Holographic pH Sensors - Holographic Sensors - page 74

Fig. 3.22 Flow rates of Procion MX-K dyed/plain Whatman filter/chromatography papers.

a - c Five different types of dyed test strips (8 cm 8 mm) along with control strips were submerged

into a water reservoir and the water front reach was recorded. Red arrows show the water front as a
function of time. d Flow rate to wet 7 cm distance for Whatman filter/chromatography papers at 23
°

×

C, e Average fl flow rates of the dyed papers compared to their controls

hydrophobicity of the fibres, and the viscosity of the fl fluid. Dyeing paper strips with

Procion MX-K black slightly in flow characteristics rendering the

dyed test strips more or less hydrophobic (Fig. 3.22 e).
Holographic

fl uenced capillary fl

fl flakes were produced by separating the polymer matrix from its

substrate. Free- flakes produced visual colour changes

due to variation in pH from 5.0 to 8.0 (Fig. 3.23 a). Figure 3.23 b illustrates
holographic sensors on paper strips for monitoring pH in the metabolic range.
Figure 3.23 c shows the readouts for holographic pH sensor

fl oating holographic sensor fl

fl flakes in (i) free-

fl floating, (ii) paper- and (iii) nitrocellulose-backed forms. The holographic fl akes

(6 mol% MAA) swelled 120 nm as the pH was increased from 4 to 8. This Bragg

peak shift is about the half of shift obtained by the pH sensors attached to a
substrate. The difference in the Bragg peak shifts might be attributed to degree of
freedoms to expand. Figure 3.23 d illustrates the geometry of a polymer matrix.
When the polymer matrix is attached to a substrate, it can only expand normal

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