Eﬀect of thermodynamic history on secondary relaxation in the glassy state S. Shariﬁ a, * , D. Prevosto a,b , S. Capaccioli b,c , M. Lucchesi a,b , M. Paluch d a PolyLab-CNR, Largo B. Pontecorvo 3, I-56127 Pisa, Italy b Dipartimento di Fisica, Universita ` di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy c CNR-INFM, CRS SOFT, Piazzale Aldo Moro 2, I-00185 Roma, Italy d Institute of Physics, Silesian University, Uniwersytecka 4, 40-007 Katowice, Poland Available online 4 October 2007 Abstract We investigated by dielectric spectroscopy the eﬀect that the thermodynamic history of a glass has on the secondary relaxation pro- cess. In particular we focused our attention to glassy states at the same conditions of temperature and pressure but reached with diﬀerent combinations of variation of the external parameters. Our analysis shows that the eﬀect of thermodynamic history on the relaxation fre- quency is related to the activation volume of the process: secondary processes with larger activation volume present a larger eﬀect of the thermodynamic history. This demonstrates an important role of density in determining such behavior in glassy systems. Ó 2007 Elsevier B.V. All rights reserved. PACS: 77.22.Gm; 61.43.Fs; 05.70.a Keywords: Dielectric properties; Pressure eﬀects; Thermodynamics; Secondary relaxation 1. Introduction The glassy state is a nonequilibrium state of materials [1]. As a consequence, the observed thermodynamic and relaxation properties slowly evolve with time because of the evolution of the molecular conﬁguration towards a state with lower energy [2]. The relaxation strength, De, of the secondary process was observed to decrease [3,4] or to vary nonmonotonously [5,6] with time at ﬁxed ther- modynamic conditions in the glassy state. Another conse- quence of the nonequilibrium condition of glasses is that thermodynamic and relaxation properties show diﬀerent values when measured in the glassy state at ﬁxed thermody- namic condition subsequently to diﬀerent vitriﬁcation his- tories [7–9]. For example, this was observed for the relaxation frequency of several secondary processes [3,10] consequently to cooling with diﬀerent rates, or after vitriﬁ- cation combining diﬀerent sequences of cooling and com- pression steps [11–13]. The reason why secondary processes are inﬂuenced by the thermodynamic history of the glass is not clear at all, and the microscopic mecha- nisms at the basis of such dependence are unknown. The situation is even more complicated since the molecular mechanisms at the basis of secondary process are not clear at all. Some secondary relaxations are interpreted in terms of small rotations of molecular subgroups decoupled from the whole molecule [14]. Another interpretation is that sec- ondary processes originate from local, non-cooperative, reorientation of the whole molecule (Johari–Goldstein, JG, process) [15,16]. A route to distinguish JG and non- JG processes on the basis of their dynamic properties is reported on previous publications [16,17]. A greater sensi- tivity to the thermodynamic history is expected for second- ary processes of JG type due to their intermolecular origin. In this work we present the study of the inﬂuence of the glass thermodynamic history on the secondary processes of 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.03.044 * Corresponding author. Tel.: +39 050 2214322; fax: +39 050 2214333. E-mail address: shariﬁ@df.unipi.it (S. Shariﬁ). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 353 (2007) 4313–4317