Preparation And Application Of Smart Gels With Multiple Stimulus Responses Based On Host-Guest And Hydrogen Bond Interactions

Smart gel is a soft material whose properties(including gel volume,optical properties,mechanical properties,hydrophilicity/hydrophobicity,etc.)can be significantly transformed with changes in solvent composition,temperature,light,electricity,pH,etc.It has important applications in flexible electronic devices,drug mitigation,memory element switching,artificial muscles and actuators,visualized optical sensing elements,etc.Previous research has mostly focused on the construction and application of single stimulus-responsive gel materials.In today’s growing demand for functional materials,smart gels with multiple responsiveness are receiving more and more attention.On this basis,this paper designs and synthesizes a series of smart gels with multiple responses to external stimuli using host-guest interactions and hydrogen bonding interactions,investigates the mechanisms and possible synergistic effects of different stimulus responses,and explores their applications in the fields of flexible electronic devices,information encryption,electronic skin and flexible wearable devices.The main work of this paper has the following aspects:(1)Hydrogels with electrical and temperature multiple stimuli response are prepared using the host-guest interactions existing between β-cyclodextrin(β-CD)and amphiphilic polyacrylamide(PC14AM)and ferrocenecarboxylic acid,respectively.The amphiphilic polyacrylamide(PC14AM)is obtained by the base polymerization reaction of the amphiphilic monomer 2-acrylamido tetradecyl sulfonate with and hydrophilic acrylamide in water.We have investigated the phase transition process of this system and the results show that the phase transition temperature of the system varies with the ratio of β-cyclodextrin and hydrophobic long chain containing polyacrylamide in the range of 30-80℃.Due to the stronger host-guest interaction between β-cyclodextrin and ferrocenecarboxylic acid,the introduction of ferrocenecarboxylic acid in the binary gel described above competes with the amphiphilic polyacrylamide to achieve the synergistic effect of two independent signals.With different voltage stimuli(+1.5 V or-1.5 V),this ternary composite system can be Gel-Sol transition and its dynamic rheological properties can be varied up to three orders of magnitude(0.1-100 Pa/s).(2)Smart hydrogels that are responsive to stimuli such as temperature and pH are prepared using hydrogen bonding interactions between hydroxypropyl cellulose and acrylamide-acrylic acid copolymers.Firstly,their light transmission properties at different temperatures are investigated.And its swelling kinetics and optical transmittance under different pH environments are investigated.The results indicate that under acidic conditions,the prepared hydrogels exhibit properties similar to those of the high critical point(UCST=37℃)when the external temperature rises.In contrast,under neutral conditions,the prepared hydrogels change from colorless and transparent to white and opaque when the external temperature increases,exhibiting a transition behavior similar to that of the low critical solubility temperature(LCST=37℃).The fine tuning of the temperature response behavior of the hydrogels is achieved by changing the pH value and modulating the force between hydroxypropyl cellulose and acrylamide and acrylic acid copolymers.It is also used in the fields of smart windows,multiple information encryption and anti-counterfeiting.(3)Smart hydrogels with dual temperature response are prepared using hydrogen bonding interactions between acrylic acid-acrylamide copolymer and hydroxypropyl cellulose.Based on the previous section,the optical permeability of this type of hydrogel in a wide temperature range is investigated in depth.The results show that the gel changes from white opaque state to colorless transparent state when the external temperature is warmed up from 20℃ to 37℃,and changes from colorless transparent state to white opaque state when the temperature is continued to increase(from 38℃to 50℃).Moreover,the introduction of amphiphilic hydrophobic quaternary ammonium monomer enhances the swelling resistance,mechanical properties(breaking stress:1.1 MPa,elongation at break:1183%)and electrical conductivity(0.163 S/m)of the gel,making it available for stress and temperature sensing,and it exhibits high response sensitivity(GF=1.32 at 0-400%)and good stability,which can be used in ionic skin,flexible wearable devices,etc.(4)Smart organogels with sensitive response to stress/strain are prepared by dissolving small amounts of potassium iodide in glycerol using hydrogen bonding interactions between poly-N-hydroxyethylacrylamide and glycerol molecules.Their mechanical,electrical and adhesion properties are investigated over a wide temperature range.It is shown that the gel can maintain good electrical conductivity(3.82-10-3 S/m),transparency(90%)and-mechanical properties(stress at break:1.75 MPa,elongation at break:700%)between-80℃ and 100℃,and can be used in extreme environments such as low temperature and dryness.Also,since the gel is sensitive to salt water,the introduction of water and ions will enhance the electrical conductivity of the gel,which is expected to be a wearable sweat detection material.The hydrogen bond between the propylene glycol and polymer chain segments can be broken by adding water,and the water evaporation can re-bond the hydrogen bond between the propylene glycol and polymer chain segments to realize the remodeling and recycling of this gel.The results of this paper not only provide new solutions for the molecular design and preparation of smart gels with multiple stimulus response based on host-guest interactions or hydrogen bonding interactions,but also can provide references for the application of smart gels in flexible electronic devices,wearable devices,artificial muscles and sensors,information writing and encryption,and artificial skin.