Ultra-thin and strong formvar-based membranes with controlled porosity for micro- and nano-scale systems

Abstract

We present a methodology for developing ultra-thin and strong formvar-based membranes with controlled morphologies. Formvar is a thin hydrophilic and oleophilic polymer inert to most chemicals and resistant to radiation. The formvar-based membranes are viable materials as support structures in micro- and macro-scale systems depending on thinness and porosity control. Tunable sub-micron thick porous membranes with 20%-65% porosity were synthesized by controlling the ratios of formvar, glycerol, and chloroform. This synthesis process does not require complex separation or handling methods and allows for the production of strong, thin, and porous formvar-based membranes. An expansive array of these membrane characterizations including chemical compatibility, mechanical responses, wettability, as well as the mathematical simulations as a function of porosity has been presented. The wide range of chemical compatibility allows for membrane applications in various environments, where other polymers would not be suitable. Our formvar-based membranes were found to have an elastic modulus of 7.8 GPa, a surface free energy of 50 mN m and an average thickness of 125 nm. Stochastic model simulations indicate that formvar with the porosity of ∼50% is the optimal membrane formulation, allowing the most material transfer across the membrane while also withstanding the highest simulated pressure loadings before tearing. Development of novel, resilient and versatile membranes with controlled porosity offers a wide range of exciting applications in the fields of nanoscience, microfluidics, and MEMS.

Scalable and Versatile Transfer of Sensitive Two-dimensional Materials

“…Our transfer method can prepare TEM samples from nanomaterials with diverse morphologies (Figure S12 and Figure b). The widely used Formvar-based TEM grids play a pivotal role in TEM sample preparation owing to the excellent properties of Formvar (i.e., ultrastrong, chemical inertness, and exceptional radiation tolerance) . The strong adhesion energy and low stiffness of Formvar enable TEM grid to have a good conformal and tight contact with nanomaterials while detaching from substrates.…”

“…The widely used Formvar-based TEM grids play a pivotal role in TEM sample preparation owing to the excellent properties of Formvar (i.e., ultrastrong, chemical inertness, and exceptional radiation tolerance). 28 The strong adhesion energy and low stiffness of Formvar enable TEM grid to have a good conformal and tight contact with nanomaterials while detaching from substrates. These advantages lead to a high success ratio and high transfer quality (see methods and Figure S3).…”

Graphene Synthesis: Method, Exfoliation Mechanism and Large-Scale Production

“…In the transfer area up to 3 cm 2 , no folding or cracking on numerous graphene transfers via formvar was observed. By controlling the ratios of formvar, glycerol, and chloroform, Auchter et al [30] synthesized tunable submicron-thick, porous membranes with 20-65% porosity; these formvar-based membranes had an elastic modulus of 7.8 GPa, a surface free energy of 50 mN•m −1 , and an average thickness of 125 nm. To reduce defects and impurities introduced during the transfer of graphene to the insulating substrate, Brzhezinskaya et al [31] directly CVD synthesized a few-layer graphene film on the insulating piezoelectric substrate La 3 Ga 5.5 Ta 0.5 O 14 crystal.…”

Recyclable Graphene Sheets as a Growth Template for Crystalline ZnO Nanowires

“…The Raman spectrum of the transferred graphene before the ZnO growth indicates the presence of a crystalline sheet [ 29 ]. To maintain the quality of the graphene during transfer, we used our newly developed PMMA-free transfer method while minimizing introduction of defects and avoiding impurities [ 18 , 34 ].…”