A method for constructing a thermal responsive hydrogel based on solid-liquid interface repulsion and water content

Abstract

The application provides a kind of construction method of heat-responsive hydrogel based on solid-liquid interface repulsion and water content, comprising establishing the coarse-grained model of heat-responsive polymer network and water molecule system, constructing three-dimensional polymer gel network by adjusting the number of polymer chain monomer and the proportion of crosslinking agent;According to the geometric size of network, construct a simulation box and fill water beads;Under the dissipative particle dynamics model, define the interaction parameters between beads, carry out molecular dynamics simulation, count the number of polymer skeleton centroid and interface adjacent water beads, and calculate the equilibrium water content;Establish the solid-liquid interface model, calculate the equilibrium distance and interaction energy between water bead plane and polymer skeleton plane at adsorption temperature;By adjusting the number of polymer chain monomer, the polymerization degree of network is optimized, and the optimal design of heat-responsive desorption performance is realized.The method of the application is suitable for macroscopic hydrogel structure evaluation, and can quickly obtain the equilibrium water content and interface interaction energy, to guide the reasonable proportioning and preparation of hydrogel.

Description

Technical Field

[0001] This invention relates to the fields of polymer materials and water treatment, and in particular to a method for constructing thermally responsive hydrogels based on solid-liquid interfacial repulsion and water content. Background Technology

[0002] Thermally responsive hydrogels have become a research focus in recent years for applications such as dehumidification, atmospheric water collection, and thermal management. Thermally responsive hydrogels possess a critical volumetric phase transition temperature, meaning that a volumetric phase transition occurs above this critical temperature, accompanied by direct desorption of liquid water. In related applications, the main energy consumption occurs during the heating process after adsorption saturation, specifically during regeneration after dehumidification and the desorption of liquid water in atmospheric water collection. Current construction and development of thermally responsive hydrogels primarily focus on improving their equilibrium moisture content, moisture absorption rate, and mechanical properties, neglecting the analysis and consideration of desorption performance caused by their thermal response characteristics in cyclic moisture absorption and desorption applications.

[0003] Existing solutions disclose the design of polymer carriers for controlled molecular release (authorization publication number CN108416186B). This method utilizes computer molecular dynamics simulations to estimate the swelling and degradation kinetics of the polymer carrier and the release kinetics of the molecules within it by estimating the thermodynamic and transport properties of the polymer carrier, solvent, and the molecules to be released, thereby guiding polymer formulation design. However, this method requires calculating the complete molecular release process using molecular dynamics methods to determine the influence of the structure on release efficiency and rate. This calculation is complex, time-consuming, and does not consider the influence of different structures on the maximum equilibrium molecular content of the carrier. Furthermore, limited by the scale of molecular dynamics simulations, this method can only calculate the molecular release process of microgels and is not applicable to large-volume macrogels used in dehumidification and atmospheric water collection, thus failing to analyze and guide the optimal gel synthesis and preparation methods.

[0004] To achieve rapid design of thermoresponsive hydrogels by comprehensively considering equilibrium water content and thermal dehydration characteristics, this invention provides a method for constructing thermoresponsive hydrogels based on solid-liquid interfacial repulsion and water content. This method utilizes coarse-grained dissipative particle dynamics simulations to calculate the equilibrium water content by statistically analyzing the water droplet content at different degrees of polymerization. By constructing a polymer framework and water droplet microfacets and calculating the interaction forces before and after the critical volume phase transition, this method assists in designing thermoresponsive hydrogel structures that meet equilibrium water content requirements and enable rapid desorption. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing thermally responsive hydrogels based on solid-liquid interfacial repulsion and water content, which enables efficient evaluation and optimal formulation of macroscopic hydrogel structural properties by rapidly calculating equilibrium water content and solid-liquid interfacial interaction energy through molecular dynamics simulation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for constructing a thermoresponsive hydrogel based on solid-liquid interfacial repulsion and water content includes the following steps:

[0008] Step S1: Coarse-grained model

[0009] A coarse-grained model of a thermally responsive polymer network and water molecule system was established based on a molecular simulation platform.

[0010] In this model, a thermoresponsive polymer monomer is defined as a polymer bead, a crosslinking agent monomer as a crosslinking agent bead, and four water molecules as a water bead. A three-dimensional gel network structure of the thermoresponsive polymer is constructed by connecting the polymer beads and the crosslinking agent beads, forming a polymer gel network model. The number of monomers on each thermoresponsive polymer chain is adjusted during the construction of the three-dimensional gel network model to control the degree of polymerization. The number of crosslinking agent beads in the established polymer gel network model satisfies the following conditions:

[0011] In the formula, The number of crosslinking agent beads in the polymer backbone;

[0012] This represents the number of crosslinking agent sites.

