Publications by authors named "Ignacio Martin-Fabiani"

20 Publications

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Dynamical Density Functional Theory for the Drying and Stratification of Binary Colloidal Dispersions.

Langmuir 2021 Feb 20;37(4):1399-1409. Epub 2021 Jan 20.

Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, United Kingdom.

We develop a dynamical density functional theory based model for the drying of colloidal films on planar surfaces. We consider mixtures of two different sizes of hard-sphere colloids. Depending on the solvent evaporation rate and the initial concentrations of the two species, we observe varying degrees of stratification in the final dried films. Our model predicts the various structures described in the literature previously from experiments and computer simulations, in particular the small-on-top stratified films. Our model also includes the influence of adsorption of particles to the interfaces.
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http://dx.doi.org/10.1021/acs.langmuir.0c02825DOI Listing
February 2021

Evaporation-driven self-assembly of binary and ternary colloidal polymer nanocomposites for abrasion resistant applications.

J Colloid Interface Sci 2021 Jan 3;581(Pt B):729-740. Epub 2020 Aug 3.

Department of Materials, Loughborough University, Loughborough, UK.

We harness the self-assembly of aqueous binary latex/silica particle blends during drying to fabricate films segregated by size in the vertical direction. We report for the first time the experimental drying of ternary colloidal dispersions and demonstrate how a ternary film containing additional small latex particles results in improved surface stability and abrasion resistance compared with a binary film. Through atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDX), we show that the vertical distribution of filler particles and the surface morphologies of the films can be controlled by altering the evaporation rate and silica volume fraction. We report the formation of various silica superstructures at the film surface, which we attribute to a combination of diffusiophoresis and electrostatic interactions between particles. Brownian dynamics simulations of the final stages of solvent evaporation provide further evidence for this formation mechanism. We show how an additional small latex particle population results in an increased abrasion resistance of the film without altering its morphology or hardness. Our work provides a method to produce water-based coatings with enhanced abrasion resistance as well as valuable insights into the mechanisms behind the formation of colloidal superstructures.
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http://dx.doi.org/10.1016/j.jcis.2020.08.001DOI Listing
January 2021

Colloidal assembly of polydisperse particle blends during drying.

Soft Matter 2020 Sep;16(36):8453-8461

Department of Materials, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK.

In this work, we synthesize a polydisperse aqueous colloidal system composed of small and large zwitterionic particles, as well as medium sized standard acrylic particles. By assembling these dispersions into films by drying, we show using atomic force microscopy (AFM) how their top surfaces can be mostly covered by zwitterionic groups for a wide range of evaporation rates. We probe underneath the top film surface using Fourier-transform infrared (FTIR) spectroscopy - attenuated total reflection (ATR), observing that the content in zwitterionic particles of the film upper layer increases for faster evaporation rates. We show how polydisperse systems hold great potential to overcome the evaporation rate dependence of size segregation processes in drying colloidal blends, and we provide further insights into the assembly mechanisms involved. Polydisperse blends enhance the robustness of such processes for application in coatings and other soft products where evaporation rate can not be tuned.
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http://dx.doi.org/10.1039/d0sm00785dDOI Listing
September 2020

Nanocomposites of Au/Disentangled UHMWPE: A Combined Optical and Structural Study.

Molecules 2020 Jul 15;25(14). Epub 2020 Jul 15.

Department of Materials, Loughborough University, Leicestershire LE11 3TU, UK.

The term disentangled refers to polymers with fewer entanglements in the amorphous regions, a metastable condition that can significantly affect the material's properties and processing behavior. The lower entanglement density in ultra-high molecular weight polyethylene (dis-UHMWPE) facilitates the solid-state processability into uniaxially-oriented specimens reaching very high draw ratios and crystallinities. In this study, Au/dis-UHMWPE nanocomposites were formulated and processed at variable draw ratios. Polarized light microscopy suggests gold nanoparticles are oriented in arrays following the drawing of polymer chains. The structural features, upon orientation, are studied by means of Raman spectroscopy, wide- and small-angle X-ray scattering, and near-infrared spectrophotometry. Crystallinity is found to increase by 15%, as calculated by wide-angle X-ray scattering. The change in optical absorbance in the visible spectrum indicates that, with orientation, the average size of gold aggregates increases, supported quantitatively by small-angle X-ray scattering. Since the gold nanoparticles are expected to be found within amorphous chain segments, the aforementioned findings are attributed to the increase of crystallinity and thus the decrease of available (amorphous) space.
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http://dx.doi.org/10.3390/molecules25143225DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7397333PMC
July 2020

Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene.

