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Toward a quantitative theoretical method for infrared and Raman spectroscopic studies on single-crystal electrode/liquid interfaces.

ABSTRACT: In situ electrochemical infrared spectroscopy and Raman spectroscopy are powerful tools for probing potential-dependent adstructures at solid/liquid electrochemical interfaces. However, it is very difficult to quantitatively interpret the observed spectral features including potential-dependent vibrational frequency and spectral intensity, even from model systems such as single-crystal electrode/liquid interfaces. The clear understanding of electrochemical vibrational spectra has remained as a fundamental issue for four decades. Here, we have developed a method to combine computational vibrational spectroscopy tools with interfacial electrochemical models to accurately calculate the infrared and Raman spectra. We found that the solvation model and high precision level in the self-consistent-field convergence are critical elements to realize quantitative spectral predictions. This method's predictive power is verified by analysis of a classic spectroelectrochemical system, saturated CO molecules electro-adsorbed on a Pt(111) electrode. We expect that this method will pave the way to precisely reveal the physicochemical mechanism in some electrochemical processes such as electrocatalytic reactions.

SUBMITTER: Fang Y

PROVIDER: S-EPMC8148070 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:We reported recently that amphiphilic polymers can be assembled at interfaces created between aqueous phases and thermotropic liquid crystals (LCs) in ways that: (i) couple the organization of the polymer to the order of the LC and (ii) respond to changes in the properties of aqueous phases that can be characterized as changes in the optical appearance of the LC. This investigation sought to characterize the behavior of aqueous-LC interfaces decorated with uniaxially compressed thin films of polymers transferred by Langmuir-Schaefer (LS) transfer. Here, we report physicochemical characterization of interfaces created between aqueous phases and the thermotropic LC 4-cyano-4'-pentylbiphenyl (5CB) decorated with Langmuir films of a novel amphiphilic polymer (polymer 1), synthesized by the addition of hydrophobic and hydrophilic side chains to poly(2-vinyl-4,4'-dimethylazlactone). Initial characterization of this system resulted in the unexpected observation of uniform azimuthal alignment of 5CB after LS transfer of the polymer films to aqueous-5CB interfaces. This paper describes characterization of Langmuir films of polymer 1 hosted at aqueous-5CB interfaces as well as the results of our investigations into the origins of the uniform ordering of the LC observed upon LS transfer. Our results, when combined, support the conclusion that uniform azimuthal alignment of 5CB is the result of long-range ordering of polymer chains in the Langmuir films (in a preferred direction orthogonal to the direction of compression) that is generated during uniaxial compression of the films prior to LS transfer. Although past studies of Langmuir films of polymers at aqueous-air interfaces have demonstrated that in-plane alignment of polymer backbones can be induced by uniaxial compression, these past reports have generally made use of polymers with rigid backbones. One important outcome of this current study is thus the observation of anisotropy and long-range order in Langmuir films of a novel flexible polymer. A second important outcome is the observation that the existence, extent, and dynamics of this order can be identified and characterized optically by transfer of the Langmuir film to a thin film of LC. Additional characterization of Langmuir films of two other flexible polymers [poly(methyl methacrylate) and poly(vinyl stearate)] using this method also resulted in uniform azimuthal alignment of 5CB, suggesting that the generation of long-range order in uniaxially compressed Langmuir films of polymers may also occur more generally over a broader range of polymers with flexible backbones.

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Toward a quantitative theoretical method for infrared and Raman spectroscopic studies on single-crystal electrode/liquid interfaces.

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