Combining Gravimetric and Vibrational Spectroscopy Measurements to Quantify First- and Second-Shell Hydration Layers in Polyimides with Different Molecular Architectures

Abstract

In-situ Fourier transform infrared (FTIR) measurements have been carried out at different relative pressures of water vapor to study the H(2)O diffusion in three polyimides differing in their molecular structure and fluorine substitution. Spectral data have been analyzed by difference spectroscopy, least-squares curve fitting, and two-dimensional (2D) correlation spectroscopy, which provided molecular level information on the diffusion mechanism. In particular, two distinct water species were identified corresponding, respectively, to the first and second-shell hydration layers. The spectroscopic analysis demonstrated that the relative population of these species is a function of the total water content in the system. A method has been devised to quantify the water concentration in the two hydration layers, based on a combination of spectroscopic and gravimetric data. The results have been compared with those from an earlier spectroscopic approach reported in the literature and based on the analysis of the carbonyl region.

Water Sorption Thermodynamics and Mass Transport in Poly(ϵ‐Caprolactone): Interactional Issues Emerging from Vibrational Spectroscopy

“…The spectra representative of absorbed water were obtained by using as background the single-beam spectrum of the cell containing the dry PCL fi lm. It is explicitly noted that this data processing approach is equivalent to the more general difference spectroscopy method, provided that no change in sample thickness takes place during the measurement, [ 8 ] which was experimentally verifi ed in the present case. The above procedure allows us to eliminate the interference of the polymer spectrum in the regions of interest (i.e., the 3800-3100 cm − 1 range [ ν (OH)] and the 1670-1580 cm − 1 range [ δ (HOH)]).…”

“…[ 7 ] To the aim of gathering quantitative and qualitative information on these interactional issues to be used for the development of a consistent mixture thermodynamics framework, vibrational spectroscopy has proven to be a powerful tool, as demonstrated in the case of several polymer-water systems. [8][9][10][11][12] This is especially true when in situ, time-resolved FTIR spectroscopy measurements are coupled with gravimetric measurements, to provide a fi rm ground for the quantitative analysis of the populations of the interacting species. In particular, a wealth of information can be obtained that allows the identifi cation of proton-acceptor and protondonor groups, present on water molecules and on the polymer backbone, as well as the quantitative assessment of established cross-and self-HB interactions.…”

“…In particular, a wealth of information can be obtained that allows the identifi cation of proton-acceptor and protondonor groups, present on water molecules and on the polymer backbone, as well as the quantitative assessment of established cross-and self-HB interactions. [8][9][10][11][12] As far as modeling is concerned, many efforts have been carried out to model sorption thermodynamics of low-molecular-weight compounds in polymers above their glass-transition temperature. Among them, semitheoretical equation of state (EoS) approaches based on statistical thermodynamics and grounded on compressible lattice fl uid (LF) theory [13][14][15] were shown to provide an effective framework.…”

Low Humidity Characteristics of Polymer-Based Capacitive Humidity Sensors

“…The polymers used for sensing layers in modern capacitive relative humidity sensors are mainly polyimides (although Vaisala Oy used cellulose acetate). Polyimides are heterocyclic polymers which offer some very attractive features when used in capacitive sensors: outstanding thermal-oxidative and chemical stability, high glass transition temperatures, high radiative-and solvent-resistance; they exhibit very good dielectric and mechanical properties with good processability; the dielectric constant relative to water is low [14,15]. They are also easily integrated into a CMOS type integrating process.…”

Two‐Dimensional Correlation Spectroscopy: New Developments and Applications

“…The new transformed data matrix A ** is obtained by manipulating and replacing eigenvalues of A * as A * * = U S * * V T (10) where S ** is given by varying the corresponding eigenvalues in S by raising them to the power of m.…”