Study on novel hydrogels based on thermosensitive PNIPAAm with pH sensitive PDMAEMA grafts

A series of novel hydrogels based on poly(N-isopropylacrylamide) (PNIPAAm) with pendant poly(N-(2-(dimethylamino) ethyl)-methacrylamide) (PDMAEMA) grafts were designed and synthesized. The influence of the pendant PDMAEMA grafts on the properties of the resulted hydrogels was examined in terms of morphology observed by scanning electron microscopy (SEM), thermal property characterized by differential scanning calorimetry (DSC) and shrinking/swelling kinetics upon external temperature changes. In comparison with the conventional PNIPAAm hydrogels, resulting hydrogels presented favorable pH sensitivity as well as improved thermosensitive properties, including enlarged water containing capability at room temperature and faster shrinking/swelling rate upon heating. In addition, fish DNA, used as a model drug, was loaded into the hydrogels, and the controlled release behavior of the drug-loaded hydrogels at different temperatures (22 and 37 °C) was further studied.     

Temperature sensitive dendrite-shaped PNIPAAm/Dex-AI hybrid hydrogel particles: formulation and properties

The development of a new temperature sensitive hydrogel particle having biodegradable crosslinkages, composed of poly(N-isopropylacrylamide)/dextran-allyl isocyanate (PNIPAAm/Dex-AI) was prepared through precipitation polymerization. Dex-AI was used as a precursor as well as a biodegradable crosslinker for forming the network particles. Characterization data showed that these PNIPAAm/Dex-AI hydrogel particles had an average hydration diameter around 1.0 mm and showed a dendrite-like heterogeneous morphology with two different porous microstructures. The hydrogel particles exhibited a transition temperature or lower critical solution temperature (LCST) at around 25.7 °C through differential scanning calorimetry (DSC) measurement or temperature dependence study of particles volume. The freeze-dried particles swelled quickly when socked in distilled water at room temperature and large amounts of water were stored within the network before reaching the stable swollen state.     

Separation of bonito extract by composite UF membranes of sulfonated polysulfone coated on ceramics

Separation of ingredients in bonito extract was studied by a composite UF membrane of ceramic/sulfonated polysulfone (SPS). The bonito extract mainly contained inosine-5′-monophosphate (IMP), glutamic acid as a tasty ingredient and hypoxanthine, histidine as a putrefaction ingredient. The composite membrane showed a high rejection against negatively charged IMP, but permeated non-charged hypoxanthine. This is because of the negatively charged repulsion between the membrane and the solute. The permeation of amino acid could be controlled using the difference in isoelectric points of amino acids themselves. When the amino acid solution was filtrated by the composite membrane at pH 7, glutamic acid was rejected and no histidine was rejected. The charges of composite membrane were found to have an effect on the separation of ingredients in bonito extract.The composite membrane was stable within a wide pH range from 3 to 9, and had a thermal durability under 353 K.     

Fast synthesis of temperature-sensitive PNIPAAm hydrogels by microwave irradiation

A novel method, microwave irradiation synthesis, is proposed for the preparation of thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels. The PNIPAAm hydrogels were separately synthesized by using microwave irradiation method and water-bath heating method. Chemical groups, lower critical solution temperature (LCST) and surface morphology of these PNIPAAm hydrogels were characterized by FT-IR, DSC and SEM. Swelling ratios of the gels were measured gravimetrically in the temperature range from 10.0 to 60.0 °C. Results showed that (1) the use of microwave irradiation can greatly shorten the reaction time required for PNIPAAm hydrogel synthesis from several hours to several minutes in comparison with water-bath heating method, and obviously improve the yields of the PNIPAAm gels, which were up to 99% after a short reaction time; (2) SEM micrographs and textural measurement revealed that the gels synthesized using microwave irradiation had more porous structure, and their average pore sizes and specific surface areas were larger than those of the gels synthesized using water-bath heating method; and (3) the PNIPAAm hydrogels synthesized using microwave irradiation had much higher swelling ratios at 10.0 °C below the LCST, and had lower swelling ratio at 60.0 °C above the LCST compared to the hydrogels synthesized by water-bath method.     

