Structure Property Relationships Of Block Copolymers Confined Via Forced Assembly Co Extrusion For Enhanced Physical Properties

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Structure Property Relationships Of Block Copolymers Confined Via Forced Assembly Co Extrusion For Enhanced Physical Properties

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Author : Tiffani M. Burt
language : en
Publisher:
Release Date : 2013

Structure Property Relationships Of Block Copolymers Confined Via Forced Assembly Co Extrusion For Enhanced Physical Properties written by Tiffani M. Burt and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.

This dissertation is focused on the characterization of elastomeric block copolymers confined via multilayer co-extrusion technology. In this work, we utilized both self-assembly and forced assembly to achieve hierarchical design within films for mechanical enhancement. When block copolymers are forced to self-assemble in restricted geometries, their physical properties tend to deviate from the bulk behavior. An understanding of their physical properties under confinement has become imperative as technology pushes polymeric applications toward thinner geometries. This work utilizes multilayer co-extrusion as a continuous, confining mechanism to exploit the effect of confining layer and layer thickness on commercially available block copolymers. It was discovered that the morphology and orientation of the block copolymer while under confinement drastically affects the mechanical response of the multilayer films. A thorough understanding of these key factors allows for a methodology to tune the mechanical response of multilayer films via a continuous methodology.

Modeling Self Assembly And Structure Property Relationships In Block Copolymers

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Author : Manas Ravindra Shah
language : en
Publisher:
Release Date : 2009

Modeling Self Assembly And Structure Property Relationships In Block Copolymers written by Manas Ravindra Shah and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.

Block copolymers have been subject of tremendous research interest owing to their capability of undergoing self-assembly which allows them to tailor their electrical, optical, and mechanical properties. Statistical mechanics of flexible block copolymers is well understood. However, there are many unresolved issues with confinement of block copolymers as well as structure formation in block copolymers having non-flexible polymer blocks. We develop mean field theory models to address the issues arising in thermodynamics of such complex block copolymers. Also, we develop theoretical formalisms to understand the link between morphology and macroscopic properties in these block copolymers. We study the stability and ordering in thin films of flexible diblock copolymer in the presence of compressible solvent using a combined polymer mean field theory and lattice gas model for binary fluid mixtures. We utilize mean field theory model to understand the self-assembly behavior in side-chain liquid crystalline block copolymers which involve interplay between microphase separation and liquid crystalline ordering of side chain mesogenic units. We extend the field theoretic models for block copolymer to account for self-assembly in semicrystalline block copolymers. The semicrystalline chain is modeled as a semiflexible chain having non-bonded attractions between parallel bonds. We characterize the structure formation in such block copolymers as a function of the rigidity of the semicrystalline chain. Then we extend the formalism to study semicrystalline triblock and pentablock copolymers and evaluate bridging fractions in different sequences of semicrystalline multiblock copolymers. Rod-coil block copolymers have a flexible polymer covalently linked to rigid polymer. Such polymers have potential applications as organic LEDs and photovoltaic devices. We study the self-assembly of such block copolymer under confinement. To make these block copolymers viable as photovoltaic devices, we performed the photovoltaic modeling of devices based on self-assembly of block copolymers. We characterize the interplay between self-assembly and anisotropy of charge transport (arising due to rigid polymer chains) in determining the eventual photovoltaic properties.

Toward Hierarchical Material Design Via Block Copolymers In A Protic Ionic Liquid

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Author : Ru Xie
language : en
Publisher:
Release Date : 2018

Toward Hierarchical Material Design Via Block Copolymers In A Protic Ionic Liquid written by Ru Xie and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.

