Crystalline Lamellae Research Articles

Tunable Dopants with Intrinsic Counterion Separation Reveal the Effects of Electron Affinity on Dopant Intercalation and Free Carrier Production in Sequentially Doped Conjugated Polymer Films.

Carrier mobility in doped conjugated polymers is limited by Coulomb interactions with dopant counterions. This complicates studying the effect of the dopant's oxidation potential on carrier generation because different dopants have different Coulomb interactions with polarons on the polymer backbone. Here, dodecaborane (DDB)-based dopants are used, which electrostatically shield counterions from carriers and have tunable redox potentials at constant size and shape. DDB dopants produce mobile carriers due to spatial separation of the counterion, and those with greater energetic offsets produce more carriers. Neutron reflectometry indicates that dopant infiltration into conjugated polymer films is redox-potential-driven. Remarkably, X-ray scattering shows that despite their large 2-nm size, DDBs intercalate into the crystalline polymer lamellae like small molecules, indicating that this is the preferred location for dopants of any size. These findings elucidate why doping conjugated polymers usually produces integer, rather than partial charge transfer: dopant counterions effectively intercalate into the lamellae, far from the polarons on the polymer backbone. Finally, it is shown that the IR spectrum provides a simple way to determine polaron mobility. Overall, higher oxidation potentials lead to higher doping efficiencies, with values reaching 100% for driving forces sufficient to dope poorly crystalline regions of the film.

Structural and Thermodynamic Characteristics of Potato Starches Depending on the Plant Genotype and Conditions of Their Cultivation

The creation of new highly productive forms of potato by genetic engineering methods raises the question about the quality of transgenic tubers, which first of all relates to the properties of important storage compound such as starch. The article presents the results of studies aiming to the analysis of morphology, structure, and thermodynamic parameters of starch extracted from the potato tubers expressing the tms1 auxin biosynthesis gene from Agrobacterium tumefaciens and characterized by increased productivity in vitro. The transformed and control plants were cultivated in vitro on artificial sterile medium, as well as in vivo in the soil. The methods of scanning electron microscopy, wide-angle X-ray scattering, and differential scanning microcalorimetry were used in the work. It was established that the transformation of plants with the construction with the tms1 gene under the control of the patatin gene promoter causes significant changes in a number of thermodynamic parameters of starch, first of all an increase in the thickness of crystalline lamella and melting temperature, which apparently reflects the increase in the structural ordering of the main starch fraction (approximately 90%) in the tubers of these transformants. Along with this, the effect of accumulating fractions with a less ordered structure in the starch composition, correlating with the ectopic expression of the tms1 auxin biosynthesis gene, was established. At the same time, the B type of the polymorphic structure of starch remains unchanged. However, the detected changes mainly affected starch of the plants, cultivated in vitro. The starch of transgenic plants cultivated in the soil differs little in its basic characteristics from the starch of nontransgenic control plants.

Tunable High-Molecular-Weight Silk Fibroin Polypeptide Materials: Fabrication and Self-Assembly Mechanism.

Silk fibroin is a multisegment natural protein composed of a heavy (H) chain, a light (L) chain and a P25 glycoprotein chain. Herein, we developed a dialysis separation technique under reducing conditions to break the disulfide bond between the H-chain and L-chain and remove the low-molecular-weight portions of the protein. Thus, a high-molecular-weight silk fibroin polypeptide (HSF) material was obtained. SDS-PAGE electrophoresis showed that the molecular weight of HSF was over 80 kDa, similar to the size of the silk fibroin H-chain. Amino acid analysis result demonstrated that the amino acid composition of HSF was almost identical to that of H-chain composition. Importantly, the HSF material obtained has a high surface activity, which can reduce the surface tension of water to below 20 mN/m; at high temperature and high concentration, it can also form a unique nanofibrous network with a lamellar crystalline structure. HSF can further form a rod-shaped structure in a strong polar environment and become a star-shaped fibrous network in a weak polar environment. When the pH value of HSF solution was adjusted from 6 to 8, a structural transition from a folded crank sheet-like structure with micellar beads to a ring-like fibrous structure was observed. During the conversion of HSF from colloidal particles to nanofibers, its molecular conformation also transformed from random coils to β-sheets. These tunable properties indicate that HSF materials have a wide range of applications in biomedical and green chemistry fields.

