Chain Packing Structure Research Articles

Fine-Tuning the Microstructure and Photophysical Characteristics of Fluorescent Conjugated Copolymers Using Photoalignment and Liquid-Crystal Ordering.

Replicating the microstructural basis and the near 100% excitation energy transfer efficiency in naturally occurring light-harvesting complexes (LHCs) remains challenging in synthetic energy-harvesting devices. Biological photosynthesis regulates active ensembles of light-absorbing and funneling chlorophylls in proteins in response to fluctuating sunlight. Here, use of long-range liquid crystal (LC) ordering to tailor chain orientation and packing structure in liquid crystalline conjugated polymer (LCCP) layers for bio-mimicry of certain structural basis and light-harvesting properties of LHCs is reported. It is found that long-range orientational ordering in an LC phase of poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) copolymer stabilizes a small fraction of randomly-oriented F8BT nanocrystals dispersed in an amorphous matrix of F8BT chains, resembling a self-doped host-guest system whereby excitation energy funneling and photoluminescence quantum efficiencies are enhanced significantly by triggering 3D donor-to-acceptor Förster resonance energy transfer (FRET) and dominant intrachain emission in the nano-crystal acceptor. Further, photoalignment of nematic F8BT layers is combined with LC orientational ordering to fabricate large-area-extended monodomains exhibiting >60% crystallinity and ≈20nm-long interchain packing order. Remarkably, these monodomains demonstrate strong linearly polarized emission, whilst also promoting a new band-edge absorption species and an extra emissive interchain excited state as compared to the non-aligned films.

Hydroxyl-functionalized microporous polymer membranes with tunable para position substituent benzaldehydes for gas separation

We report hydroxyl-functionalized microporous polymers with tunable benzaldehyde groups for gas separation membranes. These polymers were synthesized via acid-catalyzed Friedel-Crafts polycondensation. The tunability in d-spacing and fractional free volume of these polymers depends on the para position substituents (-H, –F, -Cl, and -Br) of the benzaldehyde. Specifically, the size and polarity of the para position substituent influence the polymer chain-packing structure. Consequently, the hydroxyl-functionalized microporous polymer membrane with a larger para position substituent in the benzaldehyde group exhibited improved gas permeability. This improvement is due to enhanced gas diffusivity resulting from the inefficient polymer chain-packing structure. Furthermore, these membranes demonstrated enhanced CO2 plasticization resistance, attributable to the rigid, contorted polymer structure and the hydrogen bonding interactions between hydroxyl groups. This study provides insights into the relationship between the polymer chain-packing structure, tunable para position substituents, and molecular transport.

Two structurally new Lindqvist hexaniobate-templated silver thiolate clusters.

Two structurally new Lindqvist hexaniobate-templated silver thiolate clusters, [Nb6O19@Ag45(iPrS)23(CH3COO)14] (Ag45) and (H3O)4[Nb6O19@Ag41KS2.5O2(H2O)7.5(iPrS)24(CH3COO)5] (Ag41), were synthesized using a facile one-pot solvothermal approach. Single crystal X-ray diffraction analyses revealed the presence of a classical Lindqvist-type [Nb6O19]8- anion template, with iPrS- and CH3COO- surface-protecting ligands in both silver clusters, which can further form two-dimensional Ag45 assembly and one-dimensional Ag41 chain packing structures. Both Ag45 and Ag41 clusters exhibited intriguing photothermal conversion properties and temperature-dependent emission behavior.

Fine-tuning gas separation performance of intrinsic microporous polyimide by the regulation of atomic-level halogen substitution

The molecular structure of polymers is essential to membrane separation performance. However, the inherent relationship between molecular structure and gas separation performance of polymeric membranes is unclear. Herein, the halogen atoms (F, Cl, and Br) were introduced into intrinsic micropore polyimide (PIM-PI) to precisely regulate its interchain cavity and elucidate the structure-property relationship. Based on the pristine BAPI, the halogen atoms were precisely designed at the ortho position of the amino group and synthesized three PIM-PIs, namely BFPI, BCPI, and BBPI, respectively. Then, it can be found that the packing structure of polymer chains and fine-tuning of fractional free volume (FFV) exhibits a regular trend in halogen-containing PIM-PIs. In addition, as the van der Waals volume of halogen atoms increases, the gas permeability of halogen-containing PIM-PIs exhibits an increasing trend. Specifically, compared with BFPI, the CO2 permeability of BCPI and BBPI is increased by 48 % and 100 %, respectively. Our findings may elucidate the structure-property relationship of microporous polymer membranes and provide a brand-new insight to design an advanced high-performance membrane.

