Twin Chain Research Articles

“Twin Chain” PVA Cryogels with Controlled Tortuosity as Advanced Materials for Cleaning of Works of Art

AbstractSoft matrices with tuned properties are part of the vast landscape of innovative materials for the restoration of works of art. “Twin chain” polymer networks (TC‐PNs) based on polyvinyl alcohol have proven unique as scaffolds for Cultural Heritage cleaning. They enable optimum adaptability, adhesion, porosity, and connectivity at both micro‐ and nano‐scale resulting in superior time/space‐controlled cleaning operations. In this work, TC‐PNs properties are tuned through a mild crosslinking of the poly(vinyl alcohol) (PVA)‐porogen polymer by using sebacic, adipic, or succinic acid. The modified porogens have different structural features imparting a different phase behavior to TC‐PVAs mixtures in aqueous solution, i.e., in pre‐gel systems used to form gels through a liquid–liquid phase separation. The macro‐, micro‐, and nanoscale features of the final gels are characterized by Confocal Laser Scanning Microscopy, Small Angle X‐ray Scattering, Rheology and are related to their cleaning performances. The study shows that the gels cleaning capacity is related to their tortuosity, that can be tailored at the nanoscale. Counterintuitively gels with higher tortuosity show better performances as evidenced by the cleaning of mockups and paintings from Jean Helion, Jackson Pollock, and Tancredi Parmeggiani at Peggy Guggenheim Collection in Venice.

Tailoring the properties of poly(vinyl alcohol) “twin-chain” gels via sebacic acid decoration

HypothesisThe development of gels capable to adapt and act at the interface of rough surfaces is a central topic in modern science for Cultural Heritage preservation. To overcome the limitations of solvents or polymer solutions, commonly used in the restoration practice, poly(vinyl alcohol) (PVA) “twin–chain” polymer networks (TC-PNs) have been recently proposed. The properties of this new class of gels, that are the most performing gels available for Cultural Heritage preservation, are mostly unexplored. This paper investigates how chemical modifications affect gels’ structure and their rheological behavior, producing new gelled systems with enhanced and tunable properties for challenging applications, not restricted to Cultural Heritage preservation. ExperimentsIn this study, the PVA-TC-PNs structural and functional properties were changed by functionalization with sebacic acid into a new class of TC-PNs. Functionalization affects the porosity and nanostructure of the network, changing its uptake/release of fluids and favoring the uptake of organic solvents with various polarity, a crucial feature to boost the versatility of TC-PNs in practical applications. FindingsThe functionalized gels exhibited unprecedented performances during the cleaning of contemporary paintings from the Peggy Gugghenheim collection (Venice), whose restoration with traditional solvents and swabs would be difficult to avoid possible disfigurements to the painted layers. These results candidate the functionalized TC-PNs as a new, highly promising class of gels in art preservation.

Statistical characterization of twin transmission across grain boundaries in magnesium

A detailed statistical analysis of twin transmission (TT) across grain boundaries is performed in rolled, commercial purity magnesium compressed along the rolling direction. EBSD images are acquired from two different cuts: a section containing the rolling (RD) and normal (ND) directions; and a section at 35° to the ND which contains transverse direction (TD). An automated twinning analysis software, METIS, is used to obtain the statistical correlations between deformation twins and other microstructural features by analyzing EBSD microstructures comprising thousands of grains and twins. This detailed statistical analysis reveals that the TT propensity is sensitive to the grain boundary (GB) misorientation angle but not to the GB misorientation axis. Specifically, TT propensity decreases with increasing GB misorientation angle; however, the decreasing trend is not monotonic. Further, the detailed analysis of TT events combining macroscopic Schmid factor and the geometric measures (m’: accounts for the alignment of both twin plane normal and shear directions; m”: accounts for the alignment of only twin shear directions; and m”’: accounts for the alignment of only twin plane normal) helps in understanding and identifying the process of twin-pair formation, i.e., co-nucleation versus transmission, also to identify the role of local stresses at GBs induced by inter-grain interaction versus twinning shear transformation processes. In addition, Bayesian inference is used to draw statistically meaningful conclusions as to the likelihood of transmission given misorientation angles. Lastly, twin chain frequency as a function of chain length is predicted using the probability distribution obtained from the Bayesian inference and compared with the actual data from the EBSD microstructures.

