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NanoMat 2018
Nano Research & Applications
ISSN: 2471-9838
Page 31
April 26-27, 2018
Rome, Italy
17
th
Edition of International Conference on
Emerging Trends in
Materials Science and
Nanotechnology
T
hermosalient (TS) crystals are an emerging class of organic
materials that undergo macroscopic motion when taken
over their phase transition. The visually observable motion
occurs over distances that are several times greater compared
to the size of the crystals. Such efficient conversion of heat
into mechanical work favors these crystals for application as
thermomechanical actuators. Recent reports have shown that
crystalline organic compounds exhibit unusual polymorphism
and preferred orientation when confined within nanospaces.
Inspired by such behavior and in an attempt to observe the TS
effect at the nanoscale, 1, 2, 4, 5-tetrabromobenzene (TBB)
was selected as a model material that undergoes TS phase
transition from β to γ phase at about 40°C. To that end, TBB
was crystallized within the 20-200 nm-wide channels of anodic
aluminum oxide (AAO) templates, and its structure was studied
using two-dimensional x-ray microdiffraction (2D-µXRD) and
powder x-ray diffraction (PXRD) analyses. Whereas bulk TBB
crystallizes in the β phase at room temperature, the analysis
revealed that when confined within the anodized aluminum
oxide (AAO) nanopores, TBB crystallizes in the metastable γ
phase with preferred orientation at room temperature. Figure
1a shows the 100 nm pores of AAO templates filled with TBB,
whereas Figure 1b showsTBB crystals released after dissolving
the AAO templates. The 2D-µXRD pattern of the TBB filled AAO
template in Figure 1c shows discrete spots, revealing preferred
growth of the TBB nanocrystals. The PXRD pattern of TBB-filled
AAO template, shown in Figure 1d, is identical to that of bulk γ
phase TBB, confirming that TBB grows in the γ phase within the
nanopores. We also found that these TBB nanocrystals remain
indefinitely stable in the γ phase from cryogenic temperatures
up to nearly 80°C, where they sublime. These findings uncover
fundamental differences between nanosized organic TS
crystals and their bulk counterparts.
Figure 1: (a,b)
SEM images of TBB-filled AAO template (a) and TBB nano-
crystals obtained after dissolving the AAO template (b)&(c) 2D-µXRD pat-
tern of TBB filled AAO template. (d) PXRD pattern of crushed TBB-filled AAO
template shown together with PXRD pattern of bulk β and γ phase of TBB
crystals.
Recent Publications
1. N K Nath, M K Panda, S C Sahoo and P Naumov (2014)
Thermally induced and photoinduced mechanical
effects in molecular single crystals - a revival.
CrystEngComm 16(10):1850-1858.
2. P Naumov, S Chizhik, M K Panda, N K Nath and E
Boldyreva (2015) Mechanically responsive molecular
crystals. Chemical Reviews 115(22):12440-12490.
3. C L Jackson and G B McKenna (1996) Vitrification and
crystallization of organic liquids confined to nanoscale
pores. Chemistry of Materials 8(8):2128-2137.
4. H F Lieberman, R J Davey and D M T Newsham (2000)
Br···Br and Br···H interactions in action: polymorphism,
hopping, and twinning in 1,2,4,5-tetrabromobenzene.
Chemistry of Materials 12(2):490–494.
5. Khalil C, T Hu and P Naumov (2018) Nanoscale
crystallization
and
thermal
behaviour
of
1,2,4,5-tetrabromobenzene. CrystEngComm 20:636-
642.
Crystallization of 1, 2, 4, 5-tetrabromobenzene under nanoscale
confinement
Abdullah Khalil
1
, Chunhua Tony Hu
2
and
Panče Naumov
1
1
New York University Abu Dhabi, UAE
2
New York University, USA
Abdullah Khalil, Nano Res Appl, Volume:4
DOI: 10.21767/2471-9838-C1-008