Characterization of N-cyclohexylmethacrylamide LB thin films for room temperature vapor sensor application

This study reports the synthesis, characterization and gas sensing applications of N-cyclohexylmethacrylamide (NCMA) monomer material using FT-IR, ¹H and ¹³C NMR, UV-visible spectroscopy, Quartz Crystal Microbalance (QCM) and Langmuir-Blodgett (LB) thin film deposition techniques. The thin film deposition conditions of NCMA monomer material, which are prepared by LB film technique, are characterized by UV-visible spectroscopy and QCM system. The sensing behaviors of the LB film with respect to volatile organic compounds (VOCs) at room temperature are investigated. Surface pressure change as a function of surface area of NCMA molecule at the water surface shows a well-organized and stable monolayer at 18 mN m^?1 surface pressure value for LB film deposition. Transfer ratio values are found to be ≥ 0.94 for quartz glass and ≥ 0.93 for quartz crystal substrate. The typical frequency shift per layer is obtained 20.10 Hz/layer and the deposited mass onto a quartz crystal is calculated as 824.62 ng/layer. The sensing responses of the LB films against chloroform, dichloromethane, acetone, toluene, benzene and ethanol are measured by QCM system. The sensitivities of the NCMA LB film sensor are determined between 0.085 and 0.029 Hz ppm^?1. Sensitivities with detection limits are between 35.29 and 100.33 ppm against organic vapors. These results can be concluded that the monomer LB film sample is found to be significantly more sensitive to chloroform and dichloromethane vapors than others organic vapors used in this work. This material may find potential applications in the development of room temperature organic vapor sensing.     

Initiated chemical vapor deposition of linear and cross-linked poly(2-hydroxyethyl methacrylate) for use as thin-film hydrogels

Initiated chemical vapor deposition (iCVD) is able to synthesize linear and cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) thin films, in one step, from vapors of 2-hydroxyethyl methacrylate (HEMA), ethylene glycol diacrylate (EGDA), and tert-butyl peroxide (TBPO) without using any solvents. This all-dry technique also allows control of the cross-link density by adjusting the partial pressure of the cross-linking agent EGDA in the vapor phase. Films with specific cross-link densities and hence thermal, wetting, and swelling properties can be created in one single vacuum processing step. Through selective thermal decomposition of the initiator TBPO, films with well-defined chemical structures and full functionality retention can be deposited, which is evident in the Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. These spectroscopic methods also facilitate determination of EGDA incorporation in the cross-linked films based on the fact that HEMA contains a hydroxyl group but EGDA does not. For the linear PHEMA depositions, the growth rate was found to be nonlinear in the partial pressure of HEMA, possibly due to nonlinear multilayer adsorption and/or primary termination. The EGDA/HEMA ratio in the films systematically increased from 0.00 to 0.46 as the EGDA partial pressure was raised. The onset temperatures of decomposition were between 270 and 302 degrees C for the linear and the most cross-linked films, respectively. Thermal annealing at approximately 430 degrees C resulted in minuscule amounts of residue for all films, linear or cross-linked. The most cross-linked film had approximately 99.50% thickness removed after annealing. The contact angle was found to increase with increasing cross-link density. Significant contact-angle hysteresis was observed, indicating surface reconfiguration, and the lowest receding angle was 17 degrees for the linear film. Swelling measurements using spectroscopic ellipsometry showed that the degree of swelling decreased with increasing EGDA incorporation. The water content decreased from 35% (v/v) for the linear film to below 10% (v/v) for the most cross-linked film. These results show that iCVD is able to produce PHEMA thin films that function as hydrogels when soaked in water. The spectroscopic results, the contact-angle results, and the swelling analysis altogether prove the retention of the hydrophilic pendant groups in the iCVD process.     