Understanding cross boundary twin behaviours in AZ31 alloy by a composite Schmid factor

It is well known that twinning likely nucleates and forms pairs at grain boundaries (GBs) during the formation of hexagonal close-packed alloys. Therefore, the crystallography of GBs should be taken into account to assess the activation preference of twins (and pairs) at GBs. As Schmid factor (SF) is a grain-based parameter, it cannot predict from which GB segment, twinning prefers to nucleate. To solve this problem, recently we proposed a composite Schmid factor (CSF) that incorporates both the SF and a geometric compatibility factor (m’) between twin/slip systems in neighbouring grains. In this presentation, we first summarize the definition and calculation method of this parameter. Then, simultaneous twin nucleation and twin (or slip) stimulated twin behaviour in a twin chain were assessed by this parameter. For comparison, SF and m’ analyses were also performed. The advantages and limitations of this CSF in assessing twin behaviours were discussed.

Arrangement of Ceramides in the Skin: Sphingosine Chains Localize at a Single Position in Stratum Corneum Lipid Matrix Models.

Understanding the structure of the stratum corneum (SC) is essential to understand the skin barrier process. The long periodicity phase (LPP) is a unique trilayer lamellar structure located in the SC. Adjustments in the composition of the lipid matrix, as in many skin abnormalities, can have severe effects on the lipid organization and barrier function. Although the location of individual lipid subclasses has been identified, the lipid conformation at these locations remains uncertain. Contrast variation experiments via small-angle neutron diffraction were used to investigate the conformation of ceramide (CER) N-(tetracosanoyl)-sphingosine (NS) within both simplistic and porcine mimicking LPP models. To identify the lipid conformation of the twin chain CER NS, the chains were individually deuterated, and their scattering length profiles were calculated to identify their locations in the LPP unit cell. In the repeating trilayer unit of the LPP, the acyl chain of CER NS was located in the central and outer layers, while the sphingosine chain was located exclusively in the middle of the outer layers. Thus, for the CER NS with the acyl chain in the central layer, this demonstrates an extended conformation. Electron density distribution profiles identified that the lipid structure remains consistent regardless of the lipid’s lateral packing phase, this may be partially due to the anchoring of the extended CER NS. The presented results provide a more detailed insight on the internal arrangement of the LPP lipids and how they are expected to be arranged in healthy skin.

Methoxy-enriched cationic stilbenes as anticancer therapeutics.

Stilbene-based compounds are largely described for their antioxidant activity. But their use as anticancer chemotherapeutics is hampered by poor pharmacokinetic properties and non-selectivity towards cancer and non-cancer potency. To overcome these drawbacks, twin chain cationic lipid conjugated, methoxy-enriched stilbene derivatives were designed, synthesized and evaluated for their anticancer potency. Our findings reveal that HMSC16, a molecule with the highest number of methoxy groups and with C16-twin chain lipid, is the most potent as well as the most selective anticancer agent when compared to the other synthesized derivatives and commercially available stilbene-based drug, tamoxifen, and resveratrol. To justify these results, we have conducted a series of mechanistic experiments where we found that HMSC16 induced ROS generation, apoptosis, and autophagy by affecting the mitochondrial, lysosomal and nuclear pathways. Further cell cycle analysis data reveals that HMSC16 not only induces cell death but is also involved in the arrest of the cell cycle at the sub-G1 phase. Moreover, HMSC16 showed self-aggregation property owing to a possibly favorable hydrophilic-lipophilic balance. The self-aggregation property of HMSC16 allowed it to entrap hydrophobic drugs, withaferin. With entrapped withaferin, HMSC16 showed additive if not synergistic cell killing effect in HeLa cells. From the above results, we concluded that HMSC16 can be used not just as a drug but also as a drug delivery agent.

In situ observation of cross-grain twin pair formation in pure magnesium

ABSTRACTCross-grain twin pairing was studied utilising in situ optical microscopy and ex situ electron backscatter diffraction in extruded pure magnesium subjected to tension in the direction perpendicular to the extrusion direction. A twin chain spanning over seven grains was rapidly developed through twin propagation and conjoining. Formation of cross-grain twin pair by twin thickening was in/ex situ observed for the first time. It was confirmed that variant selection of the cross-grain twins that carry high Schmid factors, formed either by twin propagation or by twin thickening, was dominated by the strain compatibility between the neighbouring grains.

