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

Abstract

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 to ∼2880 cm 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 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.

Atmospheric β-Caryophyllene-Derived Ozonolysis Products at Interfaces

“…Spectra were normalized to the incident IR energy profile by recording a ppp-polarized nonresonant spectrum from a gold film deposited on calcium fluoride, and frequencies were calibrated to a polystyrene film measured in the C-H region. 103 We also note that large nonlinear bulk responses from β-nocaryophyllinic acid (6) were observed upon slow crystallization of the sample (see Figure S4.1), which is consistent with our earlier reports on molecular chirality in field-collected and synthetic atmospheric aerosol particles. [104][105][106] 2.3.2.…”

Orientational Analysis of Monolayers at Low Surface Concentrations Due to an Increased Signal-to-Noise Ratio (S/N) Using Broadband Sum Frequency Generation Vibrational Spectroscopy

“…The details on the SFG spectroscopic system are reported in our previous publications. [14][15][16][17] Briefly, the one-box ultrafast Ti:sapphire oscillator system from Spectra-Physics (Solstice) was utilized to generate 100 fs pulses at 795 nm with the power of $4 W before compression at a 1 kHz repetition rate. The 795 nm beam was then passed through a 50 : 50 beam splitter where the first half was directed towards a Fabry-Pérot Etalon (SLS Optics; spacing d ¼ 10.3 mm, free spectral range [FSR] ¼ 30.931 nm, effective finesse [F eff ] ¼ 71.30 at 800 nm), which converted the incoming beam into a time-asymmetric picosecond visible pulse with an $10-15 cm À1 full width half-maximum (FWHM).…”

“…1, which includes the background, non-resonance, and broadband IR pulse shape terms. The details of the fitting are available in our earlier publications [14][15][16][17]…”

“…The details about the theory and orientational analysis were reported in previous publications. [14][15][16][17] The orientational analysis provides the tilt angle and distribution angle from the surface normal direction for different vibrational modes. Determination of the orientation of interfacial molecules is important to understand the surface phenomena such as catalysis, bio-membrane functions, adsorption, and reaction mechanisms.…”

“…1, which includes the background, non-resonance, and broadband IR pulse shape terms. The details of the fitting are available in our earlier publications 14–17 where n 1 is the baseline correction factor, δω is the spectral width of the broadband IR pulse, n is a nonresonant contribution, and ϕ is the nonresonant phase factor. A q is the amplitude, ω q is the vibrational frequency, and Г q is the peak width or damping constant of the vibrational mode q.…”