Free volume

Density (ρ)  and  viscosity (η  and  ultrasonic  velocity (U)  of  different  concentration of  aqueous  Thiamine Hydrochloride  (vitamin B1)    have  been  studied  at  temperature  303K. The  measurement  of ultrasonic  velocity  were  carried  out  by  using  the  ultrasonic  pulse  eco  overlap (PEO)  technique  at  frequency  5  MHz.  Measurement  of  density  have  been  carried  out  by  using  hydrostatic  plunger method  and  viscosity  by  Oswald’s  viscometer.  The temperature 303K  have  been  kept  constant  using  thermostat  by  circulating water.  Experimental  data  have  been  used to estimate the thermo-acoustical  parameter  such  as  adiabatic compressibility (β), acoustic  impedance (z),  free length (Lf ), free  volume (Vf), relaxation  time (T)  and  Rao’s  constant (R) . Gibb’s free energy    ( ∆G). These  parameters  have  been  used  to give  the  interpretations  of  solute- solvent  interaction  of  Thiamine Hydrochloride  and  H2O  molecules. Furthermore  these  studies  provide  important  information  regarding  molecular properties  of  solute and solvent  interaction.

Keywords- Density, Viscosity, Ultrasonic velocity, Adiabatic compressibility, Free volume , Gibb’s free energy and  Thiamine Hydrochloride.

In this study, we have extended the knowledge of the dynamics of polycarbonate ~PC! far below Tg by means of positron annihilation lifetime spectroscopy ~PALS!, which is able to detect the isothermal relaxation
of the free volume after rejuvenation above Tg . The free volume relaxation patterns at different temperatures below Tg were modeled according to a phenomenological model presented by Struik to obtain the equilibrium
relaxation times of the process at each aging temperature. The dynamics of supercooled liquids above the glass transition temperature (Tg) is usually described by the Williams-Landel-Ferry (WLF) or Vogel-Fulcher-Tammann (VFT) equation. Recently, deviations from this behavior were found below Tg . In contrast, an Arrhenius-type temperature dependence was found. Our results suggest that, far below Tg , two possible scenarios can hold: (a) the relaxation process of PC is dominated by the beta process, though the fast modes of the alpha process still manifest even at the lowest investigated temperature; (b) an Arrhenius-type process, deriving from the coupling of few beta events, drives aging far below Tg. Finally, the aging process was related to a diffusion mechanism and a coupling parameter was introduced as a measure of the efficiency of the beta process in producing appreciable changes in the density. The magnitude of the coupling parameter suggests a weak coupling between the b relaxation and the physical aging process.