Advances and Applications of Block Copolymers

Polymers are materials that have constantly evolved from the beginning of their discovery until the present day. During the last few decades, polymers have been used in many areas of science and cutting-edge research and have been applied to everyday items. Many polymerization techniques, either synthetic or natural, exist to create molecularly homogeneous materials with specific properties prepared from different types of organic or even inorganic monomers

A vertical lamellae arrangement of sub-16 nm pitch (domain spacing) in a microphase separated PS-b-PEO thin film by salt addition

Ultra-small feature size (∼8 nm domain width) nanopatterns have been achieved using a symmetric polystyrene-b-polyethylene oxide (PS-b-PEO) block copolymer (BCP) of low molecular weight (PS and PEO blocks of 5.5 and 5.3 kg mol−1 respectively). The work represents the smallest feature size attained and the first observation of a well-controlled film of a perpendicularly oriented lamellar pattern in thin film form for this system. The polymer synthesized and described herein has a value χN (=7.7), below the expected BCP phase segregation limit of 10.5. These patterns were achieved by amplification of the effective interaction parameter (χeff) of the BCP system by the addition of lithium chloride (LiCl) salt. A model where the Li+ ions strongly coordinate with the PEO block without affecting the PS chain is proposed to explain the ordered self-assembly. The morphological and structural evolution for these PS-b-PEO/LiCl thin films was investigated by variation of the experimental parameters such as temperature, annealing time, salt concentrations, solution aging time, annealing solvent etc. All the experimental parameters have significant effects on the morphology, domain spacing, defectivity or surface roughness of these symmetric BCP thin films as evident from different microscopic and spectroscopic techniques. Possible hard mask applications in the area of lithography are demonstrated

Characterization of a 4-miktoarm star copolymer of the (PS-b-PI) 3 PS type by temperature gradient interaction chromatography

Abstract Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species

Biodegradation of mixture of plastic films by tailored marine consortia

Summarization: This work sheds light on the physicochemical changes of naturally weathered polymer surfaces along with changes of polymer buoyancy due to biofilm formation and degradation processes. To support the degradation hypothesis, a microcosm experiment was conducted where a mixture of naturally weathered plastic pieces was incubated with an indigenous pelagic community. A series of analyses were employed in order to describe the alteration of the physicochemical characteristics of the polymer (FTIR, SEC and GPC, sinking velocity)as well as the biofilm community (NGS). At the end of phase II, the fraction of double bonds in the surface of microbially treated PE films increased while changes were also observed in the profile of the PS films. The molecular weight of PE pieces increased with incubation time reaching the molecular weight of the virgin pieces (230,000 g mol−1)at month 5 but the buoyancy displayed no difference throughout the experimental period. The number-average molecular weight of PS pieces decreased (33% and 27% in INDG and BIOG treatment respectively), implying chain scission; accelerated (by more than 30%)sinking velocities compared to the initial weathered pieces were also measured for PS films with biofilm on their surface. The orders Rhodobacterales, Oceanospirillales and Burkholderiales dominated the distinct platisphere communities and the genera Bacillus and Pseudonocardia discriminate these assemblages from the planktonic counterpart. The functional analysis predicts overrepresentation of adhesive cells carrying xenobiotic and hydrocarbon degradation genes. Taking these into account, we can suggest that tailored marine consortia have the ability to thrive in the presence of mixtures of plastics and participate in their degradation. Παρουσιάστηκε στο: Journal of Hazardous Material

Fabrication of ultra-dense sub-10 nm in-plane Si nanowire arrays by using a novel block copolymer method: optical properties

The use of a low-χ, symmetric block copolymer as an alternative to the high-χ systems currently being translated towards industrial silicon chip manufacture has been demonstrated. Here, the methodology for generating on-chip, etch resistant masks and subsequent pattern transfer to the substrate using ultra-small dimension, lamellar, microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) is described. Well-controlled films of a perpendicularly oriented lamellar pattern with a domain size of ∼8 nm were achieved through amplification of an effective interaction parameter (χeff) of the BCP system. The self-assembled films were used as ‘templates’ for the generation of inorganic oxides nanowire arrays through selective metal ion inclusion and subsequent processing. Inclusion is a significant challenge because the lamellar systems have less chemical and mechanical robustness than the cylinder forming materials. The oxide nanowires of uniform diameter (∼8 nm) were isolated and their structure mimics the original BCP nanopatterns. We demonstrate that these lamellar phase iron oxide nanowire arrays could be used as a resist mask to fabricate densely packed, identical ordered, good fidelity silicon nanowire arrays on the substrate. Possible applications of the materials prepared are discussed, in particular, in the area of photonics and photoluminescence where the properties are found to be similar to those of surface-oxidized silicon nanocrystals and porous silicon

Carbon nanostructures derived through hypergolic reaction of conductive polymers with fuming nitric acid at ambient conditions

Hypergolic systems rely on organic fuel and a powerful oxidizer that spontaneously ignites upon contact without any external ignition source. Although their main utilization pertains to rocket fuels and propellants, it is only recently that hypergolics has been established from our group as a new general method for the synthesis of different morphologies of carbon nanostructures depending on the hypergolic pair (organic fuel-oxidizer). In search of new pairs, the hypergolic mixture described here contains polyaniline as the organic source of carbon and fuming nitric acid as strong oxidizer. Specifically, the two reagents react rapidly and spontaneously upon contact at ambient conditions to afford carbon nanosheets. Further liquid-phase exfoliation of the nanosheets in dimethylformamide results in dispersed single layers exhibiting strong Tyndall effect. The method can be extended to other conductive polymers, such as polythiophene and polypyrrole, leading to the formation of different type carbon nanostructures (e.g., photolumincent carbon dots). Apart from being a new synthesis pathway towards carbon nanomaterials and a new type of reaction for conductive polymers, the present hypergolic pairs also provide a novel set of rocket bipropellants based on conductive polymers.Web of Science266art. no. 159

