Synthesis and Self-Assembly of Polymeric Hybrid Nanomaterials

The ability to construct functional polymeric hybrid nanomaterials is critically important for many applications. In this thesis I present the synthesis of amphiphilic polymers of various compositions including insulating coil-coil, semiconducting rod-coil, semiconducting brush-coil, and bioconjugated rod-coil polymers. The self-assembly of these polymers is presented along with methodologies for controlling the organization of nanomaterials and polymers towards the construction of functional hybrid materials with controllable structures and properties. In this thesis, an analysis of the conditions necessary to stabilize the cooperative self-assembly of nanoparticles and amphiphilic block copolymers into a unique cavity-like structure is presented. This work reveals the mechanism behind the formation of the structure and presents experimental and theoretical phase maps that show the conditions required to stabilize this structure for a range of nanoparticle sizes. These self-assembly guidelines provide an essential foundation for the generation of functional composites with predesigned structures and properties. A high-yield click chemistry synthesis of an amphiphilic conjugated block copolymer with systematic block lengths that self-assembles into well-defined nanofibers whose length can be effectively controlled by varying the relative block-lengths is also presented. Furthermore, superstructures of bundled and branched nanofibers with tunable shapes, lengths, and densities were fabricated through hierarchical self-assembly. This work demonstrates that complex superstructures of organic semiconductors can be fabricated via bottom-up self-assembly approach using preformed nanofibers as building blocks. The solution phase self-assembly of an amphiphilic conjugated brush copolymer into an elongated nanoribbon structure is also reported. The subtle effects of hydrogen bonding and pi-pi stacking interactions were investigated and found to be critical in the formation of this unusual structure which has not been reported for amphiphilic conjugated block copolymers and is important because it could offer insight into how internal packing structures affect the electronic properties of the polymer. The synthesis and self-assembly of a bio-conjugated rod-coil block copolymer into distinct nanostructures is also presented. These functional bio-conjugated polymers combine the optoelectronic properties of semiconducting polymers with the bio-recognition properties of DNA and is important because it offers a new approach to forming semiconducting nanostructures with controllable geometries by self-assembly and to interface with biological molecules

Measurement of the F2 structure function in deep inelastic e+^{+}p scattering using 1994 data from the ZEUS detector at HERA

We present measurements of the structure function \Ft\ in e^+p scattering at HERA in the range 3.5\;\Gevsq < \qsd < 5000\;\Gevsq. A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At \qsd < 35 \;\Gevsq the range in x now spans 6.3\cdot 10^{-5} < x < 0.08 providing overlap with measurements from fixed target experiments. At values of Q^2 above 1000 GeV^2 the x range extends to 0.5. Systematic errors below 5\perc\ have been achieved for most of the kinematic urray, W

Comparison of ZEUS data with standard model predictions for e+p→e+Xe^+ p \rightarrow e^+ X scattering at high xx and Q2Q^2

Using the ZEUS detector at HERA, we have studied the reaction e(+)p --> e(+)X for Q(2) > 5000 GeV2 with a 20.1 pb(-1) data sample collected during the years 1993 to 1996. For Q(2) below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q(2) > 35000 GeV2. two events are observed while 0.145 +/- 0.013 events are expected, A statistical analysis of a large ensemble of simulated Standard Model experiments indicates that with probability 6.0%, an excess at least as unlikely as that observed would occur above some Q(2) cut. For x > 0.55 and y > 0.75, four events are observed where 0.91 +/- 0.08 events are expected, A statistical analysis of the two-dimensional distribution of the events in x and y yields a probability of 0.72% for the region x > 0.55 and y > 0.25 and a probability of 7.8% for the entire Q(2) > 5000 GeV2 data sample. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region

Measurement of Elastic ϕ\phi Photoproduction at HERA

The production of $\phi$ mesons in the reaction $e^{+}p \rightarrow e^{+} \phi p$ ($\phi \rightarrow K^{+}K^{-}$) at a median $Q^{2}$ of $10^{-4} \ \rm{GeV^2}$has been studied with the ZEUS detector at HERA. The differential$\phi$photoproduction cross section$d\sigma/dt$has an exponential shape and has been determined in the kinematic range$0.1<|t|<0.5 \ \rm{GeV^2}$and$60 < W < 80 \ \rm{GeV}$. An integrated cross section of$\sigma_{\gamma p \rightarrow \phi p} = 0.96 \pm 0.19^{+0.21}_{-0.18}$$\rm{\mu b}$has been obtained by extrapolating to {\it t} = 0. When compared to lower energy data, the results show a weak energy dependence of both$\sigma_{\gamma p \rightarrow \phi p}$and the slope of the$t$distribution. The$\phi$decay angular distributions are consistent with$s$-channel helicity conservation. From lower energies to HERA energies, the features of$\phi$ photoproduction are compatible with those of a soft diffractive process.Comment: 23 pages, including 6 post script figure