X-ray and Electron Diffraction Observations of Steric Zipper Interactions in Metal-Induced Peptide Cross-β Nanostructures.

The steric zipper is a common hydrophobic packing structure of peptide side chains that forms between two adjacent β-sheet layers in amyloid and related fibrils. Although previous studies have revealed that peptide fragments derived from native protein sequences exhibit steric zipper structures, their de novo designs have rarely been studied. Herein, steric zipper structures were artificially constructed in the crystalline state by metal-induced folding and assembly of tetrapeptide fragments Boc-3pa-X1-3pa-X2-OMe (3pa: β-(3-pyridyl)-l-alanine; X1 and X2: hydrophobic amino acids). Crystallographic studies revealed two types of packing structures, interdigitation and hydrophobic contact, that result in a class 1 steric zipper geometry when the X1 and X2 residues contain alkyl side chains. Furthermore, a class 3 steric zipper geometry was also observed for the first time among any reported steric zippers when using tetrapeptide fragments with (X1, X2) = (Thr, Thr) and (Phe, Leu). The system could also be extended to a knob-hole-type zipper using a pentapeptide sequence.

Synthetically tunable polymers, free volume element size distributions, and dielectric breakdown field strengths

Four polyetherimide (PEI) polymers were synthesized with different end groups, while leaving the molecular weights, glass transition temperature, thermal properties, and dielectric constant essentially unchanged. The Restricted Orientation Anisotropy Method (ROAM), an ultrafast infrared laser technique, was used to measure the films’ free volume elements (FVEs) radius probability distribution (RPD) curves. This technique exploits the observation that a vibrational probe’s molecular reorientation dynamics inside a polymer film’s FVEs are sterically restricted by the surfaces of the FVEs. The measured RPD curves displayed significant changes in shape and center positions for the PEI polymers with different end cap. The results demonstrate that structural changes to the end groups of a polymer can significantly modify its microscopic morphology, which is consistent with other experiments that observed changes in macroscopic observables. The thin film samples’ breakdown fields (EBD) were measured, and a correlation between polymer films having a higher probability of large FVEs and lower EBDs was observed. This work demonstrates that the nanoscopic chain packing structure that controls the nature of the FVEs and breakdown field properties of PEI are synthetically tunable, without the need to change the main chain chemical structure. The results provide some experimental evidence for the theoretical model of electron-acceleration inside FVEs as the microscopic origin of polymer film dielectric breakdown. The results also provide a framework for the study of other polymer dielectrics, and suggest that design of high breakdown field polymer films may involve minimizing FVE sizes, particularly the large FVE tails of the size distribution.

Chain length dependence of ZnO nanofiller–polystyrene blend coating nanofilm: Morphology, surface mechanics, photochemistry, and chain packing

Based on that chain packing which is associated with the number of entanglements per chain and thereby chain length is an influential factor closely related to the properties of polymeric coating film, the nanothin film of zinc oxide (ZnO) nanofiller–incorporated polystyrene (PS) coated on Si substrate important to electronic packaging for protecting electronic material surface is fabricated with different PS molecular weights primarily for heat–resistant coating. Synergistically, through directly–measurable film characteristics obtained using atomic force microscopy (AFM) and spectroscopy (AFS) in conjunction with Raman spectroscopy (RS), the internal structures of the films are evaluated which helps indicate the corresponding film properties tested afterwards. Considering mechanical responses of individual nanoscale surface features together with surface morphology, the optimal PS–ZnO film is pointed out which indicates improved resistance to thermal dewetting compared to pure PS films while providing sub–nanometer roughness and the highest contact area of relatively low–surface–energy sites. Correlated with Raman analysis, chain packing structure encouraging multiple amplification of incident light is ascribed to the films made of the optimal chain length which indicates and describes the observed enhancement of photocatalytic self–cleaning. This study not only contributes to the development of PS–ZnO composite for multi–function coating but also to the design of structure and inspection of nanoparticle–reinforced polymer thin films.

