Influence of nanoimprint lithography on membrane structure and performance

Abstract

a b s t r a c tImparting sub-micron periodic patterns on the surface of ultrafiltration (UF) membranes has been shown to improve their antifouling characteristics. However, the deformation mechanism underlying membrane surface-patterning with nanoimprint lithography (NIL) is currently unclear. In response to this need, this study addresses the influence of nanoimprinting on the structural and performance characteristics of a commercial polyethersulfone (PES) UF membrane. The work utilized a flat (no pattern) as well as a pattern-containing mold such that local surface deformation associated with pattern formation could be isolated from the overall mechanical deformation in compression. The mechanical properties of the UF membrane as a function of temperature and deformation rate were characterized, and the overall thickness, molecular weight cutoff, and DI water permeance were measured for membranes imprinted using the flat mold. The data show that the influence of the NIL process on the membrane structure is length-scale dependent. Furthermore, imprinting of the UF membrane with the pattern-containing mold was examined experimentally as well as with finite element simulation. Results indicate that the nonuniform contact deformation at the membraneemold interface provides the potential to optimize the NIL conditions for achieving desired pattern geometries without significantly increasing the membrane resistance.

Roll‐to‐roll nanoimprint lithography of ultrafiltration membrane

“…The pressure measured was 22 MPa and corresponds to the average pressure applied across the membrane. This pressure is much higher than any pressure previously used for nanoimprinting a UF membrane . Apparently, the ability to pattern membrane quickly is due to this high pressure.…”

“…This indicates a significant creep deformation, wherein as the rolling feed velocity is decreased, the time in which the membrane undergoes compression is increasing. Previous research also indicated that increased imprinting duration will decrease the resulting membrane permeance due to increased deformation and loss of porosity. They presented a relationship for creep strain under uniaxial stress for an open‐cell foam that shows an exponential dependence on processing time.…”

“…Directly scaling our areal production rate to ∼40 inch wide rollers (with complementary‐sized flexible patterning molds) provides ∼0.16 m 2 /min at room temperature. In prior studies of NIL membrane fabrication at elevated temperatures it was clearly shown that increasing the temperature allows similar fidelity of pattern transfer with lower contact time and forces. This would translate to higher rolling velocities in the R2RNIL process and will be studied further in our ongoing research.…”

“…The Ni shim has an order of magnitude higher modulus than the PEI, but the PEI still has an order of magnitude higher modulus than the PES membrane (0.16 GPa). 28 It can be seen that the imprinted PEI has slightly lower modulus and hardness than the unpatterned film. This could be due to the measurement artifacts from surface roughness.…”

The Key Role of Modifications in Biointerfaces toward Rendering Antibacterial and Antifouling Properties in Polymeric Membranes for Water Remediation: A Critical Assessment

“…[231] NIL is a lithographic technique which generates polymer nanostructure patterns at high-throughput and precision. [235] Lysozyme and Bacteriophages Modified Membranes: Lysozyme is a nontoxic basic protein found in egg whites, animals, and plant cells with a net positive charge at neutral pH and has an isoelectric point at pH 11. [232] Chou et al were the first to demonstrate the NIL process where they fabricated a pattern of feature size 25 nm and a period of 70 nm in a resist >100 nm and then it was transferred into PMMA using compression moulding.…”