Grafting of Acrylamide On 1, 1, 2, 2-Tetra-Chloroethane Preswelled Polyethylene Terephthalate) Films Using Azobisisobutyronitrile Initiator

Abstract

Graft polymerization of acrylamide (AAm) on 1, 1, 2, 2 tetrachloro-ethane (TCE) preswelled poly(ethylene terephthalate) (PET) films were performed with chemical initiation method using asobisiso-butyronitrile (AIBN) initiator. Temperature was found to have a greater effect on the swelling then the swelling time. Variation of the graft yield with polymerization temperature, time, AIBN concentration, AAm concentration, AIBN and AAm inclusion times were investigated. The optimum temperature for grafting was found to be 70°CC. The graft yield was observed to increase with polymerization time, AAm concentration, initiator and monomer diffusion time up to a saturation graft yield and then leveled off. An increase in AIBN concentration first enhanced the percent grafting then showed a decrease. The addition of some salts (Ni²⁺, Cr³⁺, Co²⁺, Cu²⁺) on the rate of grafting was also investigated. From the temperature dependence of the initial rate of grafting, the overall activation energy was found to be 4. 1 kcal/mol and relevant rate equation have been derived. The effect of grafting on film propities, such as water absorption capacity, intrinsic viscosity were determined. Grafted films were characterized by FTIR spectros-copy and scanning electron microscopy (SEM).     

Parylene C at subambient temperatures

Dependence of Parylene C deposition rate on dimer sublimation temperature, inert gas pressure, substrate temperature, and mass of dimer has been investigated. It was found that Parylene C deposition proceeds best at ambient temperature and produces film of optimum performance. Opacity in the film results from its rough morphology and not from the incorporation of the dimer in the film as is normally thought. This was evidenced from scanning electron microscopy and from an estimation of the volatile contents of the Parylene C films. Deposition of Parylene C at liquid nitrogen temperature proceeds via trapping of active monomer species followed by spontaneous polymerization. A quantitative study of the monomer to polymer transition by ESR spectroscopy is presented.     

Preparation and characterization of plasma-polymerized styrene thin films

Plasma-polymerized styrene (PPS) thin films (several hundred to several thousand Å thick) have been prepared under a variety of discharge conditions in a tubular reactor inductively coupled to a radio frequency (13.56 MHz) power supply. Studies have focussed on the correlation of deposited polymer structure, evidenced both at the film surface (via XPS analysis) and in the bulk polymer (via transmission FT–IR analysis) with controllable plasma parameters (coupled rf power, monomer flow rate, monomer pressure). It has been determined that the relative number of phenyl rings incorporated into the film intact is an inverse function of the power per styrene molecule ratio. Polymer deposition rate was found to be a strong function of styrene flow rate and substrate temperature. Plausible elements of the styrene plasma polymerization mechanism will be considered.     

Insights into thin, thermally responsive polymer layers through quartz crystal microbalance with dissipation

The thermodynamics of temperature-responsive polymeric layers was analyzed using a two-state coil to globule model to which the van't Hoff relationship was applied. For soluble homopolymer poly(N-isopropylacrylamide (pNIPAAm), enthalpies of transition, ΔH(vH), were calculated using varations in ultraviolet-visible (UV-vis) spectroscopy with temperature to be 8400 ± 30 and 1652 ± 4 kJ mol-cooperative unit(-1) for standard synthesis and initiated chemical vapor deposition (iCVD), respectively. For the insoluble surface-bound layer of cross-linked iCVD poly(N-isopropylacrylamide-co-di(ethylene glycol) divinyl ether) [p(NIPAAm-co-DEGDVE)], ΔH(vH) was determined to be 810 ± 30 kJ mol-cooperative unit(-1) using quartz crystal microbalance with dissipation monitoring (QCM-D). Microcalorimetry measurements showed the enthalpies per mole NIPAAm monomer to be 5.8 ± 0.2, 3.5 ± 0.6, and 3.1 ± 0.3 kJ mol-NIPAAm(-1), resulting in cooperative unit sizes of 1460 ± 60, 470 ± 80, and 260 ± 30 monomer units for the standard pNIPAAm, iCVD pNIPAAm, and p(NIPAAm-co-DEGDVE) systems, respectively. These values indicate that both per monomer enthalpic contribution as well as cooperative unit size are primary factors contributing to the variations in van't Hoff enthalpies for the three systems studied. Diffusion of bovine serum albumin (BSA) into swollen p(NIPAAm-co-DEGDVE) films below its lower critical solution temperature was elucidated via QCM-D measurements. These data provided a calculated diffusion coefficient of (3.5 ± 0.1) × 10(-14) cm(2) s(-1) of BSA into the swollen hydrogel film with a mesh size of 6.0 ± 0.2 nm (compared to the hydrodynamic radius of BSA, r(H) = 3.36 nm).     

