聚丙烯酸相对分子质量对聚苯乙烯复合乳粒形变的影响

Influences of Poly(acrylic acid) Molecular Weight on Deformation of Polystyrene Compound Droplets

为了改善激光惯性约束聚变用厚壁聚合物空心微球球形度和壁厚均匀性,文中在外水相(W2)引入聚丙烯酸(PAA),对比了不同相对分子质量PAA(L-PAA,H-PAA)与传统界面改性剂聚乙烯醇(PVA)对复合乳粒形变的影响及作用机理。结果表明,PVA通过亲疏水基团可有效稳定直径900μm复合乳粒,但大幅度降低了油水界面张力,当乳粒直径增加,油相和内水相Laplace压力降低,变形增加,PVA对直径1900μm复合乳粒稳定性下降;与PVA体系相比,LPAA体系油水界面张力大,但黏度与PVA体系基本相同,导致乳粒形成时维持力大于剥离力,不利于乳粒形成,且LPAA分子链相对较短,空间位阻较小,复合乳粒易融合、合并;H-PAA分子链长,空间位阻较大,不仅对大小直径复合乳粒稳定效果明显,而且其油水界面张力大,有利于乳粒球形化,提高了高球形度PS微球的产率。

To improve the sphericity and wall thickness uniformity of thick-walled polymer shells used for laser inertial confinement fusion, poly（acrylic acid） （PAA） was added in the external phase （W2）. The effects of PAAs with different molecular weights and poly（vinyl alcohol） （PVA） on deformation of the PS compound droplets were investigated. The experimental results show that PS compound droplets with 900μm diameter prepared with PVA are stable due to the hydrophilic and hydrophobic groups, but these groups signifcantly reduce the interracial tension, the Laplace pressure decreases with increasing the diameter, leading to the deformation increase and PS compound droplets with 1900μm diameter breaking up, forming PS droplets without the inner water （W1）. The interracial tension of PAA with lower molecular weight （L-PAA） solution is much higher than that of the PVA solution, but their viscosities are almost the same, so the drag force for forming the droplet is much lower than that force for preventing it from being separated from the tube tip, resluting in that the formation of the droplets is difficult. Moreover, two or more PS compound droplets prepared with L-PAA coalesce to form bigger droplets in a short time after the generation, probably due to relative shorter chain. PS compound droplets with both 900 tim and 1900/,m diameter prepared with PAA with higher molecular weight （H-PAA） are stable, probably due to the steric stabilization of their longer chains. Moreover, compared with PVA system, H-PAA improves the sphericity of these PS shells, due to the higher interracial tension.