Bridging Chain Research Articles

Filler free technology for enhanced thermally conductive optically transparent polymeric materials using low thermally conductive organic linkers

This work presents for the first time a non-conventional technology for higher thermally conductive optically transparent polymeric material by employing lower thermally conductive organic molecules. In last couple of decades, practically all work on thermally conductive polymer based materials has been mainly confined to conventional polymer-filler composites which comes with various challenges like high loading, expensive fillers, etc., in addition to pronounced phonon scattering at filler-polymer interface. In this work, we have thrown light on alternating yet promising strategy for thermally conductive polymer based materials without incorporating any traditional metallic, ceramic or carbon fillers. One of the fascinating fact is the achievement of effective higher thermal conductivity in spite of using constituent components with lower thermal conductivity. This was achieved by rationally designed polymer-organic molecules system where thermal conduction was induced by engineering intermolecular interaction within the polymer chain. Additionally, these materials were optically transparent. Apart from presenting these new classes of materials, this study generates some of the prominent fundamental understanding on the heat transport of polymers. Short chains of diethylene glycol (DEG) were incorporated into base polymer matrix of polyvinyl alcohol (PVA) which lead to remarkable thermal conductivity enhancement of 260% and 175% than DEG and neat PVA respectively. Phonon transport was driven by the “thermal bridges” designed through intermolecular hydrogen bonding between PVA and DEG. A further impact of the length of “thermal bridges” and its functional groups (hydroxyl, carboxyl, carbonyl) at terminal position were investigated. It was found that shorter organic molecules are more efficient in driving thermal conduction owing to less inter-chain resistance. Interestingly, these materials were found to have inverse thermal conductivity–crystallinity relationship which is usually an opposite trend to the present belief. Overall, it was found that size, molecular geometry, terminal functional group of the thermal bridging chain in host polymer are very crucial factors in determining thermal conductance. Overall, this work demonstrates an intriguing tale of engineering intermolecular interaction in polymer based material for the development of thermally conductive and optically transparent materials for thermal management applications.

Investigation of structural, spectral and thermal properties of one-dimensional polymer containing pyromellitic acid and isonicotinamide

The coordination polymer with mixed ligand [Cu2(H2O)2 (pm) (ina)2]n.3nH2O (pm = tetraanion of pyromellitic acid, ina = isonicotinamide) was studied mostly on its supramolecular architecture. Single crystals were synthesized and structural properties of the 1D polymer were characterized by Single Crystal X-ray diffraction (SCXRD), different spectroscopic methods (Infrared (IR) spectroscopy, UV–Vis spectroscopy and EPR spectroscopy), Thermal and Elemental analysis. It has been observed that complex has crystallized in the monoclinic space group P21/c. The geometric environment of Cu(II) ion is five-coordinated in slightly distorted square pyramidal geometry and τ value have found 0.13. The pyromellitate ligands connecting the metal centers act as bridge and form 1D polymer chains of 2,4 ribbon type [1]. The ladder-like polymer is connected by OH⋯O and NH⋯O hydrogen bonds to form supramolecular building. This complex consists of a 3D polymeric structure with containing planar hexacyclic and dimeric water rings. It was mainly focused on the characteristic (COO)as and (COO)s stretching vibrations of pyromellitate anion in the FT-IR investigation of the complex.

Effect of temperature on the structure and dynamics of triblock polyelectrolyte gels.

Triblock polyelectrolyte gels were characterized by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The oppositely charged end blocks self-assemble into polyelectrolyte complex cores, while the neutral poly(ethylene oxide) middle block bridges adjacent cores. The size of the polyelectrolyte complex core does not change with temperature. However, the neutral middle block displays a temperature-dependent conformation. The liquid-like order of the complex core within the gel phase leads to stretched bridging chains that approach their unperturbed dimensions with increasing concentration. A stretch ratio for bridging chains was defined as the ratio between stretched and unperturbed dimensions. A further reduction in the chain stretching occurs with increasing temperature due to solvent quality. DLS observes multiple modes consistent with a collective diffusion (fast mode) and diffusion of clusters (slow mode). The dynamics of these clusters are at length scales associated with the SANS excess scattering, but with relaxation time near the crossover frequency observed by mechanical spectroscopy.

Effect of Chain Architecture on Self-Assembled Aggregates from Cyclic AB Diblock and Linear ABA Triblock Copolymers in Solution.

