Ruiz, F. J. R.

2025

Abstract: This thesis develops a multiscale view of humidity-driven ionic transport in bioderivedpolysaccharide films of alginate (AA) and chitosan (CH), with and withoutcellulose nanofibers (CNFs), linking molecular water dynamics to macroscopic conductivity.Through-plane conductivity was measured by electrochemical impedance spectroscopy(EIS) at 10/50/80% relative humidity using thickness-averaged geometry factors andcomplementary bulk-resistance estimators with explicit uncertainties. Hydration andhydrogen-bond organization were tracked by FTIR using a robust, area-based metricS1 (integral of the OH stretch, 3600–3000 cm−1), which captures concurrent growth,broadening, and small shifts more reliably than peak height. Quasi-elastic neutronscattering (QENS), analyzed in the dynamic susceptibility representation χ′′(q, ω) afterdetailed-balance correction, resolved picosecond water motions. EIS shows that AA exhibitsa steep conductivity rise with humidity (1.13×10−4→2.48×10−4 Sm−1), whereasCH—although more conductive at matched RH—displays a milder slope (3.14 × 10−4→3.68×10−4 Sm−1). CNFs act in a material-dependent way: AA+CNFs gains modestly at80% RH (2.95 × 10−4 Sm−1; ∼+19% vs. AA), while CH+CNFs suffers a strong penalty(6.3×10−5 Sm−1). FTIR indicates a flexible, water-sensitive network in AA, homogenizedbut not overconstrained hydration in AA+CNFs, spectral rigidity in CH, and interfacialconfinement in CH+CNFs; the S1 time series show step-like increases in neat AA/CHaligned with RH setpoints that arise from sorption faster than the ∼30 min cadence.QENS confirms dual dynamical channels in AA (hydration and bulk-like water; kneenear 1012 rad s−1 with a persistent high-frequency wing) and predominantly localizedhydration in CH. Together these results show that conductivity increases when watercontent rises and retains sufficient dynamical freedom within a reorganizable network;CNFs can homogenize pathways and stabilize transport in AA, but overconstrain waterand hinder transport in CH. Limitations include the absence of QENS for CNF compositesand under-sampling of fast FTIR transients; completing the QENS map for CHand CNF-reinforced films, quantifying thermal robustness via S1 and EIS/QENS(T),and exploring controlled salt doping are identified as direct routes to optimize performance.

Keyword(s): Energy (1st) ; Materials Science (2nd) ; Soft Condensed Matter (2nd)

1. MLZ (MLZ)
2. RESEDA (RESEDA)
3. SANS1 (SANS1)

1. Measurement at external facility