Film-air Interface Research Articles

In situ neutron reflectometry study of the near-surface solvent concentration profile during solution casting

The drying process of solution cast statistical copolymer films is recorded in situ with neutron reflectometry as a function of molecular weight. P(nBA-stat-MA) with a majority of n-butyl acrylate (nBA) and a minority of methyl acrylate (MA) is dissolved in deuterated toluene and the polymer dries out due to the evaporation of toluene. The evolution of the depth dependence of the near-surface solvent concentration profile is monitored in situ. The detected kinetics deviates from a simple case II diffusion. For all probed samples we find an acceleration of the solvent evaporation for the freshly cast films which then slows down towards an equilibrium stage. With increasing molecular weight the maximum evaporation velocity decreases and equilibrium is reached later. The solvent concentration in the near-surface region is constant as a function of distance from the film–air interface except at times near the maximum evaporation speed, where solvent enrichment at the surface is found. The surface roughness depends neither on the solvent content nor on the chain length of the statistical copolymer. In the final dried films, independent of the molecular weight, a very small amount of solvent remains. Gravimetric experiments concerning the weight loss during drying show that the near-surface kinetics is different from its bulk behavior.

Growth of Compositionally Graded BST by Metal Organic Chemical Vapor Deposition

We report the growth of a compositionally stratified BaxSr1-xTiO3 (BST) thin film on MgO by metal organic chemical vapor deposition (MOCVD). Real-time control of the precursor flux based on UV absorption spectroscopy was used to systematically vary the ratio of Ba:Sr during deposition. The composition of the film with depth was measured by Rutherford backscattering spectroscopy, and x was found to decrease from 0.87 at the film-air interface to 0.43 near the film-MgO interface.

Preparation and characterization of gradient distribution of silicon in emulsion blend films

In this work, a functional gradient polymeric material derived from silicon-containing acrylate blend emulsion film is prepared in two steps. Firstly, 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate (TRIS)-modified acrylate latex is prepared using multiple emulsifiers by the two-stage semicontinuous emulsion copolymerization method. Next, blend latexes composed of TRIS-containing and TRIS-free acrylate latexes are obtained. Detailed studies on the effects of the film-formation temperature and the glass transition temperature (Tg) differences on the compositional gradient film are conducted. Surface energy analysis shows that silicon elements enriched at the film-air (F-A) interface and Tg differences facilitate the fabrication of silicon gradient in emulsion blend films. Scanning electron microscopy-energy dispersive X-ray further reveals that the concentration of silicon components varies in a gradient-like manner along the overall transaction of the film when the film-formation temperature is 55 °C. However, excessive temperature creates the formation of a segmental gradient distribution of silicon in the emulsion blend films.

Synthesis and characterization of fluorine‐containing polyacrylate latex with core–shell structure by UV‐initiated seeded emulsion polymerization

AbstractA core–shell fluorine‐containing polyacrylate emulsion was successfully prepared by UV‐initiated seeded emulsion polymerization in two stages in the presence of two photoinitiators. The water‐soluble photoinitiator for the core polymerization and the oil‐soluble photoinitiator was used for the shell polymerization. Both of the two stage polymerizations could be completed within 15 min and displayed a conversion above 94%. The emulsion and the films were characterized by Fourier transformed infrared spectrometry, transmission electron microscopy, dynamic light scattering, X‐ray photoelectron spectroscopy (XPS), contact angle (CA), and thermogravimetry analysis, respectively. The analysis results indicated that the fluorine‐containing latex particles had very small particle size (40 nm) with a core–shell structure and a narrow particle size distribution. XPS analysis revealed that a gradient concentration of fluorine excited in fluorine‐containing emulsion film from the film–air interface to the film–glass interface. In addition, the film formed from the fluorine‐containing emulsion exhibited not only higher thermal stability but also better hydrophobicity than that of the fluorine‐free emulsion. Copyright © 2010 John Wiley & Sons, Ltd.