Proc Natl Acad Sci U S A 2019 Aug 12;116(35):17163-17168. Epub 2019 Aug 12.

Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125;

Thermally conductive polymer crystals are of both fundamental and practical interest for their high thermal conductivity that exceeds that of many metals. In particular, polyethylene fibers and oriented films with uniaxial thermal conductivity exceeding 50 [Formula: see text] have been reported recently, stimulating interest into the underlying microscopic thermal transport processes. While ab initio calculations have provided insight into microscopic phonon properties for perfect crystals, such properties of actual samples have remained experimentally inaccessible. Here, we report the direct observation of thermal phonons with mean free paths up to 200 nm in semicrystalline polyethylene films using transient grating spectroscopy. Many of the mean free paths substantially exceed the crystalline domain sizes measured using small-angle X-ray scattering, indicating that thermal phonons propagate ballistically within and across the nanocrystalline domains; those transmitting across domain boundaries contribute nearly one-third of the thermal conductivity. Our work provides a direct determination of thermal phonon propagation lengths in molecular solids, yielding insights into the microscopic origins of their high thermal conductivity.
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http://dx.doi.org/10.1073/pnas.1905492116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6717268PMC
August 2019

In Situ Monitoring of Latex Film Formation by Small-Angle Neutron Scattering: Evolving Distributions of Hydrophilic Stabilizers in Drying Colloidal Films.

Langmuir 2019 Mar 1;35(10):3822-3831. Epub 2019 Mar 1.

Department of Physics , University of Surrey , Guildford GU2 7XH , U.K.

The distribution of hydrophilic species, such as surfactants, in latex films is of critical importance for the performance of adhesives, coatings, and inks, among others. However, the evolution of this distribution during the film formation process and in the resulting dried films remains insufficiently elucidated. Here, we present in situ (wet) and ex situ (dry) small-angle neutron scattering (SANS) experiments that follow the film formation of two types of latex particles, which differ in their stabilizer: either a covalently bonded poly(methacrylic acid) (PMAA) segment or a physically adsorbed surfactant (sodium dodecyl sulfate, SDS). By fitting the experimental SANS data and combining with gravimetry experiments, we have ascertained the hydrophilic species distribution within the drying film and followed its evolution by correlating the size and shape of stabilizer clusters with the drying time. The evolution of the SDS distribution over drying time is being driven by a reduction in the interfacial free energy. However, the PMAA-based stabilizer macromolecules are restricted by their covalent bonding to core polymer chains and hence form high-surface area disclike phases at the common boundary between particles and PMAA micelles. Contrary to an idealized view of film formation, PMAA does not remain in the walls of a continuous honeycomb structure. The results presented here shed new light on the nanoscale distribution of hydrophilic species in drying and ageing latex films. We provide valuable insights into the influence of the stabilizer mobility on the final structure of latex films.
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http://dx.doi.org/10.1021/acs.langmuir.8b04251DOI Listing
March 2019

Enhanced Water Barrier Properties of Surfactant-Free Polymer Films Obtained by MacroRAFT-Mediated Emulsion Polymerization.

ACS Appl Mater Interfaces 2018 Apr 21;10(13):11221-11232. Epub 2018 Mar 21.

Department of Physics , University of Surrey , Guildford GU2 7XH , U.K.