The self-assembly behaviors of two block copolymers with the same chain length but different chain architectures (cyclic AB, linear ABA) in B-selective solvents are investigated using Monte Carlo simulations. A morphological transition sequence, from spherical micelles to cylindrical micelles, to vesicles and then to multicompartment vesicles, is observed for both copolymer systems when the interaction between the solvophobic A-block and the solvent is increased. In particular, toroidal micelles could be formed in triblock systems due to the presence of the bridging chains at the parameter region between cylindrical micelles and vesicles whereas disklike micelles are formed in cyclic systems. The simulation results demonstrated that the architecture of block copolymers could be used to regulate the structural characteristics and thermal stability of these self-assembled aggregates.

Evaporation with the formation of chains of liquid bridges

The objective of the present work is to study the drying of a quasi-two-dimensional model porous medium, hereafter called the micromodel, initially filled with a pure liquid. The micromodel consists of cylinders measuring $50~\unicode[STIX]{x03BC}\text{m}$ in both height and diameter, radially arranged as a set of neighbouring spirals and sandwiched between two horizontal flat plates. As drying proceeds, air invades the pore space and elongated liquid films trapped by capillary forces form along the spirals. These films consist of ‘chains’ of liquid bridges connecting neighbouring cylinders. They provide hydraulic connectivity between the central bulk liquid cluster and the external rim of the cylinder pattern, where evaporation takes place during a first constant-evaporation-rate drying stage. The first goal of the present paper is to describe experimentally the phase distribution during drying, notably the evolution of liquid films, which controls the evaporation kinetics (e.g. the depinning of the films from the external rim signals the end of the constant-evaporation-rate period). Then, a viscocapillary model for the drying process is presented. It is based on numerical simulations of a liquid film capillary shape and viscous flow within a film. The model shows a reasonably good agreement with the experimental data. Thus, the present study is a step towards direct modelling of the effect of films on the drying of more complex porous media (e.g. packing of beads) and should be of interest for multiphase flow applications in porous media, involving transport within liquid films.

Self-locked dipillar[5]arene-based pseudo[1]rotaxanes and bispseudo[1]rotaxanes with different lengths of bridging chains

The relationships between lengths of bridging chains and self-locked behaviors of dipillar[5]arene-based pseudo[1]rotaxanes and bispseudo[1]rotaxanes were studied in detail.

A new stochastic simulation for the rheology of telechelic associating polymers

We here suggest a new Brownian dynamics algorithm for telechelic associating polymers with the aim of better understanding the complex rheological behavior of these systems and in particular of hydrophobically modified ethoxylated urethane solutions showing strain hardening in shear startup and significant deviations from the Cox–Merz rule (including shear thickening phenomena). Several molecular mechanisms have indeed been suggested to explain such a complex behavior, ranging from finite extensible nonlinear elasticity (FENE) effects, shear-induced increased association, and, very recently, flow-induced repulsive interactions between colliding flower-like micelles. The preliminary results here reported (only exploring a limited range of the wide parameter space) appear to suggest that FENE effects are mostly responsible for strain hardening, while deviations from the Cox–Merz rule are due to the persistence of bridge chains, as well as, in some cases, to the flow-induced formation of new bridges. In the explored parameter space, no significant role appears to be played by flow-induced collisions between micelles beyond that of preventing network collapse.

Salt Responsive Morphologies of ssDNA-Based Triblock Polyelectrolytes in Semi-Dilute Regime: Effect of Volume Fractions and Polyelectrolyte Length.

A comprehensive study is reported on the effect of salt concentration, polyelectrolyte block length, and polymer concentration on the morphology and structural properties of nanoaggregates self-assembled from BAB single-strand DNA (ssDNA) triblock polynucleotides in which A represents polyelectrolyte blocks and B represents hydrophobic neutral blocks. A morphological phase diagram above the gelation point is developed as a function of solvent ionic strength and polyelectrolyte block length utilizing an implicit solvent ionic strength method for dissipative particle dynamics simulations. As the solvent ionic strength increases, the self-assembled DNA network structures shrinks considerably, leading to a morphological transition from a micellar network to worm-like or hamburger-shape aggregates. This study provides insight into the network morphology and its changes by calculating the aggregation number, number of hydrophobic cores, and percentage of bridge chains in the network. The simulation results are corroborated through cryogenic transmission electron microscopy on the example of the self-assembly of ssDNA triblocks.

