Chain Distortion Research Articles

Selective directed self-assembly of coexisting morphologies using block copolymer blends.

Directed self-assembly (DSA) of block copolymers is an emergent technique for nano-lithography, but is limited in the range of structures possible in a single fabrication step. Here we expand on traditional DSA chemical patterning. A blend of lamellar- and cylinder-forming block copolymers assembles on specially designed surface chemical line gratings, leading to the simultaneous formation of coexisting ordered morphologies in separate areas of the substrate. The competing energetics of polymer chain distortions and chemical mismatch with the substrate grating bias the system towards either line/space or dot array patterns, depending on the pitch and linewidth of the prepattern. This is in contrast to the typical DSA, wherein assembly of a single-component block copolymer on chemical templates generates patterns of either lines/spaces (lamellar) or hexagonal dot arrays (cylinders). In our approach, the chemical template encodes desired local spatial arrangements of coexisting design motifs, self-assembled from a single, sophisticated resist.

Effect of chiral 2-ethylhexyl side chains on chiroptical properties of the narrow bandgap conjugated polymers PCPDTBT and PCDTPT.

Two narrow bandgap conjugated polymers containing chiral 2-ethylhexyl side chains were synthesized: poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b']dithiophene)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PCPDTBT*) and poly[(4,4-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b0]dithiophene)-2,6-diyl-alt-[1,2,5]-thiadiazolo[3,4-c]pyridine] (PCDTPT*). The presence of a chiral substituent provides a handle to study the geometry of interchain aggregates and/or the secondary structure of these conjugated polymers in solution and in thin films via circular dichroism (CD) spectroscopy, provided that the asymmetry in the side-chain is translated to the optically active conjugated backbone. CD signals are observed for PCPDTBT* and PCDTPT* in poor solvent systems, which indicate the presence of chiral ordering in the aggregates. PCPDTBT* shows greater chiral order than PCDTPT* based on their relative anisotropy factors. Additionally, GIWAXS analysis reveals that PCPDTBT* films are more ordered than what is observed for the same polymer containing racemic 2-ethylhexyl chains. Upon solution deposition, the chiral ordering is found to translate to the solid-state microstructure for PCPDTBT* but not PCDTPT*. The presence of a pyridyl nitrogen on the thiadiazolo[3,4-c]pyridine ring of PCDTPT* favors a planar conformation for the backbone such that it has a higher rotational barrier compared to PCPDTBT*. This larger rotational barrier appears to limit the ability of PCDTPT* to adopt a helical structure or relevant chain distortions for achieving chiral aggregates.

Virtual Composite Manufacturing Simulation Chain

Composite materials have been introduced in the 90’s in the car racing, naval and aeronautic sectors for weight reduction purposes. In the automotive industry, the introduction of composite materials to reduce also the weight of the vehicles leads to additional challenges for Virtual Prototyping on top of difficulties already encountered with metallic structures modeling. The impact of manufacturing on product performance is critical for composites, as the imperfections from the process may greatly affect the statics and crash performance of the final composite component. The paper will describe the state of the art of ESI Composite Solution on global composite manufacturing simulation chain (Forming, Injection, Curing, and Distortion) and how it couples to Structure/Crash through selected industrial examples.

Self-assembled phases of block copolymer blend thin films.

The patterns formed by self-assembled thin films of blended cylindrical and lamellar polystyrene-b-poly(methyl methacrylate) block copolymers can be either a spatially uniform, single type of nanostructure or separate, coexisting regions of cylinders and lamellae, depending on fractional composition and molecular weight ratio of the blend constituents. In blends of block copolymers with different molecular weights, the morphology of the smaller molecular weight component more strongly dictates the resulting pattern. Although molecular scale chain mixing distorts microdomain characteristic length scales from those of the pure components, even coexisting morphologies exhibit the same domain spacing. We quantitatively account for the phase behavior of thin-film blends of cylinders and lamellae using a physical, thermodynamic model balancing the energy of chain distortions with the entropy of mixing.

