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New aza-BODIPY pH indicators with spectral properties modulated solely by photoinduced electron transfer (PET) are presented.

The pH of concrete-based material is a key parameter for the assessment of its stability and durability, since a change in pH is usually associated with major types of chemical degradation such as carbonation, leaching and acid attacks. Conventional surface pH measurements with potentiometric flat surface electrodes have low spatial resolution, whereas optical pH visualization with indicator dyes (phenolphthalein) only indicates the areas with higher or lower pH than the pKa of the indicator. In this regard, it is key to develop wide-range imaging systems, enabling accurate and spatially resolved determination of pH variability for an advanced knowledge of degradation mechanisms. This contribution presents the enhancements made for a high-resolution optical pH imaging system based on fluorescent aza-BODIPY indicator dyes. The measurement range was increased to 6 pH units (pH 6.5 to pH 12.5) by a combination of two indicator dyes. Moreover, background scattering effects were sufficiently eliminated. With the improved sensor foils steep pH gradients (up to 3 pH units within 2 mm) were successfully recorded in various concrete specimens using a macro lens reaching a resolution of down to 35 µm per pixel.

NICKELneed for substrate-surface maintenance. The purity of the plating bath was probably responsible for preventing the development of twins in the deposit (7). Multiple twinning is believed to be responsible for the transition to polycrystallinity (13). As only pH, current density, and bath-temperature values within a narrow range used in this study resulted in monocrystalline deposits, the necessity for maintaining the proper plating variables is evident. Conclusions1. Stresses exceeding the yield strength result in a refinement of the structure of monocrystalline nickel electrodeposits.2. The stresses in a deposit can influence the value of this property in subsequent layers.3. The dislocation-cell structure developed in the near-surface regions under stress and was related to the size of the structural feature on the surface.4. It is possible to grow monocrystalline, nickel electrodeposits thicker than 100 p.m.