Self-assembly of Hollow PNIPAM Microgels to Form Discontinuously Hollow Fibers

A new kind of hollow hydrogel microfiber with discontinuous hollow structure was prepared by an ice-segregation-induced self-assembly process. Monodisperse thermo-responsive hollow poly（N-isopropylacrylamide）（PNIPAM） microgels were first synthesized by seed precipitation polymerization using colloidal Si O2 nanoparticles as seeds, followed by removing the silica cores of the formed Si O2/PNIPAM core/shell composite microgels with hydrofluoric acid. Then, the discontinuously hollow hydrogel microfibers were produced by unidirectional freezing of 1 wt% hollow PNIPAM microgel aqueous dispersion in liquid nitrogen bath, followed by freeze-drying to remove the formed ice crystals. Many orderly arrayed dents were observed on the surfaces of the hydrogel microfibers by field-emission scanning electron microscopy, indicating that they are constructed by closely packed monodisperse hollow PNIPAM microgels. The effect of freezing method and the hollow microgel concentration in the aqueous dispersion on the morphological structure of the hollow hydrogel microfibers was investigated.     

THERMAL-SENSITIVE BETA-CYCLODEXTRIN-CONTAINED POLY(N-ISOPROPYLACRYLAMIDE) HYDROGELS CROSS-LINKED BY Si―O―Si BONDS

A series of novel p（N-isopropylacrylamide） （PNIPAM） hydrogels were synthesized by radical copolymerization of N-isopropylacrylamide （NIPAM） and 3-methacryloxypropyltrimethoxysilane （MPTMS）. The copolymers were then crosslinked through hydrolysis of the siloxane in acetic acid/water mixed solvent. Beta-cyclodextrin （Beta-CD） was introduced into the polymeric networks by condensation of 3-glycidoxypropyltrimethoxysilane derived beta-cyclodextrin （KH560-beta-CD） with MPTMS under acidic condition. These gels were heterogeneous, porous and exhibited fast deswelling kinetics when the temperature was elevated to above lower critical solution temperature （LCST）. The swelling ratios of the gels containing beta-CD at room temperature were higher than that of the normal PNIPAM hydrogel, which was caused by the lower crosslinking density in beta-CD contained gels. In comparison to that of the normal PNIPAM gel, the amount of loaded-drug in the hydrogel containing beta-CD was higher, and the release time of 5-fluorouracil （5-Fu） was prolonged, which was attributed to the formation of inclusion compounds between 5-Fu and beta-CD in gel network.     

Fluorescence Quantum Efficiency Enhancement in CaWO4:Eu3+,Na+ Nanocrystals by Tridoping with F- Ions

We demonstrated that tridoping with F- ions is an effective way to improve the fluorescence quantum efficiency of CaWO4:Eu3+,Na+ nanocrystals. F--tridoped samples with different F- concentrations were synthesized by a hydrothermal process. The fluorescence spectra and decay curves were measured at room temperature. The fluorescence intensity of F--tridoped samples is about 3 times that for the non F--doped sample. The fluorescence quantum efficiency can be enhanced by 21% when the atomic ratio of F to W was 0.7.     

Simultaneous electrochemical DNA hybridization assay for PAT and FMV 35S gene sequence using quantum dots as labels

An electrochemical method for the simultaneous detection of two different DNA sequences from PAT and FMV 35S gene sequence using CdS and PbS quantum dots （QDs） as labels was described. The QDs were readily functionalized with oligonucleotides as electrochemical DNA probes and selectively hybridized to the complementary sequences immobilized on the microplate. The QDs anchored on the hybrids were dissolved in the solution by the oxidation of HNO3 and further detected by a sensitive differential pulse anodic stripping voltammetric method （DPASV）. The DPASV signals of the oxidation of Cd^2＋ and Pb^2＋ ions present in the solution were different and reflected the identity of corresponding ssDNA targets sequences.     

