Increasing Ultrasonication Time Research Articles

Vibrations of viscoelastic FG porous graphene-platelets reinforced doubly-curved shells via experimental characterisation of graphene platelets

This work explores the vibrations of viscoelastic functionally-graded (FG) porous graphene-platelets reinforced doubly-curved shallow shells via experimental characterisations of graphene platelets. In particular, the effects of ultrasonication time of graphene platelets, on the vibrations of graphene-platelets reinforced shells, are studied. This is of interest because graphene platelets are often ultrasonicated in solvents to achieve better dispersions during the fabrication of graphene-platelets/epoxy composite structures. In this study, geometric characteristics of the graphene platelets under different sonication times are quantitatively and qualitatively analysed through experimental characterisation techniques, including a laser diffraction particle size analyser, a scanning electron microscopy (SEM), and a scanning force microscopy (SFM). The geometric characteristics of graphene platelets are considered in the effective material properties using a micromechanics model of Halpin-Tsai. Different FG distributions of graphene platelets and closed-cell porosity are modelled. The Kelvin-Voigt viscoelastic model is used to consider the internal friction-induced energy dissipation for the polymeric composite shell. Hamilton’s variational principle and an assumed mode method are used to derive and solve the equations of motion, respectively, for the vibrations of the doubly-curved shells. The effects of graphene platelets sonication time, in combination with the effects of graphene platelets weight fraction, porosity coefficient, FG distributions, shell thickness ratio, and shell curvature radii, are scrutinised. The results show that increasing ultrasonication time reduces the shell’s out-of-plane dimensionless fundamental frequency as a result of the reduction in graphene platelets aspect ratio.

Fabrication of graphene from graphite using high-powered ultrasonic vibrators

This paper utilizes an efficient and environmentally friendly method for synthesizing graphene from graphite, namely liquid-phase exfoliation. High-power density ultrasonic vibrators were used to separate graphite layers into graphene in a liquid medium. During layer separation, ultrasonic waves provided mechanical energy to break the Van der Walls bonds and separate graphite layers into graphene. In our study, graphene was synthesized by ultrasonicating graphite in Tween 80 for 1 to 5 h, followed by magnetic stirring and surfactant removal. The FESEM and Raman measurements demonstrated that high-frequency ultrasound waves were effective at breaking the Van der Waals bonding force between adjacent graphite layers. Average flake sizes (lateral) were reduced with increasing ultrasonication time, reaching a minimum value of 317 nm with 5 h of ultrasonic treatment. These results show that liquid-phase exfoliation is a cost-effective method to obtain low-defect few-layer graphene.

Effects of ultrasonication time on stability, dynamic viscosity, and pumping power management of MWCNT-water nanofluid: an experimental study

It is known that ultrasonication has a certain effect on thermophysical properties and heat transfer of nanofluids. The present study is the continuation of the authors’ previous research on the effects of ultrasonication on the thermophysical properties of Multi-Walled Carbon Nanotubes (MWCNTs)-water nanofluid. Investigating the effects of ultrasonication time on samples’ stability, rheological properties, and pumping power of a water-based nanofluid containing MWCNTs nanoparticle is the main objective of the present study. The two-step method has been employed to prepared the samples. Moreover, a probe-type ultrasonic device has been used, and different ultrasonication times have been applied. The samples’ stability is investigated in different periods. The results revealed that prolonging the ultrasonication time to 60 min leads to improving the samples’ stability while prolonging ultrasonication time to higher than 60 min resulted in deteriorating the stability. As for dynamic viscosity, it is observed that increasing ultrasonication time to 60 min leads to decreasing the dynamic viscosity of the samples. As for pumping power, it is observed that the maximum increase in fanning friction factor ratio is less than 3%, which shows that adding MWCNTs to water does not impose a considerable penalty in the required energy for pumping power.