胶原温敏半互穿水凝胶的制备及其对L929细胞行为的影响

以Ⅰ型胶原和N-异丙基丙烯酰胺(NIPAAm)为主要原料,将Ⅰ型胶原引入到PNIPAAm交联网络中,制得一种具有温度响应性的半互穿水凝胶.通过红外光谱(FTIR)和扫描电镜(SEM)对PNIPAAm/CollagenⅠ半互穿水凝胶进行成分和结构的表征;通过溶胀测试和示差扫描量热法(DSC)研究了半互穿水凝胶的温敏特性,并对其表面亲疏水性进行分析;在水凝胶表面培养L929细胞,研究其增殖脱附行为.结果表明,PNIPAAm/CollagenⅠ半互穿水凝胶具有良好的温度响应性和生物相容性,与PNIPAAm水凝胶相比,PNIPAAm/CollagenⅠ半互穿水凝胶表面更有利于L929细胞的黏附增殖.将温度降至临界温度(LCST,32℃)以下,细胞从凝胶表面自发脱附.细胞染色表明,与胰蛋白酶消化相比,降温脱附的细胞损伤少,活性更高,表明PNIPAAm水凝胶中引入胶原后,生物相容性得到改善.     

Fractionation of natural and model egg-white protein solutions with modified and unmodified polysulfone UF membranes

Mostly, fractionation in laboratory experiments have been carried out with single or binary model protein solutions. The question has arisen whether these experiments can be representative for industrial and natural biological solution fractionations. In this study, a comparison of single, ternary, and natural egg-white solutions is made. Thus, fractionation of ternary mixtures of ovalbumin, conalbumin, and lysozyme and natural egg-white protein solutions at different pH and two ionic strengths was studied with unmodified and UV modified polysulfone ultrafiltration membranes. The modified membranes had an increased initial water flux and their zeta potentials were more negative than those of the unmodified membranes. The UV modified membranes became more hydrophilic due to the formation of carboxylate and sulphonate groups. In ultrafiltration of single protein solutions the highest flux reduction and the lowest protein retention were obtained with ovalbumin at its isoelectric point (pH 4.8). At this pH lysozyme and conalbumin were positively charged and highly retained because of effective size exclusion due to charge repulsion. Also, in fractionation of ternary mixtures and natural egg-white solutions, ovalbumin was the major protein that could permeate the membranes at pH 4.8. Ovalbumin was highly retained due to charge repulsion at all other tested pH values. Retention of ovalbumin and transmission of lysozyme increased in ultrafiltration of egg-white solutions in the presence of salt at pH 4.8. It could be seen clearly that the behaviour of ovalbumin being the most abundant protein, mainly determined the fractionation properties of the mixtures. Comparison of the results from fractionation of solutions of ternary model proteins and natural egg-whites showed that retention was lower and flux reduction smaller in UF of the natural egg-white solutions. This was probably due to interaction of proteins or/and salts presents in the natural egg-white solutions, which could not be modelled by the main protein components. On the whole it seemed as the proteins studied behaved much in the same way in mixtures as separately.     

UF6分子的模型伸缩振动能级的计算

利用一个四参数非线性模型,对处于电子基态下的XY6型分子的X-Y键的伸缩振动进行了描述,并将其应用于计算UF6分子中U-F键的伸缩振动能级.计算中引入的模型Hamilton算符所包含的描述U-F键非谐振动的参数λ和描述U-F键之间的偶极-偶极相互作用参数ε1, ε2由实验值得出,波函数|ψn〉按形式为|n,α〉=|n1〉|n2〉|n3〉|n4〉|n5〉|n6〉的基函数集展开,从而把复杂的Hamilton方程转化为简单的矩阵代数方程.结果显示,该非线性模型能够较好地描述UF6分子的振动( 计算误差在1.0 cm-1之内 ),同时合理地预测了一些至今还未观测到的能级值.     

