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Crystalline polymer and 3D ceramic-polymer electrolytes for Li-ion batteriesHekselman, Aleksandra K. January 2014 (has links)
The research work presented in this thesis comprises a detailed investigation of conductivity mechanism in crystalline polymer electrolytes and development of a new class of ceramic-polymer composite electrolytes for Li-ion batteries. Firstly, a robust methodology for the synthesis of monodispersed poly(ethylene oxides) has been established and a series of dimethyl-protected homologues with 13, 15, 17, 28, 29, 30 ethylene oxide repeat units was prepared. The approach is based on reiterative cycles of chain extension and deprotection, followed by end-capping of the oligomeric chain ends with methyl groups. The poly(ethylene oxide) homologues show a superior level of monodispersity to previous work and were subsequently used to prepare crystalline PEO6:LiPF6 polymer electrolytes. A correlation between the number of ether oxygens in the polymer chain and the ionic conductivity of crystalline polymer electrolytes has been established. The structure and dynamics of the monodispersed complexes were studied using solid-state NMR spectroscopy for the first time. The results are in agreement with the proposed mechanism of ionic conductivity in crystalline polymer electrolytes. A new class of composite solid electrolytes for all-solid-state batteries with a lithium metal anode is reported. The composite material consists of a 3D interpenetrating network of a ceramic electrolyte, Li₁.₄Al₀.₄Ge₁.₆(PO₄)₃, and an inert polymer (polypropylene), providing continuous pathways for the ionic transport and excellent mechanical properties. 3D connectivity of this novel composite was confirmed using X-ray microtomography and AC impedance spectroscopy.
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Crystallization Kinetics of Semicrystalline Polymer Nanocomposites: Morphology–Property RelationshipAltorbaq, Abdullah Saleh January 2022 (has links)
Semicrystalline polymers constitute the majority of the commercially manufactured polymers, mostly known as commodities with low modulus and inferior properties. A robust approach used in tailoring such commodity’s properties for more advanced applications is through the incorporation of inorganic nanoparticles (NPs). Over the past half century, polymer nanocomposites (PNCs) have attracted extensive interest in fundamental research and technological applications. However, NPs have been found to result in complicated alterations in the semicrystalline polymer crystallization kinetics, and their crystalline morphology, which could either synergistically or adversely affect the final composite properties. A comprehensive understanding of this topic is still lacking, which with one could tune the final polymer properties for various cutting-edge applications. In this dissertation, we focus on the crystallization kinetics of semicrystalline PNCs and the connection between the morphology and the mechanical (and rheological) properties of such hybrid systems.
First, we control the NP dispersion and self-assembly in a semicrystalline poly(ethylene oxide) (PEO) matrix using both bare and polymer-grafted NPs. We show that bare NPs (with different sizes) and unimodal poly(methyl methacrylate) (PMMA)-g-SiO2 NPs uniformly disperse in a PEO matrix because of the favorable interaction between the matrix and the NP surface (or the PMMA brush). Grafting the latter NPs with a short dense polystyrene brush that is immiscible with PEO while varying the PMMA grafting parameters induces self-assembly and leads to various NP structures: well-dispersed, connected sheets, strings, and large aggregates.
Next, we systematically investigate the role of bare and self-assembled grafted NPs on the spherulitic growth kinetics of semicrystalline polymers. In all cases, the incorporation of spherical NPs suppresses the polymer growth kinetics. Using rheological measurements, we show that the reduction in growth is mainly attributed to the NPs increasing the melt viscosity; whereas, they minimally alter the secondary nucleation process. Surprisingly, the PNC growth kinetics is suppressed in two apparently universal manners when plotted as a function of confinement: NP dominated and brush-controlled regimes. Bare NPs and large aggregates of polymer-grafted NPs appear to nearly follow the same dependence for the role of additives on polymer viscosity, weakly suppressing the growth kinetics. On the other hand, all the other self-assembled NP structures showed much stronger growth reductions because of the larger increase in the melt viscosity by the chemically bonded brush.
