Thixotropic Characteristics Research Articles

On the thixotropy of cellulose nanofibril suspensions

The thixotropic behavior of mechanically disk refined cellulose nanofibril (CNF) aqueous suspensions with 100% fines content at 1 and 3 wt% concentrations was investigated through creep, shear-recovery, multiple-step oscillation, startup, and flow loop experiments. The CNF suspensions exhibited the key thixotropic characteristics such as reduction in viscosity over time and structure recovery after cessation of flow. The results of shear recovery and multiple-step oscillation experiments suggested that regardless of the CNF concentration, lower extents of deformation impede the ability of the suspension to recover its structure at rest and higher levels of shear rates and strain amplitudes facilitate the structure recovery. Furthermore, the results of the startup experiments indicate that CNF suspensions form structures at two different levels where the flocs erode each other during flow. The different types of loops found in the flow loop experiments performed at different shear rates and time intervals were categorized and analyzed in terms of the effects of erosion of flocs and fiber rearrangement during flow.

Flow Properties o f Tannery Waste Liquor

Objective: A water treatment facility is to be erected nearby the industrial tanning complex, recently established East of Cairo, Egypt. This paper represents a contribution to studying the flow characteristics of the produced tannery waste effluents. A dried sample of tannery waste was chemically analyzed by X-ray fluorescence and its particle size distribution was determined. Next, rheological measurements were carried out on the waste slurry produced at temperatures ranging from 10°C to 40°C and three different solid concentrations, by weight: 20%, 25%, and 30%. The results showed that all waste suspensions under all conditions of solid content and temperature behaved as shear-thinning liquids. Flow indices of all suspensions generally tended to increase with temperature and solid concentration. Activation energies for viscosity were correlated to an increase in solid concentration and showed a decreasing pattern. All samples exhibited a thixotropic character that decreased with increased temperature and dilution of the suspension. The maximum pressure drops per unit length of a pipeline used to transport the waste suspension to the treatment unit was evaluated and found to increase with solid concentration and decrease with increasing temperature. Keywords: Rheology, Tannery waste slurry, Solid content, Temperature

PERSPECTIVE: Analysis of thixotropic timescale

Thixotropy is characterized by a time-dependent rise in viscosity under no or weak flow conditions and a decrease in viscosity over time when subjected to strong flow conditions. The characteristic timescale associated with the thixotropic phenomenon, particularly how the viscosity increases with time, has been termed the thixotropic timescale. Several approaches have been suggested in the literature for estimating the thixotropic timescale. The most prominent approach, however, infers it from a specific form of a kinetic expression for structure parameter evolution. In this paper, we study the various kinds of structural kinetic models. By carefully analyzing the same, we propose a parameter for the thixotropic timescale associated with the most generic form of kinetic expression for structure parameter evolution. We observe that increasing the thixotropic timescale weakens the thixotropic character of a system when the viscosity of the structural kinetic model continuously increases over time and eventually diverges under quiescent conditions. We also propose a new phenomenological measure of the thixotropic timescale: τthix=(dlnη/dt)−1, where η is viscosity and t is time. The proposed definition allows a straightforward and unique way to determine the thixotropic timescale through experiments and agrees well with the conventional notion of thixotropy.

A new synergistic hydrocolloid with superior rheology: Locust bean /xanthan gum binary solution powdered by different drying methods

In the current study, a novel gum powder containing locust bean and xanthan gums was prepared by three different drying methods of their synergistic aqueous solutions: direct cabinet drying (CD), drying after alcohol precipitation (PD), and direct freeze drying (FD). The purpose of this process is to develop ready-to-use synergistic gum powders with improved rheological properties by modifying intermolecular interactions. Significant improvements in viscosity, consistency efficiency and pseudoplastic character were observed for PD, followed by CD and FD, as well as the higher values of G′ and G″ values of PD, indicating a stronger entanglement network development between the macromolecules for PD. PD exhibited better elasticity and shear resistance compared to FD and CD in the strain sweep test. In Lissajous curves, straight line shapes were found for synergistic solutions at low strain, which continued for increasing strain values for PD and CD. However, the pronounced viscous behavior was found for FD at 500% strain. Compared to CD and FD, PD exhibited a more desirable thixotropic character. A lower zeta potential was observed in the production of synergistic gums using the PD process. Gel strength was found to be higher for PD. Therefore, PD was a more effective method to produce a ready-to-use synergistic powder with better viscoelastic properties and a more stable solution.

