Tinh Nguyen | Ho Chi Minh city University of Economics (original) (raw)
Papers by Tinh Nguyen
Journal of Coatings Technology and Research, 2004
Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thick... more Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thickness and local surface morphology of polymer coatings during the UV degradation process. With the noninvasive feature of LSCM, one can obtain thickness information directly and nondestructively at various exposure times without destroying the specimens or deriving the thickness values from IR measurement by assuming uniform film ablation. Two acrylic polymer coatings were chosen for the study, and the physical and chemical changes of the two systems at various exposure times were measured and analyzed. Those
Journal of Macromolecular Science-polymer Reviews, 1981
Page 1. J. MACROMOL. SCI. -REV. MACROMOL. CHEM., C20( 1), 1-65 (1981) Thermal Analysis of Lignoce... more Page 1. J. MACROMOL. SCI. -REV. MACROMOL. CHEM., C20( 1), 1-65 (1981) Thermal Analysis of Lignocellulosic Materials. Part I. Unmodified Materials TINH NGUYEN Research and Engineering Technology Center ARC0 Chemical Co. ...
Journal of Composites Technology & Research, 1997
Polymer Degradation and Stability, 2002
The effects of relative humidity ranging from ≈0 to 90% on the moisture-enhanced photolysis (MEP)... more The effects of relative humidity ranging from ≈0 to 90% on the moisture-enhanced photolysis (MEP) of a partially-methylated melamine acrylic polymer coating exposed to the ultraviolet (UV)/50 °C condition were investigated. The UV source was two 1000 W xenon arc solar simulators, which provided radiation with wavelengths from 270 to 800 nm. Five different relative humidity (RH) levels were supplied by dry air/moist air mixture humidity generators. Degradation of coating films approximately 10 μm thick applied to CaF2 substrates exposed to different UV/RH conditions were measured by FTIR transmission spectroscopy using an auto-sampling device. The total degradation under UV at a particular RH consists of four modes: reactions during post curing, dark hydrolysis at a particular RH, photolysis, and MEP. Experiments were designed so that changes in MEP with RH were measured. Both the rates and magnitudes of the MEP increased with increasing RH. The MEP rates of the acrylic-melamine crosslink loss and coating oxidation increased during the early exposure stage then leveled off, but the MEP cleavage rates of the acrylic polymer segment were nearly constant with time. The two-stage degradation of melamine-acrylic structure is attributed to the heterogeneous microstructure of the coating, and the enhanced degradation is explained by a mechanism based on hydrolysis-generated formaldehyde molecules, which act as chromophores to absorb UV light and accelerate photo-oxidation.
Journal of Applied Polymer Science, 1999
Journal of Coatings Technology, 2003
Acrylic-melamine coatings are known to be susceptible to hydrolysis when exposed to water or humi... more Acrylic-melamine coatings are known to be susceptible to hydrolysis when exposed to water or humid environments. The mode and specific pathways for hydrolytic degradation of acrylic-melamine coatings exposed to water vapor in the absence of ultraviolet light are presented. Samples of a partially methylated melamine-acrylic coating applied to CaF2 substrates were subjected to five different relative humidity levels ranging from approximately 0 to 90% at 50°C. Coating degradation was measured with transmission Fourier transform infrared spectroscopy (FTIR) and tapping mode atomic force microscopy (AFM). In humid environments, partially methylated melamine-acrylic coatings undergo hydrolysis readily, causing considerable material loss and formation of mainly primary amines and carboxylic acids. The rate of hydrolysis increases with increasing RH. Hydrolytic degradation of acrylic-melamine coatings is an inhomogeneous process in which pits form, deepen, and enlarge with exposure. Such localized degradation mode suggests that hydrolysis of this material is an autocatalytic progression where acidic degradation products formed in the pits catalyze and accelerate the hydrolysis reactions.
Polymer Composites, 2001
One of the obstacles hindering the acceptance of polymer composites in civil engineering applicat... more One of the obstacles hindering the acceptance of polymer composites in civil engineering applications is the susceptibility of the polymeric matrix: to degradation that is initiated by moisture, temperature, and corrosive chemical environments. The objective of this study was to characterize chemical and physical changes in polymer matrix resins following exposure to these environments. Resin systems studied were vinyl ester and isophthalic polyester, both of which are proposed for use in construction applications. Unreinforced free films were exposed to water, alkaline and saline environments at ambient and elevated temperatures for extended periods of time. Changes in strength and thermophysical properties were evaluated through tensile testing. dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). Chemical degradation of the polymers was characterized using Fourier transform infrared (FTIR) spectroscopy. Energy dispersive X-ray (EDX) analysis of specimens following exposure was carried out to determine if ion diffusion into the bulk polymer occurred. Only minor changes in the glass transition temperatures of the polymers were observed after prolonged exposure at elevated temperature, but more substantial changes were noted in tensile strength, particularly in the case of the isophthalic polyester. Examination of the polymers following immersion in salt solution and alkaline solution showed essentially no ionic penetration into the bulk, with the exception of specimens that were visibly degraded. Spectroscopic analysis of chemical structure prior to and following exposure revealed varying degrees of ester hydrolysis.
