Preparation Of Organogel/Hydrogel Composite Materials Based On Solvent Replacement Strategy

Polymer hydrogels and organogels are bicontinuous phase gel-like materials consisting of polymers with water or organic solvents,respectively.Due to their solvent-rich properties and good biocompatibility,polymer hydrogels have a wide range of applications in tissue engineering,drug delivery,flexible electronics and many other fields.Organogels often possess characteristics such as anti-freezing and hydrophobic,which are difficult to achieve in hydrogels.In recent years,the preparation of organogel/hydrogel composite materials with macroscopic anisotropy by combining the advantages of organogels and hydrogels has become a hot research topic in the field of polymer materials today.The current strategies for the preparation of organogel/hydrogel composite materials are divided into two main types:the"adhesion" strategy,where an adhesion gel is designed to allow the attachment of the organogel and hydrogel;and the interfacial polymerization strategy,where the polymerization of the organogel/hydrogel prepolymer is initiated directly on the surface of the hydrogel/organogel.These two strategies have their advantages and disadvantages:the "adhesion" strategy is highly flexible in the design of the material structure,but produces composite materials with low interfacial strength;the interfacial polymerization strategy produces composite materials with high interfacial strength,but the design of the material structure is limited and often only two-layer structures or encapsulated structures can be obtained.How to achieve both high interfacial strength and high flexibility in structural design of composite materials is a key issue that must be overcome in current scientific research and engineering.This dissertation exploits a solvent replacement strategy to partially replace the organogel into hydrogel.Through precise molecular and structural design,the gel volume can remain almost constant during the solvent replacement process under specific conditions,resulting in organogel/hydrogel composite materials with both high interfacial strength and flexible structural design properties,providing a reference for patterning and functional design of organogel/hydrogel composite materials.We also briefly explore its application in areas such as actuators,flexible electronics,electronic skins and flexible wearable devices.The research for this dissertation includes the following four main areas:1.Low-strength organogels are prepared by copolymerizing N-(pyridin-2-yl)acrylamide with methacrylic acid in DMSO,which has strong hydrogen bonding interactions,and then replacing the DMSO solvent in the organogels with water to obtain high-strength hydrogels.The large change in gel strength is attributed to the hydrophobically enhanced hydrogen bonding interactions between two different functional groups of polymers in water.It was found that by changing the ratio of hydrophile to hydrophobic monomers in the organogel,the volume of the organogel could be constant as it was replaced by water into a high strength hydrogel.At the same time,the rheological properties of low-strength organogels satisfy the requirements of 3D printing,so we used 3D printing to prepare a series of high-strength hydrogels with different three-dimensional structures by combining solvent replacement strategies.2.High toughness,low modulus elastomeric organogels were obtained by copolymerizing N-(pyridin-2-yl)acrylamide with methacrylic acid in glycerol,which has strong hydrogen bonding interactions.Using a solvent replacement strategy to replace glycerol in the organogels with a specific concentration of salt water,high modulus and plastic hydrogels can be obtained,and the gel volume remains constant during the solvent replacement process.Based on this,organogel/hydrogel composite materials with well-defined boundaries and stable structures were patterned by solvent replacement in some areas of the organogel.The organogel/hydrogel composite materials can be used for a new type of shape memory material.3.The solvent replacement strategy was used to replace part of the glycerol in the organic gel with a 10 wt%concentration of aqueous sodium chloride solution.The replaced hydrogel,with the introduction of inorganic salt ions,increased the conductivity by four orders of magnitude compared to the organogel,and the combination of the two could prepare capacitive/resistive strain sensor based on the organogel/hydrogel composite materials.At the same time,the strain sensor can combine the advantages of the organogel and hydrogel and has good mechanical properties and anti-freezing performance.The high toughness of the organogel and the high interfacial strength between the organogel and hydrogel make the composite material highly resistant to puncture and can be used in a wide range of complex environmental conditions.4.We used a glycerol/water solvent mixture(glycerol/water volume ratio of 3:1)to replace the glycerol solvent.The modulus and volume of the organo-hydrogel after replacement were essentially the same as the organogel before replacement,but the electrical conductivity was increased by two orders of magnitude.Thus organogel/organo-hydrogel composite materials with anisotropic electrical properties and isotropic mechanical properties can be prepared using the solvent replacement strategy for simulating flexible ionic skin.It was also found that the organogels and organo-hydrogels also possess solvent-induced self-healing and adhesion properties,which have potential applications for the design of ionic skins with intrinsic stretching and self-healing capabilities.