Electron density deformations provide new insights into the spectral shift of rhodopsins

Spectral shifts of rhodopsin, which are related to variations of the electron distribution in 11-cis-retinal, are investigated here using the method of deformed atoms in molecules. We found that systems carrying the M207R and S186W mutations display large perturbations of the π-conjugated system with respect to wild-type rhodopsins. These changes agree with the predicted behavior of the bond length alternation (BLA) and the blue shifts of vertical excitation energies of these systems. The effect of the planarity of the central and Schiff-base regions of retinal chain on the electronic structure of the chromophore is also investigated. By establishing nonlinear polynomial relations between BLA, chain distortions, and vertical excitation energies, we are also able to provide a semiquantitative approach for the understanding of the mechanisms regulating spectral shifts in rhodopsin and its mutants.

Laser-Induced Distortions and Disturbance Propagation of Delocalized Electronic States in Monatomic Carbon Chains

Tight-binding electron-ion dynamics of carbon chains pumped by intense laser pulses are performed to study the interactions between monatomic carbon chains and lasers. Laser-induced distortions of carbon chains, which are enhanced by a long wavelength laser, are investigated. The carbon chains with a strong laser beam focused on one terminal are simulated to study the disturbance of electronic states. By the superposition of delocalized π band states, the disturbance propagates from the illuminated area to the non-illuminated area in a velocity of about 106 m/s at 0 K, and this velocity is weakened at room temperature due to the localization effect of thermal fluctuation.

Relaxation dynamics of poly(vinylidene fluoride) studied by dynamical mechanical measurements and dielectric spectroscopy

The aim of this study is to analyze the mobility of polymer chains in semicrystalline poly(vinylidene fluoride) (PVDF). PVDF crystallizes from the melt in the α crystalline phase. The transformation from the α phase to the electroactive β phase can be induced by stretching at temperatures in the range between 80 and 140 °C. The spherulitic structure of the crystalline phase is deformed during stretching to form fibrils oriented in the direction of the strain. The amorphous phase confined among the crystalline lamellae is distorted as well and some degree of orientation of the polymer chains is expected. Dynamic-mechanical and dielectric spectroscopy measurements were performed in PVDF films stretched to strain ratios up to 5 at temperatures between 80 and 140 °C. Dynamic-mechanical measurements were conducted between -60 °C and melting and in this temperature range the relaxation spectra show the main relaxation of the amorphous phase (called β-relaxation) and at higher temperatures a relaxation related to crystallites motions (α (c)-relaxation). Although the mean relaxation times of the β-relaxation are nearly equal in PVDF before and after crystal phase transformation, a significant change of shape of the relaxation spectrum proves the effect of chain distortion due to crystal reorganization. In stretched PVDF the elastic modulus of the polymer in the direction of deformation is significantly higher than in the transversal one, as expected by chain and crystals fibril orientation. The recovery of the deformation when the sample is heated is related with the appearance of the α (c)-relaxation. Dielectric spectroscopy spectrum shows the main relaxation of the amorphous phase and a secondary process (γ-relaxation) at lower temperatures. Stretching produces significant changes in the relaxation processes, mainly in the strength and shape of the main relaxation β. The Havriliak-Negami function has been applied to analyze the dielectric response.

On the role and impact of electromagnetic fields in ecosystems

Role and effects of electromagnetic fiin living organisms and ecosystems are discussed within a nonlinear mechanism of charge transport processes that take place during respiration and photosynthesis, as well as in hydrogen-bonded chains of water molecules. Such mechanism is based on the account of the interaction between charges and induced by the distortions of macromolecules or water chains, which results in the self-trapping of charges in soliton states. It is shown that electrosolitons have some characteristic frequency, with respect to which periodic electromagnetic fi elds have resonant effect on their dynamics and stability. At certain conditions unbiased (with zero mean-value) periodic electromagnetic radiation can cause drift of solitons along molecular chains, and, therefore, affect charge transport processes. Such drift of particles in unbiased fi elds is known as ratchet phenomenon. Similar dynamics can be caused by stochastic fi elds and takes place in water chains present in interfacial water in cells, in coherence domains of water in the atmosphere and oceans. These results can explain the mechanism of impact of the electromagnetic solar activity on metabolism of living organisms and functioning of ecosystems. Moreover, it provides the mechanism for the formation of ecosystems via fi eld-mediated exchange of information between the ecosystem elements and existence of the hierarchy of ecosystems. This study also indicates a possible danger of the electromagnetic smog on ecosystems.

