Rod-like Growth Research Articles

Nucleation and growth rate determination on alkali-activated slag under various sodium hydroxide molarity

Alkali-activated slag has been noted as one of potential alternatives to the ordinary Portland cement due to its properties including high early strength performance and capability of ambient curing. However, there is still limited studies available on elucidating the reaction processes towards producing the excellent properties. This study aims to elucidate the mechanism of alkali activation of slag under different molarities of sodium hydroxide, which is one of the most influential factors on the properties of alkali-activated slag. Heat evolution of alkali-activated slag was used as a real-time monitoring technique. For mix designation, the molarity of sodium hydroxide was varied from 6M to 14 M, with solid-to-liquid ratios of 0.6 and alkali activator ratios of 2.0 remaining constant. The calorimetric data obtained was further used for determination of degree of reaction, nucleation and growth rate mechanism using Johnson–Mehl Avrami Kolmogrov model. According to the findings, it was found that regardless of various molarity of sodium hydroxide applied, the nucleation mechanism and growth is governed by instantaneous heterogeneous nucleation with rod-like growth as the n value is approaching 1 in which is observed from the morphology of the alkali-activated slag at lowest molarity applied (6 M). Furthermore, increasing in molarity of sodium hydroxide was found to decrease the total heat evolved and the lowest was obtained when using 14 M.

Significance of microstrain in impacting band gap and photoluminescence behavior of Ce-doped ZnO thin films deposited via sol-gel process

The purpose of this study is to analyse the importance of micro-strain in affecting the band gap and photoluminescence (PL) intensity of sol-gel-spin-coated Ce-doped ZnO thin films on glass slides. The presence of the (100) plane in the fabricated thin film was discovered using x-ray diffraction thereby indicating the presence of strongly orientated monocrystalline ZnO hexagonal wurtzite phase. On doping with Ce, the micro-strain in the ZnO thin films changed from (2.49–4.84) × 10–3, and the crystallite size ranged from 26.23 to 43.03 nm. UV-visible spectroscopy revealed that the optical transparency of the undoped and Ce-doped ZnO films was between 60 to 85 percent, however the doped films’ absorption dip was slightly shifted from 378 to 380 nm. For Ce-doped ZnO thin films, the increase in band gap values determined using Tauc’s plot was in the range of 3.19 to 3.44 eV. No change in the peak of UV emission was visible in the PL emission spectra after Ce doping. The micro-strain brought on by doping ZnO with Ce controlled the decrease in PL intensity. On doping with Ce up to 3 at.%, PL intensity and micro-strain both reduced, then climbed till Ce 5 at.%, and ultimately declined when the Ce content was 6 at.%. According to studies using scanning electron microscopy, the undoped ZnO film morphology was characterised by spherical particles with rod-like growth structures. For 1, 2, 5, and 6 at.% Ce-doped ZnO thin films, this structure was changed to a nanorod-like structure with small nanorods attached to a long rod. But lengthy chain linkage structures were found in the event of 3 at.% Ce doping. The preceding results are discussed from a doping perspective.

Coexistence of rod-like and lamellar eutectic growth patterns

We present the first observations of a large-scale coexistence between rod-like and lamellar eutectic growth patterns during directional solidification of a eutectic alloy. In situ experiments with real-time optical monitoring were carried out under microgravity onboard the International Space Station (ISS). We used the transparent succinonitrile-d,camphor eutectic alloy that ordinarily forms rod-like patterns. At low growth velocity, short lamellae stabilized at the contact line with a sample glass wall. In the presence of a controlled transverse temperature gradient, the coupled-growth pattern experienced a global drift along an inclined isotherm, and a stable lamellar domain spread over the solidification front. The propagative nature of the lamellar-to-rod transition was evidenced. The advance of the lamellar/rod domain boundary was determined by a slowly amplifying varicose instability of the lamellae. On a large scale, the domain boundary underwent a dynamic faceting.