Ionic liquids and block copolymers are two representative classes of “designer compounds”, which are known for tunability and controllability of their physical and chemical properties via careful selection of their components. Hierarchically structured functional materials are synthesized by self-assembly of block copolymers in ionic liquids, where the block copolymer imparts mechanical strength to the material via self-assembly into long ranged ordered structure, and the ionic liquid imparts electrical conductivity to the system via concomitant free mobile ions. ☐ Understanding the structure-property relationship of complex fluids comprised of self-assembled block copolymer in ionic liquid paves the foundation for rational design and engineering of hierarchically structured functional materials and smart devices. Thus, the goals of this dissertation are threefold: firstly, to develop structure-property relationships for complex fluid model systems composed of self-assembled non-ionic block copolymers in a protic ionic liquid at rest and under ow deformations; secondly, to synthesize and characterize a novel hierarchically structured stretchable ion-conducting material system utilized the structure-property relationship; and lastly, with the fundamental understanding of the structure-property relevancy of the materials, to design and engineer commercializable device prototypes based on the insights extracted from customer discovery interviews. ☐ A non-ionic, spherical micellar ionic liquid complex fluid model system and a non-ionic polymerlike micellar ionic liquid complex fluid model system are explored in this dissertation using a combination of advanced rheological and neutron techniques. In the spherical micellar model systems, it was found that polymer blending is an effective route to create self-assembled complex fluid model systems with tunable microstructure and rheological properties. The study of the polymerlike micellar system reveals that non-ionic polymerlike micelles have di_erent rheological signatures than non-shear banded shear thinning surfactant wormlike micelle solutions. The structure-property relationships determined for the two model systems serve as a reference for formulating and processing non-ionic block copolymer/ionic liquid complex fluids to achieve specific structures that can be crosslinked to create new functional materials. ☐ A simplified two-step manufacturing process has been developed in this dissertation to create an ultra-stretchable conductive iono-elastomer, by self-assembly of concentrated solutions of end-functionalized block copolymers in a protic ionic liquid, followed by chemical crosslinking. The resultant iono-elastomers exhibits an unprecedented combination of high stretchability (3000% elongation and 200 MPa tensile strength at break) and mechano-electrical response. To our knowledge, the strechability is about 10 times higher than reported elastomers. Importantly, the resistance of the material decreases with extension, a unique and non-trivial material response, whose origin is postulated to be the microstructural rearrangement of the micelles. Furthermore, the incorporation of water in the ionic liquid precursor leads to estimated 8.5 times less stretchability, and strikingly, the resistance of iono-elastomer increases with increasing strain. The contrary mechano-electrical response was postulated to be due to different ion binding and transport mechanism in the presence of water. ☐ Based on the material property and customer discovery interviews, a potential application of the iono-elastomer is identified as a motion strain sensor. Significant efforts are made to develop three generations of large strain amplitude, stretchable resistive strain sensor patch prototypes. They should enable customers (e.g., athletes, patients undergoing physical therapy, physical trainers, biomechanicians, etc.) to accurately track motion and performance of specific joints and/or muscles on their smart phone, tablet or computer via Bluetooth wireless communication, with applications in motion capturing, sports performance tracking and rehabilitation monitoring. ☐ Together, advanced rheological and neutron techniques provide a platform for creating structure-property relationships that predict rheological and structural phenomena in soft materials. This research is part of a broader effort to design, synthesize and characterize novel self-assembled non-ionic polymers in ionic liquids by material scientists and engineers. Finally, this work spans interests in both fundamental investigations and technical applications of non-ionic block copolymer self-assembly in ionic liquids, suggesting that the wealth of possible chemistries and ability to create a plethora of hierarchically self-assembled microstructures should lead to many new discoveries.

Impact Of Macromolecular Design On Self Assembly Properties Of Block Copolymers

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Author : Kamlesh Ramesh Bornani
language : en
Publisher:
Release Date : 2017

Impact Of Macromolecular Design On Self Assembly Properties Of Block Copolymers written by Kamlesh Ramesh Bornani and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with Block copolymers categories.

