\”Germany should\”: A cryo-EM into the polymer microgel internal structure at a glance!

Hydrogel microspheres, also known as microgels, can be a water swellable nano-material comprising a crosslinked hydrophilic or amphiphilic polymer. Compared with the solid microspheres, which microspheres have good biocompatibility, pH, and temperature responsive characteristics, and excellent flexibility and stability, high-performance catalyst, biomolecule, drug delivery systems and the field of tissue engineering and other potential applications. Researchers by different design nanocomposite structure, gives more functional microgels, how detailed characterization microgel swollen state configuration problems become a major problem researchers. characterization methods commonly used, such as scanning electron microscopy (SEM) and transmission electron microscopy (the TEM), in characterizing nanocomposite microgel sample needs to be dried in advance, which inevitably destroy the structure of the microgel. Although scattering, SEM and the TEM low temperature, in situ atomic force microscopy (AFM) and super-resolution microscopy can give some information swollen microgel structure, but can not do anything for the internal structure. Thus, is essential for detailed characterization of the microgel nanostructures \”original.\” 《德国应化》:冷冻电镜进军高分子,微凝胶内部结构一览无余! Professor Daisuke Suzuki Shinshu University, Japan, TF low temperature electron tomography (cryo-ET), the first time a detailed structural information nanocomposite microgel [ 123]. They N- isopropylacrylamide (N), methacrylic acid (M), styrene (S) and fumaric acid (F) is a monomer, seed emulsion polymerization method to prepare a series of microgels, and a detailed characterization of the structure. It found that the number of PS NMS microgel particles and the average diameter were 140 ± 28 and 45 ± 8 nm was; added surfactant NS-SDS PS microgel having an average particle pitch of 74 nm, the internal microgel formation SDS aggregates effectively prevent fusion of polystyrene nanoparticles, academic dispute resolved on SDS long acting ; inside microgel, styrene can recognize the difference in polarity on a molecular scale by changing the spatial seed distribution carboxyl microgel prepared successfully adjustable thickness and number of layers of the multilayer nanocomposite microgel structure. The findings for the new nanocomposite microgel design opened the way. 《德国应化》:冷冻电镜进军高分子,微凝胶内部结构一览无余! Structure Characterization Nanocomposite microgel

《德国应化》:冷冻电镜进军高分子,微凝胶内部结构一览无余! FIG 1. NMS (a) FE-SEM image of microgel; (b) TEM image; (c) cryo- ET image; (d) the image segments of polystyrene microgel; (e) bar graph NM microgel diameter surface of the PS nanoparticles.
In researchers N- isopropylacrylamide (N), methacrylic acid (M) and styrene (S) is a monomer, the emulsion polymerization method to prepare nanocomposite microgel NMS, using FE-SEM and TEM structure was characterized and found on the surface of NMS microgel particles PS attached, since the microgel is deformed, its internal structure can not be determined. In contrast, cryo-ET image not only shows the overall configuration of the swollen state NMS nanocomposite microgel can clearly calculate the number of PS particles and the average diameter, were 140 ± 28 and 45 ± 8 nm, for microgel PS surface coverage was 32 ± 3%, the first time a detailed structural information microgel. They also found that there is a gap between the upper surface of the PS microgel particles, which facilitate material exchange, to achieve a reversible change in volume according to changes in temperature and pH.

Effect of surfactant on the internal structure of the microgel

《德国应化》:冷冻电镜进军高分子,微凝胶内部结构一览无余! FIG. 2. (a) NMS and (b) cryo- NM-SDS microgels internal PS nanoparticles ET image and the image segment; diameter (b) NM-SDS microgel particles inside PS histogram.
In researchers N- isopropylacrylamide (N), fumaric acid (F) and styrene (S) was synthesized as monomer NFS microgels synthesized in the addition of a surfactant SDS the NS-SDS microgel, the influence of the charged groups on SDS microgel swollen state morphology. NF microgel found inside surface of the belt can accommodate a large carboxy polystyrene particles remains colloidally stable; even in a water-swollen state, the free space inside the NFS few microgels; although similar to NFS microgel, but still we observed within the NS-SDS to the free space, which is due to micro-NS-SDS gel particles and the number of PS diameters 590 nm and 50 nm, the average particleDistance between 74 nm, a particle size larger than PS, so there must be a large amount of free space inside.
《德国应化》:冷冻电镜进军高分子,微凝胶内部结构一览无余! FIG 3. NS-SDS nanocomposite microgel SEP FIG.
Surprisingly, the filling rate NS-SDS PS nanocomposite microgel particles up inside the lower case 73 ± 2%, the phenomenon does not occur PS particles fuse. In previous studies, when the concentration of styrene using the same, without the addition of SDS easily PS particles formed by fusion of larger particles. Since it is difficult to determine the internal structure of NS-SDS microgels by conventional characterization, SDS has been unable to explain the role of charged groups within the microgel.

In this study, cryo-ET characterized found inside microgel formation SDS aggregates act as nucleation points polystyrene, PS prevented fusion particles, solved the problem of long academic debate. Synthesis of controlled thickness and number of layers microgel

《德国应化》:冷冻电镜进军高分子,微凝胶内部结构一览无余! Fig 4. (a) an image segment and N-NM-S nanocomposite microgel (b) cryo-ET image; (c) N-NM-S, (d) N-NM-NM-S and thin cross-sectional TEM (e) N-NM-NM-NF-S nanocomposite microgel image.
Researchers seed by seed precipitation polymerization microgel N (nuclear) -NM (shell) was prepared, and then carried out polymerization of styrene, preparation of a three-layer nanocomposite microgel, Cryo -ET image clearly shows the absence of PS between the PS core (first layer) and PS shell (third layer), a styrene monomer demonstrate the difference in polarity on the molecular scale can identify microgel. Seeds by changing the spatial distribution of the microgel carboxy, achieve the purpose of adjusting the microgel and the thickness of the layers.

Summary

In order to clarify the internal structure of the nanocomposite microgel Professor Daisuke Suzuki TF Shinshu University, Japan, using cryo-ET technology, detailed structural information acquired complex microgels nano original state. NMS and found that the number average diameter of the composite nano microgel PS particles were 140 ± 28 and 45 ± 8 nm, PS surface coverage of 32 ± 3%; NS-SDS microgels PS mean distance between grains of 74 nm, a particle size larger than itself, and therefore there must be a lot of free space inside, and the inside of the microgel formed SDS aggregates act as nucleation sites for the PS, PS prevented the integration of particles; by changing the micro-seed spatial distribution of the carboxyl groups in the gel, prepared a number of layers and the thickness of the three-layer structure adjustable microgels. Original link: https: //www.onlinelibrary.wiley.com/doi/10.1002/ange.202003493

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