由於具有優異的性能，高分子奈米泡材近年來受到廣泛的重視。一般而言奈米泡的泡孔小，因而密度偏高，目前的研究中，密度能達到0.1-0.2 g/cm3的低密度密度的奈米泡材是學界研究重點。其中，若不涉及力學性質的應用，在奈米泡材中引入大泡可以成為一個解決方案，期望能同時降低密度而不喪失奈米泡沫所具有的優異性能。在這項研究中，三種不同商用的PMMA，標記為PMMA-L，PMMA-M和PMMA-H，被用作原料。通過將PMMA-L或PMMA-M與各種wt％的PMMA-H共混來製備PMMA摻混物，以獲得具有不同粘彈性的PMMA，以製造具有雙峰泡孔(bimodal foam)結構的高分子，這項研究的新穎之處在於僅通過混合不同分子量的PMMA，使用CO2作為發泡劑就可以成功地製造具有雙峰結構的泡孔。從泡孔大小分析，可以在PMMA-LH混合物和PMMA-MH摻混物中觀察到泡孔由次微米級降低到奈米級的轉變，我們的研究發現，在PMMA-L中添加30-40 wt％的PMMA-H以及在PMMA-M中添加10-20 wt％的PMMA-H時，會發生明顯的次微米-奈米級泡孔轉變。並且泡孔由閉孔泡逐漸轉變為開孔泡。從流變學的角度分析，我們發現，產生雙峰泡結構，與未發生糾纏的高分子含量有關。

Nanocellular foam and ultramicrocellular foam becomes an interesting material to be explored due to the superior properties offered. Nanofoam with low foam density in the range of 0.1-0.2 g/cm3 is a good candidate to be used as a thermal insulating material, but still challenging to be obtained. Introducing big bubbles to nanofoam can become one solution to obtain low density without losing the insulating and mechanical properties possessed by nanofoam. In this study, three grades of PMMA with different molecular weight, labeled as PMMA-L, PMMA-M, and PMMA-H were used as the raw materials. PMMA blends were prepared by blending either PMMA-L or PMMA-M with various wt% of PMMA-H, labeled as “PMMA-LH” or “PMMA-MH,” to obtain PMMA matrices with varied viscoelastic properties. The novelty of this study lies in the bimodal foam production only by blending one type of polymer with different molecular weight, thus eliminate dispersion and compatibility problems. Bimodal foams were successfully fabricated by solid-state foaming using CO2 as a blowing agent. Based on cell size analysis, the transition from ultramicrocellular to nanocellular foam can be observed in PMMA-LH blends and PMMA-MH blends at certain PMMA-H content, which is defined as the critical point. It was found that the critical points of PMMA-LH occur at the addition of 30 to 40 wt% PMMA-H, while for PMMA-MH occur at the addition of 10 to 20 wt% PMMA-H. Moreover, in those critical points, cell morphology transition from closed cell to open cell was also observed and such a result could be explained by estimating the non-entangled percentage of PMMA.

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