The generation of well-ordered complex structures from constituent block copolymeric building blocks by the spontaneous process of self-assembly is useful in various technologies. The well-defined 3D structures are dictated by complex energetic interplays and their shape is controllable by both preparative conditions and macromolecular design. This dissertation work aims at exploring the effect of chain flexibility and chain topology design changes on phase behavior of block copolymers in solution. Further, we exploit the tunable flexibility of the semiflexible polymers in studying dispersion and controlling macroscale thermal properties in polymer nanocomposites. The experimental design is based on two model systems: The first is based on polystyrene-b-poly1,3-cyclohexadiene (PS-b-PCHD). Here, the semiflexible nature of PCHD is tunable through alteration in the chain microstructure of the polymer backbone. As altered flexibility impacts the ability of chains to pack, which is shown to affect micelle morphology in solution. Further, we exploit the entropic contributions due to changes in chain configuration of PCHD (controlled through microstructure to control the dispersion of silica nanoparticles in matrices varying flexibility. Because we leave the monomer type unchanged, studying PCHD-based materials enables us to draw links between chain configuration and phase behavior. The second system is based on polystyrene-polyisoprene, (PS-PI), where multiple star copolymers were studied in a PI selective solvent. The study highlights how architecture and composition influence self-organization of the topologically-complex polymers in solution. The topological constraints introduced through architecture and composition were unable to induce any morphological changes, however design variation was successful in inducing changes in micelle size. These studies help understand the self-assembly properties of semiflexible and topologically-complex systems and provide means to control micelle properties through macromolecular design. Additionally, the macromolecular design changes also provide an opportunity to control and enhance desired properties in polymer nanocomposites. Thus, the work conducted as a part of this dissertation is very valuable to understand design-structure-property relationships by providing insights into the physics principles operating at the nanometer length scale.

Novel Applications Of Co Extruded Multilayer Polymeric Films

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Author : Shannon Renee Armstrong
language : en
Publisher:
Release Date : 2013

Novel Applications Of Co Extruded Multilayer Polymeric Films written by Shannon Renee Armstrong and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.

Multilayer co-extrusion, a highly flexible and unique process, has enabled the study of the permeation, mechanical, and optical properties of multilayer films. Gas separation membranes are strongly dependent upon the permeation of specific gases, which is controlled by the polymer structure and morphology. Poly(ether block amide) (PEBA) thermoplastic elastomers have an inherently high permeability and good selectivity for acid gases such as CO2. A series of PEBA copolymers containing poly(tetramethylene oxide) and polyamide-12 was studied to explore the influence of mechanically induced orientation and copolymer composition on gas permeability and morphology. Upon orientation, PEBA copolymers with high polyether content exhibited up to 3.5x reduction in permeation with increasing strain as a result of strain induced crystallization. To maintain high flux for membrane applications, elastic recovery and thermal treatment proved beneficial in reversing the effects of uniaxial orientation on PEBA copolymers. Gas separation membranes were produced through co-extrusion and subsequent orientation of films containing PEBA as the selective material and PP composites as the support, which are made porous through two methods: 1) inorganic fillers or 2) crystal phase transformation. Two membrane systems, PEBA/(PP + CaCO3) and PEBA/¿-PP, maintained a high CO2/O2 selectivity while exhibiting reduced permeability. Incorporation of an annealing step either before or after orientation improves the membrane gas flux by 50 to 100 %. The improvement in gas flux was a result of either elimination of strain induced crystallinity, which increases the selective layer permeability, or improvement of the PP crystal structure, which may increase pore size in the porous support layer. Forced assembly multilayer co-extrusion of commercially available polyurethane (PU) and polycaprolactone (PCL) polymers was used to create a continuous periodic alternating layer architecture that exhibits shape memory behavior. Similar shape memory properties were observed between PU/PCL layers and blends at 50/50 volume composition; however, offset compositions showed significantly different behavior. The layered structure was maintained across all compositions, as compared with blends that exhibit a composition dependent morphology. The difference in morphology was directly attributed to the difference in shape memory behavior observed between layered and blend films with domain sizes on the micro-scale. Additionally, films with layer thicknesses at the micro-scale and nano-scale were studied to determine the effects of scaling. For PU/PCL layered films, reduction in layer thicknesses lead to improved shape fixity as a result of increased levels of in-plane PCL crystal orientation. Layer multiplying melt co-extrusion is an attractive method for fabricating periodic structures with thousands of alternating polymer microlayers or nanolayers. Many advanced applications for periodic polymeric structures would be enabled by locating a photoactive dye in one or both layers. However, it is anticipated that due to the thinness of the individual layers and the relatively low molecular weight of the dye, a substantial fraction of the dye will diffuse from the doped layers into the undoped layers during melt co-extrusion. In the present study, we demonstrate two methods for confining the activity of a photoactive dye, lead phthalocyanine, to the doped layers. Polycarbonate containing lead phthalocyanine was co-extruded with undoped polyester. Using the absorption spectra, a high concentration of the monomer form was determined to persist in the polycarbonate layers, whereas the lead form was converted to the less active lead-free form in the polyester layers. In the second approach, the co-extrusion process was altered so that the alternating polycarbonate and polyester layers were separated by a thin layer of a barrier polymer. The barrier layer prevented diffusion of the dye during melt co-extrusion and the dye remained selectively in the polycarbonate layers.

