Surface and interfacial fourier transform infrared spectroscopic studies of latexes. XIV. Surface phase separation in polystyrene/poly-n-butyl acrylate latex films

This study focuses on the behavior of sodium dioctylsulfosuccinate (SDOSS) in 50/50 w/w % polystyrene/poly(butyl acrylate) (p-Sty/p-BA) latex films. Specifically, mobility and orientation are examined in the context of the film formation by the use of dynamic mechanical thermal analysis and attenuated total reflectance (ATR) Fourier transform infrared (FT-IR) spectroscopy. While for the homopolymer blends of p-Sty and p-BA, two T_g values resulting from a phase separation of p-Sty and p-BA phases are observed, only a single T_g is detected for a copolymer of the same mixture, indicating a single phase within the film. ATR FTIR spectroscopic data indicate that the phase separation of p-Sty and p-BA blends does not occur uniformly across the film. After coalescence, p-Sty particles produce a significant degree of stratification at approximately 1.6 μm from the film surface. At this depth, the polystyrene rings assume preferentially parallel orientation to the film surface. At the same time, the hydrophilic groups of SDOSS surfactant (SO⁻₃Na⁺) are oriented preferentiallyparallel to the surface. Under high relative humidity conditions, water is able to diffuse into the film and swells the surface layers, thus causing them to expand. As a result, the top, predominately poly-n-BA surface becomes “thicker», and p-Sty phase appears to be near 2.3 μm from the surface. The polystyrene rings maintain their preferential parallel orientation to the surface, but the hydrophilic groups of SDOSS are able to diffuse into the film with the water uptake and are thus not present at the filmair interface. © 1996 John Wiley & Sons, Inc.     

Surface and interfacial fourier transform infrared spectroscopic studies of latexes. XVI. Quantitative analysis of surfactant in multilayered films

Migration and concentration levels of sodium dioctylsulfosuccinate (SDOSS) surfactant molecules in 50%/50% styrene/butyl acrylate latex were detected at the film-substrate (F-S) and film-air (F-A) interfaces in mono- and double-layered films. For the purpose of quantitative analysis, absorption coefficients of the 1,056 and 1,046 cm⁻¹ bands attributed to the SO₃⁻Na⁺…HOOC and SO⁻₃Na⁺…H₂O associations, respectively, were determined. Using group theory formalism, local geometries of the SO⁻₃Na⁺ hydrophilic groups of SDOSS can be predicted. The analysis is extended to the 1,261 and 1,209 cm⁻¹ bands resulting from the S—O asymmetric stretching vibrations, due to the same SO⁻₃Na⁺ … HOOC and SO⁻₃Na⁺ … H₂O associations, and to the 1,290 and 1,236 cm⁻¹ bands, due to asymmetric stretching modes of hydrophobic tails of the SDOSS. By the use of polarization attenuated total reflectance Fourier transform infrared (ATRFT-IR) experiments, these studies show that hydrophilic SO⁻₃Na⁺ ends on SDOSS are preferentially parallel to the film surface. At the same time, hydrophobic tails are perpendicular to the surface. The assessment of the amounts of SDOSS at the F-S and F-A interfaces was obtained by quantitative ATR FTIR analysis, which was extended to the silicone-modified double-layer latex films. In this case, the concentration of SDOSS molecules decreases as the depth of penetration increases. The highest concentrations of SDOSS molecules are detected at the shallowest depths near the surface of the top layer and the interfacial regions between the latex layers. © 1996 John Wiley & Sons, Inc.     

Surface and interfacial FT–IR spectroscopic studies of latexes. VI. Orientation and spatial distribution of acid functionalities at the film–substrate interface