A purely organic D-π-A-π-D emitter with thermally activated delayed fluorescence and room temperature phosphorescence for near-white OLED

A purely organic D-π-A-π-D type emitter showing thermally activated delayed fluorescence(TADF) and room temperature phosphorescence(RTP) was designed and synthesized by utilizing the benzophenone as an acceptor and the N-phenyl-2-napthylamine as a donor moiety.It exhibits considerable TADF character in doped PMMA film and room temperature phosphorescence with a long lifetime of 74 ms at466 nm in solid state.The devices with the configuration of ITO/Mo_2 O_3(4 nm)/mCP(30 nm)/mCP:x wt%NP2 BP/TmTyPB(60 nm)/LiF(1.5 nm)/AI(100 nm) were prepared by vacuum evaporation to explore their electroluminescent performance.Intere stingly,the non-doped device has obtained near-white emission with a fluorescence emission peak at 475 nm and a phosphore scence emission peak at 563 nm having the CIE coordinate of(0.23,0.32) and the maximum external quantum efficiency of 1.09%.     

One-step synthesis of self-healable hydrogels by the spontaneous phase separation of linear multi-block copolymers during the emulsion copolymerization

Self-healable polyacrylamide-based hydrogels were prepared at room temperature via a one-step emulsion copolymerization of acrylamide(AM),dodecyl 2-methacryIate(DM),and 5-acetylaminopentyl acrylate(AAPA) using sodium dodecyl sulfonate(SDS) as the emulsifier and ammonium persulfate(APS)as the initiator.The produced linear multi-block copolymer chains are composed of randomly-linked hydrophilic polyacrylamide segments(PAM) and hydrophobic segments constituted by DM and AAPA units(P(DM-co-AAPA)).The P(DM-co-AAPA) segments will self-aggregate into hydrophobic microdomains during the polymerization process driven by the hydrophobic interactions,and finally separate from water phase,acting as the crosslinks and leading to the formation of strong hydrogels with a storage modulus as high as 400 Pa.These hydrophobic microdomains will be dissolved in water when the temperature increases to 70℃,resulting in a temperature-responsive reversible sol-gel transition of the prepared hydrogels.Furthermore,the prepared hydrogels have excellent self-healing ability.The broken hydrogels can be automatically healed into a body with a same strength within 2-min's contact.This work provides a new simple way to prepare reversible physical crosslinked hydrogel with high strength and self-healing efficiency.     

Zn_xCd_(1-x)S量子点组成与其光催化活性的关系（英文）

Aqueous colloidal dispersions containing Znx Cd1‐x S quantum dots (QDs) of different x compositions were prepared by precipitating zinc and cadmium acetates with sodium sulphide,in the presence of a cetyltrimethylammonium bromide stabilizer.Ultraviolet‐visible absorption spectroscopy was used to determine the transition energies of the QDs,which in turn were used to calculate their sizes,which depended on their composition.The QD size decreased with increasing Zn content.The photocatalytic activity of the Znx Cd1‐x S QDs was studied by the decomposition of methylene blue under ultraviolet irradiation,at a maximum intensity at 365 nm (3.4 e V).Three different photo‐catalytic activity regions were observed,which depended on the Zn content.The quantum levels of the QDs could be excited by incident irradiation,and influenced the resulting photocatalytic activity.Maximum photocatalytic activity was achieved at x = 0.6,where the QD transition energy was equal to the irradiation photon energy.The photocatalytic efficiency of the QDs depended on their surface area and arrangement of quantum levels,because of the quantum size effect.     

Study of the Electroless Silver Seed Formation on Silicon Surface

The silver seed on silicon was prepared through aqueous I-IF and AgNO3 solution at room temperature. In order to explore the formation process of silver seed on silicon, the methods of open circuit potential with time （OCP-t）, anodic stripping sweep voltammetry （ASV） and scanning tunneling microscope （STM） were used in this work. The procedure of silver nucleus growing into large particles was explained by electro-negativity. The growth mechanism of silver seed on silicon has been presented： at first, the silver monolayer and multilayer firstly grows onto silicon without fully covering the surface at the expense of silicon etching due to the silver seed attracting the electron from silicon, after that, the monolayer coalesces together, forming continuous grain film with some silver atoms diffusing into the silicon and the multilayer still grows thick simultaneously.     

Simple preparation and catalytic properties of ZnO for ozonation degradation of phenol in water

ZnO particles about 200 nm were prepared through a facile hydrothermal method.Compared with single ozonation,the degradation efficiency of phenol increased about 23.7%and the degradation efficiency of intermediates improved about four times in the presence of ZnO at 298 K.In addition,the catalyst had good stability in the ozonation process.The influence of temperature was investigated and it was found that the better catalysis efficiency could be obtained at lower temperature.     