The presence of low-molar-mass surfactants in latex films results in detrimental effects on their water permeability, gloss, and adhesion. For applications such as coatings, there is a need to develop formulations that do not contain surfactants and have better water barrier properties. Having previously reported the synthesis of surfactant-free latex particles in water using low amounts (<2 wt %) of chains synthesized by controlled radical polymerization (Lesage de la Haye et al. Macromolecules 2017, 50, 9315-9328), here we study the water barrier properties of films made from these particles and their application in anticorrosion coatings. When films cast from aqueous dispersions of acrylate copolymer particles stabilized with poly(sodium 4-styrenesulfonate) (PSSNa) were immersed in water for 3 days, they sorbed only 4 wt % water. This uptake is only slightly higher than the value predicted for the pure copolymer, indicating that the negative effects of any particle boundaries and hydrophilic-stabilizing molecules are minimal. This sorption of liquid water is 5 times lower than what is found in films cast from particles stabilized with the same proportion of poly(methacrylic acid) (PMAA), which is more hydrophilic than PSSNa. In water vapor with 90% relative humidity, the PSSNa-based film had an equilibrium sorption of only 4 wt %. A small increase in the PMAA content has a strong and negative impact on the barrier properties. Nuclear magnetic resonance relaxometry on polymer films after immersion in water shows that water clusters have the smallest size in the films containing PSSNa. Furthermore, these films retain their optical clarity during immersion in liquid water for up to 90 min, whereas all other compositions quickly develop opacity ("water whitening") as a result of light scattering from sorbed water. This implies a remarkably complete coalescence and a very small density of defects, which yields properties matching those of some solvent-borne films. The latex stabilized with PSSNa is implemented as the binder in a paint formulation for application as an anticorrosive barrier coating on steel substrates and evaluated in accelerated weathering and corrosion tests. Our results demonstrate the potential of self-stabilized latex particles for the development of different applications, such as waterborne protective coatings and pressure-sensitive adhesives.
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http://dx.doi.org/10.1021/acsami.8b01040DOI Listing
April 2018

pH-Switchable Stratification of Colloidal Coatings: Surfaces "On Demand".

ACS Appl Mater Interfaces 2016 Dec 12;8(50):34755-34761. Epub 2016 Dec 12.

Department of Physics, University of Surrey , Guildford, Surrey GU2 7XH, United Kingdom.

Stratified coatings are used to provide properties at a surface, such as hardness or refractive index, which are different from underlying layers. Although time-savings are offered by self-assembly approaches, there have been no methods yet reported to offer stratification on demand. Here, we demonstrate a strategy to create self-assembled stratified coatings, which can be switched to homogeneous structures when required. We use blends of large and small colloidal polymer particle dispersions in water that self-assemble during drying because of an osmotic pressure gradient that leads to a downward velocity of larger particles. Our confocal fluorescent microscopy images reveal a distinct surface layer created by the small particles. When the pH of the initial dispersion is raised, the hydrophilic shells of the small particles swell substantially, and the stratification is switched off. Brownian dynamics simulations explain the suppression of stratification when the small particles are swollen as a result of reduced particle mobility, a drop in the pressure gradient, and less time available before particle jamming. Our strategy paves the way for applications in antireflection films and protective coatings in which the required surface composition can be achieved on demand, simply by adjusting the pH prior to deposition.
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http://dx.doi.org/10.1021/acsami.6b12015DOI Listing
December 2016

Dynamic Stratification in Drying Films of Colloidal Mixtures.

Phys Rev Lett 2016 Mar 18;116(11):118301. Epub 2016 Mar 18.

Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom.

In simulations and experiments, we study the drying of films containing mixtures of large and small colloidal particles in water. During drying, the mixture stratifies into a layer of the larger particles at the bottom with a layer of the smaller particles on top. We developed a model to show that a gradient in osmotic pressure, which develops dynamically during drying, is responsible for the segregation mechanism behind stratification.
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http://dx.doi.org/10.1103/PhysRevLett.116.118301DOI Listing
March 2016

In situ monitoring of laser-induced periodic surface structures formation on polymer films by grazing incidence small-angle X-ray scattering.

Langmuir 2015 Apr 26;31(13):3973-81. Epub 2015 Mar 26.

‡Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121, 28006 Madrid, Spain.