Given our prior knowledge of the PNC growth kinetics, we then draw generalized trends for the role of bare and grafted NPs in nucleating semicrystalline polymers. This is achieved by comparing the polymer crystallization kinetics in the presence of large, asymmetric, immobile fillers (selected from the well-established literature) to those smaller, spherical, mobile NPs (examined throughout this thesis). Generally, NPs serve as heterogenous nucleation sites when incorporated at smaller amounts, leading to accelerated crystallization kinetics. At larger filler contents, NPs confine the polymer chains into smaller domains and become more susceptible to aggregation, which results in antinucleating effects and suppressing the crystallization rate. Such competing effects result in a maximum nucleation efficiency at moderate filler contents. It is also worth noting that the degree of nucleation enhancement and subsequent suppression depends on the system and is controlled by NP dispersion, geometry, and surface chemistry. For example, one- and two-dimensional NPs usually result in a higher nucleation power compared to spherical NPs. Another major difference between mobile and immobile fillers is that when slowly crystallizing from the melt, the smaller diffusive NPs can be segregated and ordered into hierarchal structures (interlamellar sheets and interfibrillar and interspherulitic aggregates). This provides a much richer class of materials with a kinetics route in controlling NP assemblies.
Finally, we create robustly toughened semicrystalline polymers by confining the PEO crystallization using a densely grafted PMMA brush (i.e., PMMA-g-SiO₂) with different molecular weights. For comparison, we prepare linear PMMA/PEO blends with equivalent PMMA molecular weights and volume fractions to those of the nanocomposites. We show that PMMA-g¬-SiO₂ NPs surpass linear PMMA homopolymers in terms of toughening the PEO matrix, with the grafted system experiencing relatively higher connectivity and lower crystallinity. At moderate confinement, the nanocomposite sustains a maximum modulus increase of 42%, with around a 200-fold increase in the PEO toughness. This provides a novel route for toughening semicrystalline polymers using noncrystallizable polymer-grafted NPs.
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Dielectric relaxations in side-chain liquid crystalline polymersZhong, Zhengzhong January 1993 (has links)
No description available.
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CRYSTALLINE POLYMERS IN MULTILAYERED FILMS AND BLEND SYSTEMSZHANG, GUOJUN 02 September 2014 (has links)
No description available.
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Synthesis and characterization of liquid crystalline polyrotaxanes based on poly(azomethine)sSze, Jean Y. 19 September 2009 (has links)
Polyrotaxanes are new polymers. Macrocyclic molecules, such as crown ethers, are threaded by linear or branched polymer chains. There is no covalent bond between the crown ethers and the polymer backbone. After the crown ethers are threaded onto the polymer backbone, both ends of the polymer can be blocked by large end groups. Polyrotaxanes are the topological isomers of blends of crown ethers and polymers. This architectural modification will produce interesting chemical and physical property changes in the polymer such as T<sub>g</sub> and T<sub>m</sub>, solubility, tensile strength, flexibility of the polymer.
The study include crown ethers, blocking groups, poly(azomethine)s A and B, poly(azomethine)rotaxanes A and B synthesis, characterization, and property research.
Crown ethers, 21-crown-7, 30-crown-10, 42-crown-14, and 60-crown-20, were synthesized from oligo(ethylene glycol)s and oligo(ethylene glycol) ditosylates with 22-40% yield. The high temperature synthetic method was developed so that the percentage yield of large crown and the small crowns in the same reaction could be controlled. A new purification method, low temperature recrystallization method was developed. The crown ethers properties included melting points, decomposition temperature, chemical shift on NMR spectra were studied.
A series of blocking groups were synthesized and characterized. Several synthetic routes were studied, and the best route was the Grignard synthesis. The purification method was improved by recrystallization in cyclohexane or carbon tetrachloride. A by-product, bis(p-t-butylphenyl)methanol, was obtained. The new compounds, p-tri(p-t-butylphenyl)methylaniline and p-tri{(p-t-butylphenyl)methylphenol, were identified by ¹H NMR, FTIR, and elemental analysis.