Progress in Organic Coatings, 2003
Accelerating the photodegradation of polymeric materials is of great practical interest in weathe... more Accelerating the photodegradation of polymeric materials is of great practical interest in weathering research. Acceleration can be achieved by exposing polymeric materials to a high radiant flux; however, questions have arisen within the weathering community as to whether high radiant flux results can be extrapolated to in-service flux levels. Experiments designed to test this premise are called reciprocity law experiments. An extensive review has been conducted to assess the state-of-the-art of reciprocity law experiments in the photography, photoconductivity, photo-medicine, photobiology, and polymer photodegradation literatures. From this review, the Schwarzschild law (a power law generalization of the reciprocity law) appears to model adequately photoresponse vs. radiant flux for most materials and systems. A band theory model has been presented to explain variations in the Schwarzschild law coefficients and other experimental phenomena commonly associated with reciprocity experiments. Obstacles to the general acceptance of high radiant flux, laboratory-based experiments are discussed.
Polymer Degradation and Stability, 2002
A cumulative damage model and a laboratory apparatus are described for linking field and laborato... more A cumulative damage model and a laboratory apparatus are described for linking field and laboratory photodegradation results and for predicting the service life of polymeric materials exposed in the laboratory and field. The apparatus was designed to independently and precisely monitor and control in both space and time the three primary weathering factors causing polymeric materials to degrade when exposed in the field. These factors include temperature, relative humidity, and spectral ultraviolet radiation. A model acrylic melamine coating was exposed in the laboratory apparatus to each of 12 different spectral wavebands and four temperature and four relative humidity environments. The spectral dosage and material damage were measured for each exposure treatment and this data input into the cumulative damage model from which estimates of the spectral quantum yield were made. Variables affecting the accuracy of the measurements are discussed.
Progress in Organic Coatings, 1996
In situ and quantitative information on the water layer at the organic coating/substrate interfac... more In situ and quantitative information on the water layer at the organic coating/substrate interface is crucial for understanding and preventing the failure of organic coating systems. A technique, based on a two-layer model derived rigorously from internal reflection theory, has been developed for measuring in situ the thickness and amount of the water layer at the organic coating/substrate interface. The technique gives new insight into the processes by which water degrades the coating/substrate bonds. In this technique, a transparent or an opaque organic coating of sufficient thickness is applied to an internal reflection element (IRE) with or without a thin metallic film, which is used as the substrate. A water chamber is attached to the organic-coated specimen. After adding water to the chamber, Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectra are taken automatically at specified time intervals without disturbing the specimens or the instrument. Water uptake in the coating and FTIR-MIR spectra of water on the coating-free substrate are also used for the analysis. Examples of clear and pigmented coatings on untreated and treated substrate surfaces are given to demonstrate the technique. Results of water accumulation at the coating/iron interface with and without applied electrical potentials are given. In addition to measuring water at the coating/substrate interface, the technique provides a means for studying the transport of water through a coating adhered to a substrate. Information on water at the interface and its transport properties through coatings applied to a substrate is valuable for interpreting corrosion, blistering and delamination of organic coating systems, and for developing models for use in predicting the serivce lives of protective coatings.