Charge carrier mobility in poly[methyl(phenyl)silylene] studied by time-resolved terahertz spectroscopy and molecular modelling

Time-resolved terahertz spectroscopy and combination of quantum chemistry modeling and molecular dynamics simulations were used for the determination of charge carrier mobility in poly[methyl(phenyl)silylene]. Using time-resolved THz spectroscopy we established the on-chain charge carrier drift mobility in PMPSi as 0.02 cm(2) V(-1) s(-1). This value is low due to the formation of polarons: the hole is self-trapped in a potential formed by local chain distortion and the transient THz conductivity spectra show signatures of its oscillations within this potential well. This view is supported by the agreement between experimental and calculated values of the on-chain charge carrier mobility.

Strain localization analyses of idealized sands in biaxial tests by distinct element method

This paper presents a numerical investigation on the strain localization of an idealized sand in biaxial compression tests using the distinct element method (DEM). In addition to the dilatancy and material frictional angle, the principal stress field, and distributions of void ratio, particle velocity, and the averaged pure rotation rate (APR) in the DEM specimen are examined to illustrate the link between microscopic and macroscopic variables in the case of strain localization. The study shows that strain localization of the granular material in the tests proceeds with localizations of void ratio, strain and APR, and distortions of stress field and force chains. In addition, both thickness and inclination of the shear band change with the increasing of axial strain, with the former valued around 10-14 times of mean grain diameter and the later overall described by the Mohr-Coulomb theory.

Synthesis and Structural Characterization of La1−xAxMnO2.5 (A = Ba, Sr, Ca) Phases: Mapping the Variants of the Brownmillerite Structure

Analysis of the structural parameters of phases that adopt brownmillerite-type structures suggests the distribution of the different complex ordering schemes adopted within this structure type can be rationalized by considering both the size of the separation between the tetrahedral layers and the tetrahedral chain distortion angle. A systematic study using structural data obtained from La1−xAxMnO2,5 (A = Ba, Sr, Ca,) phases, prepared by the topotactic reduction of the analogous La1−xAxMnO3 perovskite phases, was performed to investigate this relationship. By manipulating the A-cation composition, both the tetrahedral layer separation and tetrahedral chain distortion angle in the La1−xAxMnO2,5 phases were controlled and from the data obtained a “structure map” of the different brownmillerite variants was plotted as a function of these structural parameters. This map has been extended to include a wide range of reported brownmillerite phases showing the structural ideas presented are widely applicable. The complete structural characterization of La1−xAxMnO2,5 0.1 ≤ x ≤ 0.33, A = Ba; 0.15 ≤ x ≤ 0.5 A = Sr, and 0.22 ≤ x ≤ 0.5 A = Ca is described and includes compositions which exhibit complex intralayer ordered structures and Mn2+/Mn3+ charge ordering.

Dipolar Control of Monolayer Morphology on Graphite: Self-Assembly of Anthracenes with Odd Length Diether Side Chains

The monolayers self-assembled at the solution−graphite interface by 18 1,5-bis(2,X-dioxaalkyl) anthracene derivatives bearing odd length side chains are studied using scanning tunneling microscopy and molecular mechanics (MM) simulations. 1-D molecular tapes are the key and common building block of the many morphologies self-assembled by these compounds. The dominant monolayer morphology and the extent of monolayer polymorphism depend critically on the position of the X-ether group and side chain length. MM simulations of the compounds’ different morphologies are useful tools with which to dissect, explain, and predict morphological variation and polymorphism as a function of side chain structure. The simulations reveal that the dependence on X-ether group position arises from dipolar repulsions between ether groups in adjacent tapes, dipolar attractions between ether and anthracene C−H groups in adjacent tapes, and geometric distortions of the side chains.

