“…When compared with the mole percent of PDMS in Table , the enhancement of PDMS at the surface was qualitatively shown by FTIR. However, the depth of penetration of the FTIR technology is about 400−2000 nm, which is many thousands of molecular layers, and this deeper penetration suggests that FTIR technology is not as sensitive as ESCA in discriminating between the surface chemistry changes at the upper layers. ,, 1 FTIR absorbance spectra of pure poly(ε-caprolactone) (P1), pure poly(dimethylsiloxane) (P4), PCL/PDMS/PCL copolymers with siloxane to caprolactone ratio 30/18 (P3) and 30/27 (P2).…”
The surface composition and free energy properties of two grades of amphiphilic and semicrystalline triblock copolymers consisting of a poly(dimethylsiloxane) (PDMS) midblock (Mw ∼ 2300) coupled to poly-(-caprolactone) (PCL) end blocks having differing molecular weights (Mw ∼ 2000, sample P3, and Mw ∼ 3000, sample P2) and homopolymer PCL (Mw ∼ 40 000) were investigated by Fourier transform infrared, spectroscopy, electron spectroscopy for chemical analysis (ESCA), and contact angle measurements using critical surface tension, one-liquid and two-liquid methods. ESCA showed that the molar concentration of PDMS increased from 36.5% in the bulk up to 70.2% in the surface for sample P2 and from 46.3% in the bulk up to 79.2% in the surface for sample P3 in high vacuum. This indicates that the lower surface energy PDMS microdomains were segregated in the surface region to minimize the surface energy of the copolymer. The longer the PCL block, the higher the phase separation. One-liquid contact angle results were evaluated by using van Oss, Good, and Chaudhury's Lifshitz-van der Waals and Lewis acid-base (AB) methodology, and it was determined that the basicity surface tension coefficients (γ s-) of the copolymers decreased with the increase of the PDMS content at the surface, a result in agreement with the ESCA results but not proportional to them, indicating that the surfaces of the copolymers are highly mobile and molecular rearrangement takes place upon contacting with a polar testing liquid drop. The strong AB interaction between the basic carboxyl groups of PCL segments with the Lewis acidic groups of the polar liquids restructured the surface molecular composition at the contact area by increasing PCL and decreasing PDMS concentration in polar environments. The two-liquid contact angle method was also applied, and it was determined that γ s-decreased inverse proportionally with the increase of PDMS segments. Also, it was realized that the molecular restructuring did not take place in the two-liquid method.
“…When compared with the mole percent of PDMS in Table , the enhancement of PDMS at the surface was qualitatively shown by FTIR. However, the depth of penetration of the FTIR technology is about 400−2000 nm, which is many thousands of molecular layers, and this deeper penetration suggests that FTIR technology is not as sensitive as ESCA in discriminating between the surface chemistry changes at the upper layers. ,, 1 FTIR absorbance spectra of pure poly(ε-caprolactone) (P1), pure poly(dimethylsiloxane) (P4), PCL/PDMS/PCL copolymers with siloxane to caprolactone ratio 30/18 (P3) and 30/27 (P2).…”
The surface composition and free energy properties of two grades of amphiphilic and semicrystalline triblock copolymers consisting of a poly(dimethylsiloxane) (PDMS) midblock (Mw ∼ 2300) coupled to poly-(-caprolactone) (PCL) end blocks having differing molecular weights (Mw ∼ 2000, sample P3, and Mw ∼ 3000, sample P2) and homopolymer PCL (Mw ∼ 40 000) were investigated by Fourier transform infrared, spectroscopy, electron spectroscopy for chemical analysis (ESCA), and contact angle measurements using critical surface tension, one-liquid and two-liquid methods. ESCA showed that the molar concentration of PDMS increased from 36.5% in the bulk up to 70.2% in the surface for sample P2 and from 46.3% in the bulk up to 79.2% in the surface for sample P3 in high vacuum. This indicates that the lower surface energy PDMS microdomains were segregated in the surface region to minimize the surface energy of the copolymer. The longer the PCL block, the higher the phase separation. One-liquid contact angle results were evaluated by using van Oss, Good, and Chaudhury's Lifshitz-van der Waals and Lewis acid-base (AB) methodology, and it was determined that the basicity surface tension coefficients (γ s-) of the copolymers decreased with the increase of the PDMS content at the surface, a result in agreement with the ESCA results but not proportional to them, indicating that the surfaces of the copolymers are highly mobile and molecular rearrangement takes place upon contacting with a polar testing liquid drop. The strong AB interaction between the basic carboxyl groups of PCL segments with the Lewis acidic groups of the polar liquids restructured the surface molecular composition at the contact area by increasing PCL and decreasing PDMS concentration in polar environments. The two-liquid contact angle method was also applied, and it was determined that γ s-decreased inverse proportionally with the increase of PDMS segments. Also, it was realized that the molecular restructuring did not take place in the two-liquid method.
“…Many spectroscopic techniques such as electron spectroscopy for chemical analysis (ESCA), inelastic electron tunneling spectroscopy (IETS), secondary ion mass spectroscopy (SIMS) and Fourier transform infrared spectroscopy (FTIR) are commonly used for studies on the polymer-metal interface, and these have been recently reviewed by Filbey and Wightman [ 10]. In the present study, the emphasis is placed on interfacial interactions between polar groups in ethylene copolymers and hydroxyl groups on hydrated aluminium surfaces.…”
Interfacial interactions to hydrated aluminium were examined for poly(ethylene-covinylacetate) EVA, poly(ethylene-co-butylacrylate) EBA, and poly(ethylene-co-acrylic acid) EAA. By means of IR reflection-absorption spectroscopy, the interactions between the effective functional groups were analysed at the polymer/aluminium interface. Thin copolymer films were prepared by solution casting onto aluminium, which had been hydrated by immersion in boiling water. The spectra representing the interface material revealed a strong hydrogen bond interaction between hydroxyl groups on the hydrated aluminium surface and the carbonyl oxygen in the ester group in EVA and EBA. The absorbance mode of the hydrogen bonded carbonyl was displaced to lower wavenumbers and appeared 34 cm-1 and 38 cm-1 below the 'free' carbonyl for EVA and EBA, respectively, which indicates that the hydrogen bond is very strong. For the C-O stretching mode in the ester group, a displacement of 36 cm 1 in the opposite direction was observed, also an effect due to the hydrogen bond to the carbonyl. Furthermore, it was found that the absorptivity for the hydrogen bonded carbonyl was much higher than for the 'free', and for that reason a relative absorptivity ratio between them was determined. For EAA cast onto hydrated aluminium surfaces, the absorbance mode of the carbonyl disappeared, but new peaks arose at lower wavenumbers indicative of a carboxylate. This was explained to be due to a reaction between carboxylic acid groups and aluminium hydroxyl groups on the hydrated surface.
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