Critical Model Insight into Broadband Dielectric Properties of Neopentyl Glycol (NPG)

This report presents the low-frequency (LF), static, and dynamic dielectric properties of neopentyl glycol (NPG), an orientationally disordered crystal (ODIC)-forming material important for the barocaloric effect applications. High-resolution tests were carried out for 173K<𝑇<440𝐾, in liquid, ODIC, and solid crystal phases. The support of the innovative distortion-sensitive analysis revealed a set of novel characterizations important for NPG and any ODIC-forming material. First, the dielectric constant in the liquid and ODIC phase follows the Mossotti Catastrophe-like pattern, linked to the Clausius–Mossotti local field. It challenges the heuristic paradigm forbidding such behavior for dipolar liquid dielectrics. For DC electric conductivity, the prevalence of the ‘critical and activated’ scaling relation is evidenced. It indicates that commonly applied VFT scaling might have only an effective parameterization meaning. The discussion of dielectric behavior in the low-frequency (LF) domain is worth stressing. It is significant for applications but hardly discussed due to the cognitive gap, making an analysis puzzling. For the contribution to the real part of dielectric permittivity in the LF domain, associated with translational processes, exponential changes in the liquid phase and hyperbolic changes in the ODIC phase are evidenced. The novelty also constitutes 𝑡𝑔𝛿 temperature dependence, related to energy dissipation. The results presented also reveal the strong postfreezing/pre-melting-type effects on the solid crystal side of the strongly discontinuous ODIC–solid crystal transition. So far, such a phenomenon has been observed only for the liquid–solid crystal melting transition. The discussion of a possible universal picture of the behavior in the liquid phase of liquid crystalline materials and in the liquid and ODIC phases of NPG is particularly worth stressing.The names of the individual files correspond to the numbering of the figures in the paper: Drozd-Rzoska, A.; Kalabiński, J.; Rzoska, S.J. Critical Model Insight into Broadband Dielectric Properties of Neopentyl Glycol (NPG). Materials 2024, 17, 4144. https://doi.org/10.3390/ma17164144Files included in this collection:Figure 1.txt - Frequency scans of real (𝜀′(𝑓)) contributions to dielectric permittivity in NPGFigure 2.txt - Frequency scans of the imaginary 𝜀′′(𝑓) to dielectric permittivity in NPGFigure 3.txt - Frequency-related behavior of the real part of electric conductivity in the liquid, ODIC (Phase I), and crystal (Phase II) phasesFigure 4.txt - Temperature changes in the dielectric constant in subsequent phases of NPGFigure 5.txt - Temperature evolution of the reciprocal of dielectric susceptibilityFigure 6.txt - Temperature dependence of the real part of electric conductivity for a set of frequenciesFigure 7.txt - Temperature dependence of the DC electric conductivity reciprocal in the liquid and ODIC phases of NPG, using the Arrhenius scaleFigure 8.txt - Temperature evolutions of the real (𝜀′(𝑓)) and imaginary (𝜀′′(𝑓)) parts of dielectric permittivity and for the dissipation factor, 𝐷(𝑓)=𝑡𝑎𝑛𝛿(𝑓)=𝜀′′(𝑓)/𝜀′(𝑓), for selected frequencies in tested phases of NPGFigure 9.txt - The temperature behavior of the low-frequency (LF) contribution of the real part of dielectric permittivity in NPG, presented via the semi-log scaleFigure 10.txt - The temperature behavior of the reciprocal of the low-frequency (LF) contribution to the real part of dielectric permittivity in the ODIC phase of NPG