The thixotropic characteristics of rheological parameters of waste stone-tailings cemented paste backfill and the time effect of pipeline resistance

The cemented paste backfill (CPB) involves the optimal combination of one or more solid materials with water to prepare a paste-like slurry with certain stability, fluidity, and plasticity. The paste flows as a piston flow under external force (pumping pressure) or gravity through pipelines into the underground goaf to complete backfilling operations. In order to improve the performance of the CPB, coarse aggregate is added to the CPB to form a coarse aggregate cemented paste backfill (C-CPB). The C-CPB belonged to non-Newtonian fluids and exhibited thixotropic behavior as its rheological parameters determined its flow characteristics. During the initial stage of pipeline transportation, the rheological parameters of the paste material were influenced by its thixotropic behavior and exhibited a certain degree of time dependence. The present study employed the stress relaxation method for thixotropy test to ascertain the rheological parameters of the C-CPB with respect to shear time. The results indicated that the yield stress decreased with increasing shear time with a negative exponential growth trend. A mathematical function describing the variation of yield stress with time for the paste material was established, and an estimation method for thixotropic equilibrium time of the yield stress was proposed. A Gaussian distribution function describing the variation of plastic viscosity with shear time was developed, and the thixotropic stabilization time of plastic viscosity was estimated. On this basis, a pipeline transportation resistance model considering the time-dependent rheological parameters of the C-CPB was established. Subsequently, a formula for calculating the boundary layer thickness during the initial stage of pipeline transportation was derived. The establishment of the model enables a better understanding of the resistance characteristics of the paste during the initial stage of pipeline transportation, as well as the process and patterns of boundary layer formation, which is of great significance.

Formulation and Characterization of Niacinamide and Collagen Emulsion and Its Investigation as a Potential Cosmeceutical Product

Cosmeceuticals are one of the fast-growing areas of the natural personal care industry. Cosmeceuticals are cosmetic products with medicinal or drug-like benefits that can affect the biological functioning of the skin depending on the ingredients in the composition. The development of one formulation acting on the dermis and stimulating the collagen production is very important for the hydration of the skin. The association of collagen with other ingredients can have a positive effect on increasing the natural production of collagen in the skin. An example of such an ingredient is niacinamide, which, having a recognized nutritional value, has been quite recently studied. Considering these aspects, this study focused on developing oil-in-water (O/W) emulsions, based on natural ingredients (vegetable oils, floral waters, and essential oils) and hydrolyzed collagen and niacinamide as active ingredients, and on evaluating the stability, pH, optical, superficial, rheological and textural properties, as well as microbiological tests of the emulsions, in order to investigate their potential as a cosmeceutical product. All the obtained emulsions proved to be stable at variable temperatures and had a pH value compatible with natural pH of the skin, allowing their safe application. Over goniometric analysis, a partial wetting and a hydrophilic character of the emulsions were emphasized. Following the rheological analyses, all dermatocosmetic emulsions exhibited non-Newtonian pseudoplastic behavior and a thixotropic character, these properties being very important for their production process and their application on the skin surface to generate an optimal therapeutic effect. The textural characteristics recorded for all emulsions indicated adequate spreadability at the application site. All tested samples respected the Pharmacopoeia limits of microbiological contamination. All prepared emulsions have good stability, are safe for the skin and have appropriate physicochemical and microbiological characteristics; therefore, they can be used as a cosmeceutical product.

Tribological and Rheological Study of Thixotropic Gels of 2D Nanoparticles.