Surface modification of cotton fabric with dual‐responsive PNIPAAm/chitosan nano hydrogel

The present study deals with preparing stimuli‐responsive poly N‐isopropyl acryl amide/chitosan (PNCS) nano hydrogel and looks into their effects as a surface modifying system of cotton fabric. The semi‐batch surfactant‐free emulsion polymerization method was proposed to reduce the size of particle and synthesis of PNCS nano particles. Fourier transform infrared, nuclear magnetic resonance, differential scanning calorimetry, scanning electron microscopy and dynamic light scattering methods confirmed the nano size of synthesized PNCS particles and sensitivity of these nano particles to the different temperature and pH, respectively. The water retention capacity (WRC) and carboxyl content of modified cotton with PNCS nano particles were assessed through the central composite design. The bounded PNCS nano particles to the surface of cotton fabrics made them responsive to these dual stimuli. The results demonstrated the dual effect of BTCA amount on WRC. Increase of the amount of BTCA itself led to the decrease of the WRC of modified cotton, but in the presence of PNCS, WRC was significantly increased. Copyright © 2013 John Wiley & Sons, Ltd.     

The polyurethane membranes with temperature sensitivity for water vapor permeation

The size and shape of free-volume holes available in membrane materials control the rate of gas diffusion and its permeability. Based on this principle, two segmented thermo-sensitive polyurethane (TSPU) membranes with functional gates, i.e. the ability to sense and respond to external thermo-stimuli, were synthesized and used for water vapor controllable permeation. Differential scanning calorimetry (DSC), positron annihilation lifetimes (PAL), water swelling and water vapor permeability (WVP) were used to evaluate how the structure of the polyurethane (PU) and the temperature influence the free-volume holes size and the water vapor permeability (WVP) of the PU membranes. DSC study reveals that TSPU with a glass transition or a crystalline transition reversible phase shows an obvious phase-separated structure and a phase transition temperature (defined as switch temperature, T_s). PAL study indicates that the free-volume holes size of TSPU is closely related to the T_s. When the temperature is higher than the T_s, the ortho-positronium (o-Ps) lifetime (τ₃) and the average radius (R) of free-volume holes of TSPU membrane increase dramatically. As a result, the WVP of TSPU membrane shows a dramatic increase. Additionally, the water swelling and the WVP of TSPU membrane are found to depend on the inner structure of the polymer, and they also give different responses to temperature variation. When the temperature is higher than the T_s, there is a significant increase of WVP from 3.80 kg/m² day to 7.63 kg/m² day for TSPU(a) and from 4.30 kg/m² day to 8.58 kg/m² day for TSPU(b), respectively. Phase transition accompanying significant changes in free-volume holes size and WVP can be used to develop “smart membranes” with functional gates and controllable gas permeation.     

Radiation preparation and thermo-response swelling of interpenetrating polymer network hydrogel composed of PNIPAAm and PMMA

Interpenetrating polymer network (IPN) hydrogel composed of hydrophilic poly(N-isopropylacrylamide) (PNIPAAm) and hydrophobic poly(methyl methacrylate) (PMMA) were synthesized by sequential IPN method using γ-rays from ⁶⁰Co source. Compared with pure PNIPAAm hydrogel, PNIPAAm/ PMMA IPN hydrogel not only behaved with obvious temperature sensitivity, but also had higher mechanical strength. The shrinking rate of the prepared IPN hydogel was slower than that of PNIPAAm hydrogel and the relative shrinkage was higher than that of PNIPAAm hydrogel. The IPN hydrogel with less PMMA was not stable while with more PMMA it was quite stable. In addition, the release of Methylene Blue (MB) from the IPN hydrogel was slower than that from PNIPAAm hydrogel as well.     

Low temperature plasma treatment of asymmetric polysulfone membranes for permanent hydrophilic surface modification

A plasma treatment that renders asymmetric polysulfone membranes permanently hydrophilic is reported. Our modification strategy entails treating these membranes downstream from an inductively coupled rf plasma source. Contact angle measurements confirm that the membranes are completely wettable with water as a result of H₂O plasma treatment. More importantly, the hydrophilic modification is permanent as plasma-treated membranes remain wettable for more than 16 months after plasma treatment. This treatment achieves the desired change in wettability for microporous as well as ultrafiltration polysulfone membranes, illustrating the universality of this method. XPS analysis of treated membranes demonstrates this dramatic change in wettability is a result of chemical changes in the membrane induced by plasma treatment. Moreover, the membrane modification is complete as the plasma penetrates the thickness of the membrane, thereby modifying the entire membrane cross-section.     

