Vishnyakov Aleksey, Shen Yangyang, Tomassone M Silvina
Department of Chemical and Biochemical Engineering, Rutgers the State University of New Jersey, 98 Brett Rd., Piscataway, New Jersey 08854, USA.
J Chem Phys. 2008 Nov 7;129(17):174704. doi: 10.1063/1.2994714.
We report molecular simulation studies on the interaction forces between silica nanoparticles in supercritical carbon dioxide at 318 K. Our goal is to find a better understanding of the interparticle solvation forces during rapid expansion of supercritical solutions. The parameters for interatomic potentials of fluid-fluid and solid-fluid interactions are obtained by fitting our simulations to (i) experimental bulk CO(2) phase diagram at a given temperature and pressure and (ii) CO(2) sorption isotherms on silica at normal boiling and critical temperatures. Our simulations show that the interaction forces between particles and supercritical CO(2) at near-critical pressure of p=69 atm (i.e., slightly below critical condition) reaches a minimum at distances of 0.5-0.8 nm between the outer surfaces of the particles and practically vanishes at distances of approximately 3 nm. The attraction is most prominent for densely hydroxylated particle surfaces that interact strongly with CO(2) via hydrogen bonds. The effective attraction between silica and CO(2) is significantly weaker for dehydroxylated particles. We also compared fluid sorption and interparticle forces between supercritical CO(2) and subcritical nitrogen vapor, and our results showed qualitative similarities, suggesting that the CO(2) configuration between the particles resembles a liquidlike junction.
我们报告了在318 K的超临界二氧化碳中二氧化硅纳米颗粒间相互作用力的分子模拟研究。我们的目标是更好地理解超临界溶液快速膨胀过程中的颗粒间溶剂化力。通过将我们的模拟结果与以下两项进行拟合，获得了流体 - 流体和固体 - 流体相互作用的原子间势参数：（i）给定温度和压力下的实验体相CO₂相图，以及（ii）在正常沸点和临界温度下二氧化硅上的CO₂吸附等温线。我们的模拟表明，在接近临界压力p = 69 atm（即略低于临界条件）时，颗粒与超临界CO₂之间的相互作用力在颗粒外表面间距为0.5 - 0.8 nm时达到最小值，而在约3 nm的间距时实际上消失。对于通过氢键与CO₂强烈相互作用的高度羟基化颗粒表面，吸引力最为显著。对于脱羟基化颗粒，二氧化硅与CO₂之间的有效吸引力明显较弱。我们还比较了超临界CO₂与亚临界氮气蒸气之间的流体吸附和颗粒间力，结果显示出定性的相似性，表明颗粒间的CO₂构型类似于液体连接。