Polylactide cocrystals and gels

AbstractSynthetic biodegradable polyesters have emerged as an alternative to conventional petroleum‐derived polymers for a diverse range of applications. Among these, polylactides are the most commercially successful biodegradable polymers. The presence of stereoregular chains makes poly(l‐lactide) (PLLA) and poly(d‐lactide) (PDLA) semicrystalline. The blending of enantiomeric PLLA and PDLA resulted in the stereocomplex formation due to non‐covalent interactions of enantiomeric chains. PLLA exhibits different crystalline forms depending on the crystallization conditions with different chain conformations, as well as different chain packing structures. PLLA and its blend with PDLA are known to form cocrystals with certain solvents. This review focuses mainly on the recent progress in understanding the cocrystal formation, polymorphic phase transitions of these cocrystals, gelation mechanism and stereocomplex formation in blend gels of polylactides.

Synthesis and Phase Behavior of (Semifluorinated Alkane)-Based Side-Chain Liquid Crystalline Copolymers.

Side-chain liquid crystalline polymer (SCLCP) usually contains a simple and flexible homopolymer as main chain, while its effect on the self-assembly behavior is often ignored. In this work, in order to increase the structural complexity and investigate the interaction between the main chain and mesogens, perfluorinated segments are introduced into the main chain using a photoinduced Step Transfer-Addition & Radical-Termination polymerization method, producing a novel series of SCLCPs containing 4-methoxyphenyl benzoate mesogens, soft hydrocarbon spacers, and a strictly alternating perfluoroalkyl and alkyl backbone. By adjusting the length of spacers or perfluoroalkyl segments, several mesophases with complex chain packing structures are achieved. This design strategy that constructing highly ordered liquid crystalline (LC) structures from SCLCPs with precise chemical structure provides a facile way toward novel LC nanomaterials.

Ladder polymers of intrinsic microporosity from superacid-catalyzed Friedel-Crafts polymerization for membrane gas separation

Polymers of intrinsic microporosity have attracted comprehensive attention in membrane-mediated gas separation because of their rigid and contorted structure that facilitates well-defined microporosity for fast and selective gas transport. We report a new macromolecular design synthesizes semi-ladder and fully-ladder polymers of intrinsic microporosity containing 9H -xanthene units by superacid-catalyzed Friedel-Crafts polymerization named SACPs. The prepared SACP membranes display high microporosity with amorphous chain packing structure, high FFV, and high BET surfaces areas. In particular, SACP-3 exhibited the most elevated BET surfaces area of 568 m 2 /g, fractional free volume (FFV) of 0.243, and bimodal micropore size distribution with two maxima at ∼5 and ∼8 Å, respectively. Due to its fully ladder architecture, SACP-3 exhibits highly permeable gas transport with CO 2 permeability of 6497 Barrer and CO 2 /CH 4 selectivity of 7.8, respectively. The microporosity and gas permeation properties of SACP membranes are also demonstrated to be highly tailorable by employing different monomers. The facile polymerization procedure, excellent solubility and processability, highly diverse tunability, and outstanding gas separation performance render SACP membranes attractive for many membrane-mediated gas separation processes. • A new spirobisindane-based fully-ladder polymer of intrinsic microporosity is synthesized with high BET surface area and FFV. • Superacid-catalyzed ladder polymer of intrinsic microporosity displays a bimodal micropore size distribution. • Rigid ladder polymer shows superior plasticization resistance than less microporous semi-ladder polymer.

Crystal structures and phase transition of tetrafluoroethylene-vinyl alcohol alternating copolymer