[0013] Step S2: Simulate Box Construction

[0014] A simulation box is constructed based on the geometry of the polymer gel network, and the side length of the simulation box is determined according to the size of the established polymer gel network.

[0015] Step S3: System Filling

[0016] The polymer gel network and water droplets established in step S2 were introduced into the simulation chamber. The ratio of the two was adjusted so that the system contained only a single polymer network, and the remaining space was filled with water droplets at a density of approximately 1 g / cm³. 3 Filled with water droplets.

[0017] Step S4: Defining force field parameters

[0018] Under the dissipative particle dynamics model, we define the interaction parameters between beads and inside beads at temperatures below and above the critical volume phase transition temperature, i.e., adsorption temperature and desorption temperature, and set the repulsive force parameters at the adsorption temperature and desorption temperature, respectively.

[0019] Step S5: Dynamic Calculation

[0020] Molecular dynamics simulations were performed at the adsorption and desorption temperatures, respectively. A constant-volume isothermal ensemble was used, with a simulation time of no less than 30 ns and a time step of no less than 5 fs.

[0021] Step S6: Moisture content calculation

[0022] Based on the simulation results, the centroid and radius of gyration of the polymer skeleton were calculated, and the number of water droplets inside the polymer and near the interface was counted. Calculate the moisture content and take the average of the results from multiple frames to obtain the equilibrium moisture content;

[0023] Step S7: Establishing the solid-liquid interface model

[0024] At the desorption temperature, a tangential plane model of the anhydrous polymer skeleton is established, and the corresponding water droplet subplanes are constructed to form a solid-liquid interface model.

[0025] Step S8: Calculation of solid-liquid interface equilibrium distance

[0026] Calculate the total energy of the water droplet plane and the polymer framework plane, the total energy of the water droplet plane, and the total energy of the polymer framework at the adsorption temperature;

[0027] Adjust the distance between the water droplet plane and the polymer skeleton plane so that the interaction energy between the water droplet plane and the polymer skeleton plane is 0 at the adsorption temperature. This distance is the equilibrium distance of the solid-liquid interface at the adsorption temperature.

[0028] Step S9: Calculation of interfacial interaction energy

[0029] Using the equilibrium distance obtained in step S8, the interaction between the water droplet plane and the polymer skeleton plane at the equilibrium distance of the solid-liquid interface at the desorption temperature is calculated again to characterize the interfacial interaction strength between the thermally responsive polymer and water.

[0030] Preferably, in step S1, the polymer construction module of molecular dynamics simulation software is used to establish a coarse-grained structural model of the thermally responsive polymer network and water droplets.

[0031] Preferably, in step S2, a simulation box is built in the molecular simulation platform using the structural template construction function, and the side length of the simulation box is 1.2 to 1.3 times the maximum span of the polymer network.

[0032] Preferably, in step S4, the repulsive force parameters between identical beads are calculated according to the following equation. Repulsive force parameters between thermally responsive polymer beads and water droplets And the repulsive force parameters between other different beads :

[0033]

[0034] In the formula, The repulsive force parameters between identical beads;

[0035] The repulsive force parameter between the thermally responsive polymer beads and water droplets;

[0036] The repulsive force parameters between the remaining beads;

[0037] For Flory-Huggins parameters;

[0038] Boltzmann constant;

[0039] K represents the thermodynamic temperature.

[0040] The bead number density;

[0041] These are characteristic parameters, obtained experimentally based on the thermal response polymer chain transformation characteristics; The mutation intensity was obtained from experiments on the thermal response polymer chain transformation characteristics.

[0042] The lower critical dissolution temperature is K.

[0043] Preferably, in step S6, the moisture content calculation is based on the last five frames of the simulation results, calculating the polymer skeleton centroid and radius of gyration, and counting the number of water droplets whose distance from the centroid is less than the radius of gyration. For water droplets whose distance from the center of mass is greater than the radius of gyration but whose distance is less than 0.35 nm, calculate their distance from the nearest polymer or crosslinking agent droplet and count the number of water droplets whose distance is less than 0.35 nm. ;

[0044] The equilibrium moisture content of the thermo-responsive hydrogel is obtained by averaging the moisture content of the last five frames. If the moisture content does not meet the actual use requirements, return to step S1, change the degree of polymerization of the network by adjusting the number of monomers on each thermo-responsive polymer chain, rebuild the polymer gel network model, and repeat the subsequent simulation and moisture content calculation until the target moisture content is met.

[0045] Preferably, the formula for calculating the moisture content is as follows:

[0046]

[0047] In the formula, —Moisture content, g / g;

[0048] —The number of water droplets whose distance from the center of mass is less than the radius of rotation;

[0049] —The number of all water droplets that are more than 0.35 nm away from the center of mass and less than the nearest thermally responsive polymer bead or crosslinking agent bead;

[0050] —The number of thermally responsive polymer beads in the polymer backbone;

[0051] —Molecular weight of thermally responsive polymer beads, g / mol;

[0052] — Molecular weight of crosslinking agent beads, g / mol.