Time-Resolved Characterization of Dynamic Tribochemical Processes for Dicationic Imidazolium Ionic Liquid

Dynamic tribochemical processes for dicationic ionic liquid containing a geminal imidazolium cation head group bridged by a poly(ethylene glycol) and a bis(trifluoromethylsulfonyl)imide anion were studied using time-resolved mechanically stimulated gas emission mass-spectrometry (MSGE-MS). In comparison with similar monocationic imidazolium ionic liquids with short alkyl or long polyether side chains, the dicationic ionic liquid had a lower coefficient of friction on Ti6Al4V alloy and smoother behavior. The analysis of volatile decomposition products suggested multiple tribochemical reactions in which both anionic and cationic moieties are involved. The tribochemical degradation of cations was mainly through the detachment of the side and bridging chains from the imidazolium head groups. The absence of volatile products containing nitrogen implies that the imidazole group remained unchanged. Hydrogen and water desorption were attributed to the reactions of hydrogen fluoride being a product of anion degradation with titanium and titanium oxide, respectively.

Designing Block Copolymer Architectures toward Tough Bioplastics from Natural Rosin

Resin acids (or natural rosin) are a class of abundant, renewable natural biomass. Most low molecular weight resin acid-containing polymers are very brittle due to their low chain entanglement associated with the pendant, intrinsically bulky hydrophenanthrene group. The use of block copolymer architectures can enhance chain entanglement and thus improve toughness. A–B–A type triblock and A–B–A–B–A type pentablock copolymers were synthesized by ring-opening metathesis polymerization (ROMP) with one-pot sequential monomer addition of a rosin-based monomer and norbornene. We investigated the effect of chain architecture and microphase separation on mechanical properties of both types of block copolymers. Pentablock copolymers exhibited higher strength and toughness as compared to both the triblock copolymers and the corresponding homopolymers. The greater toughness of pentablock copolymers is due to the presence of the rosin-based midblock chains that act as bridging chains between two polynorbornene domains...

F-Indices and its coindices of some classes of graphs

In this paper, first we investigate the basic properties of the F-index and its coindex of graph. Next we obtain the exact expression of F-indices and its coindices for bridge graph, chain graph and transformation of graph. Using some of these results, we have obtained the value of these indices for some important classes of chemical graphs.

Telechelic Polymer Hydrogels: Relation between the Microscopic Dynamics and Macroscopic Viscoelastic Response.

Telechelic polymers, that is, hydrophilic polymers with hydrophobic end-groups, spontaneously form hydrogels consisting of interconnected micelles. Here we investigate the relation between the microscopic dynamics determining the connectivity, that is, the lifetime of the physical bonds and the resulting rheological properties. This is achieved by quantitatively relating the chain exchange kinetics measured by time-resolved small-angle neutron scattering (TR-SANS) and the mechanical response obtained from linear oscillatory shear measurements. The results show that the characteristic relaxation time obtained from rheology coincides exactly with TR-SANS at intermediate concentrations. The activation energy, Ea, is concentration-independent and remain exactly the same as for TR-SANS. Upon crossing the melting point, a discrete change in activation energy is observed showing the contribution from the enthalpy of fusion to the release/debridging process. The results clearly show that the mechanical response and connectivity indeed are controlled by molecular exchange processes. The relaxation time at the lowest concentration is found to be faster in rheology as compared to TR-SANS, which can be quantitatively attributed to entropic forces arising from conformational deformation of bridging chains.

Development of Axially Chiral Cyclo-Biaryldiol Ligands with Adjustable Dihedral Angles.

A new type of axially chiral cyclo-[1,1'-biphenyl]-2,2'-diol (CYCNOL) ligands with adjustable dihedral angles have been developed by varying the bridge chain length. Eight-, nine- and ten-membered cyclo-ligands were prepared and evaluated by using two representative examples: enantioselective additions of diethylzinc to aldehydes and organometallic reagents to enones. The results revealed that the fine regulation of dihedral angles through variation of the bridge chain length was effective in the asymmetric synthesis.

Synthesis of a novel archaeal tetraether-type lipid containing a diorthoester group as a helper lipid for gene delivery

As an alternative to recombinant virus, synthetic carriers are widely developed for providing efficient and safe DNA delivery. To reach the nucleus where nucleic acid (NA) constructs are transcripted, chemical complexes have to overcome serious cellular traps such as endosomal escape and intracellular trafficking. Here, the design and the multi-step synthesis of a stabilizing tetraether lipid analogue of archaeal counterparts containing a diorthoester moiety in the middle of the bridging chain were described. The key step involved a double coupling reaction between two diether alcohols and a diketene acetal. Under aqueous acidic conditions, the diorthoester function of the tetraether lipid can be hydrolysed to yield two monopolar diether lipids. Applied to gene delivery in association with a cationic lipid, this new helper bipolar tetraether lipid led to lipid–DNA complexes with sizes and potential zeta values depending on the charge ratios (+/−). In addition, preliminary in vitro transfection assays supported the interest of these novel bipolar lipid-based lipoplex formulations compared to standard Lipofectamine-based formulations.