Preparation and structure of fluorinated/non-fluorinated polyacrylate gradient emulsion blend film

The emulsion blend method, which is environmentally friendly and energy saving, was used to prepare a compositional gradient film of fluorinated/non-fluorinated polyacrylate in this paper. The size and glass-transition temperature ( T g) of the emulsion particles were designed to enhance the driving force of their selective congregation and promote the formation of gradient structure. The structures and surface properties of the obtained films were characterized. The results showed that when the fluorinated components have much smaller particle size and higher T g than those of fluorine-free polyacrylate components, the gradient structures formed in the direction across the film thickness of the films. The concentration of the fluorinated component increased gradually from film–glass interface to film–air interface in the blend film, making the surface free energies of the two sides of the gradient film distinctively different.

Silica-based hybrid films with double-charged diazoniabicyclo[2.2.2]octane chloride group: Preparation and optical properties related to transition layer structure

Transparent thin films of silica-based hybrid material containing the double-charged diazoniabicyclo[2.2.2]octane chloride group were prepared by optically monitored dip-coating with regard to optical properties, measured by complementary techniques. Double-optical monitoring in real time showed that film formation was basically dominated by solvent flow. After annealing, Ellipsometry and Spectrophotometry (Envelope Method) results generally presented good agreement for the isotropic films, except when slight physical thickness non-uniformity was present. However, refractive indices determined by polarimetry (Abelès Method) at the near-surface were significantly higher than those obtained from the previous methods. Detailed analysis, as discussed, indicates the existence of a very thin transition layer with graded refractive index, increasing towards the film-air interface. Optical applicability is also considered.

Stress Fluctuations in Drying Polymer Dispersions

Drying polymer dispersions usually experience tensile stress, induced by the reduction in volume and by the rigid substrate. Due to edge-in drying, the stress is usually heterogeneous over the film. Stress peaks play a decisive role in the formation of cracks. This work relies on membrane bending, a technique that provides spatially resolved stress maps. In the experiments reported here, stress fluctuations on the order of 10% on the time scale of a few seconds were found. The stress fluctuations occur coherently over the entire drying front. Fluctuations go back to slight fluctuations in humidity of the environment (as opposed to local stress relaxations due to reorganizations of the particle network). The stress fluctuations disappear when covering the sample with a lid. They can be enhanced by blowing humid or dry air across the sample surface. Modeling builds on the assumption that all stresses go back to capillary pressure created at the menisci in between different spheres at the film-air interface. The local radius of curvature changes in response to slight variations in ambient humidity according to the Kelvin equation. The fluctuations are observed under a wide variety of drying conditions and should be included in film formation models.

Synthesis and characterization of core–shell SiO 2-fluorinated polyacrylate nanocomposite latex particles containing fluorine in the shell

The core–shell SiO 2-fluorinated polyacrylate nanocomposite latex particles containing fluorine in the shell were successfully synthesized by seeded emulsion polymerization with nano-SiO 2 as seeds. Transmission electron microscopy (TEM) confirmed that the resultant particles had the core–shell structure obviously. Scanning electron microscopy (SEM), TEM and dynamic light scattering (DLS) analysis indicated that the obtained core–shell nanocomposite latex particles were uniform and possessed narrow size distributions. The chemical components of the core–shell nanocomposite latex particles were investigated by Fourier transform infrared (FTIR) spectrometry and X-ray photoelectron spectroscopy (XPS) analysis, respectively. XPS analysis of the SiO 2-fluorinated polyacrylate nanocomposite latex films revealed that the intensity of fluorine signal in the film–air interface is higher than that in the film–glass interface. In addition, compared with the film of core–shell SiO 2-polyacrylate nanocomposite latex prepared under the similar polymerization condition, the core–shell SiO 2-fluorinated polyacrylate nanocomposite latex film showed higher contact angle and thermal stability.

