Self-assembly of polypeptide/pi-conjugated polymer/polypeptide triblock copolymers in rod-rod-rod and coll-rod-coil conformations

Self-assembly in the bulk of a series of hybrid triblock copolymers formed by a poly(9,9-dihexylfluorene-2,7-diyl) (PHF) middle block and two poly(gamma-benzyl-L-glutamate) (PBLG) end blocks has been studied. Since the alpha-helical secondary structure of the PBLG block may be either maintained or suppressed depending on the solvent casting history, the PBLG-PHF-PBLG copolymers exhibit two different conformations: a rod-rod-rod or coil-rod-coil configuration, respectively. In order to provide insight into the influence of conformation on self-aggregation of these systems, three copolymers with different block ratio were investigated in both conformations using small- and wide-angle scattering techniques and transmission electron microscopy. Time-resolved photoluminescence measurements were performed on the same samples to explore the effect of morphology on photophysical properties. The observed photoluminescence spectra and dominant excited lifetimes of the poly(9,9-dihexylfluorene-2,7-diyl) block were found to differ markedly in rod-rod-rod and coil-rodcoil configurations and were correlated to the morphology of the self-assembled triblock copolymers

Açık Erişim ve Akademik Arşiv Politikası

The purpose of this policy is to provide global open access via internet to Özyeğin University’s scientific research results within the framework of open access principles. Open Access to research publications aims to improve the recognition of the university and its researchers and also to increase the number of citation of the publications. It also ensures the rise of the prestige of the university. The content of the academic archive is composed of preprint, postprint or publisher version of the articles, conference materials, master’s theses, PhD dissertations, book chapters and other types of publications. The inputs of the projects supported by fund providers are also included in the academic archive.Bu politikanın amacı Özyeğin Üniversitesi personelinin bilimsel yayınlarının internet aracılığı ile tüm dünyaya ücretsiz olarak açık erişim prensipleri çerçevesinde erişime açık olarak sağlanmasıdır. Araştırma yayınlarının açık erişim yolu ile yayınlanması, hem üniversitenin hem de araştırmacıların tüm dünyada tanınırlığının artmasına ve araştırmaların daha fazla atıf almasına yardımcı olacak; ayrıca üniversitenin saygınlığını geliştirecektir. Kapsam içeriğinde olan yayınlar Özyeğin Üniversitesinin dış dünyaya yaptığı katkılar olan araştırma literatürü, makaleler, konferans bildirileri, yüksek lisans ve doktora tezleri, kitap bölümleri ve diğer yayınların ön baskısı, son baskısı ya da yayıncı sürümüdür. Bununla birlikte araştırma literatürü kapsamında fon sağlayıcı kuruluşlarınca desteklenen proje çıktıları da yer alır

Synthesis and characterization of novel functional electrosterically stabilized colloidal particles prepared by emulsion polymerization using a strongly ionized amphiphilic diblock copolymer

Amphiphilic diblock copolymers such as poly(styrene)-block-poly(styrene sulfonate) (PS-b-PSS) (Matsuoka, H.; Maeda, S.; Kaewsaiha, P.; Matsumoto, K. Langmuir 2004, 20, 7412), belong to a class of new polymeric surfactants that ionize strongly in aqueous media. We investigated their self-assembly behavior in aqueous solutions and used them as an emulsifier to prepare electrosterically stabilized colloidal particles of different diameters between 70 to 400 nm. We determined the size, size polydispersity, effective charge, total dissociable charge, structural ordering, and phase behavior using light scattering, transmission electron microscopy (TEM), small-angle neutron scattering (SANS), and potentiometric titration. These experiments clearly demonstrated that all of the synthesized particles were nearly monodisperse (polydispersity index ≤ 6%). The results of DLS and TEM clearly suggested the existence of hairy particles. The form factors obtained by SANS were well described by a polydisperse sphere model. The estimated total number of dissociable charges per particle was found to be larger than 10⁴e, whereas the effective charges per particle were found to be around 1000e. This significant difference suggested the confinement of charges inside the corona regions of the polyelectrolyte brush shell. Finally, these monodisperse particles were found to self-assemble into 3D ordered colloidal crystalline arrays at a low volume fraction (= 0.00074) that diffract light in the visible region

Subsecond Morphological Changes in Nafion during Water Uptake Detected by Small-Angle X-ray Scattering

The ability of Nafion® membrane to absorb water rapidly and create a network of hydrated interconnected water domains provides this material with an unmatched ability to conduct ions through a chemically and mechanically robust membrane. The morphology and composition of these hydrated membranes significantly affects their transport properties and performance. This work demonstrates that differences in interfacial interactions between the membranes exposed to vapor or liquid water can cause significant changes in kinetics of water uptake. In-situ small-angle X-ray scattering (SAXS) experiments captured the rapid swelling of the membrane in liquid water with nanostructure rearrangement on the order of seconds. For membranes in contact with water vapor, morphological changes are four-orders-of-magnitude slower than in liquid water, suggesting that interfacial resistance limits the penetration of water into the membrane. Also, upon water absorption from liquid water, a structural rearrangement from a distribution of spherical and cylindrical domains to exclusively cylindrical-like domains is suggested. These differences in water-uptake kinetics and morphology provide a new perspective into Schroeder’s Paradox, which dictates different water contents for vaporand liquid-equilibrated ionomers at unit activity. The findings of this work provide critical insights into the fast kinetics of water absorption of Nafion membrane, which can aid in the design of energy conversion devices that operate under frequent changes in environmental conditions

Morphology of supported polymer electrolyte ultra-thin films: a numerical study

Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultra-thin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films has not been sufficiently explored yet. Here, we report about Molecular Dynamics simulation investigation of the substrate effects on the ionomer ultra-thin film morphology at different hydration levels. We use a mean-field-like model we introduced in previous publications for the interaction of the hydrated Nafion ionomer with a substrate, characterized by a tunable degree of hydrophilicity. We show that the affinity of the substrate with water plays a crucial role in the molecular rearrangement of the ionomer film, resulting in completely different morphologies. Detailed structural description in different regions of the film shows evidences of strongly heterogeneous behavior. A qualitative discussion of the implications of our observations on the PEMFC catalyst layer performance is finally proposed

Protonation-Induced Microphase Separation in Thin Films of a Polyelectrolyte-Hydrophilic Diblock Copolymer

Block copolymers composed of poly(oligo ethylene glycol methyl ether methacrylate) and poly(2-vinylpyridine) are disordered in the neat state but can be induced to order by protonation of the P2VP block, demonstrating a tunable and responsive method for triggering assembly in thin films. Comparison of protonation with the addition of salts shows that microphase separation is due to selective protonation of the P2VP block. Increasing acid incorporation and increasing 2-vinylpyridine content for P2VP minority copolymers both promote increasingly phase-separated morphologies, consistent with protonation increasing the effective strength of segregation between the two blocks. The self-assembled nanostructures formed after casting from acidic solutions may be tuned based on the amount and type of acid incorporation as well as the annealing treatment applied after casting, where both aqueous and polar organic solvents are shown to be effective. Therefore, POEGMA-b-P2VP is a novel ion-containing block copolymer whose morphologies can be facilely tuned during casting and processing by controlling its exposure to acid.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001088)National Science Foundation (U.S.) (Award CMMI-1246740