Temperature dependence of structural evolution and fragility of glass-forming monohydroxy alcohols

• Correlation between mass/boiling temperature and glass transition temperature exists for monohydroxy alcohols with no phenyl ring. • Phenyl compounds have the highest structural heterogeneity. • Positive relationship between fragility and short-range structural order. The dynamic, structural, and thermodynamic properties of thirty-four monohydroxy alcohols with varying molecular architectures, including differences in alkyl chain length, OH group position, and presence/type of carbon ring, were investigated. Results of dielectric spectroscopy, temperature-modulated differential scanning calorimetry, and X-ray diffraction, were analyzed to verify correlations between the glass transition temperature ( T g ), molar mass ( M ), boiling temperature ( T b ), dynamic and thermodynamic fragility ( m α and m ), and the structurally related parameter ( S ). The collected data revealed that primary and secondary alcohols generally adhere to the correlations T g ∝ M 0.51 and T b = 132 + 2.2 T g , while alcohols with phenyl ring deviate from these trends. Moreover, it was found that the changes in the width of the main diffraction peak normalized by the peak position Δ Q M / Q M over temperature scaled by T g correspond to the variable m . However, the extent and course of this relationship varies across alcohols belonging to different structural groups. The weakest correlation and largest scatter between S and m occur for phenyl alcohols exhibiting the greatest structural heterogeneity. This study underscores the challenges of establishing universal correlations between physical variables within the diverse group of monohydroxy alcohols and emphasizes the importance of considering specific molecular features in predicting glass-forming behaviour.