Fabrication of micro- and nanostructures on polymeric materials is of high interest in technological areas of organic photonics and electronics, biomedicine, bioengineering and sensing.
Laser induced periodic surface structures (LIPSS)
In the formation of laser induced periodic surface structures (LIPSS) the interference between the incoming and the surface scattered waves plays an important role, but the whole mechanism is still not fully understood.
Irradiation at different wavelengths and with pulses in the nanosecond and femtosecond regime was performed in order to study the formation mechanism, to understand the influence of the polymer properties on the nanostructure formation, and to develop applications.
The nanostructured materials are analyzed by atomic force microscopy (AFM), grazing incidence small angle X-ray scattering (GISAXS), Raman spectroscopy, fluorescence and contact angle measurements.
We demonstrate the possibility of tuning and controlling the morphology and size of periodic structures on the surface of polymer films by varying the experimental conditions (pulse duration, wavelength, fluence and number of pulses).
References
E. Rebollar et al, Langmuir 27, 5596 (2011)
E. Rebollar et al, Appl. Phys. Lett. 100, 041106 (2012)
I. Martín-Fabiani et al, Langmuir 28, 7938 (2012)
S. Pérez et al, Appl. Phys. A 110, 683 (2013)
E. Rebollar et al, Phys. Chem. Chem. Phys. 15, 11287 (2013)
E. Rebollar et al, Phys. Chem. Chem. Phys. 16, 17551 (2014)
I. Martín-Fabiani et al, ACS Appl. Mater. Interf. 7, 3162 (2015)
E. Rebollar et al, Langmuir 31, 3973 (2015)
A. Rodríguez-Rodríguez et al, Macromolecules 48, 4024 (2015)
D. Martínez-Tong et al, ACS Appl. Mater. Interf. 7, 19611 (2015)
E. Rebollar et al, Eur. Polym. J. 73, 162 (2015)
J. Cui et al, ACS Appl. Mater. Interf. 8, 31894 (2016)
J. Cui et al, Appl. Surf. Sci. 394, 125 (2017)
R.I Rodriguez-Beltrán et al. Appl. Phys. A 123, 717 (2017)
R.I Rodríguez-Beltrán et al, Appl. Surf. Sci. 436, 1193 (2018)
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Laser microstructuring
Laser irradiation using pulses with duration in the nanosecond to the femtosecond range is investigated for surface patterning of polymers and biopolymers. Laser conditions at which foaming is produced are related to the material properties, particularly extinction coefficient and thermal parameters, which determine the amplitude of the laser-induced pressure wave. While by using longer pulses, the pressure rise is strongly material dependent, under fs irradiation the amplitude of the pressure wave is high enough to drive the nucleation and growth of bubbles, which finally lead to the observed superficial fibrilar structures or foam.
Machining and surface patterning of polymers and biopolymers using fs lasers take place with reduced mechanical and thermal deformation as compared with processing performed with longer ns laser pulses.
Chitosan irradiated with one single pulse at 248 nm and 2.2. J/cm2.
References
M. Castillejo et al, Appl. Surf. Sci. 258, 8919 (2012)
E. Rebollar et al, Appl. Surf. Sci. 302, 231 (2014)
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Additionally, the high peak intensity of focused fs laser pulses allows micromachining inside of transparent polymer and biopolymer materials based on the nonlinear character of the interaction that confines the induced changes to the focal volume.
3D bulk microstructuring of biopolymer by femtosecond laser irradiation through high numerical aperture microscope objective.
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Applications
Substrates for SERS
LIPSS on polymer films have been coated with gold by PLD. Gold coatings preserve the LIPSS integrity in the range of thicknesses studied (2-45 nm) and with a good adhesion to the polymer substrates. The reproducibility of the substrates is good and the choice of the laser irradiation parameters allows the control of the properties of the coated nanostructures. The substrates obtained were tested as SERS substrates. The enhancement factor for the gold coated substrates has been estimated to be 8 orders of magnitude, while an additional enhancement of around 10 is mediated by the presence of LIPSS.
This approach also allows reducing the quantity of metal needed to prepare SERS substrates and therefore can be extended to prepare low-cost substrates for sensitive optical chemical sensors, nanoelectronics, and biomedical devices. Additionally, the use of flexible polymer materials paves the way for a wide range of applications such as printed electronics and flexible displays.
References
E. Rebollar et al, Phys. Chem. Chem. Phys. 14, 15699 (2012)
E. Rebollar et al, J. Appl. Polym. Sci. 132, 42770 (2015)
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Cell culture
Laser induced foam structures are good runners for fabrication of cell culture substrates, since, given the open interconnected pore structure, they exhibit increased availability of adhesion sites combined with permeability to fluids. These substrates were tested as 2D scaffolds for fibroblasts cell growth.
(Left) SEM image of chitosan film irradiated with a single laser pulse at 248 nm, 20 ns, 2800 mJ/cm2 following cell culture of 3 days. (Right) Cell density on the single-pulsed KrF laser-irradiated chitosan surface compared with the corresponding to the non laser treated one.
References
M. Castillejo et al, Appl. Surf. Sci. 258, 8919 (2012)
E. Rebollar et al, Phys. Chem. Chem. Phys. 16, 17551 (2014)
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