Acorn‐Shape Polymeric Nano‐Colloids: Synthesis and Self‐Assembled Films

These studies show for the first time that the synthesis of two distinct phase-separated copolymers within one colloidal particle, i.e., poly(methyl methacrylate) (PMMA)/n-butylacrylate (nBA) and poly(nBA)/pentafluorostyrene (p-PFS) phases, results in unique acorn-shaped morphologies and are capable of coalescence. Spectroscopic and morphological analysis combined with contact angle measurements as well as thermodynamic modeling reveal that in an effort to create stable heterogeneous two-phase particle morphologies it is essential to provide desirable interfacial energetic conditions during polymerization and to utilise monomers that have a similar glass transition temperature (T(g) ). Such colloidal particles are stable and are able to self-assemble during coalescence, depending upon the surface energy of a substrate. When a particle monolayer coalesces on a high surface tension substrate, the p-PFS phase expresses itself near the film-air interface, whereas for low surface energy substrates, the p-PFS phase dominates the film-substrate interfacial regions.

Electric field induced dewetting and pattern formation in thin conducting polymer film

Electric field induced instability and two-dimensional sub-micropattern formation in thin films of polyaniline (PANi) (conducting polymer (CP)) at different levels of doping with camphor sulfonic acid (CSA) are studied experimentally. Optical microscopic and AFM analysis reveal that the application of electric field across the thin PANi-EB (emeraldine base) film–air interface between two electrodes causes instability and formation of uniformly dispersed sub-micron column/drop like elevations surrounded by annular depression. The number density and height of such pattern increase with voltage increment. Number density analysis reveals that below a threshold voltage, CP (at its base state) behaves like a dielectric polymer. On the contrary, a 50% doped PANi-ES (emeraldine salt) thin film–air interface forms stripe like on-plane pattern instead of columnar patterns while subjected to electric field. Performance study reveals faster response of columnar morphology of PANi-EB while exposed to HCl vapor compared to that of thin films of PANi-EB. The significance is in design of chemical vapor sensor of low diffusional resistance utilizing high surface to volume ratio.

Molecular aggregation states of poly{2-(perfluorooctyl)ethyl acrylate} polymer brush thin film analyzed by grazing incidence X-ray diffraction

Fluoropolymer brush with crystalline side chains was prepared by surface-initiated atom transfer radical polymerization of 2-(perfluorooctyl)ethyl acrylate (FA-C8) from a flat silicon substrate. The crystallization and the molecular aggregation structures of polymer side chain at the outermost surface and internal region in the brush film were characterized by grazing incidence X-ray diffraction (GIXD) measurement using two different incident angles of X-ray. At the air interface of PFA-C8 brush film, the rod-like Rf group was oriented perpendicular to the surface forming a hexagonal packing structure to reduce surface energy. In contrast, the oriented Rf groups parallel to the substrate coexisted at the internal region in the brush. This unique depth dependence of crystalline state of the fluoropolymer brush was observed by surface-sensitive GIXD measurement.

Preparation and characterization of soap-free fluorine-containing acrylate latex

The soap-free fluorine-containing acrylate latices were prepared by the pre-emulsification and semicontinuous polymerization method, with perfluorooctylethyl methacrylate (PFEA) as fluorinated acrylate monomer and monophosphoric acid allyloxy nonylphenoxy poly(ethyleneoxy)(10) ether as reactive emulsifier. The structure and property of latex polymers were characterized by laser particle size analyzer, attenuated total reflectance spectra of infrared, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis. The effects of polymerization conditions on the conversion and polymerization stability were discussed in detail and the optimal polymerization condition was obtained. XPS analysis indicates that the perfluoroalkyl groups have the tendency to enrich at the film–air interface. With the increasing of PFEA amount, the water absorption of the film decreases and the water contact angle of the film increases. At the same time, the thermal stability of the copolymer is greatly enhanced with the increasing of PFEA amount.

Structure and morphology of Cu/Ni film grown by electrodeposition method: A study of neutron reflectivity and AFM

We present detailed study of structure and interface morphology of an electrodeposited Cu/Ni film using X-ray diffraction, X-ray reflectivity, neutron reflectivity and atomic force microscopy (AFM) techniques. The crystalline structure of the film has been determined by X-ray diffraction, which suggest polycrystalline growth of the film. The depth profile of density in the sample has been obtained from specular X-ray and neutron reflectivity measurements. AFM image of the air–film interface shows that the surface is covered by globular islands of different sizes. The AFM height distribution of the surface clearly shows two peaks and the relief structure (islands) on the surface in the film, which can be treated as a quasi-two-level random rough surface structure. We have demonstrated that the detailed morphology of air–film interfaces, the quasi-two-level surface structure as well as morphology of the buried interfaces can be obtained from off-specular neutron reflectivity data. AFM and off-specular neutron reflectivity measurements also show that the morphologies of electrodeposited surface is distinctively different as compared to that of sputter-deposited surfaces in the sample.