Journal of Polymer Science Part B-polymer Physics, 2001
Characterization of polymer coatings microstructure is critical to the fundamental understanding ... more Characterization of polymer coatings microstructure is critical to the fundamental understanding of the corrosion of coated metals. An approach for mapping the chemical heterogeneity of a polymer system using chemical modification and tapping-mode atomic force microscopy (TMAFM) is demonstrated. This approach is based on the selective degradation of one of the phases in a multiphase polymer blend system and the ability of TMAFM to provide nanoscale lateral information about the different phases in the polymer system. Films made of a 70:30 polyethyl acrylate/polystyrene (PEA/PS) blend were exposed to a hydrolytic acidic environment and analyzed using TMAFM. Pits were observed to form in the PEA/PS blend films, and this degradation behavior was similar to that of the PEA material. Using these results, the domains in the 70:30 blend were identified as the PS-rich regions and the matrix as the PEA-rich region. This conclusion was confirmed by Fourier transform infrared-attenuated total reflection analyses that revealed the hydrolysis of the PEA material. TMAFM phase imaging was also used to follow pit growth of the blend as a function of exposure time. The usefulness of the chemical modification/AFM imaging approach in understanding the degradation process of a coating film is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1460–1470, 2001
Journal of Coatings Technology, 2001
The atomic force microscope (AFM) was used to monitor changes in surface features of an acrylic m... more The atomic force microscope (AFM) was used to monitor changes in surface features of an acrylic melamine coating that was exposed to a variety of conditions. Exposure to ultraviolet (UV) radiation and high relative humidity caused general roughening of the surface and the formation of pits. Further, the damage of the coating surface was much more substantial for exposure to high relative humidity compared to exposure to dry environments. This difference in degradation rates correlated with measurements of chemical degradation determined using infrared spectra that were acquired along with the AFM images.
Polymer Degradation and Stability, 2001
Tapping mode atomic force microscopy (AFM) was used to examine the microstructure of polyester fi... more Tapping mode atomic force microscopy (AFM) was used to examine the microstructure of polyester films before and after exposure to an alkaline solution. Phase imaging and force curves showed differences in properties between the degraded and undegraded regions. Additionally, chemical analyses of the degraded films and the immersion solutions were carried out using attenuated total reflection Fourier transform infrared spectroscopy, total carbon analysis and liquid chromatography–mass spectrometry to aid in the interpretation of AFM data. The results showed that the base-catalyzed hydrolysis of polyester was a heterogeneous process, involving the formation of pits that increase in number and size with exposure time. Information provided by this study can be used to better understand the degradation mode and mechanism of polyester coatings in alkaline media.
Macromolecules, 2000
Polymer coatings often contain degradation-susceptible regions, and corrosion of the metallic sub... more Polymer coatings often contain degradation-susceptible regions, and corrosion of the metallic substrate can occur directly underneath these regions. In this paper, the microstructure of model coating materials is investigated using atomic force microscopy (AFM). Specifically, AFM is used to study heterogeneity in thin film blends of polystyrene (PS) and polybutadiene (PB) as a function of annealing time at 80°C. PS/PB blend films with thicknesses of approximately 250 nm are prepared by spin casting from solutions onto silicon substrates. Both topographic and phase imaging in tapping mode AFM are performed on these films under ambient conditions and at different force levels using a silicon tip. For certain force levels, phase imaging provides good contrast between the phase-separated PS and PB regions, primarily because of the large compliance difference between the two materials. This contrast decreases with increasing annealing time because thermal oxidation causes cross-linking in PB, and thus, the compliance of the PB region increases toward that of PS. Nanoscale indentation measurements are then made on the observed phase-separated regions to identify these regions as PS-and PB-rich and to better understand the influence of relative surface stiffness on the phase images. Cast and free-standing films of pure PS and pure PB are also studied as a function of annealing time using AFM, contact angle measurements, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Results from studies of the individual PS and PB films are related to the AFM results for the blend films. The use of phase imaging for cure monitoring of polymers and for studies of chemically heterogeneous polymer systems is also discussed.
Langmuir, 2000
In this study, atomic force microscopy (AFM) is used to investigate the heterogeneity of blended ... more In this study, atomic force microscopy (AFM) is used to investigate the heterogeneity of blended films of poly(methyl methacrylate) (PMMA) and polybutadiene (PB) on silicon substrates before and after annealing. The blended films with different ratios of PMMA to PB are prepared by spin casting onto silicon substrates from solution. The surface morphology and composition of these cast films are investigated using tapping mode and force mode AFM. Annealing the samples in air at 75 ( 5°C causes changes in the relative chemical and mechanical differences between PMMA and PB, so the phase image contrast is studied as a function of annealing time. The effect of tapping force level on phase image contrast is also explored. To identify the different components in polymer blends and to understand the influence of relative surface stiffness on the phase images, nanoscale indentation measurements are made on the observed phase-separated regions. Interpretation of AFM results is aided by data collected from both conditioned and annealed PB and PMMA films using Fourier transform infrared spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, and contact angle measurements. A loss in phase contrast between PB-rich and PMMA-rich regions is observed as a function of heating time. This observation correlates well with the increases in glass transition temperature, modulus, and polarity of pure PB with respect to pure PMMA.
