D~r (2-9)
where q is the scattering vector, n is the refracting index, 0 is the scattering angle, Ai is the laser
wavelength, and the particle hydrodynamic radius R is calculated from Equation 2-6. Each
monodisperse population of particle sizes produces its own unique autocorrelation function
(exponential decay). Mixtures of more than one size population produce sums of exponentials,
and therefore available algorithms can be used to extract "true" size distributions from complex
samp es.g
2.4 Cyclic Voltammetry
Cyclic voltammetry was used in Chapter 6 to monitor the uptake versus time of
hydrophobic electrochemical probes inside the oil-core of the core-shell nanocapsules. In cyclic
voltammetry, the potential of a working electrode is continuously changed as a linear function of
time, with the rate of change of potential referred to as the scan rate. The potential is first
scanned in one direction and then reversed at the end of the first scan. The advantage of such a
technique in electrochemistry is that the product of the electron transfer that occurred in the
forward scan can be probed again in the reverse scan. Figure 2-7 shows the basic shape of the
current response for a cyclic voltammetry experiment. The bulk solution first contains only the
reduced form of the redox couple, so for potentials (in A) lower than the redox potential, there is
no net conversion of the reduced form into the oxidized form. As the potential is increased
toward the redox potential, a net anodic current appears and increases exponentially. As the
reduced form is oxidized, concentration gradients appear, and diffusion occurs down these
gradients. At point B anodicc peak) and beyond, the potential is sufficiently high so the reduced
species reaching the electrode are immediately oxidized, and the current therefore now depends
upon the rate of mass transfer which results in an asymmetric peak shape. In C, the potential is