Single charging events on colloidal particles in a nonpolar liquid with surfactant

Abstract

Electrical charging of colloidal particles in nonpolar liquids due to surfactant additives is investigated intensively, motivated by its importance in a variety of applications. Most methods rely on average electrophoretic mobility measurements of many particles, which provide only indirect information on the charging mechanism. In the present work, we present a method that allows us to obtain direct information on the charging mechanism, by measuring the charge fluctuations on individual particles with a precision higher than the elementary charge using optical trapping electrophoresis. We demonstrate the capabilities of the method by studying the influence of added surfactant OLOA 11000 on the charging of single colloidal PMMA particles in dodecane. The particle charge and the frequency of charging events are investigated both below and above the critical micelle concentration (CMC) and with or without applying a DC offset voltage. It is found that at least two separate charging mechanisms are present below the critical micelle concentration. One mechanism is a process where the particle is stripped from negatively charged ionic molecules. An increase in the charging frequency with increased surfactant concentration suggests a second mechanism that involves single surfactant molecules. Above the CMC, neutral inverse micelles can also be involved in the charging process.

Understanding the mechanisms of electronic ink operation

“…CCAs provided dispersity and suspension to particles while CCAs assemble in RMs. In this process, some CCAs endowed the particles and RMs with charges 29,30 . The charges of the electrophoretic particles depended on the modification of particles and functional groups of CCAs.…”

“…In the nonpolar solvent system, the charge takes the RMs as the carrier. Some particles modified by quaternization 31 or polymerization 32 of functional monomers were charged by desorption of ions to RMs physically, 33,34 as shown in Figure 4. Lewis acid‐base reaction plays a dominant role in the process of particles obtaining charge 35 .…”

Measurement of the amplitude and phase of the electrophoretic and electroosmotic mobility based on fast single‐particle tracking

“…Other techniques focus on electrophoretic measurements on a particle‐to‐particle basis, either based on optical detection with a camera [ 7 , 8 , 9 , 10 , 11 ], employing optical trapping [ 12 , 13 ], or more advanced laser scanning systems [ 14 ]. The advantage of a single‐particle measurements is that polydisperse samples can be measured accurately and that detailed phenomena, for example, single charging events [ 11 ] or single binding events can be observed.…”

“…(A)A typical image of a 1.9 μm diameter PS particle, indicating the rolling shutter direction of the camera. (B) Scheme illustrating the time correction algorithm: N + 1 samples of the x-position acquired with sample frequency f cam = 1/ t (solid dots), and samples with the corrected time (empty dots) according to Eq (13)…”

Surfactant concentration modulates the motion and placement of microparticles in an inhomogeneous electric field

“…To control a particle using an electric field, easily modified electric and dielectric properties of the particle and surrounding medium are desirable. Surfactants can modify the medium conductivity [21][22][23][24] and charge microparticles suspended in apolar liquids [24][25][26][27][28][29][30][31][32] . Although not fully understood, the modification of electrical properties of apolar colloids by surfactant addition is of great importance in industry as it is used to control the electrical properties of ink in printing processes 21 .…”