温敏型微球表面接枝交联复合凝胶的制备及性能

为改善高分子微球复合凝胶响应速率慢及韧性差的缺陷,采用非交联温敏型疏水单体组装的高分子微球作为交联剂,在不外加交联剂的条件下制备微球表面接枝交联聚丙烯酰胺复合凝胶.由于微球内部无化学交联结构,因此可通过自身可逆性结构及形态改变对复合凝胶机械性能和刺激响应特性进行调控.复合凝胶具有良好的韧性,断裂伸长率和断裂强度分别可达2400%和80 k Pa,且凝胶机械强度可通过温度进行调控.由于温敏型微球交联点的存在,采用非敏感型聚丙烯酰胺为基质的复合凝胶对温度具有良好的响应性,其响应速率较传统聚N-异丙基丙烯酰胺有机凝胶提升5~10倍.     

Immobilization of invertase on porous membranes made from modified polysulfone

The activity of invertase that was immobilized within asymmetric ultrafiltration membranes was determined as a function of the immobilization mode such as adsorption, ionic interaction and covalent bonding. For these different bonding possibilities adequate membranes were prepared from chemically modified polysulfone fitted out with the corresponding substituents. The amount of enzyme was lowest for adsorption and highest for chemical fixation. In the latter case spacers were useful because substituents adjacent to the polymer backbone caused a relatively large loss of activity which can stem either from chemical reaction or from the hampered development of the appropriate conformational structure. Compared to the activity of the native invertase the fixation yielded a remarkable reduction of activity which was compensated for by the very extended stability of the bonded enzyme.     

Benchmark Calculations on the Atomization Enthalpy, Geometry and Vibrational Frequencies of UF6 with Relativistic DFT Methods

Benchmark calculations on the molar atomization enthalpy, geometry, and vibrational frequencies of uranium hexafluoride （UF6） have been performed by using relativistic density functional theory （DFT） with various levels of relativistic effects, different types of basis sets, and exchange-correlation functionals. Scalar relativistic effects are shown to be critical for the structural properties. The spin-orbit coupling effects are important for the calculated energies, but are much less important for other calculated ground-state properties of closed-shell UF6. We conclude through systematic investigations that ZORA- and RECP-based relativistic DPT methods are both appropriate for incorporating relativistic effects. Comparisons of different types of basis sets （Slater, Gaussian, and plane-wave types） and various levels of theoretical approximation of the exchange-correlation functionals were also made.     

Plasticization of ultra-thin polysulfone membranes by carbon dioxide

Plasticization of gas separation membranes by carbon dioxide permanently alters their performance and increases the possibility of membrane failure. This is amplified in ultra-thin composite membranes, where the active polymeric layer is less than 2 μm. Here, the plasticization influence of CO₂ is measured on ultra-thin polysulfone composite membranes for a range of active layer thicknesses, at four temperatures. The resulting permeability–pressure isotherms demonstrate plasticization occurs for all thicknesses at pressures lower than has been reported for dense membranes. These isotherms were quantitatively fitted with an expanded dual-sorption model that takes into account plasticization of the membrane. The plasticization potential of CO₂ for polysulfone was found to increase with reduced active layer thickness. Similarly, the plasticization potential of CO₂ was found to decrease with temperature. These results are consistent with similar research that shows that thin films behave differently to dense membranes.     

Kinetics of bonded invertase: asymmetric polysulfone membranes

Asymmetric flat ultrafiltration membranes made from bromomethylated polysulfone were used to fix invertase chemically. The invertase reactivity of these membranes was compared with those where enzyme bonding was achieved by reacting bromomethylated polysulfone with ethylene diamine and glutaric dialdehyde which act as spacers. In both cases the invertase fixation was carried out such that its concentration at the surface facing the saccharose feed solution could be neglected The kinetic behavior of the immobilized invertase was modelled by investigating the influence of diffusive and of convective transport across the membranes. Considering axial back-mixing of the convective flow within the membrane, the reaction can be simulated at low substrate concentrations. The heterogeneous distribution of the enzyme within the membrane matrix prevents us from calculating the kinetic data of the enzymatic reaction over the entire range of parameters.     