Efficient and additive-free synthesis of morphology variant iron oxyhydroxide nanostructures for phosphate adsorption application

Iron oxyhydroxide (FeOOH) nanostructures of different shapes were successfully synthesized on flexible textile cloth of polyester using a novel and simple technique based on hydrolysis method. The technique used herein is newly designed specifically to improve the efficiency in terms of energy, simplicity and cost involved in large scale synthesis of nanostructured thin films. Additionally, the morphology of nano-sized iron oxyhydroxide could be tuned into different shapes through variation in the type of precursors used for synthesis. The uniformity and adhesion of the depositions were also found to be excellent as examined by qualitative techniques. The as-deposited samples exhibited monoclinic and orthorhombic structures of FeOOH. A significant variation in the shape of as-deposited FeOOH nanostructures with change in precursor was observed through morphological studies, which displayed lance-shaped, rounded clusters and rod-like growth features in different cases. The nanocrystalline FeOOH can be directly applied to attract and trap phosphate from water reservoirs, thus contributing to environmental solutions. The proposed technique can also be utilized to deposit larger areas, which could be suitable for practical applications.

Research on the influences of two alcohol soluble glutenins on the retrogradation of wheat amylopectin/amylose

Two alcohol soluble glutenins (ASGLUs) were extracted from gluten and further separated by column chromatography. The ASGLUs with Mw lower than 20,000 (ASGLU 1) and Mw higher than 70,000 (ASGLU 2) show the total amino acid contents of 86.71 g/100 g and 62.847 g/100 g respectively. Both of them are rich in Glu (45.574% and 43.224%) and Pro (15.447% and 16.370%) while poor in cys-s, met and lys (less than 1%). When wheat amylopectin/amylose retrogrades with those ASGLUs, the retrogradation rate of amylopectin with ASGLU 1 enhances significantly. UV–Vis, X-ray diffraction, FT-IR, DSC, CD and solid 13C NMR suggest that the double helixes of amylopectin short-chain branching are unwound during gelatinization. The hydrogen bonds of ASGLU 1 between amide and carbonyl oxygen are destroyed, meanwhile, β-sheets are unfolded. During retrogradation, ASGLU 1 with less steric hindrance gets into the crevice of amylopectin and combines with the short-chain branching by hydrogen bond. The retrogradation dynamics show that the nucleation type of amylopectin-ASGLU 1 changes from instantaneous to rod-like growth during the process of retrogradation. β-sheet of ASGLU 1 changes to β-turn and random conformations at the meantime. The results provide a key targeting to control retrogradation of dough.

Geopolymerization of class C fly ash: Reaction kinetics, microstructure properties and compressive strength of early age

The main objective in this study is to elucidate the geopolymerization of Class C fly ash at different solid-to-liquid ratio (1.0-3.0) by using heat evolution analysis. Differential Scanning Calorimeter was used to monitor heat evolution. The calculated heat evolved was utilized to analyze the reaction kinetics using Johnson-Mehl-Avrami-Kolmogrov Model and correlate with the compressive strength and microstructural properties encompassing morphology, functional group, phase analysis, and elemental distribution. The heat evolution was found to increase with increasing solid-to-liquid ratios. The nucleation mechanism of geopolymerization of Class C fly ash was governed by instantaneous heterogeneous nucleation with rod-like growth. Solid-to-liquid ratio of 2.5 was concluded as optimal ratio due to its great performance for strength development. Meanwhile the contribution of calcium (Ca) and iron (Fe) was confirmed due to the presence of Si-O-Ca and Si-O-Fe bonds in the functional group analysis, which was further confirmed by phase analysis and elemental distribution mapping.