Energetics of Hydrophobic Matching in Lipid-Protein Interactions

Lipid chain length modulates the activity of transmembrane proteins by mismatch between the hydrophobic span of the protein and that of the lipid membrane. Relative binding affinities of lipids with different chain lengths are used to estimate the excess free energy of lipid-protein interaction that arises from hydrophobic mismatch. For a wide range of integral proteins and peptides, the energy cost is much less than the elastic penalty of fully stretching or compressing the lipid chains to achieve complete hydrophobic matching. The chain length dependences of the free energies of lipid association are described by a model that combines elastic chain extension with a free energy term that depends linearly on the extent of residual mismatch. The excess free energy densities involved lie in the region of 0.5–2.0kBT.nm−2. Values of this size could arise from exposure of hydrophobic groups to polar portions of the lipid or protein, but not directly to water, or alternatively from changes in tilt of the transmembrane helices that are energetically comparable to those activating mechanosensitive channels. The influence of hydrophobic mismatch on dimerization of transmembrane helices and their transfer between lipid vesicles, and on shifts in chain-melting transitions of lipid bilayers by incorporated proteins, is analyzed by using the same thermodynamic model. Segmental order parameters confirm that elastic lipid chain distortions are insufficient to compensate fully for the mismatch, but the dependence on chain length with tryptophan-anchored peptides requires that the free energy density of hydrophobic mismatch should increase with increasing extent of mismatch.

Interchain Impacts on Electronic Structures of Heterocyclic Oligomers and Polymers Containing Group 14, 15, and 16 Heteroatoms: Quantum Chemical Calculations in Combination with Molecular Dynamics Simulations

The packing structures and packing effects on excitation energies of oligomers of polyfuran (PFu), polypyrrole (PPy), polycyclopentidene (PCp), polythiophene (PTh), polyphosphole (PPh), and polysilole (PSi) are comparatively studied by employing molecular dynamics (MD) simulations and time-dependent density functional theory (TDDFT) calculations. The dependence of packing structures on the main group of heteroatoms in the five-membered heterocyclic oligomers is exhibited from MD simulations. The planarity of backbones and the population of pi-stacked structures increase with the heteroatoms going from group 14 to group 16; i.e., PCp < PPy < PFu; PSi < PPh < PTh. The polymers with the third row elements, PSi and PPh, tend to have larger chain flexibilities in the packing systems than those with the second row elements, PCp and PPy, respectively. On the basis of the second-order Møller-Plesset perturbation (MP2) and natural bond orbital (NBO) calculations of the pi-stacked pairs, the difference in pi-stack orientations, head-to-tail vs head-to-head, between various packing systems is rationalized by individual interchain bond orbital interactions involved with heteroatoms. The packing systems with higher row elements tend to have narrower band gaps. The band gaps are closely related to the chain torsions driven by interchain interactions. The noticeable chain distortions in the packing systems of PCp, PSi, and PPh lead to the significant increase of band gaps in comparison with those appraised from periodic boundary conditions (PBC) calculations on their planar isolated chains.

Indentation size effects in polymers and related rotation gradients

Similar to metals, the hardness of many polymers increases with decreasing indentation depths at depth ranges from several microns down to several nanometers. While for metals such phenomena are commonly attributed to geometrically necessary dislocation densities, such an explanation cannot be applied to polymers. To provide a micromechanically motivated model for the indentation size effect in polymers, here we propose an elasto-plastic extension of the higher order elasticity model recently developed by the authors. In this model, size effects in polymers (as well as in nematic liquid crystals) are related to Frank elasticity arising from bending distortions of the polymer chains and their interactions. On the basis of this theory, we derive a simple model for indentation size effects in polymers. Unlike other models, our model includes only elastic size effects due to rotational gradients. It is shown that the proposed model can explain the experimentally observed size effects in polymers. Together with the existing experimental data mentioned here, new experimental data for silicon rubber are also presented and discussed.

Interacting Supply Chain Distortions: The Pricing of Internal Transfers and External Procurement

This paper examines the impact of distortions wrought by transfer pricing when a firm is engaged in both internal production and external procurement of inputs. In particular, we demonstrate that a firm can actually glean benefits from often-discussed transfer-pricing problems in dealing with an external supplier. Though transfer prices above marginal cost introduce inter-division coordination problems, they also introduce a lower willingness to pay to outside suppliers. Knowing that costly internal transfers will eat into demand, the supplier is more willing to set lower prices. Such supplier discounts can make decentralization worthwhile for the firm. This benefit of decentralization is shown to be robust to variations in both downstream and upstream competition.