Poly(azomethine)s A and B are liquid crystalline polymers. They are rigid and strong. They have high T<sub>m</sub>'s and do not dissolve in general solvents. To check the reported information, the synthesis and characterization of these polymers were repeated. They precipitated from the reaction solution when their degree of polymerization reached 3-5. They were not thermally stable and were easily hydrolyzed in strong acids and in GPC column.
In order to establish the effectiveness of the blocking groups, a monomeric rotaxane, a di(azomethine)rotaxane, was designed and synthesized. The compound was successfully isolated by multiple reprecipitations and recrystallizations. A 12% yield of this compound was obtained. The largest crown ether that the blocking group could block was 42-crown-14. / Master of Science
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Polymer electrolytes : synthesis and characterisationMaranski, Krzysztof Jerzy January 2013 (has links)
Crystalline polymer/salt complexes can conduct, in contrast to the view held for 30 years. The alpha-phase of the crystalline poly(ethylene oxide)₆:LiPF₆ is composed of tunnels formed from pairs of (CH₂-CH₂-O)ₓ chains, within which the Li⁺ ions reside and along which the latter migrate.¹ When a polydispersed polymer is used, the tunnels are composed of 2 strands, each built from a string of PEO chains of varying length. It has been suggested that the number and the arrangement of the chain ends within the tunnels affects the ionic conductivity.² Using polymers with uniform chain length is important if we are to understand the conduction mechanism since monodispersity results in the chain ends occurring at regular distances along the tunnels and imposes a coincidence of the chain ends between the two strands.² Since each Li⁺ is coordinated by 6 ether oxygens (3 oxygens from each of the two polymeric strands forming a tunnel), monodispersed PEOs with the number of ether oxygen being a multiple of 3 (NO = 3n) can form either “all-ideal” or “all-broken” coordination environments at the end of each tunnel, while for both NO = 3n-1 and NO = 3n+1 complexes, both “ideal” and “broken” coordinations must occur throughout the structure. A synthetic procedure has been developed and a series of 6 consecutive (increment of EO unit) monodispersed molecular weight PEOs have been synthesised. The synthesis involves one end protection of a high purity glycol, functionalisation of the other end, ether coupling reaction (Williamson's type ether synthesis³), deprotection and reiteration of ether coupling. The parameters of the process and purification methods have been strictly controlled to ensure unprecedented level of monodispersity for all synthesised samples. Thus obtained high purity polymers have been used to study the influence of the individual chain length on the structure and conductivity of the crystalline complexes with LiPF₆. The results support the previously suggested model of the chain-ends arrangement in the crystalline complexes prepared with monodispersed PEO² over a range of consecutive chain lengths. The synthesised complexes constitute a series of test samples for establishing detailed mechanism of ionic conductivity. Such series of monodispersed crystalline complexes have been studied and characterised here (PXRD, DSC, AC impedance) for the first time. References: 1. G. S. MacGlashan, Y. G. Andreev, P. G. Bruce, Structure of the polymer electrolyte poly(ethylene oxide)₆:LiAsF₆. Nature, 1999, 398(6730): p. 792-794. 2. E. Staunton, Y. G. Andreev, P. G. Bruce, Factors influencing the conductivity of crystalline polymer electrolytes. Faraday Discussions, 2007, 134: p. 143-156. 3. A. Williamson, Theory of Aetherification. Philosophical Magazine, 1850, 37: p. 350-356.
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Synthesis, Characterization, and Rheology of Functional and Heterocyclic Liquid Crystalline PolymersHuang, Wenyi January 2006 (has links)
No description available.
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Free volume properties of semi-crystalline polymersSweed, Muhamed 03 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Positron annihilation lifetime spectroscopy (PALS) is well established as a novel method
currently available for the study of polymers at a molecular level because of its sensitivity
to the microstructural changes in the polymer matrix. The technique provides unique, but
limited, information of the solid state structure – primarily on the nature of the free
volume (or unoccupied space) in the polymer due to the less dense packing of polymer
chains relative to in other solid materials.
In the case of completely homogeneous polymer materials the measurement and
interpretation of the positron annihilation parameters is relatively simple. However, in the
case of polymers with more complex morphologies the situation becomes less clear. This
is due to the possibility of the formation, localization and subsequent annihilation of o-Ps
(ortho-positronium) within different areas of the complex morphology. This can result in
more than one o-Ps lifetime component being present, and each of the different
components corresponds to areas with differing types and amounts of 'open spaces'.
