Comparison of surface structures of poly(ethyl methacrylate) and poly(ethyl acrylate) in different chemical environments

Abstract

Sum frequency generation (SFG) vibrational spectroscopy has been applied to investigate and compare the chemical structures of poly(ethyl methacrylate) (PEMA) and poly(ethyl acrylate) (PEA) in air, in water, and in a non-polar solvent, FC-75. SFG spectra from both polymer surfaces in air are dominated by vibrational modes from the ester ethyl side groups. The average orientation of these ester ethyl groups on the two polymer surfaces is slightly different. In water, the two polymers show markedly different restructuring behavior. The ester ethyl side chains on the PEMA surface in water reorient to tilt more toward the surface, yet remain ordered. Such a restructuring of the PEMA surface in water is reversible. However, no SFG signal was detected from the PEA/water interface, showing that the surface of PEA becomes disordered upon contacting water, and this process is irreversible. SFG results collected from the C=O range indicate that hydrogen bonding is observed for both polymer/water interfaces, but the order of C=O at the PEA/water interface is much lower than that at the PEMA/water interface. Supplemental experiments support our hypothesis that the PEA surface becomes rough and loses order gradually as it interacts with water. We have demonstrated, for the first time, that the loss of surface structural order is due to the interaction between soft PEA chains with water molecules followed by reorganization of the polymer backbone. This causes the polymer surface to become rough and disordered. However, the surface structures of PEMA and PEA in FC-75 are similar and are also similar to those in air. This indicates that not only T(g), but also the contacting medium plays an important role in determining the surface restructuring behavior of polymer materials.

Molecular level studies of polymer behaviors at the water interface using sum frequency generation vibrational spectroscopy

“…The water-induced C¼ ¼O bond changes of polyacrylates were also studied in PEMA compared to poly(ethyl acrylate) (PEA) in 2005 by Chen et al 67 Both PEMA and PEA C¼ ¼O peaks observed a red shift on immersion in water of about 10-20 cm À1 , due to hydrogen bonding between the polymer and water. PEMA also had stronger signals compared to PEA, which suggested these C¼ ¼O bonds were more highly ordered than those in PEA.…”

Dynamic structure and functionalization of polymer interfaces

“…In fact, it has been reported that the change in the interfacial conformation of poly(n-alkyl methacrylate)s upon contacting water is induced by hydrogen bonding between the carbonyl groups in the polymer side chain and water. 29,30,60 Thus, the enantioselective wetting observed here can be associated with a surface reorganization via the local conformational change of polymer chains. The decrease in the contact angle with increasing time shown in the panels (b) and (c) of Figure 4 should reflect the conformational change of the polymer chains.…”

Probing polymer surfaces and interfaces using sum frequency generation vibrational spectroscopy - a powerful nonlinear optical technique

“…When the side chain length increases, as polybutylmethacrylate (PBMA) and polyethylmethacrylate (PEMA), substantial SFG spectral change in water (compared to that in air) was observed, indicated by different symmetric and asymmetric stretching signal intensities. Detailed analysis suggested that the side chain end methyl groups "standed up" with a broad tilt angle distribution in air and "lay down" with a narrow tilt angle distribution in water on the surface [50][51][52][53]. When the side chain length further increases, as poly(noctylmethacrylate) (POMA) and poly(n-octadecylmethacrylate) (PODMA), spectral differences in water were also observed [50].…”

“…The surface structures and restructuring behaviors in water of polymethacrylates with different side chains were systematically investigated by Chen group [49][50][51][52]. It was discovered that the polymethylmethacrylate (PMMA) surface in air was dominated by the ester methyl groups with more or less a normal orientation to the surface, with a tilt angle between two extremes of 33°supposing a δ-distribution and 0°with a distribution width of 31°assuming a Gaussian distribution [49].…”