A Facile Route in Controlling the Optical Absorbance of Polyvinylpyrrolidone-Capped Silver Nanoparticles Via Chemical Reduction Technique

This work presents the synthesis of silver nanoparticles (AgNPs) capped with polyvinylpyrrolidone (PVP) via a simple chemical reduction approach. A route in controlling the optical absorbance of the AgNPs by varying the concentration of silver precursors, as reflected by the shifts and broadening of the UV-vis spectra of the AgNPs is also highlighted. Dynamic Light Scattering results revealed the narrow and small hydrodynamic size for AgNPs synthesized at low precursor concentration, while multiple hydrodynamic size peaks were observed for AgNPs produced at high precursor concentration. Likewise, Fourier transform-infrared spectroscopy confirmed the successful capping of PVP on the AgNPs through the O and N atoms as potential binding sites. Transmission electron micrographs revealed the formation of spherical PVP-capped AgNPs, having no apparent aggregation observed. A closer inspection of the micrograph showed the subsequent formation of rod-like growth template of the AgNPs, that might lead to the formation of non-spherical silver nanostructures.

One-step synthesis of dandelion-like lanthanum titanate nanostructures for enhanced photocatalytic performance

The rational design of nanomaterials with distinct exposed facets is of great importance for improving the physicochemical properties of these materials and for the study of structure–activity relationships. This work describes the first synthesis of lanthanum titanate (La2Ti2O7, LTO) with dandelion-like nanostructures via the molten salt method. The lowest synthesis temperature of 700 °C is at least 200 °C lower than that required by other methods. The dandelion structure consists of well-crystallized LTO nanorods (NRs) with sizes of less than 100 nm in the radial direction and 300–500 nm in the axial direction, which is different from the widely accepted two-dimensional form. LaOCl microplates were formed as an intermediate substrate for LTO NR growth outwards to the basal surfaces of the LaOCl crystallites. DFT calculation results showed that the strong LiCl adsorption on the (100) surface led to distinct growth of the (100) and (020) planes, thus promoting the rod-like growth of LTO along the [010] axis. In addition, the photocatalytic performance of as-prepared LTO was evaluated by determining the degradation of rhodamine B. The results suggested that the as-prepared LTO could markedly enhance the photocatalytic activity as a result of the surface heterojunction of coexposed {100} and {002} facets in LTO NRs.

Synthesis and viscoelastic properties of gemini surfactants containing redox-active ferrocenyl groups

A type of electro-responsive threadlike micelle (TLM) was formed using new cationic gemini surfactants Fc11-n-11Fc with redox-active ferrocenyl groups in the gemini alkyl chains. By varying the alkyl spacer length, we synthesized several kinds of Fc11-n-11Fc-based gemini surfactants with n = 3, 4, 6, and characterized their viscoelastic behavior, surface activity, and redox properties in aqueous solutions through the use of oscillatory rheology, surface tensiometry, cyclic voltammetry, and UV–vis spectroscopic measurements. The Fc11-4-11Fc solution was found to form highly viscous (˜103 Pa⋅s) TLMs. Unlike the monomeric surfactant, the Fc11-4-11Fc micellar solution maintained its high viscosity even after adding extra builder and/or electrolyte agents. The surface-tensiometric measurements indicate that the effective molecular area of Fc11-n-11Fc at the air/water interface systematically increased with the alkyl spacer length. Using the critical packing parameters estimated with the molecular area, Fc11-4-11Fc is expected to be the most suitable for rod-like micellar growth. Importantly, the viscosity of Fc11-4-11Fc micellar solution could be decreased to that of pure water as a response to electrochemical oxidation reaction, and recovered by the subsequent re-reduction reaction. Hence, the gemini surfactants prepared in this study are a promising class of candidates for potential smart soft material applications.

Repulsive interaction induces fibril formation and their growth

In a type-II diabetes disease, amylin protein takes an incorrect structure that leads to the formation of the amyloid fibril. The conversion mechanism of amyloid fibril is not well understood. We have observed a repulsive interaction, in terms of second virial co-efficient (A2), between protein molecules in their native state in the PBS buffer through laser light scattering technique. The A2 switches from repulsive (positive A2) to attractive (negative A2) interactions with elapsed time favoring the formation and growth of the fibril. We report aggregation and fibril growth kinetics of amylin protein in different environmental conditions. The measurement of shape factor (ρ) through light scattering experiment shows a transition from coil-like structure to rod-like growth. In addition to rod-like growth, sheet-like growth of fibril is also observed through analytical and high-resolution TEM imaging techniques. The nucleation leading to elongation of fibrils as well as stacking of individual fibril perpendicular to the fibril axis is held by hydrogen bonding observed through high-resolution TEM.