Thermo-responsive and antifouling PVDF nanocomposited membranes based on PNIPAAm modified TiO2 nanoparticles

A novel hydrophilic nanocomposite additive(TiO2-g-PNIPAAm) was synthesized by the surface modification of titanium dioxide(TiO2) with N-isopropylacrylamide(NIPAAm) via "graft-from" technique. And the nanocomposite membrane of poly(vinylidene fluoride)(PVDF)/TiO2-g-PNIPAAm was fabricated by wet phase inversion. The graft degree was obtained by thermo-gravimetric analysis(TGA). Fourier transform infrared attenuated reflection spectroscopy(FTIR-ATR) and X-ray photoelectronic spectroscopy(XPS) characterization results suggested that TiO2-g-PNIPAAm nanoparticles segregated on membrane surface during the phase separation process. Scanning electron microscopy(SEM) was conducted to investigate the surface and cross-section of the modified membranes. The water contact angle measurements confirmed that TiO2-g-PNIPAAm nanoparticles endowed PVDF membranes better hydrophlilicity and thermo-responsive properties compared with those of the pristine PVDF membrane. The water contact angle decreased from 92.8° of the PVDF membrane to 61.2° of the nanocompostie membrane. Bovine serum albumin(BSA) static and dynamic adsorption experiments suggested that excellent antifouling properties of membranes was acquired after adding TiO2-gPNIPAAm. The maximum BSA adsorption at 40 °C was about 3 times than that at 23 °C. The permeation experiments indicated the water flux recover ratio and BSA rejection ratio were improved at different temperatures.     

Performance improvement of polysulfone ultrafiltration membrane by blending with polyaniline nanofibers

Polyaniline (PANI) nanofibers were used to improve hydrophilic property and permeability of polysulfone (PS) membrane. PS membrane and PS/PANI nanofibers blended membranes with different PANI–PS mass ratios (1, 5, 10, and 15 wt.%) were prepared by phase inversion process. The blended membranes showed similar bovine serum albumin (BSA) and albumin egg (AE) rejections to PS membrane. The blended membranes had larger porosity and better hydrophilic property than PS membrane, which caused the improvement of their permeability. Pure water fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 1.6 and 2.4 times that of PS membrane, respectively. During the filtration of BSA solution, the blended membranes had slower flux decline rate than PS membrane. Moreover, stable permeate fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 2.0 and 2.5 times that of PS membrane, respectively. Compared with PS membrane, mechanical property and thermal stability of the blended membranes with less PANI–PS mass ratio, e.g. 1 wt.%, had no obvious change. For the blended membrane with PANI–PS mass ratio of 15 wt.%, breaking strength increased 28% and elongation at break decreased 30.6%.     

Modification of polysulfone membranes 4. Ammonia plasma treatment

The effect of NH₃ and NH₃/Ar plasma on ultrafiltration polysulfone membranes have been studied. Results of contact angle, FTIR-ATR and X-ray photoelectron spectroscopy experiments clearly showed that both plasmas introduced hydrophilic, nitrogen- and oxygen-containing moieties on the polymer surface and that NH₃/Ar plasma was more efficient. That plasma was also more aggressive--signs of strong etching could be seen on the SEM pictures. Redeposition of etched material seemed to take place inside the pores. On the contrary, ammonia plasma was soft and caused cleaning the surface and pores enlargement. Performance of ammonia plasma modified membranes was greatly improved and independent on solution pH. The last observation proved amphoteric character of the surface. NH₃/Ar plasma treatment gave membranes of acidic surface and filtration indices not so good as for ammonia plasma.     

Effect of gelation conditions on gas separation performance for asymmetric polysulfone membranes

Asymmetric gas separation membranes were prepared by the phase inversion technique under different gelation conditions from polysulfone/N,N-dimethylacetamide (DMAc) solutions. The dual bath method was employed to control the skin layer properties: the cast film was immersed in 2-propanol bath and water bath in sequence. The membranes were characterized by the permeance of oxygen and nitrogen gases and the observation with scanning electron microscopy (SEM). A thin layer of silicone rubber (PDMS) was laminated on the surface of each asymmetric polysulfone membrane to eliminate the effect of defects in the skin layer. The oxygen permeance was inversely proportional to the square root of immersion time in the first (2-propanol) bath. The skin layer thickness determined by SEM observation increased with an increase in the immersion time in the first bath. For a given immersion time, the oxygen permeance decreased with an increase in the polymer concentration in the casting solution. Selectivity of oxygen over nitrogen also depended both on the immersion time in the first bath and the polymer concentration.