  Cost-affordable phenolic membranes having gradient nanostructures can be
facilely synthesized from resol oligomers in the presence of ZnCl2 and
poloxamers. The gradient nanostructures are formed by stacking phenolic
nanoparticles with gradually enlarged diameters as the distance from the upper
surface increases. The use of poloxamers for creating gelation surroundings is
of great significance for controlling the growth of phenolic nanoparticles,
which in turn dictates the performance of the phenolic membranes thus-produced.
Hence, a study of the effects of poloxamers species on the preparation of the
phenolic membranes is highly demanded since such robust membranes have much
potential to be scale up for mass production. Herein, the poloxamer Pluronic
F127 (EO106-PO70-EO106; EO = ethyleneoxide, PO = propyleneoxide) was introduced
in the membrane-forming formulations. As opposed to P123 (EO20-PO70-EO20) that
we used previously, F127 possessing extended PEO chains can delay the gelation
during membrane formation. Hence, the phenolic nucleates are able to grow for
longer durations, leading to the generation of more distinct gradient
nanostructures in the phenolic membranes. Enhanced permeance can then be
realized with F127-derived phenolic membranes. We also demonstrate that L31
(EO1-PO22-EO1) with merely single terminal EO units at the ends of the PPO
block could be used to prepare gradient phenolic membranes. This work is not
only much helpful to deeply understand the design of the structural gradient in
phenolic membranes, but capable of sheding light on the development of such
intriguing structures for water purification.