Fidelity of Holographic Lithography for Fabrication of 3D SU-8 Photonic Structures and How to Minimize Distortion by Optical Design

AbstractTheoretical analysis can impart great benefits on the rationale design of 3D photonic structures by revealing the underlying mechanisms of structural distortion during each processing step. In this report, we quantitatively study the distortion of a three-term diamond-like structure fabricated in SU-8 polymer by four-beam interference lithography, which can be attributed to refraction at the air-film interface, and resist film shrinkage during lithographic process. In study of photonic bandgap (PBG) properties of Si photonic crystals templated by the SU-8 structures, we find that the distortion has degraded the quality of PBGs. Furthermore, we theoretically design new optical setups to fabricate three-term diamond-like structure with minimal deformation. Instead of single exposure of four beams, we use triple exposure of two beams, one from the central beam and the other from the side beam each time. A set of new linear polarization vectors is suggested to enhance the contrast between the minimal and maximal intensities of interference pattern.

Characterizing the Distribution of Nonylphenol Ethoxylate Surfactants in Water-Based Pressure-Sensitive Adhesive Films using Atomic-Force and Confocal Raman Microscopy

Surfactant distributions in model pressure-sensitive adhesive (PSA) films were investigated using atomic force microscopy (AFM) and confocal Raman microscopy (CRM). The PSAs are water-based acrylics synthesized with n-butyl acrylate, vinyl acetate, and methacrylic acid and two commercially available surfactants, disodium (nonylphenoxypolyethoxy)ethyl sulfosuccinate (anionic) and nonylphenoxypoly(ethyleneoxy) ethanol (nonionic). The ratio of these surfactants was varied, while the total surfactant content was held constant. AFM images demonstrate the tendency of anionic surfactant to accumulate at the film surfaces and retard latex particle coalescence. CRM, which was introduced here as a means of providing quantitative depth profiling of surfactant concentration in latex adhesive films, confirms that the anionic surfactant tends to migrate to the film interfaces. This is consistent with its greater water solubility, which causes it to be transported by convective flow during the film coalescence process. The behavior of the nonionic surfactant is consistent with its greater compatibility with the polymer, showing little enrichment at film interfaces and little lateral variability in concentration measurements made via CRM. Surfactant distributions near film interfaces determined via CRM are well fit by an exponential decay model, in which concentrations drop from their highs at interfaces to plateau values in the film bulk. It was observed that decay constants are larger at the film-air interface compared with those obtained at the film-substrate side indicating differences in the mechanism involved. In general, it is shown here that CRM acts as a powerful compliment to AFM in characterizing the distribution of surfactant species in PSA film formation.

Preparation and characterization of emulsifier-free core–shell interpenetrating polymer network-fluorinated polyacrylate latex particles

The emulsifier-free core–shell interpenetrating polymer network (IPN) fluorinated polyacrylate latex particles with fluorine rich in shell were prepared by emulsifier-free seeded emulsion polymerization with water as the reaction medium. The fluorinated copolymer could be fixed on the particle surface due to the formation of interpenetrating polymer network. The resultant core–shell particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) analysis, Fourier transform infrared (FTIR) spectrometry, X-ray photoelectron spectroscopy (XPS) analysis and thermogravimetric analysis (TGA). The core–shell particles possessed very narrow monomodal particle size distributions. XPS analysis of the latex film displayed that perfluoroalkyl groups had the tendency to enrich at surface and there was a gradient concentration of fluorine in the structure of the latex film from the film–air interface to the film–glass interface. In addition, compared with the latex film of crosslinked polyacrylate prepared under the same condition, the emulsifier-free core–shell IPN-fluorinated polyacrylate latex film showed better thermal stability, higher contact angle and lower water uptake.