Synthesis and self-assembly of polymeric hybrid nanomaterials

The ability to construct functional polymeric hybrid nanomaterials is critically important for many applications. In this thesis I present the synthesis of amphiphilic polymers of various compositions including insulating coil-coil, semiconducting rod-coil, semiconducting brush-coil, and bioconjugated rod-coil polymers. The self-assembly of these polymers is presented along with methodologies for controlling the organization of nanomaterials and polymers towards the construction of functional hybrid materials with controllable structures and properties. In this thesis, an analysis of the conditions necessary to stabilize the cooperative self-assembly of nanoparticles and amphiphilic block copolymers into a unique cavity-like structure is presented. This work reveals the mechanism behind the formation of the structure and presents experimental and theoretical phase maps that show the conditions required to stabilize this structure for a range of nanoparticle sizes. These self-assembly guidelines provide an essential foundation for the generation of functional composites with predesigned structures and properties. A high-yield click chemistry synthesis of an amphiphilic conjugated block copolymer with systematic block lengths that self-assembles into well-defined nanofibers whose length can be effectively controlled by varying the relative block-lengths is also presented. Furthermore, superstructures of bundled and branched nanofibers with tunable shapes, lengths, and densities were fabricated through hierarchical self-assembly. This work demonstrates that complex superstructures of organic semiconductors can be fabricated via bottom-up self-assembly approach using preformed nanofibers as building blocks. The solution phase self-assembly of an amphiphilic conjugated brush copolymer into an elongated nanoribbon structure is also reported. The subtle effects of hydrogen bonding and pi-pi stacking interactions were investigated and found to be critical in the formation of this unusual structure which has not been reported for amphiphilic conjugated block copolymers and is important because it could offer insight into how internal packing structures affect the electronic properties of the polymer. The synthesis and self-assembly of a bio-conjugated rod-coil block copolymer into distinct nanostructures is also presented. These functional bio-conjugated polymers combine the optoelectronic properties of semiconducting polymers with the bio-recognition properties of DNA and is important because it offers a new approach to forming semiconducting nanostructures with controllable geometries by self-assembly and to interface with biological molecules

Hierarchical Self-Assembly of Amphiphilic Semiconducting Polymers into Isolated, Bundled, and Branched Nanofibers

Herein, we report a high-yield click synthesis and self-assembly of conjugated amphiphilic block copolymers of polythiophene (PHT) and polyethylene glycol (PEG) and their superstructures. A series of different length PHT_<i>m</i>-<i>b</i>-PEG_<i>n</i> with well-defined relative block lengths was synthesized by a click-coupling reaction and self-assembled into uniform and stably suspended nanofibers in selective solvents. The length of nanofibers was controllable by varying the relative block lengths while keeping other dimensions and optical properties unaffected for a broad range of <i>f</i>_PHT (0.41 to 0.82), which indicates that the packing of PHT dominates the self-assembly of PHT_<i>m</i>-<i>b</i>-PEG_<i>n</i>. Furthermore, superstructures of bundled and branched nanofibers were fabricated through the self-assembly of PHT_<i>m</i>-<i>b</i>-PEG_<i>n</i> and preformed PHT nanofibers. The shape, length, and density of the hierarchical assembly structures can be controlled by varying the solvent quality, polymer lengths, and block copolymer/homopolymer ratio. This work demonstrates that complex superstructures of organic semiconductors can be fabricated through the bottom-up approach using preformed nanofibers as building blocks

Self-Assembly of Amphiphilic Conjugated Diblock Copolymers into One-Dimensional Nanoribbons

The colloidal self-assembly of a new conjugated diblock copolymer of a polythiophene derivative, poly­[3-(2,5,8,11-tetraoxatridecanyl)­thiophene]-<i>block</i>-poly­(ethylene glycol) (PTOTT-<i>b</i>-PEG), led to various well-defined assembly structures such as vesicles, sheets, and nanoribbons. A unique and technologically relevant nanoribbon structure with a dimension reaching tens of micrometers was formed in water when polar protic solvents were used as initial cosolvents. Self-assembly of PTOTT-<i>b</i>-PEG in various solvent compositions and polymer concentrations indicated that the hydrogen bonding between the diblock copolymer and the self-assembly medium plays an important role in determining the self-assembly structure and that the final assembly structure should be the result of a delicate interplay between hydrogen bonding and π–π interactions. This study demonstrates that the addition of hydrogen bonding capability and amphiphilicity in the self-assembly of conjugated polymers can lead to many interesting well-defined assembly structures that are not typically found in conjugated polymers

Oxidation-Induced Photoluminescence of Conjugated Polymers

Here, we report an unusual oxidation-induced photoluminescence (PL) turn-on response of a poly­(3-alkoxythiophene), poly­(3-{2-[2-(2-ethoxyethoxy)­ethoxy]­ethoxy}­thiophene) (PEEEET). PEEEET shows a significantly red-shifted absorption spectrum compared to polyalkylthiophenes and is almost nonfluorescent (quantum yield ≪ 1%) in its pristine state. The introduction of sulfonyl defects along the polymer backbone by the oxidation of PEEEET with <i>meta</i>-chloroperbenzoic acid (<i>m</i>-CPBA) increased the emission quantum yield with the intensity increasing with the degree of oxidation. Molecular modeling data indicated that the oxidation-induced PL increase cannot be explained by the nature of monomer units and radiative rate changes. We attributed the enhanced fluorescence to the reduced nonradiative rate caused by the increased band gap, according to the energy gap law, which is consistent with the observed blue shifts in absorption and PL spectra accompanied by the PL increase