Journal of Coatings Technology and Research, 2004
Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thick... more Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thickness and local surface morphology of polymer coatings during the UV degradation process. With the noninvasive feature of LSCM, one can obtain thickness information directly and nondestructively at various exposure times without destroying the specimens or deriving the thickness values from IR measurement by assuming uniform film ablation. Two acrylic polymer coatings were chosen for the study, and the physical and chemical changes of the two systems at various exposure times were measured and analyzed. Those
Journal of Macromolecular Science-polymer Reviews, 1981
Page 1. J. MACROMOL. SCI. -REV. MACROMOL. CHEM., C20( 1), 1-65 (1981) Thermal Analysis of Lignoce... more Page 1. J. MACROMOL. SCI. -REV. MACROMOL. CHEM., C20( 1), 1-65 (1981) Thermal Analysis of Lignocellulosic Materials. Part I. Unmodified Materials TINH NGUYEN Research and Engineering Technology Center ARC0 Chemical Co. ...
Journal of Composites Technology & Research, 1997
Polymer Degradation and Stability, 2002
The effects of relative humidity ranging from ≈0 to 90% on the moisture-enhanced photolysis (MEP)... more The effects of relative humidity ranging from ≈0 to 90% on the moisture-enhanced photolysis (MEP) of a partially-methylated melamine acrylic polymer coating exposed to the ultraviolet (UV)/50 °C condition were investigated. The UV source was two 1000 W xenon arc solar simulators, which provided radiation with wavelengths from 270 to 800 nm. Five different relative humidity (RH) levels were supplied by dry air/moist air mixture humidity generators. Degradation of coating films approximately 10 μm thick applied to CaF2 substrates exposed to different UV/RH conditions were measured by FTIR transmission spectroscopy using an auto-sampling device. The total degradation under UV at a particular RH consists of four modes: reactions during post curing, dark hydrolysis at a particular RH, photolysis, and MEP. Experiments were designed so that changes in MEP with RH were measured. Both the rates and magnitudes of the MEP increased with increasing RH. The MEP rates of the acrylic-melamine crosslink loss and coating oxidation increased during the early exposure stage then leveled off, but the MEP cleavage rates of the acrylic polymer segment were nearly constant with time. The two-stage degradation of melamine-acrylic structure is attributed to the heterogeneous microstructure of the coating, and the enhanced degradation is explained by a mechanism based on hydrolysis-generated formaldehyde molecules, which act as chromophores to absorb UV light and accelerate photo-oxidation.
Journal of Applied Polymer Science, 1999
Journal of Coatings Technology, 2003
Acrylic-melamine coatings are known to be susceptible to hydrolysis when exposed to water or humi... more Acrylic-melamine coatings are known to be susceptible to hydrolysis when exposed to water or humid environments. The mode and specific pathways for hydrolytic degradation of acrylic-melamine coatings exposed to water vapor in the absence of ultraviolet light are presented. Samples of a partially methylated melamine-acrylic coating applied to CaF2 substrates were subjected to five different relative humidity levels ranging from approximately 0 to 90% at 50°C. Coating degradation was measured with transmission Fourier transform infrared spectroscopy (FTIR) and tapping mode atomic force microscopy (AFM). In humid environments, partially methylated melamine-acrylic coatings undergo hydrolysis readily, causing considerable material loss and formation of mainly primary amines and carboxylic acids. The rate of hydrolysis increases with increasing RH. Hydrolytic degradation of acrylic-melamine coatings is an inhomogeneous process in which pits form, deepen, and enlarge with exposure. Such localized degradation mode suggests that hydrolysis of this material is an autocatalytic progression where acidic degradation products formed in the pits catalyze and accelerate the hydrolysis reactions.
Polymer Composites, 2001
One of the obstacles hindering the acceptance of polymer composites in civil engineering applicat... more One of the obstacles hindering the acceptance of polymer composites in civil engineering applications is the susceptibility of the polymeric matrix: to degradation that is initiated by moisture, temperature, and corrosive chemical environments. The objective of this study was to characterize chemical and physical changes in polymer matrix resins following exposure to these environments. Resin systems studied were vinyl ester and isophthalic polyester, both of which are proposed for use in construction applications. Unreinforced free films were exposed to water, alkaline and saline environments at ambient and elevated temperatures for extended periods of time. Changes in strength and thermophysical properties were evaluated through tensile testing. dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). Chemical degradation of the polymers was characterized using Fourier transform infrared (FTIR) spectroscopy. Energy dispersive X-ray (EDX) analysis of specimens following exposure was carried out to determine if ion diffusion into the bulk polymer occurred. Only minor changes in the glass transition temperatures of the polymers were observed after prolonged exposure at elevated temperature, but more substantial changes were noted in tensile strength, particularly in the case of the isophthalic polyester. Examination of the polymers following immersion in salt solution and alkaline solution showed essentially no ionic penetration into the bulk, with the exception of specimens that were visibly degraded. Spectroscopic analysis of chemical structure prior to and following exposure revealed varying degrees of ester hydrolysis.