Crystal structure and thermally-induced phase transition have been studied for a novel fluorine polymer or tetrafluoroethylene-vinyl alcohol (TFE-VA) alternating copolymer on the basis of the X-ray diffraction and infrared spectroscopic data analyses. The copolymer exhibits the three kinds of crystalline modification depending on the crystallization conditions. The crystal modification β is obtained by casting from the organic solution at room temperature. The molecular chains are slightly contracted from the zigzag conformation and are packed in the orthorhombic unit cell (a = 9.48 Å, b = 5.38 Å and c (chain axis) = 9.84 Å) with the space group symmetry of P21cn. The heating of the β form above 170 °C causes the irreversible transition to the high-temperature α form (αHT). The thus-created αΗΤ phase cannot change back to the β form anymore. The cooling from the melt induces the crystallization to the αHT phase at first, which transforms to the low-temperature α phase (αLT) apparently continuously and reversibly below 135 °C. The αLT form consists of the statistically disordered packing of the almost fully-extended chains in the unit cell of a = 9.58 Å, b = 5.48 Å and c (chain axis) = 5.01 Å. The αHT takes the similar crystal structure to that of the αLT, but the zigzag chains are packed in the slightly larger unit cell of a = 10.01 Å, b = 5.64 Å and c (chain axis) = 5.02 Å (at 170 °C) in more highly disordered state with thermally-activated motion of the chains. In these crystalline phases, the hydrogen bonds of F⋯H-O and O⋯H-O types are formed to stabilize the chain packing structures.

Preparation of Nitrogen Analogues of Ceramide and Studies of Their Aggregation in Sphingomyelin Bilayers.

Ceramides can regulate biological processes probably through the formation of laterally segregated and highly packed ceramide-rich domains in lipid bilayers. In the course of preparation of its analogues, we found that a hydrogen-bond-competent functional group in the C1 position is necessary to form ceramide-rich domains in lipid bilayers [Matsufuji; Langmuir 2018]. Hence, in the present study, we newly synthesized three ceramide analogues: CerN3, CerNH2, and CerNHAc, in which the 1-OH group of ceramide is substituted with a nitrogen functionality. CerNH2 and CerNHAc are capable of forming hydrogen bonds in their headgroups, whereas CerN3 is not. Fluorescent microscopy observation and differential scanning calorimetry analysis disclosed that these ceramide analogues formed ceramide-rich phases in sphingomyelin bilayers, although their thermal stability was slightly inferior to that of normal ceramides. Moreover, wide-angle X-ray diffraction analysis showed that the chain packing structure of ceramide-rich phases of CerNHAc and CerN3 was similar to that of normal ceramide, while the CerNH2-rich phase showed a slightly looser chain packing due to the formation of CerNH3+. Although the domain formation of CerN3 was unexpected because of the lack of hydrogen-bond capability in the headgroup, it may become a promising tool for investigating the mechanistic link between the ceramide-rich phase and the ceramide-related biological functions owing to its Raman activity and applicability to click chemistry.

Influence of Tacticity on the Crystal Structures of Hydrogenated Ring-Opened Poly(norbornene)s

The crystal structures of highly crystalline isotactic and syndiotactic hydrogenated poly(norbornene)s [H-poly(NB)s], synthesized by the stereospecific ring-opening metathesis polymerizations of norbornene followed by complete hydrogenation, have been determined for the first time on the basis of the X-ray diffraction data analyses. The similarity and difference of the chain conformation and the chain packing mode in the crystal lattice have been clarified among the three kinds of H-poly(NB) samples (syndiotactic, isotactic, and atactic species). The molecular chains were found to take essentially the planar zigzag conformation at room temperature with slight torsional angle fluctuations around the skeletal C–C bonds. The cyclopentylene rings were found to protrude from the plane of the skeletal polymer chain in various different ways depending on the tacticity, resulting in the difference of the whole shape of the chains and then the difference of the chain packing structure. The melting point was found to be different depending on the tacticity: 178, 148, and 134 °C for the isotactic, atactic, and syndiotactic H-poly(NB)s, respectively. The difference in the thermal behavior has been discussed qualitatively on the basis of these structural pieces of information.

Amino Acids and Their N-Acetylated Derivatives Maintain the Skin's Barrier Function.

The hydrocarbon-chain packing structure of intercellular lipids in the stratum corneum (SC) is critical to the skin's barrier function. We previously found that formation of V-shaped ceramide reduces the barrier function of skin. There are few agents, apart from ceramides and fatty acids that can improve the orthorhombic packing (Orth) ratio of the intercellular lipid packing structure. In this study, we investigated agents that directly increase the Orth ratio. We selected an intercellular lipid model consisting of ceramide, cholesterol, and palmitic acid and performed differential scanning calorimetry. We focused on natural moisturizing factor components in the SC, and therefore investigated amino acids and their derivatives. The results of our intercellular lipid model-based study indicate that N-acetyl-L-hydroxyproline (AHYP), remarkably, maintains the lamellar structure. We verified the effect of AHYP on the lamellar structure and hydrocarbon chain packing structure of intercellular lipids using time-resolved X-ray diffraction measurements of human SC. We also determined the direct physicochemical effects of AHYP on the Orth ratio of the hydrocarbon-chain packing structure. Hence, the results of our human SC study suggest that AHYP preserves skin barrier function by maintaining the hydrocarbon-chain packing structure of intercellular lipids via electrostatic repulsion. These findings will facilitate the development of skincare formulation that can maintain the skin's barrier function.

