Surface Tension Obtained from Various Smectic-A Liqujd-Crystal Free-Standing Films

1997 ◽  
Vol 302 (1) ◽  
pp. 181-186 ◽  
Author(s):  
P. Mach ◽  
S. Grantz ◽  
T. Stoebe ◽  
C. C. Huang
Keyword(s):  
Surface Tension ◽  
Free Standing ◽  
Smectic A

scholarly journals Interface Characteristics of Neat Melts and Binary Mixtures of Polyethylenes from Atomistic Molecular Dynamics Simulations

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1059
Author(s):  
Sanghun Lee ◽  
Curtis W. Frank ◽  
Do Y. Yoon
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Molecular Dynamics Simulations ◽  
Binary Mixtures ◽  
Surface Segregation ◽  
Surface Region ◽  
Polymer Chains ◽  
Methyl Groups ◽  
Free Standing ◽  
Dynamics Simulations

Molecular dynamics simulations of free-standing thin films of neat melts of polyethylene (PE) chains up to C150H302 and their binary mixtures with n-C13H28 are performed employing a united atom model. We estimate the surface tension values of PE melts from the atomic virial tensor over a range of temperatures, which are in good agreement with experimental results. Compared with short n-alkane systems, there is an enhanced surface segregation of methyl chain ends in longer PE chains. Moreover, the methyl groups become more segregated in the surface region with decreasing temperature, leading to the conclusion that the surface-segregation of methyl chain ends mainly arises from the enthalpic origin attributed to the lower cohesive energy density of terminal methyl groups. In the mixtures of two different chain lengths, the shorter chains are more likely to be found in the surface region, and this molecular segregation in moderately asymmetric mixtures in the chain length (C13H28 + C44H90) is dominated by the enthalpic effect of methyl chain ends. Such molecular segregation is further enhanced and dominated by the entropic effect of conformational constraints in the surface for the highly asymmetric mixtures containing long polymer chains (C13H28 + C150H3020). The estimated surface tension values of the mixtures are consistent with the observed molecular segregation characteristics. Despite this molecular segregation, the normalized density of methyl chain ends of the longer chain is more strongly enhanced, as compared with the all-segment density of the longer chain itself, in the surface region of melt mixtures. In addition, the molecular segregation results in higher order parameter of the shorter-chain segments at the surface and deeper persistence of surface-induced segmental order into the film for the longer chains, as compared with those in neat melt films.

Surface tension of free-standing liquid-crystal films

1994 ◽  
Vol 49 (5) ◽  
pp. R3587-R3590 ◽  
Author(s):  
T. Stoebe ◽  
P. Mach ◽  
C. C. Huang
Keyword(s):  
Surface Tension ◽  
Liquid Crystal ◽  
Free Standing ◽  
Liquid Crystal Films ◽  
Crystal Films

scholarly journals Dynamics of Dislocations in Smectic A Liquid Crystals Doped with Nanoparticles

Crystals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 400 ◽  
Author(s):  
Patrick Oswald
Keyword(s):  
Liquid Crystals ◽  
Experimental Results ◽  
Free Standing ◽  
Plastic Properties ◽  
Smectic A ◽  
Linear Defects ◽  
Smectic A Phase ◽  
Dynamical Properties ◽  
Edge Dislocations ◽  
Smectic A Liquid Crystals

Edge dislocations are linear defects that locally break the positional order of the layers in smectic A liquid crystals. As in usual solids, these defects play a central role for explaining the plastic properties of the smectic A phase. This work focuses on the dynamical properties of dislocations in bulk samples prepared between two glass plates and in free-standing films. The emphasis will be put on the measurement of the mobility of edge dislocations in liquid crystals either pure or doped with nanoparticles. The experimental results will be compared to the existing models.

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