Self Assembled Patterns Of Block Copolymer Homopolymer Blends

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Author : Dongsik Park
language : en
Publisher:
Release Date : 2008

Self Assembled Patterns Of Block Copolymer Homopolymer Blends written by Dongsik Park and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Block copolymers categories.

Many researchers have studied the orientation behavior of block copolymers (BCPs) with the most recent works directed towards nanotechnologies. Self-assembly of block copolymers is very relevant in controlling periodic nanostructures for nanotechnological applications. Nanotechnological applications of BCPs are possible due to their physical properties related to mass and energy transport, as well as mechanical, electrical, and optical properties. These properties provide substantial benefits in nanostructure membranes, nanotemplates, photonic crystals, and high-density information storage media. In many applications, such nanopatterns need to be achieved as ordered and tunable structures. Consequently, the control of orientation of such structures with defect-free ordering on larger length scales still remain as major research challenge in many cases. In addition to their pure block forms, blends of copolymers with other polymers offer productive research areas in relation to nanostructural self-assembly. We prepared well-aligned nanocylinders into block copolymer over the enhanced sample area and scale of height without any external field applications or modification of interaction between the sample and the substrate. Self-assembled 3-dimensional perpendicular cylinder orientation was achieved mainly by blending of minority homopolymer into the blockcopolymer. Thus, this study investigated a spontaneous and simple method for the orientation of perpendicular cylinders in BCP/homopolymer mixtures on a preferential substrate, by increasing the interaction force between the homologous polymer pair at a fixed composition of minority block component. Since the thermodynamical changes have been simply accomplished by the control of incompatibility between the block components, the intrinsic advantages of block copolymer nanopatterning, such as fast and spontaneous 3-dimensional nanopatterning with a high thermodynamic stability and reproducibility, have been completely preserved in this fabrication strategy. By exploiting thermodynamical changes using temperature variation and by blending a homopolymer with well controlled molecular weight, we illustrated that redistribution of homopolymer resulted in a shift of phase boundaries and in the stabilization of well-ordered structures to create new opportunities for nanotechnologies.

Confined Crystallization Crystalline Phase Deformation And Their Effects On The Properties Of Crystalline Polymers

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Author : Haopeng Wang
language : en
Publisher:
Release Date : 2009

Confined Crystallization Crystalline Phase Deformation And Their Effects On The Properties Of Crystalline Polymers written by Haopeng Wang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with Crystalline polymers categories.

