Properties Of Thin Polymer Films Research Articles

Increase the Reliability and Applicability of Quartz Crystal Resonator Coupled with Other Instruments

The principle and applications of quartz-crystal resonator systems and the methods to increase their reliability and applicability coupled with other instruments were reported. The principle of quartz-crystal resonator system was documented with based on the three basic concepts for mass, viscosity, and viscoelastic changes. In the preliminary discussion, the realization of a resonant frequency-resonant resistance diagram was described in detail. As the examples of quartz-crystal resonator applications with introducing the resonant resistance concept and the resonant frequency, the fabrication of a carbon-coated quartz crystal sensor and monitoring changes in the viscoelastic properties of thin polymer films were carefully discussed. Examples for increasing their reliability and applicability of quartz crystal resonator systems combined with UV-visible spectroscopy, Atomic Force Microscope (AFM), Surface Plasmon Resonance (SPR), or Charge Coupled Device (CdCD) camera were described.

Is ballistic transportation or quantum confinement responsible for changes in the electrical properties of thin polymer films?

Resistivities of thin polymer films increase abruptly with decreasing thickness, although the corresponding decline in resistance plateaus below a certain thickness. One can jump to the incorrect conclusion that quantum confinement and surface scattering are responsible for this behaviour, and we highlight the pitfalls of committing such an error.

Tailoring the Chain Packing in Ultrathin Polyelectrolyte Films Formed by Sequential Adsorption: Nanoscale Probing by Positron Annihilation Spectroscopy

Depth profiling experiments by positron annihilation spectroscopy have been used to investigate the free volume element size and concentration in films assembled using the layer-by-layer (LbL) adsorption method. Films prepared from strong polyelectrolytes, weak polyelectrolytes, hydrogen-bonding polymers, and blended polyelectrolyte multilayers have different chain packing that is reflected in the free volume characteristics. The influence of various parameters on free volume, such as number of bilayers, salt concentration, solution pH, and molecular weight, has been systematically studied. The free volume cavity diameters vary from 4 to 6 Å, and the free volume concentrations vary from (1.1-4.3) × 10(20) cm(-3), depending on the choice of assembly polymers and conditions. Films assembled from strong polyelectrolytes have fewer free volume cavities with a larger average size than films prepared from weak polyelectrolytes. Blending the weak polyanion poly(acrylic acid), PAA, with the strong polyanion poly(styrene sulfonate), PSS, to layer alternately with the polycation poly(allyamine hydrochloride), PAH, is shown to be a viable method to achieve intermediate free volume characteristics in these LbL films. An increase in salt concentration of the adsorption solutions for films prepared from strong polyelectrolytes makes these films tend toward weaker polyelectrolyte free volume characteristics. Hydrogen-bonded layered films show larger free volume element size and concentration than do their electrostatically bonded counterparts, while reducing the molecular weight of these hydrogen-bonded polymers results in slightly reduced free volume size and concentration. A study of the effect of solution pH on films prepared from weak polyelectrolytes shows that when both polyelectrolytes are substantially charged in solution (assembly pH = 7.5), the chains pack similarly to strong polyelectrolytes (i.e., lower free volume concentration), but with smaller average cavity sizes. These results give, for the first time, a clear indication of how the free volume profile develops in LbL thin films, offering numerous methods to tailor the Ångström-scale free volume properties by judicious selection of the assembly polymers and conditions. These findings can be potentially exploited to tailor the properties of thin polymer films for applications spanning membranes, sensing, and drug delivery.

Mechanical characterization of polymeric thin films by atomic force microscopy based techniques

Polymeric thin films have been awakening continuous and growing interest for application in nanotechnology. For such applications, the assessment of their (nano)mechanical properties is a key issue, since they may dramatically vary between the bulk and the thin film state, even for the same polymer. Therefore, techniques are required for the in situ characterization of mechanical properties of thin films that must be nondestructive or only minimally destructive. Also, they must also be able to probe nanometer-thick ultrathin films and layers and capable of imaging the mechanical properties of the sample with nanometer lateral resolution, since, for instance, at these scales blends or copolymers are not uniform, their phases being separated. Atomic force microscopy (AFM) has been proposed as a tool for the development of a number of techniques that match such requirements. In this review, we describe the state of the art of the main AFM-based methods for qualitative and quantitative single-point measurements and imaging of mechanical properties of polymeric thin films, illustrating their specific merits and limitations.