Synthesis and photophysical properties of Ir(iii)/Re(i) dyads: control of Ir→Re photoinduced energy transfer.

A series of dinuclear Ir(iii)/Re(i) complexes has been prepared based on a family of symmetrical bridging ligands containing two bidentate N,N'-chelating pyrazolyl-pyridine termini, connected by a central aromatic or aliphatic spacer. The Ir(iii) termini are based on {Ir(F2ppy)2}(+) units (where F2ppy is the cyclometallating anion of a fluorinated phenylpyridine) and the Re(i) termini are based on {Re(CO)3Cl} units. Both types of terminus are luminescent, with the Ir-based unit showing characteristic strong, structured phosphorescence in the blue region (maximum 452 nm) with a triplet excited state energy of 22 200 cm(-1) and the Re-based unit showing much weaker and lower-energy phosphorescence (maximum 530 nm) with a triplet excited state energy of 21 300 cm(-1). The energy gradient between the two excited states allows for partial Ir→Re photoinduced energy-transfer, with substantial (but incomplete) quenching of the higher-energy Ir-based emission component and sensitised emission - evidenced by an obvious grow-in component - on the lower-energy Re-based emission. The Ir→Re energy-transfer rate constants vary over the range 1-8 × 10(7) s(-1) depending on the bridging ligand: there is no simple correlation between bridging ligand structure and energy-transfer rate, possibly because this will depend substantially on the conformation of these flexible molecules in solution. To test the role of ligand conformation further, we investigated a complex in which the bridging chain is a (CH2CH2O)6 unit whose conformation is known to be solvent-polarity dependent, with such chains adopting an open, elongated conformation in water and more compact, folded conformations in organic solvents. There was a clear link between the rate and extent of Ir→Re energy-transfer which reduced in polar solvents as the chain became elongated and the Ir/Re separation was larger; and increased in less polar solvents as the chain adopted a more compact conformation and the Ir/Re separation was reduced.

Self-organization of hydrophobic-capped triblock copolymers with a polyelectrolyte midblock: a coarse-grained molecular dynamics simulation study.

We present the results of a Langevin dynamics simulation study of micellar organization and hydrogel formation in the solutions of coarse-grained ABA copolymer chains. Polymer chains are modeled as bead-spring chains of Lennard-Jones particles by explicit treatment of ionic species in implicit solvent. The studied copolymer is composed of a polyelectrolyte midblock flanked by two hydrophobic endblocks. We explore the self-assembly of copolymer solutions at a fixed polymer concentration and temperature upon systematic variation of the midblock charge fraction, valency of neutralizing counterions, and the stiffness and length of hydrophobic endblocks. Minimization of the surface energy, conformational entropy of the midblock chains, electrostatic repulsion of midblock charges, and the translational entropy of counterions are found to play central roles in controlling the self-organization features of copolymer solutions. Flower-like micelles with A-blocks forming the core of spherical aggregates and B-blocks constituting the micelle corona are established for the neutral midblocks. Increasing the charge content of B chains lowers the fraction of loop conformations and yields a spanning hydrogel network with midblocks bridging the hydrophobic clusters. Counterion valence is shown to exert a strong effect on the micelle size and network structure. The increase in the rigidity of terminal A-blocks increases the fraction of bridging chains and results in the formation of a hydrogel network with bundle-like hydrophobic domains. Longer endblocks are shown to increase the hydrophobic cluster size and enhance the bridged midblock fraction. The qualitative agreement between the experimental and theoretical studies is also discussed. The comprehensive molecular picture provides a framework for the future studies of stimuli-responsive copolymer systems.

The length of the bridging chain in ansa-metallocenes influences their antiproliferative activity against triple negative breast cancer cells (TNBC).