The formation of laser-induced periodic surface structures (LIPSS) on model spin-coated polymer films has been followed in situ by grazing incidence small-angle X-ray scattering (GISAXS) using synchrotron radiation. The samples were irradiated at different repetition rates ranging from 1 up to 10 Hz by using the fourth harmonic of a Nd:YAG laser (266 nm) with pulses of 8 ns. Simultaneously, GISAXS patterns were acquired during laser irradiation. The variation of both the GISAXS signal with the number of pulses and the LIPSS period with laser irradiation time is revealing key kinetic aspects of the nanostructure formation process. By considering LIPSS as one-dimensional paracrystalline lattice and using a correlation found between the paracrystalline disorder parameter, g, and the number of reflections observed in the GISAXS patterns, the variation of the structural order of LIPSS can be assessed. The role of the laser repetition rate in the nanostructure formation has been clarified. For high pulse repetition rates (i.e., 10 Hz), LIPSS evolve in time to reach the expected period matching the wavelength of the irradiating laser. For lower pulse repetition rates LIPSS formation is less effective, and the period of the ripples never reaches the wavelength value. Results support and provide information on the existence of a feedback mechanism for LIPSS formation in polymer films.
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http://dx.doi.org/10.1021/acs.langmuir.5b00285DOI Listing
April 2015

Mapping the structural order of laser-induced periodic surface structures in thin polymer films by microfocus beam grazing incidence small-angle X-ray scattering.

ACS Appl Mater Interfaces 2015 Feb 2;7(5):3162-9. Epub 2015 Feb 2.

Department of Physics, University of Surrey , Guildford GU2 7XH, United Kingdom.

In this work we present an accurate mapping of the structural order of laser-induced periodic surface structures (LIPSS) in spin-coated thin polymer films, via a microfocus beam grazing incidence small-angle X-ray scattering (μGISAXS) scan, GISAXS modeling, and atomic force microscopy imaging all along the scanned area. This combined study has allowed the evaluation of the effects on LIPSS formation due to nonhomogeneous spatial distribution of the laser pulse energy, mapping with micrometric resolution the evolution of the period and degree of structural order of LIPSS across the laser beam diameter in a direction perpendicular to the polarization vector. The experiments presented go one step further toward controlling nanostructure formation in LIPSS through a deep understanding of the parameters that influence this process.
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http://dx.doi.org/10.1021/am5074968DOI Listing
February 2015

Micro- and submicrostructuring thin polymer films with two and three-beam single pulse laser interference lithography.

Langmuir 2014 Jul 18;30(29):8973-9. Epub 2014 Jul 18.

Instituto de Estructura de la Materia (IEM-CSIC) , Serrano 121, 28006 Madrid, Spain.

In this work we report the application of two and three-beam single pulse laser interference lithography to thin polymer films of poly(trimethylene terephthalate) (PTT). By irradiating the sample surface with temporary and spatially overlapped single pulses from two or three coherent beams and changing the angles of incidence, we have accomplished the fabrication of large-area polymer micro and submicrogratings as well as submicrometric cavities arranged in a hexagonal lattice. The characterization of the structures in real space by atomic force microscopy (AFM) and scanning electron microscopy (SEM) has allowed us to determine the formation mechanism of the microgratings to be based on different ablation regimes depending on the local fluence. Moreover, complementary characterization of the submicrometric cavities in reciprocal space by grazing incidence small-angle X-ray scattering (GISAXS) confirms the existence of large areas where two-dimensional order is present. The experiments presented in this work demonstrate the suitability of single pulse laser interference lithography for micro and submicrostructuring polymer films, opening up new possibilities for patterning and paving the way for potential applications where polymer structures are involved.
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http://dx.doi.org/10.1021/la5021059DOI Listing
July 2014

Nanostructuring thin polymer films with optical near fields.

ACS Appl Mater Interfaces 2013 Nov 1;5(21):11402-8. Epub 2013 Nov 1.

Instituto de Estructura de la Materia, IEM-CSIC , Serrano 121, 28006 Madrid, Spain.

