Sabapathy Manigandan, Md Khalid Zubair, Kumar Hemant, Ramamirtham Sashikumar, Mani Ethayaraja, Basavaraj Madivala G
Advanced Colloid and Interfacial Engineering Laboratory, Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India.
Polymer Engineering and Colloid Science Laboratory (PECS), Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu 600036, India.
Langmuir. 2022 Jun 21;38(24):7433-7441. doi: 10.1021/acs.langmuir.2c00348. Epub 2022 Jun 9.
We exploit the aggregation between oppositely charged particles to visualize and quantify the equilibrium position of charged colloidal particles at the fluid-water interface. A dispersion of commercially available charge-stabilized nanoparticles was used as the aqueous phase to create oil-water and air-water interfaces. The colloidal particles whose charge was opposite that of the nanoparticles in the aqueous phase were deposited at the chosen fluid-water interface. Heteroaggregation, i.e., aggregation between oppositely charged particles, leads to the deposition of nanoparticles onto the larger particle located at the interface; however, this only occurs on the surface of the particle in contact with the aqueous phase. This selective deposition of nanoparticles on the surfaces of the particles exposed to water enables the distinct visualization of the circular three-phase contact line around the particles positioned at the fluid-water interface. Since the electrostatic association between the nanoparticles and the colloids at interfaces is strong, the nanoparticle assembly on the larger particles is preserved even after being transferred to solid substrates via dip-coating. This facilitates the easy visualization of the contact line by electron microscopy and the determination of the equilibrium contact angle of colloidal particles (θ) at the fluid-water interface. The suitability of the method is demonstrated by the measurement of the three-phase contact angle of positively and negatively charged polystyrene particles located at fluid-water interfaces by considering particles with sizes varying from 220 nm to 8.71 μm. The study highlights the effect of the size ratio between the nanoparticles in the aqueous phase and the colloidal particles on the accuracy of the measurement of θ.
我们利用带相反电荷粒子之间的聚集作用，来可视化和量化带电胶体粒子在液 - 水界面处的平衡位置。使用市售的电荷稳定化纳米颗粒分散体作为水相，以创建油 - 水界面和空气 - 水界面。将电荷与水相中纳米颗粒电荷相反的胶体粒子沉积在选定的液 - 水界面处。异质聚集，即带相反电荷粒子之间的聚集，导致纳米颗粒沉积到位于界面处的较大颗粒上；然而，这仅发生在与水相接触的颗粒表面。纳米颗粒在暴露于水的颗粒表面上的这种选择性沉积，使得能够清晰地可视化位于液 - 水界面处的颗粒周围的圆形三相接触线。由于纳米颗粒与界面处胶体之间的静电缔合很强，即使通过浸涂转移到固体基板上后，较大颗粒上的纳米颗粒组装体仍得以保留。这便于通过电子显微镜轻松可视化接触线，并确定胶体粒子在液 - 水界面处的平衡接触角（θ）。通过测量尺寸从220 nm到8.71 μm不等的位于液 - 水界面处的带正电和带负电聚苯乙烯颗粒的三相接触角，证明了该方法的适用性。该研究突出了水相中纳米颗粒与胶体粒子之间的尺寸比对θ测量准确性的影响。
