Preparation And Helical Motion Of Nanogel Crosslinking-Based PAAm-BZ Selfoscillating Gel

Soft robots driven by chemical reactions are directional,controllable and adaptive,which have important potential applications in the fields of targeted drug release,bioengineering and environmental remediation.In recent years,using nonlinear chemical oscillation reactions to drive complex motions of active systems has gradually become a hot spot for basic research on bionic motion.Belousov-Zhabotinsky(BZ)reaction,as a typical chemical oscillation reaction,is an ideal driving force for soft robots.The BZ self-oscillating gels obtained by coupling this system with polymer gels can spontaneously realize chemical-mechanical energy conversion to produce directional motions such as photophobic-phototropic locomotion,reciprocating migration.The current research on BZ gels still has the following problems that need to be solved: first,the mechanical properties of traditional BZ gels are weak and the stimulus responsiveness is slow.It is mainly manifested in that the BZ gel is easily damaged under mechanical stress,which makes it difficult to maintain the stable structure and long-range motion function of the BZ gel,and the response lag caused by the spatial diffusion effect.Second,there are fewer studies on the design and regulation of BZ gel bionic motion in high-dimensional(≥ 2D)environments.At present,experimental studies on BZ gel locomotion are still mainly in one dimension(1D,xdirection)with simple motion patterns,which have a large gap with the actual environment and future applications.Based on the above problems,this thesis firstly prepared BZ gels with high mechanical properties and fast responsiveness by microgel cross-linking method using acrylamide(AAm)as monomer;Secondly,explored the helical motion of BZ gel driven by chemical wave in 2D environment(x-y direction)and the dynamic origin cause of its generation;On this basis,the multi-mode helical motions of BZ gel are realized and the motion mode transformation law is obtained.The specific results of the study are as follows:First of all,high-performance BZ gels were prepared,which have excellent mechanical properties and fast response function.The conventional method of preparing BZ gels leads to inhomogeneous gel structure due to random cross-linking of cross-linking agents in the network,which makes the gels suffer from weak mechanical properties and slow response speed.Without introducing other components and reducing the input of raw materials,this thesis adopts the microgel crosslinking method,using microgel as the crosslinking agent to make the single molecular chain and chain orderly crosslinked,improving the uniformity of the gel structure.NCBZ gel(Nanogel crosslinking-based BZ gel)has higher mechanical properties than conventional BZ gel in tensile,puncture,twist,cut and rheology tests.The optimum mechanical properties of NCBZ gel have 7 times higher tensile strength than conventional gel;The results of microstructure reaction stability test showed that NCBZ gel still had a complete gel skeleton after 7 hours of reaction in BZ solution;The results of BZ gel kinetics tests showed that the response speed of NCBZ gels was 2.1 times faster than that of conventional gels,and its fast response was due to the homogeneous spatial structure of NCBZ gels,which eliminated the hysteresis of chemical-mechanical oscillation of gels.Secondly,in 2D environment,experiments and numerical simulations realized the helical motion of BZ gel driven by asymmetric chemical waves and revealed the origin of helical motion.In the experimental study,it was found that asymmetric chemical waves(pulse and spiral waves)could drive the gel along a helical trajectory in a 2D environment by tracking the trajectory of the center point of the gel.The positions of the pulse wave excitation point and the spiral wave-tip relative to the gel are the controlling factors for the direction of gel motion and the helical trajectory chiral transition.The vector decomposition of BZ gel motion shows that the asymmetric chemical wave can drive the gel to produce forward-backward peristalsis motion in the x and y axes simultaneously,which is not synchronized with an obvious phase difference,inducing the superposition of the trajectory in the two directions to form the helical motion;In terms of theoretical analysis,the g LSM model of BZ gels is constructed based on the Oregonator model,and the results matching the experiment were obtained through simulation,based on this the chemical dynamic origin of the helical motion pattern generation is explored,i.e.,the existence of phase differences between the orthogonal components of chemical signals in 2D space.Finally,the multi-mode helical motion of spiral wave-driven BZ gels was investigated,and the effect of wave-tip motion behavior on the helical motion of the gels was explored.The experimental results show that the spiral wave-driven BZ gel produces large circular motion,and the basic component unit of the trajectory is the small helical trajectory.The gel motion mode was mainly influenced by the motion mode of wave-tip,and three basic motion modes were obtained: ACC(A-anticlockwise,C-clockwise),AAA and CAC by changing the BZ substrate concentration to regulate the wave-tip wandering and drifting mode.ACC and CAC are the main forms of gel motion,and the motion range of the spiral wave-tip is small(about 30°);The spiral wave-tip motion in AAA motion mode is within 60°;In addition,the interaction of wave-tip wandering and drift can induce a change of the gel motion mode,and the positive or negative phase differences determine the direction of helical trajectory.The change of spiral wave dynamics state is the fundamental reason for the different helical motion modes of the BZ gel.In summary,the NCBZ gel synthesized in this thesis has better mechanical and response properties than the conventional BZ gel,providing an experimental basis for in-depth research on the bionic motion of gel;Studying the internal mechanism of different motion modes of BZ gel driven by chemical waves in a 2D environment is helpful in revealing the dynamic origin of bionic motion of active substances,and provides a new method for complex motion design of soft robots and intelligent materials.This thesis contains 100 Figures,5 Tables and 181 References.