A nascent but promising solution to the world’s water scarcity problems could be water purification by direct solar vapor generation

Although desalination methods like membrane distillation and reverse osmosis have been employed to provide clean water to millions around the world, small-scale desalination for off-grid purposes remains hampered by cost and energy consumption challenges. Direct solar vapor generation is an off-grid distillation technology that, while still early stage, is attracting attention. For this reason a team of researchers from Khalifa University has been undertaking research on the topic.

Afra S. Alketbi, PhD student in Engineering, and Dr. Aikifa Raza, Research Scientist in the Department of Mechanical Engineering, developed a micro-3D printed hydrogel device to be used in direct solar vapor generation (DSVG). Their new device is portable and highly efficient, promising great potential for use in commercial DSVG systems. Alketbi and Dr. Raza collaborated with Muhammad Sajjad, PhD student , Dr. Hongxia Li, Postdoctoral Fellow, Dr. Faisal AlMarzooqi, Assistant Professor of Chemical Engineering, and Prof. TieJun Zhang, Professor of Mechanical Engineering. The results were published in the.

Direct solar vapor generation involves harvesting the heat from the sun to convert water into vapor, which is then condensed and collected to provide clean water. Sounds simple and it is: the oldest desalination technology is the solar still, a simple device that uses the energy from sunlight to purify water. Salty water is placed in the still and an angled piece of glass or plastic is placed above. The sunshine evaporates the water, which then condenses on the surface above before running down the surface to collect in a separate trough. The impurities and salt remain in the bottom of the still and the water in the trough is clean, pure drinking water. This is the basic principle behind DSVG but the key step—evaporation—is proving a roadblock for commercialization.

“Direct solar vapor generation provides a sustainable and eco-friendly solution to the current global water scarcity challenges,” Prof. Zhang said. “However, existing systems using natural sunlight suffer from low water yield and need a lot of energy to start the evaporation process. If we could find new materials that reduce the heat needed for water vaporization, we could boost this process and make it commercially viable. This is where hydrogels could help.”

Hydrogels are a 3D network of hydrophilic (water loving) polymers that can swell in water while maintaining their structure. They are dynamic and highly tunable, which makes them flexible for use at different operating conditions. In this work, KU researchers developed a temperature responsive copolymer with tunable wettability and water releasing behavior.��

They leveraged 3D-printing to create a solar-powered desalination device with micro-channels and an anisotropic, or unsymmetrical crystalline, structure. The device’s hydrophilic polymeric network can maintain an uninterrupted water supply: as the water evaporates, more is drawn into the hydrogel through capillary action, inspired by the way water moves in plants.

The KU researchers modified the top surface of their device with light absorbing materials using a novel method. Photothermal materials have been utilized in floating DSVG systems as they have the ability to absorb a high amount of solar energy. This helps regulate localized heating and produce water vapor. Materials suspended in the water absorb the sun’s energy and transfer the heat to the water wetting their surface and thereby quickly generating clean water vapor.

“Developing novel materials that can yield high amounts of water vapors utilizing less energy, in addition to efficient solar-to-thermal energy conversion, are highly desired to push forward the applications of the solar energy-water nexus,” Dr. Raza said. “Hydrogels are gaining immense popularity due to their multifunctionality and biocompatibility, as well as their unique ability to encapsulate a large amount of water.”

“Because of the superior light absorption properties and water retention/activation within our hydrogel anisotropic structure, and the rapid water movement through our 3D printed microchannel network, our device achieves a remarkable water evaporation rate without solar concentration,” Alketbi said.

“In combination with high-resolution 3D printing, our hydrogel technology empowers high-performance solar distillation while offering great opportunities for digital design and accelerated development of new desalination devices,” she added.

Manufacturing this hydrogel requires a highly specialized 3D printing technique. Recent advances in additive manufacturing allow hydrogel fabrication to overcome the limitations of conventional fabrication methods. Light-based stereolithography, used in this work, is one such technique whereby a light source—a laser or projector—cures liquid ink into solid complex architectures.�� 

The research group is now establishing a spin-off company with support from the to produce high-end valuable products through advanced additive manufacturing.

At KIC, the startup is currently being commercialized through a structured three-month incubation program focused on imparting the founders with business, marketing, finance and legal skills.��

Jade Sterling
Science Writer
22 February 2022

The post Floating Hydrogels Could Produce Eco-friendly Clean Water from Salty Water appeared first on Khalifa University.

