Preparation Of SiO₂ Colloidal Probes And Their Application In The Simulation Of Particle-surface Interaction Processes

This paper mainly studied the preparation method of the colloidal probes and their application to the simulation of particle interactions.At first,a brief review on the development of the Atomic Force Microscope(AFM) with respect to its principle and the working mode,then surface electrical properties of aqueous particles were summarized,fundamental theories and calculation methods of particle interactions including Van Der Waals force, double electrical layer force,DLVO theory,and Derjaguin approximation were discussed in detail.The synthesis and manufacturing method of particles as the tip of the colloidal probes were described and application of the colloidal probes in the force measurement and the conversion of force-distance curves were performed.Characterization of particles as the tip of colloidal probs and the hydroxyl poly-aluminium i.e.polyaluminum chloride(PAC1) samples were carried out.Based on the insight into the preparation of the colloidal probes in the literature,a new fabrication method had been developed by using a dual-way 3D movement platform.Making use of the setup of a new instrumental device for colloidal probe fabrication,SiO₂ colloidal probes were successfully prepared.By intergrating the SiO₂ colloidal probe into the liquid cell on the AFM,experiments for force measurement at the different ionic strength in the NaCl solution were conducted.The spring constants of the cantilever were calibrated according to the Cleveland method,and the conversion from the original data to the force-distance or force/radius-distance curves was obtained with satisfactory results referring to the Ducker's classical paper.Furthermore,force measurements were also carried out at the different ionic strength in the NaCl solution with the SiO₂ colloidal probe coated with absorbed PAC1 in order to gain insights into the interaction mechanisms of different PAC1 species.In the summary,the preparation method of the colloidal probes and their application to the simulation of particle interactions have been established in this paper.The main results and conclusions are as follows:1.Silica particles used in this paper are in the form of sphere with a smooth surface,so they can be ideally used in the preparation of the colloidal probes.Sample substrates prepared from the polished silicon crystal wafers are very flat with low RMS roughness,and can be available with easy for the force measurement experiments.2.Compared to both the double-wire and the cantilever movement methods,the dual-way 3D movement platform method adopted in this paper offers much advantage as it is very simple,convenient and easy of use with good performance.It is useful in the batch production of the colloidal probes in the laboratory.The method has been used to successfully fabricate the SiO₂ colloidal probes with 2 micron in diameter and therefore provides a promising approach for the preparation of colloidal probes with the particle size till to 1 microm in diameter.3.Spring constants of the probe cantilever were calibrated by the Cleveland method.The method is found to be a good and widely used method with least parameter to be specified as it just needs to measure the resonate frequency.Another aproach of the Cleveland method by measuring the resonate frequency of both the bare and particle-glued cantilevers to calibrate the spring constant is also proved to be good.4.The conversion of force curves were performed by Excel software or MATLAB program.Based on the principle of the data conversion,a procedure of the transformation process was given in full detail.5.Through the setup of the instrumental device and the method development of the colloidal probes preparation,primary results for the force measurement application of the SiO₂ colloidal probes in AFM were presented with good prospective in the simulation and characterization of particle interactions to gain insights into the underlying mechanisms.