[0053] Preferably, in step S7, the surface cutting function of the molecular simulation platform is used to cut a plane on the polymer backbone that does not contain water droplets at the desorption temperature. The thickness of the cut plane is greater than or equal to 1 nm, and it must be ensured that the cut plane can fill the simulation box in the planar direction. The structural template function of the molecular simulation platform is used to establish a structure with a density of 1 g / cm³. 3 The water droplet layer was constructed, and a water droplet plane with a thickness of 1 nm was cut out. The polymer skeleton plane and the water droplet plane were established through the stacking construction function of the molecular simulation platform, and the thickness of the upper vacuum layer was ensured to be not less than 5 nm.

[0054] Preferably, in step S8, the interaction energy between the water droplet plane and the polymer framework plane at the adsorption temperature is calculated:

[0055]

[0056] In the formula: —Interaction energy between PNIPAM gel network microplanar layer and water droplet microplanar layer, kCal / mol;

[0057] —The total energy of the system consisting of the PNIPAM gel network microplanar layer and the water droplet microplanar layer, kCal / mol;

[0058] —Total energy of the PNIPAM gel network microplanar layer, kCal / mol;

[0059] —Total energy of water droplet microplane layer, kCal / mol;

[0060] Adjust the distance between the water droplet plane and the polymer skeleton plane, when The distance when =0 is the equilibrium distance between the solid and liquid interfaces.

[0061] Preferably, in step S9, the number of crosslinking agent beads and thermally responsive polymer beads in the polymer backbone is counted based on the simulation results, and the ratio of the amount of thermally responsive polymer monomer and crosslinking agent added is calculated, as follows:

[0062]

[0063] In the formula: —Mass of thermally responsive polymer monomers, in grams;

[0064] — Crosslinking agent mass, g.

[0065] Preferably, the method further includes step S10: structural optimization design. By adjusting the number of monomers in a single thermoresponsive polymer chain within the thermoresponsive polymer network, steps S1 to S9 are repeated to obtain the equilibrium water content and interaction energy at different degrees of polymerization. When the calculated interaction energy is higher than 57.28 kcal / mol, the structure is determined to meet the target desorption rate requirement.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] This invention controls the degree of polymerization of the polymer network by adjusting the number of monomers on each thermally responsive polymer chain when establishing the polymer gel network model, thereby achieving precise control of the polymer network structure and providing an accurate basis for subsequent water content calculation and solid-liquid interface analysis.

[0068] This invention uses molecular dynamics simulation results to statistically determine the centroid and radius of gyration of the polymer skeleton, and calculates the number of water droplets near the interface, thereby achieving accurate characterization of the equilibrium water content of the hydrogel, and thus enabling the prediction and control of water adsorption and release behavior.

[0069] This invention achieves quantitative analysis of the interaction forces between hydrogels and water by establishing a solid-liquid interface model and calculating the equilibrium distance and interaction energy between the water droplet plane and the polymer skeleton plane, providing a basis for optimizing material properties.

[0070] This invention uses statistical analysis of the number of crosslinking agent beads and thermally responsive polymer beads in the polymer backbone, and calculates the addition ratio of monomers and crosslinking agents, to achieve precise control of the composition ratio of hydrogels, improve the repeatability and stability of material preparation, and help determine the optimal synthesis ratio of macroscopic hydrogels.

[0071] This invention achieves optimized design of hydrogel structure by repeatedly constructing a network model by adjusting the number of monomers in the polymer chain and calculating the equilibrium water content and interfacial interaction energy under different degrees of polymerization. This enables the final material to meet the target desorption rate and water absorption performance requirements. At the same time, key performance parameters can be obtained by performing only two simulations on polymers with a small number of particles in the system. The calculation time is less than 10 hours, which improves the simulation efficiency.

[0072] In summary, this invention establishes a polymer gel network model of macroscopic hydrogels by performing molecular dynamics simulations on thermally responsive polymer networks, and calculates their equilibrium water content and solid-liquid interfacial interaction energy, enabling rapid and accurate evaluation of hydrogel structural properties. Compared to existing technologies, this invention only requires two simulations of polymers with a small number of particles in the system to obtain key performance parameters, with a computation time typically less than 10 hours. Furthermore, the method of this invention can effectively guide the optimal synthesis ratio of macroscopic hydrogels, providing an efficient and reliable design scheme for the rational preparation and application of hydrogels. Attached Figure Description

[0073] Figure 1 A flowchart illustrating the steps of a method for constructing a thermo-responsive hydrogel based on solid-liquid interfacial repulsion and water content, provided for embodiments of the present invention;

[0074] Figure 2 A schematic diagram of a thermally responsive polymer-water system model with different degrees of polymerization, constructed using a thermally responsive hydrogel construction method based on solid-liquid interfacial repulsion and water content, is provided for embodiments of the present invention.