Enhancing the Formation of Porous Potato Starch by Combining α‐Amylase or Glucoamylase Digestion with Acid Hydrolysis

AbstractGranular porous starch has been prepared from A‐type starch, but not from B‐type starch, due, in part, to the smooth, dense surface of B‐type starch. This study prepares and characterizes acid‐hydrolyzed common corn (A‐type) and potato (B‐type) starches, followed by digestion with α‐amylase or glucoamylase. The results show that, compared to corn starch, potato starch is hydrolyzed faster by acid, whereas the degree of enzyme digestion varies with the starches and enzymes. The acid hydrolyzing conditions destabilize the crystalline lamellae and consequently increase the degree of binding and digestion in both enzymes, which result in the formation of the porous structure in the potato starch. A more defined porous structure is observed in the potato starch after the combination of extended acid hydrolysis and enzyme digestion. B‐type porous starch can be a better colonic delivery system compared to A‐type porous starch due to its more resistance to enzyme digestion.

Effects of various oil extraction methods on the gelatinization and retrogradation properties of starches isolated from tigernut (Cyperus esculentus) tuber meals

Gelatinization and retrogradation characteristics of starches from tigernut (Cyperus esculentus) tuber before and after various oil extraction processes were studied in this investigation. The results indicated that starches isolated from tigernut tuber after the various oil extraction processes varied significantly in gelatinization and retrogradation properties. The starches isolated from the cakes of tigernut tuber after hot press extraction exhibited higher retrogradation tendency and relatively less shear-thinning than other starch samples. The results of FT-IR, XRD, and NMR analysis indicated that oil extraction had an unfavorable influence on starch retrogradation, which may be due to structural changes caused by oil extraction processes. In particular, oil extraction led to more efficient packing of double helices in the crystalline lamella of the starches during storage. Retrogradation of the starch gels also reduced the water holding capacities of the starches. The starch sample isolated from the cake after cold press extraction exhibited the highest water absorption capacity among the five samples for all storage times. This investigation provides valuable novel information for the industrial utilization of tigernut tuber starches isolated from meals and cakes after oil extraction.

Tribological Behavior of a Self-Lubricant Surface Film of H<sub>3</sub>BO<sub>3 </sub>Formed on a Borided Biomedical Steel by a Post-Treatment

This paper evaluates the tribological behavior of borided AISI 316L steel after being exposed to a secondary process to form a thin film of a solid lubricant. The process known as Short Annealing Process (SAP), allows creating a thin film of boric acid (H3BO3) on the surface of metallic materials previously exposed to boriding. The H3BO3 film acts like solid lubricant due to its lamellar crystalline structure. First samples of AISI 316L were exposed to boriding to temperatures of 875, 925 and 975 °C during 2, 4 and 6 h each temperature. Then, samples were heated to 750 °C during 5 min and cooled to room temperature at 60 % of Relative Humidity. The tribological behavior of the treated samples was evaluated by pin-on-disk test equipped with friction coefficient measurement system. Samples were characterized by Scanning Electron Microscopy, X-Ray Diffraction and Vickers microhardness test. The results showed an evident influence of the experimental parameters on the thickness of the boride layers and their mechanical properties. The layer ́s thickness was ranged from 10.51±0.71 to 51.57±5.12 μm. The hardness of the coatings was increased from 264 to 1685 HV. Finally, the Coefficient of Friction was diminished from values of 0.7 for the as-received material to 0.29 for the borided samples and to 0.06 for those after SAP, which indicates that the post-treatment SAP enhances the tribological properties of the biomedical steel.