Energy‐induced polymorphic changes in poly(vinylidene fluoride): How ultrasonication results in polymer with predominantly γ phase

ABSTRACTSelf‐polarized poly(vinylidene fluoride) (PVDF) films were prepared via solution crystallization technique wherein the polymorphism of the films was controlled from α phase (>85%) to γ phase (>90%) by varying the time of ultrasonication. On increasing ultrasonication time up to 60 min, γ phase crystallites were found to be self‐aligned in the matrix while an equal proportion of α and γ phases coexist in the PVDF films ultrasonicated for 120 min. The phase conversion as well as inversion was evident from Fourier transform infrared, X‐ray diffraction, and differential scanning calorimetry analyses. Microscopic images of films ultrasonicated for 60 min showed a scrolled lamellar morphology while those sonicated for 120 min showed mixture of scrolled lamellar and spherulitic morphology. With the help of computational studies, it is explained that a large amount of energy is required for transforming trans‐gauche‐trans‐gauche into trans‐trans‐trans‐gauche conformation which is provided by ultrasonication. The mechanism of γ phase formation is proposed based on the experimental and theoretical approaches. Our studies show that just by tuning the time of ultrasonication, PVDF films with various morphologies can be processed; either one with predominantly electroactive γ phase with superior electrical properties or one with equal proportion of α and γ phases with superior mechanical properties. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 40–50

Isolation and Characterization of Cellulose Micro/Nanofibrils from Douglas Fir

Cellulose micro/nanofibrils were successfully extracted from softwood Douglas fir in three distinct stages. Initially raw Douglas fir wood chips were subjected to a hot water extraction (HWE) treatment. Then HWE treated cellulosic fibers underwent a bleaching process followed by a mild ultrasonication. Chemical composition analysis according to ASTM standards confirmed that most of hemicelluloses and nearly all lignin were removed during the first two stages, respectively. Microscopy studies showed formation of nanofibrils during the ultrasonication process, and increasing ultrasonication time led to generation of greater percentage of nanofibrils. With the removal of the matrix materials, the crystallinity of the cellulosic fibers was increased, whereas thermal stability was maintained. HWE opened up the cell wall structure, thereby facilitating the subsequent fractionation into micro/nanofibrils. The obtained cellulose micro/nanofibrils could serve as reinforcing material in composite products or raw material for other applications, such as filtration membrane.

Emulsification properties of pea protein isolate using homogenization, microfluidization and ultrasonication

Pea protein isolate (PPI) is used in many food formulations, due to its low cost, commercial availability and excellent amino acid profile. The objective of this study was to determine the emulsification properties of PPI. Particle size of PPI powders showed neither temperature (25–65°C) nor time (up to 24h) increased solubilisation of powder particles during mixing. Heating PPI dispersions (10%, w/w, protein) from 45 to 90°C led to an increase in storage modulus (G′; Pa) at 71°C, indicating the onset of protein aggregation. Gel formation occurred at 79°C (G′>1Pa). Pea protein-stabilised emulsions made using homogenization (15MPa; 1 pass) or microfluidization (50MPa; 1 pass) resulted in the formation of cold-set gels, with gel strength increasing with increasing oil concentration and fluidic pressure. Droplet size and viscosity of pea protein-stabilised emulsions decreased and increased, respectively, with increasing ultrasonication time. Overall, ultrasonication (<50°C) can create a uniform droplet size emulsion, while, homogenization and microfluidization can produce cold-set gels for use in a wide-range of food applications.

Ultrasonication of chitosan nanoparticle suspension: Influence on particle size

Chitosan nanoparticles have been prepared using an ionic gelation method. The effects of freeze-drying, cryoprotectant (d-trehalose) utilisation and ultrasonication time on the mean particle size, size distribution and stability of nanoparticles were investigated. The size distribution results indicated that freeze-drying caused the particles to agglomerate. Addition of the cryoprotectant and ultrasonication led to a decrease in the particle size. However the sizes of the nanoparticles increased with increasing ultrasonication time. Transmission electron microscopy images revealed that spherical chitosan nanoparticles ranging from 3 to 12nm were obtained by means of freeze-drying in the presence of cryoprotectant and ultrasonication. These results suggest that cryoprotectant utilisation and controlled ultrasonic treatment are effective for imparting nanoparticle stability.

Microencapsulation of wheat germ oil.