[0075] Figure 3 A schematic diagram of the equilibrium distance of a thermally responsive hydrogel low-temperature polymer-water microplane based on a method for constructing thermally responsive hydrogels based on solid-liquid interface repulsion and water content is provided for embodiments of the present invention.

[0076] Figure 4 This diagram illustrates the calculation results of equilibrium water content and interaction energy of a thermally responsive hydrogel based on a solid-liquid interface repulsion and water content construction method, as provided in an embodiment of the present invention. Detailed Implementation

[0077] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0078] like Figure 1 As shown in this embodiment, a method for constructing a thermo-responsive hydrogel based on solid-liquid interfacial repulsion and water content is provided, comprising the following steps:

[0079] Step S1: Coarse-grained model (establishing coarse-grained structures of thermally responsive polymers and water droplets)

[0080] A coarse-grained structural model of a thermally responsive polymer network and water droplets was established using the polymer building module of a molecular dynamics simulation software.

[0081] In this model, a thermoresponsive polymer monomer is defined as a polymer bead, a crosslinking agent monomer as a crosslinking agent bead, and four water molecules as a water bead. A three-dimensional gel network structure of the thermoresponsive polymer is constructed by connecting the polymer beads and the crosslinking agent beads, forming a polymer gel network model. The number of monomers on each thermoresponsive polymer chain is adjusted during the construction of the three-dimensional gel network model to control the degree of polymerization. The number of crosslinking agent beads in the established polymer gel network model satisfies the following conditions:

[0082]

[0083] In the formula, The number of crosslinking agent beads in the polymer backbone;

[0084] This represents the number of crosslinking agent sites.

[0085] Step S2: Simulation Box Setup (Building a polymer-water system simulation box)

[0086] The simulation box was created using the Build Mesostructure Template function. The side length of the simulation box was determined based on the size of the polymer gel network. The side length of the simulation box was 1.2 to 1.3 times the maximum span of the polymer network.

[0087] Step S3: System filling (simulating box filling with polymer and water droplets)

[0088] The polymer gel network and water droplets established in step S2 were introduced into the simulation chamber. The ratio of the two was adjusted so that the system contained only a single polymer network, and the remaining space contained water droplets at a density of approximately 1 g / cm³. 3 Filled with water droplets.

[0089] Step S4: Define force field parameters (calculate the repulsive force parameters between beads at the adsorption and desorption temperatures)

[0090] Under the dissipative particle dynamics model, we define the interaction parameters between beads and inside beads at temperatures below and above the critical volume phase transition temperature, i.e., adsorption temperature and desorption temperature, and set the repulsive force parameters at the adsorption temperature and desorption temperature, respectively.

[0091] Calculate the repulsive force parameters between identical beads using the following equation. Repulsive force parameters between thermally responsive polymer beads and water droplets And the repulsive force parameters between other different beads :

[0092]

[0093] In the formula, The repulsive force parameters between identical beads;

[0094] The repulsive force parameter between the thermally responsive polymer beads and water droplets;

[0095] The repulsive force parameters between the remaining beads;

[0096] The Flory-Huggins parameters (which can be obtained from literature, experiments, or by building a full-atom model of the molecule using Materials Studio software and calculating the cohesive energy)

[0097] Boltzmann constant;

[0098] K represents the thermodynamic temperature.

[0099] The bead number density;

[0100] These are characteristic parameters, obtained experimentally based on the thermal response polymer chain transformation characteristics; The mutation intensity was obtained from experiments on the thermal response polymer chain transformation characteristics.

[0101] The lower critical dissolution temperature is K.

[0102] Step S5: Kinetic calculations (kinetic equilibrium conformation calculations based on adsorption and desorption temperatures)

[0103] Molecular dynamics simulations were performed at the adsorption and desorption temperatures, respectively. A constant-volume isothermal ensemble was used, with a simulation time of no less than 30 ns and a time step of no less than 5 fs.