Progress in Organic Coatings, 2003
Accelerating the photodegradation of polymeric materials is of great practical interest in weathe... more Accelerating the photodegradation of polymeric materials is of great practical interest in weathering research. Acceleration can be achieved by exposing polymeric materials to a high radiant flux; however, questions have arisen within the weathering community as to whether high radiant flux results can be extrapolated to in-service flux levels. Experiments designed to test this premise are called reciprocity law experiments. An extensive review has been conducted to assess the state-of-the-art of reciprocity law experiments in the photography, photoconductivity, photo-medicine, photobiology, and polymer photodegradation literatures. From this review, the Schwarzschild law (a power law generalization of the reciprocity law) appears to model adequately photoresponse vs. radiant flux for most materials and systems. A band theory model has been presented to explain variations in the Schwarzschild law coefficients and other experimental phenomena commonly associated with reciprocity experiments. Obstacles to the general acceptance of high radiant flux, laboratory-based experiments are discussed.
Polymer Degradation and Stability, 2002
A cumulative damage model and a laboratory apparatus are described for linking field and laborato... more A cumulative damage model and a laboratory apparatus are described for linking field and laboratory photodegradation results and for predicting the service life of polymeric materials exposed in the laboratory and field. The apparatus was designed to independently and precisely monitor and control in both space and time the three primary weathering factors causing polymeric materials to degrade when exposed in the field. These factors include temperature, relative humidity, and spectral ultraviolet radiation. A model acrylic melamine coating was exposed in the laboratory apparatus to each of 12 different spectral wavebands and four temperature and four relative humidity environments. The spectral dosage and material damage were measured for each exposure treatment and this data input into the cumulative damage model from which estimates of the spectral quantum yield were made. Variables affecting the accuracy of the measurements are discussed.
Progress in Organic Coatings, 1996
In situ and quantitative information on the water layer at the organic coating/substrate interfac... more In situ and quantitative information on the water layer at the organic coating/substrate interface is crucial for understanding and preventing the failure of organic coating systems. A technique, based on a two-layer model derived rigorously from internal reflection theory, has been developed for measuring in situ the thickness and amount of the water layer at the organic coating/substrate interface. The technique gives new insight into the processes by which water degrades the coating/substrate bonds. In this technique, a transparent or an opaque organic coating of sufficient thickness is applied to an internal reflection element (IRE) with or without a thin metallic film, which is used as the substrate. A water chamber is attached to the organic-coated specimen. After adding water to the chamber, Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectra are taken automatically at specified time intervals without disturbing the specimens or the instrument. Water uptake in the coating and FTIR-MIR spectra of water on the coating-free substrate are also used for the analysis. Examples of clear and pigmented coatings on untreated and treated substrate surfaces are given to demonstrate the technique. Results of water accumulation at the coating/iron interface with and without applied electrical potentials are given. In addition to measuring water at the coating/substrate interface, the technique provides a means for studying the transport of water through a coating adhered to a substrate. Information on water at the interface and its transport properties through coatings applied to a substrate is valuable for interpreting corrosion, blistering and delamination of organic coating systems, and for developing models for use in predicting the serivce lives of protective coatings.
