George Floudas

University of Ioannina | UOI · Department of Physics

Binary blends of polyterpenes are employed comprising cis ‐1,4‐polyfarnesene (PF) with a bottlebrush architecture, and linear cis ‐1,4‐polyisoprene (PI) as model systems toward supersoft polymer melts. The bottlebrush PF results in a low plateau modulus ( Pa) that can further be reduced with the addition of PI. Depending on the fraction of short PI...

The self‐assembly and dynamics of amphiphilic diblock copolymers composed of densely grafted poly(oligo ethylene glycol methacrylate) (POEGMA) and poly(lauryl methacrylate) (PLMA) by means of calorimetry, small‐angle X‐ray scattering (SAXS), and dielectric spectroscopy are investigated. It is reported that the inherent immiscibility between the par...

Oscillations in the chemical or physical properties of materials, composed of an odd or even number of connected repeating methylene units, are a well-known phenomenon in organic chemistry and materials science. So far, such behavior has not been reported for the important class of materials, perovskite semiconductors. This work reports a distinct...

We present a detailed computational study on the temperature effect of the dynamics and the interfacial width of unentangled cis-1,4 polybutadiene linear chains confined between strongly attractive alumina layers via long, several μs, atomistic molecular dynamics simulations for a wide range of temperatures (143–473 K). We examine the spatial gradi...

The topology of a polymer profoundly influences its behavior. However, its effect on imbibition dynamics remains poorly understood. In the present work, capillary filling (during imbibition and following full imbibition) of star polymer melts was investigated by molecular dynamics simulations with a coarse-grained model. The reversal of imbibition...

We report the imbibition and adsorption kinetics of a series of symmetric linear/star cis-1,4-polyisoprene blends within the long channels of self-ordered nanoporous anodic aluminum oxide (abbreviated: AAO). Using in situ nanodielectric spectroscopy, we followed the evolution of the longest chain modes in the blends with a judicious selection of mo...

A terrylenedicarboximide–anthraquinone dyad, FTQ, with absorption in the second near-infrared region (NIR-II) is obtained as a high-performance chromophore for photothermal therapy (PTT). The synthetic route proceeds by C–N coupling of amino-substituted terrylenedicarboximide (TMI) and 1,4-dichloroanthraquinone followed by alkaline-promoted dehydro...

Using in situ nanodielectric spectroscopy, we report the imbibition kinetics of star cis-1,4-polyisoprenes in alumina nanopores as a function of chain architecture (linear vs multiarm stars), pore size, molar mass, and temperature. We demonstrate that the imbibition kinetics of star cis-1,4-polyisoprenes proceeds via a slow adsorption mechanism, ab...

1-propanol/water mixtures over the whole composition range (0 < XV ≤ 1; XV is the 1-propanol volume fraction) are shown to be structurally and dynamically heterogeneous. By combining structural (x-ray diffraction), thermodynamic (differential scanning calorimetry) and dynamical probes (dielectric spectroscopy) we construct the pertinent phase diagr...

The conductivity of ionic liquids (ILs) in nanopores is essential when considering their application as materials for energy. However, no consensus has been reached about the influence of confinement on the mobility of the ions. A series of ILs bearing the same cation, 1-butyl-3-methylimidazolium ([BMIM]+), and six different anions ([Cl]-, [Br]-, [...

Semicrystalline polymers are solids that are supposed to flow only above their melting temperature. By using confinement within nanoscopic cylindrical pores, we show that a semicrystalline polymer can flow at temperatures below the melting point with a viscosity intermediate to the melt and crystal states. During this process, the capillary force i...

We performed molecular dynamics simulations with a coarse-grained model to investigate the capillary filling dynamics of polymer chains in nanopores. Short chains fill slower than predicted by the Lucas-Washburn equation but long chains fill faster. The analysis shows that the combination of the confinement effect on the free energy of chains and t...

We provide a fundamental understanding of the interaction between cis-1,4-polybtadiene (PB) and the alumina (001) surface via a computational multi-stage methodology involving density functional theory (DFT) calculations and atomistic simulations. The latter were performed via newly derived, computationally efficient, pairwise-additive, parametric...

A series of completely amorphous polymer brushes composed of grafted copolymer electrolytes based on the ion-containing block of poly(acrylic acid-co-oligo ethylene glycol acrylate) (P(AA-co-OEGA)) doped with LiCF3SO3 (LiTf) or LiN(SO2CF3) (LiTFSI) and the glassy polystyrene (PS) block are synthesized and studied with respect to the structural, the...

