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Nanothermodynamics.
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In any thermodynamic system, including nanosystems,
the free energy change during sorption is related to its internal
stressing. However, experimental evidences of energy flow between
thermodynamic states before and after sorption of a small number
of molecules in nanosystems are rare, due to the minute energy flow
and sub-nm strain variation.
In this work, it is shown that the entropic variation during isothermal
and isobaric sorption of gaseous (water or methanol) molecules in
an ensemble of photon induced nano-voids within a PDMS matrix, is
proportional to the number of nano-voids and the entropic nanothermodynamic
potential is the outcome of the confinement of translational motion
of the adsorbed molecules within the nano-voids. Following irradiation
of PDMS with a molecular fluorine laser at 157 nm, white light reflectance
spectroscopy establishes the relation between the entropic variation,
via the sub-nm strain field, and the external parameters (number
of photons and adsorbed molecules). Moreover, the contribution of
entropic, internal, chemical and surface energy components in the
stressing field is analyzed by nanoindentation and atomic force
microscopy.
The methodology allows the identification of nanothermodynamic potentials
and strain field variations in thin polymeric layers at pJ and sub-nm
levels.
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AFM
surface images of PDMS films before sorption. The laser fluence
is per laser pulse.
(a):
Non-irradiated film. (b):
200 laser pulses (lp). (c): 400 lp. (d): 500 lp (e): 600 lp. (f):
1000 lp.
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Surface
parameters of irradiated PDMS films. (a) Before sorption. (b)
After sorption.
(Black plot) Surface roughness (Ra).
(Red plot) Root mean square surface roughness ( Rms).
(Green plot) Surface roughness histograms
(Z) (z-axis).
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AFM
image of "lakes" (orange) and "islands" (gray)
of a non-irradiated matrix for a fractal area of 2X 103
nmXnm and average
height Z set to its half maximum value at 1.13 nm.
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(a)
Concentration of "lakes" for different size fractals vs
the number of laser pulses.
(b) Fractal dimension vs number of laser pulses for different small
fractal sizes. The concentration of small size nano-voids is increasing
following VUV irradiation.
(c) Fractal dimension vs fractal size at different number of laser
pulses.
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(a)
Power spectra of surface along the axes. The origin of the anisotropy
is attributed to the polarized laser beam that directs the dissociated
moieties along a preferable direction. (a), (b) axes of non-irradiated
matrix. (c),(d) axes of irradiated matrix (500 laser pulses).
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Force-distance
curves of PDMS surface irradiated at different laser fluence
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(a)
Tip-surface adhesion force of irradiated PDMS at different laser
fluence (per laser pulse).
(b)
Young's modulus of PDMS surface irradiated at different laser fluence
(per laser pulse).
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Relative
strain of the 712 nm PDMS thick layer at different irradiating conditions
and concentration of analytes measured with WLRS.
(a) Water (b) Methanol.
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Left:
Relative entropic strain of PDMS layer during sorption of analytes
at different ratios of the concentration of nano-voids and polymeric
sites to analytes x(n).
(a) x>1 (b) x<1The experimental configuration corresponds
to x>1.
Right:
(a) Relative strain at different laser pulses and dipole interaction
energies. The best fit for both analytes (methanol/water), is for
x>1.
(b) Relative strain at different number of laser pulses and ratio
of nano-voids to the polymeric sites. The best fit for both analytes
is for x>1.
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(a)
Simplified 2-D Permutation diagram for the Flory-Huggins model:
One polymeric site and one analyte molecule occupy separate places
in the net. Polymeric sites (
), nano-voids (
), analyte molecules (
). The model corresponds to a "multiset permutation" of
Na analytes and Nv nano-voids.
(b) Current model: A different number of analyte molecules are trapped
within nano-voids. The model corresponds to a number of "combinations
without repetition" of analytes and nano-voids. In the case
of strong polar interactions, the motion of analytes is restricted
by the polymeric sites too.
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Relevant
Publications
- Entropic
nanothermodynamic potential from molecular trapping within photon
induced nano-voids in photon processed PDMS layers.
A. C. Cefalas, E. Sarantopoulou, Z. Kollia, M. Kitsara, I. Raptis
and E. Bakalis,
Soft Matter 8, 5561 (2012).
DOI:10.1039/C2SM07141J
- Surface
nano/micro functionalization of PMMA thin films by 157 nm irradiation
for sensing applications.
E. Sarantopoulou, Z. Kollia, A.C. Cefalas, K. Manoli, M. Sanopoulou,
D. Goustouridis, S. Chatzandroulis and I. Raptis
Appl. Surf. Sci., 254, 1710 (2008).
DOI:
10.1016/j.apsusc.2007.07.138
- Surface
modification of polymeric thin films with vacuum ultraviolet light.
E. Sarantopoulou, J. Kovac, Z. Kollia, I. Raptis, S. Kobe and
A. C. Cefalas,
Surf. Interface Anal. 40 (3-4), 400 (2008).
DOI: 10.1002/sia.2776
- Enhancement
of Sensing Properties of Thin Poly(Methyl Methacrylate) Films
by VUV Modification.
I. Raptis, J. Kovac M. Chatzichristidi, E. Sarantopoulou, Z. Kollia,
S. Kobe and A. C. Cefalas,
JLMN-Journal of Laser Micro/Nanoengineering, 2, 200 (2007).
Conference
Presentations
- Entropic
nanothermodynamic potential from molecular trapping within photon
processed polymeric layers.
A.C. Cefalas, E. Sarantopoulou, Z. Kollia,
M. Kitsara, I. Raptis and E. Bakalis,
3rd International Nanotechnology Conference and Exhibition, NanoIsrael
2012,
Tel-Aviv, Israel, 26-27 March, 2012.
- Microfabrication of sensing
properties.
E. Sarantopoulou, Z. Kollia, K. Manoli, M. Saropoulou, D. Goustouridis,
S. Chatzandroulis and I. Raptis,
14th Internasional Conference on solid state sensors, Lyon France,
June 10-14 (2007).
- Enhancement
of sensing properties of thin poly(methyl methacrylate) films
by VUV modification.
I. Raptis, J. Kovac, M. Chatzichristidi, E. Sarantopoulou,
Z. Kollia, S. Kobe and A. C. Cefalas,
8th International Symposium on Laser Precision Microfabrication
(2007).
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48,
Vassileos Constantinou Aven. 11635 Athens, Greece
Tel: +30 210 7273840, Fax: +30 210 7273842, email :ccefalas@eie.gr
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