[0104] Step S6: Moisture content calculation (statistical analysis of bead coordinates, calculation of equilibrium moisture content)

[0105] The moisture content calculation is based on the last five frames of the simulation results. The centroid and radius of gyration of the polymer skeleton are calculated, and the number of water droplets whose distance from the centroid is less than the radius of gyration is counted. For water droplets whose distance from the center of mass is greater than the radius of gyration but whose distance is less than 0.35 nm, calculate their distance from the nearest polymer or crosslinking agent droplet and count the number of water droplets whose distance is less than 0.35 nm. ;

[0106] The formula for calculating moisture content is as follows:

[0107]

[0108] In the formula, —Moisture content, g / g;

[0109] —The number of water droplets whose distance from the center of mass is less than the radius of rotation;

[0110] —The number of all water droplets that are more than 0.35 nm away from the center of mass and less than the nearest thermally responsive polymer bead or crosslinking agent bead;

[0111] —The number of thermally responsive polymer beads in the polymer backbone;

[0112] —Molecular weight of thermally responsive polymer beads, g / mol;

[0113] — Molecular weight of crosslinking agent beads, g / mol.

[0114] The equilibrium moisture content of the thermally responsive hydrogel is obtained by averaging the moisture content of the last five frames. If the moisture content does not meet the requirements, the process returns to step S1. The degree of polymerization of the network is changed by adjusting the number of monomers on each thermally responsive polymer chain. The polymer gel network model is re-established, and subsequent simulations and moisture content calculations are repeated until the target moisture content is met.

[0115] Furthermore, if the moisture content does not meet the requirements, return to step S1 to adjust the degree of polymerization;

[0116] Step S7: Establishing the solid-liquid interface model (tangential plane between polymer and water droplet layers)

[0117] The Cleave Surface function of the Build module was used to cut a plane onto the polymer backbone, which contained no water droplets at the desorption temperature. The thickness of the cut plane was greater than or equal to 1 nm, and it was necessary to ensure that the cut plane could completely fill the simulation box. A BuildMesostructure Template was used to build a structure with a density of 1 g / cm³. 3 A water droplet layer was constructed, and a water droplet plane with a thickness of 1 nm was cut out. The Build Layers function of the Build module was used to build the polymer framework plane and the water droplet plane, ensuring that the thickness of the upper vacuum layer was not less than 5 nm.

[0118] Step S8: Calculation of solid-liquid interface equilibrium distance (calculation of interplane interaction energy at adsorption temperature)

[0119] Calculate the interaction energy between the water droplet plane and the polymer backbone plane at the adsorption temperature:

[0120]

[0121] In the formula: —Interaction energy between PNIPAM gel network microplanar layer and water droplet microplanar layer, kCal / mol;

[0122] —The total energy of the system consisting of the PNIPAM gel network microplanar layer and the water droplet microplanar layer, kCal / mol;

[0123] —Total energy of the PNIPAM gel network microplanar layer, kCal / mol;

[0124] —Total energy of the water droplet microplane layer, kCal / mol.

[0125] Adjust the distance between the water droplet plane and the polymer skeleton plane, when The distance when =0 is the equilibrium distance between the solid and liquid interfaces.

[0126] Step S9: Calculate the interfacial interaction energy (calculate the interplane interaction energy at the desorption temperature) and (calculate the amount of monomer and crosslinking agent added).

[0127] Using the equilibrium distance obtained in step S8, the interaction between the water droplet plane and the polymer skeleton plane at the equilibrium distance of the solid-liquid interface at the desorption temperature is calculated again using the Mesocite module Calculation, in order to characterize the strength of the interfacial interaction between the thermally responsive polymer and water.

[0128] Calculate the amount of monomer and crosslinking agent added:

[0129] Based on the simulation results, the number of crosslinking agent beads and thermally responsive polymer beads in the polymer backbone were counted, and the ratio of thermally responsive polymer monomers to crosslinking agents was calculated using the following formula:

[0130]

[0131] In the formula: —Mass of thermally responsive polymer monomers, in grams;

[0132] — Crosslinking agent mass, g.

[0133] Step S10: Structural optimization design (adjusting the degree of aggregation)

[0134] By adjusting the number of monomers in a single thermoresponsive polymer chain in the thermoresponsive polymer network, steps S1 to S9 are repeated to obtain the equilibrium water content and interaction energy at different degrees of polymerization. When the calculated interaction energy is higher than 57.28 kcal / mol, the structure is determined to meet the target desorption rate requirement.

[0135] The following detailed explanation uses specific examples:

[0136] Using a thermoresponsive polymer hydrogel based on NIPAM as a thermoresponsive polymer monomer and MBA as a crosslinking agent as an example, its preparation structure was analyzed by calculating its equilibrium water content and interaction energy, and its actual preparation ratio was guided.

[0137] Step S1: Coarse-grained model establishment (construction of thermally responsive polymer-water droplet network)

[0138] The Build Polymers function of Material Studio molecular dynamics simulation software was used to construct a network of thermoresponsive polymers and coarse-grained structures of water droplets. One NIPAM monomer was considered one bead, one MBA monomer was considered one bead, and four water molecules were considered one water droplet. MBA is a crosslinking agent with four sites; therefore, the number of crosslinking agent beads contained in the constructed thermoresponsive polymer network is 39.