The non-equilibrium dynamics of linear and star-shaped cis-1,4 polyisoprenes confined within nanoporous alumina is explored as a function of pore size, d, molar mass, and functionality (f = 2, 6, and 64). Two thermal protocols are tested: one resembling a quasi-static process (I) and another involving fast cooling followed by annealing (II). Althou...

High molar mass copolymers with a tapered interface are mechanically tough materials with an accessible order-to-disorder transition temperature and hence processability. We report the first ordering kinetics for a tapered tetrablock copolymer in comparison to a conventional diblock copolymer made sequentially. We show that tapered copolymers belon...

Although several phase diagrams of block copolymers prepared by sequential monomer addition are known today, the phase diagrams of the corresponding tapered copolymers have not been reported in detail and this despite the industrial importance of the latter. A phase diagram based on a series of tapered diblock copolymers is reported, generated by t...

We report the effect of confinement on the dynamics of three monohydroxy alcohols (1-propanol, 2-ethyl-1-hexanol, and 4-methyl-3-heptanol) differing in their chemical structure and, consequently, in the dielectric strength of the “Debye” process. Density functional theory calculations in bulk 1-propanol identified both linear and ring-like associat...

Cryo-enzymology provides the possibility to develop unconventional biological reactions and detect intermediates in ultrafast enzymatic catalysis processes, but also illuminates the understanding of life principles in extremely cold environments. The scarcity of biological or biomimetic host systems that provide liquid water at subzero temperatures...

Melts of multiarm stars of 1,4-polybutadiene (dendrimer arborescent hybrids) with very high branching functionality (f) and small arm molar mass behave as jammed colloids and show distinct layers of segmental mobility. Three mobility layers were identified, comprising outer, intermediate, and near-core segments, all displaying a Vogel-Fulcher-Tamma...

Diblock copolymer electrolytes based on a π-conjugated polyfluorene (PF) backbone were synthesized comprising nanodomains of a polymerized ionic liquid (PIL) and of a solid polymer electrolyte (SPE). The former consists of a single-ion conductor based on an imidazolium alkyl chain with a [Br]- counteranion grafted on the PF backbone. The latter con...

The polarity of all-cis-multifluorinated cyclohexanes can be fine-tuned by the number and relative orientation of fluoro substituents, giving rise to a series of compounds with strong dipole moments. Simulations provided the energetics, the dipole moments, and the respective molecular polarizabilities, while dielectric spectroscopy gave information...

Front Cover: The poor mechanical properties of diblock copolymers can be enhanced by blending with tapered multiblock copolymers. In article number 2000373, George Floudas, Holger Frey, and co‐workers demonstrate enhanced elastic response and toughness introduced by the addition of a limited amount of a multiblock copolymer. These results may guide...

This work explores the scope and limitations of enhancing the poor mechanical properties of diblock copolymers by blending with tapered multiblock copolymers of styrene (S) and isoprene (I), P(I‐co‐S)n. Blending of different tapered diblock copolymers (n = 1; Mn = 80 and 240 kg mol−1, 50 wt% polyisoprene (PI) units, lamellar morphologies) affords b...

The phase state and molecular dynamics of 1-dodecanol are studied in the bulk and under nanometer confinement within self-ordered nanoporous alumina templates. A rotator phase in the bulk is absent under confinement. A nematic liquid crystalline phase is formed instead in pores with diameters from 400 down to 25 nm. Results are based on the changes...

Using in situ nanodielectric spectroscopy we demonstrate that the imbibition kinetics of cis-1,4-polyisoprene in native alumina nanopores proceeds in two time regimes both with higher effective viscosity than bulk. This finding is discussed by a microscopic picture that considers the competition from an increasing number of chains entering the pore...

Mapping the spatial and temporal heterogeneities in miscible polymer blends is critical for understanding and further improving their material properties. However, a complete picture on the heterogeneous dynamics is often obscured in ensemble measurements. Herein, the spatial and temporal heterogeneities in fully miscible polystyrene/oligostyrene b...

The year 2020 marks the 100th anniversary of the first article on polymerization, published by Hermann Staudinger. It is Staudinger who realized that polymers consist of long chains of covalently linked building blocks. Polymers have had a tremendous impact on the society ever since this initial publication. People live in a world that is almost im...