Polyaniline film deposition from the oxidative polymerization of aniline using K2Cr2O7

The deposition of the polyaniline (PANI) films was monitored using the quartz crystal microbalance (QCM) technique. The films were grown from an aqueous dilute hydrochloric acid solution by the chemical oxidation of aniline using potassium dichromate (KDC). The effect of the initial molar ratio of the KDC/aniline on the yield and the growth rate of the PANI films were studied. There is no optimum initial molar ratio of KDC/aniline of PANI film deposition. Also there was a small depletion period and no degradation to the deposited PANI films. The order of the polymerization kinetics was studied with respect to KDC. The UV-visible spectra of the PANI films grown onto a glass support immersed into the bulk solution were measured. The absorption of the PANI film with the time of polymerization was compared to the growth of the PANI film thickness with time determined from the QCM technique. The characteristics of the PANI film deposition were compared to the corresponding ones that were observed during the oxidative polymerization of aniline with ammonium persulphate (APS).     

Surface characterization of the SiOx films prepared by a remote atmospheric pressure plasma jet

The deposition rate and surface properties of SiO_x films were prepared and investigated using remote atmospheric pressure plasma (APP) jet. The APP, generated with low frequency power at 16 kHz, was fed with tetraethoxysilane (TEOS)/air gas mixture. After deposition, the SiO_x films were analyzed for chemical characteristics, elemental composition, surface morphology, and hardness. It was found that the deposition substrate temperature is the key factor to affect the deposition rate of remote APP chemical vapor deposition process. Fourier transform infrared (FTIR) spectra indicated that APP deposited SiO_x films are an inorganic feature. XPS examination revealed that the SiO_x films contained approximately 30% silicon, 58% oxygen and 12% carbon. Atomic forced microscopy (AFM) analysis results indicated a smooth surface of SiO_x films in deposition under higher substrate temperature. Also, pencil hardness tests indicated that the hardness of APP deposited SiO_x films was greatly improved with increasing substrate temperatures. Copyright © 2008 John Wiley & Sons, Ltd.     

紫外光引发LDPE膜接枝含氟丙烯酸酯的研究

通过紫外光引发表面接枝聚合反应的方法 ,把含氟丙烯酸酯单体R 5 6 1 0引到LDPE薄膜上 .对经丁酮抽提后的接枝膜进行FTIR、ESCA、SEM和DSC等表征 ,证实含氟聚合物以化学键的方式接枝在LDPE基体膜上 .在一定范围内 ,增加紫外光强、引发剂和单体浓度以及反应温度等均有利于提高接枝率 .经计算R 5 6 1 0的紫外光引发接枝聚合反应总活化能为 5 4 2kJ mol.接枝膜的接触角随着接枝率的提高逐步增大 ,直至趋于恒定 .作者提出接枝膜存在一个在接触角测定时影响基体膜与探测水滴相互作用过程的边界层 .当接枝率较低、接枝层厚度小于边界层临界厚度时 ,基体LDPE影响接触角的大小 ,但随着接枝率提高 ,接枝层逐渐变厚 ,氟聚合物层对接触角的贡献逐渐占优势 ,导致接触角随之增大 .当接枝率超过一定值以后 ,接枝层厚度超过边界层临界厚度 ,接枝层对接枝膜的接触角起全部贡献 ,接触角测定值随之稳定     

Polymerization of para-xylylene derivatives (parylene polymerization). IV. Effects of the sublimation rate of di-p-xylylene on the morphology and crystallinity of parylene N deposited at different temperatures

