Molecular Dynamics Study of a Crystalline Cluster Undergoing a Second-Order Transition. An Inchoate Model of Acetylene

1997 ◽  
Vol 101 (7) ◽  
pp. 1299-1304 ◽  
Author(s):  
Prakriteswar Santikary ◽  
Lawrence S. Bartell
Keyword(s):  
Molecular Dynamics ◽  
Second Order ◽  
Order Transition ◽  
Second Order Transition

NMR · NQR and DTA · DSC Studies of Phase Transitions in Pyridinium Tetrachloropalladate(II) and Pyridinium Tetrachloroplatinate(II)

1998 ◽  
Vol 53 (6-7) ◽  
pp. 419-426 ◽  
Author(s):  
Tetsuo Asaji ◽  
Keizo Horiuchi ◽  
Takehiko Chiba ◽  
Takashige Shimizu ◽  
Ryuichi Ikeda
Keyword(s):  
Phase Transitions ◽  
Low Temperatures ◽  
Structural Phase ◽  
Orientational Order ◽  
Second Order ◽  
Order Transition ◽  
Spin Lattice Relaxation ◽  
Potential Wells ◽  
H Nmr ◽  
Second Order Transition

Abstract From the measurements of DTA • DSC and the temperature dependences of 35Cl NQR frequencies, phase transitions were detected at 150 K, 168 K, and 172 K for (pyH)2 [PtCl4], and at 241 K for (PyH)2 [PdCl4]. In order to elucidate the motional state of the constituent ions in the crystals in connection with the structural phase transitions, the 35Cl NQR and 1H NMR spin-lattice relaxation times and the second moment of the 1H NMR line were measured as functions of temperature. For both compounds, the potential wells for the cationic reorientation are suggested to be highly nonequivalent at low temperatures. Above 168 K, the pyridinium ions in (pyH)2[PtCl4] are expected to reorient between almost equivalent potential wells. As for (pyH)2[PdCl4], it is expected that the orientational order of the cation still remains even above the second order transition at 241 K. A change of the potential curve from two-unequal to three-unequal wells is proposed as a possible mechanism of the second order transition. The activation energies for the cationic motion in the respective model potential are derived for both compounds at high and low temperatures.

Refractometric Determination of Second-Order Transition Temperatures in Polymers. IV. Butadiene-Acrylo-Nitrile Copolymers

1949 ◽  
Vol 22 (2) ◽  
pp. 402-404 ◽  
Author(s):  
Richard H. Wiley ◽  
G. M. Brauer
Keyword(s):  
Low Temperature ◽  
Linear Relation ◽  
Second Order ◽  
Order Transition ◽  
Copolymer Composition ◽  
Transition Temperatures ◽  
Second Order Transition ◽  
Refractometric Determination ◽  
Acrylonitrile Copolymers

Abstract A previous study of the low-temperature properties of a series of vulcanized butadiene-acrylonitrile copolymers indicated an approximately linear relation between composition and brittle temperature. This study provides information relating low-temperature properties to copolymer composition for a series of industrially available butadiene-acrylonitrile copolymers of varying acrylonitrile content. The refractometric technique for determining second-order transition temperatures (Tm) as previously described was used to determine Tm.

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