School of Chemical and Process Engineering, University of Leeds , Leeds, U.K.
Faculty of Engineering, Architecture and Information Technology, The University of Queensland , St. Lucia, QLD, Australia.
Langmuir. 2017 Jul 5;33(26):6528-6539. doi: 10.1021/acs.langmuir.7b00723. Epub 2017 Jun 21.
The current study examined the foaming behavior of poly(vinylpyrrolidone) (PVP)-silica composite nanoparticles. Individually, the two components, PVP and silica nanoparticles, exhibited very little potential to partition at the air-water interface, and as such, stable foams could not be generated. In contrast, combining the two components to form silica-PVP core-shell nanocomposites led to good "foamability" and long-term foam stability. Addition of an electrolyte (NaSO) was shown to have a marked effect on the foam stability. By varying the concentration of electrolyte between 0 and 0.55 M, three regions of foam stability were observed: rapid foam collapse at low electrolyte concentrations, delayed foam collapse at intermediate concentrations, and long-term stability (∼10 days) at the highest electrolyte concentration. The observed transitions in foam stability were better understood by studying the microstructure and physical and mechanical properties of the particle-laden interface. For rapidly collapsing foams the nanocomposite particles were weakly retained at the air-water interface. The interfaces in this case were characterized as being "liquid-like" and the foams collapsed within 100 min. At an intermediate electrolyte concentration (0.1 M), delayed foam collapse over ∼16 h was observed. The particle-laden interface was shown to be pseudo-solid-like as measured under shear and compression. The increased interfacial rigidity was attributed to adhesion between interpenetrating polymer layers. For the most stable foam (prepared in 0.55 M NaSO), the ratio of the viscoelastic moduli, G'/G″, was found to be equal to ∼3, confirming a strongly elastic interfacial layer. Using optical microscopy, enhanced foam stability was assessed and attributed to a change in the mechanism of foam collapse. Bubble-bubble coalescence was found to be significantly retarded by the aggregation of nanocomposite particles, with the long-term destabilization being recognized to result from bubble coarsening. For rapidly destabilizing foams, the contribution from bubble-bubble coalescence was shown to be more significant.
当前研究考察了聚（N-乙烯基吡咯烷酮）（PVP）-二氧化硅复合纳米粒子的发泡行为。单独地，这两种成分，PVP 和二氧化硅纳米粒子，在空气-水界面上几乎没有表现出分离的潜力，因此，无法产生稳定的泡沫。相比之下，将这两种成分组合形成二氧化硅-PVP 核壳纳米复合材料，导致了良好的“发泡能力”和长期泡沫稳定性。添加电解质（NaSO）被证明对泡沫稳定性有显著影响。通过在 0 到 0.55 M 之间变化电解质的浓度，可以观察到三个泡沫稳定性区域：在低电解质浓度下泡沫迅速崩溃，在中间浓度下泡沫延迟崩溃，以及在最高电解质浓度下长期稳定（约 10 天）。通过研究颗粒负载界面的微观结构、物理和机械性能，可以更好地理解泡沫稳定性的转变。对于迅速崩溃的泡沫，纳米复合材料颗粒在空气-水界面上弱保留。在这种情况下，界面被表征为“液态”，泡沫在 100 分钟内崩溃。在中间电解质浓度（0.1 M）下，观察到约 16 小时的延迟泡沫崩溃。如在剪切和压缩下测量的那样，颗粒负载界面被证明是类固态的。界面刚性的增加归因于互穿聚合物层之间的粘附。对于最稳定的泡沫（在 0.55 M NaSO 中制备），发现粘性弹性模量 G'/G″的比值等于约 3，确认了一个强弹性界面层。使用光学显微镜评估增强的泡沫稳定性，并将其归因于泡沫崩溃机制的变化。发现纳米复合材料颗粒的聚集显著延迟了气泡-气泡聚并，长期失稳被认为是由于气泡粗化所致。对于迅速失稳的泡沫，气泡-气泡聚并的贡献被证明更为显著。
