Abstract
The project is aimed at solving the problems of creating universal soft robots using 3D printing, whose movement is controlled by various external stimuli, such as magnetic and electric fields, UV radiation, pressure, etc., for widespread use in medicine, various fields of science and national economy. The main objectives of the project are to create (a) a block copolymer thermoplastic polymer matrix that provides the desired melt rheology and physical and mechanical properties of finished products, and (b) a set of fillers that perform the functions of susceptibility to one or another external control influence, and (c) development of theoretical models of a composite material to identify the fundamental relationship between its composition and properties and optimize its parameters.
Research done during the first year of the project
In the first stage of the project, the main attention was paid to the preparation of polysiloxane-urethane matrices and magnetically active materials based on them. A new synthetic approach was developed to obtain linear copolymers based on polyorganosiloxanes and urethanes. The new synthetic approach is based on the azide-alkyne cycloaddition reaction, which allows easy control of the synthesis process under simple conditions. Copolymers with different lengths of the siloxane block were synthesized, characterized by modern physical methods and their rheological properties were studied. The resulting materials were used for the first time in the process of 3D printing with thermoplastic polymers. The possibility of high-quality 3D printing of standard structures of varying complexity using the developed materials was demonstrated. A technique for introducing carbonyl iron magnetic particles into synthesized copolymer matrices was developed, and magnetic-polymer composites were obtained whose rheological properties can be controlled by a magnetic field.
Thermoplastic matrices of polyurea-siloxane have been synthesized by the polycondensation method using different commercially available products. The synthesis was scaled up and the influence of various factors on it was studied: stirring intensity, type of solvent, ratio of initial reagents involved in the polycondensation; optimal conditions for carrying out the synthesis were determined. 10 g of polysiloxaneurea was prepared for further introduction of a magnetic filler. Methods were developed to modify the surface of the carbonyl iron microparticles to improve compatibility with the polymer matrix. 50 g of carbonyl iron with a shell of aminopropyltriethoxysilane and 50 g of carbonyl iron with a shell of methyltriethoxysilane were obtained. The presence of the shell was confirmed by scanning electron microscopy with energy dispersive microanalysis. Based on polysiloxaneurea matrices and modified iron particles, samples of magnetic-polymer composites were obtained, their magnetorheological properties were studied and it was shown that they are regulated by an external magnetic field.
Together with Chinese colleagues, magnetically active materials have been developed based on commercially available thermoplastic polyurethane filled with microparticles of a magnetically hard neodymium-iron-boron alloy. The results of 3D printing soft robots using this material will be analyzed. In addition, soft bending actuators have been developed and fabricated by the Chinese project team using 3D printing technology with plain and conductive thermoplastic polyurethane filaments.
A theoretical study of the properties of polymer composites was carried out based on the consideration of mesoscopic cells of the material volume containing one or more filler particles. Using finite element modeling, a three-dimensional cubic cell of the material containing spherical, cubic, cylindrical and ellipsoidal inclusions was considered. To study the influence of filler parameters on the mechanical characteristics of a polymer composite, boundary value problems of uniaxial compression of a material cell and filler particle rotation were considered. It was shown that substantial control over the mechanical properties of composites using fillers with different Young’s moduli is possible only for fillers made from soft materials, the Young’s modulus of which is no more than 100 times higher than the Young’s modulus of the polymer matrix. In order to study the effect of surface treatment of filler particles on the properties of a polymer composite and improve the convergence of numerical solutions of mesoscopic mechanics problems, material cells containing inclusions surrounded by soft shells were constructed. It was demonstrated that even at low filler concentrations for the case of soft polymer matrices, it is possible to obtain the widest range of changes in the elastic modulus of a material cell (about 10%) using relatively soft shells around the filler particles. The results obtained during the modeling process will allow us to describe new ways to fine-tune the mechanical properties of polymer composites.
Based on the results of the work, three collaborative papers have been written, one of which has been accepted for publication in the highly rated first quartile journal Bio-Design and Manufacturing, and the other two are under review.