Structure, rheology and electrospinning of zein and poly(ethylene oxide) in aqueous ethanol solutions

Electrospun fiber mats (EFM) integrated proteins and biocompatible polymers have been widely used as tissue scaffold, wound dressing and food packaging. The morphology of EFM has strong correlation with the structure and rheology of the solutions. We studied the structure and rheology of polyethylene oxide (PEO) and zein in 80% ethanol aqueous solutions and the resulted EFM. In solutions, zein with rod-like conformation tends to aggregate and form oligomer, the number of proteins in the oligomer spans from 2.5 to 55.2, while PEO always behaves like Gaussian chain in good solvent. Zein preferred to distribute along PEO chains in their mixed solutions, and the structures decomposed from small angle X-ray scattering have consistent relaxation spatial-temporal characteristics with rheological behaviors. Further, the aging of zein solutions enhanced shear thinning and resulted thicker fibers in EFM, which are attributed to the rod-like growth of zein aggregates. Aggregates in viscous media with long enough relaxation time are probably crucial for the formation of continuous electrospun fibers or ribbons. This study provides a clear correlation of the structure, rheology of solutions with the morphologies of EFM made up of proteins and polymers.

MreB Senses Local Gaussian Curvature to Pattern Rod-Like Growth of the Bacterial Cell Wall

Over the past few years we have developed an image-processing framework that allows us to extract precise 3D shapes of bacterial cells from fluorescence microscopy data. This active mesh approach minimizes the difference between an observed Z-stack and model shapes that have been convolved with the experimental point spread function. From these xyz coordinates, we calculate geometric parameters such as local curvatures, surface areas, and the relative enrichment of fluorescent signals. Our fluorescent signal is the concentration of the bacterial actin homolog MreB. We have integrated a fluorescent sandwich fusion of MreB with msfGFP at the native locus. This construct has unperturbed mass-doubling times and a proper rod-like shape.We have previously shown in both two and three dimensions that MreB is enriched at negative curvatures and away from positive curvatures [Ursell et al. PNAS 2014]. Here we show in the straight rod Escherichia coli and the curved rod Caulobacter crescentus that MreB senses local surface curvature and, as a result, helps ensure rod-like growth of the cell. The curvature sensed by Escherchia coli MreB is the Gaussian curvature of the surface, the product of the two principal curvatures. Using MreB point mutants that have altered curvature sensitivities, we are testing the hypothesis that cells straighten deformations by patterning growth at the proper geometry. To stably generate their comma shaped geometry, Caulobacter crescentus have developed ways to overcome this straightening mechanism. The enrichment profile of CcMreB shows a plateau in enrichment at small, positive Gaussian curvature values that depends on the protein crescentin. In addition to its structural role in bending the cell, we propose a mechanism whereby crescentin alters the curvature preference of MreB and allows the stabile propagation of the Caulobacter shape.

RodZ links MreB to cell wall synthesis to mediate MreB rotation and robust morphogenesis

The rod shape of most bacteria requires the actin homolog, MreB. Whereas MreB was initially thought to statically define rod shape, recent studies found that MreB dynamically rotates around the cell circumference dependent on cell wall synthesis. However, the mechanism by which cytoplasmic MreB is linked to extracytoplasmic cell wall synthesis and the function of this linkage for morphogenesis has remained unclear. Here we demonstrate that the transmembrane protein RodZ mediates MreB rotation by directly or indirectly coupling MreB to cell wall synthesis enzymes. Furthermore, we map the RodZ domains that link MreB to cell wall synthesis and identify mreB mutants that suppress the shape defect of ΔrodZ without restoring rotation, uncoupling rotation from rod-like growth. Surprisingly, MreB rotation is dispensable for rod-like shape determination under standard laboratory conditions but is required for the robustness of rod shape and growth under conditions of cell wall stress.