SYNTHESIS OF OLIGOMERS CONTAINING 5-FLUOROURACIL

The condensation oligomers of 5-fluorouracil were prepared by reaction of 2,4-bis-(trimethyl-silyloxy)-5-fluoropyrimidine) with various dicarboxylic chlorides, e.g.The structures of obtained oligomers were characterized by IR and the oligomers were then hydrolyzed in acid, alkaline and neutral media at room temperature respectively. The amount of 5-fluorouracil released was quantitated by measuring its UV absorbance at 265.5nm. However in the case of oligomers containing phenylene moiety, 5-fluorouracil was not detected when the hydrolysis was conducted in acid or neutral medium, while in the case of oligomers containing methylene moiety, hydrolysis proceeded easily in acid, alkaline and neutral media.     

Synthesis and optical properties of thiol-stabilized PbS nanocrystals

Thiol-capped water-soluble PbS nanocrystals (NCs) stabilized with 1-thioglycerol, dithioglycerol, or a mixture of 1-thioglycerol/dithioglycerol (TGL/DTG) were prepared via one-stage synthesis at room temperature. We found that NCs stabilized with a TGL/DTG mixture show efficient and stable infrared photoluminescence centered in the second "biological window" (1050-1200 nm). Under optimized conditions, full width at half-maximum of the PL emission peak was from 70 to 100 nm. PbS NCs were stable to precipitation and aggregation for the time period from 2 to 3 months when stored in the dark under room temperature. Room-temperature photoluminescence quantum efficiency of NCs was from 7 to 10%. When NCs were stored at 37 degrees C, their PL emission red-shifted, consistent with the NC growth.     

聚(N-异丙基丙烯酰胺)水凝胶微球体积相变的研究

窄分散的聚（Ｎ 异丙基丙烯酰胺）水凝胶微球用乳液聚合方法制备，并用动态和静态光散射对其体积相变进行了研究．与水中聚（Ｎ 异丙基丙烯酰胺）线性单链比较，水中凝胶微球的体积相变温度较高，对温度的响应比较平缓．相变是连续的，有别于大块凝胶非连续的体积变化．在体积相变过程中，凝胶微球始终是密度均一的热力学稳定球体．从相变过程网络密度的变化可以确定，绝大部分的水在收缩过程被排了出来，但在紧缩的凝胶微球中仍含有约７０％的水．     

水溶性发光金量子点灵敏检测L-半胱氨酸

室温下一步合成了一种蓝色发光金量子点。 该金量子点具有良好的水溶性和生物相容性,金量子点平均粒径为3.0 nm,在波长305 nm光激发下,发射430 nm蓝色荧光。 实验发现,一定量L-半胱氨酸对金量子点430 nm处荧光发射有显著的增强作用,由此可建立一种简单、迅速、灵敏检测L-半胱氨酸的新方法。在最佳条件下,金量子点荧光强度与L-半胱氨酸在0~4.0 μmol/L浓度范围内呈线性关系,线性相关系数R2=0.9976,对2.0 μmol/L L-半胱氨酸的11次测定结果的相对标准偏差（RSD）为2.8%,以3倍标准偏差计算本法对L-半胱氨酸测定的检出限为5 nmol/L。     

Synthesis and light scattering study of microgels with interpenetrating polymer networks

Monodispersed microgels composed of poly(acrylic acid) (PAAc) and poly(N-isopropylacrylamide) (PNIPAM) interpenetrating polymer networks (IPN) were synthesized by a two-step method, first preparing PNIPAM microgel and then polymerizing acrylic acid that interpenetrates into the PNIPAM network. The growth kinetics of the IPN particle formation was obtained by measuring the turbidity and particle hydrodynamic radius (Rh) as a function of reaction time. IPN and PNIPAM microgels were characterized and compared by dynamic and static light scattering techniques. The concentrated aqueous solutions of the PNIPAM-PAAc IPN microgels exhibit an inverse thermoreversible gelation. In contrast to polymer solutions of poly(NIPAM-co-AAc) that have the inverse thermoreversible gelation, our system can self-assemble into an ordered structure, displaying bright colors. Furthermore, IPN microgels undergo the reversible volume phase transitions in response to both pH and temperature changes associated with PAAc and PNIPAM networks, respectively.     