Microwave synthesis, characterization and perspectives of wood pencil-derived carbon

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount of waste into added value carbon product. In particular, we demonstrate the microwave synthesis of carbon from the wood pencil with and without chemical activation. This could be a process stage before the final recycling of the expensive graphite core. In the latter case, irradiation of the wood pencil in a domestic microwave oven heats up the pencil's graphite core, thus inducing carbonization of its wood casing. The carbonized product consists of amorphous carbon nanosheets having relatively low surface area. However, if the wood pencil is soaked in 50% KOH aqueous solution prior to microwave irradiation, a significantly higher surface area of carbon is obtained, consisting of irregular-shaped porous particles. Consequently, the obtained carbon can easily decolorize a methylene blue aqueous solution, can be used to make pocket warmers or gunpowder, and lastly, serves as an excellent adsorbent towards Cr(VI) removal from water, showing a maximum adsorption capacity of 70-75 mg/g within 24 h at 23 degrees C, pH = 3.Web of Science121art. no. 41

Alternating Gyroid Network Structure in an ABC Miktoarm Terpolymer Comprised of Polystyrene and Two Polydienes

The synthesis, molecular and morphological characterization of a 3-miktoarm star terpolymer of polystyrene (PS, M¯¯¯¯n = 61.0 kg/mol), polybutadiene (PB, M¯¯¯¯n = 38.2 kg/mol) and polyisoprene (PI, M¯¯¯¯n = 29.2 kg/mol), corresponding to volume fractions (φ) of 0.46, 0.31 and 0.23 respectively, was studied. The major difference of the present material from previous ABC miktoarm stars (which is a star architecture bearing three different segments, all connected to a single junction point) with the same block components is the high 3,4-microstructure (55%) of the PI chains. The interaction parameter and the degree of polymerization of the two polydienes is sufficiently positive to create a three-phase microdomain structure as evidenced by differential scanning calorimetry and transmission electron microscopy (TEM). These results in combination with small-angle X-ray scattering (SAXS) and birefringence experiments suggest a cubic tricontinuous network structure, based on the I4132 space group never reported previously for such an architecture

Macromolecular architecture: novel block copolymers of styrenia (A) / isoprene (B) of the (AB)_n=1,2,3A and (AB)_3A(BA)_3 type, synthesis, characterization, morphology

By combining anionic polymerization and chlorosilane chemistry novel block polymers of the aba type, miktoarm star block copolymers of the A (AB)_2A(BA)_3 type and bridged block copolymers of the A(AB)_2A(AB)_3 type were synthesized. A is polystyrene and B is polysoprene. Characterization with various methods (sec, mo, laccs, sec-uv, h-nmr) showed that these polymers are novel molecules with certain structure and small polydispersity in molecular weight and composition. The equilibrium morphology in solid state at strong segregation was studied by tem, saxs and computer simulations. Behavior analogous to diblock copolymers was observed . Lamellar morphology was observed in all samples, except from two triblocks which exhibited cubic microdomains. The appearance of such structure in both sides at the phase diagram, for volume fractions of polysterene 0.64 and 0.33 is very important and is observed for the first time. By combining tem, saxs and computer simulations it was verified that this structure is the gyroid.Με συνδυασμό ανιοντικού πολυμερισμού και χημείας χλωροσμανιών παρασκευάστηκαν τρισυσταδικά συμπολύμερα του τύπου ΑΒΑ, μικτόκλωνα αστεροειδή συμπολύμερα κατά συστάδες του τύπου Α(ΒΑ)_2, Α(ΒΑ)_3 και γεφυροποιημένα συμπολημερή κατά συστάδες του τύπου Α(ΑΒ)_2 Α(ΑΒ)_3.Το Α αντιστοιχεί σε πολυστυρένιο και το Β σε πολυσοπρένιο. Ο χαρακτηρισμός των συμπολυμερών με διάφορες μεθόδους (sec, mo, lalls, sec-uv, h-nmr) έδειξε ότι πρόκειται για πρότυπα μόρια με καθορισμένη δομή και μικρή κατανομή ως προς το μοριακό βάρος και τη σύσταση. Μελετήθηκε η μορφολογία ισορροπίας σε στερεά κατάσταση στο όριοισχυρού διαχωρισμού με twm, saxs και εξομοίωση προβολών. Παρατηρήθηκε συμπεριφορά αντίστοιχη με εκείνη των δισυσταδικών συμπολυμερών. Εμφανίστηκε φυλλοειδής μορφολογία εκτός δύο τρισυσταδικών συμπολυμερών που εμφάνισαν κυβική δισυνεχή δομή. Βασικό είναι το γεγονός της εμφάνισης της δομής αυτής και στις δυο΄πλευρές του διαγράμματος φάσεων, για κλάσματα λογκου ως προς πολυστυρένιο 0.64 και 0.33. Απο συνδυασμένη μελέτη tem, saxs και εξομοίωσης προβολών αποδείκτηκε ότι η δομή είναι η gyroid