Alkaline hydrolysis of electrospun PAN/h-BN composite nanofibres: Structural and chemical baseline for ionic electroactive polymer applications

Abstract

Electrospun polyacrylonitrile (PAN) / hexagonal boron nitride (h-BN) composite nanofibre membranes (h-BN: 0–40 wt%) were hydrolyzed with equimolar (2.0 M) NaOH and KOH, and the resulting fifteen compositions were characterized by SEM, ATR-FTIR, XRD, n -butanol porosimetry, and gravimetric water uptake. The objective is mechanistic: to elucidate how cation identity (Na + vs K + ) and h-BN loading govern carboxylate formation and the accompanying structural evolution. ATR-FTIR confirms predominant retention of the ionic carboxylate salt form (–COO − Na + and –COO − K + ) after deionized-water washing. KOH produces an apparent degree of hydrolysis (DoH) approximately 5–6 times higher than equimolar NaOH (29–58% vs 5–11%), attributable not to cation hydration alone but to a combination of OH− nucleophilicity, cation-dependent swelling, and counterion polyion interactions. Three quantitative relationships derived exclusively from measured quantities are reported: DoH from FTIR, swelling ratio Q and hydration-induced linear expansion ε hyd from water uptake (thermodynamic upper bounds), and an apparent shift in average interchain correlation distance Δd app from XRD. A convergence of four directly-measured observables at K-PAN-20 wt%: anomalously low DoH (29 ± 4%), best fibre morphology and lowest diameter CV (56.6%) in the KOH series, maintained open porosity (79.7%), lowest water uptake (9 ± 1%), supported by subordinate structural indicators (near-zero Δd app and the largest apparent Scherrer crystallite size), is consistent with an h-BN surface-coverage effect moderating OH − access to PAN at this loading. The mechanistic picture and the K-PAN-20 wt% optimum establish a comparative structural and chemical baseline for the system and motivate direct surface-sensitive investigation (XPS, cross-sectional TEM) of the proposed coverage effect.