Phase Behavior And Interfacial Properties Of PNIPAM Microgels:Mesoscopic Simulations

PNIPAM(Poly(N-isopropylacrylamide))microgels are constituent of amphophilic network polymers,which swell but do not dissolve into aqueous solution.PNIPAM microgels have been used as nanodevices,biomedical carriers,chemical separation materials,smart catalytic carriers et al.However,remarkable development toward highly functional and intelligent polymers is needed,which is one of the major problems in the applications of PNIPAM microgels.Interface confinement has a significant role in the microstructure and physicochemical of microgel,thus limiting their highly functional and intelligent expression.Therefore,there still needs to understand the polymeric configuration structure-properties relationship,specifically under the interfacial confinement conditions.In this dissertation,a mesoscopic method was constructed to describe the phase behavior and interfacial properties of PNIPAM microgels,as well as provide helpful ideas for experimentation.This dissertation is composed of the following several parts:(1)The swelling/deswelling behavior of PNIPAM microgel is dominated by temperature.Based on Langevin dynamics integrating Lennard-Jones and Morse potentials,a novel methodology was proposed to investigate the temperature-dependent phase behavior of PNIPAM microgels.This method showed a good agreement with experimental characteristics of PNIPAM microgels,such as volume phase transition temperature,temperature-dependent diameter,and structural morphologies(2)Based on this proposed method,the temperature-dependent phase behavior of PNIPAM microgel was systematically studied.During the deswelling dynamics,microgels progressively undergo three microphase transition stages:(?)the polymeric chains in the microgels gradually aggregate into dispersed nanogel fragments,(?)and then transform into sponge gels,(?)ultimately generate ribbonlike gels.(3)The interfacial properties of PNIPAM microgel were systematically investigated.Once the microgel adsorbs onto the substrates,a crossover adsorption regime between polymeric wetting and colloidal adhesion was observed.With the help of machine learning,a three-dimensional phase diagram of the adsorption regime was presented under wide condition parameters(environmental temperature,crosslink density,interfacial interaction strength).The predictive ability of machine learning is accurate,and it can be extended into interfacial engineering.Inspired by the microgel capsules,the temperature-switchable sensors are devised.Compared to the solid microgels,microgel capsules exhibit tunable reflectivity or thickness by simply varying the system temperature because the hollow structure in microgel capsules decreases the interfacial confinement effects.Meanwhile,this device shows good repeatability and sensitivity.(4)The self-engulfing behavior of nanoparticle-anchored microgel is explored.The anchoring depth of nanoparticle in the microgel matrix or surface is controlled by environmental temperature.Specifically,three self-engulfing states,including full-engulfing,half-engulfing,and surface contact,were identified.Different adhesive states in these systems are controlled by the complementary balance of interfacial elastocapillarity,where the van der Waals interaction of hybrid microgel-nanoparticle offers the capillary force while the internally networked structure of microgel reinforces the elasticity repulsion.Besides,the interfacial elastocapillarity can be exploited as a powerful approach to design hybrid Janus particles with tunable topologies and delicate physicochemical properties.(5)With the assistance of large-scale dissipative particle dynamics simulations,the membrane wrapping pathway of injectable hydrogels was observed.In the wrapping process,the injectable hydrogels undergo two different dynamics stages:transform from vertical capillary adhesion to laterally compressed wrapping.These two dynamics stages are attributed to the elastocapillary deformation of networked gels and nanoscale confinement of the bilayer membrane,respectively.Compared with rigid nanoparticles,injectable hydrogels takes a long time to be fully wrapped owing to the high energy barriers and wrapping induced shape deformation.These results provide theoretical guidance for the design and fabrication of injectable hydrogel-based drug carriers and tissue engineering.