In this study a detailed and systematic approach was taken to study the positron
annihilation parameters in various semi-crystalline polymers and to correlate these to the
chain structure and morphology of the materials. The study focused specifically on
polyolefin polymers as these are the most widely used semi-crystalline materials, but
more importantly, they offer the possibility to produce a variety of morphological
complexity by simple manipulation of the chain structure – while there is essentially no
difference in the chemical composition of the materials. The copolymers were selected to
study the influence of short-chain branching (amount and length), short-chain branching
distribution and tacticity on the morphology, and subsequent positron annihilation
lifetime parameters.
Three separate topics were addressed. First, preparative temperature rising elution
fractionation was used to isolate polymer samples that are homogeneously crystallisable
and to produce a series of polymers with differing chain structure and resultant
morphologies. Second, additional series were produced by removing specific
crystallisable fractions from the bulk materials. Third, the temperature variation of the
samples as they approach and go through the crystalline melting point was studied. All the raw positron data were found to be best fitted with a four-component
positron annihilation lifetime analysis. The longest lifetime (which is attributed to
annihilation of o-Ps in the amorphous phase of the materials) showed systematic
variations with the degree and nature of the short-chain branding, tacticity variation, a
combination of both short-chain branching and tacticity, and changes in the amorphous
phase as a result of heating. The third lifetime component (which is attributed to o-Ps
annihilation in or around the crystalline areas of the materials) showed less variation
across the sample series. Typically, greater variations were observed in the propylene
copolymers than in the ethylene copolymers, which are reflective of the more complex
chain structure and corresponding morphology in the propylene copolymer series. Direct
evidence for a contribution from the nature of the amorphous phase to the bulk
microhardness of the sample was also found. / AFRIKAANSE OPSOMMING: Positronvernietigingsleeftydspektroskopie (PALS) is goed gevestig as ‘n nuwe metode
vir die studie van polimere op molekulêrevlak agv die sensitiwiteit van die metode vir
mikrostrukturele veranderings in die polimeermatriks. Hierdie tegniek verskaf unieke,
maar beperkte, inligting aangaande die vastetoestandstruktuur – veral aangaande die aard
van die vryevolume (of onbesette spasie) in die polimeer as gevolg van die minder digte
verpakking van polimeerkettings relatief tot in ander vastestowwe.
In die geval van volledig homogene polimeriese materiale is die meet en
interpretasie van die positronvernietigingsparameters relatief eenvoudig. Maar in die
geval van polimere met meer komplekse morfologieë is die situasie minder duidelik. Die
rede hiervoor is die moontlikheid vir die formasie, lokalisering en gevolglike vernietiging
van o-Ps (orto-positronium) in die verskillende areas van die komplekse morfologie. Dit
kan tot gevolg hê dat meer as een o-Ps komponent teenwoordig is en waar elk van die
verskillende komponente ooreenstem met areas met verskillende tipes en hoeveelhede
'oop spasies'.
In hierdie studie is ‘n sistematiese, in-diepte benadering gebruik om die
positronvernietigingsparameters in verskeie semikristallyne polimere te bestudeer en
hulle te korreleer met dié van die kettingstruktuur en die morfologieë van die materiale.
Hierdie studie het spesifiek gefokus op poliolefiene aangesien hulle die mees algemene
semikristallyne materiale is wat gebruik word en, nog meer belangrik, hulle bied die
geleentheid om verskeie komplekse morfologieë te lewer dmv eenvoudige manipulasie
van die kettingstrukture – terwyl daar basies geen verandering in die
chemiesesamestelling van die materiale is nie. Die kopolimere is gekies om die invloed
van kort-ketting vertakking (lengte en hoeveelheid), kort-ketting vertakking verspreiding
en taktisiteit op die morfologie en vervolgens die positronvernietigingsleeftyd parameters
te bestudeer.
