a fast intrachain hopping along side chains and a slow interchain hopping between side chains. Taken together, the relaxation processes and ion transport mechanisms identified in POEM provide useful insights into design of more effective solid polymer electrolytes.

Role of molecular architecture in interfacial self-adhesion of polyethylene films

The influence of molecular architecture on interfacial self-adhesion above polyethylene film melt temperature was examined in this study. The investigated molecular structures include molecular weight (Mw), molecular weight distribution, long chain branch amount and distribution and short chain branch among and along polyethylene chains. The long chain branches concentration was quantified using gel permeation chromatography and short branches concentration using nuclear magnetic resonance techniques. The adhesion strength was measured immediately after melt bonding using a T-Peel test. The results showed that increasing Mw resulted in higher adhesion strength in linear metallocene ethylene α-olefins. Low long chain branch concentrations hinder reptation motion and diffusion, and result in lower adhesion strength. Low density polyethylene with highly branched chains yielded very low self-adhesion. A drastic difference in adhesion strength between metallocene and conventional linear low density polyethylene is attributed to homogeneity versus heterogeneity of composition distribution. The low interfacial self-adhesion in conventional polyethylene was concluded to be due to enrichment of highly branched low molecular weight chains at the film surface. These segregated chains at the interface diffuse before the high molecular weight chains located in the bulk.

How Different Molecular Architectures Influence the Dynamics of H-Bonded Structures in Glass-Forming Monohydroxy Alcohols.

Primary alcohols have been an active area of research since the beginning of the 20th century. The main problem in studying monohydroxy alcohols is the molecular origin of the slower Debye relaxation, whereas the faster process, recognized as structural relaxation, remains much less investigated. This is because in many primary alcohols the structural process is strongly overlapped by the dominating Debye relaxation. Additionally, there is still no answer for many fundamental questions concerning the origin of the molecular characteristic properties of these materials. One of them is the role of molecular architecture in the formation of hydrogen-bonded structures and its potential connection to the relaxation dynamics of Debye and structural relaxation processes. In this article, we present the results of ambient and high-pressure dielectric studies of monohydroxy alcohols with similar chemical structures but different carbon chain lengths (2-ethyl-1-butanol and 2-ethyl-1-hexanol) and positions of the OH- group (2-methyl-2-hexanol and 2-methyl-3-hexanol). New data are compared with previously collected results for 5-methyl-2-hexanol. We note that differences in molecular architecture have a significant influence on the formation of hydrogen-bonded structures, which is reflected in the behavior of the Debye and structural relaxation processes. Intriguingly, studying the relaxation dynamics in monohydroxy alcohols at high pressures of up to p = 1700 MPa delivers a fundamental bridge to understand the potential connection between molecular conformation and its response to the characteristic properties of these materials.

Computational Design of Multi-component Bio-Inspired Bilayer Membranes

Our investigation is motivated by the need to design bilayer membranes with tunable interfacial and mechanical properties for use in a range of applications, such as targeted drug delivery, sensing and imaging. We draw inspiration from biological cell membranes and focus on their principal constituents. In this paper, we present our results on the role of molecular architecture on the interfacial, structural and dynamical properties of bio-inspired membranes. We focus on four lipid architectures with variations in the head group shape and the hydrocarbon tail length. Each lipid species is composed of a hydrophilic head group and two hydrophobic tails. In addition, we study a model of the Cholesterol molecule to understand the interfacial properties of a bilayer membrane composed of rigid, single-tail molecular species. We demonstrate the properties of the bilayer membranes to be determined by the molecular architecture and rigidity of the constituent species. Finally, we demonstrate the formation of a stable mixed bilayer membrane composed of Cholesterol and one of the phospholipid species. Our approach can be adopted to design multi-component bilayer membranes with tunable interfacial and mechanical properties. We use a Molecular Dynamics-based mesoscopic simulation technique called Dissipative Particle Dynamics that resolves the molecular details of the components through soft-sphere coarse-grained models and reproduces the hydrodynamic behavior of the system over extended time scales.

