Georgios Sakellariou

Bio: Georgios Sakellariou is an academic researcher from National and Kapodistrian University of Athens. The author has contributed to research in topics: Polymerization & Copolymer. The author has an hindex of 21, co-authored 56 publications receiving 1671 citations. Previous affiliations of Georgios Sakellariou include Oak Ridge National Laboratory & University of Tennessee.

Synthesis of Well-Defined Polypeptide-Based Materials via the Ring-Opening Polymerization of α-Amino Acid N-Carboxyanhydrides

Abstract: Since 1906, when Leuchs synthesized the first R-amino acid N-carboxyanhydrides (NCAs),1 later referred to as Leuchs’ anhydrides, a great number of publications dealing with the ring-opening polymerization (ROP) of these monomers (Scheme 1) has accumulated. This interest stems from the wide variety of polypeptides that this polymerization can generate. The synthetic polypeptides produced from the NCAs, although far from being monodisperse or constructed from a precise sequence and composition of R-amino acid residues, possess the ability, as their natural relative-proteins, to form R-helix and -sheet motifs. These secondary structures contribute significantly to the self-assembling character of polypeptide chains, leading to novel supramolecular structures with potential biomedical and pharmaceutical applications.2 As for their natural counterparts, it is important for such synthetic polypeptides to be well-defined with high molecular and structural homogeneity in order to favor their selfassembly into precisely defined nanostructures, a requirement for appropriate functionality. It was not until 1997, when Deming3 reported the first living initiating system for the ROP of NCAs, that the synthesis of well-defined polypeptides was achieved. Following this first report, other alternative living initiating systems or methods have also been developed. These living systems lead to well-defined homo-/copolypeptides and hybrids, with high molecular weight and structural homogeneity. Nevertheless, the earlier studies served as the springboard for developments in the whole area of polypeptide synthesis. Several excellent reviews4 have been dedicated to the ROP of NCAs, elucidating the mechanistic aspects of this polymerization. However, only a few have addressed the synthesis of polypeptide-based materials with different macromolecular architectures.4c,5,6 This review is divided into three parts. The first highlights the mechanistic developments of the ROP of NCAs from the conventional to the living initiating systems/methods; the second is dedicated to the synthesis of polypeptides and polypeptide hybrids with different macromolecular architectures; and the third deals with surface-bound polypeptides. Surface-bound polypeptides were incorporated in the review due to the great interest in biologically active surfaces for medical diagnostics and sensors.7

Non-covalent functionalization of carbon nanotubes with polymers

Abstract: Carbon nanotubes have emerged as very promising materials in various research fields spanning from biotechnology to energy storage and transformation. Their poor solubility in aqueous and organic solvents and limited compatibility with polymer matrices are major drawbacks, rendering these materials incapable of achieving their full potential. Covalent or non-covalent functionalization with polymers is considered a major key in circumventing this issue. In this feature article, the non-covalent functionalization through various types of interactions between polymers and carbon nanotubes is highlighted and their potential applications are discussed.

Surface-initiated polymerization from carbon nanotubes: strategies and perspectives

Abstract: Carbon nanotubes (CNTs) represent one of the most promising materials in nanoscience today, with their unique electronic, chemical and mechanical properties. Strong van der Waals interactions and poor solubility greatly affect their potential for applications in various fields. In the past decade, great efforts have been undertaken to modify CNTs into organophilic material via covalent and non-covalent grafting strategies. This review focuses on advances in various strategies used for the surface initiated polymerization and provides perspectives on grafting polymers covalently from CNTs.

Interfacial Energy and Glass Temperature of Polymers Confined to Nanoporous Alumina

Abstract: We report on the effect of interfacial energy on the glass temperature, Tg, of several amorphous polymers with various glass temperatures and polymer/substrate interactions confined within self-ordered nanoporous alumina (AAO). The polymers studied include poly(phenylmethylsiloxane) (PMPS), poly(vinyl acetate) (PVAc), 1,4-polybutadiene (PB), oligostyrene (PS), and poly(dimethylsiloxane) (PDMS). The segmental dynamics and associated Tg’s are studied by means of dielectric spectroscopy. The interfacial energy for the polymer/substrate interface, γSL, is calculated with Young’s equation whereas the AAO membrane surface energy is obtained by measuring contact angles for several reference liquids. We find that interfacial energy plays a significant role in the segmental dynamics of polymers under confinement within AAO. There is a trend for a decreasing glass temperature relative to the bulk with increasing interfacial energy. PDMS exhibits the highest interfacial energy and the highest reduction in glass temp...

Dynamics of Entangled cis-1,4-Polyisoprene Confined to Nanoporous Alumina

Abstract: The dynamics of unentangled cis-1,4-polyisoprene confined within self-ordered nanoporous alumina (AAO) is studied as a function of molecular weight (5000–300 g/mol) and pore size (400–25 nm) with dielectric spectroscopy. The main effects are the pronounced broadening of both segmental and chain modes with decreasing AAO pore diameter. This suggests that the global chain relaxation is retarded on confinement. Remarkably, the distribution of relaxation times is broadened even within pores with size 50 times the unperturbed chain dimensions. The glass temperature is unaffected by confinement. These results are discussed in terms of confinement and adsorption effects. Confinement effects are negligible for the studied molecular weights. Chain adsorption, on the other hand, involves time and length scales distinctly different from the bulk that can account for the experimental findings.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Current progress on the chemical modification of carbon nanotubes.

Abstract: 2.3. Ionic Liquids (ILs) 5374 2.4. Complexation Reactions on Oxidized CNTs 5375 2.5. Halogenation 5376 2.6. Cycloaddition Reactions 5377 2.7. Radical Additions 5379 2.8. Nucleophilic Additions 5381 2.9. Electrophilic Additions 5381 2.10. Electrochemical Modifications 5381 2.11. Plasma-Activation 5381 2.12. Mechanochemical Functionalizations 5382 3. Noncovalent Interactions 5382 3.1. Polynuclear Aromatic Compounds 5382 3.2. Interactions with Other Substances 5384 3.3. Interactions with Biomolecules 5385 4. Endohedral Filling 5386 4.1. Encapsulation of Fullerenes 5386 4.2. Encapsulation of Organic Substances 5387 4.3. Encapsulation of Inorganic Substances 5387 5. Decoration of CNTs with Metal Nanoparticles 5388 5.1. Covalent Linkage 5388 5.2. Direct Formation on Defect Sites 5388 5.3. Electroless Deposition 5388 5.4. Electrodeposition 5389 5.5. Chemical Decoration 5390 5.6. Deposition of Nanoparticles onto CNTs 5391 5.7. π-π Stacking and Electrostatic Interactions 5391 6. Concluding Remarks 5392 7. Acknowledgments 5392 8. References 5392

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

Abstract: The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ev...