Rotational Diffusion of Guest Molecules Confined in Uni-directional Nanopores

  • Wycliffe K. Kipnusu
  • Ciprian Iacob
  • Malgorzata Jasiurkowska-Delaporte
  • Wilhelm Kossack
  • Joshua R. Sangoro
  • Friedrich Kremer
Part of the Advances in Dielectrics book series (ADVDIELECT)


Broadband dielectric spectroscopy (BDS) is employed to study the rotational diffusion of Tris(2-ethylhexyl)phosphate (TEHP), a glass-former, and 4-heptyl-4\(^\prime \)-isothiocyanatobiphenyl (7BT), a liquid crystal, both confined in nanoporous silica membranes having uni-directional pores with diameters in the range 4–10.4 nm. It is observed that upon cooling, the glassy dynamics (\(\alpha \)-process) of TEHP is enhanced near the calorimetric glass transition. This confinement effect is attributed to a slight reduction in density of the liquid in the nanopores. The secondary \(\beta \)-relaxation in TEHP is however unaffected by the geometrical confinement. Silanization of the inner pore surfaces has no measurable effect on the mobility of the guest molecules. For the case of liquid crystal 7BT, two relaxation processes originating from librations about the molecule’s short (\(\delta \)-process) and long axes (\(\beta _{\text {LC}}\)-process) are observed. The former becomes suppressed with decreasing pore diameter, while the latter is nearly unaffected with a tendency to become faster with decreasing pore diameter, an effect caused by orientational ordering due to geometrical constraints.


Uni-directional nanopores Rotational diffusion Electrochemical etching 4-heptyl-4\(^\prime \)-isothiocyanatobiphenyl 



Broadband dielectric spectroscopy




4-heptyl-4\(^\prime \)-isothiocyanatobiphenyl


Nuclear magnetic resonance


Differential scanning calorimetry




Liquid crystals


Smectic E


Hydrofluoric acid




Porous silicon

pSiO\(_{2 }\)

Porous silica


Scanning electron micrograph








Fourier transform infrared


Hewlett Packard










Relaxation time distribution





\(T_{\text {g}}\)

Glass transition temperature


Density functional theory







Financial support by the DFG (Germany), within IRTG “Diffusion in Porous Materials,” SFB/TRR 102 within the project “Polymers Under Multiple Constrains,” Alexander von Humboldt Foundation and Leipzig School of Natural Sciences, “Building with Molecules and Nano-Objects” (BuildMoNa) is gratefully acknowledged.


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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Wycliffe K. Kipnusu
    • 1
  • Ciprian Iacob
    • 2
  • Malgorzata Jasiurkowska-Delaporte
    • 3
  • Wilhelm Kossack
    • 1
  • Joshua R. Sangoro
    • 4
  • Friedrich Kremer
    • 1
  1. 1.Institute of Experimental Physics IUniversity of LeipzigLeipzigGermany
  2. 2.Department of Materials Science and EngineeringPenn State UniversityUniversity ParkUSA
  3. 3.NanoBioMedical CentreAdam Mickiewicz UniversityPoznanPoland
  4. 4.Department of Chemical and Biomolecular EngineeringUniversity of TennesseeKnoxvilleUSA

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