With the recent advances in processing and catalyst technology, novel morphologies have been created in crystalline polymers and they are expected to substantially impact the properties. To reveal the structure-property relationships of some of these novel polymeric systems becomes the primary focus of this work. In the first part, using an innovative layer-multiplying coextrusion process to obtain assemblies with thousands of polymer nanolayers, dominating "in-plane" lamellar crystals were created when the confined poly(ethylene oxide) (PEO) layers were made progressively thinner. When the thickness was confined to 25 nanometers, the PEO crystallized as single, high-aspect-ratio lamellae that resembled single crystals. This crystallization habit imparted more than two orders of magnitude reduction in the gas permeability. The dramatic decrease in gas permeability was attributed to the reduced diffusion coefficient, because of the increase in gas diffusion path length through the in-plane lamellae. The temperature dependence of lamellar orientation and the crystallization kinetics in the confined nanolayers were also investigated. The novel olefinic block copolymer (OBC) studied in the second part consisted of long crystallizable sequences with low comonomer content alternating with rubbery amorphous blocks with high comonomer content. The crystallizable blocks formed lamellae that organized into space-filling spherulites even when the fraction of crystallizable block was so low that the crystallinity was only 7%. These unusual spherulites were highly elastic and recovered from strains as high as 300%. These "elastic spherulites" imparted higher strain recovery and temperature resistance than the conventional random copolymers that depend on isolated, fringed micellar-like crystals to provide the junctions for the elastomeric network. In the third part, positron annihilation lifetime spectroscopy (PALS) was used to obtain the temperature dependence of the free volume hole size in propylene/ethylene copolymers over a range in comonomer content. Above the glass transition temperature (Tg), the reduced free volume hole size and the densification of the amorphous phase were attributed to constraint imposed on rubbery amorphous chain segments by attached chain segments in crystals. However constant free volume fraction was found at Tg, across the crystallinity range of the copolymers, in agreement with the iso-free volume concept of glass transition.

Studies Of Block Copolymer Thin Films And Mixtures With An Ionic Liquid

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Author : Justin Virgili
language : en
Publisher:
Release Date : 2009

Studies Of Block Copolymer Thin Films And Mixtures With An Ionic Liquid written by Justin Virgili and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.

Block copolymers are capable of self-assembling into structures on the 10-100 nm length scale. Structures of this size are attractive for applications such as nanopatterning and electrochemical membrane materials. However, block copolymer self-assembly in these examples is complicated by the presence of surfaces in the case of thin films and the presence of an additive, such as an ionic liquid, in the case of electrochemical membrane materials. Improved understanding of the structure and thermodynamics of such systems is necessary for the development of structure-property relationships in applications for block copolymers, such as nanopatterning and electrochemical devices. To address the challenge of block copolymer thin film characterization over large areas, resonant soft X-ray scattering (RSoXS) has been applied to characterize order formation in copolymer thin films. Using theory and experiment, the dramatic chemical sensitivity of RSoXS to subtle differences in the bonding energies of different blocks of a copolymer is demonstrated. The unambiguous identification of structure and domain size in block copolymer thin films using RSoXS enables a quantitative comparison of the bulk block copolymer structure and domain size, leading to improved understanding of the impact of surfaces on block copolymer self-assembly. The self-assembly of block copolymer/ionic liquid mixtures has been characterized as a function of block copolymer composition and molecular weight, mixture composition, and temperature using small-angle X-ray scattering (SAXS), optical transmission characterization, wide-angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC). The resulting phase behavior is reminiscent to that of block copolymer mixtures with a selective molecular solvent and lamellar, cylindrical, ordered spherical micelles, and disordered phases are observed. Analysis of order-disorder transitions and molecular weight scaling analysis qualitatively indicates that the segregation strength between block copolymer phases increases with ionic liquid loading. DSC characterization of the thermal properties of the block copolymer/ionic liquid mixtures reveals two composition dependent regimes. At high block copolymer concentrations, a "salt-like" regime corresponding to an increase in the block copolymer glass transition temperature is observed, while at intermediate block copolymer concentrations, a "solvent-like" regime corresponding to a decrease in the block copolymer glass transition temperature is observed. The distribution of ionic liquid within microphase-separated domains of a block copolymer has been characterized using contrast matched small-angle neutron scattering (SANS) and DSC. The ionic liquid is shown to partition selectively into domains formed by one block of a block copolymer in agreement with studies of the phase behavior of ionic liquid/block copolymer mixtures. Unexpected differences in ionic liquid partitioning are observed in mixtures containing a deuterated versus hydrogenated ionic liquid.

