Akbulut Mustafa, Reddy Naveen K, Bechtloff Bernd, Koltzenburg Sebastian, Vermant Jan, Prud'homme Robert K
Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Langmuir. 2008 Sep 2;24(17):9636-41. doi: 10.1021/la800487b. Epub 2008 Aug 8.
Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the surface, but moreover, flow can induce changes in the conformation of macromolecules in solution by providing sufficient stresses to perturb the segmental distribution function. However, there are few studies where the effect of flow on macromolecules has been shown to alter the structure of macromolecules adsorbed on surfaces. We have studied how the local energy dissipation alters the adsorption of gelatin onto polystyrene nanoparticles ( r = 85 nm). The change in the nature of the adsorbed layer is manifest in the change in the ability of the nanoparticles to resist aggregation. Circular dichroism spectroscopy was used to assess conformational changes in gelatin, and dynamic light scattering was used to assess the colloid stability. Experiments were conducted in a vortex jet mixer where energy density and mixing times have been quantified; mixing of the gelatin and unstable nanoparticles occurs on the order of milliseconds. The adsorption of the gelatin provides steric stabilization to the nanoparticles. We found that the stability of the gelatin-adsorbed nanoparticles increased with increasing mixing velocities: when the mixing velocities were changed from 0.9 to 550 m/s, the radius of the nanoclusters (aggregates) formed 12 h after the mixing decreased from 2620 to 600 nm. Increasing temperature also gave rise to similar trends in the stability behavior with increasing temperature, leading to increasing colloid stability. Linear flow birefringence studies also suggested that the velocity fields in the mixer are sufficiently strong to produce conformational changes in the gelatin. These results suggest that the energy dissipation produced by mixing can activate conformational changes in gelatin to alter its adsorption on the surfaces of nanoparticles. Understanding how such conformational changes in gelatin can be driven by local fluid mechanics and how these changes are related to the adsorption behavior of gelatin is very important both industrially and scientifically.
流动可以通过改变向表面的传质速率来改变溶质在表面的吸附速率，但此外，流动还可以通过提供足够的应力来扰动链段分布函数，从而引起溶液中大分子构象的变化。然而，很少有研究表明流动对大分子的影响会改变吸附在表面的大分子结构。我们研究了局部能量耗散如何改变明胶在聚苯乙烯纳米颗粒（r = 85 nm）上的吸附。吸附层性质的变化表现为纳米颗粒抗聚集能力的改变。利用圆二色光谱来评估明胶的构象变化，利用动态光散射来评估胶体稳定性。实验在涡旋射流混合器中进行，其中能量密度和混合时间已被量化；明胶和不稳定纳米颗粒的混合发生在毫秒级。明胶的吸附为纳米颗粒提供了空间稳定作用。我们发现，随着混合速度的增加，吸附了明胶的纳米颗粒的稳定性增加：当混合速度从0.9 m/s 变为 550 m/s 时，混合 12 小时后形成的纳米团簇（聚集体）半径从 2620 nm 减小到 600 nm。温度升高也导致稳定性行为出现类似趋势，随着温度升高，胶体稳定性增加。线性流动双折射研究还表明，混合器中的速度场足够强，能够使明胶发生构象变化。这些结果表明，混合产生 的能量耗散可以激活明胶的构象变化，从而改变其在纳米颗粒表面的吸附。了解明胶的这种构象变化如何由局部流体力学驱动以及这些变化如何与明胶的吸附行为相关，在工业和科学上都非常重要。