Drie onderwerpe is aangespreek. Eerstens, preparatiewe
temperatuurstygingelueringsfraksionering (prep-TREF) is gebruik om polimeermonsters
wat homogeenkristalliseerbaar is te isoleer om sodoende 'n reeks polimere met
verskillende kettingstrukture, en gevolglike morfologieë, te lewer. Tweedens, 'n addisionele reekse monsters is berei deur die verwydering van spesifieke kristalliseerbare
fraksies vanaf die grootmaatmonsters. Derdens, die temperatuurverandering van die
monsters wanneer die monsters naby aan die kristallyne smeltpunt is en wanneer hulle
deur die kristallyne smeltpunt gaan is bestudeer.
Daar is bevind dat alle rou positrondata ten beste gepas het in 'n vier-komponent
positronvernietigingsleeftydanalise. Die langste leeftyd (wat toegeskryf is aan
vernietiging van o-Ps in die amorfe fase van die materiaal) het sistematiese variasies
getoon met die volgende: hoeveelheid en aard van die kort-kettingvertaking, verandering
in taktisiteit, 'n kombinasie van beide kort-kettingvertakking en taktisiteit en veranderings
in die amorfiesefase as gevolg van verhitting. Die derde leeftyd komponent (wat
toegeskryf is aan die o-Ps vernietiging in of rondom die kristallyne areas van die
materiale) het minder variasie in hierdie reeks monsters getoon. Daar is tipies meer
variasie waargeneem in die propileenkopolimere as in die etileenkopolimere, wat ’n
weerspieëling is van die meer komplekse kettingstruktuur en ooreenstemmende
morfologie in die propileenkopolomeerreeks. Direkte bewys vir 'n bydrag van die aard
van die amorfe fase tot die grootmaat mikrohardheid van monsters is ook bevind.
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Surface bioactivity enhancement of polyetheretherketone (PEEK) by plasma immersion ion implantationLui, So-ching., 雷素青. January 2009 (has links)
published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy
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L'orientation et la propriété de mémoire de forme des polymères cristallins liquides à chaînes latérales covalents et supramoléculairesFu, Shangyi January 2016 (has links)
In many studies of the side-chain liquid crystalline polymers (SCLCPs) bearing azobenzene mesogens as pendant groups, obtaining the orientation of azobenzene mesogens at a macroscopic scale as well as its control is important, because it impacts many properties related to the cooperative motion characteristic of liquid crystals and the trans-cis photoisomerization of the azobenzene molecules. Various means can be used to align the mesogens in the polymers, including rubbed surface, mechanical stretching or shearing, and electric or magnetic field. In the case of azobenzene-containing SCLCPs, another method consists in using linearly polarized light (LPL) to induce orientation of azobenzene mesogens perpendicular to the polarization direction of the excitation light, and such photoinduced orientation has been the subject of numerous studies. In the first study realized in this thesis (Chapter 1), we carried out the first systematic investigation on the interplay of the mechanically and optically induced orientation of azobenzene mesogens as well as the effect of thermal annealing in a SCLCP and a diblock copolymer comprising two SCLCPs bearing azobenzene and biphenyl mesogens, respectively. Using a supporting-film approach previously developed by our group, a given polymer film can be first stretched in either the nematic or smectic phase to yield orientation of azobenzene mesogens either parallel or perpendicular to the strain direction, then exposed to unpolarized UV light to erase the mechanically induced orientation upon the trans–cis isomerization, followed by linearly polarized visible light for photoinduced reorientation as a result of the cis–trans backisomerization, and finally heated to different LC phases for thermal annealing. Using infrared dichroism to monitor the change in orientation degree, the results of this study have unveiled complex and different orientational behavior and coupling effects for the homopolymer of poly{6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate} (PAzMA) and the diblock copolymer of PAzMA-block- poly{6-[4-(4-cyanophenyl) phenoxy]hexyl methacrylate} (PAzMA-PBiPh). Most notably for the homopolymer, the stretching-induced orientation exerts no memory effect on the photoinduced reorientation, the direction of which is determined by the polarization of the visible light regardless of the mechanically induced orientation direction in the stretched film. Moreover, subsequent thermal annealing in the nematic phase leads to parallel orientation independently of the initial mechanically or photoinduced orientation direction. By contrast, the