Orientation of Thin Polyamide Layer-by-Layer Films on Non-Porous Substrates
Tawanda J. Zimudzi, Sarah E. Sheffield, Kathleen E. Feldman, Peter Beaucage, Dean DeLongchamp, Douglas I. Kushner, Christopher Stafford, Michael A. Hickner
The orientation of polyamide thin films on non-porous substrates was investigated using Fourier transform infrared (FTIR) spectroscopy and corroborated by near edge X-ray absorption fine structure (NEXAFS) measurements. Polyamide films comprised of m-phenylene diamine and trimesoyl chloride were synthesized via a layer-by-layer deposition process on both gold and silicon surfaces, where the number of sequential monomer deposition steps (cycles) determines the overall polyamide film thickness. These films represent model materials for metrology development that can be applied to the selective layers in reverse osmosis (RO) membranes. Using the fingerprint region in the infrared spectrum for m-phenylene diamine-trimesoyl chloride system, peaks were identified that could be used as diagnostic modes for molecular orientation analysis. At extremely low cycle numbers, FTIR measurements suggest the MPD- derived aromatic rings exhibited a tilt angle of ≈6° from the surface parallel while the carbonyl group of the amide was similarly oriented with an average tilt angle of ≈17°. The FTIR results are in agreement with NEXAFS results, which indicate the aromatic rings at the first half layer-by-layer cycle are oriented parallel to the surface. Both FTIR and NEXAFS measurements further show high anisotropy at low cycle numbers, which completely disappear at cycle numbers greater than 60 (≈13 nm films).
, Sheffield, S.
, Feldman, K.
, Beaucage, P.
, DeLongchamp, D.
, Kushner, D.
, Stafford, C.
and Hickner, M.
Orientation of Thin Polyamide Layer-by-Layer Films on Non-Porous Substrates, Macromolecules, [online], https://doi.org/10.1021/acs.macromol.1c02109, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=930711
(Accessed September 26, 2023)