Kim A-Reum, Mitra Sushanta K, Zhao Boxin
Department of Chemical Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada; Department of Mechanical & Mechatronics Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Department of Mechanical & Mechatronics Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
J Colloid Interface Sci. 2024 Dec 15;676:1109-1117. doi: 10.1016/j.jcis.2024.07.112. Epub 2024 Jul 14.
Soft materials, particularly elastomers, are extensively studied, but investigations into purely soft gel contact systems are limited due to their complex dual phases consisting of polymer and free liquids. While Dual Wavelength-Reflection Interference Confocal Microscopy (DW-RICM) is effective for noninvasively visualizing interfaces from a bottom view, it faces challenges in gel studies due to close refractive indices of polymeric networks and free liquids. We hypothesize that modulating the refractive index of soft gels using nanoparticles (NPs) enhances the visualization of contact zone beneath the free surface, providing insights into the configuration of phase-separated free oil within gel-on-gel contact systems.
Gel-on-gel contact systems were fabricated using immiscible organogels and hydrogels. Titanium dioxide (TiO) NPs were introduced into the organogel to modulate refractive indices. Given the lack of prior studies on the hidden contact zone between gels, various techniques, including DW-RICM, side-view imaging, and inverted optical microscopy, were employed to observe and validate our findings. Comparative analyses were conducted with elastomer-on-rigid, elastomer-on-gel, and gel-on-rigid contact systems.
Our investigation demonstrated that a minimal amount of TiO NPs effectively delineates the direct contact radius between organogel polymeric networks and hydrogel surfaces. Comparative experiments showed that TiO addition did not alter the gels' mechanical and surface properties but significantly enhanced information on gel contact deformation. This enhanced visualization technique has the potential to advance our understanding of adhesive contacts in gels, providing valuable insights into interface phenomena involving biological soft tissues and cells.
软材料，特别是弹性体，已得到广泛研究，但对纯软凝胶接触系统的研究有限，因为它们由聚合物和游离液体组成的复杂双相结构。虽然双波长反射干涉共聚焦显微镜（DW-RICM）能有效地从底部视图对界面进行无创可视化，但由于聚合物网络和游离液体的折射率相近，在凝胶研究中面临挑战。我们假设使用纳米颗粒（NPs）调节软凝胶的折射率可增强对自由表面下方接触区的可视化，从而深入了解凝胶-凝胶接触系统中相分离的游离油的构型。
使用不混溶的有机凝胶和水凝胶制备凝胶-凝胶接触系统。将二氧化钛（TiO）纳米颗粒引入有机凝胶中以调节折射率。鉴于此前缺乏对凝胶之间隐藏接触区的研究，我们采用了多种技术，包括DW-RICM、侧视图成像和倒置光学显微镜，来观察和验证我们的发现。对弹性体-刚性、弹性体-凝胶和凝胶-刚性接触系统进行了对比分析。
我们的研究表明，极少量的TiO纳米颗粒能有效勾勒出有机凝胶聚合物网络与水凝胶表面之间的直接接触半径。对比实验表明，添加TiO不会改变凝胶的机械性能和表面性质，但能显著增强有关凝胶接触变形的信息。这种增强的可视化技术有可能推动我们对凝胶中粘附接触的理解，为涉及生物软组织和细胞的界面现象提供有价值的见解。
