Sum-Frequency Generation Spectroscopy of Cinnamate Modified Cellulosic Polymer at the Air–Water Interface

Abstract

Monolayers of a cellulosic polymer bearing cinnamate groups were characterized at the air-water interface by combining isotherm measurements, Brewster angle microscopy, and infrared-visible sum-frequency generation (SFG) spectroscopy. This spectroscopic technique was used to detect the photochemical behavior of the cinnamate groups upon UV photoirradiation of the monolayers. From the disappearance of the C═C mode and the absence of a change in the C═O mode, it could be concluded that isomerization is the dominant photoreaction for a monolayer of this polymer. This conclusion was corroborated by a comparison of the spectra of the monolayer after irradiation with spectra measured for monolayers spread from preirradiated solutions, for which it is known that isomerization is the main process.

Surface Pressure-Induced Interdiffused Structure Evidenced by Neutron Reflectometry in Cellulose Acetate/Polybutadiene Langmuir Films

“…Significant differences have been reported in literature depending on the substituents of cellulose hydroxyl groups but also on similar cellulose derivatives. Limiting area values of 52 Å 2 have been reported by Cohen-Atiya et al for the same CA polymer at 23 ± 2 °C while a value of 37 Å 2 closer to the one obtained in this work was determined by Hittmeier et al for a CA polymer of unknown molecular weight with 42 wt % acetate (∼40% in this work). , Our results are also in agreement with the values determined for other more voluminous cellulose derivatives such as cellulose acetate butyrate (48 Å 2 ) or cellulose ethers with one, two, or three long alkyl chains (33, 55, and 62 Å 2 , respectively). , Considering that the estimated area of a glucose ring is in the ranges 45–55 Å 2 and 20–25 Å 2 parallel or perpendicular to the ring plane, respectively, this suggests an average tilt of the CA monomer with respect to the water surface in the condensed phase.…”

“…23,24 Our results are also in agreement with the values determined for other more voluminous cellulose derivatives such as cellulose acetate butyrate (48 Å 2 ) or cellulose ethers with one, two, or three long alkyl chains (33, 55, and 62 Å 2 , respectively). 25,26 Considering that the estimated area of a glucose ring is in the ranges 45−55 Å 2 and 20−25 Å 2 parallel or perpendicular to the ring plane, respectively, this suggests an average tilt of the CA monomer with respect to the water surface in the condensed phase.…”

Influence of High pH on the Organization of Acetonitrile at the Silica/Water Interface Studied by Sum Frequency Generation Spectroscopy

“…To more quantitatively determine the contribution from the methyl groups of ACN, the spectra were fitted using eq that relates the SFG intensity to the second-order susceptibility χ (2) , modeled as the absolute square of the sum of a nonresonant contribution and Lorentzian functions that represent each vibrational mode. The resulting Lorentzian peak amplitude and width ratios ( A /Γ) are proportional to the number and net alignment of the corresponding interfacial molecules. , From the fitting of the ppp-SFG spectra that corresponded to the ACN–H 2 O mixture, we extracted two methyl symmetric stretch A /Γ values for each pH, which have been attributed to the two “leaflets” that form the ACN bilayer . On the basis of previous reports, we assigned the higher frequency peak at near-neutral pH to acetonitrile molecules that make up the inner leaflet (CH 3 -ss2) and assigned the dominant peak at lower wavenumber at neutral pH to acetonitrile molecules that make up the outer leaflet (CH 3 -ss1). , This difference in frequency was attributed to the dissimilar local environments of the inner and outer leaflets. , Furthermore, as simulations and experiments have suggested, a repeatable bilayer structure leads to effective cancellation of SFG, thereby contributing little to the overall signal; therefore, we assumed that most of the SFG signal originated from the first bilayer located closest to the silica interface. , One methyl asymmetric stretch and a broad peak centered above 3100 cm –1 accounting for strongly hydrogen bonded water were also included in the spectral fitting of the ppp-SFG.…”

Surface-charge-induced orientation of interfacial water suppresses heterogeneous ice nucleation on <i>α</i>-alumina (0001)

“…The optical properties of the atmosphere play a key role in determining the climate through a combination of reflected incident solar radiation and trapping of outgoing infrared ra-diation. These processes occur in the clouds and are strongly influenced by the formation of ice particles in clouds (Baker and Peter, 2008), which can occur in two manners: either homogeneously, typically at temperatures below −38 • C, or, when formed above this temperature, through a heterogeneous nucleation process triggered by aerosol particles present in clouds (Pruppacher and Klett, 1997). The heterogeneous freezing of supercooled water on an ice-nucleating agent constitutes the main mechanism of ice particle formation in the atmosphere (Baker and Peter, 2008;Murray et al, 2012;Hoose and Möhler, 2012;Ladino Moreno et al, 2013).…”