Kumkum Ahmed

The effect of cross linker concentration in the physical properties of shape memory gel

The shape memory hydrogels were synthesized and studied the physical properties. The gels were made by a hydrophilic monomer named N, N-dimethyl acrylamide (DMAAm) and a hydrophobic monomer named stearyl acrylate (SA). The water-swollen hydrogels show well transparency and shape memory property while gels absorb large water content. The properties were characterized by varying the cross-link concentration, whereas the concentration of other chemical components was remained constant. In this study, the DMAAm and the SA ratio was 3:1 to make one mole solution. It is observed that the swelling ratio slightly depends on the cross-link concentration at certain amount. However, mechanical properties strongly depend on the cross-link concentration. Thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC spactra of dried samples exhibits complex crystalline nature, while swollen samples show homogeneous crystallinity. A well thermal stability is observed regard less of cross-link concentration.

3D printing of shape memory hydrogels with tunable mechanical properties

Utilization of soft material like hydrogels for task-specific applications such as in soft robotics requires freedom in the manufacturing process and designability. Here, we have developed highly robust thermoresponsive poly(dimethyl acrylamide-co-stearyl acrylate and/or lauryl acrylate) (PDMAAm-co-SA and/or LA)-based shape memory gels (SMGs) using a customized optical 3D gel printer. This process enabled rapid and moldless fabrication of SMGs with a variety of shapes and sizes. By varying the compositions of the constituent monomers, a wide variety of SMGs with tunable mechanical, thermal, optical and swelling properties have been obtained. Printed SMGs with excellent fixity and recovery ratios have exhibited a wide range of values of Youngs modulus (0.04-17.35 MPa) and strain (612-2363%) at room temperature when the acrylate co-monomer (SA and LA) content was varied and the value of strain has been found to be enhanced at elevated temperatures. Thermogravimetric analysis (TGA) of the SMGs shows one step peak degradation (407-417 °C) regardless of composition after an initial mass loss due to water evaporation. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) revealed variable transition temperatures (29-49.5 °C) depending on the SA and LA content. SMGs with all of the composition ratios possess high transparency with variable swelling degrees in water and different organic solvents and exhibit refractive index values in the range of intraocular lenses, making them suitable for applications in the optical field. These unique properties of 3D printed SMGs with free formability and tunable properties are expected to generate rapid demand in a variety of sectors in biomedicine, robotics and sensing applications.

Development of multi-material 3D printer

We are developing a Multi Material 3D printer to print an object with different kind of soft and hard material in a single run. It is expected that the combination of printing soft and hard material will be a new kind of 3D printer. Our main printing material is conductive based soft filament made by our laboratory “Soft and Wet Matter Engineering Laboratory”, other different soft filament and hard plastic filament to create fully functional, multi material objects in a single printing run with greater variety and lower cost than other single material printing. In addition, we are developing a special type of Extruder, by using this we will be able to print both soft and hard material with one printer. This will be a new era of 3D printer. Such kind of 3D printer will possibly be a good STEM tool in medical sector and robotics.

Ionic liquid in 3D printing (Conference Presentation)

Ionic liquids (ILs) are fascinating materials with unique physicochemical properties like non-volatility, non-flammability, wide electrochemical window, high thermal stability and high ionic conductivity. They offer numerous possibilities in the fields ranging from electrochemistry to mechanical engineering however their employment in the 3D printing technology is very limited till to date. One of the big challenges of using 3D printing for materials is a careful selection of component material with a perfect concentration and an appropriate method. In this study, we focused on the potential of ILs on 3D printing technology covering the most popular printing methods named fused deposition modeling (FDM) and stereolithography (SLA) process. For FDM process IL-based conductive nanocomposite filaments have been developed and printed via 3D printing process along with their material characterization. In a different approach, ionic gels in IL medium have been successfully printed by SLA process with precise structures of microscale resolution. Conductive, mechanical and other physicochemical properties have been explored to get the proper understanding of the ionic gel materials.