Journal of Polymer Science Part B-polymer Physics, 2001
Characterization of polymer coatings microstructure is critical to the fundamental understanding ... more Characterization of polymer coatings microstructure is critical to the fundamental understanding of the corrosion of coated metals. An approach for mapping the chemical heterogeneity of a polymer system using chemical modification and tapping-mode atomic force microscopy (TMAFM) is demonstrated. This approach is based on the selective degradation of one of the phases in a multiphase polymer blend system and the ability of TMAFM to provide nanoscale lateral information about the different phases in the polymer system. Films made of a 70:30 polyethyl acrylate/polystyrene (PEA/PS) blend were exposed to a hydrolytic acidic environment and analyzed using TMAFM. Pits were observed to form in the PEA/PS blend films, and this degradation behavior was similar to that of the PEA material. Using these results, the domains in the 70:30 blend were identified as the PS-rich regions and the matrix as the PEA-rich region. This conclusion was confirmed by Fourier transform infrared-attenuated total reflection analyses that revealed the hydrolysis of the PEA material. TMAFM phase imaging was also used to follow pit growth of the blend as a function of exposure time. The usefulness of the chemical modification/AFM imaging approach in understanding the degradation process of a coating film is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1460–1470, 2001
Journal of Coatings Technology, 2001
The atomic force microscope (AFM) was used to monitor changes in surface features of an acrylic m... more The atomic force microscope (AFM) was used to monitor changes in surface features of an acrylic melamine coating that was exposed to a variety of conditions. Exposure to ultraviolet (UV) radiation and high relative humidity caused general roughening of the surface and the formation of pits. Further, the damage of the coating surface was much more substantial for exposure to high relative humidity compared to exposure to dry environments. This difference in degradation rates correlated with measurements of chemical degradation determined using infrared spectra that were acquired along with the AFM images.
Polymer Degradation and Stability, 2001
Tapping mode atomic force microscopy (AFM) was used to examine the microstructure of polyester fi... more Tapping mode atomic force microscopy (AFM) was used to examine the microstructure of polyester films before and after exposure to an alkaline solution. Phase imaging and force curves showed differences in properties between the degraded and undegraded regions. Additionally, chemical analyses of the degraded films and the immersion solutions were carried out using attenuated total reflection Fourier transform infrared spectroscopy, total carbon analysis and liquid chromatography–mass spectrometry to aid in the interpretation of AFM data. The results showed that the base-catalyzed hydrolysis of polyester was a heterogeneous process, involving the formation of pits that increase in number and size with exposure time. Information provided by this study can be used to better understand the degradation mode and mechanism of polyester coatings in alkaline media.
Macromolecules, 2000
Polymer coatings often contain degradation-susceptible regions, and corrosion of the metallic sub... more Polymer coatings often contain degradation-susceptible regions, and corrosion of the metallic substrate can occur directly underneath these regions. In this paper, the microstructure of model coating materials is investigated using atomic force microscopy (AFM). Specifically, AFM is used to study heterogeneity in thin film blends of polystyrene (PS) and polybutadiene (PB) as a function of annealing time at 80°C. PS/PB blend films with thicknesses of approximately 250 nm are prepared by spin casting from solutions onto silicon substrates. Both topographic and phase imaging in tapping mode AFM are performed on these films under ambient conditions and at different force levels using a silicon tip. For certain force levels, phase imaging provides good contrast between the phase-separated PS and PB regions, primarily because of the large compliance difference between the two materials. This contrast decreases with increasing annealing time because thermal oxidation causes cross-linking in PB, and thus, the compliance of the PB region increases toward that of PS. Nanoscale indentation measurements are then made on the observed phase-separated regions to identify these regions as PS-and PB-rich and to better understand the influence of relative surface stiffness on the phase images. Cast and free-standing films of pure PS and pure PB are also studied as a function of annealing time using AFM, contact angle measurements, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Results from studies of the individual PS and PB films are related to the AFM results for the blend films. The use of phase imaging for cure monitoring of polymers and for studies of chemically heterogeneous polymer systems is also discussed.
Langmuir, 2000
In this study, atomic force microscopy (AFM) is used to investigate the heterogeneity of blended ... more In this study, atomic force microscopy (AFM) is used to investigate the heterogeneity of blended films of poly(methyl methacrylate) (PMMA) and polybutadiene (PB) on silicon substrates before and after annealing. The blended films with different ratios of PMMA to PB are prepared by spin casting onto silicon substrates from solution. The surface morphology and composition of these cast films are investigated using tapping mode and force mode AFM. Annealing the samples in air at 75 ( 5°C causes changes in the relative chemical and mechanical differences between PMMA and PB, so the phase image contrast is studied as a function of annealing time. The effect of tapping force level on phase image contrast is also explored. To identify the different components in polymer blends and to understand the influence of relative surface stiffness on the phase images, nanoscale indentation measurements are made on the observed phase-separated regions. Interpretation of AFM results is aided by data collected from both conditioned and annealed PB and PMMA films using Fourier transform infrared spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, and contact angle measurements. A loss in phase contrast between PB-rich and PMMA-rich regions is observed as a function of heating time. This observation correlates well with the increases in glass transition temperature, modulus, and polarity of pure PB with respect to pure PMMA.