Hexamethyldisilazane vapor treatment of plasma damaged nanoporous methylsilsesquioxane films: Structural and electrical characteristics

Repair of plasma damaged nanoporous organosilicate films carried out by hexamethyldisilazane (HMDS) vapor treatment was investigated as a function of temperature. Capacitance–voltage measurements were carried out before and after HMDS vapor treatment. The dielectric constant measurements confirm that the HMDS vapor treatment facilitates only partial curing of the plasma damaged films, as also observed from the Fourier transform infrared absorption measurements. Bias temperature stress measurements for samples with copper (Cu) metal electrodes reveal a shift of − 35 V in the capacitance–voltage curve for samples cured at 55 °C whereas negligible shift is observed for samples treated above 80 °C. This behavior suggests the existence of a dense solid layer on the top surface of the samples treated above 80 °C, hindering the diffusion or movement of Cu ions into the dielectric. Direct imaging of the HMDS vapor treated plasma damaged films using scanning electron microscope clearly shows the existence of two distinct layers, with the top layer (at the film–air interface) being denser than the bottom layer at the film–substrate interface.

Emulsifier-free core–shell polyacrylate latex nanoparticles containing fluorine and silicon in shell

The emulsifier-free core–shell polyacrylate latex nanoparticles containing fluorine and silicon in shell were successfully synthesized by emulsifier-free seeded emulsion polymerization with water as the reaction medium. The silicon-containing fluorinated polymer could be fixed on the surface of polyacrylate nanoparticles due to the formation of the crosslinked network structure. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis indicated that the obtained emulsifier-free core–shell nanoparticles were uniform and possessed narrow size distributions. The core–shell structure and chemical components of the emulsifier-free core–shell nanoparticles were investigated by TEM and Fourier transform infrared (FTIR) spectrometry, respectively. X-ray photoelectron spectroscopy (XPS) analysis and contact angle measurement on the latex films proved the propensity of fluorine and silicon enrichment at film–air interface. In addition, the thermal stability of the latex films was improved with increasing the concentration of fluorine and silicon.

In-situ X-ray Reflectivity Study of Alkane Films Grown from the Vapor Phase

We carried out in-situ X-ray reflectivity study of nine n-alkane chains (CnH2n+2) on Si substrate, n in the range of 17-30. These films formed under vacuum at equilibrium vapor pressure of the respective alkane molecule. For all the alkanes studied we found a bilayer structure on the substrate, a higher density vertical layer at the air-film interface with the layer thickness equal to the all-trans length of the respective molecule, and a lower density layer below it with the molecules lying horizontal on the substrate. This model was earlier proposed for C32 films on Si by Volkmann et al.11 We observe that this model can fit the entire range of data from C17 to C30 in our experiments.

SU-FF-T-194: Effect of Processor Temperature On Film Dosimetry:

Radiographic films have proven to be an important dosimetric tool for dose verification in advance treatment techniques such as IMRT,IGRT and SRT etc. Optical density (OD) is related to dose, and depends on various parameters including beam energy, depth, field size, film batch, dose,dose rate, air film interface, post exposure processing time and temperature of the processor. Most of these parameters have been studied for the XV and EDR films used in radiation oncology, however; there is no information on the functional form of OD with processor temperature, which is investigated in this study. Films were exposed with 6 MV photon beam and were processed in a Kodak X‐OMAT 5000 RA processor. For sensitometric evaluation, films were processed at clinically set 95° F. A batch of films with same dose was processed at different temperatures in the range of 85°–105° F by changing the processor temperature in service mode with proper password and instructions. At each setup of temperature, enough time was given to change the display status from “WAIT” to “READY” sign. Additional 10 minutes were given after ready sign to stabilize the temperature further. One set of film from XV and EDR was processed at each temperature setting. It is observed that for a given dose, OD is linearly dependent on the processor temperature within narrow range of the temperature. It is also known that OD versus dose curve is a quadratic function. Combining these two functions provides OD in a quadratic function of the processor temperature. It is concluded that estimation of dose with film is strongly dependent on the processor temperature that should be maintained constant to reduce dosimetric uncertainty for XV and EDR films. Processor temperature should also be studied for each institution to estimate the correct OD and errors in dosimetry.