Low-flux scanning electron diffraction reveals substructures inside the ordered membrane domain

Ordered/disordered phase separation occurring in bio-membranes has piqued researchers’ interest because these ordered domains, called lipid rafts, regulate important biological functions. The structure of the ordered domain has been examined with artificial membranes, which undergo macroscopic ordered/disordered phase separation. However, owing to technical difficulties, the local structure inside ordered domains remains unknown. In this study, we employed electron diffraction to examine the packing structure of the lipid carbon chains in the ordered domain. First, we prepared dehydrated monolayer samples using a rapid-freezing and sublimation protocol, which attenuates the shrinkage of the chain-packing lattice in the dehydration process. Then, we optimised the electron flux to minimise beam damage to the monolayer sample. Finally, we developed low-flux scanning electron diffraction and assessed the chain packing structure inside the ordered domain formed in a distearoylphosphatidylcholine/dioleoylphosphatidylcholine binary monolayer. Consequently, we discovered that the ordered domain contains multiple subdomains with different crystallographic axes. Moreover, the size of the subdomain is larger in the domain centre than that near the phase boundary. To our knowledge, this is the first study to reveal the chain packing structures inside an ordered domain.

Moisturizing mechanism of glycerol and diglycerol on human stratum corneum studied by synchrotron X-ray diffraction.

Polyols are moisturizers used in cosmetics. Using X-ray diffraction, we studied the moisturizingmechanism of polyol solutions in the stratum corneum (SC). We examined whether glycerol disrupts the ordered hydrocarbon chain packing structure in isolated SC, as previously proposed in an SC lipid model. The SC samples were prepared by treatment with water and aqueous solutions of glycerol, diglycerol and glycerol/diglycerol. To examine the differences in the water-retention efficiency of polyols, using a solution cell, we performed dynamic X-ray diffraction to analyse the structural changes that occurred during water removal from the hydrated samples by a stream of dry nitrogen gas. We focused on two structures, the orthorhombic hydrocarbon chain packing structure in the intercellular lipids and the soft keratin in the corneocytes where most of the water is stored. The spacing formed by the soft keratin in the corneocytes immersed in a solution of water and diglycerol solution decreased rapidly by water removal. In contrast, it decreased gradually in the corneocytes immersed in a solution of glycerol and glycerol/diglycerol, indicating that the glycerol-containing solutions maintained the hydrated state of the corneocytes for longer. Furthermore, the characteristic change of the spacing in the orthorhombic hydrocarbon chain packing structure over time was observed during the drying process. The hydrated state was maintained longer, in water, followed by glycerol, diglycerol and glycerol/diglycerol, in increasing order. This is the first study to report such characteristic properties that could be indicators of the capacity of the SC to regulate water. The dynamic X-ray diffraction experiment on the structure of the soft keratin and the orthorhombic hydrocarbon chain packing structure during the drying of the hydrated SC provides an insight into the moisturizing mechanism of the polyol solutions in the SC. The results show that the glycerol/diglycerol solution functions as an effective SC moisturizer at the molecular level. Further, it was confirmed that the behaviour of glycerol in the isolated SC varies from that proposed in the SC lipid model, wherein glycerol was proposed to prevent the formation of a regular hydrocarbon chain packing structure.

Optimizing the Interdomain Spacing in Alicyclic Polythiourea toward High-Energy-Storable Dielectric Material.

