Direct measurement of electrostatic interactions between poly(methyl methacrylate) microspheres with optical laser tweezers

Abstract

Strong electrostatic repulsive forces between PMMA particles in CHB/decane mixtures were directly measured with optical laser tweezers.

Approaching the hard sphere limit in colloids suitable for confocal microscopy – the end of a decade lasting quest

“…The origin for this strange behavior is unknown. We speculate that it may be correlated with adhesive fixing the cover slide to the glass tube 32…”

“…28 However, this modifies the hard sphere interaction as charges are introduced. 29–32 Adding salts to screen the charges like tetrabutyl ammonium bromide improves the situation. 25,33 Unfortunately, a 3-component solvent is not easy to handle and some components may cause swelling of the particles and affect the homogeneous distribution of the dye.…”

Temporal Evolution of Interparticle Potentials of PMMA Colloids in CHB/Decalin

“…18 In addition, strong variations of parameters like Debye lengths, particle ζ potentials, and particle charges are commonly observed even for samples prepared in the same manner. 19 Since the electrostatic properties of dispersed colloids are known to be very susceptible to impurities such as ions or glue residues introduced by the sample chamber preparation, 20 one usually assumes imperfections in the preparation as causes for the observed variations.…”

“…The bottom whole was covered with a coverslip and the edges were sealed with an epoxy resin (UHU Plus Sofortfest). As the resin is known to influence the interparticle potential when not properly hardened, 20 we waited at least 12 h before filling in the sample liquid. After the liquid was inserted with a glass pipet, another glass coverslip was put on the top hole and sealed with epoxy resin.…”

“…Indirect information about the potential between pairs of particles has been obtained in different manners: by comparing the radial distribution function of a particle ensemble with results of its theoretical description or simulation results, − by measuring the conductivity and mobility with electrophoresis, ,,,,, and by examination of the crystallization behavior of dispersions as a function of volume fraction. ,,, Direct measurements of interparticle forces are possible using optical tweezers to trap particles while monitoring their interaction via distance measurements. Variations of this approach have been used to study interparticle potentials in a number of different systems. ,,− …”