The effect of the sublimation rate of di-p-xylylene on the crystallinity and morphology of Parylene N deposited on stainless steel was studied as a function of substrate temperature. For a given rate of dimer sublimation, the deposition rate increases with decreasing substrate temperature. Increasing the sublimation rate of the dimer increases the deposition rate 10-fold, decreases the crystallinity, and shifts the appearance of the hexagonal β structure towards higher substrate temperature for samples synthesized from room temperature (RT) to ?60°C. Solution annealing resulting from solvent extraction, and isothermal annealing, increase the crystallinity of the polymers and result in structures containing both α and β polymorphs. The surface topology, as revealed by scanning electron microscopy (SEM), for polymers synthesized from RT to ?40°C shows a globular structure, whereas low temperature samples exhibit a rod-type morphology. For higher sublimation rates of the dimer, SEM micrographs show that oligomeric species start appearing on the polymer films after a period of 4–5 days. Solvent extraction removes the oligomeric crystals, and GPC analysis of the resulting extract indicates that most of the oligomers range in molecular weight from 100 to 900. The cross-sectional morphology for fractured low temperature samples, however, reveals different morphologies as polymerization proceeds. It is postulated that in the temperature range ?50 to ?78°C, both surface condensation and surface adsorption of monomer occurs, leading to different morphologies and lower crystallinity. The polymer synthesized at liquid nitrogen temperature shows the presence of voids along with different morphologies. X-ray diffractograms of polymers synthesized at liquid nitrogen reveal a considerable amount of amorphous phase in the films. Hence, it is inferred that, although the liquid nitrogen polymerization is a solid state polymerization of the crystalline monomer, it does not lead to 100% crystalline material, and the reasons for this are discussed.     

Atomic layer deposition of TiO2 from TiI4 and H2O onto SiO2 surfaces: ab initio calculations of the initial reaction mechanisms

The initial surface reactions involved in the atomic layer deposition (ALD) of TiO2 from TiI4 and H2O onto a SiO2 substrate have been investigated using electronic structure calculations based on cluster models. The detailed atomic growth mechanisms on different types of functionalities on the SiO2 substrate have been proposed. The effects of quantum tunneling and hindered rotations of adsorbates on the rate of surface reactions have been investigated. The effects of tunneling were found to be negligible for all reactions, because typical ALD temperatures range from 150 to 450 degrees C. However, the rotational contributions to the rate constants must be taken into account in certain cases. All of the three surface functionalities investigated exhibit high chemical reactivity toward TiI4 precursors at typical ALD temperatures. The rate constants of the second half-reactions between Ti intermediates and H2O are 5-8 orders of magnitude smaller than the first half-reactions between TiI4 and the surface functionalities. Although the iodine release reaction has been used to explain previous experimental measurements, it is predicted to be unfavorable (kinetically and thermodynamically) and is unlikely to occur at typical ALD temperatures. Substitution of TiI4 with TiCl4 as the metal precursor can increase the binding energies of the absorbates onto the surface due to the high electronegativity of the Cl ligands. However, the activation barriers are not significantly different between these two metal precursors. More importantly, our calculations predict that TiI4 precursors tend to produce TiO2 films with fewer impurities than the TiCl4 precursors.     

Initiated chemical vapor deposition of alternating copolymers of styrene and maleic anhydride

Initiated chemical vapor deposition (iCVD) of alternating copolymer thin films has been achieved for the first time. Copolymerization is desirable for maleic anhydride (Ma) since this monomer does not homopolymerize to an appreciable extent. At conditions where the observed deposition rates for styrene (S) and Ma homopolymers were only 0 and 5.5 nm/min, respectively, combining the two monomers resulted in a much higher deposition rate of 75.4 nm/min. iCVD processes utilize low energy (<30 W) to generate peroxy radicals from initiator molecules while avoiding degradation of functional groups in the monomers. Indeed, full retention of the anhydride functionality from the Ma monomer and avoidance of undesirable side reactions was observed in iCVD of poly(styrene-alt-maleic anhydride) (PSMa) copolymer films. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and 13C nuclear magnetic resonance (NMR) conclusively demonstrate that all of the copolymer films contain 50% styrene and 50% Ma (within experimental error), irrespective of gas feed ratios employed during the deposition. The 13C NMR signal in the 136-140 ppm region from the quaternary carbon in styrene and additional distortionless enhancement polarization transfer experiments confirmed that the copolymers are strictly alternating. Varying the gas feed ratio of Ma to styrene provided control over deposition rates and number-average molecular weights. Number-average molecular weights varied from 1380 to 4680 g/mol, and deposition rates varied from 6.3 to 75.4 nm/min.     