Facile Assembly of 3D Binary Colloidal Crystals from Soft Microgel Spheres

It still remains a big challenge to fabricate binary colloidal crystals (binary CCs) from hard colloidal spheres, although a lot of efforts have been made. Here, for the first time, binary CCs are assembled from soft hydrogel spheres, PNIPAM microgels, instead of hard spheres. Different from hard spheres, microgel binary CCs can be facilely fabricated by simply heating binary microgel dispersions to 37 °C and then allowing them to cool back to room temperature. The formation of highly ordered structure is indicated by the appearance of an iridescent color and a sharp Bragg diffraction peak. Compared with hard sphere binary CCs, the assembly of PNIPAM microgel binary CCs is much simpler, faster and with a higher “atom” economy. The easy formation of PNIPAM microgel binary CC is attributed to the thermosensitivity and soft nature of the PNIPAM microgel spheres. In addition, PNIPAM microgel binary CCs can respond to temperature change, and their stop band can be tuned by changing the concentration of the dispersion.

     

Switchable photoluminescence of CdTe nanocrystals by temperature-responsive microgels

In the present study, we report a method for preparing a fluorescent thermosensitive hybrid material based on monodisperse, thermosensitive poly( N-isopropyl acrylamide) (PNIPAM) microgels covered with CdTe nanocrystals of 3.2 nm diameter. The CdTe nanocrystals were covalently immobilized on the surface of PNIPAM microgels. The chemical environment around the CdTe nanocrystals was modified by changing the temperature and inducing the microgel volume-phase transition. This change provoked a steep variation in the nanocrystal photoluminescence (PL) intensity in such a way that when the temperature was under the low critical solution temperature (LCST) of the polymer (36 degrees C) the PL of the nanocrystals was strongly quenched, whereas above the LCST the PL intensity was restored.     

Poly (N-isopropylacrylamide) microgel based assemblies for organic dye removal from water: microgel diameter effects

Poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgel based assemblies (aggregates) were synthesized from microgels of various diameters via polymerization of the crosslinker N,N′-methylenebisacrylamide (BIS) in the presence of microgels in solution. We investigated the ability of the respective aggregates to remove the organic, azo dye molecule 4-(2-hydroxy-1-napthylazo) benzenesulfonic acid sodium salt (Orange II) from water at both room and elevated temperatures. The results from the microgel aggregates made from 1.1-μm-diameter [Parasuraman and Serpe. ACS Applied Materials & Interfaces, 2011] microgels were compared to aggregates synthesized from 321-nm and 1.43-μm-diameter microgels. Aggregates made from the same size microgels showed increased uptake efficiency as the concentration of BIS in the aggregates was increased, while for a given BIS concentration, the uptake efficiency increased with increasing microgel size in the aggregate. We attribute this to the “nature” of the aggregates; aggregates have void space between the microgels that can serve as reservoirs for Orange II uptake—the void spaces are hypothesized to increase with larger diameter microgels. By exploiting the thermoresponsive nature of the microgels, and microgel based aggregates, 85.3 % removal efficiencies can be achieved. Finally, all uptake trends for the aggregates, at room temperature, were fit with a Langmuir sorption isotherm model.     

Temperature-modulated photoluminescence of quantum dots

Cadmium sulfide (CdS) quantum dots (QDs) grafted with thermoresponsive poly( N-isopropylacrylamide) chains have been prepared. As the temperature increases, PNIPAM chains shrink and aggregate so that the QDs exhibit enhanced fluorescence emission. At a temperature around the lower critical solution temperature (LCST) of PNIPAM, the fluorescence exhibits a maximum intensity. Our experiments reveal that the fluorescence emission is determined by the interactions between QDs as a function of the interdot distance. The optical interdot distance for the maximum luminescence intensity is approximately 10 nm. The chain length of PNIPAM also has an effect on the luminescence. Short PNIPAM chains are difficult to associate, leading to a large interdot distance, so that the luminescence intensity changes slightly with temperature.     

高密度、长波长InGaAs量子点材料的制备与表征

利用MOCVD外延生长技术, 对InAs/GaAs量子点材料的生长参数进行调节, 获得了高密度(~5×1010 cm^-2)的InAs量子点. 室温荧光光谱表明, 覆盖厚度为5 nm的InGaAs(In组分的摩尔分数为12%)低应变层量子点材料的基态发光波长为1.346 μm, 光谱线宽为24 meV. 研究结果表明, 利用较低温度生长InAs量子点, 结合较高In组分的InGaAs低应变层量子点材料可以实现发光波长红移, 有效地改善材料的光学特性.