Wheat germ oil (WGO) is beneficial for health since it is a rich source of omega-3, omega-6 and tocopherol. However, as it contains polyunsaturated fatty acids, it is prone to oxidation. The aim of this study was to encapsulate wheat germ oil and determine the effects of core to coating ratio, coating materials ratio and ultrasonication time on particle size distribution of emulsions and encapsulation efficiency (EE) and surface morphology of capsules. Maltodextrin (MD) and whey protein concentrate (WPC) at different ratios (3:1, 2:2, 1:3) were used as coating materials. Total solid content of samples was 40% (w/w). Five core to coating ratios (1:8, 1:4, 1:2, 3:4, 1:1) were tried. Ultrasound was used at 320W and 20kHz for 2, 5, 10min to obtain emulsions. Then, emulsions were freeze dried to obtain microcapsules. It was observed that, increasing WPC ratio in the coating resulted in higher encapsulation efficiency and smaller particle size. Microcapsules prepared with MD:WPC ratio of 1:3 were found to have higher EE (74.35-89.62%). Increase in oil load led to decrease in EE. Thus 1:8 core to coating ratio gave better results. Increasing ultrasonication time also had a positive effect on encapsulation efficiency.

Ultrasonication assisted production of silver nanowires with low aspect ratio and their optical properties

We investigated a facial method to produce silver nanowires with low aspect ratio by fragmentizing as produced long silver nanowires. The length of silver nanowires can be shortened in a controllable manner by increasing ultrasonication time or ultrasonication power. However, excessively large ultrasonication power caused a problem of agglomeration of nanowires. From UV absorption spectra, it was found that the UV absorption characteristic of silver nanowires is not affected by ultrasonication assisted fragmentation indicating that one dimensional structure of silver nanowires is maintained during the fragmentation process.

Ultrasonic treatment of polyacrylic acid sodium/NaA zeolite hybrid membranes for the pervaporation dehydration of ethanol

ABSTRACTUltrasonics was used to improve the dispersion of NaA zeolite in polyacrylic acid sodium (PAAS) membranes. The effect of ultrasonication time on the dispersion of NaA zeolite in the membranes, the membrane structure, and performance were investigated. The casting solution and resulting membranes were characterized by viscosity measurement, polarizing optical microscopy (POM), scanning electron microscopy, and X‐ray diffraction (XRD). With increasing ultrasonication time, the viscosity of the casting solution decreased as the chain entanglements decreased. The POM and XRD results showed that crystallization occurred in the PAAS membrane after ultrasonic processing. A more homogeneous morphology was obtained due to improvement in the dispersion of zeolite under ultrasonic treatment for 0.5–1.0 h. As a result, the separation performance was enhanced. The water/ethanol separation factor increased from 176.2 to 577.8. However, the relative separation factor decreased when the ultrasonic time exceeded 2.5 h, due to the appearance of a lamellar structure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3979–3984, 2013

Using power ultrasound for cold gelation of kappa-carrageenan in presence of sodium ions

Abstract Usually a heating stage is required to solubilize kappa carrageenan dispersions for gel formation on cooling. This work reports cold gelation of kappa carrageenan in the presence of sodium ions using power ultrasound without using any heating stage. Carrageenan gels were prepared using ultrasound in the presence or absence of NaCl and their textural properties were compared with the gels prepared with conventional heating method. Mechanical properties of the gels strongly increased with ultrasonication time up to a certain level, and further sonication reduced mechanical characteristics. Addition of Na+ ions after ultrasonication was more effective in increasing textural hardness than when Na+ is present during ultrasonication. Microscopic images demonstrated that increasing ultrasonication time up to a certain level leads to coherent gel networks and further ultrasound has a negative impact on the gel network. Solubility and intrinsic viscosity results are also presented. Moreover, Maxwell model with three elements was used to analyze stress relaxation data. Industrial relevance So far, all documented reports have indicated that to induce gelation of kappa carrageenan dispersions a preheating step is required followed by cooling. In the present work, using power ultrasound a new method for cold gelation of carrageenan dispersions is introduced. Using ultrasound, food and non-food processors can use kappa carrageenan as a viscosifying and gelling agent without using heating.

