Average particle diameters and electrophoretic mobilites of poly(N-isopropylacrylamide) latex were measured as a function of temperature. Diameters decreased from 788 nm at 10 °C to 380 nm at 50 °C in 0.001 M KC1; the corresponding electrophoretic mobilities increased from -0.193 X 10""8 (18 °C) to -3.06 x 10*8 m2 V'1 s'1 (47 °C). The most dramatic changes with temperature occurred around 31 °C, the lower critical solution temperature of poly(TV-isopropylacrylamide) in water. The increased electrophoretic mobility with temperature reflected increasing charge density when the particle diameter decreased. Charge density increased with decreasing particle diameter because the number of charged groups per particle was constant.

A new value for the depolarization ratio of pure water has been measured at 514.5 nm using an argon ion laser light source and photon counting detection. This depolarization ratio is lower than any previous literature value by a substantial amount. Stray light and photometer geometry are shown to be responsible for overestimated values reported previously. The depolarization ratio is also shown to be a function of the portion of the spectrum being investigated. With no filters we find ρv=0.026. The magnitude of error due to finite acceptance angle is calculated and shown to be substantial. Depolarization ratios using 0.46 and 22.5 nm filters (half-peak bandwidth) are reported.

We report the first measurements of the new approach of hydrodynamic fingerprinting. The hydrodynamic fingerprint is the isothermal contour diagram of the hydrodynamic size as a function of pH and pX (the logarithm of the conductivity fitS/cm)). The general applications of fingerprinting are discussed, and we compare hydrodynamic fingerprints with electrophoretic fingerprints on similar systems. The electrophoretic fingerprint is the isothermal isomobility contour diagram in the pH-pX domain. Measurements are reported on five model polystyrene latexes with carboxyl or sulfate surface groups (ranging from 401 to 1050 nm) from the Interfacial Dynamics Corp. We find that the hydrodynamic size depends on pH, pX, and time, and is generally larger than the electron microscopy size. The hydrodynamic fingerprint, like the electrophoretic fingerprint, is a characteristic pattern of a particular colloidal system. The advantages of the colloid system variable pX over the classical ionic strength are illustrated. The fingerprinting approach is a correlation of variables that can be used to spot errors and assess the general

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An electrophoretic fingerprint of a CD4+ T-cell (H9) has been produced for the first time. Samples were taken from three separate cultures prepared at different times to obtain a general characterization of the cells. The availability of commercial instrumentation equipped with an auto-titrator has made possible the application of both the 2-dimensional and 3-dimensional representation of electrophoretic fingerprinting. The 2-dimensional treatment has been used to assess the reliability of the data and has detected hysteresis as a possible second-order effect. The 3-dimensional representation has been used to explore the data needed for a reliable overall pattern that characterizes the conditions of pH and conductivity required for an effective microbicide. The dome negative maximum in the electrophoretic fingerprint at high pH, along with the line of zero mobility (LZM) and a dome positive maximum at low pH, are interpreted as evidence for surface carboxyl groups prominent in the alkaline regime and surface amino groups prominent in the acid regime, suggesting that the H9 cell surface is zwitterionic. This has important implications as to the choice and design of microbicide actives.