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.

纳米级现象的研究与环境保护和验证纳米级污染的新快递和非感染方法有关，对于改善生活质量并有助于创造更有效，更清洁的制造过程至关重要。如果可以在分子尺度研究胶体颗粒的界面相互作用，则可以显着完善水纯化和质量控制技术。这项研究的目的是利用和扩展第二次谐波生成（SHG）的非线性光学方法的能力，以研究微米大小胶体颗粒界面的纳米级相互作用。更具体地说，SHG将研究阳离子和阴离子表面活性剂在微米大小的二氧化硅和氧化铝颗粒上的吸附。 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。由于某些方法论问题和缺乏有关粒子表面抗活性剂相互作用性质的广泛了解，因此尚未在微米大小颗粒表面研究纳米级结构的应用。预计这项研究将为颗粒表面上的吸附过程带来新的了解，这将有助于进一步促进SHG方法在胶体颗粒上研究表面活性剂纳米级结构的应用。将基于可用的FemtoSecond激光构建SHG光谱仪，并将用于这些研究。它将与化学系约翰·康博伊（John Conboy）教授合作建造，他在振动频率产生光谱方面拥有丰富的经验，并且还是研究团队的高级成员。他和冶金工程系的博士后研究员Zhorro Nickolov博士将在所有研究问题上与PI紧密合作。由带电颗粒界面定向的水分子的SHG将被监测，作为溶液中表面活性剂浓度的函数。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SHG信号的相应减少，该信号可以测量和量化。或者，染料在基本红外波长处共同吸收并因此具有强烈的SHG信号，将吸附在颗粒表面上，并用于建立恒定的高水平SHG信号。然后，将添加表面活性剂，并导致染料从颗粒表面置换，SHG信号将减小。因此，在两种情况下，都可以评估表面活性剂吸附能和表面覆盖率。提案中的风险要素与区分粒子界面和SHG信号的SHG信号的必要性有关，这些信号可能由大部分粒子以及大量水产生。同样，应考虑表面活性剂与染料之间的竞争，以在颗粒表面吸附。该项目将对胶体系统中纳米级现象的研究的前进以及创建对粒子界面上进行高水平的非智能研究的能力。