Initiation and strain compatibility of connected extension twins in AZ31 magnesium alloy at high temperature

Uniaxial compression tests were carried out at 350°C and a strain rate of 0.3s−1 on as-extruded AZ31 magnesium alloy samples. At a true strain of −0.1, extension twin pairs in a grain and twin chains across adjacent grains were detected. The orientation of selected twins and their host grains were determined by electron backscattered diffraction (EBSD) techniques. The Schmid factors (SFs), accommodation strains and geometric compatibility factors (m′) were calculated. Analysis of the data indicated that the formation of twin pair and twin chain was related to the SF and m′. Regarding to twin chain across adjacent grains, accommodation strain was also involved. The selection of twin variants in twin chain was generally determined by m′. When the twins required the operation of pyramidal slip or twinning in adjacent grain, the corresponding connected twins with a relative high m′ were selected in this adjacent grain.

Two in one: switchable ion conductivity and white light emission integrated in an iodoplumbate-based twin chain hybrid crystal.

An iodoplumbate-based hybrid, [C7-Apy][PbI3] (1), where C7-Apy(+) = 1-heptyl-4-aminopyridinium, was prepared using a simple solution process. Three sequential phase transitions occur in the range of 402-443 K. In both the lowest and highest temperature phases, hybrid crystal 1 is composed of discrete [Pb2I6]∞ twin chains surrounded by C7-Apy(+) cations. The connectivity between PbI6 octahedra within a [Pb2I6]∞ twin chain and the arrangement of cations are quite difference between the lowest and highest temperature phases. Hybrid crystal 1 shows switchable ion conductivity due to the structural phase transition and white light emission attributed to the broad band semiconductor emission of the twin chain. The former functionality has potential application in ion conductor devices; the single-phase white light emitter is a useful material in low-cost, easily-made, high-efficiency white light-emitting diodes.

The activation of twinning and texture evolution during bending of friction stir welded magnesium alloys

The present study aims to investigate the twinning behavior and texture evolution during bending of a friction stir welded (FSW) AZ31 Mg alloy. Two kinds of three-point bending tests (designated as Surface test and Base test) were applied at room temperature. Strong texture-dependent twinning characteristics were revealed after bending. The largest numbers of extension twins were observed in SZ-side after Surface test and in SZ-center after Base test. The texture-dependent twinning activity was well explained by the calculated Schmid factor based on a speculated local stress state. Some extension twins were likely connected with each other and formed twin chain or twin band, and most of the neighboring twins present a high geometrical compatibility factor (larger than 0.8), implying that the local strain compatibility played an important role in the formation of connected twins.

Development of new estradiol-cationic lipid hybrids: Ten-carbon twin chain cationic lipid is a more suitable partner for estradiol to elicit better anticancer activity

The present study illustrates the synthesis and anticancer evaluation of six, ten, twelve and fourteen carbon chain containing cationic lipidated-estradiol hybrids. Previously, we have established the lipidation strategy to introduce anticancer activities in various pharmacophores including estradiol (ES). In this structure activity study the length of the carbon chain is narrowed down between C6–C14 to screen out the most potent anticancer molecule among the class. Among the newly developed ES-cationic lipid conjugates, ten-carbon chain containing derivative, ES-C10 (5c) exhibited 4–12 folds better anticancer activity than the previously established derivative, ES-C8 (5b) in various cancer cells of different origin. Moreover cytotoxicity of this molecule was not observed in non-cancer cells. Notably, in spite of bearing estrogenic moiety, ES-C10 exhibited anticancer activity irrespective of estrogen receptor (ER) expression status. ES-C10 exhibited prominent sub-G0 arrest of cancer cells with concomitant induction of apoptosis and demonstrated significant inhibition of tumor growth in mouse melanoma model. Collectively, ES-C10 exemplifies the development of an anticancer agent with broader activity against cancer cells of different origins.

THE ANALYSIS OF THE TRIBOLOGICAL PROPERTIES OF THE ARMOURED FACE CONVEYOR CHAIN RACE / BADANIA WŁASNOŚCI TRIBOLOGICZNYCH PŁYTY ŚLIZGOWEJ PRZENOŚNIKA ZGRZEBŁOWEGO

Generally, the power and capacity of the armoured face conveyor (AFC) are determined by the motor size, pan width and chain size. It is well known that the dynamic behaviour of an AFC drive has a significant influence on tension in the AFC chain, and is therefore critical in determining the reliability of the chain and the entire AFC system. However, the chain long service life is also affected by tribological contact with the chain race plate of the AFC and with the coal. The main objective of this work was to determine the tribological properties of AFC twin chain race (top plate). Characterization of the twin chain race, made of the Hardox 450 abrasion resistant steel, included microstructural examination by light microscopy, hardness test, X-ray diffraction and examination of tribological properties. The studies were carried out on samples cut from top plate of the whitdrawn face conveyor twin chain race. It was found, that the Hardox450 steel has quite good wear resistance for such purpose as AFC twin chain race. It is possible to use more wear resistant material than Hardox 450 steel but it would cause premature wear of the AFC chain.