[0139] Step S2: Simulation Box Construction (Building a Polymer-Water System Box)

[0140] The simulation box was built using the Build Mesostructure Template, where N represents the degree of aggregation. In the models with aggregation degrees of 10, 15, 30, 75 and 150, the side lengths of the simulation box were 60 Å, 80 Å, 120 Å, 140 Å and 180 Å, respectively.

[0141] Step S3: System filling (simulating box filling with polymer network and water droplets)

[0142] The established thermally responsive polymer gel network and water droplets were added to the simulation chamber using Build Mesostructure. By adjusting the ratio of the thermally responsive polymer gel network to water droplets, the simulation chamber contained only one thermally responsive polymer network, with the rest filled with water droplets. The fill density was set to 1 g / cm³. 3 ;like Figure 2 The figure shows a schematic diagram of a polymer-water system model under different degrees of polymerization. Figure 2 The figure shows the distribution of polymer networks and water droplets with N representing the degree of polymerization, and the degree of polymerization being 10, 15, 30, 75 and 150.

[0143] Step S4: Define force field parameters (adsorption temperature and desorption temperature, setting the repulsive force between beads)

[0144] Based on the established thermally responsive hydrogel simulation box, the DPD option of the Forcefield Manager in the Mesocite module was used to define the repulsive force parameters between and within the beads at the adsorption temperature (temperature below the critical volume phase transition temperature) and desorption temperature (temperature above the critical volume phase transition temperature), respectively, and the corresponding force field parameters were generated. The repulsive force parameters between NIPAM beads and water beads, and the repulsive force parameters within all beads, can be directly calculated using formulas. The Flory-Huggins parameters required for calculating the interaction energy between NIPAM beads and MBA beads, and between MBA beads and water beads, were first established using Materials Studio to create a molecular combinatorial model, relaxed using the Forcite module, and then calculated using Cohesive EnergyDesity. The repulsive force parameters of each bead are shown in the table below:

[0145]

[0146] Repulsive force parameters at 25℃ Taking the table as an example, the repulsive force parameters between any two of the vertical NIPAM, MBA, and Water elements and the horizontal NIPAM, MBA, and Water elements are shown. This refers to the repulsive force parameters between NIPAM beads, between NIPAM beads and MBA beads, between NIPAM beads and water beads, between MBA beads, between MBA beads and water beads, and between water beads. Repulsive force parameters at 60℃ The table shows the repulsive force parameters at the same temperature of 25℃. Explanation of the table.

[0147] Step S5: Kinetic Calculations (Molecular Dynamics Simulation)

[0148] Molecular dynamics calculations were performed at the adsorption temperature (25℃) and desorption temperature (60℃) using the Calculation function of the Mesocite module. The Task was Dynamic, the ensemble was NVT, the total simulation time was 30 ns, the time step was 5 fs, the temperature controller was Velocity Scale, and the allowable temperature difference was 0.01 K.

[0149] Step S6: Moisture content calculation (statistical analysis of polymer skeleton and water droplet coordinates)

[0150] Based on the last five frames of the simulation results, the coordinates of all NIPAM beads, MBA beads, and water beads at the adsorption and desorption temperatures were statistically analyzed, and an Excel file containing the coordinates of each bead was output using a Perl script. A Matlab program was then used to calculate the centroid and radius of gyration of the polymer framework based on the coordinates of each NIPAM and MBA bead, and the number of water beads whose distance from the centroid was less than the radius of gyration was counted. For water droplets whose distance from the center of mass is greater than the radius of gyration, calculate their distance to the nearest NIPAM or MBA droplet, and count the number of all water droplets whose distance is less than 0.35 nm. Based on the formula for calculating water content, the water content was calculated simultaneously in the Matlab program, and the equilibrium water contents of hydrogels with degrees of polymerization of 10, 15, 30, 75 and 150 were 1.16 g / g, 2.07 g / g, 4.23 g / g, 8.04 g / g and 20.02 g / g, respectively.

[0151] like Figure 4 The figure shows the calculated results of equilibrium water content and interfacial interaction energy of thermally responsive hydrogels under different degrees of polymerization. The figure indicates that as the degree of polymerization increases, the equilibrium water content increases, while the interaction energy decreases, thus guiding the selection of the optimal degree of polymerization.

[0152] Step S7: Establishing the solid-liquid interface model (tangential plane between polymer skeleton and water droplet layer)

[0153] The Cleave Surface function of the Build module was used to cut a plane from the equilibrium conformation of the polymer backbone without water droplets at the desorption temperature. The thickness of the cut plane was 1 nm. A Mesostructure Template with a density of 1 g / cm³ was then used to construct the structure. 3 A water droplet layer was constructed, and a water droplet plane with a thickness of 1 nm was cut out. The polymer framework plane and the water droplet plane were built using the Build Layers function of the Build module, with a 10 nm upper vacuum layer.