Swelling with a Near-Θ Solvent as a Means to Modify the Properties of Polymer Thin Films

The effect of swelling with a near-Θ solvent on the thermal expansion and dewetting behavior of polystyrene films is studied. Spin-coating a film from a near-Θ solvent has been found to produce a chain conformation further from equilibrium than that by spin-coating from a good solvent. Swelling a film with a near-Θ solvent is expected to produce a similar effect. We find that there is a significant thermal contraction in the films swelled with decalin—a Θ-solvent of polystyrene at 16 °C. The size of this thermal contraction decreases as the sample is aged, and appears to be due to the solvent used and not the solvent quality. On the other hand, the effect of aging on the dewetting behavior is seen to depend on the solvent quality similar to that for the films spun-cast from a near-Θ solvent, with an offset attributable to the swelling conditions and initial chain conformation of the film. Our result suggests that the thermal expansion is not nearly as sensitive to the film’s chain conformation as is the d...

Measurement of the elastic modulus of polymeric films using an AFM with a steel micro-spherical probe tip

The elastic moduli of polystyrene (PS), polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) films were evaluated using an Atomic Force Microscope (AFM) with a steel micro-spherical probe tip. The elastic moduli of the polymeric films were determined with respect to indentation depth using the Hertz and Johnson-Kendall-Roberts (JKR) models. The measured elastic moduli of PS, PMMA and PDMS were determined to be 2.6 GPa, 0.74 GPa, and 4 MPa at indentation depths of 1.7 nm, 4 nm, and 120 nm, respectively. These results confirm the validity of the proposed method for effectively measuring the elastic properties of polymeric thin films.

Investigation of optical properties of thin polymer films

Several types of optical polymer materials produced by Eastman Chemical Company were studied. Thin films deposited on glass substrates from solutions were prepared and studied to reveal their refractometric, dispersive and transmission properties in the visible and infrared spectral regions. The refractive indices were measured by means of two modifications of a laser microrefractometer.

Three-Dimensional Packing Structure and Electronic Properties of Biaxially Oriented Poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) Films

We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT-C(14)) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C(12) to C(14) and C(16) are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films.

A Novel Plasma Technique for Surface Treatment: The Plasma Expander

This paper describes a new plasma treatment method: the plasma expander. In this approach, expanding shock waves are generated in a vacuum chamber by pulsed plasmas. Collisions of fast species in the waves modify the properties of solid surfaces exposed to the plasma. The degree of such modification is governed by the energy delivered by the plasma exposure. To confirm the efficacy of this approach, modifications induced in the properties of thin polymer films produced by plasma-enhanced chemical vapor deposition by exposure to nitrogen plasma shock waves were investigated. The films were prepared from benzene radio frequency plasmas and subsequently exposed to different quantities of nitrogen shock waves <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Nw</i> . The effects of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Nw</i> on the wettability, molecular structure, and mechanical properties of the films were studied. Fourier transform infrared spectroscopy revealed that greater <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Nw</i> resulted in the loss of C-H groups and the rupture of benzene aromatic rings observed in the structure of the as-deposited films. Furthermore, the contact angle strongly increased and the hardness, evaluated by nanoindentation, increased up to fourfold with the increase in the intensity of the treatment.

Properties of Polymer Thin Films Studied by Direct Observation of Single Chains

Properties of polymer materials originate from the large degree of freedom of a single polymer chain. The direct observation of the conformation of single polymer chains would provide much information for the fundamental understanding of the properties of polymers. Fluorescence imaging techniques are suitable for the selective observation of individual molecules embedded in a bulk medium; however, the spatial resolution of conventional optical microscopy is limited to ∼200 nm by the diffraction limit. This paper reviews the state-of-the-art optical imaging techniques that enable to obtain a fluorescence image with a nanometoric spatial resolution and describes its application for the direct imaging of the conformation of individual polymer chains. The conformation of poly(alkyl methacrylate) chains in thin films and micro-phase separation structures of a block copolymer is discussed.

Surface wrinkling in liquid crystal elastomers

Structured surfaces give rise to novel and potentially useful properties such as controllable wettability and structural colour. Here, we demonstrate structured surfaces via reversible surface wrinkling in liquid crystal elastomers (LCEs). A thin polymer film deposited on top of a shape-responsive LCE exhibits a reversible, periodic surface wrinkling pattern in response to temperature changes. The orientation of the wrinkles depends on the orientation of the nematic director and the temperature at which the bilayer is prepared, and the wrinkles can be re-oriented in a single sample by heating or cooling the sample above or below the preparation temperature. We show that this bilayer system can be used to measure the modulus of nanoscale thin poly(styrene) films deposited on the LCE. Additionally, when a micron-thick polymer film is deposited on top of an LCE, the bilayer exhibits reversible curling with temperature. This system provides a simple method for measuring the mechanical properties of thin polymer films without the need for clamping and mechanical stretching and provides a new approach to generate reversible, microstructured surfaces.