Formation of dimeric carboxylic acid functional groups observed at the film-substrate interface of ethyl acrylate/methacrylic acid (EA/MAA) and butyl acrylate / methyl meth-acrylate / methacrylic acid (BA/MMA/MAA) latex films prepared on a high surface tension substrate, such as liquid mercury, is observed when sodium dioctyl sulfosuccinate (SDOSS) is employed as the synthetic emulsifier. To address the acid species assembled at this interface due to the inability of SDOSS to effectively alleviate interfacial tension and to assess the orientation and spatial configuration of acid groups species at the interface, polarized attenuated total reflectance, Fourier-transform infrared spectroscopy (ATR FT–IR) is employed. It is found that the acid dimer rings adopt an average “on-edge” configuration at the interface with the hydrogen-bonded rings perpendicular to the film-mercury interface. This configuration serves to provide not only the necessary interfacial acid-dimer layer, but also facilitates favorable ring–ring interactions between groups of opposite polarity on adjacent rings. This study indicates that the on-edge configuration may also serve to reduce unfavorable interactions between the polar acid functionality and the less polar components present in the bulk of the coalesced latexes. © 1993 John Wiley & Sons, Inc.     

Surface and interfacial FT–IR spectroscopic studies of latexes. VIII. The effect of particle and copolymer composition on surfactant exudation in styrene-n-butyl acrylate copolymer latex films

Polarized attenuated total reflection Fourier transform infrared (ATR FT–IR) spectroscopy was used to identify the mobility and surfactant exudation of sodium dioctyl sulfocuccinate (SDOSS) surfactant molecules to the film–air (F–A) and film–substrate (F–S) interfaces in styrene/n-butyl acrylate (Sty/n-BA) latex films. It was found that, depending upon the latex particle composition, the surfactant molecules could be driven to the F–A or F–S interfaces. The primary factors that governed the direction of exudation were the compatibility of the latex components, interfacial film-substrate surface tension, and the chemical composition of the latex particles. Concentration, as well as orientation, of the hydrophilic SONa⁺ surfactant ends changed as a function of depth and the latex particle composition. © 1993 John Wiley & Sons, Inc.     

Surface and interfacial FTIR spectroscopic studies of latexes. IV. The effect of surfactant structure on the copolymer–surfactant interactions

The interactions between sodium dodecylbenzene sulfonate (SDBS) and the components of an ethyl acrylate/methacrylic acid (EA/MAA) copolymer latex were examined and the influences of using D₂O as the synthetic suspension medium were investigated. Whereas it is found that D₂O has no detectable influence on the fully coalesced latex films, the film coalescence conditions are shown to significantly affect the nature of surfactant interactions within the film matrix. When films are prepared and stored under controllable low atmospheric water-vapor concentrations, hydrogen-bonding interactions between the surfactant SO₃^?Na⁺ groups and the copolymer acid functionality dominate. However, coalescence and storage of the films under higher relative humidity conditions results in a displacement of these interactions in favor of the hydrated form of the surfactant. It is also shown that the presence of an aromatic ring adjacent to the surfactant sulfonate group exerts an influence on the nature of the SO₃^? ··· HOOC interactions within the copolymer matrix. Relative to sodium dioctyl sulfosuccinate (SDOSS), the aromatic group near hydrophilic end of SDBS increases the strength of the S? O bond in the presence of acid interactions. © 1993 John Wiley & Sons, Inc.     

Surface and interfacial FTIR spectroscopic studies of latexes. XI. The effect of Sty/n-BA copolymer composition on the orientation of SDOSS surfactant molecules

These studies examine how various latex copolymer compositions, ranging from 100% n-BA to 50%/50% Sty/n-BA, may influence sodium dioctylsulfosuccinate (SDOSS) mobility, diffusion, and orientation near the film–air (F–A) and film–substrate (F–S) interfaces. Polarized attenuated total reflection Fourier transform infrared spectroscopy is utilized to examine the surfactant behavior in Sty/n–BA latexes at the F–A and F–S interfaces. Based on the analysis developed for the purpose of these studies, the highest concentration of SDOSS is detected near the F–A interface for 50%/50% Sty/n-BA compositions. However, when the content of styrene in Sty/n-BA compositions. However, when the content of styrene in Sty/n-BA copolymer is diminished, the highest content of SDOSS is detected near the F–S interface. This behavior is particularly evident for 100% poly(n-BA) latexes. When SDOSS molecules are near the F–A and F–S interfaces, the SO₃⁻Na⁺ hydrophilic ends are preferentially parallel to the surface, whereas hydrophobic tails are perpendicular. © 1996 John Wiley & Sons, Inc.