A thixotropic colloidal gel constituting an aqueous dispersion of synthetic clay Laponite with varying concentrations of salt has been studied for its rheological and tribological performance as a lubricant. We observed that the incorporation of NaCl induces notable enhancements in the colloidal gel's relaxation time, elastic modulus, and yield stress. Although an increase in NaCl concentration decreases the material's relaxation time dependence on waiting time (tw), overall, the strength of its thixotropic character has been observed to increase with an increase in salt concentration. The analysis of friction and wear indicated that the utilization of a thixotropic colloidal gel of Laponite with a higher concentration of NaCl resulted in progressively greater reductions in both the coefficient of friction and specific wear rates under various load-speed conditions. Severe abrasive wear on disc surface under dry test, gradually mitigated upon the introduction of these lubricants. Two simultaneous lubricating mechanisms, first, the smooth sliding of the friction pair, facilitated by the alignment of Laponite particles in the direction of shear forces, and second, the stable structure of Laponite, coupled with the addition of NaCl, enabling continuous replenishment of the wear track with lubricant, are attributed to lubrication effectiveness.

A co-assembly process for high strength and injectable dual network gels with sustained doxorubicin release performance.

Adopting a non-covalent co-assembly strategy shows great potential in loading drugs efficiently and safely in drug delivery systems. However, finding an efficient method for developing high strength gels with thixotropic characteristics is still challenging. In this work, by hybridizing the low molecular weight gelator fluorenylmethyloxycarbonyl-phenylalanine (Fmoc-F) (first single network, 1st SN) and alginate (second single network, 2nd SN) into a dual network (DN) gel, gels with high strength as well as thixotropy were prepared efficiently. The DN gels showed high strength (103 Pa in SN gels and 105 Pa in DN gels) and thixotropic characteristics (yield strain <25%; recovery ratio >85% within 100 seconds). The application performance was verified by loading doxorubicin (DOX), showing better encapsulation capacity (77.06% in 1st SN, 59.11% in 2nd SN and 96.71% in DN) and sustained release performance (lasting one week under physiological conditions) than single network gels. Experimental and DFT results allowed the elaboration of the specific non-covalent co-assembly mechanism for DN gel formation and DOX loading. The DN gels were formed by co-assembly driven by H-bond and π-π stacking interactions and then strengthened by Ca2+-coupling. Most DOX molecules co-assembled with Fmoc-F and alginate through π-π stacking and H-bond interactions (DOX-I), with a few free DOX molecules (DOX-II) left. Proven by the release dynamics test, DOX was released through a diffusion-erosion process, in an order of DOX-I first and then DOX-II. This work suggests that non-covalent co-assembly is a useful technique for effective material strengthening and drug delivery.

Emulsion System With Nanoparticles Suitable for High-Temperature, High-Salinity Reservoirs

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 211167, “Selective and Reversible Water-Shutoff Agent Based on Emulsion System With Nanoparticles Suitable for Carbonate Reservoirs at High-Temperature and High-Salinity Conditions,” by Masashi Abe, SPE, Jumpei Furuno, and Satoru Murakami, Nissan Chemical Corporation, et al. The paper has not been peer reviewed. _ The complete paper presents the evaluation results of a water-shutoff (WSO) agent based on an emulsion-type chemical material with nanoparticles. The WSO agent, which the authors call an emulsion system with nanoparticles (ESN), has several advantages to existing polymer and gel materials, including high thermal stability, low sensitivity to mineralization, thixotropic characteristics, selectivity of blocking effects for oil and water, and reversibility of blocking effects. In WSO applications, these properties of ESN could be well-suited for improved oil recovery. Introduction ESN is recognized as a proven technology for carbonate reservoirs. However, the reservoir under study did not feature harsh conditions; therefore, this work evaluated ESN potential for carbonate reservoirs in the UAE typically having high-temperature and high-salinity conditions. A primary purpose of the technology, aside from improved oil recovery, is contributing to greenhouse-gas emission reduction and building competitive low-CO2-intensity oil-brand value. In general, produced water volume dramatically increases in maturing oil fields. Reducing water production also can contribute to saving water injection from a reservoir-voidage-replacement viewpoint. Therefore, the functional chemical WSO concept has a significant effect on contributing to the International Energy Agency’s sustainable development scenario. Materials and Physicochemical Property Tests Oil, Water, and Carbonate Core. Dead oil is sampled from an offshore carbonate field in the Middle East containing light crude oil (32.3 °API). Brine and plug core properties are summarized in Tables 1 and 2 of the complete paper. For thermal-stability tests, both brines were used for making the ESN. The WSO coreflood tests used the ESN made with injection water. Advanced Features of ESN. Rheology. The viscosity of ESN is controllable by changing the water/oil ratio; viscosity becomes lower with increasing oil content and higher with increasing water content. These components were stirred, and two ESN samples were prepared using Crude Oil A (from Oil Field A, UAE) or diesel oil. The samples are referred to as Crude Oil A-based ESN and Diesel Oil-based ESN in this paper. Both ESN samples showed similar viscosity curves; such thixotropic characteristics are an important property of ESN. ESN is flowable at stirring conditions. In particular, the viscosity of ESN can be decreased to less than 50 cp at high shear rates, so it can be injected into the reservoir by pumping. On the other hand, ESN becomes highly viscous and less flowable when no energy is applied to it (the ESN surface looks semisolid in this condition). In field operations, the viscosity of ESN decreases depending on the pressure generated by injection pumps on the surface. However, the injection pressure also releases in a radial direction from the bottomhole zone. As a result, ESN recovers a high-viscosity state because of decreasing shear rate with pressure release.

