Chain-Length-Dependent Relaxation Scenarios in an Oligomeric Glass-Forming System: From Merged to Well-Separated<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>β</mml:mi></mml:math>Loss Peaks

Mattsson, Johan; Bergman, Rikard; Jacobsson, Per; Börjesson, Lars

doi:10.1103/physrevlett.90.075702

Cited by 76 publications

(38 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Apart for the pendant ethyl group in place of the methyl group, POB has the same chemical structure as PPG (their structures are depicted in Figure 1). PPG has been the subject of many studies, by dielectric spectroscopy 10,14,15,57,58,59,60,61,62,63 and other techniques 64,65,66,67 .…”

mentioning

confidence: 99%

Temperature and Density Effects on the Local Segmental and Global Chain Dynamics of Poly(oxybutylene)

Casalini

Roland

2005

Macromolecules

View full text Add to dashboard Cite

Dielectric spectroscopy measurements over a broad range of temperature and pressure were carried out on poly(oxybutylene) (POB), a type-A polymer (dielectrically-active normal mode). There are three dynamic processes appearing at lower frequency, the normal and segmental relaxation modes, and a conductivity arising from ionic impurities. In combination with pressure-volume-temperature measurements, the dielectric data were used to assess the respective roles of thermal energy and density in controlling the relaxation times and their variation with T and P. We find that the local segmental and the global relaxation times are both a single function of the product of the temperature times the specific volume, with the latter raised to the power of 2.65. The fact that this scaling exponent is the same for both modes indicates they are governed by the same local friction coefficient, an idea common to most models of polymer dynamics. Nevertheless, near T g , their temperature dependences diverge. The magnitude of the scaling exponent reflects the relatively weak effect of density on the relaxation times. This is usual for polymers, as the intramolecular bonding, and thus interactions between directly bonded segments, are only weakly sensitive to pressure. This insensitivity also means that the chain end-to-end distance is invariant to P, conferring a near pressure-independence of the (density-normalized) normal mode dielectric strength.The ionic conductivity dominates the low frequency portion of the spectra. At lower temperatures and higher pressures, this conductivity becomes decoupled from the relaxation modes (different T-dependence), and exhibits a significantly weaker density effect. At frequencies higher than the structural relaxation, both an excess wing on the flank of the α-peak and a secondary relaxation are observed. From their relative sensitivities to pressure, we ascribe the former to an unresolved Johari-Goldstein (JG) relaxation, while the higher frequency peak is unrelated to the glass transition. These designations are consistent with the relaxation time calculated for the JG process. 2The dynamic properties of the POB are essentially the same as those of polypropylene glycol, in accord with their similar chemical structures. However, POB is less fragile (weaker T gnormalized temperature dependence), its relaxation times less sensitive to density changes, and facilitating the measurements herein, its normal mode has a substantially larger dielectric strength

show abstract

mentioning

confidence: 99%

Temperature and Density Effects on the Local Segmental and Global Chain Dynamics of Poly(oxybutylene)

Casalini

Roland

2005

Macromolecules

View full text Add to dashboard Cite

show abstract

“…The main goal of our work is the investigation of the relaxation mechanism at the basis of the EW. To extend the results of previous papers [12,23,24,30], we investigated the possibility to transform the EW into a secondary peak by changing intermolecular coupling among the investigated molecules. In our work we changed intermolecular coupling by mixing the polar TBP and Qn with 3Styr.…”

Section: Resultsmentioning

confidence: 99%

“…Similarly, dielectric spectra of the trimer of propylene glycol at high pressure showed an EW that, after aging below T g , transformed into a shoulder [25]. Dielectric measurements on a family of polyalcohols and polymers showed that the secondary relaxation peak gets close to the structural with decreasing the number of repeating units, until it merges forming an EW [12,27,28]. The application of very high pressure transform the EW of threithol and glycerol into a partially merged secondary peak [27].…”

Section: Excess Wing and Johari-goldstein Relaxation In Binary Mixturmentioning

confidence: 99%

“…[1][2][3] and references therein), and the recent investigations about the origin of secondary relaxation in for glass formers [4][5][6][7][8][9][10][11][12] raised the question whether the secondary process is an universal feature of the relaxation dynamics. Experimentally, more than one secondary process can be observed in some glass formers with complex molecular structure [6,9,10].…”

Section: Excess Wing and Johari-goldstein Relaxation In Binary Mixturmentioning

confidence: 99%

“…According to Eq. (1) for a fixed value of τ α,max (or ν α,max ) the separation of the JG peak must be larger for greater values of n. In both polyalcohols and oligomers, for larger number of repeating units a larger value of n was observed and accordingly a secondary peak separated from the structural [4,12,[28][29]. Instead, for short oligomers a smaller value of n was found and the secondary peak was replaced by an EW.…”

Section: Excess Wing and Johari-goldstein Relaxation In Binary Mixturmentioning

confidence: 99%

See 2 more Smart Citations