Freeze-thaw stability, glass transition, and retrogradation of high hydrostatic pressure-assisted hydroxypropylated corn starch

Effects of high hydrostatic pressure (HHP) and the propylene oxide (PO) concentration on the freeze-thaw stability, glass transition temperature (Tg′), and retrogradation degree of HHP-assisted hydroxypropylated corn starch were investigated. HHP-assisted hydroxypropylated corn starches were prepared using propylene oxide (4, 8, and 12%, v/w) at 25°C for 15 min under HHP (100, 200, 300, and 400 MPa). The freeze-thaw stability, Tg′, ice melting enthalpy (H i ), and retrogradation degree of HHP-assisted hydroxypropylated corn starches showed patterns different from native corn starch. In general, higher pressures and PO levels lowered Tg′ and H i values, and the retrogradation degree. The highest freeze-thaw stability was observed in HHP-assisted hydroxypropylated corn starch prepared using 12% PO at 400 MPa for 15 min. Retrogradation kinetics of hydroxypropylated corn starch gels observed from the glass transition temperature, ice melting enthalpy, and retrogradation degree revealed that recrystallization occurred with instantaneous nucleation, followed by rod-like growth of crystals.

A Caulobacter MreB mutant with irregular cell shape exhibits compensatory widening to maintain a preferred surface area to volume ratio.

Rod-shaped bacteria typically elongate at a uniform width. To investigate the genetic and physiological determinants involved in this process, we studied a mutation in the morphogenetic protein MreB in Caulobacter crescentus that gives rise to cells with a variable-width phenotype, where cells have regions that are both thinner and wider than wild-type. During growth, individual cells develop a balance of wide and thin regions, and mutant MreB dynamically localizes to poles and thin regions. Surprisingly, the surface area to volume ratio of these irregularly shaped cells is, on average, very similar to wild-type. We propose that, while mutant MreB localizes to thin regions and promotes rod-like growth there, wide regions develop as a compensatory mechanism, allowing cells to maintain a wild-type-like surface area to volume ratio. To support this model, we have shown that cell widening is abrogated in growth conditions that promote higher surface area to volume ratios, and we have observed individual cells with high ratios return to wild-type levels over several hours by developing wide regions, suggesting that compensation can take place at the level of individual cells.

Kinetic Study on the Isothermal and Nonisothermal Crystallization of Monoglyceride Organogels

The isothermal and nonisothermal crystallization kinetics of monoglyceride (MAG) organogels were studied by pulsed nuclear magnetic resonance (pNMR) and differential scanning calorimetry (DSC), respectively. The Avrami equation was used to describe the isothermal crystallization kinetics and experimental data fitted the equation fairly well. Results showed that the crystal growth of MAG organogels was a rod-like growth of instantaneous nuclei at higher degrees of supercooling and a plate-like form with high nucleation rate at lower degrees of supercooling. The exothermic peak in nonisothermal DSC curves for the MAG organogels became wider and shifted to lower temperature when the cooling rate increased, and nonisothermal crystallization was analyzed by Mo equation. Results indicated that at the same crystallization time, to get a higher degree of relative crystallinity, a higher cooling rate was necessary. The activation energy of nonisothermal crystallization was calculated as 739.59 kJ/mol according to the Kissinger method. Therefore, as the results of the isothermal and nonisothermal crystallization kinetics for the MAG organogels obtained, the crystallization rate, crystal nucleation, and growth during the crystallization process could be preliminarily monitored through temperature and cooling rate regulation, which laid the foundation for the real industrial manufacture and application of the MAG organogels.

Dynamic instabilities of rod-like eutectic growth patterns: A real-time study

We present a real-time experimental study of the rod-like growth patterns formed during directional solidification in a non-faceted transparent eutectic alloy, succinonitrile–(d)camphor. Slightly convex isotherms were used to slowly increase the pattern spacing λ from an appropriate starting value to the threshold spacing for rod elimination or rod-splitting instabilities allowing a quantitative determination of these thresholds as a function of the solidification rate V. We show that the threshold spacing for rod splitting obeys the general λ∼V−1/2 scaling law of eutectic growth, whereas the threshold spacing for rod elimination deviates from this law at low V, exhibiting the same overstability effect as previously reported for lamellar eutectic patterns. We demonstrate that topological defects (walls between hexagon domains) play an important role in rod-splitting processes. We also describe a spatially incoherent mode of oscillation that we observed in disordered rod-like patterns.