Hydrogels aren’t new but conventional fabrication methods leave much to be desired in controlling their detailed structure and properties. A team of researchers from Khalifa University, led by Prof. TieJun Zhang, has investigated how 3D printing can produce hydrogel devices for myriad advanced applications.��

The soft, pliable and thin material that make up more than 90 percent of contact lenses prescribed in the United States are made possible by hydrogels: water-swollen polymeric materials that maintain a 3D structure.

But hydrogels have far more applications than just correcting vision: They are one of the most promising materials, revolutionizing many applications including artificial organs, drug delivery, soft electronics, and enhanced water evaporation and purification.

The 3D network of hydrophilic polymers that can swell in water while maintaining their structure is dynamic, tuneable, harmless to living tissue, biodegradable, and capable of encapsulating large amounts of water.

Recent advances in additive manufacturing — or 3D printing — allow hydrogel fabrication to overcome the limitations of conventional fabrication methods.��

Light-based stereolithography is one such additive manufacturing technique. A light source — a laser or projector — cures liquid resin into hardened plastic. When these resins are exposed to certain wavelengths of light, short molecular chains join together, polymerizing monomers into solidified rigid or flexible shapes. This technique is highly accurate and offers the sharpest details and smoothest surface finishes of all 3D-printing techniques. The main benefit, however, is its versatility.

Khalifa University PhD student Afra S. Alketbi investigated how curing and ink formulation affect the toughening or hardening of the 3D-printed hydrogels. Ms. Alketbi worked with Dr. Hongxia Li, Postdoctoral Fellow; Dr. Aikifa Raza, Research Scientist; Dr. TieJun Zhang, Professor of Mechanical Engineering; and Prof. Yunfeng Shi from Rensselaer Polytechnic Institute (RPI), USA. The researchers found that a hydrogel’s elasticity and pore formation highly depends on the exposure time, light intensity, and the associated degree of crosslinking. Their results were published in.��

When chemically crosslinked hydrogels are produced by stereolithography, the covalent bonding between the chains offers enhanced mechanical strength. However, this mechanical strength is also strongly related to the precursor solution — the 3D printer ”ink.” This dictates the mechanical properties and physical integrity of the resulting hydrogels, along with other physical properties such as how the hydrogels swell with water and their water content once swollen. The researchers also discuss how the addition of solvent to dilute the precursor solution or to allow for the direct print of hydrogels, when using water as the solvent, imposes a new set of challenges. Solvents can hinder the polymerization process and lead to reduced crosslinking and compromised structural integrity.

“This work provides new molecular insights into the relationship between processing and the resulting structure developed by stereolithographic-hydrogel printing.”

To better understand how solvents, the precursor solution, and the amount and intensity of light affect the production of hydrogels, the researchers used molecular simulation. In collaboration with Prof. Shi from RPI in the USA, they combined simulations with mechanical testing of tangible polymers to gain a molecular-level insight into the photo-crosslinked polymers produced by 3D printing.

Various computational methods were used to reveal key morphological features such as the molecular pores and the extent of curing, while swelling dynamics were monitored using environmental scanning electron microscopy. Their results show that the cross-linking density is vital to the physical properties and mechanical integrity of 3D-printed hydrogels during swelling and deswelling.

Light intensity and exposure time can influence photopolymerized polymers to exhibit different characteristics,  Ms. Alketbi said. “We found that the degree of curing is critical to the structure of the hydrogels produced,” she added, “and the strength of the cross-linking determines the hydrogel’s performance when swollen.”

The researchers also found that when hydrogels are prepared with low exposure to the light source, the molecular network can irreversibly collapse.

The video shows swelling and bending of hydrogel micropillars.

The team’s method of visualizing hydrogel swelling and bending behaviors at the microscale can also be used to characterize hydrogel devices and evaluate their performance in situ. The new molecular insights from this work will assist in developing hydrogels for further applications and can also be applied to other photo-crosslinkable polymeric systems. This work was supported by a 2019 Abu Dhabi Award for Research Excellence.

Jade Sterling
Science Writer
23 September 2021

The post Insights into 3D Printing of Hydrogels appeared first on Khalifa University.