Plasma polymerization of phenyl isothiocyanate

Thin polymer films were obtained by plasma polymerization of phenyl isothiocyanate. Polymerizations were carried out in rf (13.56 MHz) glow discharge generated in an electrodeless flow system. It was found that this monomer produces uniform films with a wide range of thicknesses, from hundreds of nanometers to tens of micrometers. The deposition rate appeared to be dependent on the substrate distance from the monomer inlet. The chemical structure of plasma polymer was characterized by using elemental analysis, IR spectroscopy, gas chromatography, and mass spectrometry. Elemental analysis showed that the composition of polymer depends on the substrate position in the reactor. It was observed that sulphur content decreased with increasing the substrate distance from the monomer inlet, whereas nitrogen content appeared to increase. The IR data revealed significant decrease in —NCS groups content in the polymer as compared with the monomer spectrum and indicated for the appearance of new absorption bands corresponding to the ? CN and C? H aliphatic, groups. The results account for a strong fragmentation of monomer in plasma involved in decomposition of isothiocyanate group and phenyl ring. The soluble fraction of polymeric material was examined by gas chromatography and then the separated products were analyzed by mass spectrometry. The soluble fraction was found to be composed of numerous low molecular-weight compounds. Identification of their structure revealed the presence of residual monomer, thiophenol, cyanobenzene, diphenyl, diphenyl sulphide, diphenyl disulphide, phenyl thiocyanate, dicyanobenzene, phenatroline, and some other oligomeric products. Formation of these compounds proves high susceptibility of ? NCS group in the monomer towards different fragmentation reactions. The surface free energy and electrical conductivity of polymer films were evaluated. The surface free energy value was very close to those estimated for plasma polymers deposited from other benzene derivatives. The low electrical conductivity manifested by the investigated polymeric material indicated for its dielectric character. The photoelectrical measurements revealed some photoconductivity effect in this material.     

Incorporation of Linear Spacer Molecules in Vapor Deposited Silicone Polymer Thin Films

Poly (trivinyl-trimethyl-cyclotrisiloxane) or polyV(3)D(3) is a promising insulating thin film known for its potential application in neural probe fabrication. However, its time-consuming synthesis rate renders it impractical for manufacturing standards. Previously, the growth mechanism of polyV(3)D(3) was shown to be affected by significant steric barriers. This article describes the synthesis of a copolymer of polyV(3)D(3) via initiated chemical vapor deposition (iCVD) using V(3)D(3) as the monomer, hexavinyl disiloxane (HVDS) as a spacer, and tert-butyl peroxide (TBP) as the initiator to obtain nearly a 4-fold increase in deposition rate. The film formation kinetics is limited by the adsorption of the reactive species on the surface of the substrate with an activation energy of -41.5 kJ/mol with respect to substrate temperature. The films deposited are insoluble in polar and non polar solvents due to their extremely crosslinked structure. They have excellent adhesion to silicon substrates and their adhesion properties are retained after soaking in a variety of solvents. Spectroscopic evidence shows that the films do not vary in structure after boiling in DI water for 1 hour, illustrating hydrolytic stability. PolyV(3)D(3)-HVDS has a bulk resistivity of 5.6 (±1) × 10(14) Ω-cm, which is comparable to that of parylene-C; the insulating thin film currently used in neuroprosthetic devices.     

Positive-tone nanopatterning of chemical vapor deposited polyacrylic thin films

Terpolymers of methyl alpha-chloroacrylate (MCA), methacrylic acid (MAA), and methacrylic anhydride (MAH) were synthesized by initiated chemical vapor deposition (iCVD) of MCA and MAA followed by low-temperature annealing that partially converts MAA into MAH. The MAA composition in the iCVD copolymer can be systematically varied between 37 and 85 mol % by adjusting the gas feed fractions of monomers. Study of the monomer reactivity ratios and the copolymer molecular weights supports the hypothesis of a surface propagation mechanism during the iCVD copolymerization. The carboxylic dehydration reaction at the annealing temperature of 160 degrees C is dominated by a mechanism of intramolecular cyclization, resulting in intramolecular MAH anhydride formation while preventing crosslink formation. The incorporation of highly electron-withdrawing anhydride functionality enhances chain scission susceptibility under electron-beam irradiation. P(MCA-MAA-MAH) terpolymer thin films can be completely developed at dosages as low as 20 microC/cm2 at 50 kV. High-quality positive-tone patterns were created with 60 nm feature size achieved in the vapor deposited films.     