Chain arrangements of selectively deuterated poly(ε-caprolactone) copolymers as revealed by neutron scattering

The chain arrangement within the crystalline lamellae has been the focus of polymer crystallization. In this study, a series of protiated (H) and deuterated (D) poly(ε-caprolactone) (PCL) blends, block and random copolymers were investigated by small-angle neutron scattering (SANS) measurements. The spatial inhomogeneities of block copolymers were analyzed via Debye-Bueche method and temperature dependence of Flory-Huggins interaction parameter χ in the melt was extracted from fitting the scattering data to the random phase approximation model. Studying the changes of SANS signals further revealed that the copolymers exhibit cooling rate-dependent crystallization behaviors. A unique SANS double-peak pattern was found in D4/D10 50/50 blend and D10-D0-D10 triblock copolymers (where D0, D4, and D10 indicate PCL with different levels of deuteration), as a result of two types of contrasts: scattering length density (SLD) difference between lamellae of different components and density difference between amorphous and lamellar domains. These detailed findings complement our understanding of the complex crystallization processes of deuterated polyesters, which also suggest an avenue for fine control of crystal structures that adds to materials design.

Insights into the hierarchical structure and digestibility of starch in heat-moisture treated adlay seeds

In the present study, starches isolated from heat-moisture treated (HMT) adlay seeds were characterized with hierarchical structures and digestibility to understand the relationships in structural and digestible behaviors of starches in a HMT starch-based food system. The results indicated that HMT not only caused the disorganizations of hierarchical structures, but also promoted the molecular rearrangements and reassembly of starch chains to form a new ordered molecular aggregation architecture (i.e., highly ordered molecular structure, amylose-lipids complexes and thicker crystalline lamella). And the reinforced molecular interactions between starch molecules during HMT occurred to form more densely ordered structure, thus reducing the digestibility and digestion rate coefficients (k) of adlay starch. Particularly, HMT applied directly in adlay seeds with 30% moisture content displayed the highest resistant starch level (20.6%) and lowest k (2.74 × 10−3 min−1). Thus, the results are useful to realize the desired regulation of starch digestibility in adlay products following HMT.

Chain length effect on the structure and thermotropic phase transitions of solid catanionic complexes built of cetyltrimethylammonium bromide and saturated n-fatty acids

Chain length effect on the structure and thermotropic properties of asymmetric solid catanionic complexes (CAC) built of cetyltrimethylammonium bromide (C16TABr) and saturated n-fatty acids (CnSFA, CnH2nO2, n = 12, 18, 20, and 22) was investigated by XRD, DSC, and FTIR spectroscopy. All CAC show a lamellar crystalline structure and a series of solid–solid phase transitions below the melting point. The phase transitions are suggested to be caused by sequential melting of the methylene chains in the hydrophobic layer followed by a change in the crystalline structure. C16TABr stabilizes the bilayer structure of CAC and raises its melting point compared to initial CnSFA.

Polaron hopping barriers and rates in semiconducting polymers.

Conjugated polymers are potential next-generation materials for organic electronic devices. The ability of these materials to transport charges is a key factor limiting their performance. Charge carriers in conjugated polymers are localized by disorder and polaronic effects. Charge transport in these materials is often described by thermally activated hopping, with a rate given by Marcus theory. The polaron hopping activation energy determines the temperature dependence of the Marcus rate. This energy barrier is dictated by the transition state, in which the charge carrier is equally divided between the initial and final locations. The prefactor for the polaron hopping rate is set by the charge tunneling rate between the initial and final locations. We use a tight-binding polaron model, in which charge carriers are stabilized by both nuclear reorganization and polarization of the surrounding dielectric, to compute the activation energy, charge tunneling rate and overall rate constant for intrachain and interchain charge hopping processes in poly(3-hexylthiophene) (P3HT) crystalline lamellae and amorphous melts. Charge transport in these two environments is limited by interchain hopping processes. Both hopping barriers and rates predicted by the model are in good agreement with experiments on a variety of crystalline and amorphous P3HT materials. Qualitatively, the barriers largely depend on how well the transition state is stabilized by polarization effects, and on the hopping integral between the initial and final locations, both of which penalize hopping over longer distances.