In the present work, we report on the application of optical near fields to nanostructuring of poly(trimethylene terephthalate) (PTT) thin films. By exposure to a single ultraviolet nanosecond laser pulse, the spatial intensity modulation of the near-field distribution created by a silica microsphere is imprinted into the films. Setting different angles of incidence of the laser, elliptical or circular periodic ring patterns can be produced with periods as small as half the laser wavelength used. These highly complex patterns show optical and topographical contrast and can be characterized by optical microscopy (OM) and atomic force microscopy (AFM). We demonstrate the key role of the laser wavelength and coherence length in achieving smooth, extended patterns in PTT by using excimer laser (193 nm) and Nd:YAG laser (266 nm) pulses. Reference experiments performed in Ge2Sb2Te5 (GST) demonstrate that nanopatterning in PTT is triggered by ablation as opposed to GST, in which nanopatterning originates from laser-induced phase change, accompanied by a small topographical contrast. The experiments presented in this work demonstrate the suitability of optical near fields for structuring polymer films, opening up new possibilities for nanopatterning and paving the way for potential applications where optical near fields and polymer nanostructures are involved.
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http://dx.doi.org/10.1021/am4036543DOI Listing
November 2013

Assessment of femtosecond laser induced periodic surface structures on polymer films.

Phys Chem Chem Phys 2013 Jul 3;15(27):11287-98. Epub 2013 Jun 3.

Instituto de Química Física Rocasolano, IQFR-CSIC, Serrano 119, 28006 Madrid, Spain.

In this work we present the formation of laser induced periodic surface structures (LIPSS) on spin-coated thin films of several model aromatic polymers including poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly carbonate bis-phenol A upon irradiation with femtosecond pulses of 795 and 265 nm at fluences well below the ablation threshold. LIPSS are formed with period lengths similar to the laser wavelength and parallel to the direction of the laser polarization vector. Formation of LIPSS upon IR irradiation at 795 nm, a wavelength at which the polymers absorb weakly, contrasts with the absence of LIPSS in this spectral range upon irradiation with nanosecond pulses. Real and reciprocal space characterization of LIPSS obtained by Atomic Force Microscopy (AFM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS), respectively, yields well correlated morphological information. Comparison of experimental and simulated GISAXS patterns suggests that LIPSS can be suitably described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice. Fluorescence measurements, after laser irradiation, provide indirect information about dynamics and structure of the polymer at the molecular level. Our results indicate that the LIPSS are formed by interference of the incident and surface scattered waves. As a result of this process, heating of the polymer surface above its glass transition temperature takes place enabling LIPSS formation.
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http://dx.doi.org/10.1039/c3cp51523kDOI Listing
July 2013

Understanding crystallization features of P(VDF-TrFE) copolymers under confinement to optimize ferroelectricity in nanostructures.

Nanoscale 2013 Jul 28;5(13):6006-12. Epub 2013 May 28.

Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain.

The successful development of ferroelectric polymer devices depends on the effective fabrication of polar ferroelectric crystalline nanostructures. We demonstrate, by scanning X-ray microdiffraction using synchrotron light, the heterogeneous character of high aspect ratio one-dimensional nanoarrays of poly(vinylidene fluoride-co-trifluoroethylene) copolymers supported by a residual polymer film. They were prepared by melt and solution template wetting, using porous anodic aluminum oxide as a template. The spatial evolution of different polymorphs from the mixture of paraelectric and ferroelectric crystal forms (residual film) to the pure ferroelectric form (nanoarray) is evidenced for the samples prepared by solution wetting. However, for samples prepared by melt wetting the ferroelectric phase is exclusively obtained in both the residual film and nanoarray. The crystal nuclei formed in the polymer film connected to the nanoarray play a key role in determining the formation of a crystallinity distribution gradient, where the crystallinity decreases along the first 5-10 microns in the nanorods reaching a steady value afterwards. The minimum decrease in crystallinity is revealed for samples prepared by melt wetting. The results reported in this work endeavour to enhance the understanding of crystallization under confinement for ferroelectric copolymers and reveal the parameters for improving the ferroelectric character of polymer nanostructures.
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http://dx.doi.org/10.1039/c3nr00516jDOI Listing
July 2013

Crystallization under one-dimensional confinement in alumina nanopores of poly(trimethylene terephthalate) and its composites with single wall carbon nanotubes.

