The relaxation behavior of supercooled and glassy imidacloprid

Abstract

Employing dielectric spectroscopy, oscillatory shear rheology, and calorimetry, the present work explores the molecular dynamics of the widely used insecticide imidacloprid above and below its glass transition temperature. In its supercooled liquid regime, the applied techniques yield good agreement regarding the characteristic structural (alpha) relaxation times of this material. In addition, the generalized Gemant–DiMarzio–Bishop model provides a good conversion between the frequency-dependent dielectric and shear mechanical responses in its viscous state, allowing for an assessment of imidacloprid’s molecular hydrodynamic radius. In order to characterize the molecular dynamics in its glassy regime, we employ several approaches. These include the application of frequency–temperature superposition (FTS) to its isostructural dielectric and rheological responses as well as use of dielectric and calorimetric physical aging and the Adam–Gibbs–Vogel model. While the latter approach and dielectric FTS provide relaxation times that are close to each other, the other methods predict notably longer times that are closer to those reflecting a complete recovery of ergodicity. This seemingly conflicting dissimilarity demonstrates that the molecular dynamics of glassy imidacloprid strongly depends on its thermal history, with high relevance for the use of this insecticide as an active ingredient in technological applications.

Predicting Dielectric and Shear-Rheology Properties of Glass-Forming Pharmaceutical Liquids from Each Other: Applications and Limitations

“…However, it turns out that by and large λ –1 and the dielectric relaxation strength Δε are correlated. This is demonstrated in Figure where we collect all λ –1 and Δε data available to us (see also refs and as well as Appendix C). Despite some “scatter”, in Figure , one recognizes that, disregarding the data for NIC which we will discuss below, λ –1 and Δε are approximately proportional to each other.…”

“…For ASA, based on Δε = 1–4, an estimate for λ –1 is given. The data for tripropylene glycol (TPG), propylene carbonate (PC), and a mixture of N -methylformamide (NMF) with N -ethylacetamide (NEA), here called NEA-NMF, are from ref , those for imidacloprid (IMI) from ref , and those for IBU from ref . For polyphenylether (PPE), triphenylethylene (TPE), and nifedipine (NIF), see Appendix C. All other data refer to the present work.…”

Characterizing Phase Separation of Amorphous Solid Dispersions Containing Imidacloprid

“…It can crystallize in six different polymorphs, with the most stable one (modification I) being the starting substance for the current investigations. The high polarity of IMI is marked by its large dielectric strength (Δε ≈ 45 at room temperature) . General-purpose fully amorphous polystyrene (PS), kindly provided by Ineos Group (styrolution 153F, stated purity >99.9 wt %, dispersity = 2.8), was the polymeric excipient of the ASDs examined in this study.…”

“…The high polarity of IMI is marked by its large dielectric strength (Δε ≈ 45 at room temperature). 37 General-purpose fully amorphous polystyrene (PS), kindly provided by Ineos Group (styrolution 153F, stated purity >99.9 wt %, dispersity = 2.8), was the polymeric excipient of the ASDs examined in this study. Table 1 summarizes the relevant properties of IMI and PS, while the molecular structures of these substances are depicted in Figure 1.…”

Two-Step Aging of Highly Polar Glass

“… 2 For instance, the specific volume, enthalpy, relaxation dynamics, or dc-conductivity change during the equilibration process below the glass transition temperature, T g . 3 This phenomenon, known as structural recovery or physical aging, can ultimately affect the use of diverse materials, including polymers, 4 ion-conductors, 5 inorganic glasses, 6 composites, or pharmaceuticals, 7 in modern technologies. Therefore, it is essential to monitor the fluctuations of physical quantities after quenching.…”