Instantaneous Gelation of a Self-Healable Wide-Bandgap Semiconducting Supramolecular Mg(II)-Metallohydrogel: An Efficient Nonvolatile Memory Design with Supreme Endurance

An efficient strategy for room-temperature, atmospheric-pressure synthesis of a supramolecular metallohydrogel of the Mg(II) ion, i.e., Mg@3AP, using the metal-coordinating organic ligand 3-amino-1-propanol as a low-molecular-weight gelator (LMWG) in a water medium has been developed. Through a rheological analysis, we looked into the mechanical properties of the supramolecular Mg(II)-metallohydrogel. The self-healing nature of the metallohydrogel is confirmed along with the thixotropic characteristics. Investigation using field emission scanning electron microscopy revealed the hierarchical network of the supramolecular metallohydrogel. The EDX elemental mapping confirms the primary chemical constituents of the metallohydrogel. The possible metallohydrogel formation strategy has been analyzed through FT-IR spectroscopic studies. In this work, Schottky diode structures in a metal–semiconductor–metal geometry structures based on a magnesium(II) metallohydrogel (Mg@3AP) have been constructed, and charge transport behavior has been observed. Furthermore, here, it is demonstrated that the resistive random access memory (RRAM) device based on Mg@3AP exhibits bipolar resistive switching behavior at room temperature and ambient conditions. We have also looked into the switching mechanism through the formation (rupture) of conductive filaments between the metal electrodes to understand the process of resistive switching behavior. With a high on/off ratio (∼100), this RRAM device exhibits remarkable switching endurance over 10,000 switching cycles. These structures are suitable for use in nonvolatile memory design, neuromorphic computing, flexible electronics, and optoelectronics, among other fields, due to their simple fabrication procedures, reliable resistive switching behavior, and stability of the current system.

Study on Thixotropic Properties of Asphalt Mastics Based on Energy Viewpoint

An asphalt mastic has thixotropic characteristics that significantly influence its fatigue and healing performance. Therefore, understanding the thixotropy of an asphalt mastic is clearly of great importance. However, research in this area is still in the early stages. This study focuses on self-heating as one of the biasing performances of asphalt material by analyzing the viscosity, stress, and hysteresis loops the of asphalt mastics under cyclic shear loading. Twelve types of asphalt mastics fabricated with asphalt, as well as different types of mineral filler, were selected to examine thixotropy. In addition, the filler/asphalt ratio was examined via the hysteresis technique to analyze the hysteresis loop and the viscosity–shear rate. The thixotropic potential function was also studied from the energy viewpoint. The results show that asphalt mastics with different asphalt binders, mineral fillers, and filler volume fractions showed hysteresis loops for shear stress versus shear rate diagrams. With an increase in the loading times of the cyclic load, the area of the hysteresis loop gradually decreases, and the hysteresis area most likely features a relatively stable value. The thixotropy of the asphalt can be significantly reduced by adding filler, and different types of mineral filler can slightly influence the thixotropy. The viscosity decreases with an increase in the shear rate, and it gradually recovers with a decrease in the shear rate. The greater the filler/asphalt ratio, the greater the viscosity, and the faster the viscosity’s descent is with the prolongation of time. Due to the existence of a higher amount of filler content, the recovery of a viscosity crack is more difficult. For asphalt mastics with high filler/asphalt ratios, the thixotropic mechanism can be explained via particle agglomeration and the depolymerization theory. For asphalt mastics with low and medium filler/asphalt ratios, the thixotropic mechanism can be explained via the particle chain theory. The damage and recovery of the internal structure of an asphalt mastic can be characterized by the structural failure potential function and the structural recovery potential function, respectively.

