NER: In-Situ Second Harmonic Generation Studies to Describe Nanoscale Phenomena at the Surfaces of Microparticles

NER：描述微粒表面纳米级现象的原位二次谐波产生研究

• 批准号: 0210879
• 负责人: Jan Miller
• 金额: $ 9万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-15 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0210879&HistoricalAwards=false
• 关键词: NER; Situ; Second; Harmonic; Generation

Studies of nanoscale phenomena relevant to environmental preservation and verification of new express and nonintrusive methods to control pollution on the nanoscale are of tremendous importance to improve quality of life and help in the creation of more efficient and clean manufacturing processes. Water purification and quality control techniques can be significantly refined if interactions at the interfaces of colloidal particles can be investigated at the molecular scale. The objective of this research is to exploit and extend the capabilities of the non-linear optical method of second harmonic generation (SHG) to study model nanoscale interactions at the interface of micron-size colloidal particles. More specifically, the adsorption of cationic and anionic surfactants at micron-size charged silica and alumina particles in water will be investigated by SHG. SHG is a second-order nonlinear optical process and has been proven to be highly surface-specific probe of interfacial structure and surfactant adsorption at surfaces in particular. Its application to study nanoscale structures at the surfaces of micron-size particles has not been developed to its full potential due to some methodological problems and lack of extensive knowledge about the nature of the particle-surfactant interactions. It is expected that this research will bring new understanding of the adsorption processes at the particle surfaces, which will help to further promote the application of the SHG method to study surfactant nanoscale structures on colloidal particles.A SHG spectrometer will be built based on an available femtosecond laser and will be employed for these studies. It will be built in collaboration with Prof. John Conboy, Department of Chemistry, who has rich experience in vibrational sum frequency generation spectroscopy and is also a senior member of the research team. He and Dr. Zhorro Nickolov, who is a Postdoctoral Fellow in the Department of Metallurgical Engineering, will be closely collaborating with the PI on all research issues. SHG of water molecules oriented by the charged particle interfaces will be monitored as a function of surfactant concentration in the solution. The adsorption of the surfactant is expected to reduce the polarization of the interfacial water molecules by screening the surface charge of the microparticles. This would lead to a corresponding decrease in the SHG signal which can than be measured and quantified. Alternatively, dyes resonantly absorbing at the fundamental infrared wavelength and therefore having a strong SHG signal, will be adsorbed at the particle surfaces and used to establish a constant high level of SHG signal. Then the surfactant will be added and as a result of displacing the dye from the particle surfaces the SHG signal will decrease. Consequently surfactant adsorption free energy and surface coverage can be evaluated in both cases. The risk elements in the proposal are connected with the necessity to discriminate between the SHG signals characterizing the particle interface and SHG signals which may be generated by the bulk of the particles, and by bulk water. Also, the competition between the surfactant and the dye for adsorption at the particle surfaces should be accounted for. The project will have a significant impact on advancing of the research in nanoscale phenomena in colloidal systems and on creating capabilities to perform high-level in-situ nonintrusive studies on particle interfaces.

对与环境保护相关的纳米级现象的研究以及对控制纳米级污染的新的快速和非侵入性方法的验证对于提高生活质量并帮助创建更高效​​和清洁的制造工艺具有极其重要的意义。如果可以在分子尺度上研究胶体颗粒界面的相互作用，则可以显着改进水净化和质量控制技术。本研究的目的是开发和扩展二次谐波产生 (SHG) 非线性光学方法的功能，以研究微米级胶体颗粒界面处的纳米级相互作用模型。更具体地说，将通过SHG 研究水中微米尺寸带电二氧化硅和氧化铝颗粒对阳离子和阴离子表面活性剂的吸附。 SHG 是一种二阶非线性光学过程，已被证明是界面结构和表面活性剂吸附的高度表面特异性探针。由于一些方法学问题以及缺乏对颗粒-表面活性剂相互作用性质的广泛了解，其在研究微米级颗粒表面纳米级结构方面的应用尚未充分发挥其潜力。预计该研究将为颗粒表面的吸附过程带来新的认识，有助于进一步推动SHG方法在胶体颗粒表面活性剂纳米尺度结构研究中的应用。飞秒激光将用于这些研究。该项目将与化学系的John Conboy教授合作建设，他在振动和频发生光谱方面拥有丰富的经验，也是研究团队的资深成员。他和冶金工程系博士后 Zhorro Nickolov 博士将在所有研究问题上与 PI 密切合作。由带电粒子界面定向的水分子的二次谐波将作为溶液中表面活性剂浓度的函数进行监测。表面活性剂的吸附有望通过筛选微粒的表面电荷来减少界面水分子的极化。这将导致二次谐波信号相应减少，然后可以对其进行测量和量化。或者，在基本红外波长处共振吸收并因此具有强 SHG 信号的染料将被吸附在颗粒表面并用于建立恒定的高水平 SHG 信号。然后添加表面活性剂，由于从颗粒表面置换染料，SHG 信号将会减弱。因此，在这两种情况下都可以评估表面活性剂吸附自由能和表面覆盖率。该提案中的风险要素与区分表征颗粒界面的二次谐波信号和可能由大量颗粒和大量水产生的二次谐波信号的必要性有关。此外，还应考虑表面活性剂和染料之间在颗粒表面吸附的竞争。该项目将对胶体系统纳米级现象的研究进展以及创建对颗粒界面进行高水平原位非侵入性研究的能力产生重大影响。