HMDSO plasma treatment as alternative to modify structural properties of granular starch

In the present study, the effect of plasma treatment on the structural properties of three granular corn starches (normal, Hylon V and Hylon VII) was investigated. Thermal (TGA/DSC), structural (XRD/FTIR) and chemical (XPS) properties were evaluated. Plasma treatment resulted in partial evaporation of water molecules changing the organization level of the double helices in the crystalline lamellae. Moreover, XRD results suggested a decrease of the long-range crystallinity and suggested changes in amylose chains after treatments. The crosslinking of modified amylose chains measured by XPS analysis resulted in variations in the gelatinization parameters as well as in its heterogeneous crystalline structure. The results indicate that the type and extent of changes in the structure of plasma-treated corn starch depends on the distribution of the water molecules inside the crystalline regions (helical water) and on the amylose content. In addition, the obtained results indicated that plasma treatment is a suitable method to modify starch without any incorporation of new elements from hexamethyldisiloxane (HMDSO), which only promotes stronger interactions between the starch main components.

Controlling the Growth of Stacks of Correlated Lamellar Crystals of a Block Copolymer

In the crystallization of polymers, besides monolamellar polymer crystals, stacks of correlated lamellae with a unique orientation and signatures of single crystals have often been observed. However, we still lack a generic criterion for such stacking, that is, vertical growth of polymer crystals. Here, by employing self-induced nucleation on the fold surface of a basal lamella for generating appropriate seeds, we identify experimental conditions allowing for a controlled formation of stacks of crystalline lamellae of a block copolymer. Adopting a two-step crystallization procedure, we decoupled nucleation and growth conditions of stacked lamellae and thereby favored vertical growth of polymer crystals in thin films. A sufficient reservoir of molten polymers in combination with slow lateral growth of the basal lamella is required for observing the formation of stacks of correlated lamellae. Taking this path, we were able to form stacks reaching heights of about 10 times the initial film thickness.

Molecular transport through 3-hydroxybutyrate co-3-hydroxyhexanoate biopolymer films with dispersed graphene oxide nanoparticles: Gas barrier, structural and mechanical properties

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) nanocomposite films containing 0.25 wt % of Graphene Oxide (GO) nanoparticles were prepared by solution-casting and characterized by Differential Scanning Calorimetry (DSC), X-Rays Diffraction (XRD) and Positron Annihilation Lifetime Spectroscopy (PALS). Gas transport properties were analyzed in the 295–343 K interval using CO2, N2, D2 and He. Neat PHBH films showed a semi-crystalline structure with lamellar crystalline domains of 30 ± 1 and 5 ± 1 nm size in the (020) and (002) direction, respectively. GO dispersion increases the PHBH crystalline fraction from 0.28 to 0.60 wt. % without changing the size of crystalline domains and the structure of the PHBH free volume. Nanocomposite films show mechanical properties similar to those of the neat PHBH film but improved gas barrier properties as consequence of the larger number density the of gas- impermeable crystalline domains.

Theory of statistics of ties, loops, and tails in semicrystalline polymers.

Polymer crystals grown from melts consist of alternating lamellar crystalline regions and amorphous regions. We study the statistics of ties: chains which bridge the adjacent lamellae, loops: chains which come out of one lamella and enter back into the same lamella before reaching the other lamellae, and tails: chains which end in an amorphous region. We develop a theory to calculate the probabilities of formation of ties, loops, and tails with consideration of finite chain length and cooperative incorporation of a chain into multiple lamellae. The results of our numerical calculations based on a field-theoretic formalism show that the fraction of ties increases with increasing chain length, and it decreases with increasing interlamellar separation. In the limiting case of an infinite chain confined between only two walls, we recover the classical results of the gambler's ruin model. We show that the density anomaly encountered in previous theories is avoided naturally in the present theory without forcing the majority of stems to form tight loops. The derived results on the probability of tie chains in the amorphous regions are pertinent to the mechanical properties of semicrystalline polymers.

Soft Chemical Synthesis of HxCrS2: An Antiferromagnetic Material with Alternating Amorphous and Crystalline Layers.