Structure Property Relationships Of Pems Using Fluorous Ionic Copolymers

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Author : Ming Wai Emily Tsang
language : en
Publisher:
Release Date : 2011

Structure Property Relationships Of Pems Using Fluorous Ionic Copolymers written by Ming Wai Emily Tsang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with Copolymers categories.

Proton exchange membranes (PEMs) are a key component in PEM fuel cells, serving as both a fuel separator and an electrolyte. The goal of this thesis work is to investigate structure-property relationships in PEMs. Specifically, the role of polymer microstructure on membrane morphology and physicochemical properties is examined. This is achieved by the design, synthesis and characterization of model polymers with controlled chain architectures and chemical composition, leading to membranes with controlled nanophase-separated morphologies, from which the influence of morphology upon proton transport and other membrane properties is investigated. Two classes of model polymer systems were devised and studied: diblock copolymers of sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) [P(VDF-co-HFP)-b-SPS]; and graft copolymers of sulfonated poly([vinylidene difluoride-co-chlorotrifluoropropylene]-g-styrene) [P(VDF-co-CTFE)-g-SPS]. These model polymer systems are of interest due to chemical dissimilarity between the hydrophobic fluoropolymer segments and the hydrophilic sulfonated polystyrene segments, which promote phase separation into ionic and non-ionic domains. In addition, controlled radical polymerization techniques were employed to grow the polystyrene segments, which provide high degrees of structural control. Macromolecular structural parameters, such as block ratio, graft length and degree of sulfonation, were systematically varied to determine the effects of polymer microstructure on morphology and proton conductivity. One of the key findings obtained from this work is that block ionomers, whether linear or graft structure, with a lower content of the acid-bearing constituent block (i.e., polystyrene block) gave enhanced proton conductivity at a given ion content. This is attributed to the relatively high degree of sulfonation required and therefore, closer spatial proximity between sulfonic acid groups, which allows for the formation of purer and more percolated ionic aggregates within the proton-conducting domains. Additionally, direct comparison between the diblock and the graft copolymers revealed that the formation of smaller-scale ionic domains is preferable for PEMs because of reduced water swelling which mitigates acid dilution at high ion contents. Furthermore, membranes with smaller-scale ionic domains provided enhanced water retention and proton conduction under low humidity and high temperature conditions. The knowledge gained from this thesis work provides useful insights into aspects of membrane design and preferred structures.

Gradient Mutilayered Films And Confined Crystallization Of Polymer Nanolayers By Forced Assembly Coextrusion

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Author : Michael T. Ponting
language : en
Publisher:
Release Date : 2010

Gradient Mutilayered Films And Confined Crystallization Of Polymer Nanolayers By Forced Assembly Coextrusion written by Michael T. Ponting and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.

Forced assembly polymer coextrusion utilizes layer multiplication to produce films with tens or thousands of micron to nanometer thick layers. Projects utilizing this coextrusion technique will be described including the development of gradient layer thickness polymer films and gas barrier enhancement in polycaprolactone nanolayered films. The development of novel uneven split layer multiplying dies has produced gradient multilayer films with at least a 10X difference between the thickest and thinnest layers. This new technology has created gradient layer thickness multilayer films that exhibit novel optical reflections or unique mechanical properties. Crystallization of polycaprolactone in micron to nanometer thick multilayers induced a thickness dependent confinement mechanism altering the polymer crystal habit from unoriented spherulites (micron layers) to high-aspect ratio, single or stacked lamellae (nanolayers) oriented parallel to the layer boundary. Highly oriented, single lamellae PCL layer films exhibited more than a two order of magnitude improvement in oxygen barrier as a result of the increased diffusion path length (tortuosity) around the high aspect ratio lamellae crystals. The effect of the confining layer - PCL structure-property relationship was examined by coextrusion of PCL against a series of amorphous and crystalline materials.