Conjugation-break flexible spacers in-between π-conjugated segments were utilized herein, towards processable perylene diimide (PDI) based polymers. Aromatic-aliphatic PDI-based polymers were developed via the two-phase polyetherification of a phenol-difunctional PDI monomer and aliphatic dibromides. These polyethers presented excellent solubility...

Two series of well-defined multiblock four-arm tapered star copolymers with “arms” of the type poly(styrene)-block-poly(isoprene-grad-styrene), (SI/S)4, were synthesized on a multigram scale with short reaction times. Targeted molecular weight (M) values ranged from 80 to 240 kg mol–1 with polystyrene (PS) compositions of 40 and 60 wt %. Narrowly d...

The self-assembly and the dynamics of a H-shaped copolymer composed of polyethylene mid-block and four poly(ethylene oxide) arms (PE-b-4PEO) are investigated in the bulk and under severe confinement into nanometer spaced LAPONITE® clay particles by means of small- and wide-angle X-ray diffraction (SAXS, WAXS), differential scanning calorimetry (DSC...

Disentangling temporally-overlapping charge carrier recombination events in organic bulk heterojunctions by optical spectroscopy is challenging. Here, a new methodology for employing delayed luminescence spectroscopy is presented. The proposed method is capable of distinguishing between recombination of spatially-separated charge carriers and trap-...

The eutectic mixture of liquid crystals E7 is studied in confinement by means of thermal and dielectric measurements. The uniform 1-D confinement provided by self-ordered nanoporous alumina leads to a decrease in the nematic to isotropic transition temperature due to interaction with the pore surface, e.g. surface anchoring. The prevalence of certa...

A fluid dynamic model for imbibition into closed-end, axisymmetric pores having diameters that change as a function of the pore depth is presented. Despite the fact that liquid invasion into nonbranched closed-end pores is characterized by a wealth of different transient and/or metastable nonequilibrium stages related to precursor film formation, w...

The dynamics of a series of entangled cis-1,4-polyisoprenes located within self-ordered nanoporous alumina templates are studied as a function of the degree of confinement, 2Rg/d (Rg is the radius of gyration and d is the pore diameter) with dielectric spectroscopy and temperature-modulated differential scanning calorimetry. For the higher molecula...

Low power density of polymer piezoelectric nanogenerators is a major hurdle for their application as a potential mode of powering wearable and portable electronic devices. To increase the efficiency, here we suggest use of porous piezoelectric poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanofibers. However, designing a process that...

The crystallization and dynamics of water confined in model mesoporous silica particles (MPS, pore diameters ranging from 2.1 nm to 5 nm; pore length ~ 1μm) are studied in homogeneous aqueous suspensions by dielectric spectroscopy, differential scanning calorimetry and nuclear magnetic resonance (NMR) techniques. We establish the phase diagram (T v...

Polyesters from 2,5-furandicarboxylic acid are considered as biobased alternatives to their terephthalate counterparts. This work is focused on polymer blends comprised of furan-based polyesters differing by one or two methylene groups in their repeat units. Blends of Poly(ethylene 2,5-furandicarboxylate) (PEF) and poly(propylene 2,5-furandicarboxy...

The synthesis of tapered multiblock copolymers by statistical living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in cyclohexane is based on vastly different reactivity ratios of I and 4MS (r I = 25.4 and r 4MS = 0.007). A library of tapered multiblock copolymers was prepared with different molecular weights (appr...

To explore the potential of myrcene (Myr) as a bio-based monoterpene comonomer for styrenic copolymers and to establish its general applicability for the carbanionic copolymerisation, several statistical copolymerisations of myrcene and common monomers like isoprene (I), styrene (S) and 4 methylstyrene (4MS) were carried out in cyclohexane and moni...

The living anionic copolymerization of isoprene and styrene in cyclohexane affords tapered block copolymers due to the highly disparate reactivity ratios of rI = 12.8 and rS = 0.051. Repeated addition of a mixture of these monomers was exploited to generate tapered multiblock copolymer architectures of the (AB)n type with up to 10 blocks (1 ≤ n ≤ 5...

Statistical and block copolymerization of poly(l-lactide) (PLLA) and poly(ϵ-caprolactone) (PCL) macromonomers having an end norbornenyl group was performed via ring-opening metathesis polymerization (ROMP) to produce the corresponding statistical and block brush copolymers consisting of PLLA and PCL side chains on a polynorbornene (PNBE) backbone....

