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