Impact of chain architecture (branching) on the thermal and mechanical behavior of polystyrene thin films

AbstractThe modulus and glass transition temperature (Tg) of ultrathin films of polystyrene (PS) with different branching architectures are examined via surface wrinkling and the discontinuity in the thermal expansion as determined from spectroscopic ellipsometry, respectively. Branching of the PS is systematically varied using multifunctional monomers to create comb, centipede, and star architectures with similar molecular masses. The bulk‐like (thick film) Tg for these polymers is 103 ± 2 °C and independent of branching and all films thinner than 40 nm exhibit reductions in Tg. There are subtle differences between the architectures with reductions in Tg for linear (25 °C), centipede (40 °C), comb (9 °C), and 4 armed star (9 °C) PS for ≈ 5 nm films. Interestingly, the room temperature modulus of the thick films is dependent upon the chain architecture with the star and comb polymers being the most compliant (≈2 GPa) whereas the centipede PS is most rigid (≈4 GPa). The comb PS exhibits no thickness dependence in moduli, whereas all other PS architectures examined show a decrease in modulus as the film thickness is decreased below ∼40 nm. We hypothesize that the chain conformation leads to the apparent susceptibility of the polymer to reductions in moduli in thin films. These results provide insight into potential origins for thickness dependent properties of polymer thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Influence of Chain Stiffness on Thermal and Mechanical Properties of Polymer Thin Films

The effect of main chain stiffness and side chain flexibility on the elastic modulus and glass transition temperature (Tg) of thin polymer films is investigated using nontraditional polymers formed from 5-(2-phenylethylnorbornene). Depending on the polymerization route chosen, the resulting polymer backbone is comprised of either bicyclic (norbornyl) units, which leads to a relatively rigid polymer with a high bulk Tg, or monocyclic (cyclopentyl) units, which leads to a more flexible structure with a lower bulk Tg. The modulus and Tg of the rigid bicyclic polymer are thickness independent down to <10 nm, whereas the modulus of the more flexible monocyclic polymer decreases with decreasing thickness. By hydrogenation of the pendant phenyl ring to the cyclohexyl counterpart, we illustrate that minor changes in the relative flexibility of the side chain do not impact the observed thin film behavior. To further support our hypothesis that main chain stiffness (persistence length) plays a central role in confinement-induced changes in physical properties, a series of arylate/phosphonate copolymers, where the addition of phosphonate groups decreases the overall stiffness of the polymer backbone, are also examined. Similar to the polynorbornenes, the poly(arylate-co-phosphonate) polymers exhibit more pronounced thickness-dependent properties as the stiffness of the backbone decreases. We believe based upon our results that examination of chain flexibility in the thin film glass community for future works would be extremely useful in elucidating the physical origins of observed phenomena.

Interfacial and Substrate Effects on Local Elastic Properties of Polymers Using Coupled Experiments and Modeling of Nanoindentation

AbstractThe mechanical properties of polymers near interfaces are important in a number of different fields. For almost two decades, the local dynamics of thin polymer films have been studied in great detail. However, development of an understanding of local mechanical properties has been hindered by the necessary proximity of stiff substrates: mechanical measurements are confounded by interaction with the substrate, convoluting polymer, and substrate properties. In this paper, local elastic properties of thin polymer films near interfaces are directly probed for the first time via nanoindentation experiments on thin films coupled with finite element modeling. A comprehensive set of experimental and numerical modeling results are presented for poly(methyl methacrylate) (PMMA) revealing separately the effects of substrate and interphase polymer. Results indicate the attractive surface significantly affects the properties up to hundreds of nanometers. This new, direct approach to measure local mechanical properties provides new fundamental understanding of interfacial and small‐scale behaviors in polymers and soft matter for application advances in nanocomposites, microelectronics, and biopolymers.

Functionalization of polymer multilayer thin films for novel biomedical applications

The design of functional polymer multilayer thin films with nanometer scale control is of great interest for biomedical applications such as tissue engineering, targeted drug delivery, controlled release system, and regenera- tive medicine. Various functions and properties of polymer thin films can be easily programmed and realized by the layer-by-layer assembly strategy, which is a facile and versatile deposition method to prepare well-defined biomedical multilayer platforms due to its benign process to prepare films under mild conditions and the capability of incorporating bioactive materials at a desired location within the films. Particularly, the fine tuning of physicochemical and biologic- al properties of multilayer thin films is significantly important for designing novel biomedical platforms capable of adjusting the cellular functions. In this review, we focus on the overall background of the layer-by-layer assembly as well as the tuning of multilayer film properties and the programming of biological functions into the polymer thin films with a view on the control of cellular functions. Furthermore, we highlighted the recent achievements toward the design of novel biomedical platforms based on functionalized polymer multilayer thin films.