Computational Design of Multi-component Bio-Inspired Bilayer Membranes

Our investigation is motivated by the need to design bilayer membranes with tunable interfacial and mechanical properties for use in a range of applications, such as targeted drug delivery, sensing and imaging. We draw inspiration from biological cell membranes and focus on their principal constituents. In this paper, we present our results on the role of molecular architecture on the interfacial, structural and dynamical properties of bio-inspired membranes. We focus on four lipid architectures with variations in the head group shape and the hydrocarbon tail length. Each lipid species is composed of a hydrophilic head group and two hydrophobic tails. In addition, we study a model of the Cholesterol molecule to understand the interfacial properties of a bilayer membrane composed of rigid, single-tail molecular species. We demonstrate the properties of the bilayer membranes to be determined by the molecular architecture and rigidity of the constituent species. Finally, we demonstrate the formation of a stable mixed bilayer membrane composed of Cholesterol and one of the phospholipid species. Our approach can be adopted to design multi-component bilayer membranes with tunable interfacial and mechanical properties. We use a Molecular Dynamics-based mesoscopic simulation technique called Dissipative Particle Dynamics that resolves the molecular details of the components through soft-sphere coarse-grained models and reproduces the hydrodynamic behavior of the system over extended time scales.

Role of molecular architecture on the relative efficacy of aurein 2.5 and modelin 5

In order to gain an insight into the mechanism of antimicrobial peptide action, aurein 2.5 and modelin-5 were studied. When tested against Staphylococcus aureus, aurein 2.5 showed approximately 5-fold greater efficacy even though the higher net positive charge and higher helix stability shown by modelin-5 would have predicated modelin-5 to be the more effective antimicrobial. However, in the presence of S. aureus membrane mimics, aurein 2.5 showed greater helical content (75% helical) relative to modelin-5 (51% helical) indicative of increase in membrane association. This was supported by monolayer data showing that aurein 2.5 (6.6mNm−1) generated greater pressure changes than modelin-5 (5.3mNm−1). Peptide monolayers indicted that modelin-5 formed a helix horizontal to the plane of an asymmetric interface which would be supported by the even distribution of charge and hydrophobicity along the helical long axis and facilitate lysis by non-specific membrane binding. In contrast, a groove structure observed on the surface of aurein 2.5 was predicted to be the cause of enhanced lipid binding (Kd=75μM) relative to modelin-5 (Kd=118μM) and the balance of hydrophobicity along the aurein 2.5 long axis supported deep penetration into the membrane in a tilt formation. This oblique orientation generates greater lytic efficacy in high anionic lipid (71%) compared to modelin-5 (32%).

Role of Molecular Architecture on the Vitrification of Polymer Thin Films

We show that thin film star-shaped macromolecules exhibit significant differences in their average vitrification behavior, in both magnitude and thickness dependence, from their linear analogs. This behavior is dictated by a combination of their functionality and arm length. Additionally, the glass transition temperature at the free surface of a star-shaped molecule film may be higher than that of the interior, in contrast to their linear analogs where the opposite is true. These findings have implications for other properties, due largely to the origins, entropic, of this behavior.

Role of Molecular Architecture in Organic Photovoltaic Cells

What are the stumbling blocks for achieving high-efficiency organic photovoltaic devices? This question is examined from a molecular architecture and molecular packing perspective. The intermolecular interaction between the electron donor and electron acceptor influences the charge separation. The packing of electron donors and acceptors influences the charge transport. Therefore, there is a need to strike a balance between the charge-transfer interactions and packing interactions and obtain nanoscale segregated morphologies for efficient charge separation and charge transport. Molecular architecture is key toward striking this balance and, therefore, its impact on charge-transfer interactions and packing interactions; thus, the active-layer morphology and photovoltaic metrics are examined. A variety of molecular architectures for the packing of π-conjugated organic molecules to structures relevant for photovoltaic devices is also discussed.

