Relaxation dynamics of water in the aqueous mixtures of propylene glycol oligomers at ambient and elevated pressure 6 th International Discussion Meeting on Relaxations in Complex Systems, ROME 2009 Katarzyna Grzybowska Institute of Physics University of Silesia in Katowice POLAND Collaborators: University of Silesia, Poland: Marian Paluch Andrzej Grzybowski Sebastian Pawlus Università di Pisa, Italy: Simone Capaccioli Daniele Prevosto Sergiy Ancherbak

Material Molecular weight M w [g/mol] Number of mers p Structural formula dimer of propylene glycol (DPG) 1342 trimer of propylene glycol (TPG) 1923 PPG ~ 7 p-1 To prepare water mixtures we used polypropylene glycols (PPG) (=diols) of different chain lengths

Water mixtures of propylene glycol oligomers At atmospheric pressure it has been studied over 20 water mixtures of polypropylene glycols (DPG, TPG, and PPG 400) with different content of water with different content of water For the mixture PPG %H 2 O it has been performed dielectric measurements at elevated pressure: P = 360 MPa P = 500 MPa P = 1800 MPa

Water significantly changes the relaxation dynamics of PPG: Dielectric measurements of water mixtures of PPG at P=0.1 MPa DPG+H 2 O (liquid state) DPG+H 2 O (liquid state) α-relaxation ν- ν-relaxation TPG+H 2 O (glassy state) TPG+H 2 O (glassy state) ν- ν-relaxation 1) Appearing of a new additional - relaxation process  -process ν-process reflects mainly the water dynamics in the mixture The spectacular increase in dielectric strenght Δε ν with increasing of water content in solution

2) Even a small amount of water added to pure PPG results in a slowdown of the  -relaxation observed in anhydrous PPG and the drop of Δε  of the  -relaxation observed in anhydrous PPG and the drop of Δε  Hindering of the reorientations of PPG OH groups by H-bonds formed between water molecules and OH groups of PPG ν-process ν-process PPG 400+H 2 O (glassy state) PPG 400+H 2 O (glassy state)  -process  -process originates from some reorientations of terminal parts of PPG molecules containing OH groups K. Grzybowska, et al. J. Chem. Phys (2008); K. Grzybowska, et al. J. Phys.: Condens. Matter 19, (2007)

Temeperature dependences of dielectric relaxation times for water mixtures of PPG at P=0.1 MPa VFT eq. Arrhenius law

Activation enery E a of ν and  -processes obtained at T<T g from Arrhenius eq. vs mole fraction of water at P=0.1 MPa I. Takei, Physics and Chemistry of Ice, Cambiridge (2007) R.P. Auty, R.H. Cole, J. Chem. Phys. 20, 1309 (1952) J. Chem. Phys. 20, 1309 (1952) S. Cerveny, et al., Phys. Rev. Lett. 93, (2004)

α -process ν- ν-process Dielectric spectra of the mixture PPG+26%H 2 O at high pressure α -process ν- ν-process α – process α –process ν- ν-process ( α- peak is hidden (α-peak is hidden due to a high contribution of dc-conductivity to ε”) P=0.1 MPa P=500 MPa P=1.8 GPa

P=500MPa T=-41 o C P=0.1 MPa T=-75 o C decade PPG % H 2 O Near the glass transition, the ν- relaxation is less sensitive to changes of pressure and temperature than α- process Property typical for JG-process In this respect the ν-relaxation can be considered as a secondary relaxation reflecting some local dynamics of water component in the aqueous mixture the separation between α and processes is one decade greater in the case of measurement at 500 MPa than that for ambient pressure process has the same sensitivity to pressure and temperature like typical JG secondary relaxation in many glass forming-liquids process has the same sensitivity to pressure and temperature like typical JG secondary relaxation in many glass forming-liquids

α-processes VFT equation at T>T g for medium P T g ( τ α =100s ) Relaxation map for PPG %H 2 O at high pressures T g =267 K (P=1.8 GPa) 1.8GPa Tg=267 K Tg (P=0) =193K, Π=298MPa, β =0,17 τ cross =T cross Arrhenius equation at T<T g for all P pressure considerably influences the nature of -process dynamic crossover T g of the water mixture increase with increasing P ν relaxation time (τ ν cross ) at the dynamic crossover decreases exponentially with compression τ ν cross (P→∞)=3  s

Ea of -process in the liquid state of the mixture evaluated from Arrhenius eq. evaluated from Arrhenius eq. (for P=0.1 MPa and 1.8GPa at T>Tg) and VFT eq. (for P=360 and 500 MPa at T g =T cross ) Ea of -process in the glassy state of the mixture evaluated from Arrhenius eq. R. Casalini, C. M. Roland, Phys. Rev. B 71, (2005) Non- associated liquids Unusual pressure dependences of -process activation energies and fragility of the mixture PPG400+26%H 2 O Initially the increase in pressure can facilitate the hydrogen bonds forming, whereas P>1 GPa may significant reducing of H-bonds in the water clusters in mixture

SUMMARY It has been found that pressure considerably affects the relaxation dynamics of water mixture of PPG 400. In the whole pressure range (0.1MPa-1.8GPa) we observed the dynamic crossover of -relaxation times) In the whole pressure range (0.1MPa-1.8GPa) we observed the dynamic crossover of -relaxation times) At medium pressures (360 and 500 MPa), -relaxation times reveal fragile-to-strong dynamic crossover At medium pressures (360 and 500 MPa), -relaxation times reveal fragile-to-strong dynamic crossover X-Q. Chu et al., (2008); L. Liu et al., Phys. Rev. Lett (2005). Confined water in porous silica material Protein hydration water PPG % H 2 O In contrary to confined water the dependence T cross (P) for water mixture has an increasing character and we cannot relate it to the liquid-liquid phase transition line in a T-P plane. LDL HDL

E a (P) for the -relaxation is nonmonotonic and reveals a maximum, while the Arrhenius activation energy for the confined water process decreases with increasing P at T<T cross. For water mixture, E a (P) for the -relaxation is nonmonotonic and reveals a maximum, while the Arrhenius activation energy for the confined water process decreases with increasing P at T<T cross. PPG % H 2 O 2-D confined protein hydration water For PPG400+26%H 2 O, the crossover relaxation time τ ν cross decreases exponentially with increasing P, whereas for confined water τ cross (P)  const. Supercooled water in the mixture of PPG have different properties than pure supercooled confined water. Our findings indicate that process should be rather considered as a secondary relaxation reflecting some local dynamics of water component in the aqueous mixture