Effects of High Power Ultrasonic Pretreatment on Physicochemical Quality and Enzymatic Activities of Dried Longan

The physicochemical quality and inactivation of polyphenol oxidase (PPO), peroxidase (POD) in dried longan with high power ultrasonic pretreatment was investigated. Effect of high power ultrasonication was compared with a traditional chemical pretreatment with potassium metabisulfite and non-pretreatment. Chemical qualities, such as aw, MC, TSS, and TA of the ultrasonic pretreated dried longan samples were significantly lower than those of the control samples (P£0.05), whereas their pH were higher than those of the control samples. Increase in ultrasonication time resulted in decreases of aw, MC, TSS, and TA, but an increase of pH. The firmness, lightness (L*), and yellowness (b*) values increased and redness (a*) values decreased when the sample was pretreated with increasing ultrasonication time. The application of high power ultrasonic pretreatment for 10, 20, and 30 min could reduce PPO activity by 49.99%, 57.18%, and 70.68%, and POD activity by 47.63%, 86.16%, and 94.06%, respectively. The PPO and POD activities were significantly decreased with increasing ultrasonication time. Panelists were most satisfied with sensory properties of the dried longan with 30 min of high power ultrasonic pretreatment.

Preparation of nanocrystalline cellulose via ultrasound and its reinforcement capability for poly(vinyl alcohol) composites

Rod-shaped nanocrystalline cellulose (NCC) was prepared from microcrystalline cellulose (MCC) using the purely physical method of high-intensity ultrasonication. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction was used for the characterization of the morphology and crystal structure of the material. The thermal properties were investigated using thermogravimetric analysis. The reinforcement capabilities of the obtained NCC were investigated by adding it to poly(vinyl alcohol) (PVA) via the solution casting method. The results revealed that the prepared NCC had a rod-shaped structure, with diameters between 10 and 20 nm and lengths between 50 and 250 nm. X-ray diffraction results indicated that the NCC had the cellulose I crystal structure similar to that of MCC. The crystallinity of the NCC decreased with increasing ultrasonication time. The ultrasonic effect was non-selective, which means it can remove amorphous cellulose and crystalline cellulose. Because of the nanoscale size and large number of free-end chains, the NCC degraded at a slightly lower temperature, which resulted in increased char residue (9.6–16.1%), compared with that of the MCC (6.2%). The storage modulus of the nanocomposite films were significantly improved compared with that of pure PVA films. The modulus of PVA with 8 wt.% NCC was 2.40× larger than that of pure PVA.

Effect of ultrasonication on the properties of skim milk used in the formation of acid gels

Abstract Skim milk was ultrasonicated for times up to 30 min either with or without temperature control. Ultrasonication (US) without temperature control resulted in the generation of considerable heat, with the milk reaching ∼ 95 °C within 15 min of treatment. The whey proteins were denatured. Changes to the casein micelle size were observed, with decreases during the early stages of US and increases (because of aggregation) on prolonged treatment. Significant κ-casein dissociated from the micelles. Acid gels prepared from these ultrasonicated samples increased in firmness (final G′) up to a maximum final G′ after ∼ 15 min of US, followed by a decrease from this maximum on prolonged treatment. US with temperature control demonstrated that the denaturation of the whey proteins was entirely due to the heat generated during US, although the casein micelle size was still reduced. Acid gels prepared from ultrasonicated skim milk in which the temperature remained below the denaturation temperature of the whey proteins had low final G′, although a small increase was observed with increasing US time. Acid gels prepared from the samples that were ultrasonicated at temperatures above the denaturation temperature of the whey proteins had higher final G′, which could reach values similar to those obtained by the conventional heating of milk. The results of this study indicate that, in skim milk, most of the effect of US can be related to the heat generated from the treatment, with US itself having only a small effect on the milk when the temperatures are controlled. Industrial relevance The control and the manipulation of the firmness of acid skim milk gels are important in many dairy food applications such as yoghurts and some types of cheese. US is an emerging technology that could be used to process skim milk for use in acid gelled products. This study has demonstrated that acid gel firmness can be substantially manipulated when skim milk is ultrasonically treated before acidification; however, most of the effect is due to the heat generated during US treatment. As the effects of US are similar to those obtained through conventional heating processes, and as US can control spoilage microorganisms, using US under controlled temperature conditions could be an alternative to conventional heating to give desired functional properties and storage stability to milk products. However, the temperature/denaturation/aggregation would need to be carefully controlled to minimize the detrimental effects of excessive heating.

Effect of degree of deacetylation of chitosan on the kinetics of ultrasonic degradation of chitosan

AbstractThe objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003