We report a new HxCrS2-based crystalline/amorphous layered material synthesized by soft chemical methods. We study the structural nature and composition of this material with atomic resolution scanning transmission electron microscopy (STEM), revealing a complex structure consisting of alternating layers of amorphous and crystalline lamellae. Furthermore, the magnetic properties show evidence for increased magnetic frustration compared to the parent compound NaCrS2. Finally, we show that this material can be exfoliated, thus providing a facile synthesis method for chromium-sulfide-based ultrathin layers. The material reported herein can not only be a source of new thin TMD-related sheets for potential application in catalysis but also be of interest for realizing new 2D magnetic materials.

Further investigation of the relationship between polymer structure and HDPE post yield properties

Using typical characterization methods (hyphenated chromatography and calorimetry), the effects of molecular weight and short chain branching (SCB) on relative rates of crystallization and the resulting effects on the post yield tensile properties were quantified for a robust set of high-density polyethylene samples. A semi-empirical chain folding equation coupled with the new structure parameters PSP4 (tie molecule content) and the average number of lamella segments per chain (ALSC) were proposed. These parameters are based on a random polymer walk, including passes through the crystalline lamella, the number of times a chain folds in each lamella and the subsequent effects on the end to end distance of the polymer chain, <R>. Intuitively, the current approach is expected to yield enhanced correlations to mechanical performance since, in addition to maintaining the improvements in lamella size calculation, persistence length dependence on SCB content, and multi-ties per chain, it also accounts for polymer chain folding and lamella orientation. Results showed that homopolymers had a significantly higher level of chain folding compared to copolymers. Moreover, as the length of the SCB increased from ethyl to butyl, less folding was predicted thereby leaving more of the polymer chain to form tie molecules. The quantity PSP43/ALSC, exhibited a linear relationship with strain hardening modulus (SHM) with excellent correlation for a diverse set of unimodal and bimodal resins made using different catalyst systems, which included homopolymers, copolymers, and blends of different catalyst type and modality. Given the simplicity of calculation, use of actual polymer data, and the good predictability offered for SHM for a diverse set of resins, these primary structure parameters (PSP4 and ALSC) have high potential to contribute to the in-depth understanding of polymer structure-property relationships.

Structural evolution of flow-oriented high density polyethylene upon heating: In situ SAXS and WAXD studies

The structural evolution of micro-injection molded high density polyethylene (HDPE) at the molecular and lamellar levels was investigated as a function of temperature during heating process using wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The molded sample exhibits a peculiar multilayer structure of skin and shear layers, and is marked by the existence of shish-kebab-like structure with two populations of lamellar stacks. The variations of the long period as well as the average thicknesses of lamellar and amorphous regions with temperature were determined from one-dimensional correlation functions for the respective lamellar stacks. The average length and the misorientation of shish-like formation were calculated using Ruland equation, and the results indicate that the shish-like structure grows in the longitudinal direction with increasing temperature via incorporation of several partially relaxed chains as a result of autocatalytic process. In addition, the degree of orientation of the chains in the crystalline phase was found to increase slightly with increasing temperature below 100 °C, which could be traced back to the formation of additional crystallites with a low degree of orientation after injection molding. These crystalline lamellae built up during the secondary crystallization are less thermally stable than the primary ones, and therefore are melted selectively upon annealing at relatively lower temperatures yielding an overall increase in the molecular orientation.

Hierarchical Morphology of Poly(ether ether ketone) Aerogels.

The phase diagram for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in 4-chlorophenol (4CP) was constructed over broad temperature and concentration ranges, revealing that PEEK is capable of dissolving and forming gels in both 4CP and dichloroacetic acid (DCA) up to a concentration of 25 wt %. Highly porous aerogels of PEEK were prepared through simple solvent exchange followed by one of two drying methods of solvent removal from the wet gel: freeze-drying or supercritical CO2 fluid extraction (SC-drying). The field-emission scanning electron microscopy analysis showed that gelation of PEEK in 4CP, followed by SC-drying, produced aerogels with well-defined lamellar aggregates as compared to less ordered aggregates formed from DCA. Mechanical properties (in compression) were shown to improve with increasing density, resulting in equivalent compressive moduli at comparable density, regardless of the preparation method (gelation solvent selection, concentration variation, or drying method). Nitrogen adsorption-desorption isotherms indicate that PEEK aerogels are comprised of mesopores (2-50 nm diameter pores) formed from stacked crystalline lamella. PEEK aerogels prepared using SC-drying exhibit higher Brunauer-Emmett-Teller surface areas than freeze-dried aerogels of comparable density. The ultra-small-angle X-ray scattering/small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering analysis revealed a hierarchical morphology of the PEEK aerogels with structural features from PEEK crystallites to agglomerates of stacked lamella that spanned a wide range of length scales. SANS contrast-matching confirmed that the morphological origin of the principle scattering feature in PEEK aerogels is stacked crystalline lamella. Nitrogen sorption measurements of porosity and the specific surface area of the PEEK aerogels were correlated with the SAXS analysis to reveal a remarkably high surface area attributed to the platelet-like, lamellar morphology. Contact angle and contact angle hysteresis (CAH) revealed that low-density PEEK aerogels (ρ < 0.15 g/cm3) have water contact angles above the superhydrophobicity cutoff angle (>150°) and a very low CAH near 1°.