Research done during the second year of the project
The first and key task of the project was the synthesis of novel polymer matrices to create composite materials suitable for 3D printing. At the initial stage, we proposed a new method of synthesizing thermoplastic copolymers based on polydimethylsiloxanes (PDMS) with urethane fragments via the azide-alkyne cycloaddition reaction. This reaction can be carried out either without a catalyst or in the presence of a cheap catalyst, such as monovalent copper. During the reporting period, we varied the reaction conditions, including the type of catalyst and solvents, temperature, and other parameters. The main criteria for evaluating the effectiveness of these conditions were the balance between the simplicity of the reaction setup and the resulting copolymers’ molecular-weight characteristics (high molecular weight, narrow molecular-weight distribution) and reproducibility of experiments. The best results were achieved using porous copper as the catalyst in ether solvents at low temperatures. This method demonstrated good scalability, producing a PDMS-based copolymer with a peak molecular weight of 5.1 kDa in quantities of approximately 40 g for subsequent use as the polymer base of composite filaments for 3D printing.
The development of thermoplastic polyureasiloxane matrices and magnetoactive materials based on them continued. Components for synthesizing polyureasiloxane were prepared, and 150 g of the polymer was produced. Using the material, pure filaments and filaments with varying degrees of carbonyl iron particle loading (30%, 50%, 70% by weight) were fabricated on a single-screw extruder for 3D printing. The magnetic filler particles were shown to be uniformly distributed within the polymer matrix. Test models (disk, coarse mesh, fine mesh, square) were successfully 3D-printed, with samples exhibiting good adhesion to the printer bed, interlayer sintering, and geometry retention.
Magnetoactive filaments based on commercially available thermoplastic polyurethane (TPU) were produced by mixing TPU with carbonyl iron particles (50% by weight), both untreated and surface-treated for improved dispersion. Test samples were printed using the resulting composite filament, and their mechanical properties were evaluated. Samples made using treated iron particles exhibited better mechanical properties. Initial experiments on 3D printing samples with a gradient distribution of magnetic particles within the sample were also conducted.
In collaboration with Chinese partners, compositions for self-healing filaments were developed based on TPU, adhesive particles, a mixture of neodymium-iron-boron magnetic particles, and iron oxide. Multifunctional soft robots were created using these compositions.
For the first time, a series of photoactive linear liquid crystalline hybrid copolymers with a novel azobenzene-triazole-siloxane molecular architecture were synthesized and characterized via azide-alkyne cycloaddition. The chemical structures, molecular morphologies, thermodynamic properties of thermotropic liquid crystalline and photoisomerization behaviors, and the influence of molecular composition on microstructural morphology and the ability of the azobenzene-siloxane copolymers to self-assemble into lamellar structures with micron-sized spherulitic textures were investigated. The kinetics of reversible trans-cis photoisomerization and the relationship between polymer molecular composition and their photoinduced isomerization behavior were also studied.
The morphology and anisotropy of physically cross-linked fibers of novel liquid crystalline polymers produced via simple melt processing were examined. The findings provide important insights into the structure-property relationships of photoactive hybrid linear azobenzene-siloxane liquid crystalline polymers, which can be utilized for developing new or improving existing photoactive polymers.
The influence of triazole modification of urethane segments on intermolecular interactions and conformational properties was investigated using atomistic molecular dynamics. Comparative analysis of the conformational behavior of single modified and unmodified urethane segments and their melts revealed how triazole groups affect the extent and distribution of hydrogen bonding in these systems depending on temperature. A series of model compounds containing triazole and urethane fragments was synthesized to experimentally confirm hydrogen bonding identified in simulations.
Using previously developed mesoscopic model of the local properties of polymer composites, the dependences of the mechanical properties of multi-particle material cells on the ferromagnetic properties of filler particles, their shape anisotropy, size, and the Young’s modulus of the shell surrounding the particles. The presence of an interfacial shell between filler particles and the polymer matrix was theoretically described as an effective change in filler concentration. This was achieved using a scaling law for the dependence of the material’s elasticity modulus on filler concentration. It was shown that the interfacial shell could enhance the material reinforcement during particle clustering and significantly influence the anisotropy of the composite properties. The reinforcement effect of the interfacial shell reduced the degree of filler restructuring while improving system stability and preventing matrix rupturing.
The results of this work were presented at four conferences and published in six articles.