diblock copolymer displays a strong orientation memory effect. Regardless of the condition used, either for photoinduced reorientation or thermal annealing in the liquid crystalline phase, only the initial stretching-induced perpendicular orientation of azobenzene mesogens can be recovered. The reported findings provide new insight into the different orientation mechanisms, and help understand the important issue of orientation induction and control in azobenzene-containing SCLCPs. The second study presented in this thesis (Chapter 2) deals with supramolecular side-chain liquid crystalline polymers (S-SCLCPs), in which side-group mesogens are linked to the chain backbone through non-covalent interactions such as hydrogen bonding. Little is known about the mechanically induced orientation of mesogens in S-SCLCPs. In contrast to covalent SCLCPs, free-standing, solution-cast thin films of a S-SCLCP, built up with 4-(4’-heptylphenyl) azophenol (7PAP) H-bonded to poly(4-vinyl pyridine) (P4VP), display excellent stretchability. Taking advantage of this finding, we investigated the stretching-induced orientation and the viscoelastic behavior of this S-SCLCP, and the results revealed major differences between supramolecular and covalent SCLCPs. For covalent SCLCPs, the strong coupling between chain backbone and side-group mesogens means that the two constituents can mutually influence each other; the lack of chain entanglements is a manifestation of this coupling effect, which accounts for the difficulty in obtaining freestanding and mechanically stretchable films. Upon elongation of a covalent SCLCP film cast on a supporting film, the mechanical force acts on the coupled polymer backbone and mesogenic side groups, and the latter orients cooperatively and efficiently (high orientation degree), which, in turn, imposes an anisotropic conformation of the chain backbone (low orientation degree). In the case of the S-SCLCP of P4VP-7PAP, the coupling between the side-group mesogens and the chain backbone is much weakened owing to the dynamic dissociation/association of the H-bonds linking the two constituents. The consequence of this decoupling is readily observable from the viscoelastic behavior. The average molecular weight between entanglements is basically unchanged in both the smectic and isotropic phase, and is similar to non-liquid crystalline samples. As a result, the S-SCLCP can easily form freestanding and stretchable films. Furthermore, the stretching induced orientation behavior of P4VP-7PAP is totally different. Stretching in the smectic phase results in a very low degree of orientation of the side-group mesogens even at a large strain (500%), while the orientation of the main chain backbone develops steadily with increasing the strain, much the same way as amorphous polymers. The results imply that upon stretching, the mechanical force is mostly coupled to the polymer backbone and leads to its orientation, while the main chain orientation exerts little effect on orienting the H-bonded mesogenic side groups. This surprising finding is explained by the likelihood that during stretching in the smectic phase (at relatively higher temperatures) the dynamic dissociation of the H-bonds allow the side-group mesogens to be decoupled from the chain backbone and relax quickly. In the third project (Chapter 3), we investigated the shape memory properties of a S-SCLCP prepared by tethering two azobenzene mesogens, namely, 7PAP and 4-(4'-ethoxyphenyl) azophenol (2OPAP), to P4VP through H-bonding. The results revealed that, despite the dynamic nature of the linking H-bonds, the supramolecular SCLCP behaves similarly to covalent SCLCP by exhibiting a two-stage thermally triggered shape recovery process governed by both the glass transition and the LC-isotropic phase transition. The ability for the supramolecular SCLCP to store part of the strain energy above T[subscript g] in the LC phase enables the triple-shape memory property. Moreover, thanks to the azobenzene mesogens used, which can undergo trans-cis photoisomerization, exposure the supramolecular SCLCP to UV light can also trigger the shape recovery process, thus enabling the remote activation and the spatiotemporal control of the shape memory. By measuring the generated contractile force and its removal upon turning on and off the UV light, respectively, on an elongated film under constant strain, it seems that the optically triggered shape recovery stems from a combination of a photothermal effect and an effect of photoplasticization or of an order-disorder phase transition resulting from the trans-cis photoisomerization of azobenzene mesogens.
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