In order to examine whether the length of the bridging chain in ansa-ferrocenes affects their antiproliferative activity against MDA-MB-231 triple negative breast cancer cell lines (TNBC), we synthesized derivatives of the type 1-[bis-(4-hydroxyphenyl)]methylidene-[n]ferrocenophane and 1-[(4-hydroxyphenyl)-phenyl]methylidene-[n]ferrocenophane with n = 3, 4, 5. We found that the derivatives of [3]ferrocenophane, the compounds with the shortest bridging chains, are the most active. IC50 values were 0.09 ± 0.01, 2.41 ± 0.10, and 1.85 ± 0.25 μM for the dihydroxyphenyl derivatives, with n = 3, 4, 5, respectively. These differences can be explained in terms of modification of the key metabolites (radical versus quinone methides) within the ansa series depending on the length of the bridging chain. The derivative of [5]ferrocenophane, possessing two -[bis-(4-hydroxyphenyl)]methylidene groups, was also prepared. Surprisingly, this relatively large molecule is also active (IC50 = 2.7 ± 0.3 μM). Two ruthenocenophane analogs were also synthesized. These ruthenium compounds are practically inactive against MDA-MB-231 cells. The unusual chemistry of these different compounds is discussed in terms of elucidating the mechanism underlying their diverse antiproliferative activity, and their specific advantages are evaluated.

Topological constraints of network chains in telechelic associative polymer gels.

We present an analysis of topological constraints of network chains, in particular entanglements, in ABA telechelic associative polymer gels generated by Brownian dynamics technique with a B selective solvent. We find two fundamental types of entanglements formed by bridge chains: first, two or more bridge chains linking different micelles impose topological constraints on each other because they cannot cross, denoted as type-I entanglement; second, two or more bridge chains linking a pair of micelles are twisted together, denoted as type-II entanglement. More complex constraints are composed of both types. There is no difference between type-I and type-II entanglements in polymer melts, but in gels, only type-I entanglement provides extra junctions that can significantly affect the modulus. The dependences of entanglement on chain length and concentration are investigated. The simulations reveal that even at low concentrations where only parts of long chains are entangled, they can provide a considerable number of junctions.

Hybrid micellar network hydrogels of thermosensitive ABA triblock copolymer and polymer brush-grafted nanoparticles: Effect of LCST transition of polymer brushes on gel property

This article presents a study of the effect of LCST transition of polymer brushes on properties of hybrid micellar network hydrogels of a thermosensitive ABA triblock copolymer and polymer brush-grafted nanoparticles (hairy NPs) with NPs initially residing outside the core of micelles. Four batches of thermosensitive polymer brush-grafted, 20 nm silica NPs with different lower critical solution temperatures (LCSTs) and a thermosensitive ABA triblock copolymer composed of a poly(ethylene oxide) central block and thermosensitive outer blocks (ABA-N) were prepared. The LCSTs of hairy NPs were significantly higher than the critical micellization temperature of ABA-N, resulting in the NPs being initially located outside the core of micelles. The effects of LCST transition of hairy NPs and NP-to-polymer mass ratio on properties of hybrid micellar hydrogels of ABA-N with a concentration of 10 wt% and hairy NPs were investigated by rheological measurements. For all hybrid hydrogels studied in this work, the dynamic storage modulus G′ exhibited a sharp increase on top of a plateau that was forming in the heating ramp at a temperature corresponding to the LCST transition of hairy NPs. This phenomenon was caused by the collapse of the brushes on NPs triggering the absorption of thermosensitive outer blocks of ABA-N molecules in the dangling and loop forms and the reorganization of the 3-D gel network structure, which increased the density of bridging chains and thus the G′. This explanation was supported by the results from fluorescence resonance energy transfer studies. The maximum values of G′ (G′max) of the gels containing higher LCST hairy NPs were noticeably lower compared with the gels with lower LCST hairy NPs and the gel with no NPs. The G′max of all hybrid hydrogels decreased gradually with the increase of the NP-to-polymer ratio.

Allium Discoloration: Color Compounds Formed during Pinking of Onion and Leek.

Structures and formation pathways of compounds responsible for pink discoloration of onion and leek were studied. A procedure was developed for the isolation and purification of the color compounds from various model systems and their identification by HPLC-DAD-MS/MS. In total, structures of 15 major color compounds were tentatively determined. It was found that the pigment is a complex mixture of highly conjugated species composed of two N-substituted 3,4-dimethylpyrrole-derived rings linked by either a methine or a propenylidine bridge. These two-ring units are further modified by various C1- and C3-side chains. Experiments with isotope-labeled thiosulfinates revealed that the methine bridge and C1-side chains originate from the methyl group of methiin, whereas the C3 units are derived from the propenyl group of isoalliin.