Ultra-thin and strong formvar-based membranes with controlled morphologies were developed via a simple synthesis technique. This thin hydrophilic and oleophilic polymer possesses very interesting morphological properties including being inert to most chemicals and resistant to radiation. Tunable porous membranes (porosity ranges from 20 to 60%) were synthesized by controlling the ratios of formvar, glycerol, and chloroform; and varying the sonication time. While the porosity can be altered, the hydrophilicity and oleophilicity is fundamental to the formvar itself and is independent of synthesis conditions. The formvar-based membranes were found to have an elastic modulus of 7.8 GPa (twice as high as previously reported values) with an average thickness of 125 nm. The figure below shows the SEM images of holey formvar structure (A) and lacey structure (B) along with a 3D render AFM image of a high porosity holey formvar sample (C). To demonstrate the versatility of this membrane, we performed chemical compatibility testing revealing that only chloroform had a destructive effect fully dissolving the formvar in a few minutes. High concentrations of HCl (above 6M) were found to have minor deleterious effects after an hour of exposure. Moreover, a numerical model was used to demonstrate the feasibility of the membranes with a range of porosity in realistic conditions in nano- and micro-devices. These thorough simulations revealed that the membrane with the highest porosity of ~50% exhibited the lowest probability of failure in a pressurized system.

Additionally, the unique mechanical properties and chemical resistivity of formvar, provide the opportunity for using these type of membranes in certain environmental conditions to transfer and handle various 2D materials, where other polymer types would not be suited for. More specifically, due to the ease at which formvar dissolves in chloroform, for the first time we utilize the formvar-based membranes for large-area graphene transfer. Compared to other polymer-based transfer techniques, our novel method allows for a cleaner and a faster transfer of graphene sheets onto a variety of substrates, including commercial TEM grids, silicon dioxide and glass. Various spectroscopy and microscopy analyses demonstrated the effectiveness of this formvar-based transfer technique for large-area crystalline graphene sheets. The formvar removal is one to two orders of magnitude faster than other reported PMMA-based transfer methods. Moreover, formvar can be applied to large-area graphene sheets limiting the transfer dimensions only to that of catalyst size utilized for graphene growth. Ultimately, the development of ultra-strong and versatile membrane materials can allow for major advances across a wide range of important applications in microscale to nanoscale fluidics and nano-electronic devices.