Preparation Of Hybrid Microgels In Acoustic Suspension Droplets

Microgels are a kind of porous polymer soft-solid particles with micron size in diameter and cross-linked network structure.The integrity,permeability,stimulus response of microgels make them have the promising applications of many fields,such as sensing,catalysis,biomedicine and templated-method preparation.Hybrid microgels containing metal nanoparticles as functional composite materials have attracted great attention in recent years due to their potential applications on various fields.As templates,microgels can control the sizes of nanoparticles,and then stabilize the as-synthesized nanoparticles through the confinement of the porous structure.However,due to the limited mass and heat transfer inside the porous structure of microgels,there are some difficult unsolved problems in the preparation of hybrid microgels:（1）Due to mass transfer limitations,the core-shell structure is to be preferred for the templated-prepared hybrid microgels.Inversely,preparation of hybrid microgels with distributing uniformly nanoparticles throughout the microgels is still a big challenge;（2）The control of nanoparticle size and crystal form inside porous structure of microgels is very limited.Acoustic levitation is a technology aimed to countering gravity factors and realizing the levitation of condensed matters.It is expected to obtain the microgels with novel structures in the acoustic levitation droplets;The unique heat and mass transfer method helps to control the heat and mass transfer process inside the porous structure of microgels,so that the formation of the internal porous structure and chemical reactions inside microgels have a high degree of control.In this thesis,we intend to levitate microgels in acoustic field using the acoustic levitation technology,eliminating the usage of necessary container for the conventional chemical reaction process.It is expected to obtain microgels with special structures and performance,subsequently laying the foundation for the studies on wall effects of chemical reactions and chemical preparation.Specifically,P（NIPAM-co-MAA）nanoscale microgels acted as templates were first prepared by the precipitation polymerization method;the ultrasonic levitation instrument platform for levitation experiments were set up;the stabilization and changes in temperature of levitation droplets containing pure solvents and microgels suspensions were systematically investigated.On this basis,the CuS-P（NIPAM-co-MAA）and CdS-P（NIPAM-co-MAA）hybrid microgels were prepared in acoustic levitated droplets using as-synthesized P（NIPAM-co-MAA）microgels as the template.It was demonstrated that the special mass transfer mode in the acoustic levitated droplets has a significant effect on the distribution of nanoparticles inside the microgels.Specifically,the following two aspects have been carried out:In the first part of this thesis,a series of P（NIPAM-co-MAA）nanoscale microgels with different monomer and cross-linker contents were first prepared by precipitation polymerization and using NIPAM and MAA as comonomers,BIS as cross-linker,and KPS as initiator.All as-synthesized microgels exhibit uniform sizes of about 210-280 nm.SEM and DLS test results showed that the sizes of microgels increase from 213 to 281 nm with increasing the contents of MAA from 0 to 30 mol%,and the size of microgels increase from 238 to 275 nm with increasing contents of cross-linker from 1 to 5 mol%.It is noted that the swelling rate of the microgels decreased with increase of content of cross-linker.In addition,it was found that the VPTT of the microgels was 32.5℃ by DLS measurements,and as-synthesized microgels show the excellent reversible temperature responsiveness.At the same time,the levitation stability and volatility of pure solvents at different frequencies were systematically tested using the preliminary ultrasonic levitation device.The experimental results show that almost all of the organic solvents are extremely volatile in the acoustic field and the stability time is extremely short.However,deionized water has excellent stability in the acoustic field and can be stably levitated for more than 2 h.On this basis,the deionized water suspension including microgels is stably levitated in the acoustic field.And then no change in the volume during levitation of nearly 1 h,and the temperature of the microgels droplets in different frequency bands changed in the range of 0.4℃,it is about 1℃ slightly lower than room temperature.The TEM and DLS test results show that the levitation for 1 h in the acoustic field did not destroy the structure of the microgels,and their particle sizes remained almost unchanged.In the second part of this thesis,the CuS-P（NIPAM-co-MAA）and CdS-P（NIPAM-co-MAA）hybrids microgels were prepared by in-situ synthesizing method in acoustic levitation droplets using ay-synthesized microgels acted as templated.In order to study influence of the containerless effect and the special mass transfer mode on the structure of the hybrid microgels in the acoustic field,we prepared CuS-P（NIPAM-co-MAA）and CdS-P（NIPAM-co-MAA）hybrid microgels under conventional conditions（gravitational field,flask acted as reaction vessel,and magnetic agitation）,wherein the resulted hybrid microgel acted as a control system.Other than that,reaction conditions were exactly the same between the acoustic levitated and conventional preparation process.For the CuS-P（NIPAM-co-MAA）hybrid microgels,the TEM test results show that the CuS nanoparticles in the hybrid microgels originated from acoustic levitation droplets can be uniformly distributed in the entire network structure of microgels,and the average size is about 7.13 nm.Under conventional conditions,however,the core-shell structure inside the hybrid microgels is produced,and then the average size of CuS nanoparticles is about 5.79 nm.Furthermore,the AAS results show that the CuS loading in the hybrid microgels originated from acoustic levitation droplets is 6.07%,and the CuS loading in the hybrid microgels under normal conditions is 2.99%.Obviously,the faster mass transfer in the acoustic levitated droplets makes the better distribution and the higher content of CuS nanoparticles inside mirogels.As for CdS-P（NIPAM-co-MAA）hybrid microgels,CdS nanoparticles originated from acoustic levitation droplets shows the better distribution inside microgels,but no observance of the difference of the size and contents of CdS nanoparticles between in the two different preparation approach.In addition,the research results show that the contents of cross-linker and MAA,and the concentrations of metal salt solutions also have a significant impact on the distribution and contents of inorganic nanoparticles of the resulted hybrid microgels.HR-TEM tests show that CuS and CdS nanoparticles have high-resolution lattices,and the CuS-P（NIPAM-co-MAA）hybrid microgels and CdS-P（NIPAM-co-MAA）hybrid microgels prepared in the acoustic levitation instrument show better crystallinity.