Study of Thixotropic Characteristics of a Kerosene Gel Propellant by Bayesian Optimization

The rheological behavior of gel propellants is crucial for their practical applications, especially in the rocket engine and ramjet fields. The thixotropic characteristics of gel propellants are an important component of their rheological properties and have a notable impact on their flow and injection process. However, most gel propellants contain rich, dynamic cross-linked network structures, which impart complex non-Newtonian fluid properties, and it is difficult to establish a unified mathematical model. In view of this, this study addresses the thixotropy of a prepared RP-3 kerosene gel and determines the mathematical model and model parameters describing its thixotropy. Experiments show that the kerosene gel exhibits shear-thinning properties as well as thixotropy. To describe the microstructural changes in the gel, three thixotropic constitutive models are introduced to analyze the rheological data, and the constitutive equation parameters are optimized. The three models are all structural dynamic models, which can be used to describe microstructural changes within the material. In addition, the fitting of the constitutive equation is a multiparameter optimization problem, and an appropriate optimization method must be used for parameter fitting. Therefore, the Bayesian optimization method combined with Gaussian process regression and the upper confidence bound (UCB) acquisition function is used in the multiparameter fitting of the constitutive models. Both experiments and numerical results show that the thixotropic model, which introduces a pre-factor with shear strain and assumes that the breakdown of the gel structure is related to energy dissipation rather than the shear rate, has a better fitting effect and prediction ability with regard to the gel. Combined with transient experiments at different shear rates, the model parameters of the constitutive law can be determined quickly by applying the Bayesian optimization method.

Technology of magnetophoresis of topical nonsteroidal anti-inflammatory drugs in osteoarthritis (clinical and experimental study)

BACKGROUND: The high degree of evidence for the use of pharmacotherapy currently does not cause doctors to doubt, however, the use of non-pharmacological approaches in general and physical factors in particular is the subject of many years of discussion for them. One of the main places in the pharmacotherapy of osteoarthritis is occupied by nonsteroidal anti-inflammatory drugs, while our interest is associated with a group of so-called topical drugs.&#x0D; AIM: In order to methodically substantiate the application of the magnetophoresis technology of the topical form of nimesulide in an experimental study, the influence of the magnetic field on the spectroscopic and thixotropic characteristics of the drug was determined, and the clinical efficacy of the combined use of magnetotherapy and the transdermal form of nimesulide in comparison with the application of the drug and magnetic therapy with a pulsed low-frequency magnetic field was determined.&#x0D; MATERIAL AND METHODS: A randomized study involving 60 patients with osteoarthritis of the knee joints was performed. The experimental part of the study on the effect of the magnetic field on the structure and properties of the gel form of the preparation containing 1% nimesulide (chemical formula: 4'-nitro-2'-phenoxy-methane sulfonanilide) was carried out in laboratory conditions. The clinical part of the study included the use of local therapy (application of nimesulide gel in an amount of 24 g) to the skin in the knee joint area, followed by the placement of inductors of the ALMAG+ magnetic therapy apparatus on the medial and lateral surfaces of the knee joint. The impact was carried out according to the recommended "3+1" program.&#x0D; RESULTS: An analysis of the effectiveness of therapy conducted in a group of 60 patients with osteoarthritis of the knee joints showed high efficiency, expediency and safety of the use of the technology under study in the treatment of patients with joint diseases.&#x0D; CONCLUSION: Due to the synergistic effect on the pathogenesis of articular syndrome, the gel form of nimesulide and the magnetic field have a unidirectional effect: anti-inflammatory, decongestant, analgesic, microcirculatory. In addition, the magnetic field enhances the absorption and flow of the drug into the tissues, being a physical enhancer (amplifier), which significantly affects the result of treatment.

