Mussel-inspired chemistry has attracted widespread interest in membrane science and technology. Demonstrating the rapid growth of this field over the past several years, substantial progress has been achieved in both mussel-inspired chemistry and membrane surface engineering based on musselinspired coatings. At this stage, it is valuable to summarize the most recent and distinctive developments, as well as to frame the challenges and opportunities remaining in this field. In this review, we present recent advances in rapid and controllable deposition of mussel-inspired coatings, dopamine-assisted co-deposition technology and photo-initiated grafting directly on mussel-inspired coatings. Some of these technologies have not yet been employed directly in membrane science. Beyond discussing advances in conventional membrane processes, we discuss emerging applications of mussel-inspired coatings in membranes, including as a skin layer in nanofiltration, interlayer in metalorganic framework based membranes, hydrophilic layer in Janus membranes and protective layer in catalytic membranes. Finally, we raise some critical unsolved challenges in this field and propose some potential pathways to address them.

Sequential infiltration synthesis (SIS) is an emerging materials growth method by which inorganic metal oxides are nucleated and grown within the free volume of polymers in association with chemical functional groups in the polymer. SIS enables the growth of novel polymer-inorganic hybrid materials, porous inorganic materials, and spatially templated nanoscale devices of relevance to a host of technological applications. Although SIS borrows from the precursors and equipment of atomic layer deposition (ALD), the chemistry and physics of SIS differ in important ways. These differences arise from the permeable three-dimensional distribution of functional groups in polymers in SIS, which contrast to the typically impermeable two-dimensional distribution of active sites on solid surfaces in ALD. In SIS, metal-organic vapor-phase precursors dissolve and diffuse into polymers and interact with these functional groups through reversible complex formation and/or irreversible chemical reactions. In this perspective, we describe the thermodynamics and kinetics of SIS and attempt to disentangle the tightly coupled physical and chemical processes that underlie this method. We discuss the various experimental, computational, and theoretical efforts that provide insight into SIS mechanisms and identify approaches that may fill out current gaps in knowledge and expand the utilization of SIS.

The sequential infiltration synthesis (SIS) of group 13 indium and gallium oxides (In 2 O 3 and Ga 2 O 3 ) into poly(methyl methacrylate) (PMMA) thin films is demonstrated using trimethylindium (TMIn) and trimethylgallium (TMGa), respectively, with water. In situ Fourier transform infrared (FTIR) spectroscopy reveals that these metal alkyl precursors reversibly associate with the carbonyl groups of PMMA in analogy to trimethylaluminum (TMAl), however, with significantly lower affinity. This is demonstrated to have important kinetic consequences that dramatically alter the synthetic parameters required to achieve material growth. Ab initio density functional theory simulations of the methyl methacrylate monomer with group 13 metal alkyls corroborate association energy that is 3× greater for TMAl than for either TMIn or TMGa. As a consequence, the kinetics of activated diffusion within the film is observed to be far more rapid for TMIn and TMGa than for TMAl. Spectroscopic ellipsometry and scanning electron microscopy, in combination with Hall effect measurements of SIS-derived In 2 O 3 films, demonstrate that SIS enables rapid growth of thin films with continuous electrically conductive pathways after postannealing. Notably, SIS with TMIn and water enables the growth of In 2 O 3 at 80 °C, well below the onset temperature of atomic layer deposition (ALD) using these precursors.