Binding Geometry of Hydrogen-Bonded Chain Motif in Self-Assembled Gratings and Layers on Ag(111)

Upon adsorption on the (111) facet of Ag, 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid (PVBA) self-assembles into a highly ordered, chiral twin chain structure at submonolayer coverages with domains that can extend for micrometers in one dimension. Using polarization-dependent measurements of C and N K-shell excitations in near-edge X-ray absorption fine structure (NEXAFS) spectra, we determine the binding geometry of single PVBA molecules within this unique ensemble for both low and high coverage regimes. At submonolayer coverage, the molecule is twisted to facilitate the formation of hydrogen bonds. The gas-phase planarity is gradually recovered as the coverage is increased, with complete planarity coinciding with loss of order in the overlayer. Thermal treatment of the PVBA film results in deprotonation of the carboxyl tail of the molecule, but despite the suppression of the stabilizing hydrogen-bonds, the overlayer remains ordered.

Synthesis, Crystal and Electronic Structures, and Magnetic Properties of LiLn9Mo16O35 (Ln=La, Ce, Pr, and Nd) Compounds Containing the Original Cluster Mo16O36

The new compounds LiLn(9)Mo(16)O(35) (Ln=La, Ce, Pr, and Nd) were synthesized from stoichiometric mixtures of Li(2)MoO(4), Ln(2)O(3), Pr(6)O(11) or CeO(2), MoO(3), and Mo heated at 1600 °C for 48 h in a molybdenum crucible sealed under a low argon pressure. The crystal structure, determined from a single crystal of the Nd member, showed that the main building block is the Mo(16)O(36) unit, the Mo(16) core of which is totally new and results from the fusion of two bioctahedral Mo(10) clusters. It can also be viewed as a fragment of an infinite twin chain of edge-sharing Mo(6) octahedra. The Mo(16)O(36) cluster units share some oxygen atoms to form infinite chains running parallel to the b axis, which are separated by the rare-earth and lithium cations. (7)Li-NMR experiments, carried out at high field on the nonmagnetic LiLa(9)Mo(16)O(35), provided insights into the local environment of the lithium ions. Magnetic susceptibility measurements confirmed the trivalent oxidation state of the magnetic rare-earth cations and indicated the absence of localized moments on the Mo(16) clusters. The electronic structure of the LiLn(9)Mo(16)O(35) compounds was analyzed using molecular and periodic quantum calculations. The study of the molecular orbital diagrams of isolated Mo(16)O(36) models allowed the understanding of this unique metallic architecture. Periodic density functional theory calculations demonstrated that few interactions occur between the Mo(16) clusters, and predicted semiconducting properties for LiLn(9)Mo(16)O(35) as a band gap of 0.57 eV was computed for the lanthanum phase.

Features of Highly Twinned Microstructures Produced by GBE in FCC Materials

The proportion of low ΣCSL boundaries of single phase brass, Ni based Alloy 690, 304 stainless steel and Pb alloy were enhanced to about 70% (according to Palumbo–Aust criterion) which mainly were Σ3n (n = 1, 2, 3…) types by small amount of deformation and recrystallization annealing. All the resulting microstructures were constituted of large size grain-cluster, in which all the orientation relationships between any two grains (no matter adjacent or not) could be described by Σ3n misorientations according to twin chain analyzing. Twin relationships up to 8th generation (Σ38) were found in one of such clusters. The outer boundaries of grain-clusters were crystallographically random with the adjacent clusters. In the case of high proportion of low ΣCSL boundaries, the connectivity of random boundary network was not fragmented obviously when the Palumbo–Aust criterion was used, whereas substantially interrupted when the Brandon criterion was applied.