Camouflaged Carborarods Derived fromB-Permethyl-1,12-diethynyl-para- andB-Octamethyl-1,7-diethylnyl-meta-carborane Modules

Rigid camouflaged carborarods constructed from the corresponding C,C'-diethynyl derivatives of B-decamethyl-1,12-dicarbadodecaborane(12) (6) and B-octamethyl-1,7-dicarbadodecaborane(12) (48) have been synthesized by largely conventional organic transformations. These carborarods are the longest discrete rod species available by this method in which B-methylated p-carborane and m-carborane cages are linked through their carbon vertices by using butadiynylene moieties. They exhibit enhanced solubility in common organic solvents relative to all other presently known carborane-based rigid-rod molecules. The oxidative coupling of bis(ethynyl) derivatives of 6 generates oligomers containing, on average, 16 carborane modules. The structural characterization of the corresponding dimeric species revealed that the carborarods possess a sinusoidal chain distortion in the solid state. The stereoelectronic properties of these and related model carborarods were evaluated by using molecular dimensions as a monitor for the comparison of computational and experimental methods. In addition, the effect of exhaustive B-methylation of 12- and 10-vertex para-carborane cages in a series of model C,C'-diethynyl derivatives was similarly investigated by computational and structural studies. As expected, a correlation of intercage C--C bond lengths with cage size was observed and was attributed to hybridization effects. B-Permethylation had no significant structural effect with either 10- or 12-vertex cage derivatives. Relative to unsubstituted compounds, thermal and chemical stabilities of B-permethylated derivatives were increased through the operation of a steric "bumper-car" process, and solubilities in organic solvents were enhanced. The formation of linear, sterically encumbered platina-carborarods using ethynyl derivatives of 6 as precursors is described.

The influence of PPV chain aggregated structure on optical properties

A comparison has been made on the fluorescence of the poly ( p-phenylenevinylene) (PPV) that without filtering the low molecular weight molecules (sample A) with the PPV of the low molecular weight molecules filtered (sample B). Although there is no obvious difference found in the FT-IR and Raman spectra between two samples, in the photoluminescence spectrum of the sample A, the peak at 510 nm is not appeared and the fluorescence intensity for the peak at 550 nm is increased. Under the high pressure condition the fluorescence peak at 520 nm, which corresponds to the peak at 510 nm of the usual PPV, is observed. Applying high pressure to the sample A or by filtering the low molecular weight molecules, the chain aggregated structure is modified, resulting in a change in the PPV chain distortion degree.

Unusual Expansion and Contraction in Ultrathin Glassy Polycarbonate Films

The thermal expansion behavior of thin polycarbonate (PC) films supported on hydrophilic and hydrophobic silicon substrates is studied with specular X-ray reflectivity. These measurements suggest a suppression of the apparent glass transition temperature (Tg) with decreasing film thickness h on hydrophilic silicon oxide substrates, while no evidence for an h-dependent Tg shift is observed on hydrophobic passivated silicon substrates. More interestingly, we find that when h is comparable to the bulk radius of gyration, the expansion becomes nonmonotonic with temperature T in a reversible manner. Cooling one of these ultrathin PC films well below the apparent Tg gives rise to an apparently negative coefficient of thermal expansion (CTE). This unusual behavior stems from the fact that nominally Rg-thick glassy films exhibit an appreciable isothermal thickening over extended periods of time, with the propensity for this thickening increasing with the depth of cooling into the glassy state; normal thermal contraction upon cooling becomes convoluted with the sub-Tg thickening phenomenon. This is counterintuitive since deep in the glassy state the molecular mobility is anticipated to be small. The magnitude and rate of the isothermal thickening depend on the ratio of the macromolecular size to the film thickness, suggesting that chain distortion by the film boundaries is associated with this effect. The surface energy of the supporting substrate also influences these unusual behaviors.

Helix Distortion and Crystal Structure of the α-Form of Poly(l-lactide)

The crystal structure of the α-form of poly(l-lactide) was analyzed by the linked-atom least-squares refinements for the X-ray fiber diffraction data. The space group was orthorhombic P212121, and the unit cell contained the antiparallel two chains. The chain conformation was the 2-fold s(15*2/7) helix distorted periodically from the regular s(3*10/7) helix. The ester groups were deformed from the planar trans conformation. Potential energy calculations suggested that the periodic chain distortion resulted from the impartial stress distribution due to the interchain interactions.