ACS Appl Mater Interfaces 2013 Jun 28;5(11):5324-9. Epub 2013 May 28.

Instituto de Estructura de la Materia (IEM-CSIC), Madrid, Spain.

We report the preparation of semicrystalline polymer nanorods of PTT and of its nanocomposites with SWCNTs by infiltration of the molten polymer into disordered anodic alumina membranes. An accurate study of the crystalline orientation of these systems has been accomplished by means of X-ray microdiffraction. While polymer residual film exhibits isotropic character, edge-on lamellae are formed upon approaching the polymer/membrane interface. This effect might be due to the elongational flow that takes place in the molten state as polymer chains infiltrate the AAO membrane. At the interface, edge-on and flat-on crystalline lamellae coexist as a consequence of the strong interaction between the polymer and the AAO surface. Inside the nanopores, the confined environment induces a kinetic selection of polymer crystals which only allows the growth of crystalline lamellae with its a-axis parallel to that of the pore. In the case of PTT/SWCNT nanocomposites, this effect, in conjunction with the strong interaction between polymer and AAO surface, seems to prevail over the templating effect of the carbon nanotubes and a similar orientation to that of the neat PTT case is observed.
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http://dx.doi.org/10.1021/am401194pDOI Listing
June 2013

Gold coatings on polymer laser induced periodic surface structures: assessment as substrates for surface-enhanced Raman scattering.

Phys Chem Chem Phys 2012 Dec 19;14(45):15699-705. Epub 2012 Oct 19.

Instituto de Química Física Rocasolano, IQFR-CSIC, Serrano 119, 28006 Madrid, Spain.

We report on the fabrication of gold coated nanostructured polymer thin films and on their characterization as substrates for surface enhanced Raman spectroscopy (SERS). Laser induced periodic surface structures (LIPSS) were obtained on thin polymer films of poly(trimethylene terephthalate) (PTT) upon laser irradiation with the fourth harmonic of a Nd:YAG laser (266 nm, pulse duration 6 ns) resulting in a period close to the incident wavelength. The nanostructured polymer substrates were coated with a nanoparticle assembled gold layer by pulsed laser deposition using the fifth harmonic of a Nd:YAG laser (213 nm, pulse duration 15 ns). Different deposition times resulted in thicknesses from a few nanometres up to several tens of nanometres. Analysis by atomic force microscopy and grazing incident small angle X-ray scattering showed that gold coating preserved the LIPSS relief. The capabilities of the produced nanostructures as substrates for SERS have been investigated using benzenethiol as a test molecule. The SERS signal is substantially larger than that observed for a gold-coated flat substrate. Advantages of this new type of SERS substrates are discussed.
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http://dx.doi.org/10.1039/c2cp43049eDOI Listing
December 2012

Assessment and formation mechanism of laser-induced periodic surface structures on polymer spin-coated films in real and reciprocal space.

Langmuir 2011 May 1;27(9):5596-606. Epub 2011 Apr 1.

Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Científicas, Serrano 119, 28006 Madrid, Spain.

In this work we evaluate the potential of grazing incidence X-ray scattering techniques in the investigation of laser-induced periodic surface structures (LIPSSs) in a series of strongly absorbing model spin-coated polymer films which are amorphous, such as poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(carbonate bisphenol A), and in a weaker absorbing polymer, such as semicrystalline poly(vinylidene fluoride), over a narrow range of fluences. Irradiation was performed with pulses of 6 ns at 266 nm, and LIPSSs with period lengths similar to the laser wavelength and parallel to the laser polarization direction are formed by devitrification of the film surface at temperatures above the characteristic glass transition temperature of the polymers. No crystallization of the surface is induced by laser irradiation, and crystallinity of the material prevents LIPSS formation. The structural information obtained by both atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS) correlates satisfactorily. Comparison of experimental and simulated GISAXS patterns suggests that LIPSSs can be well described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice.
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http://dx.doi.org/10.1021/la200451cDOI Listing
May 2011