We have developed two different methods for fabrication of hierarchically porous composites which are environmentally friendly, inexpensive and give a large amount of control over the composite microstructure. The hydrogel bead templating method involved introducing a slurry of hydrogel beads as templates into a gypsum slurry that, upon drying, left pores reflecting their size. The overall porosity reflected the volume percentage of hydrogel bead slurry used. Using mixtures of large and small hydrogel beads in controlled volume ratios as templates, we produced hierarchically porous gypsum composites that had tailorable microstructures at the same overall porosity. The viscous trapping method involved utilisation of an aqueous solution of a thickening agent, methylcellulose, during the setting process of an aqueous gypsum slurry. The methylcellulose solution traps the hydrated gypsum particles in solution and stops their sedimentation as the continuous gypsum network forms, allowing formation of an expanded microstructure. This method allows a good degree of control over the porosity which is directly controlled by the volume percentage of methylcellulose solution used. The mechanical strength of the porous composites decreased as the porosity increased. The composites with smaller pores had increased compressional strength and Young's modulus compared to the ones produced with large pores, at constant porosity. The hierarchically porous gypsum composites showed an intermediate Young's modulus and an increased compressional strength. We also studied the sound transmission loss of these hierarchically porous composites. We found that the ones produced by the viscous trapping method had a lower sound transmission loss over the frequency range investigated as the overall porosity was increased. We demonstrated the effect of the composite pore size at a constant porosity on the sound transmission loss. Our experiments showed that porous composites with large pores showed increased sound transmission loss at lower sound frequencies compared to those with small pores. As the sound frequency increased, the difference between their STL spectra decreased and at the higher frequency range (>2420 Hz) the composites with smaller pores began to perform better. The hierarchically porous composite had an intermediate STL spectrum, suggesting a way of tailoring the hierarchically porous structure at constant porosity to achieve desired sound insulating properties at certain frequencies.

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水凝胶模板和粘滞捕集技术生产的多层多孔复合材料的声传输损失

我们已经开发了两种不同的制造分层多孔复合材料的方法，这些方法对环境友好，价格低廉，并且可以对复合材料的微结构进行大量控制。水凝胶珠子模板化方法涉及将水凝胶珠子的浆料作为模板引入石膏浆料中，该石膏浆料在干燥后留下反映其尺寸的孔。总孔隙率反映了所使用的水凝胶珠粒浆料的体积百分比。使用体积比可控的大大小小的水凝胶珠粒的混合物作为模板，我们生产了在相同总孔隙率下具有可定制微结构的分层多孔石膏复合材料。粘性捕集方法涉及在含水石膏浆料的凝固过程中利用增稠剂甲基纤维素的水溶液。甲基纤维素溶液将水合石膏颗粒捕获在溶液中，并在连续的石膏网络形成时停止其沉淀，从而允许形成膨胀的微结构。该方法可以很好地控制孔隙度，该孔隙度直接由所使用的甲基纤维素溶液的体积百分比控制。多孔复合材料的机械强度随着孔隙率的增加而降低。在恒定的孔隙率下，与具有较大孔的复合材料相比，具有较小孔的复合材料具有更高的抗压强度和杨氏模量。分层多孔石膏复合材料表现出中等的杨氏模量和增加的抗压强度。我们还研究了这些分层多孔复合材料的声传输损耗。我们发现，随着总孔隙率的增加，在整个研究的频率范围内，通过粘性捕集法生产的声波具有较低的传声损耗。我们证明了在恒定孔隙率下复合孔径对传声损失的影响。我们的实验表明，与具有小孔的那些相比，具有大孔的多孔复合材料在较低的声音频率下显示出增加的声音传输损失。随着声音频率的增加，它们的STL频谱之间的差异减小，并且在较高的频率范围（> 2420 Hz）下，具有较小孔的复合材料开始表现更好。分层多孔复合材料具有中等的STL光谱，