Mechanical Strength Improved by 1600% while Weight Reduced by 50%

A collaborative team of researchers from Khalifa University, Kingston University, and the University of Liverpool have leveraged the unique capabilities of additive manufacturing – or 3-dimensional (3D) printing – to design ultra-strong, lightweight and functional components that will make the structures of unmanned aerial vehicles (UAVs) significantly lighter and stronger, allowing for advanced applications. The results of their research were also published on 3Dprint.com, an authority on the 3D printing industry.

KU’s research team, led by Associate Professor of Aerospace Engineering Dr. Yahya Hashem Abdallah Zweiri, was able to increase the mechanical strength of 3D printed plastic parts by 1600% through a sandwich-structured composite solution and reduce the weight of 3D printed drone structures by 50% through topology infill optimization methods, which optimize the material layout within its design space and its interior structure. Results will support the advancement of the UAE’s national innovation goals, specifically in the targeted area of autonomous transportation, which is identified by the UAE Economic Vision 2030 as a key area of focus.

“3D printing has been limited by factors like production costs and low material strength, underscoring the need for disruptive developments in advanced manufacturing. With so many of KU and the UAE’s goals dependent on climate and energy research, and so much of that research dependent upon drones, it was prudent that we focus our 3D printing research on more practical applications like drone tech,” said Dr. Zweiri. “Our contributions to 3D printing materials and production methods have enabled the production of lightweight, low-density drones that are able to carry bigger payloads, such as larger batteries or additional electronic components and hardware.”

Traditional manufacturing methods produced drones that, despite being dense and heavy, had relatively low tensile strength, making them brittle. This limited the potential application of drones for industrial and research purposes in military, agricultural, search and rescue, telecommunications, transportation, topography, mapping, and surveillance, where robust UAVs play unique roles with varied hardware and electronics.

Typically the methods to improve the structural integrity of 3D printed plastics such as resin filling, ultrasonic strengthening, and infrared laser heating, have only been able to improve the strength of printed parts by 45%, 22%, and 50%, respectively. However, these improvements are incremental advancements compared to the results achieved by KU researchers through use of the sandwich-structured composite solution and topology infill optimization methods.

A sandwich-structured composite is a special class of composite materials that are fabricated by sandwiching a lightweight but thick core between two thin but stiff skins. Topology optimization works by finding the best distribution of material given an optimization goal and constraints, while infill optimization works in a similar way, filling in the interior structure of the design in the most ideal way given the goals and limitations of the structure and materials used.

“Our focus has been to retain the advantages of 3D printing, which enables rapid manufacturing of complex geometries, and applying simple post-processing steps to make 3D-printed drones far more resilient, lighter, and therefore more useful for local industry and research purposes. To reduce the weight, we developed a unique topology and infill optimization method that employs unique geometries to create lighter, porous structures,” said Dr. Zweiri.

Less dense core material will inevitably lead to weaker components and structures, which by itself doesn’t improve the efficacy of drone technology. However, when combined with CFRP laminates, the structure is not only lighter but significantly stronger.

By reducing the weight and simultaneously increasing the strength of 3D printed components, KU’s research collaboration has enabled drones to increase flight-time through use of larger batteries, collect more data through more complex sensors, and perform more specialized tasks with heavier hardware.

Drone technology has improved drastically over the past decade with numerous improvements in electronics, computer processing, production methods, and core materials. Based on a Wohlers Associates report, the estimated global market for 3D printing was more than USD5.1 billion in 2015, with a corporate annual growth rate of more than 25.9%. As technological advancements in 3D printing drives cost down and improve efficiencies, the market is expected to grow to USD21 billion by 2020.

Beyond use in UAVs, the contributions of Dr. Zweiri’s team and collaborating researchers have many practical applications in other fields of research and industries. The lightweight and strong structures they developed through synergy between CFRP and 3D printed material, are noncorrosive and thus have wide ranging utility in space, robotics, and biomedical research. His research is expected to further the advancement of 3D printing, autonomous transportation, and synthetic materials manufacturing while contributing to the UAE’s innovative knowledge economy.

the full article.

Zaman Khan
News and Features Writer
Date: 26/02/209

The post Ultra-Light and Strong Drones Possible through New 3D Printing Innovation appeared first on Khalifa University.