Pasting and rheological properties of water caltrop starch as affected by the addition of konjac glucomannan, guar gum and xanthan gum

Water caltrop starch (WCS) isolated from the dehydrated water caltrop (DWCS) showed higher content of protein and ash as compared to starch isolated from fresh water caltrop (FWCS), leading to slightly lower starch purity. However, the pasting profiles of DWCS and FWCS are similar under a constant solid content of 4% (w/w). WCS/gum mixed systems contain 0.3%–0.9% gum generally showed higher pasting temperature, peak viscosity, and final viscosity than the starch alone system. The increase in peak and final viscosity during rapid-viscosity analysis was most pronounced for WCS/gum mixed systems with konjac glucomannan (KG), followed by guar gum (GG) and xanthan gum (XG). All WCS/gum mixed systems showed shear thinning and thixotropic characteristics. The extent of pseudoplasticity and shear stability, as evidenced by the smaller flow behavior index (n) and area of the hysteresis loop, was most pronounced for WCS/gum mixed system with XG, followed by mixed systems with GG and KG. Dynamic viscoelastic analysis revealed that the addition of gum increased both the storage and loss moduli of WCS, and lowered the frequency dependence of the loss factor significantly. However, the loss factor of WCS/gum mixed systems was generally higher than that of the starch alone system, implying the addition of gums modified the rheological characteristic of WCS to more viscous dominant behavior.

Nanogels as Potential Delivery Vehicles in Improving the Therapeutic Efficacy of Phytopharmaceuticals.

Nanogel is a promising drug delivery approach to improve the pharmacokinetics and pharmacodynamic prospect of phytopharmaceuticals. In the present review, phytopharmaceuticals with astonishing therapeutic utilities are being explored. However, their in vivo delivery is challenging, owing to poor biopharmaceutical attributes that impact their drug release profile, skin penetration, and the reach of optimal therapeutic concentrations to the target site. Nanogel and its advanced version in the form of nanoemulgel (oil-in-water nanoemulsion integrated gel matrix) offer better therapeutic prospects than other conventional counterparts for improving the biopharmaceutical attributes and thus therapeutic efficacy of phytopharmaceuticals. Nanoemulgel-loaded phytopharmaceuticals could substantially improve permeation behavior across skin barriers, subsequently enhancing the delivery and therapeutic effectiveness of the bioactive compound. Furthermore, the thixotropic characteristics of polymeric hydrogel utilized in the fabrication of nanogel/nanoemulgel-based drug delivery systems have also imparted improvements in the biopharmaceutical attributes of loaded phytopharmaceuticals. This formulation approach is about to be rife in the coming decades. Thus, the current review throws light on the recent studies demonstrating the role of nanogels in enhancing the delivery of bioactive compounds for treating various disease conditions and the challenges faced in their clinical translation.

Structural Characterization and Rheological and Antioxidant Properties of Novel Polysaccharide from Calcareous Red Seaweed.

A novel sulfated xylogalactan (JASX) was extracted and purified from the rhodophyceae Jania adhaerens. JASX was characterized by chromatography (GC/MS-EI and SEC/MALLS) and spectroscopy (ATR-FTIR and 1H/13C NMR) techniques. Results showed that JASX was constituted by repeating units of (→3)-β-d-Galp-(1,4)-3,6-α-l-AnGalp-(1→)n and (→3)-β-d-Galp-(1,4)-α-l-Galp-(1→)n substituted on O-2 and O-3 of the α-(1,4)-l-Galp units by methoxy and/or sulfate groups but also on O-6 of the β-(1,3)-d-Galp mainly by β-xylosyl side chains and less by methoxy and/or sulfate groups. The Mw, Mn, Đ, [η] and C* of JASX were respectively 600 and 160 kDa, 3.7, 102 mL.g−1 and 7.0 g.L−1. JASX exhibited pseudoplastic behavior influenced by temperature and monovalent salts and highly correlated to the power-law model and the Arrhenius relationship. JASX presented thixotropic characteristics, a gel-like viscoelastic behavior and a great viscoelasticity character. JASX showed important antioxidant activities, outlining its potential as a natural additive to produce functional foods.

3D Printing of Hybrid-Hydrogel Materials for Tissue Engineering: a Critical Review.