Branched chitosans: Effects of branching parameters on rheological and mechanical properties

Chitosan continues to be studied as a promising biomaterial for tissue repair and regeneration applications. However, chitosan structures show a large reduction in tensile strength in the wet state. Methods for improving the wet strength of chitosan materials may broaden its applicability as a tissue scaffold for applications requiring significant load bearing capacity. In this study, the role of molecular architecture in defining the mechanical properties of hydrated chitosan membranes was examined. Specifically, branched chitosan molecules were synthesized with a range of branch lengths and branch densities. Physical and mechanical properties were characterized using viscometry, FTIR spectroscopy, and tensile testing measurements, and the results were correlated with the postulated architecture of the linear and branched chitosan materials. Both branch density and branch length were found to influence the mechanical properties of chitosan membranes. For example, high-molecular-weight (600 kDa) chitosans grafted with 80 kDa branches exhibited up to twofold increases in both tensile strength and extensibility. FTIR results indicated that these increases correlated with enhanced levels of hydrogen bonding in the branched materials. Vascular smooth muscle cells cultured on cast membranes of the branched chitosans exhibited no differences in adhesion or spreading as compared to the linear polymer. The results indicate that the mechanical properties of chitosan materials can be improved by the induction of a branched molecular architecture.

The role of molecular architecture and layer composition on the properties and performance of CuPc-C 60 photovoltaic devices

We have studied the effects of molecular architecture, co-deposition and annealing on the properties and performance of photovoltaic cells based on copper phthalocyanine (CuPc)–fullerene (C 60) heterojunctions. Significant improvements in performance are achieved when mixed CuPc:C 60 layers are incorporated into the device structure due to the creation of an intermolecularly mixed donor (D)–acceptor (A) blend that favours efficient exciton dissociation. We utilise the control afforded by organic molecular beam deposition to show that the mixed-layer composition plays an important role in determining device performance and correlate device efficiency to the morphological and spectroscopic properties of the organic layers. A maximum power conversion efficiency of η p = 1.17% is achieved for devices containing a mixed layer of ratio 75:25 CuPc:C 60 surrounded by thin continuous layers of pure organic material at the electrode interfaces. A structure containing a compositional gradient where the CuPc:C 60 composition is varied from purely D to purely A via three mixed layers of increasing A composition leads to a further improvements in efficiency ( η p = 1.36%). Finally, we use thermal annealing to show how structural defects and morphological templating of organic thin films reduces the interfacial area for exciton separation and yields poor device performance.

Role of Molecular Architecture in Mechanical Failure of Glassy/Semicrystalline Block Copolymers: ECE vs CECEC Lamellae. Volume 36, Number 7, April 8, 2003, pp 2190−2193.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionRole of Molecular Architecture in Mechanical Failure of Glassy/Semicrystalline Block Copolymers: ECE vs CECEC Lamellae. Volume 36, Number 7, April 8, 2003, pp 2190−2193.T. J. Hermel, S. F. Hahn, K. A. Chaffin, W. W. Gerberich, and F. S. BatesCite this: Macromolecules 2003, 36, 16, 6280Publication Date (Web):July 17, 2003Publication History Published online17 July 2003Published inissue 1 August 2003https://doi.org/10.1021/ma030338oCopyright © 2003 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views351Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (10 KB) Get e-Alerts Get e-Alerts

Role of Molecular Architecture in Mechanical Failure of Glassy/Semicrystalline Block Copolymers: CEC vs CECEC Lamellae

