Meaurement Of The Interaction Between Two Colloidal Particles And The Hydrodynamic Interactions Between Colloidal Particles And Interfaces

Optical tweezers are a noninvasive way to manipulate fluid suspended microscopic objects in three dimensions using a single laser beam focused by a microscope objective lens of high numerical aperture (NA). Since their invention just over 20 years ago, optical traps have emerged as a powerful tool with broad-reaching applications in biology and physics for their ability to easily measure piconewton forces and subnanometer motions of micron-sized objects. Optical techniques offer a highly controlled driving mechanism that avoids any physical contact with the outside world.It is very important to measure the interaction potential between two micro-scale colloidal particles in the domination of scientific research and manufacture. A mechanical chopper was designed based on a programmable logic controller, servo motor amplifier, servo motor and encoder. The interaction potential measurement system is constructed by the mechanical chopper and dual optical tweezers. The programmable chopper was synchronized with a CCD camera and switch the optical tweezers on and off accurately. The apparatus was very highly automatic. The characteristic of the system such as the design of the chopper, the switching time of the blinking optical tweezers, the tuning scope, the origin position return function, the compatibility and the usability of the system was discussed. The system was used to measure the interaction potential of a pair of polystyrene spheres. The consistency between the measured result and the Darjaguin-Landau-Verwey-Overbeek theory demonstrates the reliability of DLVO theory. The apparatus provides an effective technique for measuring the interaction potential between two micro colloid particles.In recent years, reports of an attractive pair potential of a like charged pair of colloids, a pair of dielectric plates, and a plate and a sphere embedded in an electrolyte solution have appeared. An attractive minimum has been reported at small as well as large interparticle distance in bulk solution and at large interparticle distance in a confined fluid. This paper presents a computer simulation model, for studying the regulation and equilibrium of electric double-layer while two colloidal particles approach each other. The computer results and reports of some important papers are in good agreement. The steric stabilization, which is imparted by polymer molecules grafted onto the colloidal particles, is extensively employed. This paper attempts to study the steric stabilization of Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)(PEO-PPO-PEO) triblock copolymers using the blinking optical tweezers, the turbidity and the zeta potential. The results of three methods are in good agreement.A particle's hydrodynamic coupling to interfaces is an interaction existed widely in dispersion. The hydrodynamic interactions can exert an influence on the Brownian motion and diffusion of particles, which will affect the particles' collision kinetics. In this article, we investigate the diffusion of particles confined by one parallel plane interface using optical induced rotation. The experimental results are consistent with the theory on the hydrodynamic interactions of the particles with interfaces.The methods, which are based on measuring the intensity of polarized components of the light, for determining the phase retardation and identifying the fast axis of a wave plate are discussed. It is concluded that the real phase retardation and fast axis of a wave plate cannot be determined by this kind of methods because the phase retardation of a wave plate is a multiple valued function of the light intensity. A method for measuring phase retardation and fast axis of a wave plate using Michelson Interferometer is brought forward, in which the rainbow fringe of the Michelson Interferometer could be used as an indicator for the zero optical path difference. The method was demonstrated by measuring a commercial wave plate. The influence of the optical dispersion of the wave plate material to the measurement is analyzed and the applicable scope of the method is discussed.