Key natural polymers, known as hydrogels, are an important group of materials in design of tissue-engineered constructs that can provide suitable habitat for cell attachment and proliferation. However, in comparison to tissues within the body, these hydrogels display poor mechanical properties. Such properties cause challenges in 3D printing of hydrogel scaffolds as well as their surgical handling after fabrication. For this reason, the purpose of this study is to critically review the 3D printing processes of hydrogels and their characteristics for tissue engineering application. A search of Google Scholar and PubMed has been performed from 2003 to February 2022 using a combination of keywords. A review of the types of 3D printing is presented. Additionally, different types of hydrogels and nano-biocomposite materials for 3D printing application are critically reviewed. The rheological properties and crosslinking mechanisms for the hydrogels are assessed. Extrusion-based 3D printing is the most common practice for constructing hydrogel-based scaffolds, and it allows for the use of varying types of polymers to enhance the properties and printability of the hydrogel-based scaffolds. Rheology has been found to be exceedingly important in the 3D printing process; however, shear-thinning and thixotropic characteristics should also be present in the hydrogel. Despite these features of extrusion-based 3D printing, there are limitations to its printing resolution and scale. Combining natural and synthetic polymers and a variety of nanomaterials, such as metal, metal oxide, non-metal, and polymeric, can enhance the properties of hydrogel and provide additional functionality to their 3D-printed constructs.

Self-Assembling Oligo(2-oxazoline) Organogelators for the Encapsulation and Slow Release of Bioactive Volatiles.

Herein, we report a class of distinctive supramolecular nanostructures in situ-generated from the cationic ring-opening polymerization of a particular 2-oxazoline monomer, i.e., 2-(N-tert-butyloxycarbonylaminomethyl)-2-oxazoline (Ox1). Driven by side-chain hydrogen bonding between neighboring molecules and van der Waals interactions, the growing oligomers of Ox1 precipitate in the form of macroscopic platelets when the degree of polymerization reaches 5–7. A similar self-assembly occurred in the block copolymerization of 2-ethyl-2-oxazoline (EtOx) or 2-pentyl-2-oxazoline (PeOx) and Ox1 as the second monomer. These polymeric aggregates were found to disassemble into rod-like nanoparticles under appropriate conditions, and to form stable organogels in some polar solvents like dimethylformamide as well as in natural liquid fragrances such as (R)-carvone, citronellal, and (R)-limonene. Scanning electron microscopy revealed that the morphology of their xerogels was solvent-dependent, mainly with a lamellar or fibrous structure. The rheology measurements confirmed the as-obtained organogels feature an obvious thixotropic character. The storage modulus was about 7–10 times higher than the loss modulus, indicating the physical crosslinking in the gel. The fragrance release profiles showed that the presented supramolecular gel system exhibits good sustained-release effect for the loaded bioactive volatiles.

Study on the prediction method of thixotropy of water-in-oil waxy crude oil emulsions

The thixotropy of water-in-waxy crude emulsion is the basic data used for flow safety studies of oil-water mixed pipelines. This work studied the shearing rate of a water-in-waxy crude oil emulsion under constant shear stress loading conditions. A relative shear rate was defined. A prediction method was developed to estimate the thixotropy of a waxy crude oil emulsion under constant shear stress loading conditions. The method only requires the thixotropy data of 3 water content emulsions and dehydrated crude oil, it can estimate the thixotropic characteristics of the oil-water-waxy crude oil emulsion of any volume of water content.

Molecular dynamics simulation of yield thixotropy of crude oil systems

In the work, molecular dynamics simulation is employed to analyze the micro mechanism of the yield thixotropy of crude oil. The effects of different shear rates on the yield thixotropic characteristics of the crude oil systems are investigated based on the Shengli crude oil system and the Nanyang crude oil system. The yield thixotropic mechanism of the crude oil systems is revealed by analyzing the orientation of the crude oil molecules, the extension degree in the molecular chain of crude oil, and the energy of the system. The results show that at the beginning of shearing, the molecular chain of crude oil gradually curls to prevent the changes in molecular orientation, and then a small amount of distortion occurs and the shear stress gradually increases. In the process of shear failure, the number of trans configuration molecules gradually increases and the number of Ponzi configuration and homeopathic configuration molecules decreases. The molecular chain of the crude oil gradually extends and the crude oil molecules show a directional arrangement consistent with shear direction, and the shear stress decreases.