Fabrication of shape memory gels using 3D printer (Conference Presentation)

Hydrogels are three-dimensional polymeric networks capable of absorbing large amounts of water or biological fluids. Due to their high water content, porosity and low friction they closely simulate natural living tissue. The properties of a polymer gel depend on the chemical structures of the component molecule and can be controlled or tuned by external stimuli such as heat, optics, solvent, and pH. Shape-memory gels (SMGs) are unique materials that have the ability to return from a temporary deformed state to their permanent i.e. original shape induced by an external stimulus like temperature change. Poly(dimethyl acrylamide-co-stearyl acrylate) (DMMA-co-SA)-based SMGs show such behavior with high mechanical strength, transparency and moderate water content (≈30wt%). In this work, we applied stereolithography process to fabricate DMMA-co-SA SMGs and printed sample models like gel sheets and tubes. However, printing a transparent SMG was not an easy task due to several problems like sample turbidity, swelling during printing and shape deformation. We critically maintained these uses and compared the properties of 3D printed SMGs with that of conventionally synthesized SMGs. Finally, we analyzed the limitation and potential of 3D printing process and discussed a suitable approach for application of 3D printed SMGs as an actuator.

Poly ionic liquid-based nano composites for smart electro-mechanical devices

Conducting polymer composites become increasingly significant for variety of applications in electrical and mechanical devices. Poly (ionic liquid)s (PILs) achieved remarkable interest in this field for the unique properties and added advantages in mechanical stability, improved processability, durability, and spatial controllability. Carbon nanotube (CNT) as filler material to the matrix of PIL can achieve the desired composite material with improved electrical and mechanical properties. In this work, we developed PIL-CNT nanocomposites by using quaternary ammonium type IL monomer and multiwall CNT. Their mechanical, thermal and thermomechanical properties have been studied and future possibilities of employing in electromechanical devices have been explored.

Development of ionic gels using thiol-based monomers in ionic liquid

Ionic gels (IGs) using ionic liquids (ILs) can propose diverse applications in the field of optics, sensors and separation have opened wide prospects in materials science. ILs have attracted remarkable interest for gel polymer electrolytes and batteries based on their useful properties such as non-volatility, non-flammability, a wide electrochemical window, high thermal stability and a high ionic conductivity. The formation of gel in IL media makes it possible to immobilize ILs within organic or inorganic matrices and to take advantage of their unique properties in the solid state, thus eliminating some shortcomings related to shaping and risk of leakage. In this work for the first time we used multifunctional thiol monomers having uniform structure and good compatibility with the IL of our interest. Therefore we focused on developing thiol monomer-based IGs using multifunctional thiol monomers and acrylate crosslinkers utilizing thiol-ene reaction between monomer and crosslinking molecules in an IL medium and characterize their physico-chemical properties like thermal, conductive, mechanical properties etc.. This work has been focused mainly to improve the mechanical strength of IGs and make prospects of IGs in tribology and lubricants.

Ionic liquid based multifunctional double network gel

Gels are a promising class of soft and wet materials with diverse application in tissue engineering and bio-medical purpose. In order to accelerate the development of gels, it is required to synthesize multi-functional gels of high mechanical strength, ultra low surface friction and suitable elastic modulus with a variety of methods and new materials. Among many types of gel ionic gel made from ionic liquids (ILs) could be used for diverse applications in electrochemical devices and in the field of tribology. IL, a promising materials for lubrication, is a salt with a melting point lower than 100 °C. As a lubricant, ILs are characterized by an extremely low vapor pressure, high thermal stability and high ion conductivity. In this work a novel approach of making double network DN ionic gel using IL has been made utilizing photo polymerization process. A hydrophobic monomer Methyl methacrylate (MMA) has been used as a first network and a hydrophobic IL monomer, N,N-diethyl-N-(2-mthacryloylethyl)-N-methylammonium bistrifluoromethylsulfonyl)imide (DEMM-TFSI) has been used as a second network using photo initiator benzophenon and crosslinker triethylene glycol dimethacrylate (TEGDMA). The resulting DN ionic gel shows transparency, flexibility, high thermal stability, good mechanical toughness and low friction coefficient value which can be a potential candidate as a gel slider in different mechanical devices and can open a new area in the field of gel tribology.