Determination of oxygen permeabilities in thin polymer films using quenching of upconverted fluorescence in porphyrins

Proof-of-principle is demonstrated for a method of measuring the oxygen diffusion properties of thin polymer films based on quenching of the delayed upconverted S2 fluorescence of Zn(II) meso-tetraphenylporphine (ZnTPP). Empirical oxygen diffusion coefficients and permeability coefficients for poly(vinyl alcohol) (PVA) have been computed using Stern–Volmer kinetics in the steady-state regime and a nonlinear gas solubility model in the time domain. Simplified dual-mode theory has been used to calculate crude theoretical oxygen permeability coefficients to compare with the experimental values. It is confirmed that oxygen permeability in the PVA matrix is controlled largely by the characteristics of the polymer matrix, particularly its water content and distribution.

Quantifying the Stress Relaxation Modulus of Polymer Thin Films via Thermal Wrinkling

The viscoelastic properties of polymer thin films can have a significant impact on the performance in many small-scale devices. In this work, we use a phenomenon based on a thermally induced instability, termed thermal wrinkling, to measure viscoelastic properties of polystyrene films as a function of geometric confinement via changes in film thickness. With application of the appropriate buckling mechanics model for incompressible and geometrically confined films, we estimate the stress-relaxation modulus of polystyrene films by measuring the time-evolved wrinkle wavelength at fixed annealing temperatures. Specifically, we use time-temperature superposition to shift the stress relaxation curves and generate a modulus master curve for polystyrene films investigated here. On the basis of this master curve, we are able to identify the rubbery plateau, terminal relaxation time, and viscous flow region as a function of annealing time and temperatures that are well-above its glass transition. Our measurement technique and analysis provide an alternative means to measure viscoelastic properties and relaxation behavior of geometrically confined polymer films.

Facile measurement of polymer film thickness ranging from nanometer to micrometer scale using atomic force microscopy

AbstractAs many properties of polymer thin films critically depend on their thickness, a convenient and cost‐effective method for precise measurement of film thickness in a wide range is highly desirable. Here, we present a method which enables polymer film thickness, ranging from nanometer to micrometer scale, to be facilely determined by measuring the height of an artificially created film step on smooth substrates with atomic force microscopy (AFM). Three polymeric films (polystyrene, poly(methyl methacrylate) and poly(styrene–ethylene/butylene–styrene) films), spin‐coated on either mica or quartz substrate with thickness ranging from 5.7 nm to 4.4 µm, were employed to demonstrate the procedure and feasibility of our method. The proposed method is particularly suitable for thicker polymer films, thus complementing the traditional AFM ‘tip‐scratch’ method which is generally limited to polymer films of no more than 100 nm thickness. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Possible origin of thickness‐dependent deviations from bulk properties of thin polymer films

Journal of Polymer Science Part B: Polymer PhysicsVolume 48, Issue 24 p. 2544-2547 Viewpoint Possible origin of thickness-dependent deviations from bulk properties of thin polymer films Günter Reiter, Corresponding Author Günter Reiter guenter.reiter@physik.uni-freiburg.de Physikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanyPhysikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanySearch for more papers by this authorSimone Napolitano, Simone Napolitano Laboratory for Acoustics and Thermal Physics, Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, BelgiumSearch for more papers by this author Günter Reiter, Corresponding Author Günter Reiter guenter.reiter@physik.uni-freiburg.de Physikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanyPhysikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, GermanySearch for more papers by this authorSimone Napolitano, Simone Napolitano Laboratory for Acoustics and Thermal Physics, Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, BelgiumSearch for more papers by this author First published: 07 September 2010 https://doi.org/10.1002/polb.22134Citations: 60Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume48, Issue2415 December 2010Pages 2544-2547 RelatedInformation

Mechanical properties of thin polymer films on stiff substrates

Force-displacement curves have been acquired with a commercial atomic force microscope on thin films of poly(n-butyl methacrylate) on glass substrates in order to examine the so-called "mechanical double layer" topic, i.e. the influence of the substrate on the mechanical properties of the film in dependence of the film thickness. The hyperbolic fit, a novel semi-empirical equation introduced in previous articles, has been further corroborated. The interpretation of this equation has been deepened, yielding a quantitative and demonstrative characterization of the mechanical properties of double layers. Provided that the Young's moduli of bulk polymer and substrate are measured from the deformation curves, this mathematical model permits to fit the deformation-force curves on the double layers and to determine the thickness of the polymer films in wide range (0-200 nm).