Film thickness studies for the chemically synthesized conducting polyaniline

The chemical oxidation of aniline with ammonium persulphate (APS) in aqueous acidic medium to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. PANI films can also grow onto glass supports immersed in the reaction mixture during the polymerization. The optical absorption for these films was measured. Multilayer deposition of polymer films onto the gold electrode of QCM and onto the glass supports from consecutive repetitive treatments by the reaction mixture containing aniline and APS, were studied. The induction period, the yield and the growth rate of the polymer films during the multilayer deposition were discussed. A relation between the thickness of the films determined, from QCM technique and the optical absorption of the films was established. The electrical conductivity of the PANI films was also measured.     

Preparation and surface properties of novel low surface free energy fluorinated silane-functional polybenzoxazine films

A novel fluorinated silane-functional benzoxazine monomer is synthesized, and the structure is characterized by FTIR and (1)H NMR. Chemical bonds Si-O-Si linkage between the benzoxazine monomer and the substrate are identified through the variation of water contact angles. The low surface free energy calculation and mechanism of the benzoxazine polymer films are proved through contact angle measurement and FTIR. The film formation property and thermal stability of the polybenzoxazine are also investigated. These results clearly show that this novel polybenzoxazine can not only bond to the substrate but also possess even lower surface free energy which is 15.5 mJ/m(2). The polymer also possesses well thermal stability with a glass transition temperature of 188 °C and the 5% weight loss temperatures of 276 °C.     

Estimation of the electron-collision initiation rate constant for the plasma polymerization and deposition of ethane using a transport-based model

The plasma polymerization and deposition of ethane in a parallel-plate electrode system was predicted using gas-phase transport equations and published gas-phase kinetic rate constants, with the assumption that the deposition rate was limited by the production of monomer free radicals and their diffusion to the deposition surface. The kinetic rate constant for radical initiation by electron collision with ethane was adjusted to bring the modelpredictionsfor mass deposition into line with experimental measurements reported in the literature for 12 combinations of power, gas fowrate, and pressure. Furthermore, the shapes of the predicted deposition profiles were made to closely match the experimental profiles by introducing an adjustable parameter to account for plasma boundary effects and two coefficients to account for nonradical polymerization (constant for all conditions). The best-fit electron-collision initiation constant was compared with theoretical predictions for oxygen and hydrogen in a manner explainable by bond strengths and vibrational degrees of freedom.     

Preparation,characterization, and properties of fluorinated polyurethanes

Novel fluorinated polyurethanes (FPUs) were prepared by living radical polymerization of polyurethanes and hexafluorobutyl acrylate. The structures of the FPUs were characterized by FTIR, ¹H NMR, GPC, DSC, and XPS. The fluorinated polyurethane polymerization was investigated and showed monomer conversion, and molecular weight increased with increasing reaction time. In this way, the fluorine content in polyurethane could be easily adjusted by controlling the content of the fluorinated acrylate monomer. The mechanical evaluation shows that FPUs exhibit good mechanical properties. Morphology of FPU films was observed by scanning electron spectroscopy. The effects of the fluorine content on the surface properties and oxidative stability of FPUs were investigated. FPUs films were devoid of significant surface degradation after immersion in 20% H₂O₂ and 0.1 M CoCl₂ at 37 °C for 5 weeks. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3248–3256, 2009     

Plasma polymerization. VI. An ESCA investigation of the RF plasma polymerization of perfluoro-2-butyl tetrahydrofuran

Perfluoro-2-butyl tetrahydrofuran was polymerized by an RF glow discharge technique and detailed ESCA studies were made of the resultant films. The rate of film deposition was sensitively dependent on the W/FM parameter and the site of deposition. The ESCA data show that the molecular rearrangement accompanying plasma polymerization and the oxygen functionality is at a significantly lower level than the starting material. Under appropriate conditions plasma polymerization produces material with a C:F stoichiometry of 1:2, although the ESCA data show that the polymer is drastically different from PTFE. ESCA studies are also reported on thin films of the monomer studied at low temperature.