The structure of spray-dried detergent powders

The complex multiscale structure of spray dried detergent granules has been characterized using a complementary range of techniques including scanning electron microscopy (SEM), image analysis, wide angle and small angle X-ray scattering (WAXS, SAXS) and X-ray microtomography. A complex composite structure is revealed due to the multiphase nature of the starting slurry and its evolution during the drying process. Four simple model formulations based on linear alkylbenzene sulphonate (NaLAS) and sodium sulphate were used to probe the influence of initial slurry water content and binder, sodium silicate (SiO_2:nNa_2 O), on the structure. The structure revealed can be viewed as a continuous matrix consisting of NaLAS, sodium sulphate and binder in which large, dense, crystals of sodium sulphate are embedded. These large crystals were initially undissolved in the slurry and are consequently reduced in number in the product made from higher water content slurry. Air is also dispersed in this matrix at two length scales, large vacuoles, typically larger than 0.1x the particle diameter driven by ‘puffing’ i.e. water boiling, and micro-scale porosity which evolved during the crystallisation of the drying matrix. The matrix is formed from the dried slurry liquid phases and is a composite structure of binder, dried surfactant liquid crystalline phase and sub-micron scale crystallites of sodium sulphate. The liquid phase compositions change with the slurry water content, as well as the addition of binder; this changes both the sulphate polymorphs present and the spacing of the liquid crystalline lamellae, i.e. d-spacing, of the NaLAS phase. The composition and crystalline structure of the surface is also affected. The particle morphology can also be significantly affected with the high initial moisture content particle having a distinct agglomerated and blistered structure. The multiscale influence of formulation on particle structure, and consequently product properties and performance, highlights the challenge in predictive design of these important detergent products.

Relationships between crystalline structure and the thermal behavior of poly(ethylene 2,5‐furandicarboxylate): An in situ simultaneous SAXS‐WAXS study

Poly(ethylene 2,5‐furandicarboxylate) (PEF) is an emerging bio‐based polymer with interesting thermal and barrier properties. In this study, the melting behavior of PEF was investigated in situ by means of simultaneous wide and small angle X‐ray scattering (WAXS and SAXS) measurements coupled with DSC measurements. This study gives the first evidence of what happens from a structural point of view during the multiple melting behavior of PEF, which is composed of three distinct events, taking into account the nature of the initial crystalline phase present. The first result is that the α′ form, induced at low crystallization temperature, does not undergo any phase transformation upon heating revealing its stable character. Second, the comparison of the SAXS and WAXS results with the DSC ones showed that the multiple melting behavior observed is attributed to a melting–recrystallization–melting process. Third, this work also definitely shows that the low amplitude melting endotherm observed in the DSC thermograms is ascribed to the melting of secondary crystals. Finally, SAXS‐WAXS results led to the conclusion that the secondary crystals cannot be depicted by the commonly accepted lamellar insertion model. Another microstructural representation of these secondary crystals is proposed. In this model, the secondary crystals consist of bundles of macromolecules, which formed small crystalline entities located between the primary crystalline lamellae stacks. POLYM. ENG. SCI., 59:1667–1677 2019. © 2019 Society of Plastics Engineers