Impact of solution hydrodynamics on the deposition of CaSO4 on brass

ABSTRACT An investigation was conducted to study the impact of solution hydrodynamics on the deposition of calcium sulfate scale on commercial brass by using a rotating cylinder electrode system at various pre-set rotational speeds, at 60 and 70°C on 120 and 600 grits polished cylindrical specimens. The effects of temperature, surface roughness, and flow conditions on the deposition of calcium sulfate scale on brass are presented. The results indicate the influence of solution hydrodynamics on the rate of calcium sulfate scale deposition on brass specimens by delineating the competing effect between the scale deposition and scale removal process that is occurring simultaneously under the fluid flow conditions generated in the study. The morphology of deposited crystals was obtained from scanning electron microscope (SEM) micrographs and composition was determined with energy dispersive X-ray spectrometer (EDS) method. The SEM analysis revealed prismatic needle- and rod-like crystals growth structure at nu...

Correlations of Properties and Structures at Different Length Scales of Hydro- and Organo-gels Based onN-Alkyl-(R)-12-Hydroxyoctadecylammonium Chlorides

The self-assembly and gelating ability of a set of N-alkyl-(R)-12-hydroxyoctadecylammonium chlorides (NCl-n, where n = 0-6, 18 is the length of the alkyl chain on nitrogen) are described. Several are found to be ambidextrous (gelating both water and a variety of organic liquids) and very efficient (needing less than ca. 0.5 wt % at room temperature). Structure-property correlations at different distance scales of the NCl-n in their hydro- and organo-gels and neat, solid states have been made using X-ray diffraction, neutron scattering, thermal, optical, cryo-SEM and rheological techniques. The self-assembled fibrillar networks consist of spherulitic objects with fibers whose diameters and degrees of twisting differ in the hydro- and organo-gels. Increasing n (and, thus, the molecular length) increases the width of the fibers in their hydrogels; an irregular, less pronounced trend between n and fiber width is observed in the corresponding toluene gels. Time-dependent, small angle neutron scattering data for the isothermal sol-to-gel transformation of sols of NCl-18/toluene to their gels, treated according to Avrami theory, indicate heterogeneous nucleation involving rodlike growth. Rheological studies of gels of NCl-3 in water and toluene confirm their viscoelastic nature and show that the hydrogel is mechanically stronger than the toluene gel. Models for the different molecular packing arrangements within the fibrillar gel networks of the hydro- and organogels have been inferred from X-ray diffraction. The variations in the fibrillar networks provide a comprehensive picture and detailed insights into why seemingly very similar NCl-n behave very differently during their self-assembly processes in water and organic liquids. It is shown that the NCl-n provide a versatile platform for interrogating fundamental questions regarding the links between molecular structure and one-dimensional self-aggregation, leading to gelation.

The effect of surface charge and KNO 3 additive on the crystallization of potassium chloride

In this study, crystal growth and dissolution rates of potassium chloride crystals in pure solution and in the presence of potassium nitrate were investigated in a stagnant type single crystal cell using an image analyzer system. Closely sized seed crystals were separated with respect to their surface potentials using an electrostatic separator and then growth and dissolution behavior of potassium chloride crystals having different surface charges were systematically measured in pure solution and at 10, 100 and 1000 ppm additive concentrations at around 20 °C. In high supersaturation levels, very thin but very long rod-like growth, growing perpendicular to the surface, were observed. This is considered to result from surface nucleation. A dead zone was detected and its width was a function of surface potential of seed crystals. It was determined that, potassium nitrate additive, which has a common ion with KCl leads to increase the surface potential but not to affect the growth behavior, significantly.