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTADDITION / CORRECTIONThis article has been corrected. View the notice.Role of Molecular Architecture in Mechanical Failure of Glassy/Semicrystalline Block Copolymers: CEC vs CECEC LamellaeT. J. Hermel, S. F. Hahn, K. A. Chaffin, W. W. Gerberich, and F. S. BatesView Author Information Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455; Dow Chemical Company, Midland, Michigan 48674; and Medtronic Corp., Brooklyn Center, Minnesota 55430 Cite this: Macromolecules 2003, 36, 7, 2190–2193Publication Date (Web):March 11, 2003Publication History Received12 December 2002Revised8 February 2003Published online11 March 2003Published inissue 1 April 2003https://doi.org/10.1021/ma021754wCopyright © 2003 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views946Altmetric-Citations66LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (226 KB) Get e-AlertsSUBJECTS:Copolymers,Deformation,Materials,Transmission electron microscopy,X-ray scattering Get e-Alerts

Role of Molecular Architecture in Polymer Diffusion: A PGSE-NMR Study of Linear and Cyclic Poly(ethylene oxide)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRole of Molecular Architecture in Polymer Diffusion: A PGSE-NMR Study of Linear and Cyclic Poly(ethylene oxide)P. C. Griffiths, P. Stilbs, G. E. Yu, and C. BoothCite this: J. Phys. Chem. 1995, 99, 45, 16752–16756Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/j100045a041RIGHTS & PERMISSIONSArticle Views384Altmetric-Citations45LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (597 KB) Get e-Alerts

Toughening of polystyrene and poly(phenylene oxide) matrices with elastomeric styrene‐based block copolymers: Role of molecular architecture

AbstractThe effects of the molecular architecture of elastomeric styrene‐based block copolymers on efficiency of toughening a brittle (polystyrene) and a ductile [a miscible blend of 80% phenylene oxide copolymer and 20% polystyrene (80PEC)] polymer were explored experimentally. Toughening appears to be mainly controlled by the blend morphology, which is determined by the rheological characteristics of the block copolymer relative to that of the matrix. The formation of dispersed particles during melt blending in a Brabender Plasticorder is strongly influenced by the ratio of the matrix and block copolymer viscosities (estimated here by Brabender torque). The size of the dispersed particles was found to be proportional to the 1.77 power of the torque ratio when this ratio is greater than unity. Thus, to a first approximation the effect of block copolymer architecture on toughening efficiency is related to how this structure affects the rheological behavior of the copolymer. Excellent toughness of polystyrene was achieved when the particle size was larger than 1–2 μm. The 80PEC resin is best toughened by block copolymers that form a cocontinuous phase morphology. The extent of toughening of this matrix appears to be a strong function of the styrene block molecular weight, whereas this structural feature seems to have no significant effect in toughening polystyrene.

The Effect of Molecular Architecture on the Phase Diagram and Mobility of a Polymer Blend Exhibiting a Lower Critical Solution Temperature: Cycles Mixed with Linear Chains.

AbstractWe examine the role of molecular architecture on the phase diagram of the PS/PVME (poly[styrenel /poly[vinyl methyl ether]) blend, a mixture which in previous studies with linear chains exhibited a lower critical solution temperature, (LCST) i.e. it phase separated on heating. In this investigation, two blends with components exceeding the critical molecular weight for entanglement were compared: one consisting of linear PS and PVME and a second with cyclic PS and linear PVME. Cloud point experiments over a broad composition range reveal that the blend containing cyclic PS undergoes phase separation at temperatures 7-8 °C higher than the analogous linear blend. In other words, the mixture of cycles and linear chains is more thermodynamically stable than the mixture of two linear chains.The LCST nature of the system facilitates examining chain mobility by considering the phase separation kinetics. Time-resolved light scattering studies of blends near their critical compositions tracked the spinodal decomposition following a rapid temperature jump from the one-phase to the two-phase region. An analysis of the scattering intensity growth ultimately led to mutual diffusion coefficients whose temperature dependence confirmed the observed cloud points. An approximation of the second derivative of the free energy function based on SANS studies of the linear PS/PVME blend allowed us to estimate mutual mobilities. The values determined for the cycle-containing blend were considerably lower than those for the blend of linear chains at these molecular weights.