Organic dielectric materials have been widely developed and investigated for energy storage capacitors. However, challenges remain in terms of the relatively low dielectric constant and energy density. Enhancing the dipolar polarization to increase the dielectric constant is considered to be an effective way to improve the energy density of polymer dielectrics. Herein, enlightened by the chain-packing structure that affects the dipolar relaxation behavior, a simple and low-cost approach is proposed to tailor the interdomain spacing in an alicyclic polythiourea (PTU) by changing quenching temperatures and further facilitate the dipolar polarization. It is found that the large interdomain spacing is beneficial to promote the localized motion of segmental chains in amorphous regions, but at the same time inevitably reduces the dipole density. Therefore, in order to achieve the highest dielectric constant in the PTU, there is an optimal value for the interdomain spacing. It is worth noting that the dielectric constant of PTU increases from 5.7 to 10, and thus the energy density increases by 53% to 16.3 J cm-3 . It proposes a simple and feasible strategy to further improve the energy density through optimizing the interdomain spacing toward high-energy-storable dielectric material.

Microstructure Induced Rigidity of Polysiloxane Yielding Hierarchical Self‐Assembly of Alkyl Side Chains

AbstractThe influence of a backbone microstructure on the side chain crystallization of a comb‐like polymer is analyzed systematically using a tailor‐made random versus block siloxane copolymer system. While the side alkyl chains of the random siloxane undergo a stepwise order–disorder (OD) transition to form well‐ordered orthorhombic structure at low temperature, the packing structure of the alkyl chains pertaining to the block siloxane maintains their original hexagonal lattice up to a temperature of as low as 173 K. The unit lattice ordering of side alkyl chains in the random siloxane polymer is also accompanied by a major restructuring of the backbone conformation ultimately losing out long range ordered structure in the solid state. The OD transitions of side alkyl chains and their dynamic relationship with the backbone conformation are established unambiguously by a combination of temperature dependent small‐angle X‐ray and wide‐angle X‐ray scattering techniques. The observed conformational variations in random versus block polymers are explicitly discussed in terms of molecular chain mobility and theory of macromolecular chain conformation.

Relationship of Distribution of Carboxy Groups to Molar Mass Distribution of TEMPO-Oxidized Algal, Cotton, and Wood Cellulose Nanofibrils.

Distributions of carboxy groups among the molecules in 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) prepared from wood, cotton, and algal celluloses were investigated. Most C6-carboxy groups in TOCNs were esterified with anthracene-methyl (-CH2C14H9) groups, showing an ultraviolet light (UV) absorption peak at 365 nm. The anthracene-methylated TOCNs were dissolved in 8% (w/w) lithium chloride/N,N-dimethylacetamide (LiCl/DMAc). After dilution to 1% LiCl/DMAc, the solutions were subjected to size-exclusion chromatography with multiangle laser-light scattering, refractive index, and UV detection. For algal TOCN, C6-carboxy group-rich molecules were present predominantly in the low-molar-mass region, which was consistent with the core-clad cellulose chain packing structures in individual algal cellulose microfibrils and partial depolymerization of the oxidized cellulose molecules. In contrast, wood and cotton TOCNs had almost homogeneous distributions of C6-carboxy groups in all molar mass regions, which could not be explained in terms of the simple core-clad cellulose chain packing structures.

Molecular structure engineering of dielectric fluorinated polymers for enhanced performances of triboelectric nanogenerators

Fluorinated polymers have been widely used in triboelectric sensors, displays, and energy harvesting devices because of their superior electron affinity, which leads to the negative triboelectric materials. While previous reports have shown that the control of dielectric constants of fluorinated polymers can increase the triboelectric output performance, the exact relationship between the molecular structures of fluorinated polymers and the resulting triboelectric properties is still elusive. In this study, we demonstrate that the molecular chain structures of the fluorinated polymers depending on the number of fluorine units, the molecular weight (Mw), and conditions such as spin rate and annealing temperature directly affect the relative dielectric constants of dielectric layers and the triboelectric polarity, which are closely related to the triboelectric output performance. We observe that the polymer chain packing structures result in the increase of the relative dielectric constants, thus leading to the improvement of triboelectric output currents. Among the fluorinated polymers used in this study, a poly (2,2,2-trifluoroethyl methacrylate) polymer with three fluorine units and Mw of ~ 20 kg/mol shows the best triboelectric output performance. Our molecular engineering strategy to control the dielectric constants of fluorinated polymers can be a robust platform for the fundamental studies of triboelectric materials and their applications in diverse energy harvesting and sensing devices.