Ultralight Si3N4 ceramic foams have been successfully prepared through particle‐stabilized foams method, which is based on the adsorption of in situ hydrophobized Si3N4 particles to the liquid/air interface of the foams. Here, we firstly used a long‐chain surfactant cetyltrimethylammonium chloride to render the Si3N4 particles partially hydrophobic. By tailoring the surfactant concentration and pH values of the suspensions, the wet foams were stabilized to avoid coarsening and coalescence. SEM results show that the Si3N4 ceramic foams possess single strut walls with elongated β‐Si3N4 grains interlocking with each other, and their pores are uniform with an average pore size of 95 μm. The obtained ceramic foams maintain compressive strength of 1.34 ± 0.13 MPa with porosity of 92.0%, when the suspension contains 3 mmol/L surfactant at the pH of 11.0. 相似文献
Ceramic/polyaniline composite porous membranes are successfully made by diffusing ammonium peroxydisulfate and aniline into inorganic membrane disks. The ceramic disks are fabricated by mixing CMC, water, kaolin and alumina followed by the processes of drying, milling, sieving, pressing at 4000 pounds, and firing. The pore size of the disk is approximately 1 m.When the concentration of the oxidant is 0.25 M and that of the monomer is 1 M, the incorporation of polyaniline into the ceramic disks levels off after about 40 hours. The maximum incorporation percentage is approximately 4.86 wt% (0.18 g of polymer/3.7 g of disk). Characterizations of the ceramic disk and its composites include N2-flow tests, solubility tests, BET, SEM, OM and acid diffusion studies. Nitrogen-flow tests indicate that the incorporated polyaniline is structurally unstable. However, after applying N2 gas of 23 psig for about 40 min, no further degradation is observed in these composite membranes even under 40 psig of N2 gas. BET shows that the surface area of the composite is greater than that of the ceramic disk. SEM reveals that polyaniline is grown on the surface of the pores of the ceramic disks. Time constants, corresponding to the time when the pH value reaches 36.8% of the initial value, are estimated from the results of acid diffusion studies. The magnitude of the time constant is in the following order: ceramic/Peani base > ceramic/Peani salt > ceramic/Pani base > ceramic/Pani salt > plain ceramic. 相似文献
The demand for wearable electronics has resulted in an increasing interest in the development of functional fibers, with a specific focus upon the development of electrically conductive fibers incorporable into garments. However, the production of thermally conductive fibers for heat dissipation has been largely neglected. Owing to the very rapid development of miniaturized wearable electronics, there is an increasing need for the development of thermally conductive fibers as heat sinks and thermal management processes. In this study, thermally conductive but electrically insulating boron nitride nanopowder (BNNP) fillers are used to effectively enhance the thermal conductivity and mechanical properties of elastomeric polyurethane fibers. Thermal conductivity enhancement of more than 160% is achieved at very low loadings of BNNP (less than 5 wt%) with an improvement in the mechanical properties of the unmodified fiber. These thermally conductive fibers are also incorporated into 3D textile structures as a proof of processability. 相似文献
研究出一种具有较好稳定性、保温性能、力学性能和阻燃性能的酚醛树脂(PF)/可发性聚苯乙烯(EPS)复合泡沫塑料。在PF泡沫塑料颗粒基体中加入EPS发泡颗粒,充分混合固化,使PF泡沫塑料颗粒与EPS发泡颗粒紧密结合,EPS发泡颗粒被PF泡沫塑料颗粒包围并相互隔离,再用模具发泡成型得到该复合泡沫塑料。实验结果表明,PF的含量越高,稳定性、力学性能和阻燃性能越好,保温性能呈现先升高后下降的趋势,当PF的含量为80%时,PF/EPS复合泡沫塑料的表观密度为38.4 kg/m3,热导率为0.024 W/(m·K),弯曲强度为0.134 k Pa,压缩强度为323 k Pa,极限氧指数为47.9%,烟密度等级小于15,热释放速率峰值小于250 k W/m2,综合性能最好。 相似文献
Necking propagation (NP) is an important phenomenon that is facilitated by the superductility of many materials, although necking is often considered to be a type of unstable and heterogeneous deformation under tensile loading. In this study, the NP of samples produced with injection molding of polypropylene (PP) and high-density polyethylene (HDPE) blends with or without a blowing agent was investigated by standard tensile testing, and the foam morphology and cellular structure were characterized with scanning electron microscopy. It was found that the foam parts fabricated with the PP/HDPE blends had the ability to be superductile under a low tensile test speed, which was attributed to the necking spreading throughout the tested gauge section stably and reliably. However, the NP of the foam PP/HDPE blend samples strongly depended on the distribution of the cellular foam. To investigate the relationship between the cellular structure and NP, a design of experiment approach based on the Taguchi method was used to fabricate many samples with different foam structures. The tensile test results of these samples suggested that the cellular uniformity, which was determined based on the statistical results of the fracture surface morphology, played an important role in the NP. The results suggested that there is a close relationship between the NP and the cellular uniformity. Using nonlinear fitting, it was straightforward to obtain a model between the NP length and cellular uniformity index for PP/HDPE molded foam parts. 相似文献
MWNTs of various sizes were compounded into SPI matrix by solution mixing and then compression‐molded into nanocomposite sheets, which were characterized by XRD, SEM, TEM, and tensile and water uptake testing. The resultant nanocomposites showed improved mechanical performance and higher water resistance depending on MWNT size and content. This work details a strategy to achieve improved performance, especially in terms of mechanical properties, using MWNTs of various sizes to regulate the entanglement and penetration between SPI and MWNTs.
Changing the pore morphology of hydrogels can be an effective strategy to modulate their drug release profiles. Herein, Pluronic F127 was used to change the three-dimensional pore morphology of crosslinked poly(N-isopropylacrylamide-co-acrylic acid) (P[NIPAm-co-AAc]) hydrogels. F127 reduced the pore diameters from 20 ± 4 to 2.9 ± 0.4 μm and from 11 ± 1 to 1.4 ± 0.4 μm in hydrogels synthesized at 8 and 30°C, respectively. Small-angle X-ray scattering indicates that the segregation of the F127 during the polymerization process induces F127 phase transitions from unimers (at 8°C) or cubic-packed micelles (at 30°C) to a lamellar structure. P(NIPAm-co-AAc) hydrogels charged with S-nitrosoglutathione (GSNO), released nitric oxide (NO) spontaneously during hydration. The decrease in the pore diameter led to a twofold to threefold increase in the rate of water absorption and a fourfold to sixfold increase in the rate of NO release of the hydrogels. F127 can be used to change the pore morphology of P(NIPAm-co-AAc) hydrogels, with concomitant changes in their rate of hydration and NO release from GSNO, opening a new perspective for their use in topical NO delivery. 相似文献