Microstructure and incubation processes in composite liquid crystalline material (5CB) filled with multi walled carbon nanotubes

Abstract

This work reports a study on microstructure, electrical conductivity and phase transitions of 5CB(4-pentyl-49-cyanobiphenyl) + multi-walled carbon nanotubes (MWCNTs) composite materials. The concentration of MWCNTs was varied within 0.025 and 1 wt.%. The unmodified (o) and modified (m) MWCNTs were used. The mild milling was applied for shortening length of MWCNTs. Direct microscopic observation of composites at different concentrations C of MWCNTs evidenced the presence of aggregation and percolation processes. Formation of percolation networks was observed at C p L 0.025 -0.05% wt and C=C p L 0.1 -0.25% wt for o-MWCNTs and m-MWCNTs composites, respectively. Increase of the percolation threshold for m-MWCNTs, possibly, reflected their smaller aspect ratio r. The conductivity exponents were approximately the same (t L 3.3 l 0.1) for both o-MWCNTs and m-MWCNTs. The microstructure of MWCNT aggregates was not stable in time. The initially formed loose aggregates (L-aggregates) transformed into the more compact C-aggregates during the incubation time of one week. The incubation resulted in decrease of anisotropy, change in phase behaviour near the nematic-isotropic transition, and influenced external electric field response of the studied composite material. Inkubation führt zu einer Abnahme der Anisotropie, einem Wechsel der Phase in der Nähe der nematischen-isotropen Umwandlung und beeinflusst die Antwort auf ein externes elektrisches Feld der studierten Kompositmaterialien.

Liquid crystal suspensions of carbon nanotubes assisted by organically modified Laponite nanoplatelets

“…In accordance with previous studies [39], aging of the E7+CNT samples frequently resulted in gradual grow of the aggregates of CNTs and changing of electro-optic response. Long-term experiments with E7+CNTs+LapO suspensions did not reveal such changes at least over 3 months period.…”

Carbon Nanotubes in Liquid Crystals: Fundamental Properties and Applications

“…The structure of MWCNT aggregates in LC suspensions composites is not stable in time and change continuously after the sample preparation [140,141]. Typically, at small concentration (<0.001 wt%), the individual CNTs are rather uniformly distributed inside nematic matrix.…”

Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

“…Table 2 provides a short summary of the reported effects. As can be seen, both decrease [118,119,[121][122][123][124][125][126][127][143][144][145][146][147][148][149][150][151][152] and increase [105,120,[128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][150][151][152][153] in the electrical conductivity of liquid crystals doped with carbon-based nanomaterials were reported.…”

“…The electrical properties of liquid crystals doped with carbon nanotubes (CNT) were explored in numerous papers [105,116,. The majority of these manuscripts [105,116,117,[128][129][130][131][132][133][134][135][136][137][138][139][140][141][142] report the enhancement of the electrical conductivity  of liquid crystals doped with carbon nanotubes. The increase in  is associated with the percolation phenomenon and high intrinsic electrical conductivity of carbon nanotubes: a sharp transition from the ionic conductivity to the dominating charge hopping conductivity occurs at a certain concentration called the percolation concentration [105,116].…”