Stimuli-responsive Pickering foams have attracted wide attention due to their good stability and controllable foamability. In this work, pH-switchable Pickering foams were constructed using particles from amino acids with metal ions as stabilizers. Some hydrophobic amino acids, phenylalanine, leucine and tryptophan, can induce the production of particles with suitable wettability in the case of combination with some metal ions at their deprotonated forms, and further form Pickering foams. The foams exhibit good stability and can be cycled between foaming and defoaming forms by modulating pH of solutions. When pH was increased, the amino acids were in anionic forms and could easily coordinate with metal ions, forming insoluble particles to stabilize the foams. As pH was decreased, the protonation of amino acids led to the disappearance of particles, resulting in the defoaming state. This work proposes a simple method to prepare Pickering foams with environmentally friendly amino acids as the raw materials, providing a new idea for the construction of stimuli-responsive disperse systems.
Waterborne polyurethane (WPU) latex nanoparticles with proven interfacial activity were utilized to stabilize air–water interfaces of Pickering foams through interfacial interaction with hydrophobic fumed silica particles (SPs). The rheological properties of the Pickering foam were tailored through adjustment of their SP content, which influenced their formability and stability. A Pickering foam stabilized with WPU and SPs was used as a template to prepare a WPU–SP composite porous film. The as-prepared film had intact open-cell porous structures, which increased its water absorption and water-vapor permeability. The porous film was used as a middle layer in the preparation of synthetic leather via a four-step “drying method”. Compared with commercial synthetic leather, the lab-made synthetic leather with a middle layer made of the WPU–SP composite porous film exhibited a richer porous structure, acceptable wetting on a fabric substrate, a thicker porous layer, and higher water-vapor permeability. This work provides a novel and facile approach for preparing WPU–SP Pickering foams. Furthermore, the foams have the potential to function as a sustainable material for creating a porous-structured synthetic leather made from WPU, which may be utilized as an alternative to solvent-based synthetic leather.
危险品化学品经营许可证（带存储）