[0154] Step S8: Calculation of solid-liquid interface equilibrium distance (interplane interaction energy at adsorption temperature)

[0155] The Mesocite module's Calculation function was used to calculate the total energy of the water droplet plane and the polymer framework plane at the adsorption temperature, with the Task selected as Dynamic. The equilibrium distance where the interaction energy is zero was calculated to be 5 Å for different distances between the water droplet plane and the polymer framework plane, and this equilibrium distance is independent of the degree of polymerization. Figure 3The figure shows a schematic diagram of the thermal response of the polymer-water microplane equilibrium distance at the adsorption temperature. The figure illustrates how the polymer-water microplane interaction energy varies with the microplane distance.

[0156] Step S9: Calculation of interfacial interaction energy and determination of monomer / crosslinker ratio (at desorption temperature)

[0157] Based on the equilibrium distance obtained in step S8, the interaction energy between the water droplet plane and the polymer backbone plane at the equilibrium distance of the solid-liquid interface at the desorption temperature was calculated again using the Mesocite module Calculation. The interaction energies for hydrogels with degrees of polymerization of 10, 15, 30, 75, and 150 were 94.27 kCal / mol, 93.26 kCal / mol, 69.14 kCal / mol, 60.94 kCal / mol, and 49.62 kCal / mol, respectively. The degrees of polymerization with interaction energies higher than 57.28 kCal / mol were 10, 15, 30, and 75. To maximize the equilibrium water content of the PNIPAM and MBA-based thermally responsive hydrogels, a degree of polymerization of 75 was chosen. Statistical analysis using Materials Studio software revealed a bead ratio of approximately 111.8:1 for NIPAM and MBA, corresponding to a mass ratio of 1 g: 6 mg.

[0158] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a thermo-responsive hydrogel based on solid-liquid interface repulsion and water content, characterized in that, The method comprises the following steps: Step S1: coarse-grained model A coarse-grained model of the thermal responsive polymer network and water molecule system is established based on a molecular simulation platform; wherein one thermo-responsive polymer monomer is defined as one polymer bead, one crosslinker monomer is defined as one crosslinker bead, and four water molecules are defined as one water bead; a three-dimensional gel network structure of the thermo-responsive polymer is constructed by connecting the polymer beads and the crosslinker beads, and a polymer gel network model is formed; the number of monomers on each thermo-responsive polymer chain is adjusted when the three-dimensional gel network model of the thermo-responsive polymer is constructed, so as to control the network polymerization degree, and the number of crosslinker beads in the polymer gel network model established satisfies: , wherein is the number of crosslinker beads in the polymer backbone; n is the number of crosslinker sites; Step S2: simulation box establishment A simulation box is constructed based on the geometric size of the polymer gel network, and the edge length of the simulation box is determined according to the size of the established polymer gel network; Step S3: system filling The polymer gel network established in step S2 and the water beads are introduced into the simulation box by adjusting the proportion of the two to make the system only contain a single polymer network, and the rest of the space is filled with water beads with a density of 1 g / cm 3 ​ Step S4: force field parameter definition Under the dissipative particle dynamics model, the interaction parameters between and within the beads are defined respectively at temperatures below and above the critical volume phase transition temperature, i.e. the adsorption temperature and the desorption temperature, and the repulsion force parameters at the adsorption temperature and the desorption temperature are set respectively; Step S5: dynamic calculation Molecular dynamics simulation is performed at the adsorption temperature and the desorption temperature respectively; a constant volume and constant temperature ensemble is adopted, the simulation time is not less than 30 ns, and the time step is not less than 5 fs; Step S6: water content calculation Based on the simulation results, the polymer skeleton centroid and the radius of gyration are calculated, and the number of water droplets inside the polymer and near the interface is counted The water content is calculated, and the equilibrium water content is obtained by averaging the results of multiple frames. Step S7: solid-liquid interface model establishment A tangent plane model of the polymer skeleton in the water-free state is established at the desorption temperature, and a corresponding water bead plane is constructed to form a solid-liquid interface model; Step S8: solid-liquid interface equilibrium distance calculation The total energy of the water bead plane and the polymer skeleton plane, the total energy of the water bead plane and the total energy of the polymer skeleton at the adsorption temperature are calculated; The distance between the water bead plane and the polymer skeleton plane is adjusted so that the interaction energy between the water bead plane and the polymer skeleton plane at the adsorption temperature is 0, and this distance is the equilibrium distance of the solid-liquid interface at the adsorption temperature; Step S9: interface interaction energy calculation Using the equilibrium distance obtained in step S8, the interaction between the water bead plane and the polymer skeleton plane at the equilibrium distance of the solid-liquid interface at the desorption temperature is calculated again to represent the interface interaction strength between the thermal responsive polymer and water.

