Sum frequency generation vibrational spectroscopy of methacrylate-based functional monomers at the hydrophilic solid-liquid interface.

2-Substituted ethyl methacrylate monomers were characterized using sum frequency generation vibrational spectroscopy (SFGVS) to study the effect of substituent groups in the organization of the monomers at the monomer-hydrophilic quartz interface. The SFG spectra of the methacrylate-based functional monomers collected at the hydrophilic quartz interface were found to be different from those collected at the air-monomer interface. The various spectral profiles indicated different conformations of the molecular groups at the solid-liquid interface. Moreover, a peak shift of the methyl symmetric stretch from ∼2900 cm-1 to ∼2880 cm-1 was observed from the air-liquid to solid-liquid interface, respectively. This observation of peak shifting is due to two factors: (1) a change in the chemical environment of the methacrylate-based monomer from air-to-liquid surfaces and (2) interaction between the ester carbonyl group of the monomer and the surface hydroxyl silanol group of the amorphous quartz surface. Also, the monomers were characterized in the carbonyl region, which showed the presence of the C[double bond, length as m-dash]O stretch in the SFG spectrum. This result is indicative of the hydrogen bonding interactions existing between the carbonyl group of the monomers and the Si-OH groups of the hydrophilic quartz interface. In addition, the changes in the SFG intensity of the C[double bond, length as m-dash]O peak at ∼1730 cm-1 revealed that the conformation of the C[double bond, length as m-dash]O groups is affected by bulky substituents. Furthermore, the conformational changes of these functionalized monomers at the hydrophilic solid-neat liquid interface was investigated using SFGVS.