Twinning-induced sluggish evolution of texture during recrystallization in AISI 316L stainless steel after cold rolling

This paper deals with the evolution of texture in AISI 316L austenitic stainless steel during annealing after 95 pct cold rolling. After 95 pct cold rolling, the texture is mainly of the brass type {110}〈112〉, along with a scatter toward the S orientation {123}〈634〉 and Goss orientation {011}〈100〉. Weak evidence of Cu component is observed at this high deformation level. During annealing, recovery is observed before any detectable recrystallization. Recrystallization proceeds through nucleation of subgrain by twinning within the deformed matrix and, later, preferential growth of those to consume the deformed matrix. After recrystallization, the overall texture intensity was weak; however, there are some discernible texture components. There was no existence of the brass component at this stage. Major components are centered on Goss orientation and Cu component {112}〈111〉 as well as the BR component {236}〈385〉. Also, a few orientations come up after recrystallization (i.e., {142}〈2−11〉 and {012}〈221〉). With increase in annealing temperature, the textural evolution shows emergence of weak texture with another new component, {197}〈211〉. The evolution of texture was correlated with the deformation texture through twin chain reaction.

Building Supramolecular Nanostructures at Surfaces by Hydrogen Bonding Fruitful discussions with A. de Vita, B. Müller, and H. Brune are acknowleged.

The fine balancing of the lateral intermolecular interactions and the bonding to the substrate enables the self-assembly of supramolecular nanostructures at surfaces to be achieved. The scanning tunneling microscopy image shows the formation of a twin chain of 4-[trans-2-(pyrid-4-yl)vinyl]benzoic acid deposited on an Ag(111) surface in ultra-high vacuum.

Stabilization of acid phosphatase in DDDACl/n-butyl acetate reverse micelles

Storage stability of acid phosphatase entrapped in reverse micelles was studied. Supramolecular systems were prepared with a cationic twin chain surfactant, didodecyldimethylammonium chloride (DDDAC1), n-butyl acetate as an organic solvent and different water percentages. The rate of enzyme deactivation was monitored in the temperature interval from 20 to 45 °C, at bulk pH from 4.8 to 6.4, either unstirred conditions or under convective mixing from 250 to 750 rev min−1, water-to-surfactant molar ratio (w0) equal to 11.4, 12.7, 14.2 and with the following buffers, Na-citrate, Li-citrate, K-citrate, Na-propionate. Acid phosphatase entrapped in buffer pools of reverse micelles exhibited enhanced stability in comparison with the enzyme in the pure aqueous phase. Half-life was up to 4 times larger. Both the chemicals used for buffer preparation and buffer pH change, within one unit, were found to influence the rate of acid phosphatase deactivation. The activation energy of enzyme deactivation process in micellar systems was slightly increasing with w0 but the values were not very different from the one in aqueous phase (145.3 kJ mol−1). The rate of deactivation of enzyme confined in the micelles when shear stress was applied was reduced in comparison with that of the free protein, even though the percentage loss was greater.

The Formation of Twins in Recrystallized Binary Al-1.3%Mn

Local texture analysis in sheets of cold-rolled and recrystallization-annealed binary Al-1.3%Mn revealed a number of twin grain boundaries, including one twin chain of third generation. The formation mechanism of these twins was traced by means of electron backscattering diffraction analysis of the twinned grains and the surrounding matrix at the early stages of recrystallization. The results obtained suggest that the twins do not form by conventional recrystallization twinning, but the twin boundaries are rather the result of an impingement between newly formed recrystallized grains and subgrains of the as-deformed matrix, which were already in twin relation. Consequently, the formation of twins does not lead to the generation of new orientations and, hence, does not affect the recrystallization texture. Besides the twins, other coincidence site–lattice orientation relations were frequently observed, which also could be tracked to the as-deformed state.

An investigation by interactive electron backscatter pattern analysis of processing and superplasticity in an aluminum-magnesium alloy

Tensile specimens from an Al-lOMg-0.lZr alloy, thermomechanically processed (TMP) according to two different schedules and deformed superplastically at 300 °C, were examined using electron backscatter pattern (EBSP) imaging in the scanning electron microscope (SEM) with computer-aided analysis. The TMP schedules differed only in the duration of the interpass anneal (IPA) time between successive rolling passes. Microtexture, grain misorientation angle distribution, and grain boundary character were analyzed for both undeformed grip and deformed gage sections of these tensile specimens. Microtexture analysis revealed the same texture components, primarily brass and S, in the undeformed grip sections of both TMP materials, while analysis of deformed gage sections revealed only a decrease in texture with no new components evident. Material processed with a prolonged IPA time exhibited highly superplastic response and contained a high proportion of boundaries of 5 to 15 deg misorientation. Material processed with a short IPA time exhibited lower superplastic elongations and contained higher-order twin boundaries, suggesting that the twin chain mechanism is active during TMP. The observed difference in tensile behavior appears to be the result of extended recovery during TMP of the more ductile material evidenced by the development of a greater proportion of boundaries of 5 to 15 deg misorientation.