2. The method according to claim 1, wherein the method is characterized by, In step S1, a coarse-grained structure model of the thermal responsive polymer network and water beads is established by using the polymer construction module of the molecular dynamics simulation software.

3. The method according to claim 1, wherein the method is characterized by, In step S2, the simulation box is established by using the structure template construction function in the molecular simulation platform, and the edge length of the simulation box is 1.2-1.3 times the maximum span of the polymer network.

4. The method according to claim 1, wherein the method is characterized by, The step S4, the same beads between the repulsion parameter is calculated according to the following equation , the repulsion parameter between the thermal response polymer beads and water beads And the rest of the different beads between the repulsion parameter : ， wherein is the same as the repulsion parameter between beads; is the repulsion parameter between the heat-responsive polymer beads and the water beads; represents the repulsive parameter between the remaining beads; wherein Fl is the Flory-Huggins parameter; B is the Boltzmann constant; T is the thermodynamic temperature, K; wherein: n is 1, 2, 3, 4, 5, The characteristic parameters are obtained from the thermal response polymer chain transition characteristic experiment. The mutation intensity is obtained from the thermal response polymer chain transition characteristic experiment. LCST = lower critical solution temperature, K.

5. The method according to claim 1, wherein the method is characterized by, In step S6, the water content calculation is based on the last five frames of the simulation output, the polymer backbone center of mass and the gyration radius are calculated, and the number of water beads within the gyration radius of the center of mass is counted , and the number of water beads whose distance from the center of mass is greater than the gyration radius but whose distance from the nearest polymer or crosslinker bead is less than 0.35 nm is counted ; The water contents of the last five frames are averaged to obtain the equilibrium water content of the thermal responsive hydrogel; when the water content does not meet the actual use requirements, return to step S1, adjust the number of monomers on each thermal responsive polymer chain to change the network polymerization degree, and then establish the polymer gel network model again, repeat the subsequent simulation and water content calculation until the target water content is met.

6. A method for constructing a thermal responsive hydrogel based on solid-liquid interface repulsion and water content according to any one of claims 1 or 5, characterized in that, The water content calculation formula is as follows: ， In the formula, - water content, g / g; - the number of water droplets having a distance to the center of less than the radius of gyration; - the number of all water beads with a distance to the center of mass greater than the radius of gyration and a distance to the nearest thermo-responsive polymer bead or crosslinker bead less than 0.35 nm; - the number of thermoresponsive polymer beads in the polymer backbone; - thermal responsive polymer bead molecular weight, g / mol; - Crosslinker bead molecular weight, g / mol.

7. The method according to claim 1, wherein the method is characterized by, In step S7, the tangent plane of the polymer skeleton without water beads at the desorption temperature is cut by using the surface cutting function of the molecular simulation platform, the thickness of the cut plane is greater than or equal to 1 nm, and it is required to ensure that the cut plane can fill the simulation box in the plane direction; A water bead sublayer with a density of 1 g / cm 3 was established using the structure template function of the molecular simulation platform, and a water bead subplane with a thickness of 1 nm was cut. The polymer skeleton plane and the water bead plane are established by using the layer construction function of the molecular simulation platform, and it is required to ensure that the thickness of the upper vacuum layer is not less than 5 nm.

8. The method according to claim 1, wherein the method is characterized by, In step S8, the interaction energy between the water bead plane and the polymer skeleton plane at the adsorption temperature is calculated: ， wherein: - PNIPAM gel network microplane layer and water bead microplane layer interaction energy, kCal / mol; - Total energy of the system consisting of PNIPAM gel network microplane layers and water bead microplane layers, kCal / mol; - Total energy of PNIPAM gel network microplane layer, kCal / mol; - Total energy of the water-bead microfacets layer, kCal / mol; Adjust the distance between the water bead plane and the polymer skeleton plane, when The distance at = 0 is the solid-liquid interface equilibrium distance.

9. The method according to claim 6, wherein the method is characterized by, In the step S9, the number of crosslinking agent beads and the number of thermal responsive polymer beads in the polymer skeleton are counted according to the simulation result, the addition amount ratio of the thermal responsive polymer monomer and the crosslinking agent is calculated, and the formula is as follows: ， In the formula: — mass of thermally responsive polymer monomer, g; - crosslinker mass, g.

10. The method according to claim 1, wherein the method is characterized by, Further comprising a step S10: structure optimization design, by adjusting the monomer number of a single thermal responsive polymer chain in the network of the thermal responsive polymer, repeating the steps S1-S9, obtaining the equilibrium moisture content and the interaction energy under different polymerization degrees, and when the calculated interaction energy is higher than 57.28 kCal / mol, it is determined that the structure can meet the target desorption rate requirement.

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