Single ion conductors, based on polymerized ionic liquids (PILs) with a polythiophene backbone bearing imidazolium salts with butyl, hexyl, octyl, and decyl side groups and six different counteranions ([Br]⁻, [BF4]⁻, [ClO4]⁻, [PF6]⁻, picrate, and [B(Ph)4]⁻), are synthesized and studied with respect to the thermal, structural, and ion-conductivity p...

Subtle alterations in the mid-block of polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) have a significant impact on the mechanical properties of the resulting microphase separated materials. In samples with high butylene content, the ethylene-co-butylene (EB) phase behaves as a rubber, as seen by differential scanning calorimetry (DS...

A series of blends of furan‐based green polyesters, for eco‐friendly packaging materials, are synthesized. Poly(ethylene 2,5‐furandicarboxylate) (PEF), poly(propylene 2,5‐furandicarboxylate) (PPF), and poly(butylene 2,5‐furandicarboxylate) (PBF) are synthesized by applying melt polycondensation. Blends of the above polyesters with 50/50 w/w composi...

A unified theory for the imbibition dynamics of entangled polymer melting into nanopores is presented. Experiments demonstrate the validity of t1/2 dependence but contradict the predictions of the classical Lucas–Washburn equation because of the prefactor. A reversal in dynamics of capillary filling is reported with increasing polymer molecular wei...

Local polymer dynamics are studied in polymers bearing dipoles rigidly attached to the backbone. The compounds are based on cyano-substituted dihydrobenzimidazoles bearing ultrastrong dipole moments (∼12 D per repeat unit) incorporated in a poly-p-phenylene backbone, giving rise to polymers with rigid dipoles perpendicular to the chain. They belong...

We studied experimentally the influence of interfaces on the dynamics in thin polymer films at temperatures far above the glass temperature (Tg + 80 °C). Polyisoprene (PI) was employed as a model system. We examined glass substrate supported films with thicknesses (d) spanning the range from 10 μm to 10 nm that correspond to d/Rg from 400 to 1, whe...

Altering the stereochemistry of a single double bond in the side group of a polymer resulted in systems with unprecedented local dynamics. These include (i) the appearance of three segmental processes in the cis-polymers all with Vogel–Fulcher–Tammann (VFT) temperature dependence, (ii) the low steepness index associated with fragility, m, and (iii)...

The crystallization and dynamics of hyperbranched poly(ethylene oxide) (hbPEO), obtained from the direct random copolymerization of EO and glycidol (PEO-co-PG), are studied both in bulk and within nanoporous alumina (AAO). Copolymerization decreases the degree of crystallinity and lowers the crystallization and melting temperatures as compared to l...

The effect of oxygen substitution is studied in two homologous compounds of n-cyanobiphenyls with n=8 in the bulk and under confinemnet within self-ordered nanoporous alumina (AAO). Oxygen substitution in 8OCB increases the dipole moment and stabilizes the crystalline, smectic and nematic phases to higher temperatures relative to 8CB. Within their...

Permeability is the key property of nanocapsules because it dictates the release rate of encapsulated payloads. Herein, we engineer the crystallinity of polymers confined in the shell of nanocapsules. Nanocapsules with crystalline shells are formed from polyurea and polyphosphoester. The thermal properties, such as crystallization temperature and d...

Benzothiadiazoles are important electron acceptors and are frequently employed as electron-deficient components of donor-acceptor polymers. We report the effect of nitrile-functionalities on the reactivity, steric hindrance, optoelectronic properties and dielectric permittivity in dicyanobenzothioadiazole (DCNBT). Dielectric spectroscopy in the bul...

Capillary penetration of a series of entangled poly(ethylene oxide) melts within nanopores of self-ordered alumina follows an approximate t1/2 behavior according to the Lucas-Washburn equation; t is the time. However, the dependence on the capillary diameter deviates from the predicted proportionality to d1/2; d is the pore diameter. We observed a...

Random copolymers—usually considered as dynamically homogeneous with a single glass temperature—can show dynamic heterogeneity by appropriate choice of their repeat units. Random copolymers based on polymethacrylates with polyhedral oligomeric silsesquioxane (POSS) moieties as side groups substituted with seven isobutyl ((i-Bu)7POSS-OSiMe2(CH2)3-MA...