Gallium And Its Alloy-Based Polymer Composites:Preparation,Properties,and Applications

With rapid innovations in technology,the modern electronics industry is developing towards a trend of lightweight,flexibility,energy efficiency,and high integration,which provides new demands for the required materials on weight,processability,cost,and thermal/electrical conductivity.In recent years,gallium and its alloys（GaLMs）have been applied to prepare gallium-based polymer composites（Ga PCs）by compounding with polymer materials due to the unique properties of GaLMs such as low melting point,low modulus,high thermal/electrical conductivity,and biocompatibility.The main research purpose of Ga PCs is to integrate the advantageous properties of GaLMs and polymers.However,Ga PCs currently have some challenges with electrical conductivity and scalable processability,making Ga PCs difficult to meet the requirements of emerging applications such as flexible consumer electronics,wearable devices,and soft robots.Therefore,further research is needed on the interdisciplinary between GaLMs and polymers.Based on the above discussion,this dissertation comprehensively utilizes the physical/chemical properties of GaLMs and the theory of polymer science to design and prepare novel Ga PCs.In terms of scientific principles,this dissertation aims at the findings of new cross-interactions between GaLMs and polymers and the exploration of the mechanisms of new interactions;as for materials performances,this dissertation devotes to achieving complementary enhancements of GaLMs and polymers and prepare Ga PCs with combined advantageous properties.The main research contents are as follows:（1）To address the weakly conductive stability of conjugated conductive polymers,GaLMs are utilized to enhance the conjugated conductive polymers.GaLMs(Ga₉₅Zn₅,melting point 25.8℃)and poly（3,4-ethylenedioxythiophene）:poly（styrene sulfonate）（PEDOT:PSS）are fabricated as Ga Zn-PEDOT:PSS water-based conductive ink by probe sonication.The Ga Zn nanoparticles（～550 nm）and PEDOT:PSS forms a core-shell structure through double ion interaction bridged by the PSS segment.Ga Zn can enhance the conductivity of PEDOT:PSS printed films,and the surface resistivity of20%Ga Zn-PEDOT:PSS printed films（2.5×10⁵Ω/sq）decreases compared with that of PEDOT:PSS films（3.8×10⁶Ω/sq）.Due to the low modulus properties,Ga Zn can spontaneously and instantly（～2 s）repair the printed circuits of PEDOT:PSS under external damages,effectively enhancing the conductive stability of PEDOT:PSS.In addition,the excellent solvent-processability of PEDOT:PSS entails conductive ink printing on various substrate surfaces by direct writing,screen printing,injection printing,etc.（2）In response to the low conductive sensitivity of flexible polymer materials,this study manages to enhance the flexible polymers by GaLMs.Ga is dispersed in acrylamide/acrylic acid hydroxyethyl ester（AM/HEA）through probe sonication,and Ga-PAM/PHEA hydrogel composites are produced via in-situ polymerization from the Ga-AM/HEA.During the tensile test,Ga with low modulus acts as the stress concentration point and dissipates a large amount of tensile stress,thus toughening the hydrogel（elongation at break:～1500%）that is much higher than neat hydrogel（～396%）.The pressure-resistance response of the hydrogel is significantly enhanced by Ga,and the pressure-resistance response sensitivity of 10%Ga-PAM/PHEA(0.160k Pa^-1)is one order of magnitude higher than that of neat PAM/PHEA(0.012 k Pa^-1).Due to the asymmetrical deformation of Ga droplets in the hydrogel,10%Ga-PAM/PHEA hydrogel has a unique anisotropic stress-resistance response relationship and can be developed as an anisotropic resistance sensor to discern the letters,handwriting,and gestures.（3）Regarding the crystallization of thermoplastic polymers,GaLMs are developed as nucleating agents for thermoplastic polymers.Ga and polylactide（PLLA）are thermally molded as Ga-PLLA composites via classic twin-screw extrusion.The non-isothermal and isothermal crystallization behaviors of Ga-PLLA are systematically investigated using differential scanning calorimetry（DSC）and Avrami theory,and the results show that Ga can act as a liquid-state nucleating agent for PLLA to promote its crystallization.The nucleation mechanism is derived from a chemical reaction:firstly,reducible Ga is oxidized in the high-temperature environment during thermal processing;secondly,the oxide of Ga reacts with the carboxyl group on the end of PLLA chains to form carboxylate;a large number of carboxylates aggregate near the PLLA end groups to form ion clusters;and the ion clusters serve as new heterogeneous nucleation sites,inducing PLLA chain nucleation.（4）To address the difficulty of molding GaLMs,thermoplastic polymers are utilized to enhance the processability of GaLMs and achieve thermoplastic molding of GaLMs.The solid fraction of Ga₁₀Sn₉₀ at different temperatures is calculated based on the Ga Sn alloy phase diagram using the Scheil formula.Changing the processing temperature can match the viscosity of Ga₁₀Sn₉₀ and PLLA.Under rheological matching,the synchronous deformation migration between Ga Sn and PLLA is achieved in the thermoplastic processing field.As a result,Ga₁₀Sn₉₀ and PLLA are uniformly distributed,and conductive plastic materials（PBMs）with high conductivity（1.1×10⁶ S/m）are prepared under the guidance of rheological matching.SEM-EDS and Monte Carlo simulations confirm the validity of the rheological matching for preparing high-conductivity PBMs.The rheological matching established the connection between GaLMs rheology and polymer rheology,successfully integrating the advantageous properties of GaLMs and polymers.